Hurricane Imaging Radiometer (HIRAD) Tropical Rainfall Retrievals

The Hurricane Imaging Radiometer (HIRAD) is an airborne passive microwave remote sensor, developed to measure wind speed and rain rate in hurricanes. This dissertation concerns the development of a signal processing algorithm to infer tropical rainfall from HIRAD radiance (brightness temperature, Tb) measurements. The basis of the rain rate retrieval algorithm is an improved forward microwave radiative transfer model (RTM) that incorporates the HIRAD multi-antenna-beam geometry, and uses semi-empirical coefficients derived from an airborne experiment that occurred in the Gulf of Mexico off Tampa Bay in 2013. During this flight, HIRAD observed a squall line of thunderstorms simultaneously with an airborne meteorological radar (High Altitude Wind and Rain Profiler, HIWRAP), located on the same airplane. Also, ground based NEXRAD radars from the National Weather Service (located at Tampa and Tallahassee) provided high resolution simultaneous rain rate measurements. Using NEXRAD rainfall as the surface truth input to the HIRAD RTM, empirical rain microwave absorption coefficients were tuned to match the measured brightness temperatures. Also, the collocated HIWRAP radar reflectivity (dBZ) measurements were cross correlated with NEXRAD to derive the empirical HIWRAP radar reflectivity to rain rate relationship. Finally, the HIRAD measured Tbs were input to the HIRAD rain retrieval algorithm to derive estimates of rain rate, which were validated using the independent HIWRAP measurements of rain rate

Hurricane Imaging Radiometer (Hirad) Wind Speed Retrieval Using Radar Rain Rate

This paper presents novel results of active/passive microwave retrievals of ocean surface wind speed and path average rain rate for hurricane Patricia in the Pacific Ocean on October 22, 2015. These observations are the result of coordinated near-simultaneous flights between a high-altitude NASA aircraft operating the Hurricane Imaging Radiometer (HIRAD), and a NOAA \u27hurricane hunter\u27 lower-altitude aircraft operating a Lower-Fuselage Precipitation Radar (LFR) and a Stepped Frequency Microwave Radiometer (SFMR). Using sensor fusion, the resulting wind speed and rain rate retrievals provide unprecedented high-resolution coverage of the wind and rain structure of this powerful hurricane

Removal Of Artifacts From Hurricane Imaging Radiometer Tb Images

The Hurricane Imaging (microwave) Radiometer (HIRAD) is an airborne remote sensor designed to measure the ocean surface wind speed in hurricanes in the presence of strong tropical rainfall. This sensor employs the synthetic thinned-array radiometer (STAR) technology to produce high-resolution and wide-swath (∼60 km) images of ocean brightness temperature (Tb) with spatial resolutions of a few km. Unfortunately, the ocean Tb images are frequently corrupted by linear \u27stripes\u27 produced in the along-track direction; and the removal of these artifacts using DSP techniques is the subject of this paper. We will present a case study of severe striping that would make the data useless for remote sensing ocean wind speed and rain rate. We describe the man-interactive procedure developed to remove these image artifacts, which preserve the geophysical Tb image content. After removing the stripes, we show that the wind speed and rain rate features in the Tb image are preserved

Validation of the Hurricane Imaging Radiometer Forward Radiative Transfer Model for a Convective Rain Event

The airborne Hurricane Imaging Radiometer (HIRAD) was developed to remotely sense hurricane surface wind speed (WS) and rain rate (RR) from a high-altitude aircraft. The approach was to obtain simultaneous brightness temperature measurements over a wide frequency range to independently retrieve the WS and RR. In the absence of rain, the WS retrieval has been robust; however, for moderate to high rain rates, the joint WS/RR retrieval has not been successful. The objective of this paper was to resolve this issue by developing an improved forward radiative transfer model (RTM) for the HIRAD cross-track viewing geometry, with separated upwelling and specularly reflected downwelling atmospheric paths. Furthermore, this paper presents empirical results from an unplanned opportunity that occurred when HIRAD measured brightness temperatures over an intense tropical squall line, which was simultaneously observed by a ground based NEXRAD (Next Generation Weather Radar) radar. The independently derived NEXRAD RR created the simultaneous 3D rain field “surface truth”, which was used as an input to the RTM to generate HIRAD modeled brightness temperatures. This paper presents favorable results of comparisons of theoretical and the simultaneous, collocated HIRAD brightness temperature measurements that validate the accuracy of this new HIRAD RTM