This paper reviews hardware for the Cloud Profiling Radar System (CPRS) and presents dual-frequency measurements that illustrate how CPRS reflectivity data may be used for cloud particle sizing. Reflectivity data show Mie scattering in the ice region, melting layer, and rain region of a stratiform cloud with light, broken precipitation. Measurements of Ze{sub 95} and Ze{sub 33} with and without precipitation show that differential attenuation is low and does not dominate the reflectivity differences. A theoretical model of Ze{sub 95} - Ze{sub 33} versus mean particle diameter for monodisperse and Gaussian size distributions of water droplets is presented to illustrate the concept of particle sizing using dual-wavelength reflectivity data.

Spatial variations in the time-average level of microwave backscatter from the ocean surface are often observable and are related to variations in surface roughness. Spatial variability is also observable in the modulations of radar backscatter. The authors report observations of such variability in measurements obtained with the FOPAIR imaging radar. This radar provides image sequences of the zeroth and first moments of the Doppler spectrum. Spectral analysis performed on each image pixel's time-series yields a set of backscatter and velocity variance images, with each image tuned to a particular frequency. The authors present open ocean data obtained from the R/P FLIP during the 1995 Marine Boundary Layer Experiment during the early development of a storm. At low (swell) frequencies, the authors observe spatial variations in modulation with a mottled, somewhat random structure. The spatial variation of the structure seen at this frequency is finer than the wavelength of the corresponding long waves. At higher frequencies near and beyond the wind-wave peak, linear structures roughly aligned with the wind direction are evident in several cases. The crosswind spatial frequency of these structures was observed to correlate with the temporal frequency. These patterns were most observable early in the development of the storm and appear to be a consequence of wave-wave interference under gradually turning wind conditions

One of the primary objectives of the Fall 1997 IOP was to intercompare Ka-band (350Hz) and W-band (95GHz) cloud radar observations and verify system calibrations. During September 1997, several cloud radars were deployed at the Southern Great Plains (SOP) Cloud and Radiation Testbed (CART) site, including the full time operation 35 GHz CART Millimeter-wave Cloud Radar (MMCR), the University of Massachusetts (UMass) single antenna 33GHz/95 GHz Cloud Profiling Radar System (CPRS), the 95 GHz Wyoming Cloud Radar (WCR) flown on the University of Wyoming King Air, the University of Utah 95 GHz radar and the dual-antenna Pennsylvania State University 94 GHz radar. In this paper the authors discuss several issues relevant to comparison of ground-based radars, including the detection and filtering of insect returns. Preliminary comparisons of ground-based Ka-band radar reflectivity data and comparisons with airborne radar reflectivity measurements are also presented.

The University of Massachusetts Microwave Remote Sensing Laboratory and NASA Jet Propulsion Laboratory have developed a 95 GHz airborne radar system for remote sensing of clouds. This instrument was recently operated aboard NASA's DC-8 Airborne Laboratory and participated in the Cloud Layer Experiment (CLEX) in the central U.S. and in the Southern Alps Experiment (SALPEX) in New Zealand. The development of this system was motivated by the need for a sensitive, well-calibrated millimeter-wave cloud radar that can probe clouds from above. This geometry avoids the attenuation suffered by ground based systems that look up through precipitation and also simulates the viewing geometry of a spaceborne sensor. This paper describes the design and operating characteristics of the instrument as well as preliminary results from the initial deployments. Engineering test flights were conducted during June 1996, concurrent with CLEX. The instrument also collected data during two flights from California to Hawaii and New Zealand and another flight near New Zealand. Data from the flights are used to demonstrate the instruments capabilities. The data from both experiments are classified into the four classes of cloud systems used by the GEWEX Cloud System Study (GCSS). Reflectivity statistics for each class of cloud system are presented.

The University of Massachusetts' Microwave Remote Sensing Laboratory (MIRSL) has developed a unique high spatial resolution multiparameter radar under sponsorship from the Department of Energy's Atmospheric Radiation Measurement (ARM) program. The Cloud Profiling Radar System (CPRS) uses a single one-meter diameter dielectric lens antenna to make collocated polarimetric and Doppler measurements at both 33 GHz and 95 GHz. The polarization of each transmitted pulse at either frequency can be selected on a pulse-to-pulse basis. The radar and supporting hardware are mounted on a truck that serves as a mobile laboratory. The truck-based platform permits CPRS to operate in remote locations and also serves as an economical means of transporting the system.

Quadrant Engineering has recently developed a compact, low power, marine boundary layer radar wind profiler (MBL Profiler) suitable for installation on a small boat or on a buoy. The MBL-Profiler utilizes high-efficiency radar and data acquisition componentry to minimize power consumption, with the radar and data system requiring approximately 60 W for full power operation. Additional power of about 15 W will be required to operate a low power PC and telemetry system. If used intermittently, (30 minute consensus wind estimate, every 2 hours), the system will draw less than 20 W average power, making it suitable for battery-powered operation. Motion compensation is achieved entirely in software. During data acquisition the position of the antenna is constantly monitored by storing the output of two tilt sensors and a compass. This is sufficient information to provide an accurate estimate of average wind speed and direction.

The Microwave Remote Sensing Laboratory (MIRSL) at the University of Massachusetts has developed a unique high-resolution Cloud Profiling Radar System (CPRS). This radar is capable of producing detailed three-dimensional images of cloud parameters which should improve our understanding of the composition and dynamics of non-precipitating clouds. This paper briefly describes the CPRS hardware and presents collocated dual-frequency cloud images taken in initial field trials during the summer of 1993.

Polarimetric radar measurements carried out at 95 and 225 GHz are presented for fresh and refrozen snow cover. These data indicate that the Mueller matrix for snow cover consisting of spherical ice particles has a relatively simple form, with 10 of the 16 elements approximately zero. Measurements of new-fallen snow consisting of predominantly nonspherical snow crystals are also presented. The anisotropic structure of such snow cover results in a more complex Mueller matrix, fitting the general form for natural surfaces. An analytic expression for the Mueller matrix of isotropic snow cover is derived by computing the response of a semi-infinite layer of scatterers that are insensitive to the orientation of the incident polarization. This matrix is shown to accurately predict the polarimetric response of the snow cover comprised of spherical ice particles based solely on copolarized and cross-polarized radar cross-section measurements. >

Range measurements made by satellite radar altimeters experience an electromagnetic (EM) bias toward the troughs of ocean waves. Measurements taken with the NASA altimeter on the TOPEX/Poseidon satellite in a series of aircraft flights during the Surface Wave Dynamics Experiment (SWADE) indicate that EM bias is slightly higher at 5.3 GHz than at 13.6 GHz, and that the magnitudes of both biases increase with increasing wind speed, as does their difference. Tower, airborne, and satellite measurements show a consistency in the characteristics of the wind speed dependence but suggest that bias decreases with increasing altitude. The airborne measurements appear to be the most reasonable basis for correcting the NASA altimeter range data from the TOPEX/POSEIDON satellite. A preliminary analysis of data acquired at 20.3 m/s in the Southern Ocean Waves Experiment (SOWEX) has given confidence that the quadratic models for the prelaunch EM bias corrections are more appropriate for wind speed dependence than linear models. >

Two high-power millimeter-wave polarimeters, operating at 95 and 225 GHz, have been developed by the University of Massachusetts Microwave Remote Sensing Laboratory for field experimentation. Utilizing these instruments, polarimetric measurements of backscatter from snowcover were carried out between 1989-1992 for both fresh and refrozen snowcover. These data indicate that the Mueller matrix for snowcover consisting of spherical ice particles (sleet) has a relatively simple form, with ten of the sixteen elements approximately zero. Measurements of new-fallen snow consisting of predominantly nonspherical snow crystals exhibited more complex scattering behavior, fitting the general form of the Mueller matrix for natural surfaces.<>

The proposed Cloud Profiling Radar System (CPRS) is a two frequency (35 GHz, 95 GHz) polarimetric radar with a single reflector-lens antenna. The system will be used to perform three dimensional Doppler and polarimetric measurements on clouds. The various subsystems are currently being developed and this report gives technical details about the status of these subsystems. This report also updates other research activities. 7 figs.

This paper describes the first polarimetric radar measurements of foliage made in the 220 GHz transmission window. A noncoherent, 60 W peak-power polarimetric radar was used to directly measure the target Mueller matrix by measuring the scattered polarization state for either four or six incident polarizations. Measurements of deciduous trees indicate that waves scattered from erectophil trees (vertically oriented leaves) are more highly polarized than waves scattered from planophil trees (horizontally oriented leaves) for near-grazing incidence angles. White Pine trees, which have thin needles, were the least polarized of all trees studied. A comparison of the Mueller matrices of 11 independent footprints taken from 7 White Pine trees showed a high degree of consistency between measurements.

With the availability of scatterometers at millimeter wavelengths, it is important to understand the scattering mechanisms of vegetation canopies. Until now little has been known about how leaves scatter at frequencies above 35 GHz. Modern network analyzers now make it possible to measure the backscattering cross section of single leaves at 94 GHz.

Radio communications in 1977 includes diverse fields of engineering that were unheard of at the beginning of the century when engineers struggled with pioneering studies of radio telegraphy. Today, exhaustive efforts in communications and information theory, as well as fundamental studies of radio science, have resulted in a technology that allows efficient communication between individuals and machines. The evolution of this technology in the United

The spontaneous emission of longitudinal waves in various gas discharges (air, argon, helium and. neon) has been observed experimentally to agree with the dispersion relationship obtained from theory. The power spectral density of electron oscillations has been measured with a wide dispersion microwave spectrum analyser coupled to a specially designed plasma filled capacitor. The emission from these oscillations is seen to be strongly dependent on the electron-neutral collision frequency and the spacing between the two conducting plates.