08-ActiveMicrowave

08-ActiveMicrowave - ESM 266: Active microwave remote...

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1 ESM 266: Active microwave  ESM 266: Active microwave  remote sensing remote sensing Jeff Dozier
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2 Active and passive remote sensing Active and passive remote sensing Passive: uses natural energy, either reflected sunlight or emitted thermal or microwave radiation Active: sensor creates its own energy Transmitted toward Earth Interacts with atmosphere and/or surface Reflects back toward sensor (backscatter)
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3 Widely used active remote sensing systems Widely used active remote sensing systems Active microwave (radar) long-wavelength microwaves (1-100cm) recording the amount of energy back-scattered from the terrain 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
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4 Frequency-wavelength relation Frequency-wavelength relation Generally in the microwave part of the spectrum we use frequency instead of wavelength Typically measured in s 1 , called Hertz (Hz) Most often Gigahertz (GHz) = 10 9 Hz ( 29 ( 29 8 -1 Frequency where speed of light = Useful 3.00 tric 10 m s 30 GHz cm k c c ν λ = = =
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5 Microwave band codes 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 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 Unusual names are an artifact of the original secret work on radar remote sensing in World War II
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Sending and receiving a pulse of microwave  Sending and receiving a pulse of microwave  radiation radiation transmitted pulse backscattered pulse antenna Transmitter Duplexer • sends and receives Pulse Generator CRT Display or Digital Recorder Receiver b. a. antenna
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SIR-C/X-SAR images  SIR-C/X-SAR images  of Rondonia, Brazil of Rondonia, Brazil April 10, 1994
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8 Advantages of radar Advantages of radar All weather, day or night Some areas of Earth are persistently cloud covered Penetrates clouds, vegetation, dry soil, dry snow Sensitive to water content, surface roughness Can measure waves in water Sensitive to polarization and frequency Interferometry (later) using 2 receiving antennas
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9 Disadvantages of radar Disadvantages of radar Penetrates clouds, vegetation, dry soil, dry snow
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08-ActiveMicrowave - ESM 266: Active microwave remote...

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