Sea State Climate Change Initiative

Annual cycle of Significant Wave Heights (SWH) derived from Jason-3 satellite altimetry data using DGFI-TUM's dedicated retracking algorithm WHALES. Units are meters.

The general condition of the ocean due to the action of wind waves and swell is defined as Sea State and constitute a very important parameter for ocean weather and climate. The Sea State has therefore been included in the list of Essential Climate Variables that the Climate Change Initiative of the European Space Agency studies. The aim of this project is to develop a consistent multi-decadal global record on sea state parameters (principally Significant Wave Height, but potentially also mean square slope, wind speed, wave period and wave spectra). This will be achieved through careful retuning of altimeter algorithms and processing of SAR data, coupled with stringent quality control, independent assessment and climate evaluation.

DGFI-TUM is highly involved in the project, which involves a large number of European public and private institutions, and leads the Algorithm Development (AD) Team for the Satellite Altimetry part. The AD is responsible for the development of new estimation techniques that are able to improve the signal-to-noise ratio of the sea state parameters. Secondly, it has to guarantee that the strategy of choice is able to deliver estimations that are consistent during the 25 years of altimetry data in terms of biases and, as much as possible, in terms of performances. If on one side this means that the application of the same algorithm to all the missions could be an advantage, on the other side we shall not ignore the wider possibilities and better performances that the Delay-Doppler processing in Cryosat-2 and the Sentinels provide. The team will start the work with several efforts in parallel: the ideas for a subwaveform retracker focused on the wave estimations will be presented, as well as the current status of the Adaptive Numerical Retracker for sea state and advanced techniques to exploit the stack information of SAR altimetry.

The other main duty is the planning and execution of an algorithm testing phase open to all external participants, in which the criteria for the evaluation of the algorithms and the final selection shall be established. Aside from typical criteria (bias with ground truth measured by buoys, comparison with model simulation of waves and wind), other priorities in the evaluation of the performances, aimed at maximising the scientific exploitation of the future dataset will be discussed: for example, the accuracy for retrieving large wave heights and the performances in coastal zone.

More information about the project and the collaboration partners can be found on ESA's project website.

Selected Publications

Passaro M., Hemer M., Quartly G.D., Schwatke C., Dettmering D., Seitz F.: Global coastal attenuation of wind-waves observed with radar altimetry. Nature Communications, 12, 3812, 10.1038/s41467-021-23982-4, 2021 (Open Access)
Schlembach F., Passaro M., Quartly G.D., Kurekin A., Nencioli F., Dodet G., Piollé J.-F., Ardhuin F., Bidlot J., Schwatke C., Seitz F., Cipollini P., Donlon C.: Round Robin Assessment of Radar Altimeter Low Resolution Mode and Delay-Doppler Retracking Algorithms for Significant Wave Height. Remote Sensing, 12(8), 1254, 10.3390/rs12081254, 2020 (Open Access)
Dodet G., Piolle, J.-F., Quilfen Y., Abdalla S., Accensi M., Ardhuin F., Ash E., Bidlot J.-R., Gommenginger C., Marechal G., Passaro M., Quartly G., Stopa J., Timmermans B., Young I., Cipollini P., Donlon C.: The Sea State CCI dataset v1: towards a sea state climate data record based on satellite observations. Earth System Science Data, 12(3), 1929-1951, 10.5194/essd-12-1929-2020, 2020 (Open Access)
Ardhuin F., Stopa J.E., Chapron B., Collard F., Husson R., Jensen R.E., Johannessen J., Mouche A., Passaro M., Quartly G.D., Swail V., Young I.: Observing Sea States. Frontiers in Marine Science, 10.3389/fmars.2019.00124, 2019 (Open Access)

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