“Sea states”, or wave conditions, have been observed for centuries in ships' logs and other historical documents. Now new technologies allow for long-term, precise measurements that can help with activities such as shipping and harbour operations, and inform climate science.
International review every ten years
Once a decade, a community of experts in the field come together for an international review of Ocean Observing Systems. With that taking place this September, scientists have been chronicling the changes in measurements, recording and coverage of many different oceanic variables. The community White Paper on Sea States has just been published for open access in Frontiers in Marine Science, and includes a summary of altimetry by Dr Graham Quartly at PML and Dr Marcello Passaro from Technologische Universität, München.
Radar technology to study waves
Altimetry involves sending radar pulses down from satellites to the surface of the sea and recording the timing and shape of the reflected echo. The shape of the return gives scientists information on the height of waves directly below the satellite. By combining results of these remote sensing techniques with numerical models of waves and in situ data from equipment such as wave buoys, scientists can produce a clearer image of sea states.
With measurements going back for more than 30 years, altimetry can provide valuable long-term data for studying how the sea has changed and the frequency of extreme events. This can inform climate research, revealing regions with large waves and more intense storms, and how these are changing in relation to other factors. A better understanding of the average conditions in an area and its likely extremes can also help to plan and prepare for activities including improving safety at sea and designing vessels and infrastructure. As technology continues to develop, scientists can build a more detailed picture of changing sea states into the future.
Over 30 years of measurements
"Radar altimeters provide all-weather coverage of waves over most of the global ocean" commented Dr. Quartly. "We now have over 30 years of nearly continuous measurements and have been tackling the challenge of integrating the records from different sensors to create a consistent dataset. These, added to the long records from wave buoys at coastal sites, enable climate scientists to study the long-term changes in waves."