For over 30 years the ocean surface has been monitored by satellite-borne radar altimeters bouncing radar pulses off the surface. As the pulses reflect off the wave crests earlier than from the troughs, the shape of the "radar echo" gives us information on the wave height.
The data from ten different satellite missions have now been brought together and intercalibrated under the auspices of the European Space Agency's Climate Change Initiative (CCI) and are described in a new paper.
The CCI project has been developing these long-term consistent datasets of many Essential Climate Variables (ECVs) to provide the stable foundation for studies into all aspects of climate change.
With wave height, the environmental interests range from safety of shipping and offshore platforms to the availability of wave power, and from fears of coastal inundations to changes in CO2 uptake through increased wave-breaking.
Dr Graham Quartly, PML Earth Observation Scientist and one of the paper’s co-authors, said: “This paper describes the version 1 dataset produced at the beginning of the project. At PML, we have already been working with researchers at Technischen Universität München (TUM) to assess improvements to the algorithms to then feed into a revised dataset. This will particularly address the challenge of enabling consistent wave monitoring in the coastal zone.”
Some of this further work has now also been published By Dr Quartly and Dr Andrey Kurekin, both at PML. This focussed on how validation procedures, which check how well the wave height assessments are performing, pair altimeters with the buoys providing in situ comparison data.
The research showed how using a median average of data could reduce sensitivity to outliers, particularly when a larger number of observations contributed to this median. The validation procedures could also be improved by choosing pairs of buoys and altimeter tracks that showed good consistency.
Dr Quartly said: “This work builds on the foundation of the initial dataset research, but also demonstrates an innovative procedure that could easily be used in other data validation exercises.”
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