Geos 3 wave height measurements: An assessment during high sea state conditions in the North Atlantic

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Abstract
During February 1976 a concentrated effort was made to monitor the sea state in the North Atlantic Ocean using Geos 3 radar altimeter wave form data and specialized data processing techniques. The average wave form was computed and fitted in a least squares sense by an error function whose slope is directly relatable to the ocean's significant wave height. The resulting measurements were compared with various sets of truth data. Underflights of Geos 3 orbits were made by a NASA C‐54 aircraft equipped with two narrow pulse radar systems. Additionally, buoy measurements from selected National Data Buoy Office data buoys, hindcasts from experienced analysts in the National Weather Service, and shipboard observations and wave recorder data from Ocean Weather Station ships located in the North Atlantic were collected for comparison with the satellite information. Excellent agreement exists between the aircraft, buoy, and satellite data. Contour maps produced twice daily for February using Geos 3 measurements are compared with the computer‐produced operational hindcast maps from the Navy Fleet Numerical Weather Central and the National Meteorological Center and are found to compare favorably with the Navy product. Differences between the Geos 3 measured magnitudes and locations of major significant wave height features with those found on the operational maps can be explained as the result of atmospheric primitive‐equation model tendencies to underestimate systematically the intensity of oceanic cyclones and to underestimate their speed of movement across the ocean. Using the interpolated wave height values from the Geos 3 February contour maps at the location of Ocean Weather Station Lima, it is shown that the quality of the Geos 3 map is degraded mainly when the narrow swath width of the satellite ground track does not overlay the ocean region with the highest sea state. Even so, the interpolated Geos 3 measurements are in closer agreement with Ocean Weather Station Lima wave recorder data than are Lima shipboard observations of sea state. Hence the satellite altimeter measurements are of better quality than routinely used significant wave height observations, are produced globally, and should be utilized in activities such as ship routing and weather forecasting.