OC3522Summer 2001 OC Remote Sensing of the Atmosphere and Ocean - Summer 2001 Active Microwave Radar

Radars are “active” remote sensors in that they transmit photons (energy) and measure those that get scattered back to the satellite. Satellite based radars are designed to detected physical characteristics of the surface or atmosphere. Since they are not usually interested in the gaseous constituents of the atmosphere, they typically operate at frequencies below 15 GHz to improve transmittance.

GTGT Radar Equation Let's express it in symbols and words Received Power = WTWT W T /4  r 2 r W  A Radiant intensity (W/m 2 ) incident on the target X Radar Scattering Cross-section of the target X Fraction of the scattered power received by the radar

Scattering cross Section,  o There are two primary mechanisms which contribute to  o (1) Specular Reflection Near vertical incidence reflection off mirror-like facets Important for  25°) 0  increased wind speed

LBLB   (2) Resonant (Bragg) Scatter  > 20° (occurs at all  but dominates here) off-nadir so polarization is important Ocean wave-length of importance: L fLfL LBLB increased wind speed  o depends on: polarization wavelength zenith angle wave spectrum (are there enough L B 's?) and wave spectrum in 2-D projection of L B fronts along line of sight

increased wind speed