Impact of Ships and Ocean Fronts on Coastal Sea Surface Wind Measurements From the Advanced Scatterometer

Abstract

In this paper, the capability of the advanced scatterometer (ASCAT) in measuring surface wind speed in coastal waters of China was first evaluated by comparing with in situ wind observations from 13 moored buoys during the period from July 2013 to December 2015. The scatterometer performs well in most coastal regions of China. However, a sharp reduction in wind speed retrieval accuracy is found in areas adjacent to the Yangtze River estuary. The mean bias and root-mean-square error between ASCAT wind speeds and buoy measurements reach up to 3.44 and ${\text{4.06 m}}\cdot {\text{s}}^{- 1}$ , respectively. This large overestimation of surface wind is also observed in Sentinel-1A synthetic aperture radar (SAR) derived wind speeds. The analysis of quasi-synchronous SAR images and sea surface temperature observations shows that the overestimation of the scatterometer or SAR winds is mainly caused by the effects of ships or ocean thermal fronts due to the complicated thermodynamic and hydrodynamic characteristics of the study area on radar backscatter signal. These effects should be taken into account or marked as flags in activities generating or using scatterometer or SAR wind products.