principles of remote sensing

Principles of Remote Sensing Image from NASA Goddard Space Flight Center, NOAA GOES-8 satellite, 2 Sep 94, 1800 UT

CS 128/ES 228 - Lecture 9a

Scanning planet Earth from space


History of remote sensingEarliest vehicle was ? Tournachon (Nadar) took 1st aerial photograph in 1858 (since lost) Earliest conserved aerial photograph: Boston, J. Black, 1860 Early applications were in military reconnaissance


WWII heavy use of aerial reconnaissanceImages: Avery. 1977. Interpretation of Aerial Photographs. 3rd ed. Burgess Press, Minneapolis, MN.


Spy planes & the Cold War


Satellite sensingRussian Sputnik (1957) - radio transmitter only Rapid response by US: CORONA (1960) Early applications: military reconnaissance


Advantages of satellitesWide coverage Vertical (orthogonal) view Multi-spectral data bands Rapid data collection


Sources of EM radiationKey distinction:passive sensingactive sensing Spectral signaturesTop: Lo & Yeung, fig. 8.1 Bottom: ASTER Spectral Library (http://speclib.jpl.nasa.gov)


Types of EM radiation usedThree important spectral bands:visible light infrared radiationmicrowave radiationImage from NASA 1987. SAR: Synthetic Aperture Radar. Earth Observing System, Vol. IIf.


Atmospheric attenuationScatteringcaused by aerosols (water vapor, dust, smoke) more intense at shorter wavelengths why the sky is blue

Absorptioncaused by gas molecules (H2O, CO2, O2, O3) each molecule absorbs at a specific wave-length result: atmospheric transmission windows


Transmission windows UV-visible-IR MicrowaveImage from NASA 1987. From Pattern to Process: The Strategy of the Earth Observing System. Vol. II.


Classes of sensorsPhotographicpanchromatic color

Infrared (IR)film (near IR)thermal IR sensors for longer wave-lengthsMulti-spectral scanners sensors for many wavelengths image scanned across sensorsRadarRAdio Detection And Ranging active imaging


Visual sensors: film typespanchromatic near-infrared color

Both images from Committee on Earth Observation Satellites http://ceos.cnes.fr:8100/cdrom-98/ceos1/irsd/content.htm


Infrared sensorsIR penetrates haze and light cloud cover can be used at night used by military for camouflage detection IR signature often distinct from visible image


Color IR filmUsed with yellow (blue-absorbing) filter 3 primary pigments, but not true (visible) color - green vegetation = red - clear water = dark blue - turbid water = bright blue - soil = green - urban areas = pale blue

Top image: Committee on Earth Observation Satellites http://ceos.cnes.fr:8100/cdrom-98/ceos1/irsd/content.htmBottom image: Avery. 1977. Interpretation of Aerial Photographs. 3rd ed. Burgess Press, Minneapolis, MN.


Multispectral sensorsVisible + IR spectra Comparison of film and electronic sensor spectral bandsTop: Avery 1977. Interpretation of Aerial Photography. Burgess Publ., NinneapolisBottom: ASTER Science page (http://www.science.aster.ersdac.or.jp/users/parte1/02-5.htm#3)


Radar sensorsactive sensing day & night, all weather less affected by scattering (aerosols) vertical or oblique perspectiveLo & Yeung, fig. 8.13


Uses of radar: altimetry satellite-nadir distance geoid & topographic measurements sea elevation, tides & currents wave/storm measurements

Both images from NASA 1987. Altimetric System. Earth Observing System, Vol. IIh.


Uses of radar: SAR glaciology hydrology vegetation science geology

Image from NASA 1987. SAR: Synthetic Aperture Radar. Earth Observing System, Vol. IIf.


Sensor resolutionSpatial: size of smallest objects visible on ground. Ranges from < 1m to > 1 km. Inversely related to area covered by image Spectral: wavelengths recorded. Ex. panchromatic film (~0.2 0.7 m); Landsat Thematic Mapper bands (0.06 to 0.24 m wide) Radiometric: # bits/pixel. Ex. Landsat TM (8 bit); AVRIS (12 bit) Temporal: for satellite, time to repeat coverage. Ex. Landsats 5 & 7 (16 days)


Spatial resolution: analog (film) imagesDepends on:lens quality & camera stability size of negative film grain

High quality aerial photograph:up to 60 lines/mm 9 x 9 (23 x 23 cm) negative scanned at 3000 dpi = ~725 megapixels if 8 bit image depth, >5 GB image size


Ground resolutionG. R. = scale factor / film resolution


Spatial resolution: digital (satellite) imagesA sampler of recent (civilian) satellites:


Satellite image resolutionQuickbird 2Commercial venture 0.63 m resolution U.S. trying to discourage open access to finer resolution images Digitalglobe.com


Satellite orbitsGeostationary36,000 km above equator Polarvarying heights often in Sun-synchronous orbits

Both diagrams from European Organisation for the Exploitation of Meteorological Satelliteswww.eumetsat.de/en/mtp/space/polar.html


Satellite coverageGeostationaryno polar coveragecoverage is 24/7low ground reso-lution (~ 1 km) Polarglobal coveragecoverage is dis-continuous

Both diagrams from European Organisation for the Exploitation of Meteorological Satelliteswww.eumetsat.de/en/mtp/space/polar.html


Geostationary orbitsEx. GOES satellitesMeteorological satellites GOES-8 at 75oW, GOES-9 at 135oW 5 bands (1 visible, 4 thermal infrared)

Image from NASA Goddard Space Flight Center, NOAA GOES satellite, Hurricane Floyd, 15 Sep 99


Polar orbitsEx. Landsat & Terra satellites705 km height, ~100 minute orbit 185 km swath

16 day repeat Sun-synchronous orbits (~0945 a.m. equator crossing)

Orbit tracking data from NASA http://liftoff.msfc.nasa.gov/realtime/JTrack/eos.html, 5 Mar 03


principles of remote sensing

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