Wind Determination from Nimbus 5 Observations in the 6.3μm Water Vapor Band

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Abstract
Temperature Humidity Infrared Radiometer (THIR) data of adjacent Nimbus 5 orbits have been used to derive winds in the upper troposphere from the radiance measured in a wide spectral interval within the 6.3 μm water vapor band. The radiation in this spectral channel stems primarily from water vapor emission at ∼400 mb and/or emission of high clouds. The horizontal resolution at the subsatellite point is ∼23 km. For this purpose the digital data in overlapping swaths of consecutive orbits first have been enhanced to detect clear contours using the gradient method and the algorithm of Smith and Davis. Wind vectors computed from the displacements of the contours agree well with conventional data. The rms deviation between the derived wind velocities and the radiosonde data is 5–6 m s−1 for a mean wind speed of 30 m s−1. The rms deviation of the wind direction is about 21°. Systematic deviations can be explained by interfering cirrus clouds and by time differences between radiosonde and satellite measurements. The method is especially limited by the low spatial resolution of the THIR. The conditions can be improved by using Meteosat data available now.

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