Characteristics of the Mirror Image of Precipitation Observed by the TRMM Precipitation Radar

Abstract

A mirror image is a virtual image of precipitation from below the ocean surface when an airborne or a spaceborne radar is used to view rainfall over the ocean. It is due to a reflection of energy from the sea surface tothe precipitation and back to the radar via a second reflection at the sea surface. The mirror image characteristics were investigated using Tropical Rainfall Measuring Mission (TRMM) precipitation radar data and the following was 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, the mirror echo intensity is nearly proportional to the direct echo power except near the radar noise level. 4) In the strong rain region, rain attenuation effects clearly appear. 5) The ratio of the mirror echo power to the direct echo power is affected by the rain attenuation, which varies with the brightband height and the range of the target rain from surface. Further, a simple simulation was performed in order to confirm the above characteristics. The signal fluctuation, noise contamination, rain attenuation, and surface cross section are taken into account in the simulation. The results of simulation confirmed the observation results.