Retrieval of Sea Surface Wind Speed from Spaceborne SAR over the Arctic Marginal Ice Zone with a Neural Network

Abstract

In this paper, we presented a method for retrieving sea surface wind speed (SSWS) from Sentinel-1 synthetic aperture radar (SAR) horizontal-horizontal (HH) polarization data in extra-wide (EW) swath mode, which have been extensively acquired over the Arctic for polar monitoring. In contrast to the conventional algorithm, i.e., using a geophysical model function (GMF) to retrieve SSWS by spaceborne SAR, we introduced an alternative retrieval method based on a GMF-guided neural network. The SAR normalized radar cross section, incidence angle, and wind direction are used as the inputs of a back propagation (BP) neural network, and the output is the SSWS. The network is developed based on 11,431 HH-polarized EW images acquired in the marginal ice zone (MIZ) of the Arctic from 2015 to 2018 and their collocated scatterometer wind measurements. Verification of the neural network based on the testing dataset yields a bias of 0.23 m/s and a root mean square error (RMSE) of 1.25 m/s compared to the scatterometer wind data for wind speeds less than approximately 30 m/s. Further comparison of the SAR retrieved SSWS with independent buoy measurements shows a bias and RMSE of 0.12 m/s and 1.42 m/s, respectively. We also analyzed the uncertainty of the retrieval when reanalysis model wind direction data are used as inputs to the neural network. By combining the detected sea ice cover information based on SAR data, sea ice and marine-meteorological parameters can be derived simultaneously by spaceborne SAR at a high spatial resolution in the Arctic.

Retrieval of Ocean Wave Heights From Spaceborne SAR in the Arctic Ocean With a Neural Network

“…In particular, an increasing underestimation trend with sea state is not observed. We recently used the same way to solve the underestimation of SSW retrievals by the same S1 EW data in HH polarization (Li, Qin, et al, 2020).…”

“…As most of the S1 EW and IW data acquired over in situ buoys are in VV polarization, we found only 305 pairs of S1 data and National Data Buoy Center (NDBC) buoy data in the period from October 2014 to October 2019 (Li, Qin, et al, 2020). Therefore, in this study, we used RA measurements of SWH in the Arctic ocean as ground truth to develop the BPNN model.…”

A New Cyclic Iterative Correction Algorithm for Retrieving Sea Surface Wind Speed Based on a Multilayer-Medium Model

“…Meanwhile, SAR technology and SAR image technology are developed to retrieve sea surface wind speed [30]- [37] recently. Its fundamental principles of retrieving sea surface wind speed are to depend on relationships between backscattering coefficient (or received power or SAR image power) and wind speed, or relationships between the received power waveform and wind speed [38]- [40]. In view of the huge amount of data, artificial neural network technology [40] is introduced for training to establish the model of scattering power, or power waveform and sea surface wind speed.…”

“…Its fundamental principles of retrieving sea surface wind speed are to depend on relationships between backscattering coefficient (or received power or SAR image power) and wind speed, or relationships between the received power waveform and wind speed [38]- [40]. In view of the huge amount of data, artificial neural network technology [40] is introduced for training to establish the model of scattering power, or power waveform and sea surface wind speed. These models mainly depend on the relationships between the sea surface wind speed and those relative parameters(scattering power or waveform) at C band.…”

“…These models mainly depend on the relationships between the sea surface wind speed and those relative parameters(scattering power or waveform) at C band. And also the scattering mechanism (scattering angle, polarity, time delay and et al) [40] is so complex that the improvement of the accuracy of retrieving wind speed is still 1.5m/s or more than. The effects of rainfall and whitecaps still exist although rainfall and whitecaps have little attenuation of the electromagnetic scattering at C band.…”