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Globwave: a Global Wave Data Portal GLOBWAVE: A GLOBAL WAVE DATA PORTAL Farquhar, C.R.1, Deighton, H.1, Busswell, G.1, Snaith, H.M. 2, Ash, E.3, Collard, F.4, Piolle, J-F.5, Poulter, D. J. S. 2, & Pinnock, S.6 1 Logica, Keats House, Leatherhead, Surrey, UK 2 National Oceanographic Centre, Southampton, UK 3 Satellite Oceanographic Consultants, UK 4 Collecte Localisation Satellites, France 5 Ifremer, France 6 ESA, ESRIN, Frascati, Rome, Italy ABSTRACT The GlobWave Project is an initiative funded by the European Space Agency (ESA) and subsidised by CNES through the Data User Element (DUE), a programmatic element of the 3rd period of the Earth Observation Envelope Programme (EOEP-3), an optional ESA programme. GlobWave is led by Logica, with key expertise provided from Satellite Oceanographic Consultants Ltd (SatOC), Collecte Localisation Satellites (CLS), Ifremer and National Oceanography Centre (NOC) and aims to improve the uptake of satellite-derived wind-wave and swell data by the scientific, operational and commercial user communities. The project, running from January 2009 – December 2012, covers the development of an integrated set of information services based on satellite wave data, and the operation and maintenance of these services for a demonstration period. This paper describes the datasets provided and the activities carried out through the project which are intended to make it easier for the global user community to use satellite wave data, to facilitate routine comparison with wave models and to stimulate the development of satellite wave data assimilation. 1. INTRODUCTION The ESA GlobWave project is a three year initiative, funded by ESA and CNES, serving the needs of satellite wave product users across the globe. GlobWave provides free access to consolidated satellite wave data and products from both SAR and altimeter missions in a common netCDF format. Both historic and near real-time data are provided, with the latter being available within 1 hour of receiving the data from the relevant agency. In addition, GlobWave provides comparisons with in situ measurements, interactive data analysis tools and a pilot spatial and spectral wave forecast verification scheme for operational forecast production centres. 2. BACKGROUND Significant efforts have been made in the past to provide integrated and harmonized 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 [1]. Despite the important benefits of the application of wave observations from space, and the relatively good availability of satellite wave data, uptake by the potential user community had been 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. GlobWave aims to address these needs and the needs of the user community gathered from a regular series of user consultations held since 2007 by providing a "one stop shop" for satellite wave data and to encourage widespread added value initiatives, like the assimilation of altimeter and SAR data into models. Information on wind-driven sea surface waves is of high importance to shipping, offshore industries, coastal engineering, weather forecasting, coastal zone management, and even tourism. Safe transport of goods and people by ships, and of fishing fleets, is dependent on a timely knowledge of the sea state. Although ships and offshore installations are designed to withstand extreme weather conditions, the risk of accidents is higher under severe and unusual sea states, such as rogue wave and cross seas. Marine engineering operations, such as those performed by the oil industry, aquaculture and offshore wind power operators, are also very sensitive to sea state. In addition, 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. 3. GLOBWAVE DATA Since it began in January 2009, GlobWave has successfully increased the uptake of satellite-derived wind-wave and swell data by the scientific, operational and commercial user communities. This has been achieved by adhering to the core objective of providing a uniform, harmonized, quality controlled, multi-sensor set of satellite wave data and ancillary information in a common format, with a consistent characterization of errors and biases [2]. 3.1 GlobWave Satellite Database GlobWave satellite wave data is collected from both altimeters (ERS-1, ERS-2, ENVISAT, Topex/POSEIDON, Jason-1, Jason-2, CryoSAT, GEOSAT and GEOSAT Follow On) and from ESA Synthetic Aperture Radar (SAR) missions, namely ERS-1, ERS-2 and ENVISAT. In the future, such measurements will be continued by several missions, including ESA's upcoming Sentinel series. GlobWave satellite data is available both in near real-time and delayed mode. The delayed mode data consists of 12 data streams from 9 satellites from as far back as 1985. The near real-time data consists of 4 data streams from 3 satellites and is available from GlobWave within about 3 hours of the actual observation from space. To aid widespread usage, all GlobWave data streams come in the same format, which is netCDF-3 with CF (v1.4) conventions. Each product file will contain relevant wave related parameters from the native product plus additional quality information such as various error characteristics and ancillary data such as bathymetry and sea surface temperature, wind speed and direction. In addition, GlobWave provides comparisons with in situ data for the purposes of calibration and validation of the satellite data. Such in situ data can be from buoys networks around the globe including POSIEDON, UK Met Office, Météo-France, NODC and CDIP. Another core objective is to demonstrate new types of satellite wave data products, such those based on new retrieval techniques, new types of satellite data, merged data from different sensors, or combinations of model and satellite data . Finally, GlobWave is focused on developing and trailing a pilot facility, following the JCOMM Expert Team on Wind Waves and Storm Surges recommendations, to permit operational agencies to routinely spatially compare their wave models with satellite wave data. 3.2 Online Tool for Satellite verses In Situ Matchup Database In February 2012, GlobWave updated their online query tool, which contains a powerful search engine to find buoy / satellite overlaps based on a range of criteria including sensor / measurement, date, depth and distance to shore. Recent updates enable the display of ancillary data such as wind fields, storm paths and currents. The tool also contains extensive visualisation tools to help understand the relationships between data sets. Such visualisations include time series, histograms, directional histograms, scatterplots and time / frequency plots. New display features include display along a section, virtual buoys, intercomparisons and areal statistics. To access the tool and for further details on its capabilities please visit the GlobWave portal as shown in Figure 1. Figure 1: GlobWave Online Tool 3.3 Error Characterisation Analysis: Accuracy of Satellite Data Satellite data quality is tested by comparison with both in situ data and other satellite streams. Quality is recorded in two types of reports: I. An Annual Quality Control Report which uses delayed mode GlobWave data to perform crossover analysis and comparisons with in situ buoys. It also performs interesting comparisons between delayed mode and near real-time significant wave height measurements for Envisat, Jason-1 and Jason-2. II. Four Quarterly Quality Control Reports are also produced each year. Whereas the Annual Report focuses on delayed mode data, these analyse near real-time data and are made available on the portal shortly after each quarter. They contain a summary by month of the quality levels of the GlobWave near real-time data sets. 3.4 GlobWave Data - Statistics Areas The physical quantities measured namely altimeter (significant wave height) and SAR (Swell wave height, dominant swell direction and dominant swell wavelength) from different satellites over different regions have been compared. The Global Wave Statistics (GWS) have been calculated over selected areas representing all the major ocean basins, and being of a size suitable for meaningful statistical analysis (typically 10 degrees latitude by 20 degrees longitude). The selected areas include regions of high wave activity such as the North Atlantic and Southern Ocean, as demonstrated in Figure 2. Figure 2: Areas selected for GWS analysis 3.5 Altimetry Statistics Comparisons This section gives the Global Wave Statistics (GWS) comparisons for altimeter Significant Wave Height (SWH) measurements in selected areas for appropriate time periods and satellite combinations. The aim of this study was not to produce useful products, as the areas are too large with too much spatial variability, but rather to produce statistics from individual altimeters
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