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 ( 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

14. 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)‏

15. GOES West GOES East

19. http://rammb. cira. colostate. edu/ramsdis/onlin e/goes-west_goes-east
e/goes-west_goes-east.asp

20. 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

21. 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.

22. http://rammb. cira. colostate. edu/ramsdis/onlin e/goes-west_goes-east
e/goes-west_goes-east.asp

23. 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

24. http://rammb. cira. colostate. edu/ramsdis/onlin e/goes-west_goes-east
e/goes-west_goes-east.asp

25. 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)‏

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

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

29. 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.

31. 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

32. 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

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

38. Where to find images
arch.html (archived GOES imagery)‏
(extreme events link at bottom of page)‏
(MODIS image gallery)‏
(AIRS image gallery)‏
ml (images from multiple sensors/events)‏