The Hurricane Imaging Radiometer (HIRAD) is an airborne passive microwave radiometer designed to provide high resolution, wide swath imagery of surface wind speed in tropical cyclones from a low profile planar antenna with no mechanical scanning. Wind speed and rain rate images from HIRAD's first field campaign (GRIP, 2010) are presented here followed, by a discussion on the performance of the newly installed thermal control system during the 2012 HS3 campaign. The paper ends with a discussion on the next generation dual polarization HIRAD antenna (already designed) for a future system capable of measuring wind direction as well as wind speed.

An improved microwave radiometric ocean surface emissivity model has been developed to support forward radiative transfer modeling of brightness temperature and geophysical retrieval algorithms for the next-generation airborne Hurricane Imaging Radiometer instrument. This physically based C-band emissivity model extends current model capabilities to hurricane-force wind speeds over a wide range of incidence angles. It was primarily developed using brightness temperature observations during hurricanes with coincident high-quality surface-truth wind speeds, which were obtained using the airborne Stepped-Frequency Microwave Radiometer. Also, other ocean emissivity models available through the published literature and the spaceborne WindSat radiometer measurements were used.

The SeaWinds scatterometer, onboard the QuikSCAT satellite, infers global ocean vector winds (OVWs); however, for a number of reasons, these measurements in hurricanes are significantly degraded. This paper presents an improved hurricane OVW retrieval approach, known as Q-Winds, which is derived from combined SeaWinds active and passive measurements. In this technique, the effects of rain are implicitly included in a new geophysical model function, which relates oceanic brightness temperature and radar backscatter measurements (at the top of the atmosphere) to the surface wind vector under both clear sky and in the presence of light to moderate rain. This approach extends the useful wind speed measurement range for tropical cyclones beyond that exhibited by the standard SeaWinds Project Level-2B (L2B) 12.5-km wind vector algorithm. A description of the Q-Winds algorithm is given, and examples of OVW retrievals are presented for the Q-Winds and L2B 12.5-km algorithms for ten hurricane overpasses in 2003-2008. These data are also compared to independent surface wind vector estimates from the National Oceanic and Atmospheric Administration Hurricane Research Division's objective hurricane surface wind analysis technique known as H*Wind. These comparisons suggest that the Q-Winds OVW product agrees better with independently derived H^ Wind analysis winds than does the conventional L2B OVW product.

The Imaging Wind and Rain Airborne Profiler (IWRAP) is the first high-resolution dual-band airborne Doppler radar designed to study the inner core of tropical cyclones (TCs). IWRAP is operated from a National Oceanic and Atmospheric Administration WP-3D aircraft during missions through TCs and severe ocean storms. The system is designed to provide high-resolution dual-polarized C- and Ku-band reflectivity and Doppler velocity profiles of the atmospheric boundary layer (ABL) within the inner core precipitation bands of TCs and to study the effects precipitation has on ocean wind scatterometry as it applies to TCs. IWRAP implements a very unique measurement strategy; it profiles simultaneously at four separate incidence angles (approximately 30/spl deg/, 35/spl deg/, 40/spl deg/, and 50/spl deg/) while conically scanning at 60 rpm. A summary of the principles of operation and the design of the instrument is given, followed by examples of IWRAP's unique imaging capability. To our knowledge, these examples include the highest resolution measurements of the ABL winds in a hurricane ever obtained.

IWRAP, the imaging wind and rain airborne profiler, is the first high-resolution dual-hand airborne Doppler radar designed for studying the inner core of tropical cyclones (TCs). The system is designed to provide high-resolution, dual-polarized C and Ku-Band reflectivity and Doppler profiles of precipitation volume backscatter and ocean surface backscatter within the inner core precipitation bands of tropical cyclones (TCs). SFMR is a C-band nadir viewing radiometer used operationally to provide continuous estimates of the surface wind speed and title column average rain rate. Both IWRAP and SFMR arc operated from a National Oceanic and Atmospheric Administration (NOAA) WP-3D aircraft during missions through TCs and severe ocean storms. We present wind and reflectivity profiles of the atmospheric boundary layer within the inner-core of hurricane Isabel (2003) from IWRAP measurements. These profiles are the highest resolution measurements of the ABL winds of a hurricane ever obtained. The profiles are compared to coincident surface wind speed measurements provided by SFMR, flight level wind measurements and GPS dropsonde winds.

During the 2002 and 2003 ONR CBLAST Hurricane Program Field (HPF) and the NOAA/NESDIS Hurricane Ocean Winds and Rain Experiment, the University of Massachusetts (UMass) installed IWRAP, a conically scanning dual-band (C- and Ku-band), dual-polarized pencil-beam airborne Doppler radar that profiles the volume backscatter and Doppler velocity from rain and the backscatter from the ocean surface simultaneously at four incidence angles covering incidence angles from 25 to 55 degrees. From the measurements acquired during missions flown through hurricanes Gustav, Isadore, and Lili (2002) and Fabian and Isabel (2003), high wind regime Geophysical Model Functions have been derived at both frequencies and polarizations. Concrete saturation effects in the NRCS are presented, and sensitivity in the wind direction at high wind speed is discussed through the analysis of the second harmonic of the NRCS.

This paper presents a 3D boundary layer wind retrieval algorithm for airborne Doppler radar measurements of precipitation inside hurricanes. The data was collected, inside Hurricane Lili during NOAA's 2002 Atlantic Hurricane Ocean Winds Field Experiment with University of Massachusetts's newly developed Imaging Wind and Rain Airborne Profiler. Two forms of Kalman filters for 3D wind retrieval are analyzed for accuracy using simulations. Preliminary results of the actual 3D wind estimates using the chosen algorithm were obtained and compared with simultaneous and independent wind vector measurements by GPS dropwindsondes, surface wind speed measurements by a microwave radiometer and flight level wind vector measurements

This paper presents preliminary results of precipitation effect on microwave scatterometry wind estimates at C and Ku band. The results show that microwave scatterometer underestimates the wind speed by up to 10 m/s for rain rate condition of 15 mm/hr and wind speed condition of 25 to 30 m/s for both frequency bands

Airborne ocean backscatter dual polarization measurements at C and Ku-band obtained in high wind speed conditions (20 to 60 m/s) are presented. The VV and HH NRCS measurements are compared. The preliminary comparisons show that the HH NRCS measurements are slightly more sensitive to the surface wind speeds for high wind speed and precipitation conditions.

The University of Massachusetts (UMass), with support from ONR, NOAA and NASA, has developed a novel radar system called the Imaging Wind and Rain Airborne Profiler (IWRAP). IWRAP is a dual frequency (C/Ku band) dual polarized airborne radar that profiles the volume and surface backscatter and Doppler simultaneously at 30, 35, 40 and 50 degrees incidence, while conically scanning at 30 to 90 rpm. Its range resolution can be set at 15, 30, 60 or 120 m. From these measurements the ocean surface wind field, 3-D boundary layer winds within rain bands can be mapped. IWRAP was flown during the 2002 NOAA/NESDIS/ORA Hurricane Ocean Winds Experiment, which was conducted in conjunction with the 2002 NOAA/AOML/HRD Hurricane Field Program. This paper presents the system design, radar processing algorithms and initial results from the 2002 hurricane flights.

The NASA Scanning Radar Altimeter (SRA) sweeps a radar beam of 1/spl deg/ half-power width (two-way) across the aircraft ground track within /spl plusmn/22/spl deg/ of nadir, simultaneously measuring the backscattered power at its 36 GHz (8.3 mm) operating frequency and the range to the sea surface at 64 points spaced across the swath at 0.7/spl deg/ incidence angle intervals. Flights were made into Hurricane Humberto on 23 and 24 September 2001, aboard a WP-3D hurricane research aircraft of the NOAA Aircraft Operations Center. The ranges produce raster lines of sea surface topography at a 10 Hz rate. The SRA was primarily designed to produce sea surface directional wave spectra, but the backscattered power measurements can be used to determine path integrated rain rate below the aircraft.

The NASA Scanning Radar Altimeter (SRA) was designed primarily to measure the energetic portion of the directional wave spectrum by generating a topographic map of the sea surface. The SRA sweeps a radar beam of 1/spl deg/ (two-way) half-power width across the aircraft ground track over a swath equal to 0.8 of the aircraft height, simultaneously measuring the backscattered power at its 36 GHz (8.3 mm) operating frequency and the range to the sea surface at 64 positions at 0.7 incidence angle intervals. The maximum scan rate was 8 Hz during the Hurricane Bonnie flights, but it is presently 10 Hz. In realtime, the slant ranges are multiplied by the cosine of the off-nadir incidence angles (including the effect of aircraft roll attitude) to determine the vertical distances from the aircraft to the sea surface. These distances are subtracted from the aircraft height to produce a sea-surface elevation map which is displayed on a monitor in the aircraft to enable realtime assessments of data quality and wave properties. On 24 August 1998, the SRA, aboard a NOAA hurricane research aircraft, provided the first documentation of the directional wave spectrum throughout a hurricane in open water when Hurricane Bonnie was about 400 km east of Abaco Island, Bahamas. On 26 August 1998, the SRA provided the first documentation of the directional wave spectrum throughout a hurricane making landfall as Bonnie was approaching Wilmington, North Carolina.

Attempting to understand and predict weather on a local and global basis has challenged both the scientific and engineering communities. One key parameter in understanding the weather is the ocean surface wind vector because of its role in the energy exchange at the air-sea surface. scatterometers, radars that measure the reflectivity of a target offer a tool with which to remotely monitor these winds from tower-, aircraft-, and satellite-based platforms. This paper introduces three current airborne scatterometer systems, and presents data collected by these instruments under low-, moderate-, and high-wind conditions. The paper focuses on airborne scatterometers because of their ability to resolve submesoscale variations in wind fields. Discrepancies between existing theory and the observations are noted and the concerns in measuring low-wind speeds discussed. Finally, the application of using this technology for estimating the surface-wind vector during a hurricane is demonstrated.>