Ground and satellite-based radar observation comparisons: Propagation of space-based radar signals

Propagation effects in rainfall are examined for a high-frequency space-based weather radar system via comparison with polarimetric ground radar observations. Simultaneous measurements were collected from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and the National Center for Atmospheric Research (NCAR) S-Band polarimetric radar (SPOL). Ground radar data was collected during the TExas and FLorida UNderflights (TEFLUN-B) experiment in August 1998 and the Large Biosphere-Atmosphere Experiment in Amazonia (LBA) in February 1999. A theoretical model is developed to estimate specific attenuation (alpha) in the vertical direction from specific differential phase (K-DP) in the horizontal propagation direction. From this model PR attenuation is derived from ground-measured K-DP along the space radar beam. The total two-way path-integrated-attenuation (PIA) along the beam is then calculated which can also be used to determine an alpha -corrected PR return. Results indicate a significant level of attenuation in the space-radar during high rainfall events - as much as 12 dB when storm levels reach 50 dBZ near the surface. A comparison is also made between the alpha -corrected reflectivity and the PR corrected reflectivity found in the level 2 data products.