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ATS 351 Lecture 8 Satellites

ATS 351 Lecture 8 Satellites. Electromagnetic Waves. Electromagnetic Waves. Consist of an electric field and a magnetic field Polarization: describes the orientation of the electric field. Remote Sensing. Passive vs Active sensors

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ATS 351 Lecture 8 Satellites

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  1. ATS 351 Lecture 8 Satellites

  2. Electromagnetic Waves

  3. Electromagnetic Waves • Consist of an electric field and a magnetic field • Polarization: describes the orientation of the electric field.

  4. Remote Sensing • Passive vs Active sensors • Active sensors emit radiation and measure what is sent back to them • Radars are active sensors. • Passive sensors detect naturally occurring radiation • Most satellites are passive sensors.

  5. Satellite Basics • Satellites are in many different types of orbits. • Geosynchronous (36,000 km) • LEO (300-1000 km) • MEO (10,000 km) • Polar (LEO orbit) • Sunsynchronous • Molinya • Constellations • Ascending vs Descending Nodes

  6. Satellite Basics How many times a day a particular point is seen by a sunsynchronous satellite

  7. Satellite Basics Satellite constellations fly multiple satellites in varying orbits to provide maximum earth coverage. Satellite Formations fly multiple satellites in the same orbit.

  8. Satellite Basics • Most satellites carry multiple sensors • Saves money • Instrument design • Instrument launch • Multiple funders • Allows many earth/atmosphere parameters to be observed at one time

  9. Satellite Basics • Current weather satellites include radiometers, radars, and sounders • Radiometers sense emitted radiation • Radars sense reflectivity in the vertical rather than horizontal • Sounders sense profiles of radiance from many layers of the atmosphere. • Radiometers sense emitted radiation in the infrared and microwave • Brightness temperature (Tb) – The temperature of an equivalent blackbody emitting radiation. • Infrared and microwave sensors measure the emitted radiation and report it as a brightness temperature • Insert LOTS of complicated math here. • Tb = Ts

  10. Emissivity • Emissivity – amount of absorbed radiation that is emitted by a body • Has values between 0 and 1 • Ocean has an emissivity of about 0.5 • Land and cloud cover have an emissivity > 0.8 • Over land, emissivity is dependent on soil moisture and vegetation cover, and is very difficult to determine. • Over ocean, emissivity is dependent on wind speed and sea surface temperature

  11. Retrievals • A retrieval is a method by which we infer information about the atmosphere based on measured brightness temperatures • Retrievals can be used to infer • Cloud liquid water • Water vapor content • Concentrations of atmospheric gases (CO, CH4, CO2)‏ • Land surface properties (Soil Moisture, vegetation)‏ • If y is the observed brightness temperature, x is the state of the Earth/Atmosphere system, and f is a forward model that predicts y based on x: y = f(x) x = f-1(y)‏

  12. What is x? (So/4) (1-α)‏ ơ TA4 atmosphere ơ TS4 ơ TA4 surface

  13. Visible Satellite Imagery • Visible satellites basically take pictures of the earth. • Most visible satellites are in geosynchronous orbit. • In the US, we use the GOES satellites. • GOES: Geostationary Operational Environmental Satellites • GOES satellites carry 5 sensors • Visible (.6 microns)‏ • Shortwave IR (3.9 microns)‏ • Water Vapor (6.7 microns)‏ • Infrared (11 microns)‏ • Infrared (12 microns)‏

  14. GOES West GOES East

  15. http://rammb.cira.colostate.edu/ramsdis/online/goes-west_goes-east.asphttp://rammb.cira.colostate.edu/ramsdis/online/goes-west_goes-east.asp

  16. Visible Satellite Imagery • Advantages • Always located in the same place (homogeneous sampling)‏ • View at an angle to give some information about vertical development of clouds • Can be used to monitor snow cover • High spatial resolution (GOES Vis: 1km)‏ • Disadvantages • Cannot be used at night • Views of the poles are limited due to the viewing angle • Not very useful for retrievals

  17. Infrared Satellite Imagery • Displays the brightness temperature calculated based on the amount of sensed infrared radiation. • Useful for determining whether clouds are convective or stratiform. • Land surfaces appear warmer than cloud. • Land surface emissivity is very close to 1 in the infrared.

  18. http://rammb.cira.colostate.edu/ramsdis/online/goes-west_goes-east.asphttp://rammb.cira.colostate.edu/ramsdis/online/goes-west_goes-east.asp

  19. Infrared Satellite Imagery • Advantages • Can infer cloud heights by temperature • Can be used at night • Can be combined with visible imagery to infer cloud types • Can be color enhanced • Can be used in retrievals

  20. http://rammb.cira.colostate.edu/ramsdis/online/goes-west_goes-east.asphttp://rammb.cira.colostate.edu/ramsdis/online/goes-west_goes-east.asp

  21. Some satellites using IR frequencies • MODIS (MODerate resolution Infrared Spectroradiometer)‏ • AIRS (Atmospheric Infrared Sounder)‏ • GOES (Geostationary Operational Environmental Satellite)‏ • AVHRR (Advanced Very High Resolution Radiometer)‏ • MOPITT (Measurements Of Pollution in The Troposphere)‏

  22. Southwest Asian Dust Storm image from MODIS at 500m resolution

  23. AIRS Retrieved Temperature Isotherms over Southern Europe viewed from the west, September 8, 2002

  24. Water Vapor Imagery • Retrieved water vapor based on sensed emissivity • Shows where significant weather systems are located • Uses infrared wavelengths • Remember: water vapor is a strong absorber of IR radiation.

  25. Microwave Satellite Imagery • Senses emitted radiation in the microwave frequencies • Also frequently used in retrievals. • Land surface emissivity in the microwave averages 0.95. • Most microwave sensors carry radiometers in multiple frequencies • Allows for varying resolutions • Useful in retrievals • Atmospheric water vapor absorbs at ~22 GHz

  26. Microwave Sensors • AMSR-E (Advanced Microwave Scanning Radiometer for EOS)‏ • TRMM (Tropical Rainfall Measuring Mission)‏ • TMI (TRMM Microwave Imager)‏ • TRMM-PR (Precipitation Radar)‏ • VIRS (Visible and Infrared Satellite)‏ • SSM/I – Special Sensor Microwave Imager • AMSU – Advanced Microwave Sounding Unit

  27. Cloudsat • Cloud Profiling Radar • 94 GHZ • Measures the power backscattered by clouds as a function of distance from the radar

  28. Where to find images • http://virga.sfsu.edu/crws/archive/satimgs_month_arch.html (archived GOES imagery)‏ • http://trmm.gsfc.nasa.gov/ (extreme events link at bottom of page)‏ • http://modis.gsfc.nasa.gov/gallery/ (MODIS image gallery)‏ • http://daac.gsfc.nasa.gov/AIRS/gallery.shtml (AIRS image gallery)‏ • http://www.eorc.jaxa.jp/en/imgdata/latest/index.html (images from multiple sensors/events)‏

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