An Analytical Method for Dynamic Wave-Related Errors of Interferometric SAR Ocean Altimetry under Multiple Sea States

Yao Chen,Mo Huang,Changyuan Wang,Tao Duan,Yuanyuan Zhang

doi:10.3390/rs13050986

Abstract

The spaceborne interferometric synthetic aperture radar (InSAR) is expected to measure the sea surface height (SSH) with high accuracy over a wide swath. Since centimeter-level accuracy is required to monitor the ocean sub-mesoscale dynamics, the high accuracy implies that the altimetric errors should be totally understood and strictly controlled. However, for the dynamic waves, they move randomly all the time, and this will lead to significant altimetric errors. This study proposes an analytical method for the dynamic wave-related errors of InSAR SSH measurement based on the wave spectrum and electromagnetic scattering model. Additionally, the mechanisms of the dynamic wave-related errors of InSAR altimetry are analyzed, and the detailed numerical model is derived. The proposed analytical method is validated with NASA’s Surface Water and Ocean Topography (SWOT) project error budget, and the Root-Mean-Square Errors (RMSEs) are in good agreement (0.2486 and 0.2470 cm on a 0.5 km2 grid, respectively). Instead of analysis for a typical project, the proposed method can be applied to different radar parameters under multiple sea states. The RMSEs of Ka-band under low sea state, moderate sea state, and high sea state are 0.2670, 1.3154, and 6.6361 cm, respectively. Moreover, the RMSEs of X-band and Ku-band are also simulated and presented. The experimental results demonstrate that the dynamic wave-related errors of InSAR altimetry are not sensitive to the frequencies but are sensitive to the sea states. The error compensation method is necessary for moderate and higher sea states for centimetric accuracy requirements. This can provide feasible suggestions on system design and error budget for the future interferometric wide-swath altimeter.

Highlights

Sea surface height (SSH) has received unprecedented attention due to the significant application value in understanding the ocean dynamics, such as currents, eddies, fronts, and turbulence [1]
An analytical method for wave-related errors of interferometric synthetic aperture radar (InSAR) altimetry is proposed in this paper based on the wave spectrum and EM scattering model, and the error numerical model was derived
The proposed error analytical method takes into account both the ocean characteristics and the InSAR working characteristics, which can better simulate the distribution of errors as in the actual ocean scene

Summary

Introduction

Sea surface height (SSH) has received unprecedented attention due to the significant application value in understanding the ocean dynamics, such as currents, eddies, fronts, and turbulence [1]. Spaceborne radar altimetry was proposed in the 1960s and has the ability to measure the SSH with global and frequent high precision [2]. These powerful remote sensing observations of SSH allow us to better monitor the ocean dynamics and make better use of the Earth’s resources. Conventional nadir altimeters, such as the operational Jason-3 or HY-2A/B/C, have a restriction on spatial resolution strongly related to the latitude and only measure a twodimensional ocean surface topography (OST) larger than ~ 100 km [6]. The spatial resolution unit could be largely divided into three ascensive phases, namely, the “diamond”, the “grid”, and the “pixel” phases [7].

Methods

Results

Discussion

Conclusion