Ocean Observing and Climate Research Group
Satellite wave climatologies
The prime objective of our work is to build long-term climatologies of ocean significant wave height (Hs) and wave period based on satellite altimeter datasets. The development of such global climatologies is driven by the need to validate present day operational wave forecasting systems, as well as to improve our understanding of the role of waves in atmosphere-ocean dynamics, ocean surface transport and mixing, and to facilitate the detection and measurement of global climate change as revealed in ocean wave parameters. Typical applications also include better estimation of ocean-based renewable energy resources and improved estimation of extreme sea states.The basic methodology is first to calibrate altimeter-derived Hs and wave period estimates against a network of in situ buoy measurements. The wave period parameter we present here is the zero-crossing period, Tz, which is calculated from Hs and radar backscatter coefficient, sigma-0, using the algorithm of Mackay et al. (JGR, 113, C03029, 2008). In this study, we use buoy data extracted from the National Data Buoy Center (NDBC) database, made available freely online by the US National Oceanic and Atmospheric Administration.
The development of these satellite-derived wave climatologies is part of Theme 10 of Oceans 2025.
Global wave climatology datasets now available
Initial global datasets of calibrated wave period, Tz, and significant wave height, Hs, are now available on a regular 2 deg x 2 deg grid, month by month. Altimeter data have been calibrated against buoy data up to and including December 2008 (if the altimeter was, of course, still operational then). You can download tar archives of these data at the links below:- TOPEX Tz and Hs for Jan 1993 - Oct 2005 (102 Mb).
- ERS-2 Tz and Hs for May 1995 - Dec 2008 (108 Mb).
Every ascii file has a simple format in which each line contains: longitude (degrees E), latitude (degrees N), Hs (in metres), Tz (in seconds). Missing data are indicated by -999.0 values. We used a Gaussian gridding scheme with the full-width at half-maximum and the search radius both set to 300 km (see sample figure at bottom of page). We used a sliding calibration window of one year in duration. See paper (reference below) for further details.
Combined satellite wave climatologies for Tz and Hs are also available. These span 16 complete years from Jan 1993 - Dec 2008:
The combined monthly climatologies were created by simple arithmetic averaging of the single-altimeter climatologies for coincident months. For example, between October 2002 and September 2008 inclusive, the merged dataset was created by averaging the monthly data from all five available altimeters: TOPEX, Envisat, Jason-1, ERS-2 and Geosat Follow-On.
Next, we will be working on applying optimal interpolation and will then make improved gridded data products available.
Movies of gridded wave period and Hs data also now available
You can download provisional sample movies of global Gaussian-gridded data for TOPEX wave period and Hs data:
TOPEX-derived Tz: Jan 1993 - December 2004 (Click image for gif movie: make take a few seconds to load)
TOPEX-derived Hs: Jan 1993 - December 2004 (Click image for gif movie: make take a few seconds to load)
You can also download QuickTime versions here:
Further information
A paper describing the preparation of the climatologies has been submitted: David Cromwell and Christine Gommenginger, 'Calibrating altimeter measurements of ocean surface waves to develop long-term global climatologies', Journal of Atmospheric and Oceanic Technology, submitted, July 2010. For further info, please email Christine: cg1@noc.soton.ac.uk
Figure: Gridded calibrated TOPEX-derived significant wave height for December 2004. We used a Gaussian gridding scheme with the full-width at half-maximum and the search radius both set to 300 km.
