The National Research Council of Canada (NRC) operates NRC Airborne W-band (NAW) cloud radar onboard the NRC Convair-580 research aircraft. In this study, we implemented and tested a passive channel to the W-band radar, enabling the reception of radiometric and radar measurements of clouds in an interleaving mode, unlike CloudSat Cloud Profiling Radar. This paper presents the calibration procedure of the new radiometric mode and its verification against a radiative transfer model under clear-sky conditions. In the analysis, we include the derivation of a robust temperature-dependent correction that mitigates environmental bias in the sky data. Calibrated brightness temperatures show great sensitivity to liquid clouds, as shown by staircase sampling of a warm stratocumulus cloud deck.

The University of Wyoming (UW) acquired a new compact airborne pulsed Ka-band (8-mm wavelength) Precipitation Radar (KPR) in 2016. Developed by ProSensing Inc. in collaboration with the UW Atmospheric Science Department, this radar operates from a standard Particle Measurement Systems (PMS) canister. Key components are an arbitrary transmit pulse waveform generator, a 10 W solid state power amplifier, and a pair of 14 cm diameter flat plate slotted waveguide array antennas for interleaved profiling above and below the aircraft. KPR is installed on the right wing of the UW King Air research aircraft (UWKA). The combined use of KPR, UWKA 3-mm wavelength cloud radar (WCR), cloud lidar (WCL), and in situ instruments allows for a better retrieval of cloud and precipitation properties and analysis of weather processes. In this paper we present this new Ka-band radar and show an example of the synergy between the in situ and the remote sensing instruments on board UWKA.

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 plusmn1, plusmn3, plusmn7, and plusmn14 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.

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 1, 183.31 3, 183.31 7, and 183.31 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.

Millimeter-wave radars have been used since the early 1950s to study clouds and precipitation, but until recently these early instruments were limited to simple backscatter power measurements and were plagued by hardware problems. However, development of solid-state millimeter-wave componentry and high-power klystron amplifiers has spurred the evolution of reliable, coherent radars operating up to 95 GHz. In addition, advances in digital signal processing technology have resulted in single-card processors that can simultaneously execute algorithms to compute reflectivity, Doppler, and polarimetric quantities in real time. A review of the current state of the art in millimeter-wave cloud radars is presented, including a discussion of transmitters, antennas, and receiver components. Two radar systems built by the University of Massachusetts are described, including a mobile, dual-frequency (33- and 95-GHz) polarimetric radar, and an airborne 95-GHz polarimetric radar that was recently flown in a cooperative experiment with the University of Wyoming. Spaceborne applications are also discussed, especially the use of satellite-based 95-GHz radars for measuring the vertical distribution of clouds.>

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. The authors also describe the tradeoffs between spatial resolution and 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.>

An airborne C-band scatterometer system (C-Scat) has been developed to remotely sense ocean surface winds and improve upon the present understanding of the relationship between normalized radar cross section (NRCS) and ocean surface roughness influences such as wind speed and direction, wave height and slope, and the air-sea temperature difference. The scatterometer utilizes a unique frequency-steered microstrip array antenna that is installed beneath the fuselage of an airplane. The antenna is electronically scanned in elevation, from 20 degrees to 50 degrees off-nadir, and mechanically spins in azimuth. The system is capable of measuring ocean surface NRCS from altitudes as high as 25000 ft. The system is divided into four subsystems: the transmitter and receiver, the spinning antenna, the computer control and data acquisition subsystem, and the digital and analog interface electronics.>