Abstract
A methodology to obtain the sea surface temperature (SST) in the Canary-Azores-Gibraltar area has been developed. The final accuracy of the AVHRR-based SST retrievals depends both on the accuracy of the measured radiance and the accuracy of the SST retrieval algorithm that converts the measured radiance into sea surface temperature. The procedure made in this framework consists of: (i) a radiance-based non-linearity correction method; (ii) an automatic procedure for the geometric correction, achieving accuracy to the order of the pixel; (iii) an improved algorithm for cloud detection, based on the method of the multiband thresholds; (iv) a new split-window function (SWF) to perform atmospheric correction in CANIGO area. This task has been accomplished by using the matchup data set of AVHRR brightness temperature (channel 4 and 5) and in situ SST data. The matchups were carefully screened from the HRPT scenes of all seasons in 1996-1998. The temporal and spatial coincidences are within 30 minutes and one pixel resolution, respectively. Coefficients of that algorithm are estimated from regression analysis using 60 co-located in situ and satellite measurements (matchups). Error analysis has shown that SST can theoretically be retrieved to within 0.38oC RMS.
Highlights
The sea surface temperature (SST) is an important geophysical parameter essential for quantitative studies of the Earth’s atmosphere and oceans
We have applied to the data a nonlinearity radiance correction procedure and we have performed the corresponding modifications to the tests proposed by Saunders and Kriebel (1988)
We have elaborated a procedure to make the geometric correction of the Advanced VeryHigh Resolution Radiometer (AVHRR) images fully automatic by means of an orbital model and a similarity detection algorithm
Summary
The sea surface temperature (SST) is an important geophysical parameter essential for quantitative studies of the Earth’s atmosphere and oceans. This will allow us to geographically locate any pixel in the image (direct reference), or to identify the corresponding image co-ordinates on an AVHRR image, given a set of geographic co-ordinates (inverse reference): Line = F (lat,lon) This is calculated by mean of the orbital model following the procedure described by Ho and Asem (1986) (inverse referencing). The basic relations for the orbit, the scanner and the Earth are similar to the ones described by Ho and Asem (1986) Unlike this model that adjusts satellite height (hs) and inclination (i) by means of a GCP and the Bachmann and Bendix (1992) and Illera et al(1996) models, that calculate the longitude of the ascending node (λE) and the time difference between the equator crossing and the scanned line (tE) using one or several GCPs, we introduce nominal values (i, hs, λE, tE).
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