Battle With Bugs Nearly Over Thanks to New Radar

 
Published: 15 July 2005

The new W-band ARM cloud radar, or WACR, provides improved sensitivity for detecting tiny objects in the atmosphere to an altitude of 5 km. The instrument's antenna is located adjacent to the [/instruments/instrument.php?id=mmcr][millimeter wave cloud radar (MMCR)] antenna on top of the MMCR shelter; the rest of the unit is located inside (inset).

The main purpose of the millimeter wavelength cloud radar (MMCR) is to measure cloud boundaries (i.e., cloud tops and bottoms), and to record the reflectivity profile of the atmosphere up to 20 km. Unfortunately, for a great portion of the year at the ARM Southern Great Plains (SGP) site, data from the MMCR are often contaminated by “atmospheric plankton” (tiny bugs and dust particles) at altitudes up to 5 km. Researchers analyzing MMCR data from several experiments concluded that trying to differentiate between the clouds and atmospheric plankton with the current set of instruments was extremely time consuming and inexact. To solve this dilemma, a new W-band ARM cloud radar (WACR) was designed and built during the past year, and was installed in the MMCR instrument shelter at the SGP Central Facility in early July.

Built by ProSensing, the WACR is a Doppler radar that returns signals of reflectivity, velocity, and spectral width (which corresponds to turbulence). Both the WACR and MMCR have co-polarization and cross-polarization channels to differentiate between spherical (e.g., raindrops) and nonspherical (e.g., insects and ice crystals) atmospheric objects, but the new radar operates at 95 GHz, whereas the MMCR operates at 35 GHz. The new radar complements the existing MMCR by differentiating between clouds and spurious radar returns due to insects and other detritus in the lower atmosphere. By collocating these two radars and their various modes of operation, researchers will now have the data to explore dual wavelength techniques such as retrieval of drizzle parameters, etc. Deployment of the WACR represents a key milestone for user enhancements at the SGP Central Facility.