Dual-Polarized Backscatter Features of Surface Currents in the Open Ocean during Typhoon Lan (2017)

Guosheng Zhang,William Perrie

doi:10.3390/rs10060875

Abstract

Ocean surface current measurements from satellites have historically been limited. We propose a new approach to detect ocean surface currents as observed by dual-polarized (VV and VH) spaceborne synthetic aperture radar (SAR). This approach is based on the assumptions that the VH-polarized SAR signal is only generated by the effects of ocean winds creating surface waves, whereas the VV-polarization data are due to the effects of both ocean winds and surface currents. Therefore, the surface currents features may be extracted after retrieving the ocean winds from VH-polarized backscatter and inputting signal due to the wind to the VV-polarized backscatter data. To investigate the performance of this approach under extreme wind conditions, we consider a scene of C-band RADARSAT-2 dual-polarized ScanSAR images over Typhoon Lan (2017) in the open ocean, and we verify our results with current estimates from altimeter data. The ocean current features extracted from the backscatter data that were collected from the SAR images are shown to correspond to an area of strong currents and an oceanic front observed by altimeters. We suggest that the proposed method has the potential capacity to provide information about ocean surface currents from high-resolution dual-polarized ScanSAR images.

Highlights

Observations of surface currents in the open ocean have historically been limited; high-frequency (HF) radar has been used for a limited range in coastal areas and ADCP and buoy deployments have provided data at specific point locations [1]
Compared to the passive remote sensing instruments that operate from satellites in the visible and infrared bands, the microwave data such as Special Sensor Microwave Imager (SSM/I), Tropical Rainfall Measuring Mission (TRMM) imagery, Quick Scatterometer (QuikSCAT), and Advanced Scatterometer (ASCAT) have the advantage of essentially being able to work in all-weather conditions, day or night, penetrating fog and cloud [2]
To extract the current backscatter features imaged by synthetic aperture radar (SAR) under extreme wind conditions, we propose an approach for C-band RADARSAT-2 dual-polarized (VV and VH) ScanSAR images

Summary

Introduction

Observations of surface currents in the open ocean have historically been limited; high-frequency (HF) radar has been used for a limited range in coastal areas and ADCP (acoustic Doppler current profiler) and buoy deployments have provided data at specific point locations [1]. Compared to the passive remote sensing instruments that operate from satellites in the visible and infrared bands, the microwave data such as Special Sensor Microwave Imager (SSM/I), Tropical Rainfall Measuring Mission (TRMM) imagery, Quick Scatterometer (QuikSCAT), and Advanced Scatterometer (ASCAT) have the advantage of essentially being able to work in all-weather conditions, day or night, penetrating fog and cloud [2]. These instruments are sensitive to sea surface waves generated by the wind. Until the SWOT (Surface Water and Ocean Topography) satellite is launched in 2021 (https://swot.jpl.nasa.gov), only measurements of sea surface height along points of the narrow altimeter tracks are available

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