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Title: Use of TRMM Precipitation Radar to address the problem of rain detection over the oceans in passive microwave measurements
Authors: Varma, Atul Kumar
Pal, P K
Keywords: Rain detection;Brightness temperature;Petty index;Scattering index;Rain rate
Issue Date: Aug-2012
Publisher: NISCAIR-CSIR, India
PACS No.: 92.60.jf; 84.40.Xb
Abstract: Despite success of Tropical Rainfall Measuring Mission (TRMM) satellite, rain detection by passive microwave radiometers still remains a major problem. In this paper, rain detection by a passive microwave radiometer has been analyzed with concurrent observations from Precipitation Radar (PR). Considering PR based rain detection as truth, the brightness temperatures and two most commonly used brightness temperature based indices, the Petty index and the scattering index have been examined, for their usefulness in rain identification over global oceans within PR latitudinal domains. The results indicate that neither brightness temperature, nor the Petty index, and nor the scattering index alone is a good indicator for rain identification. Using concurrent PR observations, the accuracy of rain identification by Petty index and scattering index has been examined. It has been found that with 37 GHz based Petty index, threshold value of 0.8, 0.9 and 0.95 for rain/no-rain discrimination, the raining pixels that are misclassified as non-raining are 2.32, 9.97 and 21.91%, respectively, and the non-raining pixels that are misclassified as raining are 36.82, 18.87 and 10.47%, respectively. Similarly, with scattering index threshold value of 10, the non-raining pixels that are misclassified as raining are 16.53% and raining that are misclassified as non-raining are 83.42, 76.37 and 39.14% for rain rate > 0.01, > 0.1 and 1 mm h-1, respectively. These results indicate poor rain identification by both the indices, especially at low rain rates. The geographical distribution of misclassified pixels indicates that it is difficult to attribute higher misclassification to any particular geographical region. The paper presents the problem of the rain identification and discusses the possible reasons for such misidentification.
Page(s): 411-420
ISSN: 0975-105X (Online); 0367-8393 (Print)
Appears in Collections:IJRSP Vol.41(4) [August 2012]

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