Prior to the 2022 Atlantic hurricane season, a new digital receiver and arbitrary waveform generator, the Tomorrow.io ARENA 522, was integrated with the Imaging Wind and Rain Airborne Profiler (IWRAP). IWRAP is a downward-pointing system of two Doppler radars that is routinely installed on the National Oceanic and Atmospheric Administration WP-3D Hurricane Hunter airplanes for hurricane and extratropical cyclone research. The primary research applications of IWRAP have been to observe ocean and atmospheric vector winds and their effects on the surrounding media. Sampling limitations due to a time-multiplexed switching system were overcome in this hurricane season using a frequency diversity technique, enabling full multi-beam sampling for improved atmospheric boundary layer observations.

A major gap in wind vector measurements exists in the lowest levels (below 500m) of the hurricane boundary layer (HBL). The 3-dimensional Doppler measurements from the Imaging Wind and Rain Airborne Profiler (IWRAP) on board the NOAA WP-3D aircraft are showing potential to close this gap. During the 2021 hurricane season IWRAP was configured to produce near real time measurements of the HBL winds. The IWRAP's raw data acquisition system allows for full HBL atmospheric profiling all the way down to the ocean surface using the spectral processing technique. For the first time ever, high resolution HBL wind and reflectivity profiles below 500m were retrieved from IWRAP measurements in Hurricane Ida on August 29th, 2021. The spectral processing technique utilized and subsequent wind and reflectivity profiles are presented and discussed.

During the 2020 hurricane season, scientists at the National Oceanic and Atmospheric Administration (NOAA)/National Environmental Satellite, Data, and Information Service (NESDIS)/Center for Satellite Applications and Research (STAR) Ocean Surface Winds Team (OSWT) in collaboration with Remote Sensing Solutions (RSS) operated the RSS Ka-band Interferometric Altimeter (KaIA) from the NOAA WP-3D aircraft, making the first comprehensive set of airborne Ka-band radar altimeter measurements of a tropical cyclone. KaIA is a nadir-looking Ka-band interferometric radar altimeter with a real-time tracker/retracker and is capable of centimetric radar altimetry. This paper shows significant wave height (SWH) retrievals from the 2020 hurricane season and compares them to wave models, and satellite and buoy observations.

The High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) is a dual-frequency (Ka- and Ku-bands), dual-beam (30° and 40° incidence angles), and conical scanning Doppler radar designed for operation on the NASA high-altitude (~19 km) Global Hawk Unmanned Aerial System. HIWRAP was developed under the support of the NASA Instrument Incubator Program for studies of tropical storms and severe weather events. It utilizes solid-state transmitters along with a novel transmit and receive waveform scheme that results in a system with compact size, light weight, less power consumption, and lower cost compared to radars currently in use for precipitation and Doppler wind measurements. By combining volume backscattering measurements at Ku- and Ka-bands, HIWRAP is capable of imaging radar reflectivity and 3-D wind fields in clouds and precipitation. In addition, HIWRAP is also capable of measuring surface winds in an approach similar to SeaWinds on QuikSCAT. HIWRAP operating frequencies are similar to those used by the NASA Global Precipitation Measurement (GPM) Dual-frequency Precipitation Radar, making it suitable for providing airborne validation data for the GPM mission. This paper describes the scientific motivation for the development of HIWRAP as well as the system hardware, aircraft integration, and recent flight activities. Data from recent science flights are also presented.

Airborne co-polarization and cross-polarization observations of ocean surface normalized radar cross section (NRCS) were conducted over the North Atlantic during January and February 2015. Observations were made using the University of Massachusetts' Imaging Wind and Rain Airborne Profiler (IWRAP) radar system and a prototype antenna for the next-generation European scatterometer aboard MetOp-SG. Both were installed on a National Oceanic and Atmospheric Administration (NOAA) WP-3D research aircraft to characterize the wind response of the ocean-surface cross-polarization NRCS. During the flights, numerous constant-roll-angle circle maneuvers were performed at several different angles to collect NRCS measurements over a range of incidence angles. Surface winds at speeds between 8 and 34 ms-1were observed at incidence angles from 20° to 60° at all polarization combinations. The majority of measurements fell between 8 and 20 ms-1. Wind-direction dependence similar to copolarized NRCS was observed in the cross-polarized (VH) NRCS. The amplitude of the VH NRCS with respect to direction is less than that of copolarized NRCS at all wind speeds. Incidence angle dependence was also observed in the VH NRCS at all wind speeds. As a function of wind speed, the mean VH NRCS (A0) has a similar shape to the VV NRCS. The VH NRCS appears to not saturate at most incidence angles, unlike the VV and HH NRCS. VH and HH geophysical model functions (GMFs) were developed as functions of wind speed, incidence angle, and wind-relative azimuth for the wind speeds and incidence angles observed.

The NASA Goddard Space Flight Center (GSFC) High-altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) is a solid-state dual frequency Doppler radar funded by the NASA Instrument Incubator Program. It uses direct-digital-synthesizer devices to generate versatile waveforms including conventional pulses and linear frequency modulation (LFM) chirps. This letter describes a waveform used by the GSFC and the Remote Sensing Solutions to address the critical limitations of range sidelobes and blind ranges in airborne pulse-compression radar. By utilizing a frequency diversity waveform consisting of two pulses and an LFM chirp at each transmit cycle, this system provides the improved sensitivity and range resolution benefits of pulse compression on targets within the middle and high altitudes while maintaining conventional pulsed data near the radar and the surface. The data obtained by the HIWRAP during the NASA Midlatitude Continental Convective Clouds Experiment using this waveform scheme are presented.

Dual wavelength precipitation radar (DPR) is planned to be deployed in the GPM core satellite. The DPR is expected to provide improved characterization of the raindrop size distribution ( DSD), as well as rainfall rate estimation from a combination of Ku band and Ka band radar measurement [1]. The Ku band radar is nearly same as the TRMM Precipitation radar. The Ka band provides higher sensitivity and can be useful in the measurement of snow and light rain. In contrast to TRMM the dual wavelength retrieval methods will use two DSD parameters to characterize the precipitation medium. The underlying precipitation structures, hydrometeors and DSDs dictate the type of models or retrieval algorithms that can be used to estimate precipitation. Having dual wavelength radar on the ground, with the potential for in-situ observations, or coordinated observations provide excellent opportunity to develop microphysical and system models for retrievals. Therefore a beam aligned dual-wavelength system consisting of Ku and Ka bands can be very useful as a ground validation tool. In addition if these systems can be dual-polarized, then these can be self-consistent cross validation tools. This paper describes the NASA Dual polarized, dual frequency Doppler radar, developed for the ground validation program.

This paper summarizes part of the work performed on the calibration and characterization of the Dual-frequency, Dual-polarized, Doppler Radar (D3R) system. The D3R makes use of pulse compression combined with a three pulse frequency separated waveform to achieve it's sensitivity while still maintaining a blind range similar to that of a single pulse weather radar. A slightly modified receiver calibration procedure to the one used on conventional weather radar was required to accommodate the use of multiple sub-channels. The use of the calibration loop in both transceivers is described and transmitter output power is shown for a twenty four hour period. Antenna beam (Ku to Ka) co-alignment verification using solar scans is also presented followed by sphere calibration results for the Ku-band radar. Finally, Ku-band reflectivity plots for two events during May 6th, 2012 and May 7th, 2012 are presented.

The National Research Council Decadal Survey identified the need for a future mission to provide accurate real-time observations of ocean wind vectors from calm to tropical cyclone wind conditions with or without the presence of rain. Tasked by the National Oceanic and Atmospheric Administration (NOAA), the Jet Propulsion Laboratory (JPL) developed a future scatterometer design that would leverage its success on the heritage of QuikSCAT but would provide more accurate measurements under all weather conditions through the use of Ku- and C-band coincident measurements of the ocean surface. To design a cost effective instrument for all weather operations from space the existing risks need to be mitigated. The work described in this paper attempts to validate results reported at hurricane strength winds in and investigate the effects of splash caused by precipitation on the scatterometer wind estimation.

As an integral part of Global Precipitation Measurement (GPM) mission, Ground Validation (GV) program proposes to establish an independent global cross-validation process to characterize errors and quantify uncertainties in the precipitation measurements of the GPM program. A ground-based Dual-Frequency Dual-Polarized Doppler Radar (D3R) that will provide measurements at the two broadly separated frequencies (Ku- and Ka-band) is currently being developed to enable GPM ground validation, enhance understanding of the microphysical interpretation of precipitation and facilitate improvement of retrieval algorithms. The first generation D3R design will comprise of two separate co-aligned single-frequency antenna units mounted on a common pedestal with dual-frequency dual-polarized solid-state transmitter. This paper describes the salient features of this radar, the system concept and its engineering design challenges.

This paper describes some of the novel technologies adopted in the realization of the NASA Dual-frequency Dual-polarized Doppler Radar (D3R) system for to be used by the GPM ground validation program. A description of the transceivers and major trades that lead to a solid-state architecture is presented. Other aspects enabling the design such as the waveform design and generation and the digital receiver is also described. Data measured from a similar power amplifier was used to estimate the expected range side lobe performance. An estimate of the expected sensitivity based on the transceiver parameters also presented.

The economic wealth and daily lives of United States citizens and people of all nations are affected by precipitation. Accurate quantitative precipitation measurements locally and on a global scale are needed to improve our ability to forecast and our understanding of these events. Efficient resource mobilization to minimize the impact of devastating precipitation events demands accurate and timely mapping of these event as they occur. To help address these needs, Remote Sensing Solutions, working with NASA, is developing a novel solid-state, dual-polarized, dual-wavelength precipitation Doppler radar/radiometer system. The innovations necessary to realize this unique and powerful system are described and the performance presented.

IWRAP, the Imaging Wind and Rain Airborne Profiler is a conically scanning dual-band (C and Ku), dual-polarized pencil-beam airborne Doppler radar that profiles the volume reflectivity and Doppler velocity from precipitation. It also measures the ocean backscatter response especially during tropical and extra tropical cyclones. IWRAP is designed to measure troposphere winds and surface winds. Of particular importance to the storm forecasting and research community are the winds in the lower part of the hurricane boundary layer near the sea surface (lower ABL). The covariance data processing technique IWRAP traditionally employed assumes a uni-modal and symmetric Doppler spectrum and therefore, it alone is unable to account properly for the influence of the surface scattering on wind profiles in the lower ABL region. In this paper we compare covariance-based approaches and full-spectral approaches utilized to derive the true wind speed for atmospheric vertical profiles. Techniques for removal of the surface contamination and example of wind profiles retrieved from Hurricane Rita are presented.

The Microwave Remote Sensing Laboratory (MIRSL) at the University of Massachusetts developed and operates the Imaging Wind and Rain Airborne Profiler (IWRAP). With support from NASA, NOAA, and ONR, UMASS has collaborated with NOAA-NESDIS and NOAA-AOC to operate the instrument aboard the NOAA WP-3D "Hurricane Hunter" aircraft since the 2002 hurricane season and for four winter experiments sampling high-latitude storms. The goals of these experiments have been to characterize storm boundary layers and to develop improved retrievals for space-based scatterometers, specifically, NASA SeaWinds Scatterometer on QuikSCAT and Advanced Scatterometer (ASCAT) which was developed by ESA on behalf of EUMETSAT. IWRAP is a conically-scanning, dual-frequency (C-and Ku-band) coherent radar with dual-polarization capability. The incidence angles are nominally: 30, 35, 40, and 50 degrees. At times, the instrument has been configured to address specific scientific and engineering problems. Examples include: C-band measurements of high incidence angle backscatter for ASCAT validation, and C-band horizontal polarization measurements to develop a high wind speed geophysical model function (GMF). Independent measurements of surface wind speed and column integrated rain rate are made coincidently with the UMass Simultaneous Frequency Radiometer (USFMR) and AOC Stepped Frequency Microwave Radiometer (SFMR). Since 2005, IWRAP has operated in a raw data mode, recording individual radar pulses to enable the separation of near surface backscatter contributions (i.e. surface scattering versus volume scattering). The intensity of tropical cyclones ranged from tropical storm to category five hurricane, and high-latitude storms with up to hurricane force winds.

This paper describes the development of the High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) which is funded under the NASA Instrument Incubator Program (IIP) . HIWRAP is a dual-frequency (Ka- and Ku-band), dual-beam (30deg and 40deg incidence angle), conical scan, Doppler radar system designed for operation on the high-altitude (65,000 ft) Global Hawk Unmanned Aerial System (UAS). It utilizes solid state transmitters along with novel pulse compression scheme that will result in a system that is considerably more compact in size, lighter in weight, less power consumption, and ultimately cost significantly less than radars currently in use for precipitation and Doppler wind measurements. By combining measurements at Ku- and Ka-band, HIWRAP will be able to image winds by measuring volume backscattering from clouds and precipitation.

The pulse compression scheme implemented on the Imaging Wind and Rain Airborne Profiler (IWRAP) is described. Developed at the UMASS Microwave Remote Sensing Laboratory (MIRSL), IWRAP is a dual-band (C and Ku) conically scanning Doppler scatterometer designed to map the atmospheric boundary layer wind fields, ocean surface wind fields, and precipitation within tropical cyclones. IWRAP has previously been deployed using a pulsed transmit waveform with a peak transmit power of 80 watts. This limits the average transmit power and sensitivity for the system which affects the more distant range gates (especially at Ku-band). As a result, IWRAP could operate only at lower altitudes (approx. 5000 ft) causing safety concerns and limiting the missions for which it can be deployed. Increasing sensitivity was achieved by converting IWRAP to a pulse compression radar system. Pulse compression is a technique that combines the increased energy of a longer pulse with the high resolution of a short pulse by implementing a frequency modulated (FM) "chirped" transmit wave-form. This method requires advanced signal processing, in which the received signal is passed through a matched filter to compress the pulse on the receiving end. A system with various chirp/filtering schemes which UMASS has recently developed will be discussed in this paper.

During the NOAA/NESDIS 2005 Hurricane Season (HS2005) and the 2006 Winter Experiment, the University of Massachusetts (UMass) installed two instruments on the NOAA N42RF WP-3D research aircraft: the Imaging Wind and Rain Airborne Profiler (IWRAP) and the Simultaneous Frequency Microwave Radiometer (SFMR). IWRAP is a dual-band (C- and Ku), dual-polarized pencil- beam airborne radar that profiles the volume backscatter and Doppler velocity from rain and that also measures the ocean backscatter response. It simultaneously profiles along four separate incidence angles while conically scanning at 60 RPM. SFMR is a C-band nadir viewing radiometer that measures the emission from the ocean surface and intervening atmosphere simultaneously at six frequencies. It is designed to obtain the surface wind speed and the column average rain rate. Both instruments have previously been flown during the 2002, 2003 and 2004 hurricane seasons. For the HS2005, the IWRAP system was modified to implement a raw data acquisition system. The importance of the raw data system arises when trying to profile the atmosphere all the way down to the surface with a non- nadir looking radar system. With this particular geometry, problems arise mainly from the fact that both rain and ocean provide a return echo coincident in time through the antenna's main lobe. This paper shows how this limitation has been removed and presents initial results demonstrating its new capabilities to derive the atmospheric boundary layer (ABL) wind field within the inner core of hurricanes to much lower altitudes than the ones the original system was capable of, and to analyze the spectral response of the ocean backscatter and the rain under different wind and rain conditions.

During the 2002, 2003, and 2004 Hurricane seasons, and the 2005 Ocean Winds and Rain Winter Experiment, the University of Massachusetts (UMass) installed two instruments on the NOAA N42RF WP-3D research aircraft: the Imaging Wind and Rain Airborne Profiler (IWRAP) and the Simultaneous Frequency Microwave Radiometer (SFMR). IWRAP is a dual-band (C- and Ku), dual-polarized pencil-beam airborne radar that profiles the volume backscatter and Doppler velocity from rain and that also measures the ocean backscatter response. It simultaneously profiles along four separate incidence angles while conically scanning at 60 RPM. SFMR is a C-band nadir viewing radiometer that measures the emission from the ocean surface and intervening atmosphere simultaneously at six frequencies. It is designed to obtain the surface wind speed and the column average rain rate. Both instruments have previously been flown during hurricane seasons 2002, 2003 and 2004. Spectral techniques can been used to differentiate the contributions of the volume backscatter from rain from the ocean surface backscatter. Initial results from the Winter 2005 datasets are presented. Attenuation from rain is also particularly important at high microwave frequencies such as Ku-band. Thanks to IWRAP's profiling capabilities, Ku-band attenuation models and dropsize distribution (DSD) parameters of the observed precipitation from dual-wavelength techniques within tropical cyclones are presented.

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 study of high altitude clouds has motivated the development of new airborne and space-borne millimeter-wave cloud radars. Airborne millimeter-wave radars can offer better spatial resolution and sensitivity than ground-based counterparts, by avoiding water vapor attenuation in the lower atmosphere and spatial resolution degradation due to beam spreading. Furthermore, aircraft can cover large geographic areas and simulate satellite geometry. A next generation 95 GHz Compact Millimeter-wave radar (CMR) is currently under development. Incorporation of pulse compression will provide sensitivity comparable to larger klystron tube-based transmitters traditionally used in ground based 95 GHz radars. The CPU-bases signal processor will be replaced with a stand alone processor bases on re-configurable Field Programmable Gate Array Logic (FPGA). The new processor digitizes the IF signal, performs digital-in phase and quadrature phase detection, and applies the pulse-pair algorithm.

We describe a 95 GHz radar for an unmanned aerial vehicle (UAV). The radar measures vertical profiles of the reflectivity and Doppler velocity of clouds, which are then telemetered to the ground for storage. Telemetry bandwidth requires that substantial real-time data processing be done on the UAV in a low-power (less than 100 watts) and small size (less than 1 cubic foot) system. A prototype was developed in less than a year, thus a flexible programmable technology was required. Although typical remote sensing radars use DSP chips, it was determined that our power, size, performance and design-time requirements were best met using FPGA technology. Our system is based on the Giga-Ops Spectrum system which uses Xilinx FPGAs on a novel modular PCI board. Unlike numerous recent FPGA-based signal processors, this presents a new class of applications and embedded system requirements. Reconfigurable capabilities are currently being explored to support radar algorithms which can adapt to a changing environment.

Ocean radar backscatter in the presence of large waves is investigated using data acquired with the Jet Propulsion Laboratory NUSCAT radar at Ku band for horizontal and vertical polarizations and the University of Massachusetts C-SCAT radar at C band for vertical polarization during the Surface Wave Dynamics Experiment. Off-nadir backscatter data of ocean surfaces were obtained in the presence of large waves with significant wave height up to 5.6 m. In moderate-wind cases, effects of large waves are not detectable within the measurement uncertainty and no noticeable correlation between backscatter coefficients and wave height is found. Under high-wave light-wind conditions, backscatter is enhanced significantly at large incidence angles,with a weaker effect at small incidence angles. Backscatter coefficients in the wind speed range under consideration are compared with SASS-II (Ku band), CMOD3-H1 (C band), and Plant's model results which confirm the experimental observations. Variations of the friction velocity, which can give rise to the observed backscatter behaviors in the presence of large waves, are presented.>

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.>