Comparison of along-track resolution of SARAL/AltiKa and ENVISAT-RA2 satellite altimeters over continental margins

ABSTRACT

The objective of the present study is to systematically quantify the along-track resolution of Satellite for Argos and AltiKa (SARAL)/AltiKa and Environmental Satellite (ENVISAT)-RA2 altimeters over continental margins. Spectral coherence and power spectral density estimated from pairs of stacked (averaged) sea surface height (SSH) profiles from repeat tracks as a function of wave number are used to estimate along-track resolution and noise characteristics, respectively. The analyses were carried out along 96 SARAL/AltiKa and ENIVISAT-RA2 tracks covering continental margins of India, Gulf of Mexico, and South America. Our study clearly suggests that for all three sites the short-wavelength resolution of SARAL/AltiKa (15–18 km) is ~27–33% better than ENVISAT-RA2 (22–25 km) data. Variations in sediment thickness along the continental margins have significant influence in the along-track resolution of both altimeters. Strong geoid signals owing to thin sediments (0.1–0.3 km thick) along the South American margin provided higher resolution for both SARAL/AltiKa (15 km) and ENVISAT-RA2 (22 km) altimeters. Conversely, over the continental margins of India and Gulf of Mexico with huge sediment thickness (1–20 km), the resolution of SARAL/AltiKa and ENVISAT-RA2 drops to 18 and 25 km, respectively. We also observe that resolution of both altimeters is higher by 1–2 km for continental margins with narrow shelf. The present study has implications in the generation of high-resolution marine geoid and gravity anomalies using SARAL/AltiKa along with other altimeters.

Acknowledgements

This work was carried out as a part of GAP program of SAC. ENVISAT-RA2 data were downloaded from ESA (ftp://ra2-ftp-ds.eo.esa.int) and SARAL/AltiKa data were downloaded from MOSDAC (https://mosdac.gov.in). Sediment thickness data is from NCEI’s grid of global ocean sediment thickness, NOAA. Constructive suggestions from the editor, Weigen Huang, and two anonymous reviewers have helped us to improve quality of the article. We thank Nilesh Desai, I.M. Bahuguna, and Ram Rajak from SAC for their support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

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Additional information

Funding

This work was supported by the GAP program of SAC, ISRO.