In this work, we propose a novel supervised segmentation approach based on compact Operational U-Nets (Op-UNets) for detection of water regions in high-resolution synthetic aperture radar (SAR) images. The proposed approach utilizes the Segment Anything Model (SAM) for supervised training of separate compact Op-UNet model to automatically generate higher accuracy binary segmentation masks from the ground truth optical imagery. To the best of our knowledge, this is the first study that applies jointly the SAM model and compact Op-UNet architecture which utilizes the self-organized operational neural network (self-ONN) layers to improve SAR image segmentation performance with limited labeled data. The preliminary results from the performed experiments using the high-resolution SAR imagery over the coastline along Daytona Beach and Seminole, FL (from Capella Space) are presented to evaluate the performance of the proposed model with significantly reduced computational complexity.

Observations of the Tampa Bay area by the Capella SAR satellite constellation were obtained prior to, during, and after the landfall of Hurricane Ian (2022). Offshore directed winds resulted in the set-down of Tampa Bay, which was captured by one of the acquisitions. Analysis of the imagery combined with available Topo-bathy digital elevation models (TBDEMs) shows good correlation of estimated water levels between image derived and directly measured levels.

In this paper, we address the problem of combating the effect of the nonlinearities of the transmit-receive chain in solid-state radars, which are typically generated by the power amplifier in transmission. This issue is of particular importance in meteorological radar applications, as they require transmit pulses featuring very low autocorrelation sidelobes, which are significantly raised due to nonlinearities. In this work, we describe an adaptive predistortion design method based on an iterative approach in the spectral domain. The proposed method has been validated by means of hardware using a customized software radio and driving an amplifier into saturation. Two different ideal, highly performing pulse compression waveforms, expressly designed for weather radar applications, were sent to its input. The experimental results demonstrate the benefits of the proposed approach to design the digital predistortion module.

We present preliminary research on a method to estimate Vertical Air Motion (VAM) at a particular height by comparing the measured rain-rate (RR) by a vertically-pointing S-band Frequency-Modulated Continuous-Wave (FMCW) radar with that of a ground-based disdrometer. The method is based on a constrained parametric solver, assuming high correlation between 5-min averaged rain rates measured by the radar and disdrometer. The method is tested over disdrometer and radar observations during the Verification of the ORigins Tornado EXperiment in South East US (VORTEX-SE) project. Finally, the results are partially validated by means of fitting a gamma distribution to the VAM-corrected DSD profiles and studying its parameters.

Spaced-antenna (SA) retrievals are a potential means of higher spatial-resolution wind-field retrievals than currently available single weather radar techniques. Relevant literature to date has focused on theoretical, numerical or engineering aspects. In a stratiform precipitation event case study with a median spectrum width of 0.53 m/s, we evaluate SA retrievals. The X-band active phased-array spaced antenna retrievals exhibited better measurement fidelity relative to simulated performance of the S-band national weather radar testbed (NWRT). This allowed for the first interpretation and evaluation of SA retrievals on precipitation echoes. SA measurements were confirmed to be in quadrature with radial velocity estimates. This signature is qualitatively consistent with simulation predictions for a spatially invariant wind field, where the radial velocity maximum corresponds to a null in the SA retrieval. Finally, SA retrievals were in agreement with reference wind field proxies derived using Doppler beam swinging (DBS) and velocity azimuth display (VAD) techniques. Among the SA techniques implemented, the time-domain Gaussian slope at zero lag (G-SZL) algorithm was found to perform better than the frequency domain full spectral analysis (FSA) algorithm. This is because the parametric nature of the G-SZL algorithm resulted in better immunity to correlation coefficient estimation errors.

The Stepped Frequency Microwave Radiometer (SFMR) is a key instrument in tropical cyclones and high-latitude winter storms research. Through the observed brightness temperature (Tb) over a range of C-band frequencies, the SFMR derives wind-speed and rain rate. However, the instrument requires 5 to 10 seconds of averaging to cycle through all the frequencies, so regions of strong wind gradients and/or narrow rain features may be overlooked. The University of Massachusetts Amherst Microwave Remote Sensing Laboratory (MIRSL) developed a specialized version of the SFMR, the UMass Simultaneous Frequency Microwave Radiometer (USFMR) that operates six frequency channels simultaneously, eliminating the averaging time. In collaboration with NOAA/NESDIS/STAR we plan to use this instrument in studies of high latitude winter storms. We describe the instrument hardware, recent comparisons with operational SFMR measurements during hurricane flight in 2019, and current and planned investigation of retrieval inconsistencies in non-tropical cyclone environments. In collaboration with NOAA/NESDIS/STAR we plan to use this instrument in studies of high latitude winter storms. We describe the instrument hardware, recent comparisons with operational SFMR measurements during hurricane flight in 2019, and current and planned investigation of retrieval inconsistencies in non-tropical cyclone environments.

Spaced antenna (SA) radars retrieve wind-fields by tracking resolution volume sized bins of scatterers as they advect between two physically displaced antennas. To date, SA methods have been applied for profiling the ionosphere and precipitation free atmosphere. The primary technological difficulty in applying these methods to probe precipitation at microwave frequencies is the requirement for such a short antenna separation that a significant overlap in apertures is necessary. In this article, we synthesize overlapped apertures by segmenting active phased-arrays into subarrays that are multiplexed in time. Antenna pattern measurements are then employed to evaluate beamforming errors on a family of implementations. Based on measurements and Monte Carlo simulations, we find that highly overlapping apertures are most immune to beam squint errors. This is because element-level phase errors are retained on the synthesized SAs and differential beam squint errors are minimized. Finally, we demonstrate a novel method to measure relative phase center displacement between SAs that obviates the need for near-field antenna measurements.

We present the characteristics of dual-polarized weather radar variables as observed by a planar phased-array radar (PPAR) operating at X-band. The characteristics are governed by the projection of the polarizations radiated by the array into the canonical spherical coordinates defining the measurement geometry of ground-based weather radars. The direction-dependent gain and phase of the radiating elements, the orientation of the radiated polarizations, and the mechanical tilting of the array all contribute to the projection, which results in biased observations compared with those of a mechanically scanned weather radar employing a reflector antenna. We decompose the projection into components that can be separated and customized for various PPAR configurations, including consideration of possible cross-polarized radiation by the elements and the effect of a wet radome covering the array face. These are represented by matrices whose product comprises the total projection. We apply this methodology to an X-band PPAR using in-place measurements of precipitation to obtain the properties of the radiation pattern. We then obtain the resulting biases of common weather radar polarimetric variables. We show that the biases can be represented as a product of the intrinsic variables with projection- and target-dependent corrections. The projection-dependent corrections depend only upon elements of the projection matrix, while the target-dependent corrections also depend upon the intrinsic differential reflectivity and copolar or cross-polar correlation coefficients. We find that the projection-dependent corrections are sufficient to achieve acceptable bias over most of the scan range.

Beginning in 2015, scientists at the National Oceanic and Atmospheric Administration (NOAA)/NESDIS/STAR and UMass Amherst collaborated with the European Space Agency (ESA) to collect ocean surface normalized radar cross-section (NRCS) measurements at co- and cross-polarizations in extreme wind conditions from the NOAA Hurricane Hunter aircraft using a prototype antenna for the next-generation European spaceborne scatterometer. Since then, more research has been done to understand the effects of ocean-surface wind vectors on NRCS from both satellite and aircraft. Here we show the data from several seasons of flight experiments to understand the airborne measurements of NRCS in context.

Attenuated backscatter measurements from a Vaisala CL31 ceilometer and a modified form of the well-known slope method are used to derive the ceilometer extinction profiles during rain events, restricted to rainfall rates (RRs) below approximately 10 mm/h. RR estimates from collocated S-band radar and portable disdrometer are used to derive the RR-to-extinction correlation models for the ceilometer-radar and ceilometer-disdrometer combinations. Data were collected during an intensive observation period of the Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE) conducted in northern Alabama. These models are used to estimate the RR from the ceilometer observations in similar situations that do not have collocated radar or the disdrometer. Such correlation models are, however, limited by the different temporal and spatial resolutions of the measured variables, measurement capabilities of the instruments, and the inherent assumption of a homogeneous atmosphere. An empirical method based on extinction and RR uncertainty scoring and covariance fitting are proposed to solve, in part, these limitations.

In Winter 2017, the University of Massachusetts Amherst's Imaging Wind and Rain Airborne Profiler (IWRAP) was flown on a National Oceanic and Atmospheric Administration (NOAA) WP-3D Hurricane Hunter aircraft under the direction of scientists from Center for Satellite Applications and Research (STAR) at NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) over the North Atlantic ocean out of Shannon, Ireland. IWRAP is a dual-frequency, conically scanning, profiling Doppler radar initially developed by Microwave Remote Sensing Laboratory (MIRSL) at the University of Massachusetts Amherst that is routinely installed on the NOAA WP-3D research aircraft. The flight on February 6, 2017, targeted a region of high winds (greater than 30 m/s) that was also observed by the Sentinel-1B satellite's synthetic aperture radar. Sentinel-1B was configured to observe in extended wide swath mode in both VV- and VH-polarizations, whereas the IWRAP C-band radar was configured to measure all of VV-, VH-, and HH-polarizations. IWRAP and Sentinel-1B VV and VH normalized radar cross section (NRCS) at the same Earthincidence angle along the flight path match reasonably well during the entire flight, but some additional trends between aircraft and satellite can be observed. IWRAP VV-polarized NRCS generally match the CMOD5.h geophysical model function (GMF), suggesting errors in the Sentinel-1B processing chain.

The University of Massachusetts is implementing a testbed to evaluate phased-array weather radar polarimetry at X-band. The project seeks to determine the impacts of electronic scanning and associated polarization errors on weather radar measurables to analyze methods for polarimetric bias correction. The testbed consists of a planar dual-polarization X-band phased-array radar operated in tandem with a mechanically scanned polarimetric reference radar. The projection of tilted phased-array aperture polarizations to world coordinates are outlined, and direct comparisons of simultaneous weather observations by both radar systems are made along with quasi-vertical measurements of light precipitation which should reveal the array response to precipitation in the absence of differential reflectivity or differential phase.

In this paper, airborne measurements of the ocean surface normalized radar cross-section (NRCS) taken at co- and cross-polarizations in high-wind conditions are reported. The measurements were taken in Hurricane Matthew during which it was a Category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Saturation of the co-polarized NRCS and lack of saturation in the cross-polarized NRCS is observed, consistent with previous results. The results have implications for planned and future scatterometers (e.g., MetOp-SG) that aim to increase the maximum observable wind speeds by using cross-polarized measurements.

A dual-polarized X-band solid-state 1-D electronic scanning “phase-tilt” weather radar (PTWR) and its scanning geometry are presented. In this architecture, the true elevation angle decreases from the nominal array tilt angle and the true azimuth angle increases from the requested azimuth as one scans off boresight. Additionally, this scanning geometry induces a canting angle effect, which can be significant especially at higher elevation tilts. The predictions of potential biases in selected polarimetric variables due to this effect are derived. For elevation angles below 10°, where polarimetric measurements are of most value, predicted biases are negligible. The PTWR was deployed in Arlington, TX, USA, for an eight-week period during Spring 2014 collecting data on a number of weather events. The direct proximity (250 m away) of a mechanically scanning magnetron-based radar, employing a dual-polarized parabolic antenna allowed for a qualitative and quantitative data comparison. We find the differences in the observations made by the two radar systems are not attributable to the aforementioned biases, but appear primarily due to differences in sampling volumes of the two radars. We also find that at high-elevation tilts, the coupling of the true elevation angle with the array-relative azimuth scan angle complicates the interpretation of features at a constant altitude such as the melting layer.

During the Spring of 2014 a Phase-Tilt Weather Radar (PTWR) developed by the University of Massachusetts was deployed within the Dallas-Fort Worth Urban Testbed operated by the CASA Engineering Research Center. During an eight-week period it observed several weather events including severe thunderstorms and stratiform rain. Observations by the phased-array radar were compared to a nearby mechanically-scanned dual-polarized radar employing a parabolic dish with the objective of assessing the relative severity of biases in polarimetric observations by the PTWR. Such biases are due to polarization-basis rotation due to scanning along a tilted axis. It is expected these would be negligible except possibly at large (> 10°) elevation angles. At lower elevation angles where near-direct comparisons were possible, differences in observations were not uniquely attributable to this souce of error.

Recent upgrades to the University of Massachusetts (UMass) Frequency-Modulated Continuous-Wave (FMCW) S-Band boundary layer profiling radar are discussed. These include incorporation of a software radio digital receiver and associated improvements in data acquisition and signal processing. These improvements have significantly increased the unambiguous velocity capability of the radar, allowing for Doppler spectral measurement of precipitation in addition to boundary layer clear-air echoes. The system was deployed during the NOAA-sponsored VORTEX-SE experiment during Spring 2016 and will be redeployed for Spring 2017. Sample observations are shown. Finally, future system improvements are discussed.

We report on airborne measurements of the cross-polarized (VH) ocean surface normalized radar crosssection (NRCS) at incidence angles between 15° and 40° obtained at C-band in high-wind (> 30 m s−1) conditions. The present observations were taken in Hurricane Patricia on 23 October 2015 and extend the wind speed range of the existing cross-polarization ocean surface NRCS literature [1]–[4]. The NRCS at the smaller incidence angles decrease as wind speed increases, as expected. At the larger incidence angles, saturation of the NRCS is not observed up to at least 70 m s−1. The results have implications for planned and future scatterometers (e.g., MetOp-SG) that aim to increase the maximum observable wind speeds.

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.

A microwave backscattering model for ground-based remote sensing of precipitation is developed and used to analyze back scattering measurements from snowfall and rain type precipitation. Backscattering from entire precipitation region is calculated by solving vector radiative transfer (VRT) equations. Geophysical parameters for rain or snow are determined by considering altitude and latent range. VRT equations are solved numerically by using matrix doubling method to take into account multiple-scattering effects. Results from model analyses agree well with measured radar data.

We report on airborne measurements of the sea-surface normalized radar cross-section (NRCS) at incidence angles of approximately 22° obtained at both C-band and Ku-band in high-wind (> 25ms−1) conditions. Measurements obtained over numerous research flights through tropical cyclones and high-latitude winter storms between 2011 and 2014 are composited to yield geophysical model functions in rain-free conditions. The present observations extend the results of [1], who reported high-wind NRCS for incidence angles from 30° to 50°, to a smaller incidence angle. Saturation of the mean NRCS is observed at both frequencies. In some cases the NRCS is observed to decrease with increasing wind speed beyond the saturation. The results have implications for planned and future scatterometers aiming to increase the observed swath width by extending the range of incidence angles.

An adaptive solution based on an extended Kalman filter (EKF) is proposed to estimate the atmospheric boundarylayer height (ABLH) from frequency-modulated continuous-wave S-band weather-radar returns. The EKF estimator departs from previous works, in which the transition interface between the mixing layer (ML) and the free troposphere (FT) is modeled by means of an erf-like parametric function. In contrast to lidar remote sensing, where aerosols give strong backscatter returns over the whole ML, clear-air radar reflectivity returns (Bragg scattering from refractive turbulence) shows strongest returns from the ML-FT interface. In addition, they are corrupted by “insect” noise (impulsive noise associated with Rayleigh scattering from insects and birds), all of which requires a specific treatment of the problem and the measurement noise for the clear-air radar case. The proposed radar-ABLH estimation method uses: 1) a first preprocessing of the reflectivity returns based on median filtering and threshold-limited decision to obtain “clean” reflectivity signal; 2) a modified EKF with adaptive range intervals as time tracking estimator; and 3) ad hoc modeling of the observation noise covariance. The method has successfully been implemented in clear-air, single-layer, and convective boundary-layer conditions. ABLH estimates from the proposed radar-EKF method have been cross examined with those from a collocated lidar ceilometer yielding a correlation coefficient as high as ρ = 0.93 (mean signal-to-noise ratio, SNR = 18 (linear units), at the ABLH) and in relation to the classic THM.

Airborne dual-polarization observations of sea surface normalized radar cross section (NRCS) were conducted over the North Atlantic during January-February 2011. Observations were made using the University of Massachusetts' Imaging Wind and Rain Airborne Profiler radar system installed on the National Oceanic and Atmospheric Administration's WP-3D research aircraft during several winter storm events to determine the high-wind response of the sea surface NRCS for both horizontal and vertical polarizations. During the flights, the aircraft performed several constant-roll circle maneuvers to allow collection of NRCS over a range of incidence angles. We find consistency with prior reports in the polarization ratio observed at moderate incidence angles at the winds encountered. For larger incidence angles, we observe a measurable decrease in polarization ratio with increasing wind speed.

A contrast-based phase calibration algorithm for digital beamforming remote sensing radars using three contrast metrics is presented. The algorithm corrects time-varying antenna array phase errors that defocus digital beamforming remote sensing radar imagery. Amplitude errors are treated by equalizing the received powers in all elements. As such, the algorithm does not produce an absolute (or radiometric) calibration vector for the array. The performance of the algorithm is studied using a combination of simulated and real radar data under various conditions and is compared with a clutter-based calibration algorithm. An analytical proof showing that maximizing the expected value of the 4-norm metric is equivalent to phase-calibrating the image, except for a linear phase offset, is provided. We find that the clutter calibration algorithm performs best for statistically homogeneous scenes but that the contrast-calibration algorithms perform better with scenes with larger contrast ratios.

Total backscatter-coefficient inversion error bounds for the two-component lidar inversion algorithm (so-called Fernald's or Klett–Fernald–Sasano's method) are derived in analytical form in response to the following three error sources: 1) the measurement noise; 2) the user uncertainty in the backscatter-coefficient calibration; and 3) the aerosol extinction-to-backscatter ratio. The following two different types of error bounds are presented: 1) approximate error bounds using first-order error propagation and 2) exact error bounds using a total-increment method. Both error bounds are formulated in explicit analytical form, which is of advantage for practical physical sensitivity analysis and computational implementation. A Monte Carlo approach is used to validate the error bounds at 355-, 532-, and 1064-nm wavelengths.

A method is described for adjusting the far-field polarization of an electronically steered phased-array antenna. In this method, the polarization of a small subset of array elements is switched in order to reduce far-field cross-polarization of the overall array. The technique is intended for antennas used in polarimetric radars that measure quantities such as differential reflectivity$(Z_{\rm dr})$and specific differential phase$(K_{\rm DP})$. In particular, it is appropriate for lower cost arrays where only one transmit or receive polarization is active at a time. In such arrays, it will reduce the number of measurements needed by one-third. Analysis of the tradeoffs in the technique is presented as well as examples in hypothetical large arrays. Measured results are presented for a small 4$\times$4 array.

The dual-beam interferometer is an airborne instrument that combines two vertically polarized C-band along-track interferometric synthetic aperture radars (AT-InSARs) observing the surface below at different squints. The system was designed by the University of Massachusetts and saw several deployments in the early 2000s. An imagery of a small vessel with a rather pronounced wake pattern captured during one of such flights is the subject of this letter. Specifically, the interferometric phase in the turbulent wake exhibits a conspicuous banding structure that is still visible at distances more than 1 km behind the craft. The phase signatures from the fore and aft looks are combined to retrieve both longitudinal and lateral velocity components along cuts traversing the wake 400 and 750 m behind the boat. The results identify appreciable variations in the longitudinal velocity across the turbulent wake which are apparently consistent with the combined effect of the hull drag and the propeller backwash. A persistent pattern for the lateral component is also observed but is harder to interpret without the detailed knowledge of the vessel. The examples demonstrate the utility of AT-InSAR and, particularly, of a dual-beam AT-InSAR, for studies of centerline ship wakes. Readily available velocity signatures of a turbulent wake obtained with such systems can help with vessel classification tasks.

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.

Vertically polarized backscattered power, Doppler velocity, and interferometric height were measured in the nearshore ocean region using a high-resolution imaging microwave radar. The interferometric surface displacement measurements are compared with normalized radar cross sections (NRCS) and Doppler velocities, and with in situ pressure sensor estimates of wave height. The rms uncertainty in the interferometric surface displacement is computed from the data. The interferometric surface displacement measurements are intuitively satisfying in that positive displacements are generally associated with pixels that have larger NRCS values. Interferometric surface displacements compare well with heights derived from in situ pressure sensors, and we provide some possible explanations for the differences.

The Dual-Beam Interferometer is an airborne instrument that combines two along-track interferometric synthetic aperture radars observing the surface below at different squints. This configuration allows retrieving vector velocities of surface flows in a single aircraft pass. The system was designed by the University of Massachusetts and saw several deployments in the early 2000s. An imagery of a boat with a rather pronounced wake system captured during one of these flights is the subject of this paper. The velocity of the vessel is estimated based on the “train off the tracks” displacement in one of the looks. This estimate, which will be affected by uncertainty in target position due to smearing, is then used to remove unknown phase biases in the interferometric channels. Retrieved velocity variations are examined along cuts traversing the wake, with the focus on its narrow “turbulent” part. We find that the reconstructed velocities 150 m behind the boat are intuitively satisfying, but we are unable to fully account for the cross-wake component of velocity at 400 m behind the vessel.

This paper discusses the systems architecture of the CASA Phased Array Radar System, the Phase-Tilt Escan Radar System, for deployment in a CASA DCAS network of low power, solid-state phased array radars. The paper highlights the high-level system's architecture accompanied by measured data from the subsystems.

Mean longshore surface currents within the surf zone were measured using two remote sensing techniques: microwave Doppler radar and optical video. Doppler radar relies on small-scale surface roughness that scatters the incident electromagnetic radiation so that velocities are obtained from the Doppler shift of the backscattered radiation. Video relies on texture and contrast of scattered sunlight from the sea surface, and velocity estimates are determined using particle imaging velocimetry (PIV). This paper compares video PIV and Doppler radar surface velocities over a 1-km alongshore by 0.5-km cross-shore area in the surf zone of a natural beach. The two surface velocity estimates are strongly correlated (R2ges 0.79) over much of the surf zone. Estimates differ at the outer edge of the surf where strong breaking is prevalent, with radar-estimated velocities as much as 50% below the video estimates. The radar and PIV velocities at particular locations in the surf zone track each other well over a 6-h period, showing strong modulations in the mean alongshore flow occurring on 10-20-min time intervals. In one case, both systems observe a strong eddy-like mean flow pattern over a 200-m section of coastline, with the mean alongshore current changing direction at about the mid surf zone. The good spatial and temporal agreement between the two remote measurement techniques, which rely on very different mechanisms, suggests that both are reasonably approximating the true mean longshore surface velocity.

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.

Very fine space and time resolution observations of clear air reflectivity and vertical velocity were obtained in a day-time convective boundary layer by a frequency-modulated continuous-wave radar. Historically, most atmospheric FMCW radar investigations have focused on the extremely fine range resolution of which such radars are capable. When used in this mode, Doppler velocity information is usually lost due to the long integration time of the frequency sweep. That is, the effective pulse repetition frequency of the radar is so low that the Nyquist velocity interval is too narrow for useful measurements of atmospheric velocities. However, when configured for rapid profiling at the expense of either height coverage or spatial resolution, FMCW radars are capable of obtaining Doppler velocity timeseries from moderately sized resolution volumes at rates of several Hz. These are sufficient to resolve turbulent velocity variations in the inertial subrange down to timescales of approximately one second or less.

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.

Accurate detection and forecasting of severe storms has driven radar tornado probing as an important research topic that has added significantly to the understanding and prediction of severe weather phenomena. The need for close range observation, coupled with the fact that significant information is buried at low altitudes, has made mobile Doppler radars an important tool in the characterization of severe storms and related weather phenomena. The UMass XPol radar is one such truck mounted dual-polarized Doppler radar operating at 9.41 GHz. This paper documents the existing mobile radar system and presents close range, high resolution observations of Doppler velocity, reflectivity, differential reflectivity and cross-polarization correlation coefficient of a variety of storms observed during 2007. Additionally, the architecture of a planned pulse compression system upgrade is described.

The Microwave Remote Sensing Laboratory (MIRSL) at the University of Massachusetts operated its S- band Frequency Modulated Continuous Wave (FMCW) radar during the International H20 Project (IHOP_2002) over the months of May and June 2002. The radar operates at very high spatial and temporal resolutions, 2.4 m and 5 s, respectively, which allows the segregation of scatter from different scattering mechanisms. Rayleigh scattering from particulate scatterers (i.e. dust and insects) dominated the return, however Bragg scattering from turbulence was also significant, especially at the top of the afternoon convective bounday layer (CBL). Scattering from insects was isolated using a 5x5 median high-pass filter. The majority of reflectivity measurements from particulate scatterers ranged from -30 dBZ to -10 dBZ, however intense point-scatterers (> 0 dBZ) skewed the distribution which resulted in mean values much greater than the median values. There is a strong diurnal signal in the backscatter: minima in the morning and at dusk and a maximum mid-afternoon and in the nocturnal boundary layer. The strong diurnal signal suggests that with targeted allocation of radar resources return from insects can be used to monitor the clear-air CBL of the central Great Plains of North America.

The Imaging Wind and Rain Airborne Profiler (IWRAP) and Simultaneous Frequency Microwave Radiometer have been flown aboard the NOAA WP-3D "Hurricane Hunter" aircraft for the past five (2002-2006) hurricane seasons. IWRAP is a conically scanning, high resolution C- and Ku-band Doppler radar that profiles from the aircraft to ocean at four incidence angles. The microwave return from the ocean is used to infer ocean surface vector winds via scatterometry. The UMass Simultaneous Frequency Microwave Radiometer (USFMR) is a C- band radiometer that measures integrated rainfall rate and ocean surface wind speed. The combination of these two instruments allows for the determination of the effect of rain on scatterometer derived surface vector winds. Our focus is on scatterometer retrievals at an incidence angle of 50deg during Hurricanes Lili (2002) and Isabel (2003). The measurements were carried out under the Coupled Boundary Layers and Air-Sea Transfer (CBLAST) program and are the highest resolution radar measurements of the lower atmospheric boundary layer in powerful hurricanes. The retrievals at C- band use the CMOD5 geophysical model function (GMF) while those at Ku-band use one which is a synthesis of the QSCAT- 1 GMF and one developed using IWRAP data. As has been reported, the effect of rain at Ku-band is a dramatic decrease, even for wind speeds greater than 20 m s-1The atmospheric attenuation dominates these results. At C-band the primary effect is a decrease in azimuthal modulation which is especially important at high wind speeds where this modulation decreases in the absence of rain.

The ability of high-resolution imaging systems to resolve small-scale structure on the ocean surface suggests the possibility of using characteristics of Langmuir circulation to map the surface mixed-layer depth and near-surface current. We illustrate this using synthetic aperture radar and infrared imagery that are collected across the edge of the Gulf Stream (GS), which reveals surfactant streaks, or ldquowindrows,rdquo that are induced by Langmuir circulation. Based on changes in the windrow spacing and orientation, the mixed layer is estimated to deepen from 7 to 12 m across the edge of the GS and the current to increase from about 1 to 2 m/s. These spatial changes compare reasonably well with independent data, suggesting that the approach is plausible. It may also be possible to extract additional environmental information from the windrows.

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 recently established National Science Foundation Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) will be deploying the first generation of an automated network of four low-power, short-range, X-band, polarimetric, Doppler radars, known as NetRad, in central Oklahoma in late 2005. This network is developed with the goal of tracking tornadoes with high spatial and temporal resolution as well as mapping severe weather events in the lowest 2 km of the troposphere. Each radar node has been developed to accomplish this system goal through the coordinated interaction with other radars in the network via a real-time, closed-loop software control system. This paper will describe the characteristics of the individual radar nodes in the system, with emphasis on those aspects of the design that lend themselves toward operation as a coordinated network. Calibration results and performance characteristics of the single node radar of the first generation system will also be presented.

2034-2037

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.

The dual-beam interferometer consists of two interferometric synthetic aperture radars (InSARs), one squinted at 20/spl deg/ forward of broadside, and the other 20/spl deg/ aft, to allow measurement of vector surface velocity with only a single aircraft pass. Estimates of surface velocity vectors in the coastal region during high tidal flow are presented. The data were gathered over the barrier islands west of Fort Myers, Florida, as part of a March 2004 deployment. Whereas no detailed bathymetry data were available, high-quality aerial photography appears to be a useful tool in inferring bottom topography and possible current obstructions. The retrieved velocity field clearly follows the expected outflow pattern. While comparisons with tidal current magnitudes predicted by the U.S. National Ocean Service do reveal discrepancies of up to 0.5 m/s, these differences are most likely due to the contribution of ocean surface waves to the overall InSAR velocity measurement. Velocity retrievals for the same area based on the data from different tracks show good consistency. The results constitute the first demonstration of vector retrieval of the surface velocity field with a single-pass InSAR system and confirm the robustness of the dual-beam interferometry principle.

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.

We present observations of microwave radar backscattered power in the nearshore region, and results of a surface current estimation algorithm using microwave radar data. In low wind and wave conditions, patches of increased backscatter are observed in radar images. Animations of the images show these patches advected by nearshore flows such as wave induced cell circulations and longshore currents

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

The Dual Beam Interferometer (DBI) developed by University of Massachusetts (UMass) and an infrared camera operated by the Naval Research Laboratory (NRL) were jointly deployed during a March 2004 flight campaign off the east coast of Florida. Data collected produced simultaneous observations of features over the Gulf Stream's western boundary by both instruments. Use of instruments with different imaging capabilities enabled extraction of wind direction as well as current velocity measurement.

The Dual Beam Interferometer consists of two interferometric SARs, one squinted at 20 degrees forward of broadside, and the other 20 degrees aft, to allow estimation of vector surface velocity with only a single aircraft pass. It was developed by the University of Massachusetts and is operated in collaboration with the Naval Research Laboratory. The paper presents initial estimates of surface velocity vectors in the coastal region during high tidal flow. The data were gathered over the barrier islands west of Ft. Myers, Florida, as part of March 2004 deployment. While no attempt has been made at this stage to correct for Doppler contributions from surface waves, the retrieved velocity field clearly follows the expected outflow pattern, and velocity magnitudes agree well with in-situ data.

A bistatic radar system for measurement of clear-air winds is considered. The proposed system exploits bistatic Bragg scattering from refractive index turbulence which is visible to short wavelength radars (e.g. C-band and higher frequencies) for particular scattering geometries. Beam-limited scattering volume is considered, and the relative influences of Bragg scattering and Rayleigh scattering from particulate tracers are compared, as well as their influences on retrieved wind estimates. Provided system design constraints can be addressed, systems with relatively low power (e.g. hundreds of watts) are feasible.

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

A dual-beam along-track interferometric synthetic aperture radar that is entirely self-contained within an aircraft pod has been developed by the University of Massachusetts to study sea surface processes in coastal regions. The radar operates at 5.3 GHz with a bandwidth of up to 25 MHz. System hardware is described. Initial test flights aboard the National Oceanic and Atmospheric Administration's WP-3D research aircraft were performed to evaluate system performance over land and water surfaces. Imagery were collected for fore and aft squinted beams, though no interferometric data were collected. Notable look-angle dependences are observed in the sea surface normalized radar cross section under very low wind conditions.

A dual-beam along-track interferometric synthetic aperture radar which is self contained within an aircraft pod has been developed to study coastal regions. System hardware is described. Initial test flights aboard the NOAA WP-3D research aircraft were performed to evaluate system performance over land and water surfaces. Notable look-angle dependencies are observed in the sea surface NRCS under very low wind conditions.

The recent use of along-track interferometry (ATI) in synthetic aperture radar (SAR) has shown promise for synoptic measurement of ocean surface currents. ATI-SARs have been used to estimate wave fields, currents, and current features. This paper describes and analyzes a dual-beam along-track interferometer to provide spatially resolved vector surface velocity estimates with a single pass of an aircraft. The design employs a pair of interferometer beams, one squinted forward and one squinted aft. Each interferometric phase is sensitive to the component of surface Doppler velocity in the direction of the beam. Therefore, a proper combination of these measurements provides a vector surface velocity estimate in one pass of the aircraft. The authors find that precise measurements dictate widely spaced beams and that the spatial resolution for the squinted SAR is essentially identical to the sidelooking case. Practical instrument design issues are discussed, and an airborne system currently in development is described. Through computer simulation, they observe the azimuthal displacement of interferometric phases by moving surfaces identical to those of conventional SAR and find that such displacement can bias the estimated surface velocity.

A unique focused array imaging Doppler radar was used to measure directional spectra of Ocean surface waves in a nearshore experiment performed on the North Carolina Outer Banks. Radar images of the ocean surface’s Doppler velocity were used to generate two dimensional spectra of the radial component of the ocean surface velocity field. These are compared to simultaneous in-situ measurements made by a nearby array of submerged pressure sensors. Analysis of the resulting two-dimensional spectra include comparisons of dominant wave lengths, wave directions, and wave energy accounting for relative differences in water depth at the measurement locations. Limited estimates of the two-dimensional surface displacement spectrum are derived from the radar data. The radar measurements are analagous to those of interferometric synthetic aperture radars (INSAR), and the equivalent INSAR parameters are shown. The agreement between the remote and in-situ measurements suggests that an imaging Doppler radar is effective for these wave measurements at near grazing incidence angles.

FOPAIR, a FOcused Phased Array Imaging Radar, provides high-resolution X-band images of the ocean surface. The system is designed to provide high-speed imagery (up to 180 frames/s) for short range applications (50-400 m) from a fixed platform such as a pier or tower. FOPAIR employs a fast, sequentially sampled antenna array and uses a software-based beamforming technique to generate high resolution imagery without the need for multiple radar receivers or beamforming hardware typical of active phased arrays. A summary of the principles of operation and the design of the instrument is given, followed by examples of FOPAIR's imaging capability. To the authors' knowledge, these examples include the highest-resolution, highest-speed microwave images of the ocean surface produced to date. A brief comparison between FOPAIR and synthetic aperture radar techniques is also included.>