Estimation of Spaceborne Radar Signals from Polarimetric Ground Radar Observations

The Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) is one of several instruments aboard a satellite operating in a nearly circular orbit at 350 km altitude with inclination of 35 degrees and period of about 91.5 minutes. Simultaneous measurements were made between the National Center for Atmospheric Research (NCAR) S-POL radar and TRMM PR during the TExas and FLorida UNderflights (TEFLUN-B) experiment that took place near Melbourne, FL in 1998, and the Large Biosphere-Atmosphere experiment in Amazonia (LBA) near Ji-Parana, Brazil in 1999.

Intercomparisons between ground radar and PR measurements are, in principle, straightforward. However, consideration of numerous details are important to ensure proper alignment of radar observations from two distinct platforms that have different viewing aspects, operating frequencies and resolution volume sizes.

The true vertical reflectivity profile along the TRMM PR beam is quantitatively determined using ground-based polarimetric radar observations. The specific differential phase (K_dp) is calculated along the space radar beam from S-Band ground radar measurements taken along the beam. A theoretical model is used to determine the expected specific attenuation (a), at K_u-Band frequency, from S-Band K_dp measurements. The total two-way path-integrated attenuation (PIA) can then be calculated by integration of the specific attenuation over the attenuating path length at each point along the PR beam, and, thus, the true vertical reflectivity profile can be found. The theoretical a-K_dp relationship depends upon the hydrometer type which is determined via a Fuzzy-logic technique using ground-based polarimetric radar observations (Liu & Chandrasekar, 2000). Results and comparison of the a-K_dp method with the TRMM PR attenuation correction algorithm, which uses a hybrid of the Hitschfeld-Bordan and surface reference methods to estimate the true radar vertical reflectivity profile, is presented.

Liu, H. and Chandrasekar, V., 2000: Classification of Hydrometeors Based on Polarimetric Radar Measurements: Development of Fuzzy Logic and Neuro-Fuzzy Systems, and In Situ Verification, J. Atm. Oceanic Tech., 17, 140-164.