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Abstract As part of the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) field campaign, a very high-resolution, mobile, W-band Doppler radar collected near-surface (≤200 m AGL) observations in an EF-0 tornado near Tribune, Kansas, on 25 May 2010 and in sub-tornado-strength vortices near Prospect Valley, Colorado, on 26 May 2010. In the Tribune case, the tornado's condensation funnel dissipated and then reformed after a 3-min gap. In the Prospect Valley case, no condensation funnel was observed, but evidence from the highest-resolution radars in the VORTEX2 fleet indicates multiple, sub-tornado-strength vortices near the surface, some with weak-echo holes accompanying Doppler velocity couplets. Using high-resolution Doppler radar data, the authors document the full life cycle of sub-tornado-strength vortex beneath a convective storm that previously produced tornadoes. The kinematic evolution of these vortices, from genesis to decay, is investigated via ground-based velocity track display (GBVTD) analysis of the W-band velocity data. It is found that the azimuthal velocities in the Tribune tornado fluctuated in concert with the (dis)appearance of the condensation funnel. However, the dynamic pressure drop associated with the retrieved azimuthal winds was not sufficient to account for the condensation funnel. In the Prospect Valley case, the strongest and longest-lived sub-tornado-strength vortex exhibited similar azimuthal velocity structure to the Tribune tornado, but had weaker azimuthal winds. In both cases, the radius of maximum azimuthal wind was inversely related to the wind speed, and changes in the axisymmetric azimuthal component of velocity were consistent with independent indicators of vortex intensification and decay.

In this letter, 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 (PA) in transmission. This issue is of particular importance in meteorological radar applications, as they require to transmit pulse 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. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2008.10.007 Byline: George O. Marmorino (a), Geoffrey B. Smith (a), Jakov V. Toporkov (a), Mark A. Sletten (a), Dragana Perkovic (b), Stephen J. Frasier (b) Keywords: Thermal convection; Langmuir circulation; Surface mixed layer; Sea-surface temperature; Cool skin; Surfactant; Remote sensing; Infrared imagery; Synthetic aperture radar Abstract: Airborne infrared and synthetic aperture radar imagery collected over the Gulf Stream are used to examine the surface patterns of small-scale thermal convection and wind-driven Langmuir circulation. These patterns have a thermal contrast of [approximately equal to]0.25[degrees]C, which is roughly an order of magnitude larger than predicted by large-eddy simulations but consistent with the effect on surface temperature of surfactant accumulations induced by mixed-layer eddies. Author Affiliation: (a) Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375, USA (b) Microwave Remote Sensing Laboratory, University of Massachusetts, Amherst, MA 01003, USA Article History: Received 15 February 2008; Revised 20 October 2008; Accepted 28 October 2008

The dual-beam interferometer consists of two interferometric synthetic aperture radars (InSARs), one squinted at 20[degrees] forward of broadside, and the other 20[degrees] 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, FL, 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. Index Terms--Along-track interferometry, ocean surface currents, synthetic aperture radar (SAR).

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 teyclones (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[degrees], 35[degrees], 40[degrees], and 50[degrees]) 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. Index Terms--Atmospheric boundary layer (ABL), cyclone, ocean remote sensing, precipitation, scatterometry.

High-resolution dual-polarization X-band images of the ocean surface were obtained at a grazing angle of about 3 [degrees]. Area extensive imaging allowed us to study backscatter properties of sea spikes and to compare radar measurements with visual surface features evident from video recordings. The vertically polarized radar images consist of distributed scatter whose amplitude and Doppler velocity are modulated by larger scale gravity waves consistent with Bragg scattering and composite surface theory (CST). The horizontally polarized radar images are dominated by spatially discrete scattering centers (or sea spikes) moving at velocities comparable to the phase velocities of gravity waves beyond the spectral peak. These sea spikes also exist in the corresponding V-pol radar images, but are less prominent due to the dominant Bragg backscatter. Sea spikes are characterized by polarization ratios H/V that often exceed unity, typically by about 5 dB. Comparison of the larger spikes with simultaneous co-registered video recording of the surface indicates that approximately 30% of observed sea spikes are associated with actively breaking waves (whitecaps) while the remainder are identified with 'steep' wave features. By classifying the larger sea spikes according to their corresponding surface features, we find Doppler velocities for sea spikes due to whitecaps noticeably faster (about 50%) than other sea spikes, though the distributions for both overlap significantly. We also find little measurable difference in the polarization ratios of the two classes of sea spikes as observed on the open ocean. Index Terms - Sea surface electromagnetic scattering.

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 our 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.

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. We 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, we 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. Index Terms--Along-track, interferometry, ocean surface currents.

The local structure and evolution of the convective boundary layer (CBL) are studied through measurements obtained with a volume-imaging radar, the turbulent eddy profiler (TEP). TEP has the unique ability to image the temporal and spatial evolution of both the velocity field and the local refractive index structure-function parameter, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. Volumetric images consisting of several thousand pixels are typically formed in as little as 1 s. Spatial resolutions are approximately 30 m by 30 m by 30 m. CBL data obtained during an August 1996 deployment at Rocks Springs, Pennsylvania, are presented. Measurements of the vertical [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] profile are shown, exhibiting the well-known bright band near the capping inversion at [z.sub.i], as well as intermittent plumes of high [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. Horizontal profiles show coherent 100-m-scale [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and vertical velocity (w) structures that correspond to converging horizontal velocity vectors. To quantify the scales of structures, the vertical and streamwise horizontal correlation distances are calculated within the TEP field of view. To study the statistics and scales of larger structures, effective volumes larger than the TEP field of view are constructed through Taylor's hypothesis. Statistics of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and w time series are compared to an appropriately scaled large eddy simulation (LES). While w time series comparisons agree very well, the LES [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] predictions agree only with some of the measured data. Finally, the scales of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] structures in the TEP time series measurements are calculated and compared to the scales in the LES spatial domain. Good agreement is found only near the capping inversion layer, the area of largest structures. This study highlights the unique capabilities of the TEP instrument, and shows what are believed to be the first statistical comparisons of measured [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] data with LES derived results.