First Tropical Cyclone Overflightsby the

Hurricane Imaging Radiometer (HIRAD)

Chris Ruf1, Sayak Biswas2, Mark James3, Linwood Jones2, Tim Miller3

1. University of Michigan2. University of Central Florida

3. NASA Marshall Space Flight Center

College of EngineeringDepartment of Atmospheric, Oceanic & Space Sciences

IGARSS 2011Vancouver BC, CANADA

26 July 2011

26 July 11 Ruf et al., First HIRAD TC Overflights, IGARSS 2011 2 / 13

Outline

• The Hurricane Imaging Radiometer (HIRAD) is a new airborne microwave spectrometer designed to be an enhanced imaging version of the operational Stepped Frequency Microwave Radiometer (SFMR) that has been used operationally by NOAA for decades to retrieve surface winds under heavy precipitation

• Instrument development has been led by NASA Marshall Space Flight Center, The University of Central Florida and the University of Michigan

• First airborne science flights were conducted during the Genesis and Rapid Intensification Processes (GRIP) campaign in Fall 2010

• “First light” results from overflights of Hurricanes Earl and Karl are reported here

26 July 11 Ruf et al., First HIRAD TC Overflights, IGARSS 2011 3 / 13

HIRAD Instrument Overview

• Interferometric Aperture Synthesis Radiometer

• Freq: 4, 5, 6 & 6.6 GHz

• H-pol @ EIA = ± 65°

• Spatial resolution:– 2 km @ nadir

– 6 km @ edge of swath

• Swath = 3x A/C altitude– ~ 60 km for GRIP

• Software beam steering– No moving parts

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HIRAD Instrument Block Diagram

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HIRAD Integration on WB-57 Aircraft

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Hurricane Earl Best Track and HIRAD 1 Sep. Overpass

HIRAD overpass

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HIRAD flight

Hurricane Earl Max Windspeed History

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Nearly Coincident HIRAD/WB-57 and SFMR/P-3 Overpasses of Earl on 1 Sep.

Storm-centric coordinate system

• HIRAD/SFMR matchups• TBs are expected to agree only at the nadir point.

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HIRAD TB Images at 4.0, 5.0 and 6.6 GHzalong Northbound Earl Overpass

4.0 GHz 5.0 GHz 6.6 GHz

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0 10 20 30 40 50 60 70 8040

60

80

100

120

140

160

180WEST - 4&5 GHz

HIRAD Tb@ 4GHz

HIRAD Tb@ 5GHz

Model Tb@ 4GHz

Model Tb@ 5GHz

SFMR Wind +50 (m/s)

SFMR Rain +50 (mm/hr)

HIRAD/SFMR West Leg Overpass

stop startSFMR Flt Dir

“Model” data are Tb’s computed from SFMR wind & rain fields

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Hurricane Karl Best Track and 3 HIRAD Overpasses on 14, 16 & 17 Sep.

Storm center location during HIRAD overpasses indicated by triangles

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HIRAD 5 GHz TB Image for Karl16 Sep. Overpass

Storm-centric Longitude (deg)

Sto

rm-c

entr

ic L

atitu

de (

deg)

Leg 8

Leg 10

Leg 6

26 July 11 Ruf et al., First HIRAD TC Overflights, IGARSS 2011 13 / 13

Summary

• HIRAD produces SFMR-like TB images over a wide (~3x altitude) cross track swath

• Initial TB calibration/validation is possible using nearly coincident SFMR overpasses

• Final instrument calibration and the development of off-nadir versions of SFMR windspeed and rain rate retrieval algorithms are currently underway

• Future participation in NASA’s Hurricane and Severe Storm Sentinal (HS3) Earth Venture-1 mission