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Abstract
Rainfall intensity retrieval from satellite data and its comparison with the meteorological sensors suffer from a lack of data for an optimal time period. The ground-based dual-frequency microwave radiometers at Vale do Paraiba (23° S) and Alcantara (2° S), Brazil, were installed under a project, CHUVA, during 1 November to 1 December 2011 and 7 March to 7 April 2010, respectively. The results show that a 1½ h interval would be the optimal time period, providing a better accuracy than 30 min, 1 h, and 2 h intervals. The differential method was established for suitably measuring rainfall intensity using the ground-based radiometric method. The results show that the coefficient of determination () values for Vale do Paraiba and Alcantara are 0.86729 and 0.90124; correlation coefficient (r) values are 0.9312 and 0.9493; reduced chi-square (χ2) values are 2.00815 and 21.4865, and the root mean square error (RMSE) values are 0.749 and 0.900, respectively. The differential method in finding the rainfall intensity by statistical analysis was found to be a better choice than using only the brightness temperature method because the atmospheric background and the environmental influence change the brightness temperature, which is due only to the liquid content. On the other hand, ground-based radiometry is a better choice because of the fact that it always measures the downwelling radiation so little inhomogeneity is involved.
Acknowledgement
The authors are thankful to Dr L. A. T. Machado for providing the necessary data available under the CHUVA Project, Brazil.