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Satlantic and Orbital Sciences Corporation have developed a concept for a novel satellite scatterometer mission designed to retrieve the global marine wind fields on a daily basis. Using a constellation of 5 - 8 small satellites in low earth orbit, each equipped with a Ku-band scatterometer, ocean basin wide winds could be observed synoptically on time scales consistent with 12 hour weather forecasts. Traditional approaches to design of marine wind scatterometers have been based on the concept of providing a swath, e.g., 500 km wide for ERS-1, which produces bands of dense (25 km spacing, 50 km resolution) observations over the oceans. The observation frequency varies according to repeat cycles, orbit phasing and latitude. On the other hand, global forecast models generally have grids at the same or lower resolution, but evenly spaced. The mismatch in the measured fields with those of the models has reduced the utility of using satellite derived winds for operational data assimilation. The present concept is based on the premise of sampling the winds on a scale more consistent with the current generation of medium term forecast models. The observations would be assimilated into these models, and would provide more stable solutions or model states on which to provide forecasts. The scatterometers are designed to be scanning, pencil beam systems, configured with three beams looking to each side. The scanning is carried out in a fashion that allows a patch on the ocean to be observed at 4 different azimuthal angles, thus providing good resolution of directional ambiguity. Data processing is very simple, avoiding range gating or Doppler processing. The resulting downlink data rates are also low enough to allow the design of a simple, low-cost ground segment that would be designed for ease of assimilation of the global wind fields into operational models in near to real-time.
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