One of the images taken by the Global Hawk during a nighttime flight of a snow covered mountain. (Photo courtesy of Northrop Grumman.)
Unmanned aerial vehicles (UAVs) have proven to be extremely useful in collecting environmental data that can help scientists understand weather phenomena. Yet such tasks require a suitable radar system. For its most recent use on a Global Hawk UAV, for example, a series of changes and updates had to be done on the UAV synthetic aperture radar (SAR) that was previously used on the Gulfstream III (G-III). The Global Hawk’s mission was to collect data in the Canadian Arctic to study changes in topography and Arctic ice caps.
The SAR was originally developed under NASA’s Earth Science Technology Office (ESTO) to support repeat-pass radar interferometry. It has a non-pressurized, compact, pod-based, and configurable structure, which makes it suitable for multiple platforms and as a radar-technology testbed. Initial capabilities kept the radar performing at the L-band, enabled by an electronically scanned antenna. While integrated on an aircraft like the G-III, it could then target environmental applications including vegetation mapping, land-use classification, soil-moisture mapping, and archeological research.
For use on the Global Hawk, the radar had to be configured for long-duration/long-range data campaigns. Single-pass polarimetric-interferometry (SPI) at Ka-band also was enabled for ice-sheet and river topographic mapping. Two radar pods—each with its own active array antenna—were developed for the necessary high precision.
Those pods are mounted symmetrically under the Global Hawk’s wings. One, which comprises the entire radar, serves as the master pod. The other functions as the slave pod with an active antenna array and the motion measurement subsystem (to track the precise location and attitude of the slave radar antenna). The master pod provides power, radar timing, transmit chirp, and frequency up/down conversion for the slave pod. The Global Hawk also was equipped with a high-resolution camera to observe the Arctic ice caps over a 21-hr. flight.
This mission marks the Global Hawk’s first flight through Canadian civil airspace. Known for their high-altitude, long-endurance capabilities, these UAVs have been used in a variety of other environmental missions. For example, they have collected atmospheric data for NASA’s Airborne Tropical Tropopause Experiment (ATTREX), which studies hurricane formations and intensity changes.
Information for this article was gathered from the paper, “UAVSAR Instrument: Current Operations and Planned Upgrades,” and the presentation, “An Overview of UAVSAR’s New Capabilities,” from the Jet Propulsion Laboratory at the California Institute of Technology.