Sea surface current estimates off Central California as derived from enhanced AVHRR infrared images

Abstract

A technique is presented which uses an interactive computer program to estimate sea surface current velocity from the displacement of sea surface temperature (SST) patterns apparent in enhanced sequential Infrared (IR)images obtained from the NOAA-6 Advanced Very High Resolution Radiometer (AVHRR). This technique was applied to the surface currents of the California Current System using IR image data from 27 and 28 April 1981. This technique, which uses enhanced pseudocolor gradient imagery, produced more current vectors than an earlier technique developed by O'Hara (1987) which used unenhanced gray scale imagery. The resultant surface vectors agree well in direction but underestimate velocities obtained from Doppler Acoustic Log (DAL) measurements taken during the same period. The two methods produced closest agreement for current velocities of less than 40 cm/sec and with satellite-derived velocities obtained with sequential 12 hour images rather than sequential 24 hour images. Satellite-derived velocities in the rapid flow area (larger than 40 cm/sec) showed poor correspondence to DAL-measured velocities. the strong current shear in these areas may distort the surface SST patterns making identification of features between two images more difficult. the satellite derived surface velocities are assumed to be representative of the velocities of the upper mixed layer, which is usually 10 to 30 m deep in the study region.