1. A Basic Introduction to Radar Remote Sensing
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Rev. Ronald J. Wasowski, C.S.C.
Associate Professor of Environmental Science
University of Portland
Portland, Oregon
3 November 2015

2. Radar Imaging Wavelengths
Remote sensing wavelength regions and bands
Band name Wavelengths Notes
Gamma rays < 0.03 nm
X-rays 0.03 to 30 nm
Ultraviolet (UV) 0.03 to 0.4 mm
Photographic UV 0.3 to mm Film
Visible 0.4 to mm Small !
Infrared (IR) 0.7 to 100 mm
Reflected (RIR) 0.7 to mm Sunlight
Thermal (TIR) 3.0 to 14.0 mm
? ! ? ! ?
Radio
Microwave 0.1 to 100 cm Passive
Radar 0.1 to 100 cm Active
Radio > 100 cm Passive

3. Radar Imaging System Components
Seven basic system components
Pulse generator
Generate a signal of specified frequency / wavelength
Signal transmitter
Amplify and send the outgoing signal
Duplexer
Two-way switch
Alternate between outgoing & incoming radar pulse
Radar antenna
Broadcast the outgoing pulse & accept the return pulse
Receiver
Amplify the return pulse amplitude to an acceptable level
Recorder
Permanent record of the return pulse: Film or digital
Image generator
Conversion of return pulses into images

4. Radar Imaging System Components

5. Important Radar Terms Two basic types of radar imaging systems
SLAR: Side-Looking Airborne Radar
SAR: Synthetic Aperture Radar
Azimuth direction
Flight direction
Look direction
Perpendicular to the azimuth direction
Range
Near range
Far range
Depression angle
Angle below horizontal to any feature of interest
0°: The horizon
90°: Nadir

6. Important Radar Terms Illustrated

7. A Typical Radar Image: Columbia R.

8. Radar Wavelengths & Frequencies
Band Wavelength Frequency
Designation (cm) (GHz)
K to to 12.5
X to to 8.0
C to to 4.0
S to to 2.0
L 15.0 to to 1.0
P 30.0 to to 0.3

9. Depression & Incidence Angles
Depression angle g Incidence angle Q
Horizontal surface: g + Q = 90°
Q = 90° – g

10. Depression & Incidence Angles
Depression angle g Incidence angle Q
Horizontal surface: g + Q = 90°
Q = 90° – g – s
s = Slope
> 0° : Toward
< 0° : Away

11. Range Resolution of Radar Images
Increases from near range to far range

12. Radar Image Azimuth Resolution
Decreases from near- to far-range as beam widens

13. Radar Displacement & Layover
Radar image displacement
Pixel placement determined by straight-line distance
Near range has more displacement than far range
Slope effects
Slopes facing toward the radar are smaller than actual
Slopes facing away from the radar are larger than actual
Brightness effects
Slopes facing toward the radar are too bright
Slopes facing away from the radar are too dark
Radar image layover
An extreme form of displacement
An object’s top is displaced past its bottom
The object’s top is closer than its bottom

14. Radar Image Shadow

15. EMR Polarization

16. Radar Image Polarization
Primary polarization Transmitted signal
Horizontal
Near range: Electric vector parallel to hor surfaces
Far range: Electric vector parallel to hor surfaces
Vertical
Far range: Electric vector perpendicular to hor surfaces
Circular
Secondary polarization Returned signal
HH: Non-depolarized return
HV: Depolarized return Diagonal features
VV: Non-depolarized return
VH: Depolarized return Diagonal features

17. Radar System Properties
Wavelength
Short l’s
Many surfaces are rough
Insignificant feature penetration
Long l’s
Few surfaces are rough
Significant feature penetration
Still not forest cover or even grass cover ! ! !
Depression angle
Small g’s
Relatively dark signatures
Large g’s
Relatively bright signatures
Polarization
Horizontal transmitted: Consistent with terrain
Vertical transmitted Inconsistent with terrain

18. Radar Terrain Properties
Dielectric properties Electrical conductivity
Dry rock / soil: 3 < Dielectric constant < 8 Dark
Water: Dielectric constant = 80 Bright
Geometry
Micro- geometry: Surface texture = Surf. roughness
Smooth
Intermediate
Rough
Macro-geometry: Features parallel or perpendicular
Specular reflectors
One surface oriented nearly perpendicular to the look direction
Two-sided reflectors
Two perpendicular surfaces w/join line parallel to flightline
Corner reflectors
Three perpendicular surfaces open to the incident radar signal

19. A Typical Radar Image: Denver

20. Shuttle Imaging Radar: San Francisco

21. Radar Roughness: Smooth Texture
L-band (23.5 cm) wavelength
Radar-smooth surface: 0.0 cm < h < 1.0 cm
Specular reflection Total forescatter

22. Radar Roughness: Intermed. Texture
L-band (23.5 cm) wavelength
Radar-intermediate surface: 1.0 cm < h < 5.7 cm
Composite specular/diffuse scattering Much forescatter

23. Radar Roughness: Rough Texture
L-band (23.5 cm) wavelength
Radar-rough surface: 5.7 cm < h
Diffuse scattering Uniform in all directions

24. Return Intensity & Depression Angle
A continuum
Smooth surface: Approximately specular at nadir
Rough surface: Approximately uniform at all g’s

25. Shuttle Imaging Radar: Los Angeles

26. Radar Image Resolution Revisited
Principal determining characteristics
SLAR: Side Looking Airborne Radar Real aperture
Directly proportional to l
Shorter wavelengths are better Rain may interfere
Inversely proportional to antenna length
Focus beam to preserve far range azimuth resolution
Longer antennas are better Flexing may interfere
SAR: Synthetic Aperture Radar
Shorter wavelengths are better
“Fake it” by “synthesizing” a very long antenna
Use coherent radar signal “Radar laser”
Process Doppler shift data
Illuminate each target multiple times
Live with image speckle

27. A Typical Radar Image: Ice Floes

28. A Typical Radar Image: Indonesia

29. SIR L & C Radar Bands: Mt. Rainier

30. A Typical Radar Image: Clearcutting

31. Radar Relief Map: Death Valley CA

32. A Typical Radar Image: Taiwan

33. Shuttle Imaging Radar: San Andreas

34. Appalachians of Eastern Pennsylvania

35. Part of the Appalachian Mountains

36. Magellan Radar Mission to Venus