Rain rates within tropical cyclones obtained from the Stepped Frequency Microwave Radiometer (SFMR) on the NOAA WP-3D hurricane research aircraft are analyzed and validated. Airborne radar and particle image data from the same flights are interpolated or averaged into 12-s time intervals for comparing with SFMR data. Also, airborne radar data are used to categorize the SFMR data according to whether the rain rates were obtained in regions of convective or stratiform precipitation. Particle image data from the Knollenberg Particle Measurement System (PMS) Optical Array Spectrometer Probe, model OAP-2D-P are used to determine the relations between equivalent reflectivity Ze and rain rate R for different types of precipitation in tropical cyclones. These are then used to convert SFMR rain rates into equivalent SFMR Ze (and dBZ) values for comparing with radar dBZs.

The probability-matching method (PMM) is used to characterize the statistics of various rainfall measurement strategies, i.e. SFMR, PMS, tail (TA) vertically scanning Doppler radar and lower fuselage (LF) horizontally scanning weather radar on the same aircraft in the stratiform and convective regions of Hurricane Bonnie in 1998. After applying minimum detection thresholds and removing estimated biases inherent in each measurement strategy, regression relations between SFMR data and data from the 3 other kinds of instruments are obtained. Excellent correlations (about 0.99) are shown for all the linear relationships. However, the relationship between SFMR data and TA radar data is closed to 1:1. We believe that this superior result can be explained by the fact that both SFMR and TA radar are looking downward through the whole atmospheric column to the ocean surface. Independent confirmation of these results is conducted on observations from Huricane Humberto (2001).