An Unattended Cloud-Profiling Radar for Use in Climate Research

Abstract

A new millimeter-wave cloud radar (MMCR) has been designed to provide detailed, long-term observations of nonprecipitating and weakly precipitating clouds at Cloud and Radiation Testbed (CART) sites of the Department of Energy's Atmospheric Radiation Measurement (ARM) program. Scientific requirements included excellent sensitivity and vertical resolution to detect weak and thin multiple layers of ice and liquid water clouds over the sites and longterm, unattended operations in remote locales. In response to these requirements, the innovative radar design features a vertically pointing, single-polarization, Doppler system operating at 35 GHz (K a band). It uses a low-peak-power transmitter for long-term reliability and high-gain antenna and pulse-compressed waveforms to maximize sensitivity and resolution. The radar uses the same kind of signal processor as that used in commercial wind profilers. The first MMCR began operations at the CART in northern Oklahoma in late 1996 and has operated continuously there for thousands of hours. It routinely provides remarkably detailed images of the ever-changing cloud structure and kinematics over this densely instrumented site. Examples of the data are presented. The radar measurements will greatly improve quantitative documentation of cloud conditions over the CART sites and will bolster ARM research to understand how clouds impact climate through their effects on radiative transfer. Millimeter-wave radars such as the MMCR also have potential applications in the fields of aviation weather, weather modification, and basic cloud physics research.

The Cloudsat Mission and the a-Train

“…Cloud radars now operate routinely or quasiroutinely at a number of surface sites worldwide (e.g., Moran et al 1998). These millimeter-wavelength radars operate at wavelengths of approximately 3 or 8 mm (or frequencies of 94 or 35 GHz, respectively) and are currently deployed on various research aircraft.…”

Rainfall Profiling Using Atmospheric Radiation Measurement Program Vertically Pointing 8-mm Wavelength Radars

“…Since its first days in the early 1990s, the ARM program has invested heavily (both financially and intellectually) in the development of remote sensing instrumentation and methods to retrieve parameters of atmospheric water vapor and clouds in both ice and liquid phases. The K a -band (34.6 GHz) millimeter wavelength cloud radar (MMCR; Moran et al 1998) designed by the National Oceanic and Atmospheric Administration's Environmental Technology Laboratory (NOAA/ETL) has been one of the most successful ARM instruments for collecting vertically resolved cloud information. Long records of MMCR measurements are available from Cloud and Radiation Test bed (CART) sites located in the key areas over the globe, including Oklahoma, Alaska, Australia, and islands of the Pacific Ocean.…”

Millimeter-Wave Radars for Environmental Studies

“…The transmitters for 36 GHz radars are usually based on conventional magnetrons or travelling-wave tubes (TWT). The magnetron transmitters, however, often suffer from a low reliability of conventional magnetrons for this frequency band [7]. The application of TWTs makes it necessary to use a pulse compression technique, since such tubes have typically a low level of the peak power, but they can operate with a high value of the duty factor [7].…”

“…During the last decade, there are growing activities related both with the development and applications of the millimeter-wave radar systems [4][5][6][7]. Such activities have been stimulated by several international programs aimed at investigating the global climate change.…”