1. Pillars of excellent communication
Memorable
Honest
Provides context
Useful

2. Remote Sensing of the Atmosphere
Types of Observations:
1. In Situ: instrument in direct contact with “object” it senses
2. Remotely sensed: instrument not in direct contact with “object” it senses
-- uses radiation emitted or reflected by “object”
(a) Active: emit, then collect (receive) radiation (x-ray machine)
(b) Passive: receive radiation emitted or reflected by object (camera, satellite)

3. What is radiation ? -- Everything emits radiation (most is invisible)
terrestrial radiation – emitted by earth and atmosphere
-- Molecular vibration (oscillating electrons) generates radiation
Wavelength (WL)
Figure 2.2
Amplitude
-- Shorter wavelength  more energy (waves at beach analogy)

4. Type of radiation emitted depends on TEMPERATURE (what is temperature
Higher temperature 
shorter wavelengths 
higher energy
Sun emits mostly visible radiation, some ultraviolet and infrared
Earth/atmosphere system emits infrared wavelength

5. Satellite Imagery Then (1960) and now
Weather satellites measure the amount of radiation reflected or emitted at certain wavelengths.

6. GOES: Geostationary Operational Environmental Satellite
2 types of weather satellites: Geostationary & Polar-Orbiting
GOES: Geostationary Operational Environmental Satellite
Geostationary: ~22,500 miles up
Orbit at same speed earth rotates
Ideal for “movies”

7. GOES-West view
GOES-East view

8. Polar-orbiting: ~530 miles up Orbit pole to pole, image in swaths
2 types of weather satellites: Geostationary & Polar-Orbiting
Polar-orbiting: ~530 miles up
Orbit pole to pole, image in swaths
See each point about twice / day

9. Resolution: How much detail can you see?
Polar orbiters:
highest resolution ~250 m visible
Geostationary: PRE GOES-R!
highest resolution ~1 km visible
~4 km infrared

10. Thick clouds (e.g. T’storm), high albedo  bright white
3 types of weather satellite imagery
1. Visible: uses reflected visible radiation (measures albedo)
Thick clouds (e.g. T’storm), high albedo  bright white
Thin clouds (e.g. cirrus, cumulus) low albedo  not as bright

12. 2. Infrared: Uses infrared radiation emitted by clouds and earth;
2. Infrared: Uses infrared radiation emitted by clouds and earth; (warmer = more radiation emitted)
The higher (colder) the cloud, the less radiation it emits
Surface warmest (usually), emits most radiation
Useful day and night
Standard Infrared image
Hottest = brightest
Coldest = darkest

13. Bright white = cold high clouds (top of thunderstorm, ice clouds)
Visible
Standard infrared
What meteorologists show
Bright white = cold high clouds (top of thunderstorm, ice clouds)
Dull white (gray) = warmer clouds closer to ground
Dark = surface

14. “Color-enhanced” infrared

15. 3. Water Vapor Visible Infrared Water Vapor
-- Special infrared image that also “sees” invisible water vapor
-- Can only detect clouds/vapor above ~10,000 feet
-- When looped, traces high altitude winds
Water Vapor

16. Weather satellites – more than just clouds …
Water temperature
Measure infrared energy emitted by water
Convert into temperature
Wave Height

17. GOES – R (GOES 16)

18. Radio Detection And Ranging
Weather Radar
Radio Detection And Ranging
-- “Active” remote sensing
-- Originally used radio waves, now microwaves
-- Emitted radiation strikes “targets” (precipitation, birds, insects, buildings, mountains)
-- Reflected radiation collected, analyzed, displayed. (animation)

19. Weather Radar History 1957 - First network of weather radars in U.S.
B&W, no “looping”
Used heavily in WW2 (mainly detect planes & ships)
Pacific typhoon (1944)
Hurricane Carla (1961)

20. Weather Radar History
-- Current network of government radars: WSR-88D (Weather Surveillance Radar, circa 1988, with Doppler)

21. Each radar has range of ~250 miles

22. Radar- How does it work? Emits pulse (beam) of microwave radiation
Portion of radiation returns to radar
ECHO!!!!
Detects …….
INTENSITY ….. Units of dbz
Depends on … precip. density (more targets = more reflection)
LOCATION ….. V = D/T
Distance = VT / 2!

23. Radar Limitations ATTENUATION RESOLUTION RANGE INTERFERENCE
Weakening of signal with distance
Caused by …..
RESOLUTION
RANGE
Caused by ….
INTERFERENCE
Ground clutter
“Near ground” glutter
Anomalous propagation

24. Some Radar “issues” -- Snow reflects 5 times less radiation than rain
-- Easy to underestimate intensity of snowstorms
1 hr later
“Overshoot” shallow clouds at great distance

25. Some Radar “issues”
Evaporating precipitation – Radar detects precipitation, but it evaporates before reaching ground
1 hr later

26. DSM Radar – what’s this?

27. CLE radar – what’s real?

28. RADAR: DERIVED FIELDS
COMPOSITING …..
ANY LIMITATIONS?

29. Single site radar (CTP)

30. COMPOSITE RADAR
COMPOSITING …..
Differences ??
Caused by ??

31. Radar: Derived fields Estimated Precipitation
State College: 1.25” of rain occurred
Any limitations here?
Allentown: 3.25” of rain occurred

32. Radar: Derived fields Snow, mixed … How does it do it?
We don’t call it “CrapRad” for nothing!

33. RADAR: Conventional VS Dual Polarization
-- Dual polarization radar sends both a horizontal and vertical pulse
-- By analyzing the characteristics of the two pulses additional information about the size, shape, and uniformity of the target is obtained
-- This helps with target type (rain, snow, hail, debris, non-meteorological?)

34. Displaying Precipitation Intensity
“Winter Radar”
“Reflectivity” mode – shows where precip falling, and intensity
Intensity proportional to amount of radiation reflected

35. Doppler Capability
Measure winds toward and away from the radar (“Velocity Mode”)
Detect rotation inside t’storms
Great Doppler Velocity Tutorial
T’storm
View from above
Radar
Tornado in reflectivity mode (hook echo)
Tornado in velocity mode

36. Train approaches, higher pitch. Train departs, lower pitch.
Doppler effect: Pitch (frequency) of sound depends on motion of source
Train approaches, higher pitch.
Train departs, lower pitch.
Applies to radiation … frequency of reflected radiation depends on whether drops are moving toward or away from radar

37. Is this a problem?

38. Is this better?

39. How / where / when do we take regular weather observations?
Figure 1.20
Automated surface observation system (ASOS)
-- every hour (or more often) about 1500 places in U.S. (mostly airports)
Few 100 buoys (mainly just offshore)

40. How / where / when do we take regular weather observations?
-- Temp, wind, humidity measurements above ground: radiosondes (packages of weather instrumentation) via balloon
-- Twice a day (00Z and 12Z) from ~80 locations in US, few hundred more worldwide
-- Increasingly supplemented by aircraft observations and from satellites