1. Orbits and Sensors Multispectral Sensors

2. Satellite Orbits Orbital parameters can be tuned to produce particular, useful orbits Geostationary Sun synchronous (Polar, Low Earth Orbit) Geosynchronous Altimetric

3. Geostationary Orbits Geo orbit is stationary with respect to a location on the earth Circular orbit around the equator (orbital inclination = zero) Placed in high orbit (35,800 km) to match the angular velocity of Earth

4. Uses of Geostationary Orbits Weather satellites (GOES, METEOSAT) Constant monitoring Communication satellites Constant contact w/ground stations Limited spatial coverage –each satellite can only cover about 25-30% of the earth’s surface –coverage extends only to the mid-latitudes, no more than about 55 o

5. Sun-synchronous (Polar) Orbit “Low Earth Orbit” (LEO) are typically about 700 km altitude Precession of the satellite orbit is the same as the angular speed of rotation of the sun Satellite crosses the equator at the same time each day “Polar orbit” is very common –Orbital inclination is “retrograde” (typically ~98 o ) –Near circular orbits have period of about 98-102 minutes

6. Animation of GEO and LEO orbits

8. Polar Orbiting Satellite Tracks

9. Uses of Sun-Synchronous Orbits Equatorial crossing time depends on nature of application (low sun angle vs. high sun angle needs) Earth monitoring -- global coverage Good spatial resolution

10. Terra satellite overpasses for today over North America See http://www.ssec.wisc.edu/datacenter/terra/

11. Getting the Data to the Ground On-board recording and pre-processing Direct telemetry to ground stations –receive data transmissions from satellites –transmit commands to satellites (pointing, turning maneuvers, software updating Indirect transmission through Tracking and Data Relay Satellites (TDRS)

12. Imaging Systems Cross-track scanning systems –“whiskbroom” Along-track (non-scanning) system –“pushbroom”

13. Cross-track Scanner Single detector or a linear array of detectors “Back and forth” motion of the scanner creates the orbital “swath” Image is built up by movement of satellite along its orbital track Produces a wide field-of- view Pixel resolution varies with scan angle

14. Along-track scanner (Pushbroom) Linear array of detectors (aligned cross-track) –radiance passes through a lens and onto a line of detectors Image is built up by movement of the satellite along its orbital track (no scanning mirror) Multiple linear arrays are used for multi-spectral remote sensing –dispersion element splits light into different wavelengths and onto individual detectors

15. Calculating the Field of View (FOV) FOV = 2 H tan(scan angle) H = satellite altitude Example: SeaWIFS satellite altitude = 705 km Scan angle = 58.3 o FOV = 1410 x tan(58.3 o ) = 2282 km H  FOV

16. x2x2 x1x1 x x = H tan(  /2) x 2 = H tan(  /2) x 1 = x - x 2 P c = H tan(  /2) - H tan(  /2) H H/cos  sec   Cross-track pixel size

17. History of the Landsat series Currently, Landsat 5 and Landsat 7 (ETM+) are in orbit

18. Landsat MSS 1972-present

20. Band 4 (Green: 0.5 - 0.6  m) –water features (large penetration depths) –sensitivity to turbidity (suspended sediments) –sensitivity to atmospheric haze (lack of tonal contrast) Band 5 (Red: 0.6 - 0.7  m) –chlorophyll absorption region –good contrast between vegetated and non-veg. areas –haze penetration better than Band 4 Band 6 (NIR1: 0.7 - 0.8  m) and Band 7 (NIR2: 0.8 - 1.1  m) –similar for most surface features –good contrast between land and water (water is strong absorber in near IR) –both bands excellent haze penetration –Band 7 good for discrimination of snow and ice Landsat MSS Bands and their Uses

21. spectral absorptance Spectral Reflectance

23. Landsat Thematic TM 1982 - present

24. Band 1 (Blue: 0.45 - 0.52  m) –good water penetration –differentiating soil and rock surfaces from vegsmoke plumes –most sensitive to atmospheric haze Band 2 (Green: 0.52 - 0.60  m) –water turbidity differences –sediment and pollution plumes –discrimination of broad classes of vegetation Band 3 (Red: 0.63 - 0.69  m) –strong chlorophyll absorption (veg. vs. soil) –urban vs. rural areas Landsat Thematic Mapper Bands and their Uses

25. Band 4 (NIR1: 0.76 - 0.90  m) –different vegetation varieties and conditions –dry vs. moist soil –coastal wetland, swamps, flooded areas Band 5 (NIR2: 1.55 - 1.75  m) –leaf-tissue water content –soil moisture –snow vs cloud discrimination Band 6 (Thermal: 10.4 - 12.5  m) –heat mapping applications (coarse resolution) –radiant surface temperature range: - 100 o C to +150 o C Band 7 (NIR3: 2.08 - 2.35  m) –absorption band by hydrous minerals (clay, mica) –lithologic mapping (clay zones) Landsat Thematic Mapper Bands and their Uses

26. Landsat 7 Enhanced Thematic Mapper (ETM+) 1999-present 15m panchromatic band on-board calibration