Airborne Interferometric Radar Altimeter Shows Potential for Submesoscale SSHA Measurements

To date, humanity has not been able to observe two-dimensional (2D) oceanic processes at the 0.1-10 km submesoscale in the spatial domain through remote sensing. The sea surface height anomaly (SSHA) signal at this scale is small and exceeds the resolution limits of the satellite altimeters used to date.

However, oceanic processes at this scale play a critical role in the study of ocean energy transfer, cascading, and dissipation, and are crucial for research on ocean energy balance, nutrient transport, and global climate change studies.

Recently, the research team led by Prof. XU Yongsheng from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) obtained the two-dimensional along-track SSHA of about 100 km and the first broadband SSHA wavenumber spectrum using Airborne Interferometric Radar Altimeter (AIRA) observations.

The study was published in Remote Sensing on Apr. 12.

This study provides a detailed analysis of the SSHA and its wavenumber spectrum obtained by AIRA, and demonstrates the potential of AIRA for submesoscale SSHA observations. The AIRA shows a good ability to capture small-scale SSHA. In the enlarged image, waves featuring wavelengths between 50 and 150 m stand out as the most dominant feature. The submesoscale SSHA typically has magnitudes much smaller than ocean waves.

Nevertheless, it remains evident that the waves are superimposed on a background characterized by undulating heights. The SSHA spectrum from AIRA maintains a clear negative slope down to about 1 km, consistent with theoretical predictions. AIRA's resolved PSD level in the 1-10 km submesoscale range is about ten times lower than that of ICESat-2 ATL03, demonstrating AIRA's superior ability to resolve lower energy SSHA variations. The wavenumber spectrum is an important basis for evaluating the observational performance of AIRA.

"The results of this study emphasize the enormous potential of AIRA in capturing SSHA on a range of scales from oceanic waves to submesoscale," said HE Jinchao, first author of the study.

"We anticipate that our study will inspire a renewed appreciation for the potential of AIRA in detecting two-dimensional small submesoscale SSHA," added Prof. XU, corresponding author of the study. "These processes are vital for understanding ocean dynamics, marine ecosystems, and their role in the Earth's climate system."

Fig. 1 2D SSHA from AIRA measurements

Fig. 2 Comparison of the SSHA wavenumber spectrum observed by AIRA (in red) with the SSHA wavenumber spectra from satellite altimeters ICESat-2, SARAL/AltiKa, and Sentinel-6A.

He J, Xu Y, Sun H, Jiang Q, Yang L, Kong W, Liu Y. (2024). Sea Surface Height Wavenumber Spectrum from Airborne Interferometric Radar Altimeter. Remote Sensing.

(Text by XU Yongsheng)

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