Presentation on theme: "Radar Mapping. Electromagnetic EM Radiation Electric Field & Magnetic Field –Perpendicular to direction of propagation Explains light but is absolutely."— Presentation transcript:
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
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
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.
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.
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
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