RAdio Detection And Ranging LIght Detection And Ranging

RAdio Detection And Ranging LIght Detection And Ranging

A Super Simplified Radar Equation

A Super Simplified Radar Equation Marshall-Palmer DSD (1948)

Radar Rainfall for 40 d. BZ Location Canada Hawaii Midwest Australia Washington, DC Massachusetts Moscow Poon, India France Franklin, NC Rainfall rate [mm/hr] 48. 6 112. 6 50. 2 10. 2 54. 0 254. 0 40. 0 43. 0 24. 2 76. 7

Attenuating Radar Z-R a 6 a) Hitchfield-Bordan ______________ Z-Rassumed DSD ___________ 2 -way attenuation ______________ Z-R _______ 2 -way attenuation ______________ b) K-Z a 3 _______ Z-R _______ Surface reference technique _____ If o is constant, o due to rain provides 2 -way attenuation. Solve for Z-R consistent with attenuation. _____ o

Radar Retrieval

LIDAR Molecular / Aerosol / Cloud scattering A 10 cm radar w. 50 cm dish from 800 km has 60 km resolution. A Lidar at 0. 5 micron (vis) and a 50 cm focal plane has 1. 0 m resolution. In Vis/UV scattering by molecules becomes detectable. Can measure gas profiles better than with sounders.

LIDAR types DIAL – Differential Absorption Lidar RAMAN Lidar Aerosol Lidars Cloud ice Lidars Doppler Lidars

DIAL – Differential Absorption Lidar Typically in UV. Choose two closely spaced frequencies, one on an absorption line and one slightly off such that backscatter (i. e. sca, l • P(180)) is similar, but absorption (by gas in question) is much larger at the absorption line. From this, can reconstruct absorption profile and knowledge of Kabs can be turned into gas absorption Water vapor has very narrow resonances in UV. Need DIAL with very good (i. e. narrow) frequency beam. Ozone is a rather broad line and laser requirements are not as demanding.

RAMAN Lidar Backscatter from molecules, but difficult because aerosols can dominate backscattering signal and does not identify species. Raman Lidars detect elastic backscatter (same frequency as transmitted pulse), plus a much weaker signal from inelastic scattering which shifts the frequency. Comes from molecules absorbing energy, and inducing vibration & rotations that change the frequency of scattered photon by that amount. These lines are in the visible for oxygen, nitrogen and water vapor

RAMAN Lidar where n is the resonance frequency Because Raman effect is small, need large power and telescopes to makes work

Aerosol Lidars Raman (i. e. vis) measuring elastic backscatter only are useful for aerosol detection. Need to have a method for relating sca(180) to aerosol concentrations. Cloud or Depolarization Lidars Linear Depolarization ration (Iperp/Iparallel) is zero for shperical drops but grows with anisotropy of ice crystals. Can therefore detect phase of particles Doppler Lidars Measure Doppler velocity of molecules or aerosols. Difficult from space because spacecraft motion is 7, 000 m/s

ADM - AEOLUS