skylab experiments. volume 2 remote sensing of earth resources

8/8/2019 Skylab Experiments. Volume 2 Remote Sensing of Earth Resources

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f ( K A SA - F P -1 1 1 ) S K Y L A B E X P E R I M E N T S . VOLUKE 2: R E M O T E S E N S I N G OF E A R T HI R E S O U R C E S ( N 3 S A ) 39 p MF $1.


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ExperimentsVolume 2Remote Sensing ofEarth ResourcesProduced by the Skylab Program and NASA's Educat ion ProgramsDivision in Coopera t i on with the University of Colorado

N A TION A L A E R O N A U T I C S AND SPACE A D M IN IS TR A TION ,Washington, D.C. 20546, May 1973

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402/


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PREFACEThe most immediate benefits that derive from a multidisciplined scientific program such asSkylab are a large volume and wide range of scientific information. A secondary benefit isthat this very large amount of up-to-date information can be related in a timely manner tohigh school curricula. The time lag between the generation of new information and itsappearance in text books is often measured in years rather than in months.It is the intent of the Skylab Education Program to eliminate this characteristically longdelay by timely presentation of scientific information generated by the Skylab program.The objective is not to teach Skylab to the schools, but rather to use Skylab science as afocus for science education in the high schools. Readers are urged to use the descriptions ofinvestigations and scientific principles, and the demonstration concepts contained herein asstimuli in identifying potential educational benefits that the Skylab program can provide.

National Aeronautics and Space AdministrationWashington, B.C. 20546M ay 1973


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CONTENTSTITLE PAGEPREFACE iINTRODUCTION ! ivTH E SKYLAB EDUCATION PROGRAM ivAP P LI CAT I O N ivA C K N O W L E D G M E N T S v

TH E SKYLAB PROGRAM viiTH E SKYLAB SPACECRAFT viiT H E SKYLAB EARTH RESOURCES E X P E R I M E N T PROGRAM ixScheduling xiData Return xiSECTION 1-INTRODUCTION TO THE REMOTE SENSING OF EARTH RESOURCESB A C K G R O U N D 1Skylab Earth Resource Investigations 3SCIENTIFIC CONSIDERATIONS . 4Electromagnetic Radiation 4

Atmospheric Effects 8Resolution liInformation Available from Remote Sensing 11SECTION 2-MULTISPECTRAL PHOTOGRAPHIC FACILITY (S190)B A C K G R O U N D 21S CIEN TIFIC OBJECTIVES . 21Multispectral Photographic Camera (S190A) 21Earth Terrain Camera (S190B) 22E Q U I P M E N T 22Multispectral Photographic Camera (S190A) 22Earth Terrain Camera (S190B) 25

P E R F O R M A N C E 2 7Crew Activities 27Constraints 27D A T A OUTPUT 27SECTION 3INFRARED SPECTROMETER (S191)B A C K G R O U N D 29SCIENTIFIC OBJECTIVES 31E Q U I P M E N T 32P E R F O R M A N C E 37Crew Activities 37Constraints 37D A T A OUTPUT 37SECTION 4-MULTISPECTRAL SCANNER (S192)B A C K G R O U N D : 39SCIENTIFIC OBJECTIVES 39E Q U I P M E N T 40P E R F O R M A N C E 42Crew Activities 42Constraints 42DATA OUTPUT 42


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SECTION 5 M ICRO WA VE RA DIOM ETER/SCA TTEROM ETER A N D A LTIMETER(S193)B A C K G R O U N D 45SCIEN TIFIC O BJ ECTIVES '. 47E Q U I P M E N T 47D A T A O U T PU T 48

SECTION 6-L-BAND M I C R O W A V E R A D I O M E T ER (S194)B A C K G R O U N D 57SCIENTIFIC OBJECTIVES 57E Q U I P M E N T 57P E R F O R M A N C E 58Crew Activities 58Constraints 58D A T A O U T P U T 58SECTION 7-RELATED CURRICULUM ACTIVITIES

R E L A T E D C U R R I C U L U M TO P IC S 61S UG G ES TE D C L AS SR O O M D E M O N S T R A TIO N S 64SECTION 8-APPENDICESA P P E N D I X A-REMOTE SENSO R DISCUSSIO NG E N E R A L 71C A M E R A S 71Multispectral Cameras 72R A D I O M E T E R S 7 2Microwave Radiometer 72S C A N N E R S 73Infrared Scanner 73S P E C T R O M E T E R S 74

Infrared Spectrometer 74R A D A R S 75Scatterometer 75A P P E N D I X B-GLOSSARY 77A P P E N D I X C-SELECTED B I B L I O G R A P H Y 83

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INTRODUCTIONThe Skylab Education ProgramThis year the United States' first manned scientific space station, Skylab, will be launchedinto orbit and will be the facility in which successive crews of astronauts will performinvestigations in a number of scientific and technological disciplines. The program ofinvestigations can be divided into four broad categories: physical sciences, biomedicalsciences, Earth applications, and space applications.The Skylab scientific program will produce information that will increase our understandingof science and will extend our knowledgeof subjects ranging from the nature of the universeto the structure of the single human cell. It is one of the objectives of the NationalAeronautics and Space Administration that the knowledge derived from its programs bemade available to the educational community for application to school curricula in a timelymanner.For this reason, the Skylab Education Program was created to derive the maximumeducational benefits from Skylab, assist in documentation of Skylab activities, and enhancethe understanding of scientific developments.This document is one of several volumes prepared as a part of the education program. It hasthe dual purpose of i n f o r ming high school teachers about the scientific investigationsperformed in orbit, and enabling teachers to form an opinion of the educational benefits theprogram can provide.In providing information on the Skylab program, these books will def ine the objectives ofeach scientific investigation and. describe its scientific background. The descriptions willinclude discussions of the scientific principles applied in the investigations and the types ofdata generated, and the types of related information and data available from other sourcesin the Skylab program.In the preparation of these descriptions of the Skylab activities, a continuing goal has beento build a bridge between Skylab science and high school science. Discussions of thescientific background behind the Skylab investigations have been included to illustrate thescientific needs for performing those investigations in the Skylab environment. Whereverpossible, concepts for classroom activities have been included that use specific elements ofSkylab science as focal points for the increased understanding of selected subjects in thehigh school curricula. In some areas, these endorse current curriculum topics by providingpractical applications of relatively familiar, but sometimes abstract, principles. In otherareas, the goal is to provide an introduction to phenomena rarely addressed in high schoolcurricula.It is a goal of the Skylab Education Program that these volumes will stimulate the highschool teacher to the recognition that scientific programs such as Skylab produceinformation and data that neither are, nor were planned to be, the exclusive domain of asmall group of scientists, but rather that these f ind ings are available to all who desire to usethem.ApplicationReaders are urged to evaluate the investigations described herein, in terms of the subjectsthey teach and the text books and classroom aids they use. Teachers will be able to a pp l y


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the related curriculum topics as stimuli for application of Skyla b program-genera tedinformation to classroom activities. This inform ation can be in the form of film strips, voicetapes, experiment data, etc. and can be provided to fulfill teachers' expressed needs. Forexam ple, the teacher may suggest edu cational aids that can be made available from theseinformation sources, w hich would be useful in classroom situations to illustrate many of theprinciples discussed in high school curricula. These suggestions could then serve as stimulifor development of such aids.As informa tion becomes available, periodical announ cements will be distributed to teacherson the NASA Educational Programs Division mailing list. Tea chers w ishing to receive theseannouncements should send name, title, and full school mailing add ress (includ ing zip code)to:

Nat ional Aeronautics and Space A dm inistrationWashington, B.C. 20546Mail Code FEThis volume covers the broad area of earth resources in which Skylab experiments will beperformed . Includ ed is a brief d escription of the Sk ylab Progra m, its objectives and vehicles.Section 1 introduces the concept and historical significanc e of remote sensing, and discussesthe major scientific consid erations involved in rem otely sensing the earth's resources,particularly as applicable to sensing from spacecraft. Follow ing this d iscussion, sections 2through 6 provide a description of the individual Earth Resource sensors and experiments tobe performed on Skylab. Each d escription includ es a discussion of the experim entbackg round and scientific objectives, the equipm ent involved and a discussion of significantexperiment performance areas.Section 7 Related Curric ulum Activities, includ es an outline of the areas of sciencecurriculum to which experimental data, or information concerning the scientific principles,can be related (refer to Table 1 for a summary matrix of related curriculum topics). Thissection also includes a sample of suggested classroom activities which may be of interest tosome readers.Section 8 includes the following appendices: Append ix A, providing add itional remotesensor inform ation ; App end ix B, which contains a glossary of terms used in this volum e; andAp pend ix C, a selected bibliography.Ackno wledgementsValuable guidance was provided in the area of relevance to high school curricula by Dr.James R. Wailes, Professor of Science Education, School of Education, University ofColorado; assisted by Mr. Kenneth C. Jacknicke, Research Associate on leave from theUniversity of Alberta, Edmonton, Alberta, Canada; Mr. Russell Yeany, Jr. , ResearchAssociate, on leave from the Armstrong School District, Pennsylvania; and Dr. Harry Herzera n d M r . Duane Houston, Education and Research Found at ion , O klahoma StateUniversity.


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The Skylab ProgramThe Skylab orbiting space station will serve as a workshop and living quarters for theastronauts as they perform investigations in the following broad categories: physicalsciences, biomedical sciences, Ea rth applications, a nd space app lication s.During the eight-month operational lifetime of Skylab, three crews, each con sisting of threem e n , will live and work in orbit for periods of up to one m on th, two m on ths, and twomonths, respectively.The objectives for each of the categories of investigation are summarized as follows.Physical ScienceTo perform observations away from the filtering and obscuring effects ofthe Earth's atmosphere in order to increase man's knowledge of the Sun and of itsimportance to Earth and mank ind , to provide information in the field of stellar and galacticastronomy, and to increase man's knowled ge of the radiat ion and part icle environ m en t innear-Earth space and of the sources from which these phenomena emanate.Biomedical ScienceTo make observations und er cond itions different from those on Earthand thereby increase man's knowledge of the biological funct ions of living organisms, and ofthe capabilities of man to live and work for prolonged periods in the orbital environment.Earth ApplicationsT o develop techniques for observing from space and interpreting Earthphen ome na in the areas of agriculture, forestry, geology, geog raphy, ocea nograp hy, air andwater pollution, land use and meteorology, and the influence man has on these elements.Space A pplications To develop techn iques for opera tion in space in the areas of crewhabitability and mobility, a nd use the properties of weightlessness in materials research.

The Skylab SpacecraftThe five modules of the Skylab cluster are shown in the illustration.The orbital workshop is the prime living and wo rkin g quarters for the Skylab crews. Itcontains living and sleeping quarters, provision for food preparation and eating, and personalhygiene equipment. It also contains th e equipment for the biomedical science experimentsand for many of the physical science and space applications experiments. Solar arrays forgeneration of electrical power are mounted outside this mod ule.The airlock module is the prime area in which control of the cluster internal environment,and wo rkshop electrical pow er and com mu nic ation s systems, is located. It also con tains theairlock through which suited astronauts emerge to perform their activities outside th ecluster.The multiple docking adapter provides th e docking port for the command /service m odulesthat transport th e crews, and contains th e control center for the telescope mountexperiments and systems. It also houses the Earth applications experiments and spacetechnology experiments.The Ap ollo telescope m oun t houses a sophisticated solar observatory having eight telescopesobserving varying wavelengths from visible, through near and far ultraviolet, to x-ray. Itconta ins th e gyroscopes and computer of the primary system by which th e flight att itude of

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1 Apollo telescope mount2 Solar arrays3 Sleeping quarters4 Personal hygiene5 Biomedical science experiment6 Ward room

7 Orbital workshop8 Experiment compartment9 Airlock module

10 Airlock external hatch11 Mult iple docking adapter12 Earth resources experiments13 Command and service module

Station


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Skylab is maintained or changed, and i t carries solar arrays by which about half of theelectrical power used by the cluster is generated.The command and service module is the vehicle in which th e crew travels from Earth toSkylab and back to Earth, and in which supplies are conveyed to Skylab and experimentspec imens and film are brought to Earth.Skylab will fly in a circular orbit about 4 3 6 kilometers (235 nautical miles) above th esurface of Earth, and i s planned to pass over any given point within latitudes 50 north and5 0 south of the equator every five days. In its orbital configuration, Skylab will weigh over44,100 kilograms (200,000 pounds) and will contain nearly 370 cubic meters (13,000 cubicfeet) fo r work an d living space (about th e size of a three-bedroom house).T H E SKYLAB EARTH RESOURCES EXPERIMENT PROGRAMT he Earth Resources Experiment Program ( E R E P ) on Skylab contains sensors operating inselected frequency bands throughout the visible spectrum and into the microwave range.The equipment used includes:

The Multispectral Photographic camera (S190A) consisting of a group of six camerasall carefully aligned on a common target point on the earth's surface, and an EarthTerrain Camera (S190B) having larger focal length than the six multispectral camerasand therefore greater resolving power.

The Infrared Spectrometer (S191) designed to perform spectral radiance measure-ments in the visible through near-infrared ranges, as well as in the thermal infraredspectral band, on specific ground areas selected by the crew. The Multispectral Scanner (S192) which operates in thirteen discrete spectral bands( including the visible and infrared) to obtain spectral signature information foragriculture, forestry, geology, hydrology, and oceanography analysis. The Microwave Radiometer/Scatterometer and Altimeter (S193) which operates inthe microwave range and will obtain active radar back-scattering, passive microwaveemission measurements, and pulse shape altimeter measurements. And, the L-Band Radiometer (S194) which measures the brightness temperature ofthe earth's surface in the microwave region, but operates at a d i fferent wavelengththan the SI93 radiometer.

Figure 1 illustrates the principal functional inter-relationships between the various Skylabearth sensors, and shows the relationship of the spacecraft data to supporting data (i.e.,ground data, aircraft data, ship/buoy data, and other spacecraft data).

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Skylab Earth Resources Data OtherSpacecraftData

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SI 90 MultispectralPhotographicFacility(Visible & near IRdata)4 Similar spectral bands

S191 InfraredSpectrometer(Visible, near IR &thermal IR data) \

Use S191 data toremove atmosphericabsorption effectfrom S192 data.

S192 MultispectralScanner(Visible, near - IRand thermal IR data)

7 Comparable spectralbands. Compare ADPspectrum matchingofS192 data with S190direct photo inter-pretation.

\\\\\\\\\S193 Microwave

RadiometerScatterometerAnd Altimeter(Ku band microwavedata) 13.9 GHzResourceO fInterest

Use S194 datato detect cloudor moisture and seastate effects whichmay influence SI 93data.

Earth ResourceTechnology Satel-lite (ERTS)Multi-SpectralScanner

I Supporting Data

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GroundOn-Sitephysical measure-ments

Ship/BuoyPhysical on-sitemeasurements

S194 L-BandRadiometer(L band microwavedata) 1.42 GHz

^ I AircraftCorollary datafrom aircraftaltitudesFigure 1 Skylab Earth Resource Experiment Inter Relationship


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SCHEDULING O F S K Y L A B E A R T H R E S O U R C E S E X P E R I M E N T SDuring the Sky lab m ission , areas of the earth su rface will be remotely sensed that are ofparticular interest to earth resource investigators. In order to perform earth resource datapasses, it is necessary to re-orien t the Sk yla b orbital assembly from its normal attitudewherein th e solar arrays and the solar telescope point directly at the sun, to an orbital modewhich provides continuous pointing of the cameras and other earth resource sensors at theground directly below the spacecraft. A total of 60 such passes are now planned, and 5passes with Skylab in its normal solar oriented attitude are assigned for earth observationactivities. The following table illustrates the apportionment of these passes by Skylabmission:

Skylab N u m b e r o f N u m b e r o fM ission Ea rth Pointing Passes Solar Oriented PassesSL-2 14 1SL-3 26 2SL-4 20 - 2T O T A L 60 5

DATA RETURNThe Skylab earth resource sensors may be operated singly or in various combinationsdepending on the scientific requirements, or other factors such as wea ther and vehiclecapability limitations. In any event, the data will be recorded on magnetic tape and film andreturned to the N A S A Johnson Space Center fo r initial processing. From the three Skylabmissions, a total of 10,400 frames of color and 20,800 frames of black and white 70millimeter film are planned to be returned to earth from S190A; 7,200 frames of color andblack and white film will be returned from S190B; and approximately 50,400 frames of 16millimeter black and white film will be returned from the S191 data acquisition camera.Digital data will consist of a total of 25 reels of magnetic tape.Data acquired from the Earth Resource experiments conducted on the Skylab missions willbe available to the general public when cataloged and received at the Department ofInterior's, Earth Resource O bservation System (ER O S) Data Center, Sioux Falls, SouthDakota. Inquiries to E R O S may be addressed as follows:

E R O S D A T A C E N T E RSIOUX FALLS, S.D. 57198Phone: (605) 339-2270

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Section 1Introduction


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BACKGROUNDRemote sensing is the name given to the technique ofmeasuring information about a subject of interest withoutbeing in direct contact with it. The technique relies ondetecting electromagnetic radiation which is either reflectedor emitted by the subject. When applied to the earth as seenfrom orbital altitudes, remote sensing has the potential ofyielding information which is of fundamental importance foreffective use and conservation of natural resources in bothdeveloping and technically advanced nations. The SkylabEarth Resources Experiment Package (EREP) will providethe experimental data upon which to base answers to suchquestions as: which wavelength to use for a particularapplication, how many channels of data are really required,what scale and resolution should be provided, and what areaof the earth's surface should be covered at one time? Whilethese answers are needed to design the operational systems ofthe future, the data gathered during the Skylab mission alsohave immediate applications to earth resource managementand education. However, in order to more clearly understandthe earth resources experiment discussions which follow inthis volume, it is necessary to first familiarize ourselves withthe concepts of remote sensing.Remote sensing is not new to mankind. Four of man's fivesenses are remote sensors, acquiring data concerning anobject from a distance. The olfactory senses react withmolecules given off by an object, thus providing odordetection. The ear detects pressure pulses. The skin haspressure and temperature sensors that do not require contact,and the eyes are sensitive to electromagnetic radiation in the0.4 to 0.7 micrometer region (the visible spectrum).To improve upon his "data gathering" techniques there aretwo things man can do:

Better utilize his sensing devices (i.e., go to the top ofa hill for a better view) O r, develop instruments with greater sensitivity thanhis ow n fairly limited senses.

Aerial photography is an example of the combination of boththese two improvements.Photography from orbital altitudes in the visible and near-infrared spectral regions has already proven to be aninvaluable complement to survey from aircraft and fromground level for standard synoptic mapping of geographicfeatures over large areas. The use of multispectral remotesensing techniques over an extensive wavelength region hasthe potential of greatly extending the scope of this capabilityto include mapping of terrestrial resources and land uses on a

ELECTROMAGENTIC RADIA-T I O N Energy transmittedthrough space or through a ma-terial medium in the form ofelectromagnetic waves. The termcan also refer to the emissionand propagation of such energy.Whenever an electric charge os-cillates or is accelerated, a dis-turbance characterized by theexistence of electric and magnet-ic fields propagates outwardfrom it. This disturbance iscalled an electromagnetic wave.The frequency range of suchwaves is tremendous and isknown as the ELECTROMAG-NETIC SPECTRUM. All electro-magnetic waves travel with thevelocity of light.


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scientific uses. N A S A extended an invitation to potentialdomestic and foreign investigators in December 1970 tosubmit proposals for the analysis and application of earthresource scientific data to their particular areas of interest.Based on the proposals received, N A S A has selected PrincipalInvestigators to direct 148 investigations.The following table 2 shows the distribution, by majordiscipline and sub-discipline, of the experiment tasks pro-posed by these Principal Investigators. Note that someexperiments encompass multi-discipline tasks, therefore thetotal number of tasks exceed the total number of investiga-tions.

SCIENTIFIC CONSIDERATIONSElectromagnetic RadiationEach individual feature of the earth's surface emits, orreflects, radiation of different frequencies in different ways;consequently, observation in these spectral ranges, eithersingly or simultaneously, can provide a wide variety ofinformation.The total electromagnetic spectrum extends from the ex-tremely short wavelength cosmic rays to the extremely longwavelength of the earth's natural resonance. Figure 2illustrates the electromagnetic spectrum range, and empha-sizes that portion that is most familiar to the high schoolstudent.Different surface features reflect different wavelengths withdifferent intensities as illustrated in Figure 4. This figureshows that the intensity of reflected light from a packedsandy road has a radiance in the 0.6 micrometer frequencyrange seven times that of soy beans; while in the 0.9micrometer range soy beans have a radiance more than twicethat of the sandy road. The variation in reflectance oremission in different spectral frequencies is called the spectralsignature of the material.When the surveys are extended to the infrared and longermicrowave bands, the emitted radiation is significant. In thiscase, the energy sensed is solar energy which has beenabsorbed and then reradiated. Figure 3 illustrates thespectral image variations detectable in six selected spectralbands taken simultaneously of the same scene from anaircraft. The three photos on the left are in the visiblespectrum (with peaks in the violet, yellow-orange and redcolors, respectively), while the three photos on the right arein the near-IR and intermediate-IR parts of the electro-magnetic spectrum.

SPECTRAL SIGNATURE- re-fer to Glossary for definition.

SPECTRAL The distributionof electromagnetic radiation as afunction of wavelength. In thevisible range, variations arenoted by changes in color.


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Wavelength Wavelength(Nanometers) (Micrometers)

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surface of the particle. Scattering diverts some of the lightfrom the scene so that it does not enter the sensor collector,or diverts light that is not part of the scene being observedinto the sensor collector. The result in either case is areduction in contrast and clarity. Scattering is a seriousproblem in the visible portion of the spectrum where camerasare used, and it is countered by the use of polarized filters orfilters that tend to pass light that has not been scattered, andto block light that has been scattered.Weather is a principal cause of an opaque atmosphere. Theshort wavelengths of visible and infrared radiation havesuperior resolving properties, but they are absorbed orreflected by water vapor, fog, and clouds. Therefore, whenoperating in an area where weather is a problem, sensorsthat operate at the millimeter and centimeter wavelengths(microwaves) and can pass through fog and clouds with aminimum of attenuation must be used. As Figure 5 shows,however, even microwaves are scattered by rain and snow.One technique to combat the weather problem is to makerepeated passes over the area of interest taking data eachtime. As the cloud patterns change, a picture of the wholeregion can be pieced together from pictures of small,momentarily clear areas.Examining the polarization of the sensed radiation can oftenreveal information about the texture, or chemical composi-tion, of the reflecting surface, or of the intervening atmos-phere. The natural sunlight is polarized, and the polarizationis changed in varying degrees by particles in the atmosphereand by reflection from a surface. The degree to which thereflected sunlight remains polarized is useful in identifyingthe nature of the surface that reflected it, and the atmos-phere it passed through.Polarization effects and the fact that radiation in the passivemicrowave region originates from beneath the surface ofcertain terrestrial materials (e.g., ice and snow) offer promis-ing possibilities for geologic and arctic exploration. Passivemicrowave signals can also provide information about theroughness or other characteristics of land or water surfaces,which would supplement data obtained from other spectralregions.Both active and passive microwavedata collection techniqueshave the advantage that they can be used both day and nightand in the presence of cloud cover. This greatly extends theircapability for obtaining continuous information concerningthe earth's surface, regardless of time of day or some weatherconditions. It may also supply data on meteorologicalconditions in areas of cloud cover that are not obtainable inother spectral regions.

PO LAR IZ AT IO N A distinctorientation of the wave motionand travel of electromagnetic ra-diation. Discrimination tech-niques use differing and perhapscharacteristics amounts of polar-ization introduced by materialsin the radiation reflected oremitted to distinguish materialcategories.

IncidentWaveReflectedWave

RefractedWaveFor Reflection: i = i1For Reflection: sin i

sin rWhere Ci and e2 are thedielectric constants of mediums1 and 2, and N is the INDEXOFREFRACTION.


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ResolutionO ne of the strongest fac tors in sensor selection is the trad eoff between the minimum size of the feature to be studiedand th e minimum s ize that the sensor can record (spatialresolution). The spatial resolution requirements, in turn ,depend upon the resource that is being studied. Id entifyingcrops by planting pattern requires a sensor that can discrimi-nate surface features of 2 to 20 meters in size.The electromagnetic wavelength at which a sensor operatesha s a profound effect on the resolving pow er of tha t sensor.For crop identificat ion it is necessary to use either a sensorsuch as a cam era, th at operates w ith very short wa veleng ths;or if weather is a problem, the only recourse may be amicrowave radar in which case the commensurate coarserresolution must be accepted. Unfortunately, there are pre-sently no practicable high resolution sensors that canpenetrate weather.However, if gross land use mapping is the area of interest,(whether an area is desert, forest, or cultivated land) therequired size of feature can be as large as one hundredmeters. Here, cameras would give more data than needed, soa me d ium resolution rad iometer, or radar scatterometer,would probably be sufficient.Some resource sciences require high spectral, rather than highspatial, resolution. For e xam ple, if an agronomist is inter-ested in identifying crop species and health, he needs data onthe reflectance of the crop in several narrow spectral bandsindicat ing the presence or absence of chlorophyll absorption.This requires sensors that collect data simultaneously in anumber of narrow spectral bands. Candidate sensors are themultispectral scanner, the multispectral camera, or a spectro-meter.Information Available From Rem ote SensingA comprehensive remote sensing system for acquisition ofpictorial data over a broad spectral range includes three basicimaging techniques: photography, for the region from thenear ultraviolet at 0.3 micrometers to the near-infrared at 1micrometer; optical-mechanical scanning for the infraredregion between 1 and 40 micrometers (and, for some of thework, between 0.3 and 1 micrometers); and passive micro-wave, or radar, for discrete regions between 1 millimeter andseveral centimeters, or meters, in wavelength.Photographic imagery will yield data concerning the amountof solar energy reflected from selected objects on the earthand its cloud cover as a funct ion of wavelength, in selectedspectral regions. Electro-optical, or optical-mechanical scan-ning techniques are desirable to acquire digitized data over

SPATIAL The distr ibution ofelectromagnetic rad iat ion as re-lated to the location, shape andtexture of sensed phenomena .

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data in the form of an electrical output, permit computerprocessing before final recording on photographic film ormagnetic tape. Thus, the information from one spectralregion may be combined additively with that from anotherregion, for example, and a single picture produced which mayrepresent an optimum image for certain studies. Digitizingphotographic imagery data using optical scanning techniquespermits computer processing of large amounts of data muchmore rapidly than conventional manual photo interpretation.This is particularly desirable if large quantities of images arebeing produced and analyzed.Using several sensors simultaneously to detect the electro-magnetic radiation signature of a scene in many differentspectral bands (multispectral sensing) produces vast quanti-ties of data. The sheer volume of the data obtained makesdigital data processing techniques, using computers, desirablein order to allow data interpretation and analysis within areasonable time interval. The 25 reels of magnetic taperesulting from the Skylab earth resource missions arecapableof providing up to 30 to 40 gigabits (gigabit equals 109 bits)of data. A discussion of automatic data processing usingcomputers to make logical deductions identifying resourcesby their spectral signatures (automatic pattern recognition) isconsiderably beyond the scope of this volume; however, suchtechniques will provide powerful tools for the use of manySkylab earth resource investigators.Infrared and thermal imaging devices (radiometers) pro-duce recordings of the thermal structure and behavior ofthe terrestrial and meteorological environment. Scientificexperience has shown that terrestrial data in at least twospectral regions (e.g., 4.5 - 5.5 micrometers and 8.5 - 13.5micrometers) are often much more useful than either onealone, therefore several infrared channels should be provided.The surface condition of the object often affects the relativeemittance of the object. Since radiation emitted from theobjects is being measured, the sensing system can be used dayand night. Other wavelengths may be used for studies ofclouds, wind, ozone distribution as it affects ultravioletabsorption, and air pollution (wavelengths corresponding toabsorption regions in the atmosphere.)Radar imagery provides a comparative measure of thereflection from various objects on the earth or of clouds.Reflected intensity (radar back-scattering) is affected by theaspect of the terrain relative to the beam direction, by thedielectric properties and polarization (at the radar frequency)of the material, and, for elements smaller than the resolutionlimit, by element size. Scanning at small angles (near grazingincidence) yields intensity variations which are a function ofthe local slope of complex landforms; it is therefore asingularly powerful -technique for topographic mapping.

EMITTANCE- The radiantemittance of a source is thepower radiated per unit area ofsurface.

DIELECTRICS^- Materialswhich are electrical insulators. Ina more general sense, dielectricsinclude all materials except con-densed states of metals (i.e.,conductors). A dielectric is asubstance through which an elec-tric attraction or repulsion (elec-tric field) may be sustained.2


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Passive microwave scanning radiometers have not beendeveloped as extensively as the other sensors discussed hereas to resolution element size, but new tech niqu es haveimproved thermal sensitivity and speed of operation.The spectral frequencies in which each of the Skylab earthresource sensors (which are discussed in the followingsections of this volume) operates is shown in Figure 6together with the earth resources phenomena about whicheach sensor provides informa tion. M ore informa tion aboutvarious types of remote sensors can be found in A p p e n d i xA to this document.As an illustrative example of the type of informat ionobtainable, the following sequence of figures demonstratesthe types of data produced by various remote sensors tha t areused for Earth Resource Surveys. It is important to note theeffect of scale change between imagery taken from 912kilometers (ER TS- 1) com pared to photographs taken from6,096 meters (20,000 feet). The small scale (high altitude)photographs and imagery are useful fo r studying regionalphenomena and relationships but often lack the resolution todo detailed studies. Large scale photographs, such as that offigure 9, permit study and identification of small features.Figure 7 is an ERTS-1 satellite composite image of southcentral Colorado. The multispectral scanner aboard ERTStransmits fou r separate images of the sam e scene to earth.Each image represents the reflected energy from the scene ina limited spectral region, or band. Figure 7 is a black andwhite represen tation of a "false color" image which enhancesthe information available to the scientists who interpret theimage. The black square indicates the coverage of the aerialphotograph of Figure 8. The small arrow points to avegetation anomaly which we will use as an orientationl andmark .

(Figures 7, 8, 9, 11 and 12furnished by the NationalAeronautics and SpaceAdministrat ion.)

Figure 8 is black and white representation of an infraredphotograph taken from 18,290 meters (60,000 feet). Thisscene show s the Sangre de Cristo M oun tain s in the u pper halfof the frame and the San Luis Valley in the lower half. N o t ehow healthy, vigorous vegetation shows up dark in thisphoto. This is because vegetation reflects large amounts ofenergy in the near infrared from 0.7 to 1.0 micrometerswavelength. Although the h u m a n eye cannot se e this longerwavelength light (being sensitive only to light between 0 .4and 0.7 micrometers), this special film is designed to beexposed by infrared reflectance and produce a red color upo nprocessing. The inte ns ity of the color is proportiona l to thea m o u n t of reflected infrared energy. N ote ho w d ark irrigatedfields appear. The vegetation between points a-a 1 is ofparticular interest to geologists w ho are stu d yin g the geologicstructure of the area. The vegetation grows vigorously there13


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Figure 7 ERTS-1 Satellite Composite Color Image of South-Central Colorado

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5 KM

8 High Altitude Color Infrared Aerial Photograph

6


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because a fault ha s impeded the subsurface flow of waterfrom the mountains to the center of the valley. The water isforced to the surface providing fo r relatively vigorousvegetation growth. This same relationship can be seen onfault traces immediately to the east and west of fault tracea-a1. The black square indicates the coverage of the aerialphotograph of Figure 9. The small arrow points to a smallgroup of trees which serve as a landmark.Figure 9 is a large scale photograph taken from analtitude of 6,096 meters (20,000 feet). The fine resolutionmakes it possible to see individual trees and field rows. Faulttrace a-a1 is plainly visible and a topographical expression ofthe fault, known as a fault scarp, can be faintly seenextending to the southwest. Figure 10 illustrates the minorterrain variation of a fault scarp, which is marked by a dashedline on this photograph. Fault scarps are visible on other faulttraces in the Figure 9 scene as well. The small arrow points tothe same small group of trees.Figure 11 is a thermal infrared scanner image obtainedduring the early afternoon from low altitude. The lightertones indicate relatively warm areas. The dark areas, such asthat between a-a1, are relatively cool because of increasedsoil moisture and vegetation resulting in evaporative cooling.The fault scarps which extend from the areas of waterimpedance appear as light toned lines because they are beingheated more rapidly by the sun (due to the increased slopetoward the sun) than the surrounding area. The area outlinedin black is the coverage of the Figure 9 photograph. Itforms a trapezoid because of geometric distortions in thescanner system. The small arrow points to the small group oftrees.Figure 12 is an aerial photograph taken during earlymorning when the sun was only 24 above the horizon. Theshadows obtained on low sun-angle photography enhancetopographic features which may be related to geologicstructures. The fault scarp between b-b1 is enhanced andmore easily detectable because of topographic shadowing.Other fault scarps can be seen in the same area. The smallarrow points to the landmark group of trees.A sampling and condensation of numerous scientific andtechnical studies in the areas of geography, agriculture,forestry, geology, hydrology, oceanography and cartographyusing photographic data obtained from the Gemini andApollo missions and from aircraft is contained in an excellentmonograph obtainable from th e U.S. Government PrintingOffice, Washington, D.C. 20402, and may be of interest tosome readers. The monograph is titled: "Ecological Surveysfrom Space," National Aeronautics and Space Administra-tion, 1970, Monograph # SP-230. Library of Congress CardN u m b e r 76-605799. Price $1.75.

p ond i ngareaCi'w'ater movement ~

Permeable alluviumImpermeable "clay series"

Hypothetical Cross Section of aTypical Fault

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HBBFigure 10 Ground Level Photo of A Fault Scarp

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Figure 11 Thermal Infrared Scanner Imagery

Figure 12 Low Sun-Angle Aerial Photograph19


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Section 2Multispectral PhotographicFacility


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It will, thereby, afford an opportunity to determine theextent to which precision and repetitive multispectral pho-tography from space can be applied effectively to the earthresources disciplines.Earth Terrain Camera (S190B)The objective of the Earth Terrain Camera experiment is toobtain high-resolution photography in support of other EarthResource Experiment Package ( ER EP) sensors, and useroriented studies.Specifically, the objectives are:

To supply high-resolution data of small areas withinthe fields of view of the Earth Resources ExperimentPackage remote sensors to aid in interpretation of thedata gathered by these instruments. To obtain high-resolution photography that can beused in the following areas of interest:

Urban and industrial planning, including thepatterns and distributions of dwellings and facili-ties, the land use intensity, the roads, terminals,and traffic patterns. The determination of pollution boundaries, lakeand reservoir levels, and the effluents of rivers. The boundaries of crop infestation and damage,

the yield, the type and density of forested areas. The determination of drainage patterns, smallgeologic folds, and lithographic detail. The interpretation of dynamic events, such asfloods, volcanos, and earthquakes. Acquisition of ground truth data where groundsupport or aircraft are not available. Investigation of mapping applications for1:250,000 scale maps.

E Q U I P M E N TMultispectral Photographic Camera (S190A)This experiment consists of an array of six 70 millimetercameras, precisely matched and boresighted so that photo-graphs from all six cameras will be accurately in register.Thus, all of the features seen in one photograph can be

S190A Boresighted Camera

EarthInstanteousCameraField of View

All cameraField of ViewsIdentical at .Time of Exposure,Thus all FeaturesAre in Register


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experiment S065. The two color films will enhance the studyby providing a pre-registered crosscheck of the B& W imageryin two proven color combinations. Although the cameras aredesigned primarily for certain film and filter combinations,the experiment system will provide the capability fo revaluating various other film and filter combinations overseveral types of test sites (inclu d ing combina tions of filterson each lens).Spectral radiometric calibration will be performed on eachmission by photographing the moon within four days of fullmoon, during a passage of the da rk side of the earth orbit.A film vault is used for storage of the film when photographsare not being taken to protect the film from radiationdamage.Earth Terrain Camera (S190B)The Ea rth Terrain Cam era (ETC ) will be mounted in ascientific airlock in the orbital workshop mod ule d uringoperation. The scientific airlock is used as a window forviewing the earth's surface. The camera is equipped with a f/4lens with a focal length of 0.4572 meters (18 inches),providing ground coverage of approximately 109 kilometers(59 nautical miles) square surface coverage (11,881 squarekilometers area) from the orbital altitude. Refer to Figure 14.Compensation for spacecraft forward motion is provided.Sequence photography rates of 0 to 25 frames per minute arepossible, thus providing up to 85% overlap between framesand providing stereo photog raph y. Shutter speed s availableare 1/100, 1/140 and 1/200 of a second.The camera utilizes 0.127 meter (5 inch) film of 2.6 mil basesupplied in cassettes of approximately 450 frames each. Thepicture size is 0.1143 meters (4.5 inches) square. The camerais designed to utilize the following film types and filters:

Wavelength, WrattenFilm Type M icrometers Filter No.Aerial color, high 0.4 - 0.7 NeutralresolutionHigh-definition aerial 0.5 - 0.7 12black and whiteAerochrome IR, color 0.5 - 0.88 12The expected ground resolution for the proposed film andfilter combinat ions will vary from 10 meters to 46 meters(37 feet to 150 feet).

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As with the m ultispectral camera (S190A), spectral radiom et-ric calibration will be performed on each mission by photo-graphing the moon within four d a y s of full m o o n .P E R F O R M A N C ECrew ActivitiesThe Skylab Earth Resource Ex periment Package provides amanned earth observation facility with unique capabil i tiesnot presently possible with automated systems. The crewmenon board Skylab provid e th e ability to evaluate test sitecond itions, primarily wea ther and visibility, and revise photo-graphy activities as conditions warrant. For some phases ofth e operation, th e astronauts will select th e picture sequencesbased on their direct observation of the ground site usinganother earth resources instrument, th e Viewfinder andTrac king System telescope which is a part of the infraredspectrometer exper iment . Addi t ional ly , th e astronauts loadand unload camera film, set up the camera controls, removethe protective covers from the camera viewing port, installthe S190B in the scien tific airlock and make other prepara-tions for photography operations. The SI 90A camera isdesigned for inflight maintenance of critical subsystems byth e crew.ConstraintsWhile low sun angles may be desirable for some photography,such as emphasizing topographical feature shadows, mostphotography in the summer hemisphere will be obtainedwhen the sun elevation angle is greater than 30, and in thewinter hemisphere when the sun elevation is greater than 20.The angle at which the sun strikes the earth's surface affectsnot only th e quantity of light reflected to the camera, butalso affects the spectral quality of the light and producesshadows which may obscure some target areas.Weather over the test site m ay constrain certain photographicearth observation passes, if the degree of cloud coverbecomes excessive.Certain earth observation tasks m ay require supportingaircraft and ground support data to be taken within aspecified time relative to the orbital observations fo r correla-tion with Skylab generated data. Failure to obtain thesesupporting data within an acceptable time fram e may furtherrestrict performan ce of planned spacecraft data taking passes.DATA OUTPUTFollowing recovery of the SI90A flight film from eachmission, the N A S A Johnson Space Center will process and

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develop the film for distribution under stringent processquality controls to insure maximum data accuracy. Eachframe of the original film will be identified and marked withthe mission number, roll number, and frame number. Theproducts proposed for distribution to EREP Principal Investi-gators and the EROS Data Center will include secondgeneration positive1 transparencies (color and black andwhite) and second generation direct negatives (black andwhite). Enlarged paper prints,(up to 8" x 10" maximum) andcontinuous process 2X enlargements paper prints (black andwhite) of selected frames may also be produced.Computer processing of the flight magnetic tape data willprovide computer-compatible tapes and tabulated listingdefining: (1) the latitude and longitude of the principal pointand projection of the four corners of each photograph, (2 )calculated frame exposure times, (3 ) frame number, (4 ) filternumbers, (5) film type, and (6) aperture settings for eachexposure. Plots of the field-of-view of the camera groundtrack will also be available. These data outputs will be used tocompile a film catalog listing for each mission.The S190B data outputs will be similar to those previouslydiscussed for the S190A experiment.


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Sect/on 3Infrared Spectrometer


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BACKGROUNDThe atmosphere of the earth is composed of a mixture ofgases (nitrogen, oxygen, carbon dioxide, argon, ozone andminor constituents) in which are suspended a wide variety ofparticles with a great range in size and chemical compositionand which contribute to absorption and scattering ofradiation. Water vapor, carbon dioxide and ozone are theprincipal molecules which cause radiation to be absorbed, andgaseous molecules, liquid drops and solid particles suspendedin the atmosphere scatter the radiation. As a result, theradiation from a source is attenuated and the contrastbetween the background and the source may be degraded.This can come about in four ways:

Radiation from th e source may be absorbed by gasesin the path . - . . . . . . Radiation from the source may be deflected orscattered by particles suspended in the path so that itappears to come from the area which surrounds thesource The gases and particles suspended in the path maythemselves radiate There may also be scattering into the path of theradiation. Scattering agents in the path may deflect orscatter radiation in such a way that radiation whichoriginated at some distance from the object viewedmay appear to the sensor to have originated at the

source. (Refer to figure 15)The extent to which each of these effects acts upon a beamof radiation as it is transmitted through the atmospherefluctuates with time as meteorological conditions change.(The amount of water vapor in the path varies over a widerange, as does the amount of ozone. The numbers of solidparticles and liquid drops in the atmosphere also vary within.wide limits.) The resulting radiation obtained at the remotesensor differs from the radiation transmitted by the object,due to atmospheric attenuation. An example of this isthe red appearance of the setting sun where the blue light hasbeen largely scattered out of the beam in the long atmospher-ic path. Thus, the radiation reaching the sensor (the eye) hasvery little of the blue component in it, although the radiationemanating from the object being viewed did have a bluecomponent.The infrared spectrometer experiment is designed to make afun d a m en t a l evaluation of the applicability and usefulness ofsensing earth resources from orbital altitudes, in the visiblethrough near-infrared (i.e., 0.4 to 2.4 micrometers) and in thefar-infrared (i.e., 6.2 to 15.5 micrometers) spectral regions,

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Emitted Radiation fromAtmosphere \\\ /Evapotranspiration/

'\ tm /Reflected & EmittedRadiation FromVegetation

-Reflected ** /7**Sunlight /Direct / .' IISun- / / II Light// // / / // / ' I/ / Dust & ,' /-.:/: Particles '

^ . Radiation4 / from Vegetation/Reflected 4& EmittedV.

Emitted Radiationfrom GroundReflectedSunlight

Figure 15 Reflected and Emitted Radiation Energy Exchange in aNatural Environment

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and to assess the value of real-t ime identificat ion of groundsites by an astronaut.The reliability of spectral signature identification fromorbital altitudes will also be determined by comparing theinfrared spectrometer results with concurrent measurementsfrom aircraft and ground test sites. This technique has thepotential of providing a means of monitor ing from space theextent and health of surface vegetation, withou t the need forspatial resolution of individ ual plants. Geological inform ationand precision sea-surface temperature measurements will alsobe obtained.Although a similar instrument ha s been used to accumulatedata from aircraft flights, the resolution and the contrast inth e image are significantly different fo r remote sensing fromorbital altitudes. It follows, therefore , that development testsfrom spacecraft are a vital extension of similar exp erim en tswhich have been conducted from aircraft . Measurementsfrom spacecraft have many advantages of w hich vast areas ofcoverage with uniform lighting may be the most important .SCIENTIFIC OBJECTIVESThe prim ary fu nc tion of the infra red spectrometer is toquantitatively determine the effects of the atmosphericattenuation and radiat ion from surface features over a broadspectral range, and to determine the accuracy with whichsignals arriving at the sensor can be corrected for theatmospheric affects. These objectives w ill be acc om plishedthrough the collection of data concurrently in three locationsfor a given ground target: The solar radiation at the targetwill be measured on the ground; aircraft with a spectrometersimilar to the one on the Skyla b will obtain da ta from 7 ,620meters (25,000 feet); and an astronaut will record spectro-meter data while "tracking" the target from orbit. Acomparison of these data sources, and their application intoa mathematical model of the atmosphere, will be utilized todetermine th e atmospheric effects on the radiation from th escene. The data obtained will be calibrated in radiance andwavelength, throughout th e spectral region covered by thesensor, by means of internal reference infrared sources (i.e., B L A C K B O D Y R e f e r to G l o s -black bodies). . sary for d e f i n i t i o n .The field of view of the Skylab Infrared Spectrometer issmaller than that of any previous satellite spectrometer,allowing the sensor to look at relatively small sites on theground; however, this small field of view is acceptablebecause an astronaut will operate th e sensor using a View-f inder/Tracking System (V/TS) to ident i fy and t rack groundsites, thereby keeping the spectrometer field of view fixed onthe sites for several spectral scan s.

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By comparing the data collected from the Skylab IRspectrometer with the data taken simultaneously on theground and from aircraft, investigators will be .able to assesstheir requirements regarding infrared sensor c apa bility, sensi-tivity, and spectral resolution, and to evaluate the utility ofthis application of remote sensing from space.

EQUIPMENTThe infrared spectrometer has three "major elements: aCassegrain optical system which provides an image of thescene to the other two elements; a filter wheel spectrometerwhich measures the inten sity of the ima ge in various spectralbands; and an optical viewfinder system which looks alongthe same line of sight as the spectrometer and allows theoperating astronaut to view and photograph the ground site.Refer to Figure 16.A 16 millimeter data acquisition camera will be mounted tothe V/TS to allow the astronaut to photograph the site bein gtracked.The spectrometer splits the incoming radiation into shortwavelength (0.4 micrometers to 2.5 micrometers) and longwavelength (6.6 micrometers to 16.0 micrometers). Theradiation in both channels passes through a chopping wheelthat allows intermittent comparison with known calibrationsources providing a baseline of radiance (refer to Figure 17).A circularly variable filter wheel transmits individual radia-tion bands in sequence, and then the two radiation beamspass to detectors. The detector output, the difference inradiance between the incom ing rad iation and the referencesources, is recorded on magnetic tape. Acalibration sequencecan be initiated by the astronau t w hich inserts calibrationsources into the field of view of the spectrom eter.The V/TS consists of a telescope for astronaut viewing, agimballed mirror for tracking and acquisition of sites, and theoptics necessary to provide a focused radiation beam to thespectrometer. (The sensor field of view and astronauttracking capabilities are illustrated in Figure 18.)The viewfinder tracking system utilizes a telescope whichpicks up its image from a mirror mounted on the back of thesecondary mirror in the cassegrain system. This telescope hasa magnification range from 2.25 to 22.5, which allowsground coverage of 129 to 12.9 kilometers (70 to 7 nauticalmiles) in diameter. An internal alignment system using acollimator and alignm ent prism provides a precise relation-ship between the spectrometer and viewfinder fields of view.Refer to Figure 19.


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GimbaledMirrorRadiation toVTS Telescope

BlackBody Alignment'Prism CassegrainOptics

Radiation toSpectrometer

Figure 19 SI 91 Initial Optics and Alignment

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PERFORMANCECrew ActivitiesThe astronaut has less than one minute to locate the site inhis field of view. In acquiring the ground sites, the astronautmust maintain a 0.435 kilometer (0.235 nautical mile)diameter resolution element within a circle of approximately1.852 kilometer (1 nautical mile) diameter for 1 second inorder to permit one complete spectral scan (refer to Figure18).The scene in the viewfinder will be photographed with a 16millimeter camera attached to the viewfinder. The astronautwill assist in selecting secondary ground sites, if the primarysite is obscured by cloud cover, as well as other targets ofopportunity as they become available.ConstraintsData will generally be taken when the sun-elevation angle atthe ground site is greater than 20. Because the crewmemberplays a vital part in the experiment by visual recognition andtracking of the sites, it is essential that the sites have thecharacteristics necessary for this task, such as good lead-inpoints, easy recognition, and clear boundaries.Film for the camera will be stored in a vault to protect itfrom the radiation levels prevailingat the Skylab altitude.DATA OUTPUTThe SI 91 experiment photographic data outputs will besimilar to those previously discussed in the S190 experimentsection; however, the S191 film will be identified on the filmleader by roll number, by agency (NASA), and by missionnumber. The film on each 16 millimeter roll will be edgenumbered with a footage counter every fortieth frame. S191photographic catalog tabulations will include boresightcamera pulses correlated with Greenwich Mean Time (GMT),target data pulse, sun angle, spacecraft position and radio-meter calibration wheel position.The S191 sensor processed digital data outputs from NASA'sJohnson Space Center will include:Tabulationsa) Calibration wavelengths with associated responses andintermediate radiance parameters.b) Wavelengths with calculated radiances and selected datascans.

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c) Raw data from sensor data channels, with redundancysuppression optional.Plotsa) Time history plot of sensor status data in engineeringunits or raw data.b) Cross plots of aperture radiance or raw data versuswavelength.Computer Compatible Tapesa) Aperture radiance versus wavelength and spacecraft atti-tude and position. Correlated with GMT.b) GM T correlated ra w data stream.c) GMTcorrelated sensor status data in engineering units orraw counts.


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Section 4Multispectral Scanner


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BACKGROUNDThe Multispectral Scanner (S192) experiment is designed toassess the feasibility of multispectral techniques, developed inthe aircraft program, for remote sensing of earth resourcesfrom space. Specifically, attempts will be made at spectralsignature identification and mapping of agriculture, forestry,geology, hydrology, and oceanography sites.The S192 optical mechanical scanner will operate in thirteendiscrete spectral bands from 0.4 to 12.5 micrometers. Thesebands are relatively wide and are located in spectral regionswith high atmospheric transmission.The spectral range covered by the scanner overlaps that forboth the Multispectral Photographic Facility and the InfraredSpectrometer. This will permit a very useful cross check ofthe data resulting from these three experiments. Inaddition,the IR spectrometer data will hopefully provide atmosphericdensity profiles which would be extremely useful for correct-in g the primary causes of atmospheric attenuation of themultispectral scanner data.Multispectral scanners have been flown in aircraft for severalyears, and promising results have been obtained for identify-ing and mapping vegetation and surface soils. Some progresshas also been made in utilizing the remotely sensed data forassessing the health of vegetation. Achievements in this areainclude crop identification, crop inventory, soil and geologicmapping based on unique signatures for certain crops andsoils in these bands.

SCIENTIFIC OBJECTIVESThe objectives of the multispectral scanner are as follows:

To obtain quantitative radiance values simultaneouslyin several spectral bands over selected test sites in theUnited States and other areas.To evaluate the usefullness of spacecraft multispectraldata in crop identification, vegetation mapping, land-use determination, studies of ocean chlorophyll con-tent, ocean currents, water depth, identification ofcontaminated areas in large bodies of water, andsurface-temperature mapping.To evaluate and determine the feasibility of usingautomatic data processing, spectrum matching tech-niques for the identification of earth resource fea-tures from space.

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To compare the results of automatic processingtechniques with direct photointerpretation of scannerimagery generated from the different spectral bands.To compare and evaluate the imagery from theseveral spectral bands with the photography obtainedfrom the Multispectral Photographic Facility experi-ment.

E Q U I P M E N T The basic instrument design is a mechanical optical scannercombined with a folded reflecting telescope used as a radia-tion collector.The Multispectral Scanner will provide the capability forgathering high resolution, quantitative data on the radiationthat is reflected and emitted by selected test sites in thirteendiscrete spectral bands of the visible, near-IR, and thermal-IR regions of the spectrum.The SI 92 instrument contains 13 detectors, each responsiveto a different band, as shown below:

Band12345678910111213

WavelengthCoverage,Micrometers0.41.46.52.56.62.68.78.981.091.201.552.1010.20

to 0.46to .51.56.61.67.76to .88to 1.08to 1.19to 1.30to 1.75to 2.35to 12.5Incoming radiant energy is collected by a 0.43 meter (17inch) spherical collecting mirror that is the major element ofa folded reflecting telescope; the outer annulusof the field ofview is scanned by a rotating pair of mirrors, passed througha reflective Schmidt corrector mirror and constrained to passthrough a field stop which acts as the entrance slit of aprismspectrometer. A dichroic mirror is used to separate theradiation in bands 1 to 12, (short wavelength) inclusive, fromthe long wave length thermal band (band 13). Refer to Figure20 for a schematic diagram of the optic system.

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The short wavelength radiation (bands 1 to 12) is dispersedby a subtractive-type dispersion double prism, and thevarious bands are brought to focus at different positionsin the focal plane of the spectrometer. The radiation frombands 1 to 12 is then detected by amercury-cadmium-telluride (Hg:CdTe) semiconductor detector array, cooled to92 K. The detector outputs are then amplified through thepreamplifier stage before any electrical transmission takesplace.Each channel is calibrated 100 times per second. Thecalibration reference for the visible and near-IR wavelengthsis provided by a tungsten lamp. For the thermal IRwavelength, two blackbody references are provided whichoperate in the range of 240K to 320K.The Multispectral Scanner has a conical line scan with aninstantaneous square field of view of 0.182 milliradians(79.25 meter square area ground coverage). Although thescan assembly rotates a full 360 degrees, only the forward 110degree portion of the scan is used for obtaining data. Theradius of the scan circle is 41.85 kilometers (22.6 nauticalmiles), providing a swath width of 74.08 kilometers (40nautical miles) for the 110 degree portion used for takingdata (refer to Figure 21).PERFORMANCECrew ActivitiesAstronauts will operate the Multispectral Scanner in accord-ance with flight plan timelines. However, the astronaut canvastly increase the amount of useful data recorded by onlytaking data under relatively clear conditions and by limitingthe data taken to areas of interest, including some highlyinstrumented test sites and also targets of opportunity. Thisca n be done by utilizing the infrared spectrometer viewfindertelescope to evaluate test site conditions in real time duringan earth observation pass.ConstraintsThe operating constraints for this experiment consist primari-ly of obtaining data over the specific test site with anacceptable degree of cloud cover, and generally with a sunelevation at the test site equal to or greater than 30.

K = degrees Kelvin thermomet-ric scale; 0K is absoluteozero,and equals minus 273.13 C orminus 459.4F.

DATA OUTPUTThe sensor data requires extensive computer processing ofthe digital data upon recovery of the flight data tapes. Somerepresentative types of data outputs that will be available


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Section 5Microwave Radiometer/Scatterometerand Altimeter


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and at a particular temperature) is a function of the surfaceroughness of the body. Thus, the microwave radiometer/scat-terometer experiment can extract information about theroughness and apparent temperature of the terrestrial surface,when the dielectric properties are known. The surfacedielectric properties of the land vary a great deal according tomaterial composition, moisture content and the characteris-tics of vegetation. Therefore, to obtain the desired informa-tion over land coverage, the dielectric properties of groundsites must be supplied concurrent with the observations madefrom Skylab by other experimental means.Since the dielectric properties of oceans are essentially thesame everywhere, the microwave radiometer/scatterometerexperiment is suitable for establishing global patterns ofocean surface roughness and brightness temperatures. In turn,the ocean surface roughness patterns can be related to oceansurface wind patterns which can be used to aid ship naviga-tion and numerical weather prediction in oceanography andmeteorology.Radar ocean backscattering and radiometric measurementshave been carried 'out extensively by aircraft which usuallyhave high spatial resolution, but limited coverage. Spacebornemicrowave radiometer/scatterometer measurement offer ex-tensive coverage with useful resolution. The measurementsmade by N A S A Earth Resources Aircraft scatterometerstudies have led to the following conclusions:

Increasing wind speed and the related ocean surfacewavelets result in increasing values of returned energyfor all angles of incidence between 15 and 45 degrees.

As wind velocity increases, the increases of returnedenergy are substantial. The radar return is higher for upwind-downwindconditions than for crosswind conditions.

The spaceborne microwave radiometer/scatterometer mea-surement results will be used to verify these aircraft findingsat near the same radar operating frequency (13.9 GHz), andto establish the feasibility of determining patterns of oceansurface roughness and wind fields on a global scale.An altimeter experiment that shares the antenna assembly ofthe microwave radiometer/scatterometer experiment is alsoincluded in this experiment. The main purpose of thealtimeter experiment is to obtain information about oceansea state effects on transient radar pulse characteristics. Datawill be used for future altimeter design for earth physics andgeodetic applications.


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SCIENTIFIC OBJECTIVESThe purpose of this experiment is to study the application ofactive and passive microwave sensors to earth resourcesinvestigations from orbital altitudes. The microwave radio-meter/scatterometer objectives in ocean, land and instrumentstudies are:

Measure, near simultaneously, the radar backscatter-ing characteristics and microwave emission fromvarying ocean surfaces and their inter-relationships. Establish global patterns of ocean surface roughness,of wave conditions and of surface wind fields. Identify areas of clouds and rain over the ocean andobtain atmospheric attenuation data to aid in weatherprediction. Mapsnow and ice cover and seasonal advances andretreats, gross vegetation regions and their seasonalchanges, extent of recent rainfall and flooding inremote regions. Determine whether gross differences between majorworld biomes may be detected with sufficient preci-sion to be valuable. Determine the feasibility of measuring differences insoil types and texture to the precision needed forwater runoff studies, of measuring soil moisture

averages over large regions and of measuring micro-wave radiant energy output of metropolitan areas. Investigate the feasibility of removing the effects ofatmospheric attenuation on the scatterometer bymeasuring the microwave brightness temperature withboth S193 and S194 radiometers.

The purpose of the altimeter is to obtain precise altitudemeasurements of the variation of the height of the oceansurface and land features, and correlate return waveformshapes with sea states. The altimeter ha s several operationalmodes which vary transmitted pulse width, pulse spacing andreceiver bandwidths in order to provide data for design offuture systems.

BIOME A complex biotic com-munity covering a large geo-graphic area (such as tundra,desert, coral reef, woodland,etc.) and characterized by thedistinctive life forms of impor-tant climax species of plants andanimals.

EQUIPMENTThe experiment consists of an antenna and a receiver for theradiometer, scatterometer and the altimeter. The radiometeran d scatterometer may be operated together or inde-pendently, and the altimeter operates independently upon

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astronaut command. The frequency reference is a crystaloscillator whose frequency is multiplied and mixed such thatthe transmitters of both the altimeter and scatterometergenerate signals centered at 13.9 GHz.The receivers for eachinstrument also operate at 13.9 GHz. The scatterometer andaltimeter have their own transmitters and generate 8 wattsand 2 kilowatts respectively.Since the antenna is capable of scanning the received signalsfor doppler shifting by the incorporation of filters withdifferent center frequencies for each of five scan angles, thescatterometer design ha s sufficient dynamic range for deter-mining various wind, sea state, polarization, surface rough-ness and surface dielectric properties, as well as stormconditions.The radiometer senses the brightness temperature, which isbased upon the thermal emittance, surface roughness, dielec-tric properties and atmospheric absorption, and producesradiation measurements from which brightness temperaturecan be derived with a resolution of approximately 1K.The altimeter will be capable of maintaining a precision ofapproximately 0.9144 meters (1 yard), i.e., it will be able todistinguish sea states with a resolution of one yard inaveragewave height. As a 11.1 kilometer (6 nautical mile) area isbeing studied, this must be a statistical value. The altimeterreturn pulse shape reproduction, as well as precision, will beused for the design of future radar altimeters. The antennadish is 1.125 meters (44.5 inches) in diameter and the beamwidth is 1.5.The instantaneous ground coverage of the instrument is a11.1 kilometer (6 nautical mile) circle from spacecraftaltitudes. Figures 22 through 26 illustrate some of theequipment operational scanning modes.DATA OUTPUTSI 93 data "outputs available from NASA Johnson SpaceCenter computer processing of the radiometer and scatter-ometer digital data will include:Computer Compatible Tapesa) GMT correlated radiometer aperture radiance, scatter-ometer backscattering coefficients; spacecraft attitude,altitude, position; and velocity. Center of the sensorfield-of-view, and sensor status data in engineering units.b) GMTcorrelated raw data stream.


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Tabulationsa) Time history tabulation and plot of selected segmentsofraw radiometric temperature and raw backscattering data.b) Tabulation of geodetic latitude and longitude of center ofsensor field-of-view as a function of time.c) Tabulation of averaged scatterometer backscatter in agiven time interval.d) Tabulation of averaged radiometer antenna temperaturein "a- given time interval.Plotsa) Plots of the sensor field-of-view on a latitude-longitudegrid with time annotations. The sensor dwell position willbe indicated with a point representing the sensor beam

center.b) Scatterometer backscattering as a function of angle ofincidence.c) Radiometer antenna temperature as a function of angleof incidence.d) Scatterometer backscattering for each pitch offset angleas a function of roll angle for each polarization combina-tion.e) Radiometer antenna temperature for each pitch offsetangle as a function of roll angle for each polarizationcombination.S193 data outputs available from computer processing of thealtimeter data will include:Computer Compatible Tapesa) Raw data stream and sensor status data correlated withG M T .b) GMT correlated uncorrected backscatter, time history ofautomatic gain control voltage, spacecraft attitude andaltitude, location of center of sensor field-of-view, theangular difference between the center of the sensorfield-of-view and the spacecraft nadir point, and sensorstatus data. Alldata in engineering units.Tabulationsa) Time history tabulation of altimeter range.


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b) Time history tabulation of altimeter data in engineeringunits, with angular difference between center of sensorfield-of-view and spacecraft nadir point.c) Mean and standard deviation of altimeter range datarelative to spacecraft tracking altitude data.Plotsa) Average pulse shape for designated time intervals.b) Plots of selected sample/hold gate pulses as a function oftime.c) Plot of position (with respect to local vertical) of theantenna as a function of time for the nadir seeker mode.d) Plots of the sensor field-of-view at each dwell position ona latitude-longitude grid with time annotation.

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Section 6L-Band MicrowaveRadiometer


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BACKGROUNDThe L-Band Radiometer (S194) experiment is designed tosupplement the Microwave Radiometer/Scatterometer andAltimeter (S193) experiment in measuring th e brightnesstemperature of the earth's surface along the spacecraftground track. The S194 experiment is basically th e same inoperating principle as the radiometer portion of the S193experiment, except th e operating frequency is changed from13.9 GHz to 1.42 GHz. The primary function of theexperiment is to complement the measurement results ofexperiment SI93 by taking into consideration the effect ofwater vapor on radiometric measurements. By using tw ofrequencies simultaneously in measurements, corrections canbe made on radiometric data to remove the water vaporeffects.The instruments to be used in this experiment are patternedafter those which have been used in the N A S A EarthResources Aircraft Program.SCIENTIFIC OBJECTIVESThe objective of the L-Band Radiometer experiment is toevaluate the applicability of a passive microwave radiometerto the study of the earth from orbital altitude. Theradiometer will measure the brightness temperature of theterrestrial surface along the spacecraft ground track to a highdegree of accuracy. The resulting temperature will be used tocompile a surface brightness temperature map.

EQUIPMENTThe S194 antenna receives signals from the radiation emis-sion of a point on the earth surface, through any interveningclouds (i.e. water vapor). The mean value of the signal can beaccurately determined if it is observed long enough to gain ameasurable signal. The signal is compared with the measuredmean value of another signal from a calibrated source withkno wn temperature (blackbody). The comparison constitutesthe radiometric measurement and can be correlated to give ameasure of the brightness temperature of the surface, if thedielectric properties and surface roughness parameters arek n o w n .The experiment utilizes a fixed antenna that consists of aneight element by eight element planar array of dipoleradiators spaced one-half wavelength apart. (One wavelengthis approximately 21 centimeters.)The antenna has a 15 half-power beam width which impliesthat 50 percent of the energy received by the antenna will bereceived in the 15 solid pyramid centered about the verticalaxis.

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In addition, the antenna will receive over 90 percent of theenergy available in the field of view in a 36 solid pyramid.These angles are contained in the primary lobe of theantenna. The 36 angle will encompass a swath width ofapproximately 267 kilometers (144 nautical miles) at the 436kilometer orbital altitude, and the signature will be influ-enced by the entire view area. However, the signaturerecorded by the instrument will be influenced to a muchlarger degree by the brightness of the material containedwithin the 15 beam width; i.e. a 110 kilometer (60 nauticalmile) swath centered' about the nadir point (refer to Figure27) .Absolute sensor radiometric calibration will be acquired byviewing cold sk y conditions.P E R F O R M A N C ECrew ActivitiesThe astronauts will perform instrument calibrations, operateand monitor the equipment during Skylab earth observationpasses.ConstraintsThe experiment will be operated over test sites where groundtruth supporting data is available, and usually in conjunctionwith the Microwave Radiometer/Scatterometer and Altimeter(S193).DATA OUTPUTThe SI94 sensor digital data will be computer processed bythe N A S A Johnson Space Center upon recovery of eachflight magnetic tape. Some typical data outputs for the S194data include:Computer Compatible Tapesa) GM T correlated ra w data stream.b) GMT correlated antenna temperature, spacecraft attitudeand position, location of sensor field-of-view, and sensorstatus data. All data in engineering units.Plotsa) Time history plots of radiometric antenna temperature.b) Time history plot of the raw data stream.


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c) Plots of the centerline and approximate sidelines of thesensor field-of-view on a latitude-longitude grid with timeannotations.Tabulationsa) Radiometric antenna temperature including intermediateloss calculation factors.b) Tabulations of raw data stream.c) Sensor status data in engineeringunits.d ) Tabulation of sensor field-of-view, su n angle, and space-craft attitude and position.

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Section 7Related CurriculumActivities


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RELATED CUR R ICULUM TOPICSThe earth resource experimental sensors themselves presentideas for the teaching of many basic scientific concepts. Theimagery data obtained from these sensors present yet anothersource of information to enhance and extend the teachingofa variety of scientific disciplines.Because each of the sensors employs many of the same basicscientific concepts, the entire group of experiments will betreated together.

Biology Distribution of biomes. Absorption characteristics of chlorophyll. Relationship between water temperature, zooplank-

ton, and schools of fish. Migration patterns of whales and fish. Pollution concentrations in relationship to technolog-ical development, urbanization and topographic char-acteristics. Binocular vision.

Chemistry Relationship between energy absorbed and the chemi-cal nature of the material. The effects of atmospheric pollutants on the warmingand cooling of the earth's surface. The variation in reflected and emitted microwavesignal for materials of differing dielectric constant. Characteristics of infrared detectors (e.g., SiPbS,

HgCdTe) .Earth Sciences

Ground scales in imagery. Locating political boundaries. Topographical features. Distribution of soil types to climate.

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Distribution of resources with relation to politicalboundaries. Cartography. Wind patterns over oceans. Effect of large metropolitan areas with respect to

heat output, atmospheric changes, etc. Effects of cloud cover on warming and cooling of theearth's surface. The effect of surface features on cloud formation. Vertical temperature gradient in relation to cloudformation. Effect of land use on microwave radiation (stripmines, lumbering, agriculture, reservoirs, etc.). Drainage patterns in relation to substrate topography. Land use studies. Ocean currents an d migratory practices of whales andfish. Seasonal variation of icebergs and glaciers. Location of faults. Stresses upon agricultural crops.

Electronics Characteristics of detectors. Calibration of detectors. Spectrometers. Optical scanners. Microwave. Radar. Scatterometers. Radiometers. Antenna.


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Absorption and heating. Black body radiation. Particle and wave theory. Characteristics of electromagnetic radiation. Speed of light. Binocular vision (stereo photography).

Social Science Habitation concentrations in relation to natural re-sources, land area, natural transportation routes, etc.(i.e., optimum location for cities). Natural political boundaries.

SUGGESTED CLASSROOM DEMONSTRATIONSDemonstration of Color Reconstruction by Addition andSubtractionWhen red, green and blue light are projected together so thatthese impinge upon one another, the result is white light (ornearly so, because it depends upon the intensity of each