Significant efforts have been made in the past to provide integrated and harmonised satellite data sets in other fields of oceanography, such as the Medspiration project for sea surface temperature and the AVISO portal for sea surface height. However, a major effort for the satellite wave data user community has so far been lacking. GlobWave intends to redress this balance and improve the uptake of satellite wave data.
Information on wind-driven waves on the sea surface is of high importance to shipping, offshore and coastal engineering, weather forecasting, the management of coastal zones, and even tourism. Safety in the transport of goods and people by ships, and of fishing fleets, is vitally dependent on a timely knowledge of the sea state. Although ships are designed to withstand extreme weather conditions, the risk of accidents is higher under severe and unusual sea states. "Rogue waves", where the wave height exceeds twice the average, are poorly understood, but are known to occur much more often than models of wave height distributions predict. Crossseas, where two or more wave systems propagating in different directions overlap result in unpredictable and shifting wave patterns which are particularly perilous to shipping. Knowledge of wave conditions is needed for research aiming to assess the risk of such types of sea state. Marine engineering operations, such as those performed by the oil industry, aquaculture and off-shore wind farm operators, are also very sensitive to sea state.
The main driver for wave forecasting and hindcasting over the last 30 years has been the offshore oil industry, which can suffer high financial losses due to interruptions of oil production, or worse due to platform damage when operations are not shut down sufficiently in advance of approaching severe weather. Additionally, the development of wave energy needs information on wave climate to determine the optimal location for experimental rigs. Sea state is an important factor governing the air-sea fluxes of momentum, heat, water vapour and gas transfer, and needs to be accounted for in modelling the interaction of the sea with the atmosphere for accurate weather forecasting and climate research. It is also a required input parameter of the ocean-atmosphere coupling schemes of climate models, and is fundamental to the corrections required to derive climate quality sea surface topography. Waves affect sediment transport along coastlines, contributing to erosion and changing coastal morphology, and waves can combine with storm surges to increase the risk of coastal flooding. The provision of wave information to surfers is already a well developed commercial activity, but everyone who uses the sea for recreation needs information on waves, whether to make the most of large swell arriving from storms in the ocean basins, or to avoid the very same thing.
Active radar instruments onboard Earth observation satellites can provide measurements of waves on the sea surface. Altimeters on board ERS-1, TOPEX/Poseidon, ERS-2, GFO, Jason-1 and Envisat, have provided routine global measurements of significant wave height since 1992. SAR instruments on ERS-1, ERS-2 and Envisat also provide novel retrievals of wave directional spectra. These satellite wave measurements are provided as fast delivery products in BUFR format specially for meteorological agencies, as well as standard Level-1 and Level-2 wave products for general use. In the future, such measurements will be continued by several missions, including ESA's upcoming Cryosat-2, GMES Sentinel-1 and 3. The standard SAR and altimeter products do not fully sample the wave field, but are effectively point measurements spaced along the satellite track. In the case of the altimeters the measurements consist of samples spaced every few kilometres along the satellite's nadir track, while the SAR measurements are made off-nadir and with spacings of up to 100-200 km along track. In both cases, successive satellite tracks are spaced apart by up to ~3000 km at the Equator. Recent developments in the retrieval of wave information from satellites include directional wave spectra from image mode SAR data, which provide much higher resolution snapshots of the wave field, and retrievals of new types of information such as wave period and skewness from altimeter measurements.
Despite the important benefits of the application of wave observations from space, and the relatively good availability of satellite wave data, the uptake of the data by the potential user community is found to be less than optimal. For example, only very few meteorological centres routinely assimilate altimeter wave data, and fewer still assimilate the information available from SAR.
Recently ESA has upgraded and reprocessed the ESA ASAR wave mode archive, which has resulted in the removal of directional ambiguity and provided a 20dB reduction in noise. Starting in 2009, the complete ERS-1,2 and Envisat altimeter archives will be reprocessed to harmonise their quality and to adopt a common format. Together with wave measurements from several other missions (e.g.Jason-1,2 Topex/POSEIDON, GFO), these data sets provide an unprecedented information resource for the development of applications of satellite wave data.