A Dual-beam X-band Doppler Radar for Tropical Storm Research on High Altitude UAVs

Tropical storms get most of their energy transferred from the ocean surface and released as latent heat in moist convection in the eyewall. Tropical storms have been studied observationally and through numerical models for many years with the major goal of improving track and intensity forecasts. Current storm forecasting models greatly need environmental and within storm measurements (surface winds, temperature, profiled winds, and moisture, etc) over the open ocean where manned aircraft are unable to fly and satellite measurements are inadequate. With the transition of NASA's suborbital program from manned to unmanned UAV aircraft, there is strong interest in utilizing long-duration, high-altitude UAVs to provide this greatly needed information. Thus, a UAV radar with similar capabilities to ER-2 Doppler Radar (EDOP) is desirable for studying the vertical structure of tropical cyclones as well as 3D reflectivity and wind field in clouds and precipitation below the aircraft.

A dual-beam X-band Doppler radar is under development for the study of tropical storm from high altitude UAV platform, such as the Global Hawk. This new radar combines precipitation radar and scatterometer that measures both the 3D cloud/precipitation structure and surface winds with fixed nadir and conical scanning beams. The nadir beam subsystem is a magnetron based, lower cost, smaller size and lighter weight version of EDOP that has flown in various NASA field campaigns and has provided important information on hurricanes and convective systems. The conical scan subsystem uses a TWT transmitter and provides a new capability to measure surface and in-cloud/precipitation reflectivity and winds. With conical scanning of the radar beam at a 35o incidence angle at ocean surface, information of surface wind speed and direction will be derived from the surface return over a single 360o sweep. In cloud/precipitation region, the conical scanning provides a 3D structure of reflectivity and winds.