An experimental airborne remote sensing system includes a remotely controlled, lightweight, solar-powered airplane (see figure) that carries two digital-output electronic cameras and communicates with a nearby ground control and monitoring station via a wireless local-area network (WLAN). The speed of the airplane — typically <50 km/h — is low enough to enable loitering over farm fields, disaster scenes, or other areas of interest to collect high resolution digital imagery that could be delivered to end users (e.g., farm managers or disaster-relief coordinators) in nearly real time.
In addition to achieving the desired flight, remote-sensing, remote-control, and remote-monitoring capabilities, one of the goals in the development of this system has been minimizing its cost through the use of commercial off the shelf hardware and software. Accordingly, the mention of brand names in the following description of the system does not constitute an endorsement and is not intended to exclude hardware and software of different brand names that afford equivalent capabilities.
One of the camera systems — for acquiring high-resolution red/green/blue images — includes a Hasselblad 555ELD camera body assembled with a Kodak Professional DCS Pro Back 4,000-by-4,000-pixel charge-coupled-device (CCD) array and a color filter array. The other system — for imaging in three narrow wavelength bands — comprises a DuncanTech MS3100 camera with a single Nikon 35-mm lens, which, in combination with a dichroic prism, focuses incoming light through three separate narrow-band filters onto three 1,280-by-1,024-pixel CCD arrays. The three wavelength bands are 760±20, 660±10, and 580±10 nm.
The WLAN is implemented by use of Cisco Aironet 340-series Ethernet bridges, which operate at frequencies between 2.4 and 2.5 GHz. These bridges are capable of functioning as bidirectional, line of sight, high-speed data links between two or more networks (in this case, an airborne and a ground-based network). These bridges were originally designed as building-to-building links but are advertised as being capable of data rates of 11 Mb/s over distances up to 40 km. The WLAN is configured for remote control of the camera and transmission of acquired imagery to the ground station. A bridge in the airborne network serves as the link between an airborne system payload computer and an omnidirectional stub antenna on the underside of the airplane. A bridge in the ground station serves as a link between the ground antenna and a laptop computer. The remote-control software is installed in both the system payload computer and the portable laptop computer. The ground-based payload operator controls each camera remotely by use of the laptop computer.
Testing and development of the system were continuing at the time of reporting the information for this article. Particularly notable is a flight test, performed in September 2002, to demonstrate safe and effective operation of the system in an agricultural setting in FAA controlled airspace. The airplane was flown for four hours over a 15-km2 coffee plantation in Hawaii, under supervision by Honolulu air-traffic controllers as though it were a conventionally piloted aircraft. The airplane was shown to be capable of flying planned routes and to perform spontaneous maneuvers to collect imagery in cloud-free areas. The WLAN was capable of downloading image data at rates exceeding 5 Mb/s, making all image data available for viewing, enhancing, and printing within a few minutes of collection. During the latter part of the flight, the payload was operated over an established wide-area network by an operator located on the United States mainland at a distance of 4,000 km.
This work was done by Robert G. Higgins, Steve E. Dunagan, Don Sullivan, Robert Slye, and James Brass of Ames Research Center; Joe G. Leung, Bruce Gallmeyer, Michio Aoyagi, and Mei Y. Wei of Dryden Flight Research Center; Stanley R. Herwitz of Clark University; Lee Johnson and Jian Zheng of California State University; and John C. Arvesen of Kauai Airborne Sciences. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Physical Sciences category.