Evaluation of satellite rainfall data in Greece

The objective of this study is to evaluate the quality, spatial and temporal accuracy of satellite precipitation products 3B42 V6 and 3B43 V6 generated from the Tropical Rainfall Measuring Mission (TRMM). These products are gridded estimates on a 0.25° x 0.25° spatial resolution and on a 3-hour and monthly temporal resolution respectively. Validation was conducted over the Greek prefecture on monthly, seasonal and annual timescale, for a period of 12 years (1998 – 2010), using gauge observations from 35 stations of the monitoring network of Hellenic National Meteorological Service (HNMS). Moreover, it was attempted to use gauge-based gridded monthly precipitation data sets of the Global Precipitation Climatology Centre (GPCC) for the validation of satellite data on a grid bases. However, the intercomparison of HNMS and GPCC data showed high spatial and temporal variability of the accuracy of GPCC dataset and hence, it was decided not to use it as reference to evaluate the satellite data. Validation of 3B42 V6 and 3B43 V6 included two main stages. The first is the statistical analysis that includes the calculation and intercomparison of statistical indexes. The second includes the study of the spatial distribution of bias by calculating the biases of mean values for every station and constructing surfaces (grids) using geostatistical methods. Surfaces of bias were then added to the initial precipitation surfaces of satellite datasets, so as to remove the bias of latter.