Preliminary Significant Wave Height Retrieval from Interferometric Imaging Radar Altimeter Aboard the Chinese Tiangong-2 Space Laboratory

Lin Ren,Jingsong Yang,Yongjun Jia,Yunhua Zhang,Xiao Dong

doi:10.3390/rs13122413

Abstract

The interferometric imaging radar altimeter (InIRA) aboard the Chinese Tiangong-2 space laboratory is the first spaceborne imaging radar working at low incidence angles. This study focuses on the retrieval of significant wave heights (SWHs) from InIRA data. The retrieved SWHs can be used for correcting the sea state bias of InIRA-derived sea surface heights and can supplement SWH products from other spaceborne sensors. First, we analyzed tilt, range bunching and velocity bunching wave modulations at low incidence angles, and we found clear dependencies between the SWH and two defined factors, range and azimuth integration, for ocean waves in the range and azimuth directions, respectively. These dependencies were further confirmed using InIRA measurements and collocated WaveWatch III (WW3) data. Then, an empirical orthogonal SWH model using the range and azimuth integration factors as model inputs was proposed. The model was segmented by the incidence angle, and the model coefficients were estimated by fitting the collocation at each incidence angle bin. Finally, the SWHs were retrieved from InIRA data using the proposed model. The retrievals were validated using both WW3 and altimeter (JASON2, JASON3, SARAL, and HY2A) SWHs. The validation with WW3 data shows a root mean square error (RMSE) of 0.43 m, while the average RMSE with all traditional altimeter data is 0.48 m. This indicates that the InIRA can be used to measure SWHs.

Highlights

Ocean wave, as an environment dynamic variable, plays an important role in various fields, such as air–sea interaction, numerical weather prediction, oceanographic engineering and shipping
Significant wave height (SWH) is a representative wave parameter that can describe the total energy of a wave system; it is widely used in these fields
The SWHs were retrieved from the interferometric imaging radar altimeter (InIRA) data using the proposed model

Summary

Introduction

As an environment dynamic variable, plays an important role in various fields, such as air–sea interaction, numerical weather prediction, oceanographic engineering and shipping. Spaceborne radars measuring the SWH include traditional altimeters, ocean wave spectrometers (OWSs), and synthetic aperture radars (SARs). These radars have special detecting features for retrieving the SWH using different methods. The most commonly used method for SWH remote sensing is the traditional altimeter approach, which has made an important contribution to global SWH products. In this approach, the SWH is directly estimated from the leading edge slope of a radar echo, and the slope is obtained by fitting the measured waveform to a physical-based echo model [1,2,3]

Methods

Results

Discussion

Conclusion