| Summary: | Sixteen months of 1.1 km resolution NOAA-12, -14, and -16 data for the Azores region are investigated. Advanced Very High Resolution Radiometer (AVHRR) derived sea surface temperature (SST) is compared to an extensive in situ temperature measurement database, mainly constituted during fisheries campaigns. This comparison shows that SST maps include numerous pixels with temperature values below the range observed for the Azores. Low temperatures are attributed in literature to pixel contamination by cloud neighbouring and these are usually removed by eroding pixels around clouds. Results of this study show that running an erosion filter removes only two thirds of the contaminated pixels. Remnant clouds are filtered inputting threshold values to SST 8-day temperature histograms. Based on a comparison of the SST values derived on an image-by-image basis, it is also demonstrated that differences among the sensors are lower than the measurement accuracy, whilst, on the contrary, nighttime and daytime SST distributions are statistically different. Based on monthly and 15-day average computations at nighttime, AVHRR-derived SST distribution in the Azores and associated dominant space and time scales are proposed in the second part of this paper (SST distribution in the Azores region. Part II: Space and time variability and its relation to North Atlantic Oscillation).
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