Satellite images and radar observations

1
Satellite images and radar observations
2
Some Warm-up

• Clouds in sunshine look white because
• a. light of all colors is multiple scattered
  within the cloud.
• b. they contain white pigments.
• c. they have a low index of refraction.
• d. they are contrasted against blue sky.
• e. they are not able to absorb the specific
  frequency of white light.

3
Warm-up questions

• The bottoms of clouds are often gray because
• a. precipitation is imminent.
• b. they are over dark portions of the Earths
  surface.
• c. the bottoms of clouds are denser than the
  tops, and thus absorb more light.
• d. multiple scattering has removed most light
  before it reaches the bottom of the cloud.
• e. droplets or crystals within the cloud have
  dispersed most of the available light.

4
Warm - up

• What does ASOS stand for?
• a) Asymmetric Satellite Orbits
• b) Automatic Satellite Observation System
• c) Automatic Surface Observation System
• d) Geostationary Satellite for the US West Coast
• e) Polar Satellite Orbits

5
Last Warm-up question

• Which of these does not characterize a
  geostationary satellite?
• a) period of 24 hours
• b) orbital height of 800 km
• c) orbit is close to equatorial plane
• d) does not change relative position in the sky
• e) poor view of the polar regions

6
Visible Images

• Reflected and scattered solar light
• 0.4-0.7 ??m
• Light area high Albedo
• Lots of backscattering high albedo
• Stratusbright
• Cirrus grey

7
IR Images

• Terrestrial radiation
• 10-12 ??m
• light area cold surface
• Dark areas warmer surface
• Stratusgrey
• Cirrus bright

8
Water vapor images

• Emission by water vapor
• 6.5-6.9 ??m
• light area lots of water vapor
• Dark areas dry air
• 300-600 mb level
• Strong contrast strong upper winds
• High clouds (cumulonimbus calvus) bright

9
Friday, November 9, 2007 315 pm
10
Radar

• Radio Detection and Ranging
• Wave length 0.8 10 cm for weather radar
• Scattered wave radar echo

11
Weather Radar

• Reflectivity measurements
• Droplets (clouds)
• Precipitation
• Velocity measurements
• Wind speeds (speeds of droplets)
• Two types of images reflectivity and velocity
  images

12

• Wave length 0.8 10 cm for weather radar
• Location of small cloud droplets short wave
  lengths
• Doppler radar longer wave lengths

http//ww2010.atmos.uiuc.edu/(Gl)/guides/rs/rad/ba
sics/wvl.rxml
13
Doppler Radar

• Uses Doppler effect to measure frequency change
  in radar echo
• Allows to measure radial speed of droplets (away
  or toward radar)
• Two Doppler radars give complete velocity vector
• Also allows to measure reflectivity

14
Resting sound source
Frequency fs
V340m/s
Frequency fo
source at rest
observer at rest
15
Sound source moving toward observer




Observer hears increased pitch (shorter wave
length)
Frequency fo
Frequency fs
source
observer at rest
16
Sound source moving away from observer




Observer hears decreased pitch (longer wave
length)
Frequency fo
Frequency fs
observer at rest
source
17
Doppler Radar

• 155 Doppler Radar Stations nationwide

18
http//www.rap.ucar.edu/weather/radar/
Reflectivity
Velocity