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ProSensing Inc. has developed a G-band (183 GHz) water Vapor Radiometer (GVR) for long-term unattended measurements of low concentrations of atmospheric water vapor and liquid water. Precipitable water vapor (PWV) and liquid water path (LWP) are estimated from zenith brightness temperatures measured using four double-sideband receiver channels, which are centered at 183.31 [+ or -] 1, 183.31 [+ or -] 3, 183.31 [+ or -] 7, and 183.31 [+ or -] 14 GHz. A prototype ground-based version of the instrument was deployed at the Department of Energy Atmospheric Radiation Measurement program's North Slope of Alaska site near Barrow, AK, in April 2005, where it collected data continuously for one year. This paper presents design details, laboratory test results, and examples of retrieved PWV and LWP from measured brightness temperature data. Index Terms--Millimeter-wave radiometry, precipitable water vapor (PWV) and liquid water path (LWP) retrieval, remote sensing.

A new G-band (183.31-GHz) water-vapor radiometer, developed and built by ProSensing Inc., was deployed in Barrow, AK, in April 2005. The radiometer is part of a suite of instruments maintained by the Atmospheric Radiation Measurement program. The instrument measures brightness temperatures from four double-sideband channels centered at [+ or -]l, [+ or -]3, [+ or-]7, and [+ or -]14 GHz from the 183.31-GHz water-vapor line. Atmospheric emission in this spectral region is primarily due to water vapor, with some influence from liquid water. In this paper, data collected in November 2005, December 2005, and January 2006 are analyzed. Measurements are compared with simulations obtained by using a radiative transfer model. We show that the measurements agree well with model simulations. Precipitable water vapor (PWV) and liquid water path (LWP) are retrieved with a nonlinear physical algorithm, and results are compared with those from the colocated dual-channel microwave radiometer and radiosondes. Retrieval errors are estimated to be below 5% for PWV and of the order of 0.006 mm for LWP. Index Terms--Microwave radiometry, remote sensing, water-vapor retrieval, 183 GHz.

An experiment whose objective was to determine the wind and reflectivity substructure of severe convective storms is detailed. A 3-mm-wavelength (95 GHz) pulsed Doppler radar was installed in a van and operated in the Southern Plains of the United States during May and early June of 1993 and 1994. Using a narrow-beam antenna with computer-controlled scanning and positioning the van several kilometers from targets in severe thunderstorms, the authors were able to achieve 30-m spatial resolution and also obtain video documentation. A dual-polarization pulse-pair technique was used to realize a maximum unambiguous velocity of [+ or -]80 m [s.sup.-1]. Analyses of data collected in a mesocyclone near the intersection of two squall lines, in a low-precipitation storm, and in a hook echo in a supercell are discussed. A strategy to achieve 10-m spatial resolution and obtain analyses of the internal structure of tornadoes is proposed.

Polarimetric measurements contain errors owing to random thermal energy in the receiver and system phase noise. These errors can be reduced using estimation techniques that account for general properties of the Mueller matrix. In this paper, we show how Kalman filter techniques improve and speed up the estimation of a target's Mueller matrix when the noncoherent measurement technique is used. Measurements obtained with a 95-GHz polarimeter demonstrate that fewer independent samples of the backscattered fields are needed to obtain an accurate estimate if Kalman filtering is used than if a pseudo inversion process is used.

A 95 GHz dual-polarization radar system was developed and flown on the University of Wyoming King Air research aircraft, from which it measured reflectivity, depolarization, and Doppler-derived velocity mean and standard deviation of a variety of clouds. This paper describes the radar and a data acquisition system that uses commercially available digitizers, signal processors, and signal generators. We also describe the tradeoffs between spatial resolution and our ability to estimate reflectivity and velocity. This paper presents the first known airborne measurements of clouds made at 95 GHz; these are thought to be the most highly resolved millimeter-wave cloud images made to date. Depolarization, measured in terms of the linear depolarization ratio (LDR), was especially high in the melting band and in regions containing pristine ice crystals. These measurements demonstrate the advantages that high-spatial-resolution airborne millimeter-wave radars offer for the study of cloud microphysical properties.

This work describes the implementation of polarization diversity on the National Research Council Canada W-band Doppler radar and presents the first-ever airborne Doppler measurements derived via polarization diversity pulse pair processing. The polarization diversity pulse pair measurements are interleaved with standard pulse pair measurements with staggered pulse repetition frequency; this allows a better understanding of the strengths and drawbacks of polarization diversity, a methodology that has been recently proposed for wind-focussed Doppler radar space missions. Polarization diversity has the clear advantage of making possible Doppler observations of very fast de-correlating media (as expected when deploying Doppler radars on fast moving satellites) and of widening the Nyquist interval, thus enabling the observation of very high Doppler velocities (up to more than 100m/s in present work). Cross-talk between the two polarizations, mainly caused by depolarization at backscattering deteriorated the quality of the observations by introducing ghost echoes in the power signals and by increasing the noise level in the Doppler measurements. In the different cases analyzed during the field campaigns, the regions affected by cross-talk were generally associated with highly depolarized surface returns and depolarization of backscatter from hydrometeors located at short ranges from the air craft. The variance of the Doppler velocity estimates can be well predicted from theory and were also estimated directly from the observed correlation between the H-polarized and V-polarized successive pulses. The study represents a key milestone towards the implementation of polarization diver sity in Doppler space-borne radars. [ABSTRACT FROM AUTHOR]

The dryline has long been associated with the development of severe thunderstorms in the southern plains during the spring and early summer months. The propagation and structure of the dryline are closely tied to surface processes that are neither well understood nor well resolved with current observational capabilities. As a result, there are often large errors in forecasts of dryline position and structure. Improvements in radar technology have allowed for better observations of the dryline in recent years. Here, very finescale radar observations taken with the University of Massachusetts—Amherst (UMass) mobile W-band radar during an International H2O Project (IHOP) double-dryline event on 22 May 2002 in the Oklahoma panhandle are presented. The observations are placed in the context of the dryline secondary circulation, which describes flow in a plane normal to the dryline. The narrow, half-power beamwidth of the antenna on the W band (0.18°) permitted the measurements of channels of upward (8–9 m s-1 over a horizontal distance of 50–100 m) and downward vertical velocity, greater in absolute magnitude than that previously reported in dryline field studies. A ground-based variational pseudo-multiple-Doppler processing technique is introduced, which is used to decompose time series of RHI velocity data into horizontal and vertical wind components. The technique is applied to a retrograding dryline from 22 May 2002. Finescale structure of the retreating dryline interface is presented. [ABSTRACT FROM AUTHOR]

The Polarization Diversity Pulse-Pair (PDPP) technique can extend simultaneously the maximum unambiguous range and the maximum unambiguous velocity of a Doppler weather radar. This technique has been applied using a high-resolution 95-GHz radar to study the reflectivity and velocity structure in severe thunderstorms. This paper documents the technique, presents an analysis of the first two moments of the estimated mean velocity, and provides a comparison of the results with experimental data, including PDPP images of high-vorticity regions in supercell storms. [ABSTRACT FROM AUTHOR]