The themes of the 6 Workshops are shown below ... Theme 1 - Sea Surface height requirements (CLS) .... conjunction with the 'premium' research platforms.
FUTURE REQUIREMENTS FOR SATELLITE ALTIMETRY: RECOMMENDATIONS FROM THE GAMBLE PROJECT FOR FUTURE MISSIONS AND RESEARCH PROGRAMMES P. D. Cotton(1) Yves Menard(2) (1) Satellite Observing Systems (SOS), 15 Church Street, Godalming, Surrey GU7 1EL, UK (2) Centre Nationale d’Etudes Spatiales (CNES), 18 Avenue Edouard Belin, Toulouse 31-401, CEDEX 4, FRANCE ABSTRACT The GAMBLE thematic network brought together European experts in ocean altimetry to consider future developments in satellite altimetry. The aim was to provide recommendations for research activities, and future altimeter missions, that were necessary to support and build on present developments in operational oceanography and to maintain ocean monitoring programmes. This paper reviews user requirements for operational products that rely on altimeter data, and assess how well present and planned activities satisfy those requirements. It provides recommendations for future missions required to form a cost-effective, robust, operational satellite altimeter measurement system. [1] provides a full discussion. 1.
THE GAMBLE WORKSHOPS
Through a sequence of 6 Workshops investigating different aspects and uses of satellite altimetry the aim of GAMBLE was to assess the altimeter’s contribution to detecting and understanding the behaviour of two key sea surface features – surface height anomalies produced by currents, eddies, tides and special events such as El Niño – and seastate as revealed by significant wave height and surface wind speed. The themes of the 6 Workshops are shown below together with the name of the lead organisation. Theme 1 - Sea Surface height requirements (CLS) Theme 2 - Sea State requirements (ISDGM) Theme 3 - Orbit determination systems (DUT) Theme 4 - Marine Operators Requirements (SOS) Theme 5 - Research Programme (SOC) Theme 6 - Constellation Optimisation (CNES) At the start of GAMBLE some 20 organisations signed up to participate but by the time of the last WG meeting in Toulouse, representatives from over 40 laboratories had participated. In addition, a Steering Group of 6 experts drawn equally from research and marine operations was convened to provide informed comment.
2. MARINE OPERATORS’ PRIORITIES FOR IMPROVEMENTS TO SERVICES Offshore operators were asked to identify their priorities for improvements to the data products derived from satellite altimetry ([2] and [3]). 2.1 Ocean Currents In some situations, information on ocean currents can be more important than waves. For instance, strong currents in Gulf Of Mexico loop current eddies has resulted in drilling down time of periods up to 30 days, at a cost of $220K / day. Operators believed there was room for improving the quality and amount of ocean current information available. In general improved spatial resolution was seen as the main priority, to provide improved resolution of ocean mesoscale features (eddies, loop currents, etc.). In addition the spatial variability of currents is poorly understood currents at Foinaven and Schiehallion off the North West of Scotland are poorly correlated even though the two sites are only 11 km apart. 2.2 Sea State Waves remain the major source of environmental forces on offshore structures, and wave heights continue to be the “most important” parameter for planning, design and operations. The main priority for improvement was a significant enhancement in sampling in space and time (e.g. ~200km, 6 or 12 hourly). In addition it was noted that wave period measurements are important even at low wave heights: long, low swells can cause operational problems. Wave direction is important for design as well as for operational use. An important problem at higher latitudes is the sudden development of polar lows as these systems can generate severe wave conditions which present models often are unable to predict accurately. A better understanding is required of conditions in which "rogue" waves are generated.
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3. RESEARCH AND GLOBAL MONITORING REQUIREMENTS 3.1 Sea Surface Height Requirements The operational oceanography systems being developed require accurate measurements of ocean eddies and associated currents - the ocean "mesoscale". A two-satellite configuration is a minimum configuration for observing this mesoscale. For full resolution of eddies, measurements must resolve variability on the scale of the "Rossby" radius (~25 km at 40 deg N, depends heavily on latitude and stratification). Three/four interleaved satellite altimeters would allow a very good mapping of sea level and velocity. Compared to the two-satellite combination, improvement by a factor of 3 would be achieved. Velocity mapping errors will remain, however, at the level of ~20% of the signal variance because of variability on small temporal
and spatial scales. Much higher sampling rates in time (
