Ground-based and Airborne Weather Radars and Lidar for Observing Atmosphere

The Earth Observing Laboratory (EOL) at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado develops and deploys state-of-the-art radar and lidar instruments, for both ground and airborne operation, to advance scientific understanding of the atmosphere.

The ground-based S-band polarimetric radar (S-Pol) is equipped with dual-wavelength capability (S-band and K_a-band). The two radars record simultaneous dual-polarimetric measurements. Dual-polarization measurements are used for identifying rain, snow, hail and for quantifying precipitation amount. The entire S-Pol radar system, including power generators and operations control, is packaged into six 20' sea containers for transportation. S-Pol is the only S-band radar that is relatively easy to transport for deployments in the USA and overseas. Its agile radar control software makes it easily configurable to meet the individual scientific needs of researchers. In fact, many scientific users design radar scan strategies and actually operate the radar during field experiments. An advanced suite of real-time algorithms is used to provide value-added products, namely, precipitation particle types, rain rate and moisture fields.

In order to capture faster moving weather events such as tornadoes, record observations of clouds and precipitation systems over rugged mountainous terrain and observe detailed kinematics of eyewalls in hurricane rainbands over the ocean, an airborne X-band Doppler radar (ELDORA) is used. The ELDORA is a dual-beam, Doppler radar. ELDORA's two antennas extend back from the tail of a Lockheed P-3 aircraft and spin about the longitudinal axis of the aircraft. As the aircraft flies, ELDORA traces two conical helixes within 50-100 km of the aircraft. This scanning pattern enables us to observe the atmosphere with two separate looks for estimating 3-D winds. ELDORA is the only airborne Doppler radar that is sensitive enough to detect winds in the clear air.

Precipitation or cm radars are not sensitive enough to detect cloud droplets. One of the attractive features of a millimeter wave radar system is its ability to detect micron-sized particles that constitute clouds with lower than 0.1 g m^-3 liquid or ice water content. The engineering specifications of such a radar are mainly driven by climate, Earth's radiation budget, and cloud initiation studies. The EOL is in the process of building the first phase of a three phase dual wavelength W/K_a-band airborne cloud radar to be called the HIAPER Cloud Radar (HCR). This phase is a pod based W-band radar system with scanning capability. The second phase will add pulse compression and polarimetric capability to the W-band system, while the third phase will add a complementary K_a-band radar. The pod-based radar is primarily designed to fly on the Gulfstream V (GV) and C-130 aircraft. It is a part of the HIAPER (High-performance Instrumented Airborne Platform) Aircraft Instrumentation Solicitation (HAIS).

The envisioned capability of a millimeter wave radar system on HIAPER is enhanced by coordination with microwave radiometer, in situ probes, and especially by the NCAR GV High-Spectral Resolution Lidar (HSRL) which is also under construction. The lidar, designed and built by the University of Wisconsin, provides unique measurements of optical depth of clear air, clouds and precipitation. The combination of the lidar and cloud radar can be used to measure cloud fraction, precipitation rate, and scattering cross sections. Furthermore, the lidar/radar estimate of particle size coupled with Doppler velocity can provide information on particle shape. The paper will describe the capabilities of current and planned developments at the laboratory.