Characteristics of remote sensing systems

Different kinds of images

• Panchromatic image• True-color image• False-color image

Panchromatic image

• If airborne cameras use black/white film or satellite sensors use a single band, it produces panchromatic image (gray scale image)

Color composite

• Color primaries: RGB (Red, Green, Blue)

• Many colors are formed by combining color primaries in various proportions

• Same principles apply to producing color images taken from airborne cameras or satellite sensors

Greyscale vs. RGB

• Greyscale is typically used to display a single band

• RGB (“Red”, “Green”, “Blue”) images can display 3 bands, corresponding to the red, green and blue phosphors on a monitor.

True color and false color images

• True color image- the color of the image is the same as the color of the object imaged.

• A false color image is one in which the R,G, and B values do not correspond to the true colors of red, green and blue. The most commonly seen false-color images display the very-near infrared as red, red as green, and green as blue.

• For instance, different types of vegetation might appear as blue, red, green or yellow. Intuitively, vegetation would appear green.

Vegetation appear red in this color composite

Describing Sensors

- Spatial resolution

- Spectral resolution

- Temporal resolution

- Radiometric resolution

Spatial resolution

• Spatial: pixel size; The size of the smallest possible feature that can be detected.

• In a digital image, the resolution is limited by the pixel size, i.e. the smallest resolvable object cannot be smaller than the pixel size.

• Fine or high resolution image refers to one with a small resolution size. Fine details can be seen in a high resolution image.

• Coarse or low resolution image is one with a large resolution size, i.e. only coarse features can be observed in the image.

• Aerial photo has higher resolution • The image resolution and pixel size are not equivalent.

Spatial resolution

A low resolution MODIS scene (1km) A very high resolution image acquired

by the IKONOS satellite (1m)

Spectral Resolution• The number, wavelength position

and width of spectral bands a sensor has

• A band is a region of the EMR to which a set of detectors are sensitive.

• Multi-spectral sensors have a few, wide bands(several spectral bands)

• Hyper-spectral sensors have a lot of narrow bands (hundreds of spectral bands)

Spectral Resolution

Multi-spectral

hyper-spectral

Radiometric resolution

• The radiometric resolution of an imaging system describes its ability to discriminate very slight differences in energy (intensity level)

• It depends on:

1- Radiance range-bits/pixel

2- Signal to noise ratio (S/N) of the detector. The ratio of the level of the signal carrying real information to that carrying spurious information as a result of defects in the system.

Radiometric Resolution

2-bit = 4 radiance levels 8-bit = 256 radiance levels

The finer the radiometric resolution of a sensor, the more sensitive it is to detecting small differences in reflected or emitted energy .

Temporal resolution

• How frequent a given location on the earth surface can be imaged by imaging system.– For satellite image, it can be regular

(satellites are orbiting the earth in regular time interval)

Earth Resource Satellites Operating in the Optical Spectrum• Landsat • SPOT • Meteorological Satellites

– NOAA satellites – GOES satellites

• Ocean Monitoring Satellites – Radar Satellites – Seasat – ERS-1 – JERS-1 – Radarsat

Introduction

• Satellite systems operating within the optical spectrum (0.3-14 m): UV, visible, near-, mid-, and thermal IR wavelengths

• Landsat and SPOT

• Higher resolution, contemporary programs (IKONOS, QuickBird)

Earth history of space imaging

• Cameras on rockets (Germany 1891, 1907)

• 1946-1950: beginning of space RS with small cameras aboard V-2 rockets (NM, USA)

• Meteorological satellites (initial application) TIROS-1 (1960)

• Corona, a military space imaging reconnaissance program (1960 - 1972).

Earth history of space imaging

• Manned space programs:– Mercury, Gemini, Apollo– Alan Shepard (1961): Made a 15-min suborbital

Mercury flight on which 150 excellent photographs were taken

– John Glenn (1962): Made 3 historic orbits around the earth and took 48 color photographs during Mercury mission MA-6

• Gemini GT-4: geological application

• Other geographic & oceanographic phenomena

Earth history of space imaging

• Apollo 9: multispectral orbital photography for earth resource studies

• 1973: Skylab: Earth Resources Experiment Package (EREP)

• 1975: US-USSR Apollo-Soyuz Test Project (ASTP) hand-held cameras, disappointing results

Landsat Satellite Program Overview

• Earth Resources Technology Satellites (ERTS) program (1967): a planned sequence of six satellites

• In 1975, ERTS was renamed by NASA “Landsat”

Landsat Program

• During the experimental Landsat phase, imagery was disseminated by Earth Resources Observation System (EROS) Data Center at Sioux Falls, SD.

• Satellites were operated by NASA and USGS was handling the data distribution.

Landsat Program

• Gradually, NOAA took over and the Landsat program operation was transferred to a commercial firm (Earth Observation Satellite Company – EOSAT).

• Landsat-7 operation reverted to the government; EROS Data Center is the primary receiving station, processing and distributing the data.

Landsat Program

• Landsat-1,-2,-3 images are catalogued according to their location within the Worldwide Reference System (WRS), by specifying:

– a path (each orbit within a cycle)– a row (individual nominal sensor frame

centers)– a date

Landsat Program

Landsat Program

• E.g. the WRS has 251 paths for Landsat –1, -2,-3 (number of orbits to cover the Earth in 18 days).

• Paths are numbered from 001 to 251, E to W, row 60 coincides with the equator.

ERTS-1 (Landsat-1)

• Launched by a rocket on 7/23/1972

• Operated until 1/6/1978

• The first unmanned satellite specifically designed to acquire data about earth resources on a systematic, repetitive, medium resolution, multispectral basis

• 43 US states & 36 countries

Landsat Satellite Program Overview

• Landsats carried combinations of 5 types of sensors:

– Return Beam Vidicon (RBV) camera systems– Multispectral Scanner (MSS) systems– Thematic Mapper (TM)– Enhanced Thematic Mapper (ETM)– Enhanced Thematic Mapper Plus (ETM+)

Landsat 1-3 orbital characteristics

• Sun-synchronous orbits: The satellite crossed the equator at approximately the same local sun time (9:42) every day

• Lunched into circular orbits at 900 km • Near-polar orbits travels northwards on one side

of the earth and then toward the southern pole on the second half of its orbit, 14 times a day

• Passing same point every (coverage repetition) • Sensors aboard imaged only 185 km swath• Globe coverage every 18 days (20 times/year)

Sensors Onboard Landsat-1,-2,-3

• Landsat-1,-2:

– A three-channel Return Beam Vidicon (RBV) camera system

– A four-channel MSS system

Return Beam Vidicon (RBV)

• Nominal ground resolution of cameras: 80 m

• Spectral sensitivity per camera: similar to a single layer of color infrared film (band 1: green (0.475-0.575), band 2: red (0.58-0.68), band 3: near IR (0.69-0.83)

• Failed within weeks of Landsat 1

Landsat-3

• Spectral sensitivity: green to near-IR

• 30 m nominal ground resolution

MSS System

• The MSS onboard Landsat-1,-2,-3 covered a 185 km swath width in 4 wavelength bands (green, red, and 2 near-IR) designated as bands 4,5,6,7.

• Note: In Landsat-4 and -5 they were bands 1,2,3,4.

• On Landsat-3 there was a band 8 (thermal band) but this failed shortly after launch.

Orbit Characteristics of Landsat-4 & -5

• In these missions, orbits were lowered from 900 to 705 km. This was done to aid in the improvement of the ground resolution of the sensors on board.

• 14.5 orbits/day (orbit period: 98.9 min)

• 16-day repeat cycle for each satellite (coverage cycle)• Local crossing at about 9:45 am.

• Landsat-4 &-5 WRS: 233 paths (001-233, E-W), with 001 crossing the equator at 64°36’ W longitude

• Same number of rows (60 coincides with the equator)

Sensors Onboard Landsat-4 & -5

• MSS and TM sensors

• MSS transmits 15 megabits/sec

TM transmits 85 megabits/sec

• MSS data are collected using a 80-m ground resolution cell

• MSS bands 1-4 in Landsat –4 & -5 corresponds to 4-7 of the Landsat–1,-2,-3

Sensors Onboard Landsat-4 & -5

• MSS used a quantization range of 6 bits (64 digital numbers), but TM uses a range of 8 bits (256 numbers) for its onboard analog-to-digital signal conversion.

• Finer radiometric precision Greater sensitivity to changes

Sensors Onboard Landsat-4 & -5

• Thematic Mapper (TM)• TM: highly advanced sensor, improved over MSS• 7 bands, (0.45-12.5 μm)

– TM data are collected using a 30-m ground resolution cell (thermal band: 120 m).

– The size of area viewed on the ground is called the resolution cell

– TM bands are more finely tuned for vegetation discrimination than those of MSS

– TM Data are best for use in several application areas (bathymetry, rock type discrimination, etc.)

Landsat TM Vs. MSS

• TM images cover a wider range of applications than Landsat MSS images, due to more spectral bands and improved spatial resolution.

• MSS images are better for large area analyses (geologic mapping)

Landsat TM Vs. MSS

• More specific mapping (detailed land cover) is difficult on MSS because many pixels are “mixed” pixels

• TM’s decreased Instantaneous Field of view (IFOV) produces less mixed pixels

• IFOV is the angular visibility of the sensor

• Incorporation of mid-IR bands (5 & 7) has increased the vegetation discrimination of TM data

Landsat-6 Planned Mission

• Launch failure on 10/5/93

• Landsat-6 would have occupied an orbit identical to that of Landsat-4 & -5

• The sensor of this mission was the Enhanced Thematic Mapper (ETM) (same bands, same resolution)

Landsat-6 Planned Mission

• ETM’s major improvement over TM was the addition of an eighth “panchromatic” band with a spatial resolution of 15 m.

• Another improvement was the use of a 9-bit analog-to-digital converter.

Landsat-7

• This program is jointly managed by NASA and USGS (http://landsat.gsfc.nasa.gov/announcements/program_update.html)

• Launched on April 15, 1999 (http://landsat.gsfc.nasa.gov/main/project.html)

• A new sensor : Enhanced Thematic Mapper Plus (ETM+)

• Same swath as ETM, similar orbits and characteristics• Swath: The area imaged on the surface.

ETM+

• Resolution– Bands1-5, 7: 30 meters– Band 6 (Thermal band): 60 meters– Band 8 (Panchromatic band): 15 meters

• Complete global view four times a year

ETM+

• Ground transmission of data either directly or stored onboard for later transmission

• GPS is included for subsequent geometric processing of the data

• Primary receiving station: EROS Dara Center, SD

ETM+ Spectral Bands

Landsat 7 +ETM Spectral Bands

Band Wavelength/ µm

Spectral Location

Principal Applications

1 0.45-0.52

Blue Designed for water body penetration, making it useful for coastal water mapping. Also, useful for soil/vegetation discrimination, forest type mapping and cultural feature identification.

2 0.52-0.60

Green Designed to measure green reflectance peak of vegetation for vegetation discrimination and vigor assessment. Also useful for cultural feature identification

3 0.63-0.69

Red Designed to sense in a chlorophyll absorption region aiding in plant species differentiation. Also useful for cultural identification.

4 0.76-0.90

Near infrared

Useful for determining vegetation stress, vigor, and biomass content, for delineating water bodies, and for soil moisture discrimination.

5 1.55-1.75 Mid-infrared

Indicative of vegetation moisture content and soil moisture. Also useful for differentiation of snow from clouds.

6 10.4-12.5

Thermal infrared

Useful in vegetation stress analysis, soil moisture discrimination, and thermal mapping applications.

7 2.08-2.35 Mid-infrared

Useful for discrimination of mineral and rock types. Also sensitive to vegetation moisture content.

Landsat Resources

• Data acquisition

)http://landsat.usgs.gov/pathrows.php

Enhanced Thematic Mapper Plus (ETM+)

• 8 8-bit bands: bands 1-7 are the same as TM; additional panchromatic band 8, 0.52-0.90 μm

• IFOV 30 x 30m (bands 1-5 and 7), 60 x 60m (band 6), 15 x 15m (band 8); swath width 185 km.

• Images the earth once every 16 days; 1999 to present

Landsat MSS Image Interpretation

• Scale & resolution differences between conventional aerial photos & Landsat images

• Landsat imagery should be viewed as a complementary interpretive tool rather than a replacement for low altitude photography

Landsat MSS Image Interpretation

• Most Landsat MSS images can only be studied in two dimensions

• Effective resolution: 79 m

(30 m on Landsat-3 RBV)

Landsat MSS Image Interpretation

• Due to the line scanning system (one-dimensional relief displacement), Landsat images can be viewed in stereo only in areas of sidelap on adjacent orbit passes.

• Sidelap varies from 85% near the poles to 14% at the equator. Endlap is only 10%.

Landsat MSS Image Interpretation

• Small vertical exaggeration when MSS images are viewed in stereo (extreme altitude vs. base distance between images)

• Base to height ratio: 4x in stereo airphotos, 1.3x to 0.4x in Landsat MSS

• Landsat MSS imagery has been used as a planimetric mapping tool

Landsat MSS Image Interpretation

• The most appropriate band or combination of bands of MSS imagery should be selected for each interpretive use:

• Bands 4 (green) & 5 (red) for detecting cultural features (5 provides higher contrast, 4 greater water penetration)

• Bands 6 & 7 are best for delineating water bodies

• Bands 5 & 7 are best for geologic studies (the largest single use of Landsat MSS data)

Landsat MSS Image Interpretation

• Landsat satellite passes over the same area during daylight hours about 20 times/year.

• Of course, the actual number of times/year a given ground area is imaged depends on the amount of cloud cover, sun angle, and whether the satellite is in operation on any specific pass.

Terra Spacecraft

• Terra is the first of the NASA’s Earth Observing System satellite series. It was launched in December 1999 and activated for science operation on 24 February 2000.

Terra Instruments

• ASTER: Advanced Spaceborne Thermal Emission and Reflection Radiometer

• CERES: Clouds and Earth’s Radiant Energy System

• MISR: Multi-Angle Imaging Spectro-Radiometer • MODIS: Moderate Resolution Imaging

Spectrometer • MOPITT: Measurements of Pollution in the

Troposphere

New Millennium Program

• Earth Observing-1 (EO-1) is the first satellite in NASA's New Millennium Program Earth Observing series

• EO-1 has validated a multispectral instrument that is a significant improvement over the Landsat 7 ETM+ instrument

• EO-1 has validated a hyperspectral land imaging instrument and the unique science that can be performed with hyperspectral data

• EO-1 has validated the ability of a low-spatial/high-spectral resolution imager that can correct systematic errors in the apparent surface reflectances caused by atmospheric effects, primarily water vapor.

Hyperion

• The Hyperion is a high resolution hyperspectral imaging instrument

• The Hyperion images the earth's surface in 220 contiguous spectral bands with high radiometric accuracy, covering the region from 400 nm to 2.5 µm, at a ground resolution of 30 m

Hyperion Sensor Characteristics

• Spatial Resolution: 30 m • Swath Width: 7.75 km • Spectral Channels 220 unique channels. VNIR (70

channels, 356 nm - 1058 nm), SWIR (172 channels, 852 nm - 2577 nm)

• Spectral Bandwidth 10 nm (nominal) • Digitization 12 bits • Signal-to-Noise Ratio (SNR) 161 (550 nm); 147 (700

nm); 110 (1125 nm); 40 (2125 nm)• Primary uses: General earth materials mapping

geology, mining, forestry, agriculture, and environmental management

ALI (Advanced Land Imager)

• The ALI instrument features 10-meter ground resolution in the panchromatic (black-and-white) band (0.480-0.680 microns) and 30-meter ground resolution in its multispectral bands (0.4-2.4 microns)

• It covers seven of the eight bands of the current Landsat

• It is designed to produce images directly comparable to Landsat 7 ETM+, will establish data continuity with previous Landsats

Comparison of Landsat-7 ETM+ and ALI spectral bands and spatial resolutions

ETM+ ALI Band (μm) Resolution (m) Band (μm) Resolution (m) .450 - .515 30 433 - .453 30 .525 - .605 30 .450 - .510 30 .630 - .690 30 .525 - .605 30 .750 - .900 30 .630 - .690 30 1.55 - 1.75 30 .775 - .805 30

10.40 - 12.50 60 .845 - .890 30 2.09 - 2.35 30 1.20 - 1.30 30 .520 - .900 15(pan) 1.55 - 1.75 30

2.08 - 2.35 30 .480 - .680 10(pan)

AC (Atmospheric Corrector)

• The AC instrument provides the first space-based test of an Atmospheric Corrector for increasing the accuracy of surface reflectance estimates.

• The AC enables more precise predictive models to be constructed for remote sensing applications.

• It will provide significant improvements in generating accurate reflectance measurements for land imaging missions.

• It covers the 0.89-1.60 micron wavelength IR band.

EO-1 Sensors

• Hyperion

• ALI (Advanced Land Imager)

• AC (Atmospheric Corrector)

New Millennium Program

• EOS Terra– ASTER

• 15 8-bit (VNIR and SWIR), 12-bit (TIR) bands: 4 VNIR (1 NIR off-nadir); 6 SWIR; 5 TIR

• IFOV 15 x 15m (VNIR), 30 x 30m (SWIR), 90 x 90m (TIR); swath width 60 km.

• Images are not acquired based on researcher scheduling; 1999 to present

– MISR• 4 VNIR bands at 9 different angles• IFOV 275 x 275 m to 1.1 x 1.1 km (depending on view

angle); swath width 360 km.• 9 day global coverage; 1999 to present

Terra Satellite

MODIS

ASTER (TIR)

ASTER (SWIR)

ASTER (VNIR)

MISR

MOPITT

CERES

ASTER Characteristics• Wide Spectral Coverage

• 3 bands in VNIR (0.52 – 0.86 μm)

• 6 bands in SWIR (1.6 – 2.43 μm)

• 5 bands in TIR (8.125 – 11.65 μm)

• High Spatial Resolution• 15m for VNIR bands• 30m for SWIR bands• 90m for TIR bands

• Along-Track Stereo Capability• B/H 0.6• DEM Elevation accuracy:15m

(3σ)• DEM Geolocation accuracy:

50m (3σ)

ASTER consists of 3 subsystems:VNIR, SWIR and TIR.

Comparison of Landsat-7 ETM+ and ALI Spectral Bands and Spatial Resolutions

Landsat 1-3 sensors

• Multispectral Scanner (MSS) – 0.5-0.6 (green), 0.6-0.7 (red), (near IR) at 0.7-0.8,

0.8-1.1m – resolution: 79 m (1-3), 82 m (4-5) – Each MSS scene is covering a 185 x 185 km area – Return Beam Vidicon Camera (RBV) - Landsat 1 and

2 – 0.475-0.575 m (green), 0.58-0.68 m (red), 0.69-

0.83 m (near IR)– Failed within weeks of Landsat 1

Spectral sensitivity of MSS bands

Landsat 4-5 orbital characteristics

• Altitude 705 km

• Coverage cycle 16 days

• Local crossing at about 9:45am • smaller sidelap (7.6% at the equator)

Sun-synchronous orbit of Landsat 4-5

Landsat 4-5 sensors

• Thematic Mapper (TM) – launched with Landsat 4 and 5 – 7 bands, 0.45-12.5m – resolution: 30m except band 6 (thermal IR

band, 120m)

TM spectral bands

Landsat 7

• Launched on 15 April 1999

• Orbit: very similar to Landsat 4-5 – Sun-synchronous, polar – Altitude: 705 km – Repeat cycle: 16 days – Local crossing time: 10:00 am

Enhanced Thematic Mapper (ETM+)

• Scene size – 183 km cross-track – 170 km along-track

• Spectral Bands • 8 bands: all TM bands + 1 panchromatic band • Resolution

– Bands 1-5, 7: 30 metres – Band 6: 60 metres – Band 8: 15 metres