08-ActiveMicrowave

08-ActiveMicrowave - 4/30/2008 Active and passive remote...

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4/30/2008 ESM 266: Active microwave remote sensing 1 ESM 266: ESM 266: Active Active microwave microwave remote sensing 1 Jeff Dozier Active and passive remote sensing • Passive: uses natural energy, either reflected sunlight or emitted thermal or microwave radiation Active: sensor creates its own energy 2 • Active: sensor creates its own energy – Transmitted toward Earth – Interacts with atmosphere and/or surface – Reflects back toward sensor (backscatter) Widely used active remote sensing systems • Active microwave (radar) – long-wavelength microwaves (1-100cm) – recording the amount of energy back-scattered from the terrain Lida 3 Lidar – short-wavelength laser light (e.g., 0.90 μm) – recording the light back-scattered from the terrain or atmosphere • Sonar – sound waves through a water column – recording the amount of energy back-scattered from the water column or the bottom Frequency wavelength relation • Generally in the microwave part of the spectrum we use frequency instead of wavelength Frequency where speed of light c c ν λ = = 4 • Typically measured in s –1 , called Hertz (Hz) – Most often Gigahertz (GHz) = 10 9 Hz () 8- 1 = Useful 3.00 tric 10 m s 30 GHz cm k × = Microwave band codes Band Wavelength, cm Frequency, GHz Mid-IR (3-5) × 10 –4 100,000-60,000 Thermal IR (8-15) × 10 –4 37,500-20,000 K a 0.75-1.18 40.0-26.5 K 1.19-1.67 26.5-18.0 Unusual names are an artifact of the original secret work on radar remote sensing in World War II 5 K u 1.67-2.4 18.0-12.5 X 2.4-3.8 12.5-8.0 C 3.9-7.5 8.0-4.0 S 7.5-15.0 4.0-2.0 L 15.0-30.0 2.0-1.0 P 30.0-100 1.0-0.3 Sending and receiving a pulse of microwave radiation transmit ed pulse backscat ered pulse antenna Transmitter Duplexer • sends and receives Pulse Generator CRT Display or Digital Recorder Receiver b. a. antenna
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4/30/2008 ESM 266: Active microwave remote sensing 2 SIR C/X SAR images of Rondonia, Brazil April 10, 1994 Advantages of radar • All weather, day or night – Some areas of Earth are persistently cloud covered • Penetrates clouds, vegetation, dry soil, dry 8 snow • Sensitive to water content, surface roughness – Can measure waves in water • Sensitive to polarization and frequency • Interferometry (later) using 2 receiving antennas Disadvantages Disadvantages of radar of radar • Penetrates clouds, vegetation, dry soil, dry snow – Signal is integrated over a depth range and a variety of materials • Sensitive to water content, surface roughness – Small amounts of water affect signa 9 – Small amounts of water affect signal – Hard to separate the volume response from the surface response • Sensitive to polarization and frequency – Many choices for instrument, expensive to cover range of possibilities – The math can be formidable How it works Pulses of active microwave electromagnetic energy
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08-ActiveMicrowave - 4/30/2008 Active and passive remote...

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