An Observing System Experiment (OSE) Study of the Hurricane Imaging Radiometer (HIRAD) instrument

An observing system experiment (OSE) was conducted in order to explore the potential of uncrewed aircraft (UAS) observations to compliment conventional observing platforms and provide crucial data in their absence for the purpose of creating analyses of tropical cyclone (TC) surface wind fields. Atmospheric soundings, motion vectors and ocean surface wind observations were assimilated into the Hurricane Research and Forecasting model (HWRF) using the Hurricane Ensemble Data Assimilation System (HEDAS) to produce full, three-dimensional analyses suitable for model initialization. The potential value of assimilating UAS ocean-surface wind speed observations obtained from the Hurricane Imaging Radiometer (HIRAD) was then evaluated in terms of impact on the initial surface wind structure and numerical model forecasts initialized from these analyses. Possible issues specific to the assimilation of HIRAD, and surface wind speeds in general, are addressed in order to optimize the use of these data to achieve maximum benefit. We also explore the influence of HIRAD data relative to conventional ocean surface wind observations collected with the Stepped Frequency Microwave Radiometer (SFMR). Understanding how to best to assimilate HIRAD and other surface wind speed observations will help us to produce better TC wind analyses in order to provide reasonable estimates of the strength, location, timing and likely duration of damaging winds. This information can then be used by forecasters and emergency management personnel to aid in protecting lives and property.