High Altitude Integrated Wind and Rain Profiler (HIWRAP) : New transceiver development and recent observations

The HIgh-altitude  Integrated Wind and Rain Profiler (HIWRAP) :

New transceiver developments and recent observations

V. Venkatesh ^1,2, M. Perrine ¹ , G. McIntire ^1,3, M. McLinden ¹, M. Coon¹,

G. Heymsfield ¹, L. Li ¹

 1 – NASA Goddard Space Flight Center, Greenbelt, MD.

2 – Science Systems and Applications Inc., Lanham, MD.

3 – Stinger Ghaffarian Technologies Inc., Greenbelt, MD.

 

Hurricanes and tropical storms pose a significant threat to the coastal regions of the United States. The suite of instruments used to monitor these storms comprise of ground, satellite and air -borne sensors. Ground based instruments have obvious geographical limitations.  Satellite based radars (and radiometers) provide measurements of the surface wind-speed in precipitation free regions. However,  large platform speeds make it difficult for satellite-based radars to measure Doppler velocities in precipitation. Airborne radars fill in critical gaps left by the other two  platforms and  provide unique insights on the high-resolution structure and vertical-velocity evolution of tropical storms.

 

HIWRAP is a dual-frequency airborne radar that has been flying on the Global Hawk, WB-57 and ER-2 aircrafts since 2010. HIWRAP is designed to measure tropospheric wind-fields from multi-look Doppler profiles that are synthesized by virtue of scanning. To meet weight and size requirements, the original system design comprised of a 30 W (peak power) Ku- and an 8 W Ka-band solid-state transmitter.   Recent advances in microwave power combining and higher efficiency transistors allow for  increased transmitter peak power for similarly weighing solid-state power amplifiers. Herein, we discuss recent upgrades to the HIWRAP instrument (Ku-band transceiver shown in Fig. 1a) that improve sensitivity by approximately 10 dB.  

 

       

Fig. 1 : 1a (Left) - The newly developed Ku-band transceiver for the NASA HIWRAP radar. 1b (Right) -  Reflectivity measurements obtained using the newly developed Ka-band transceiver.

 

Preliminary observations from recent campaigns are presented (see Fig. 1b). We discuss results from the implemented calibration scheme wherein the measured normalized radar cross section (NRCS) at an incidence angle of approximately 9 degrees is employed to calculate the radar constant. This is because the NRCS at the specified incidence angle is invariant of surface wind conditions and allows for forcing of agreement between theoretical predictions and measurements [Li et al. (2005) and Valenzuela (1978)].