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Synthetic Aperture Radar Observations of Sea Surface Signatures of Atmospheric Gravity Waves over Coastal Waters

Werner Alpers(1), Weigen Huang(2) and Gan Xilin(2)

(1) University of Hamburg, Bundesstrasse 53, D-20146 Hamburg, Germany
(2) State Key Lab. of Satellite Ocean Environment Dyna, State Oceanic Administration, Hangzhou, China

Abstract

Synthetic aperture radar (SAR) images acquired over coastal waters often show sea surface signatures of atmospheric gravity waves (AGWs). On the other hand, on SAR images of the sea surface sea surface signatures of oceanic internal waves are often also visible which have a similar shape and which sometimes are confounded with sea surface signatures of AGWs. Here we present 6 SAR images acquired by the Advanced SAR (ASAR) onboard the European Envisat satellite over the Bohai Sea, the Yellow Sea and the Taiwan Strait of China, which all show sea surface signatures of AGWs. They have quite different shapes mainly due to the differing generation mechanisms. Evidence that the observed wave patterns visible on the ASAR images are indeed sea surface signatures of AWGs is obtained from 1) their location, 2) meteorological data obtained from radiosondes, 3) sea surface winds measured by the scatterometer onboard the Quikscat satellite, 4) re- analyzed wind fields provided by the National Center for Environmental Prediction (NCEP), and in two cases, 5) from cloud images acquired by the MERIS sensor onboard the Envisat satellite and the MODIS sensor onboard the Terra satellite. In particular, by calculating the Scorer parameter and the Richardson number, we show that for all 6 analyzed events the AGWs are trapped in the atmospheric boundary layer. Furthermore, we show that it is often possible to determine whether the wave patterns visible on SAR images of the sea surface originate from AGWs or oceanic internal waves by analyzing their shape. Based on theoretical models of the SAR imaging mechanisms of oceanic and atmospheric waves we derive rules for discriminating between radar signatures of AGWs and oceanic internal waves.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry