Abstract
This paper deals with the validation of rain rate and wind speed measurements from the High-Altitude Wind and Rain Airborne Profiler (HIWRAP), which occurred in September 2013 when the NASA Global Hawk unmanned aerial vehicle passed over an ocean rain squall line in the Gulf of Mexico near the North Florida coast. The three-dimensional atmospheric rain distribution and the associated ocean surface wind vector field were simultaneously measured by two independent remote sensing and two in situ systems, namely the ground-based National Weather Service Next-Generation Weather Radar (NEXRAD); the European Space Agency satellite Advanced Scatterometer (ASCAT), and two instrumented weather buoys. These independent measurements provided the necessary data to calibrate the HIWRAP radar using the measured ocean radar backscatter and to validate the HIWRAP rain and wind vector retrievals against NEXRAD, ASCAT and ocean buoys observations. In addition, this paper presents data processing procedures for the HIWRAP instrument, including the development of a geometric model to collocate time-morphed rain rates from the NEXRAD radar with HIWRAP atmospheric rain profiles. Results of the rain rate intercomparison are presented, and they demonstrate excellent agreement with the NEXRAD time-interpolated rain volume scans. In our analysis, we find that HIWRAP produces wind and rain rates that are consistent with the supporting ground and satellite estimates, thereby providing validation of the geolocation, the calibration, and the geophysical retrieval algorithms for the HIWRAP instrument.
Highlights
The NASA Hurricane and Severe Storm Sentinel (HS3) mission was conducted for onemonth periods in the 2012, 2013, and 2014 Atlantic Basin hurricane seasons [1]
This paper reports the first in-flight radar calibration for High-Altitude Wind and Rain Airborne Profiler (HIWRAP) to provide calibrated measurements for atmospheric rain and ocean surface roughness
The calibration was accomplished by measuring the normalized ocean radar cross-section and comparing this against modeled values using known geophysical parameters and independent collocated measurements of ocean surface wind speed and direction provided by Advanced Scatterometer (ASCAT)
Summary
The NASA Hurricane and Severe Storm Sentinel (HS3) mission was conducted for onemonth periods in the 2012, 2013, and 2014 Atlantic Basin hurricane seasons [1]. Recognizing the scientific potential of this opportunity, the decision was made to divert the aircraft and have the High-Altitude Wind and Rain Airborne Profiler (HIWRAP) [4] and other remote sensors make measurements during three passes over this northern Florida coast. Recognizing the scientific potential of this opportunity, the decision was made to divert the aircraft and have the High-Altitude Wind and Rain Airborne Profiler (HIWRAP) [4] and other remote sensors make measurements during three p2asosf e20s over this rain event The importance of this unplanned experiment was that there were simultaneous calibrated rain rate observations from the Next-Generation Weather Radar (rNaiEnXeRveAnDt.)T[h5e] tihmaptoprrtoanvcideeodf tihnidseupnepnldaennntedraeinxpreartiemmeneat swuarsemtheant ttsheforer wtheerepsriemmuieltraeneevoaulsucaaltiibornatoefdtrhaeinHrIaWteRoAbPserraviantiroantse frreommottheesNenesxitn-gGemneearsautiroenmWenetast.hSeur cRhadoaccru(NrreEnXcReAs iDn)t[h5e] hthisattopryroovfiadierdboirnndeepreencdipeintat triaoinnrreamteotme esaensusirnegmaernetsrafroer, athnedpthreismisiearemeavjaolrucaotniotnriboufttiohne oHfItWhiRsApPapreari.nFruartteherer,mthoeteresewnesriengalmsoeasismuruelmtaennetosu. The basis of this calibration involves the measurement the ocean surface normalized radar cross-section (σo), which is defined as the reflected RF energy per unit area of the ocean surface, and this ocean calibration procedure is described in Appendix A.1
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