MET4994_5994_RS_Lec18_S11

MET4994_5994_RS_Lec18_S11 - MET MET 4994 Remote Sensing:...

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MET 4994 Remote Sensing: Radar and Satellite Meteorology MET 5994 Remote Sensing in Meteorology Lecture 18: February 21, 2011 1. Curvature and Refraction 2. Radar Equation for Point Targets
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Radar Wave Propagation In the clear air without rain or cloud: the wavelength is much larger than the size of air molecules (optical regime), therefore, we have to consider refraction and/or reflection. In rain or cloud: the wavelength is comparable to the size of cloud drops or raindrops (Rayleigh or Mie regime), therefore, we have to consider scattering.
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Refractivity Complex refractive index: ri N n n i  Refractivity: refractivity of the atmosphere is dependent upon pressure, temperature, and humidity. 6 ( 1) 10 rr Nn   Radar wave propagation is more dependent upon the gradient of refractivity rather than the absolute value of refractivity at any point.
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Snell’s Law Under normal atmospheric conditions, refractivity is largest near the ground and decreases with height. Therefore, radar waves will travel faster aloft than near the surface. This bends the waves in a downward direction relative to the horizontal. Why? Snell’s Law: sin () sin ( ) ii rr r r i r u n nu 
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More Dense Medium N larger Less Dense Medium N smaller
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Curvature Curvature is the angular rate of change necessary to follow a curved path.
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This note was uploaded on 09/13/2011 for the course MET 4994 taught by Professor Haijan during the Spring '11 term at FIU.

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MET4994_5994_RS_Lec18_S11 - MET MET 4994 Remote Sensing:...

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