Three radars are better than one for Rainfall Measurement

NASA's ER-2 research aircraft
 (NASA/Gerry Heymsfield)

AMS Journals Online - Airborne Radar Observations of Severe Hailstorms: Implications for Future Spaceborne Radar

A new dual-frequency (Ku and Ka band) nadir-pointing Doppler radar on the high-altitude NASA ER-2 aircraft, called the High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP), has collected data over severe thunderstorms in Oklahoma and Kansas during the Midlatitude Continental Convective Clouds Experiment (MC3E). The overarching motivation for this study is to understand the behavior of the dual-wavelength airborne radar measurements in a global variety of thunderstorms and how these may relate to future spaceborne-radar measurements.

HIWRAP is operated at frequencies that are similar to those of the precipitation radar on the Tropical Rainfall Measuring Mission (Ku band) and the upcoming Global Precipitation Measurement mission satellite's dual-frequency (Ku and Ka bands) precipitation radar. The aircraft measurements of strong hailstorms have been combined with ground-based polarimetric measurements to obtain a better understanding of the response of the Ku- and Ka-band radar to the vertical distribution of the hydrometeors, including hail.

Data from two flight lines on 24 May 2011 are presented. Doppler velocities were ~39 m s⁻¹ at 10.7-km altitude from the first flight line early on 24 May, and the lower value of ~25 m s⁻¹ on a second flight line later in the day. Vertical motions estimated using a fall speed estimate for large graupel and hail suggested that the first storm had an updraft that possibly exceeded 60 m s⁻¹ for the more intense part of the storm. This large updraft speed along with reports of 5-cm hail at the surface, reflectivities reaching 70 dBZ at S band in the storm cores, and hail signals from polarimetric data provide a highly challenging situation for spaceborne-radar measurements in intense convective systems. The Ku- and Ka-band reflectivities rarely exceed ~47 and ~37 dBZ, respectively, in these storms.

Development of the NASA High-Altitude Imaging Wind and Rain Airborne Profiler

The scope of this paper1 is the development and recent field deployments of the High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP), which was funded under the NASA Instrument Incubator Program (IIP) [1]. HIWRAP is a dual-frequency (Ka- and Ku-band), dual-beam (30° and 40° incidence angles), conical scanning, Doppler radar system designed for operation on the NASA high-altitude (65,000 ft) Global Hawk Unmanned Aerial System (UAS).

It utilizes solid state transmitters along with a novel pulse compression scheme that results in a system with compact size, light weight, less power consumption, and low cost compared to radars currently in use for precipitation and Doppler wind measurements. By combining measurements at Ku- and Ka-band, HIWRAP is able to image winds through measuring volume backscattering from clouds and precipitation.

In addition, HIWRAP is also capable of measuring surface winds in an approach similar to SeaWinds on QuikScat. To this end, HIWRAP hardware and software development has been completed. It was installed on the NASA WB57 for instrument test flights in March, 2010 and then deployed on the NASA Global Hawk for supporting the Genesis and Rapid Intensification Processes (GRIP) field campaign in August-September, 2010. This paper describes the scientific motivations of the development of HIWRAP as well as system hardware, aircraft integration and flight missions. Preliminary data from GRIP science flights is also presented.

Three radars are better than one: Field campaign demonstrates two new instruments | (e) Science News

Rainfall comes in more than 31 flavors, from tiny cloud droplets and misty drizzle, to fat raindrops and two-inch hailstones, and, of course, everything in between. Different radar frequencies pick up different precipitation types, generally based on size and whether the particles are ice or liquid. Radars flying with multiple frequencies can study more precipitation types and identify where they occur inside clouds, giving scientists a more complete picture of the inner workings of a rainstorm.

Photos of the Day: Three Radars are Better than One

HIWRAP was developed by Goddard’s High Altitude Radar Group. The team includes (left to right): Lihua Li, Gerry McIntire, Michael Coon, Matthew McLinden, Gerry Heymsfield and Martin Perrine. McLinden led the work on the Cloud Radar System and Li led the work on EXRAD.
(NASA Goddard/Bill Hrybyk)

• HIWRAP is under the wing in the black compartment;
• Cloud Radar System is under the other wing and is not visible; and
• EXRAD radar is in the extended nose cone.