Abstract's details
CryoSat long-term ocean data analysis and validation: final words on GOP Baseline-C
CoAuthors
Event: 2023 Ocean Surface Topography Science Team Meeting
Session: Regional and Global CAL/VAL for Assembling a Climate Data Record
Presentation type: Type Poster
Contribution: PDF file
Abstract:
The ESA’s Earth Explorer CryoSat mission is primarily dedicated to precise measurement of the changes in the thickness of marine ice floating on the polar oceans and variations in the thickness of the vast ice sheets that overlie Greenland and Antarctica. With the effects of a fast-changing climate becoming apparent, particularly in polar regions, it is increasingly important to understand exactly how Earth’s ice fields are responding. Going beyond its ice-monitoring objective, CryoSat is also a valuable source of observations for measuring dramatic impacts of climate change over the ocean. The satellite’s radar altimeter measures high-resolution geophysical parameters from open ocean to coast. The CryoSat data are therefore operationally processed and analysed by ESA both over the ocean and ice surfaces with two independent processing chains following two different processing baselines.
To enable their full scientific and operational exploitation, the CryoSat ocean products continuously evolve and need to be quality-controlled and thoroughly validated via science-oriented diagnostics based on multi-platform in situ data, models and other satellite missions. In this context, the objective of our validation research is the long-term monitoring of the level-2 CryoSat Geophysical Ocean Product (GOP), by evaluating the stability of the measurement system and identifying potential biases, their patterns and drifts, over the ocean, through calibration and comparisons with concurrent altimeter data, by employing the Radar Altimeter Database System (RADS). Independently, we also address this by comparing the GOP geophysical parameters with external models and in situ measurements. This poster presents our final words on the GOP Baseline-C data.
We persistently monitored, analysed and identified systematic errors in the observations, estimated (trends in) biases in range, significant wave height, backscatter, wind speed and sea state bias, and timing biases. Highlights from our study include the results from the cross-calibration with other altimeter missions and comparison with tide gauge sea level data: GOP Baseline-C Ocean data has a –2.9 cm range bias with respect to the calibrated reference satellites in RADS and a negligible drift (<0.25 mm/yr), and a high correlation of 0.82 and low std of 5.6 cm with PSMSL tide gauge data. In addition, the comparison with other altimeters raised a concern about the correctness of the ionosphere correction implementation, and a north-south and east-west pattern in the bias was established, after separating ascending and descending passes and separating altimeter modes. A SAR-LRM bias of 1.5 cm is accounted for by a 0.6 cm sea state bias (as a result of a 10 cm significant wave height bias), and an ascending-descending bias of 0.9 cm. Despite these pending issues we conclude that they have no appreciable impact on the stability of the CryoSat measurement system: CryoSat GOP does facilitate a long-term stable measurement, and CryoSat can be regarded a reference mission in itself. In fact, we employed CryoSat GOP for calibrating Sentinel-6A which appears to have an absolute range bias of -1.1 cm, and we discovered a drifting sea level (related to a 6 cm jump in significant wave height) in Sentinel-3A and 3B after medio 2022.
To enable their full scientific and operational exploitation, the CryoSat ocean products continuously evolve and need to be quality-controlled and thoroughly validated via science-oriented diagnostics based on multi-platform in situ data, models and other satellite missions. In this context, the objective of our validation research is the long-term monitoring of the level-2 CryoSat Geophysical Ocean Product (GOP), by evaluating the stability of the measurement system and identifying potential biases, their patterns and drifts, over the ocean, through calibration and comparisons with concurrent altimeter data, by employing the Radar Altimeter Database System (RADS). Independently, we also address this by comparing the GOP geophysical parameters with external models and in situ measurements. This poster presents our final words on the GOP Baseline-C data.
We persistently monitored, analysed and identified systematic errors in the observations, estimated (trends in) biases in range, significant wave height, backscatter, wind speed and sea state bias, and timing biases. Highlights from our study include the results from the cross-calibration with other altimeter missions and comparison with tide gauge sea level data: GOP Baseline-C Ocean data has a –2.9 cm range bias with respect to the calibrated reference satellites in RADS and a negligible drift (<0.25 mm/yr), and a high correlation of 0.82 and low std of 5.6 cm with PSMSL tide gauge data. In addition, the comparison with other altimeters raised a concern about the correctness of the ionosphere correction implementation, and a north-south and east-west pattern in the bias was established, after separating ascending and descending passes and separating altimeter modes. A SAR-LRM bias of 1.5 cm is accounted for by a 0.6 cm sea state bias (as a result of a 10 cm significant wave height bias), and an ascending-descending bias of 0.9 cm. Despite these pending issues we conclude that they have no appreciable impact on the stability of the CryoSat measurement system: CryoSat GOP does facilitate a long-term stable measurement, and CryoSat can be regarded a reference mission in itself. In fact, we employed CryoSat GOP for calibrating Sentinel-6A which appears to have an absolute range bias of -1.1 cm, and we discovered a drifting sea level (related to a 6 cm jump in significant wave height) in Sentinel-3A and 3B after medio 2022.