Improved microwave radiometric imaging of surface wind speed dynamics in the hurricane eye-wall

The Hurricane Imaging Radiometer, HIRAD, a next-generation airborne microwave remote sensor under development by NASA, will expand the airborne hurricane measurement capabilities of two existing state-of-the-art microwave radiometers; the Stepped Frequency Microwave Radiometer, SFMR, and the Lightweight Rainfall Radiometer, LRR. HIRAD combines the mult-freqiency C-band channels of SFMR with the “push-broom” surface imaging of the LRR synthetic thinned array technology to provide high resolution (~2 km), wide-swath (~ 3 x AC altitude) images of ocean surface wind speed and integrated rain rate in a hurricane environment. Because of its wide-swath imaging, HIRAD can significantly improve the detection of peak winds in hurricanes that will result in more accurate hurricane intensity classification and better numerical model forecast prior to landfall.

In a companion paper submitted to this conference, the HIRAD technique is described and simulated airborne and satellite hurricane measurements are presented. This paper addresses one crutial aspect of the HIRAD design, namely, the antenna spatial sampling and its impact on the quality of the retrieved ocean surface wind field. Specifically, this paper presents simulated results of HIRAD wind speed gradient measurements in the hurricane eye-wall region. High resolution numerical model wind fields from Frances 2004 are convolved with various HIRAD antenna spatial filters and tapers to observe the impact of the antenna design on the derived wind shear. Also, the effect of rain rate on the retrieved wind gradient is an important part of this analysis.