The calibration biases of reflectivity (Z
H) and differential reflectivity (Z
DR) from an operational Mt. Bisl S-band dual polarization radar are derived to improve the accuracy of rainfall estimation. The effect of radar calibration in rain estimation is examined by using data from the dense rain gauge network.
The calibration biases of Z
H are calculated by using the self-consistency constraint between Z
H and specific differential phase shift (K
DP). This procedure is performed every 2.5 min. The biases are varied from -3.3 dB to 0.8 dB during the period between July 2010 to October 2011. The Z
DR calibration biases are obtained by two methods: 1) vertically pointing measurements, and 2) comparison of observed data with the average Z
H-Z
DR relationship derived from disdrometric data. The Z
DR biases are varied from 0.25 dB to 0.7 dB and both methods show similar results. This Z
H-Z
DR technique can be applied for a volume scan and does not require a special scan.
The rainfall relationships, R(Z
H), R(Z
H, Z
DR) and R(Z
H, ξ
DR), where ξ
DR = 10
0.1ZDR, are derived from measured disdrometer data and then adjusted with gauge data. The verification of rainfall estimation is performed by applying 1) average Z
H and Z
DR calibration biases for the entire period and 2) adaptive calibration biases that vary each rain event. The application of adaptive calibration biases is more effective for R(Z
H, Z
DR) and R(Z
H, ξ
DR) than that for R(Z
H), thus indicating the necessity of frequent calibration of Z
H and Z
DR.
View full abstract