Comparison between satellite and ground station rainfall data at a global scale

T. Dimoulas, Comparison between satellite and ground station rainfall data at a global scale, Diploma thesis, Department of Water Resources and Environmental Engineering – National Technical University of Athens, November 2016.



In the present work, our intention is to compare and evaluate the satellite products 3V42 V7 of NASA mission TRMM with the correspondent ground measurements. Satellite information is gathered from the daily rainfall records in spatial scale 0.25° x 0.25° contained in the NASA database for free use. As for terrestrial data used for comparison-evaluation of the correspondent satellite, they were drawn from the database of NOAA and are the rainfall records measured by using rain gauge. The comparison is made on a global scale and specifically cover the area from Northern latitude 50° to 50° South and West longitude 180° to 180° East, while it focuses on time period from 1 January 1998 to 31 December 2015. The evaluation of satellite records conducted in two stages. Firstly, by analyzing time-series data and second at the level of annual maximums. For the second stage examined two sub cases. In the first indent, we compared the highest ground with the corresponding satellite recordings the same day and in the second sub-case we conducted the same comparison with the maximum satellite measurements.This step was necessary because of the tremendous disagreement on the maximum incidences of terrestrial and satellite products which makes robust statistical analysis ambivalent. Only 10% of the maximum records were synchronized. For every case, we examined the efficiency, the cross-correlation coefficient, the bias of the average values, the bias of the standard deviations, the bias of asymmetric coefficients, the mean absolute error and the root of mean squared error. In addition, a spatial distribution of the error of the time-series was made by applying Kriging method using ArcGIS software. The results of this work are presented in detail in the respective chapters. In general, it is demonstrated the weakness of satellite products to simulate high rainfall, while these observations strengthen the effectiveness of surface rainfall stations for the sustainable management of water resources.

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