Characteristics of Mirror Image of Precipitation Observed by TRMM Precipitation Radar

摘要

Mirror image is a virtual image of precipitation "below" the ocean surface when we use an airborne or a spaceborne radar to view the rainfall over ocean. It is due to a double reflection, that is energy reflected from the sea surface goes to the precipitation and back to the radar via a second reflection at sea surface. We investigated the mirror image characteristics using TRMM Precipitation Radar data and found: 1) The radar can detect the mirror image clearly over the ocean, 2) the mirror image echo corresponds well to the direct rain echo at nadir and near nadir incidence angles, 3) in a weak rain region, mirror echo intensity is nearly proportional to the direct echo power except near noise level, 4) in the strong rain region, rain attenuation effect clearly appears, and 5) the ratio of mirror echo power to direct echo power is affected by the rain attenuation which varies with the bright band height and the range of the target rain from surface. Further we performed a simple simulation in order to confirm the above characteristics. The signal fluctuation, noise contamination, rain attention and surface cross section are taken into account in the simulation, and the results of simulation confirmed the observation results.