The Hurricane Imaging Radiometer (HIRAD) is a new airborne microwave remote sensor for hurricane observations that is currently under development by NASA Marshall Space Flight Center, NOAA Hurricane Research Division, the University of Central Florida and the University of Michigan. HIRAD is being designed to extend the real-time airborne ocean surface winds observation capabilities of NOAA and USAF Weather Squadron hurricane hunter aircraft. These aircraft currently carry the operational airborne Stepped Frequency Microwave Radiometer (SFMR), which measures wind speed and rain rate along the ground track directly beneath the aircraft. HIRAD will extend the SFMR coverage by providing images of the surface wind and rain field over a wide swath (~ 3 x the aircraft altitude).

This paper presents an overview of the HIRad system, which includes a top-level instrument system description, a discussion of wind and rain measurement capabilities and uncertainties and preliminary results of high-resolution numerical model simulated oceanic winds and surface rain in hurricanes by the University of Miami. These observation and model analyses will lead to the further development of an Observing System Simulation Experiment (OSSE). Analysis will also be presented of observations made by the WindSat spaceborne microwave radiometer during several hurricane overpasses. Atmospheric corrections by the higher frequency WindSat channels are used to estimate surface emissivity at the lower frequencies under moderate to strong precipitation and at hurricane force wind speeds. Comparisons between the surface emissivity estimated by WindSat and colocated estimates of surface wind speed, provided by H*Winds analysis, demonstrate that a strong sensitivity to wind speed is present at the frequencies and incidence angles planned for HIRad.

In companion paper entitled "Simulation of the Impact of New Aircraft-Based Ocean Surface Wind Measurements on H*Wind Analyses" by T. Miller et al. to be presented at the January 2008 AMS Meeting, preliminary results of an OSSE with HIRad will be presented.