Transcript Radar Mapping

Radar Mapping
Electromagnetic EM Radiation
• Electric Field &
Magnetic Field
– Perpendicular to
direction of
propagation
• Explains light but
is absolutely
fundamental for
radio spectrum
Typical Radar System
1. A pulse generator that discharges timed
pulses of microwave/radio energy
2. A transmitter
3. A duplexer that alternates the signals
involved between transmitted and
received
4. A directional antenna that shapes and
focuses each pulse into a stream
5. Receiving Antenna
Radar Bands
1. Ka Band: Frequency 40,000-26,000 MHz;
Wavelength (0.8-1.1 cm)
2. K Band: 26,500-18,500 MHz; (1.1-1.7 cm) =
Weather Radar
3. X Band: 12,500-8,000 MHz; (2.4-3.8 cm)
4. C Band: 8,000-4,000 MHz; (3.8-7.5 cm)
5. L Band: 2,000-1,000 MHz; (15.0-30.0 cm)
6. P Band: 1,000- 300 MHz; (30.0-100.0 cm)
These are all in the Microwave part of the
spectrum
About Radar
• RADAR = RAdio Detection And Ranging
• Typically radar transmitters send and
receive 1500 pulses per second
• Pulses last about .1 microsecond
• Pulses send 100-1000 waves
• What a radar actually measures is time
(between transmission and reception)
• What a radar actually receives when it’s
pointed in a certain direction isn’t always in
that direction
Some
Radar
Effects
Some Radar Effects
• Bright = rough, Dark = smooth
• Metal reflects brightly
• Metal corners or edges reflect especially
brightly
– A truck has same size radar signature as a
bomber
– Stealth = eliminate sharp edges and
conductive materials
• Look direction = Illumination on Image
What Determines Radar Echo
• Electrical properties of material (Dielectric
Constant)
– Conductive = High Dielectric Constant =
Reflective
– Non-conductive = Low Dielectric Constant =
Non-Reflective
• Roughness
– Can’t “see” things smaller than wavelength
– Corners are effective for scattering
Some Dielectric Constants
•
•
•
•
Air: 1
Teflon: 2
Glass: 5-10
Water: 80
Radar Image of ISS
Radar and Optical
Stereoscopic SLAR
Radar Stereoscopy
• Although radar images can be viewed to
give a 3-dimensional appearance, true
photogrammetry is far more complex than
with optical imaging.
• It can be done, although when NASA
began radar mapping of Venus they didn’t
yet have the ability.
Light and Radar
Light and Radar
Light Vs. Radar
How Time = Illusion
Radar Foreshortening
• With optical foreshortening, the facing side
of a mountain looks normal and the back
side looks compressed
• With radar foreshortening, the facing side
of a mountain looks normal and the back
side looks longer
• Layover: On steep slopes objects may
appear to overlap because they’re the
same distance (time) away.
Light vs. Radar
Light vs. Radar
Layover
Radar Foreshortening
Layover and Foreshortening
Underwater Radar?
Sonar View
How Time = Illusion
Sonar Views of Shipwrecks
German Bomber
Polarization
• Radar signals are polarized parallel to
their transmitting antenna
• H (horizontal) polarization = parallel to
bottom of plane
• When signals scatter, some of the
polarization is lost
• What we see depends on the orientation
of the receiving antenna
Polarization
• Imagine a signal from a perfectly
horizontal antenna
• It bounces off a perfectly flat surface
perpendicular to the beam
• A receiver parallel to the transmitting
antenna will get 100% return
• A receiver perpendicular to the
transmitting antenna will get 0% return
HV vs. HH
Multiband Color Composite
Alaska
Coast
Reflectivity
and
Penetration,
Florida
Reflectivity,
Southern
California
IR +
Radar
Radar Penetration
of Sand, Sudan
Ground Penetrating Radar
Optical and Radar Imagery
TOPEX/Poseidon
The Sea Is Not Flat
Pacific Ocean
Sea Surface
Changes
Sea Surface Radar Mapping
2004
Tsunami
Global
Wind
Speed and
Wave
Heights
Radar Image of Hawaii
Lidar
• LIght Detection And Ranging
• Uses laser pulses to measure distance
• Anything that affects light affects Lidar
– Blocked by clouds, smoke, aerosols
– Can monitor clouds, smoke, aerosols
• Records distance and direction
• Depending on processing, can image
vegetation canopy or ground
Lidar
Mount
St.
Helens
Neolithic Mound, Slovakia
Hopewell Mounds, Ohio
Hopewell Mounds Ground View
Caracol, Belize
Caracol, Belize
Caracol, Belize
Caracol, Belize, Point Cloud
Bainbridge Island, WA
Tacoma Fault and Glacial Troughs