World Wave Atlas (WWA) is our oldest wave climate product which has been on the market since 1995. It is in fact both our global satellite altimeter wind and wave database which is fully integrated with our WorldWaves product and the collective name for a series of comprehensive high resolution interactive wind and wave atlases based, primarily, on satellite altimeter data, providing accurate wind and wave climate statistics worldwide or for any country or region.
The best way to understand what World Wave Atlas can do is to download the WWA 2.0 demo, which provides data for an area of the South Pacific around the Samoan Islands, including GEOSAT, Topex/Poseidon, GFO, Envisat and Topex 2, data together with buoy data collected by OCEANOR for the South Pacific Applied Geoscience Commission (SOPAC), as part of a large wave energy resource assessment for the South Pacific, and one calibrated grid point from the WorldWaves data set, please click WWA Demo registraion in left menu.
A simple Graphical User Interface replicated below for different satellite missions (Figure 1) provides access to satellite data and if required model data.
Figure 1: Mean significant wave heights along all satellite ground tracks of a) Geosat/GFO; b) Topex/Jason and c) ERS/Envisat missions.
World Wave Atlas has both geographical and statistical modules allowing the user to analyse and present most commonly used wave and wind statistics (univariate and bivariate frequency distributions, exceedence curves, extreme statistics for significant, maximum and crest wave heights, spatial and temporal variability including along track variations, seasonal and inter-annual variability, direction roses etc.). Any area or time period can easily be selected for analysis. The World Wave Atlas data can also be provided as simple text files. The basic building block of WWA is the 10x10° square area, with one file containing each satellite for each 10x10° square for ease of access to data for one location.
The standard WWA 2.0 software package contains satellite altimeter data at full resolution from the following missions.
- Geosat (1986 –1989)
- Topex-1 (1992 – 2002)
- Topex-2 (September 2002 – 2005); this is still the Topex-1 altimeter, but moved in September 2002 to a new ground track midway between the original Topex tracks.
- Jason-1 (January 2002-2008); On the same orbit as Topex-1.
- EnviSat (October 2002 – present, ongoing)
- Geosat Follow-On (GFO) (January 2000 – 2008); on the same ground track as Geosat.
- ERS-1 (1991 to 1996)
- ERS-2 (1995 - )
- Jason-1n (2008 - ongoing), Jason-1 moved into the Topex-2 orbit.
- Jason-2 (2008 - ongoing), on the original Topex-1 orbit.
These data provide long term information on both significant wave height (at accuracies near to buoy measurements, see below) and wind speed. These data are validated and calibrated relative to buoy data and represent high accuracy information that offer good spatial information on the wave climate.
Measurements of significant wave height and wind speed are made about each 6 km along the tracks each time the satellite passes.
The satellite data have been validated through extensive intercomparisons against buoy data from around the world carried out by OCEANOR and others. For example, we earlier compiled an offshore data set consisting of co-located NOAA buoy and Topex altimeter data. The reference data set contained quality checked data from 13 buoys, totalling 1,365 data records. The data were quality controlled by a careful manual inspection, and only data from tracks that passed within 100km and 1h with re¬spect to the buoy observations were included. The result¬ing scatter plot between the buoy and altimeter wave heights is shown below. If the data are corrected for satellite dependent systematic biases, accurate wave height statistics can be provided anywhere worldwide only limited by the spatial and temporal characteristics of the satellite orbits. In fact, the accuracy of the satellite wave heights is close to that from buoys.
Figure 2 Comparison of Topex satellite altimeter data and simultaneous buoy significant wave heights. This confirms the very high quality of the satellite data. The other satellite altimeters show similar performance. The accuracy is close to that of a buoy.
It should be noted that the repeat cycle of satellites is of the order of 10-35 days. Therefore the data contained in the data set do not represent high temporal resolution of measurements. Also, only significant wave height and wind speed are available from the altimeter. In order to provide high resolution directional wave information needed for applications in the coastal zone, we combine these high precision satellite data with the best available model data in OCEANOR’s WorldWaves package.
We note that there is a delay in the availability of satellite data (a few months) so that we cannot provide data right up to date.
Other data can also be included under the WWA package and can also be analysed statistically – we tailor-make your system according to your requirements. This includes available buoy data (e.g., in the US Wave Atlases, NOAA buoy data can be included and similarly, in the Norwegian Wave Atlas, buoy and platform data) and individual WorldWaves grid points of your choice. Buoy and WorldWaves grid points are included with the demo so that you can see how this works in practice.