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Polar Orbits

Polar Orbits.

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Polar Orbits

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  1. Polar Orbits An orbit with a inclination of 90 degrees, or close to it, is called a "polar orbit." Because the Earth is rotating as the satellite follows a polar orbit, the satellite can survey the whole of the Earth's surface, including the poles, in a few days. Many observation satellites that need to cover the entire Earth are in polar or near-polar orbits. Ht ~850 Km Swath; Twice in 24 Hrs, 14 Orbits per Day; Resolution

  2. Sun-synchronous orbit: the satellite's orbital plane and the Sun's direction are always the same

  3. Geostationary Orbit A satellite that appears to remain in the same position above the Earth is called a "geostationary satellite." Revolves with same angular velocity of earth Spatial Resol. –Less; polar regions not covered.

  4. A satellite in a geosynchronous orbit goes around the Earth once a day returning to its original position

  5. Resolution (Geostationary satellite)

  6. Types of Meteorological Satellite Sensors Imagers/Scanners Sounders Microwave Visible/Infrared 10^3 to 10^6 Micron 0.4-0.7 Micron, 1-100 Micron Passive (Radiometers/ Spectrometers) Active Radar LIDAR

  7. Visible/Infrared Imaging and Sounding

  8. Solar and Terrestrial Radiances Absorption Lines

  9. Sensors

  10. GMS5 and METEOSAT sensors GMS 5

  11. Satellite imagery • VIS - imagery derived from reflected sunlight at visible • IR - imagery derived from emissions by the Earth and its atmosphere at thermal-infrared wavelengths • WV - imagery derived from water vapor emissions • 3.7μm - (channel 3) imagery from this specific wavelengths,which is in the overlap region between solar and terrestrial radiation

  12. IMAGERY • METEOSAT • VIS • IR • WV • 3.7μm • 3.7μm-IR1 (split window) • GMS 5 • VIS • IR • WV • IR1-IR2 • (split window) • INSAT-3A • VIS • IR • WV • CCD (VIS,NIR,SWIR) • (split window)

  13. NOAA-AVHRR • Polar orbiting Satellite • Resolution : 1.1 km (Nadir), 6 km Off Nadir) • Channels : Application • 0.55-0.68 Cloud Mapping • 0.75-1.1 Surface Water boundaries • 3.55-3.93 Thermal Mapping, Cloud distribution Fire detection • 10.3-11.3 Cloud distribution, SST,WV • 11.5-12.5  -do-

  14. VIS image • Available only during daytime • Intensities vary depending upon locations among the earth, the sun and the satellite. • Reflection intensities differ depending upon cloud thickness. • Lower clouds can be seen well. 05UTC 17 Nov 1999 NOAA

  15. TYPICAL ALBEDO VALUES • OCEAN / LAKES 8 % • LAND SURFACE 14 - 27 % • ICE 35 % • SNOW 80 % • CU CLOUD 30 % • CI CLOUD (THICK) 35 % • ST CLOUD 50 - 60 % • AC , AS & SC CLOUDS 68 % • TCU CLOUD 75 % • CB CLOUD 90 %

  16. CHARACTERISTIC FEATURES • BRIGHTNESS ( WHITE, GREY ) • PATTERN ( LINE, BANDS, WAVES) • STRUCTURE ( SHADOW, HIGHLIGHT ) • TEXTURE ( SMOOTHNESS ) • SHAPE ( ROUND, STRAIGHT ) • SIZE (Patterns, useful indicators of Weather System

  17. IR image • Always available • Shades of levels differ depending upon cloud heights (IR1, IR2). • Upper clouds can be seen well. 05UTC 17 Nov 1999 NOAA

  18. WV image • Always available • Shades of levels differ depending upon humidity in upper to midlevel (WV). • Upper clouds can be seen well. • Levels may vary depending upon absorption by clouds and atmosphere on the way. 05UTC 17 Nov 1999 GMS

  19. Comparison Meteosat data IR and WV 19.01.2001

  20. Meteosat7

  21. Meteosat5

  22. GMS 5 1200UTC 22 Oct 2000

  23. Representation

  24. CLOUD MATRIX I N F R A R E D DEEP CONV CB / TCU WHITE (COLD) DARK (WARM) THIN CIRRUS NO CLOUDS LOW CLOUDS DARK WHITE VISIBLE

  25. GREY SCALE MATRIX WARM SEA BLACK DARK GREY GREY WHITE I N F R A R E D FAIR WX CU ST ST, SC AC, AS THIN CI THICK CI CB, TCU AS CB ANVIL WHITE GREY DARK BLACK GREY VISIBLE

  26. IR1-IR2 • thin Ci • low cloud • volcanic ash, 05UTC 17 Nov 1999 NOAA

  27. Split Window Channel (IR1-IR2)

  28. 3.7μm image • Day time • (reflected sunlight) • snow • sea ice • Ci • Night time • (emmited radiation) • low cloud 05UTC 17 Nov 1999 NOAA

  29. 3.7μm-IR1 • Usage in night time • thin Ci • low cloud (Fog) 18UTC 9 Aug 1999 NOAA

  30. .0 Some of the GOES Imagery Applications: Channel Channel Name Central Wave-length Resolutionkm E/W x N/S Example Meteorological Applications 1 visible 0.65 µm 0.57 x 1.00 Produces high resolution black and white photographs of earth and clouds. 2 shortwave infrared 3.90 µm 2.30 x 4.00 At night, can be used to track low-level cloud fields and thus infer near-surface wind circulation. 3 water vapor channel 6.70 µm 2.30 x 8.00 1. Detects mid- and upper-level water vapor and clouds. 2. Locates and defines synoptic features such as shortwave troughs, ridges, jet streams, etc. via mesoscale regions of moistening/drying at the 300-500 mb height. 3. Can derive upper-level wind vectors (wind barbs) with the winds plotted on the image valid at the time of the winds. 4 window channel 10.70 µm 2.30 x 4.00 Cloud top temperatures, nighttime tracking of storm systems. 5 dirty window/ split window IR 12.00 µm 2.30 x 4.00 Sensitive to low level water vapor.

  31. Goes Imager Applications: • Channel 2, Short-wave Infrared Channel (3.9 µm) • Emissivity of water droplets at 3.9 µm is less than that for longer wavelengths, • Easier to identify fog and Stratiform cloudiness • Discriminate between water and ice clouds. • The 3.9 µm channel is different - emitted terrestrial radiation, and reflected solar radiation. • Fog, and cold ground. Combining this imagery with other channels resolves most of these problems. • Using Channel 2 (3.9 µm) Imagery at Night. • 3.9 µm imagery at night offers a good substitution for visible channel imagery • . It can be used to track low-level cloud fields and thus infer near-surface wind circulation. • useful in the tropics, where freezing levels are relatively high (~5 km) and conventional low-level wind data are sparse. • Channel 3, Water Vapor Channel (6.7 µm) • The 6.7 µm channel responds to mid- and upper-level water vapor and clouds. • large regions of upward (or downward) motion and consequent moistening (or drying), the water vapor data • used to locate short wave troughs, ridges, jet streams, etc. • Meso-scale regions of moistening/drying at the 300-500 mb height (such as subsidence associated with thunderstorms' anvils) have also recently come under close scrutiny using this channel's imagery Using Channel 3 (water vapor) Imagery to Derive Winds

  32. Resolution vs Fog Detection

  33. VIS and IR1997.11.7.05UTC NOAA IR VIS

  34. IR1-IR2 and 3.7μm1997.11.7.05UTC NOAA IR1-IR2 3.7μm

  35. NIGHT TIME IMAGE(1999.8.9.18UTC NOAA)

  36. SOLAR ECLIPSE emhanced VIS image VIS image 03UTC on 18 Mar,1988

  37. Characteristics of each cloud type

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