CryoSat Long-Term Ocean Data Analysis and Validation

CryoSat Long-Term Ocean Data Analysis and Validation: Final Words on GOP Baseline-C

Naeije, M.C. (TU Delft Astrodynamics & Space Missions)
Di Bella, Alessandro (ESRIN)
Geminale, Teresa (Defence & Aerospace Digital Factory)
Visser, P.N.A.M. (TU Delft Space Engineering)

Space Engineering

2023

ESA’s Earth explorer mission CryoSat-2 has an ice-monitoring objective, but it has proven to also be a valuable source of observations for measuring impacts of climate change over oceans. In this paper, we report on our long-term ocean data analysis and validation and give our final words on CryoSat-2’s Geophysical Ocean Products (GOP) Baseline-C. The validation is based on a cross comparison with concurrent altimetry and with in situ tide gauges. The highlights of our findings include GOP Baseline-C showing issues with the ionosphere and pole tide correction. The latter gives rise to an east–west pattern in range bias. Between Synthetic Aperture Radar (SAR) and Low-Resolution Mode (LRM), a 1.4 cm jump in range bias is explained by a 0.5 cm jump in sea state bias, which relates to a significant wave height SAR-LRM jump of 10.5 cm. The remaining 0.9 cm is due to a range bias between ascending and descending passes, exhibiting a clear north–south pattern and ascribed to a timing bias of +0.367 ms, affecting both time-tag and elevation. The overall range bias of GOP Baseline-C is established at −2.9 cm, referenced to all calibrated concurrent altimeter missions. The bias drift does not exceed 0.2 mm/yr, leading to the conclusion that GOP Baseline-C is substantially stable and measures up to the altimeter reference missions. This is confirmed by tide gauge comparison with a selected set of 309 PSMSL tide gauges over 2010–2022: we determined a correlation of R = 0.82, a mean standard deviation of (Formula presented.) cm (common reference and GIA corrected), and a drift of 0.17 mm/yr. In conclusion, the quality, continuity, and reference of GOP Baseline-C is exceptionally good and stable over time, and no proof of any deterioration or platform aging has been found. Any improvements for the next CryoSat-2 Baselines could come from sea state bias optimization, ionosphere and pole tide correction improvement, and applying a calibrated value for any timing biases.

altimetry
CAL/VAL
bias
CryoSat-2
GOP Baseline-C
cross-over and tide gauge analyses

http://resolver.tudelft.nl/uuid:fc6a556b-6541-40aa-bf1a-6b19c730880a

https://doi.org/10.3390/rs15225420

2072-4292

Remote Sensing, 15 (22)

Institutional Repository

journal article

© 2023 M.C. Naeije, Alessandro Di Bella, Teresa Geminale, P.N.A.M. Visser