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Validation of Rain Rate Retrievals for the Airborne Hurricane Imaging Radiometer (HIRAD)The NASA Hurricane and Severe Storm Sentinel (HS3) mission is an aircraft field measurements program using NASA's unmanned Global Hawk aircraft system for remote sensing and in situ observations of Atlantic and Caribbean Sea hurricanes. One of the principal microwave instruments is the Hurricane Imaging Radiometer (HIRAD), which measures surface wind speeds and rain rates. For validation of the HIRAD wind speed measurement in hurricanes, there exists a comprehensive set of comparisons with the Stepped Frequency Microwave Radiometer (SFMR) with in situ GPS dropwindsondes [1]. However, for rain rate measurements, there are only indirect correlations with rain imagery from other HS3 remote sensors (e.g., the dual-frequency Ka- & Ku-band doppler radar, HIWRAP), which is only qualitative in nature. However, this paper presents results from an unplanned rain rate measurement validation opportunity that occurred in 2013, when HIRAD flew over an intense tropical squall line that was simultaneously observed by the Tampa NEXRAD meteorological radar (Fig. 1). During this experiment, Global Hawk flying at an altitude of 18 km made 3 passes over the rapidly propagating thunderstorm, while the TAMPA NEXRAD perform volume scans on a 5-minute interval. Using the well-documented NEXRAD Z-R relationship, 2D images of rain rate (mm/hr) were obtained at two altitudes (3 km & 6 km), which serve as surface truth for the HIRAD rain rate retrievals. A preliminary comparison of HIRAD rain rate retrievals (image) for the first pass and the corresponding closest NEXRAD rain image is presented in Fig. 2 & 3. This paper describes the HIRAD instrument, which 1D synthetic-aperture thinned array radiometer (STAR) developed by NASA Marshall Space Flight Center [2]. The rain rate retrieval algorithm, developed by Amarin et al. [3], is based on the maximum likelihood estimation (MLE) technique, which compares the observed Tb's at the HIRAD operating frequencies of 4, 5, 6 and 6.6 GHz with corresponding theoretical Tb values from a forward radiative transfer model (RTM). The optimum solution is the integrated rain rate that minimizes the difference between RTM and observed values. Because the excess Tb from rain comes from the direct upwelling and the indirect reflected downwelling paths through the atmosphere, there are several assumptions made for the 2D rain distribution in the antenna incident plane (crosstrack to flight direction). The opportunity to knowing 2D rain surface truth from NEXRAD at two different altitudes will enable a comprehensive evaluation to be preformed and reported in this paper.
Document ID
20150022936
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Jacob, Maria Marta (National Commission of Space Activities Buenos Aires, Argentina)
Salemirad, Matin (University of Central Florida Orlando, FL, United States)
Jones, W. Linwood (University of Central Florida Orlando, FL, United States)
Biswas, Sayak (NASA Marshall Space Flight Center Huntsville, AL United States)
Cecil, Daniel (NASA Marshall Space Flight Center Huntsville, AL United States)
Date Acquired
December 11, 2015
Publication Date
July 26, 2015
Subject Category
Meteorology And Climatology
Report/Patent Number
MSFC-E-DAA-TN20510
Meeting Information
Meeting: IGARSS 2015
Location: Milan
Country: Italy
Start Date: July 26, 2015
End Date: July 31, 2015
Sponsors: Institute of Electrical and Electronics Engineers
Funding Number(s)
WBS: WBS 153351.05.05.05
CONTRACT_GRANT: NNM13AA03A
CONTRACT_GRANT: NNX11AF02G
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
hurricane
rain retrieval

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