Altimeter Height and Timing Bias Report

The objective of the SEASAT-1 height calibration activity is to obtain values of the bias in the altimeter height measurement and time tag consistent with the 10 cm precision of the instrument. Based on analysis of altimeter and tracking data from four SEASAT passes over Bermuda, we find that a constant height bias of 0.12 meters provides consistency with the sea/ground truth in the form of measured ocean surface levels from the Bermuda tide gage and geodetic leveling data between the tide gage and laser station. The uncertainty is based on our best estimate at this time of measurement errors, environmental errors and uncertainties inherent in the analysis technique employed. Since all sea truth was for significant wave heights less than 4 m, the conclusions are restricted to low sea-state conditions. From the available data the Panel was unable to resolve the timing accuracy of the data below s. This question will be considered during-further studies. It is important to note that the analysis employed is basically straightforward and provides comparison with well established and reliable sea/ground truth data sources. It is the Panel\´s conclusion that the radar altimeter instrument, having undergone development through three separate earth orbit missions (Skylab, GEOS-3, SEASAT-1), has reached a level of precision and accuracy that now permits use of the data for important quantitative oceanographic investigations and practical applications.