3D wind retrieval from downward conical scanning airborne Doppler radar

The HIWRAP (High-Altitude Imaging Wind and Rain Airborne Profiler) is an airborne dual beam and dual frequency (14 and 35 GHz) radar that was developed at NASA Goddard Space Flight Center. The first field project for HIWRAP was in the GRIP (Genesis and Rapid Intensification Process) experiment during the summer of 2010. The radar mounts on the underside of the NASA Global Hawk, an unmanned airplane. Two antennas spin about the vertical axis of the aircraft with incidence angles of 30 (inner beam) and 40 (outer beam) degrees, similar to an upside down PPI scan from a ground-based radar. Since the aircraft is moving, the antennas sweep out two spirals through the atmosphere, essentially observing the atmosphere within +- 10 (inner beam) and +-15 (outer beam) kilometers of the aircraft at resolutions of 650 meters in horizontal and 150 meters in the vertical (for GRIP). In the vertical panel through the flight line, two separate looks (forward and aft) yields two radial Doppler velocities at common points. Combining these two velocities, and using assumptions for terminal velocity, we compute the components of vertical and horizontal wind along the flight track. Such information is then used to derive the 3D wind field through VAD analysis.

In this presentation, we will show a method for the components of 3D wind in a nadir curtain below the Global Hawk. This method is applied to actual data from the GRIP field experiment. Preliminary results will be presented at conference.