Evaluation of MODIS-Aqua Sea Surface Temperature product in the inner and mid shelves of the Southwest of Buenos Aires Province, Argentina

Abstract

The validation of Sea surface Temperature (SST) provided by the MODIS-Aqua sensor (Moderate Resolution Imaging Spectroradiometer) for the inner and mid shelves of the southwest of Buenos Aires Province (Argentina), is for the first time presented. In situ data obtained with a multi-parametric sonde YSI-6600 and a CTD SBE91 between 2002 and 2011 is used to compare with the satellite SST product. The match-up exercise was established after comparing different spatial boxes, time difference windows, wind speeds, but also a coefficient of variation. The comparison exercise was made in the very coastal zone and the rest of the inner and mid-shelves separately. In the coastal zone applying a 3-by-2 pixel box and a time window of ±3 hours lead to the most accurate results, with a coefficient of correlation (r2) of 0.99, a bias of 0.62 ºC and a root-mean-square-error (RMSE) of 0.79ºC. In the inner-mid shelves when applying a coefficient of variability <0.3, a time window of ±3 hours and taking only values of wind speed > 6 m.s-1, r2 is 0.97, the bias, 0.46 ºC and the RMSE, 0.95ºC. The wind speed plays a major role in the inner-mid shelves as the SST product is affected by a stratification and formation of a diurnal thermocline in the ?skin and sub-skin layer? when the wind speed is below 6 m.s-1. The results between the two shelves are very similar. Finally, the spatial and temporal variability of SST satellite product was analyzed in the study area for the period August/2002 ? December/2010. The results evidence that inter-annual variability is not significant and that there is no positive or negative trend for the nine years of study. Seasonality is the main component of the temporal variability, which amplitude signal varies depending on bathymetry changes, physical forcing, stability of the water column and presence of flood plains.