Portable Airborne Multispectral-Imaging System
- Tuesday, 18 September 2007
This system can be put into operation almost anywhere on short notice.
A portable instrumentation system that includes an airborne and a ground-based subsystem acquires multispectral image data over swaths of terrain ranging in width from about 1/2 to 1 km. The system was developed especially for use in surveying coastal environments; it is also well suited for performing remote sensing in connection with agriculture, aquaculture, forestry, environmental decontamination, and general environmental monitoring. The system can be stowed in two suitcase-size containers that can be transported as check-in luggage on a commercial airline. Once the system has been delivered to its destination and unstowed, the airborne subsystem can be launched over unprepared terrain and controlled from the ground-based subsystem, which can be operated from a minivan or a similarly sized vehicle.
The airborne subsystem includes a small, unpiloted, remotely controlled airplane (see figure) that carries a color forward-looking video camera for navigation, three downward-looking monochrome video cameras for imaging terrain in three spectral bands, a video transmitter, and a Global Positioning System (GPS) receiver. An interference band-pass filter for one of the three spectral bands is mounted in front of the lens of each downward-looking camera. The filters can be changed in the field. The bands, each 10 nm wide, can range in wavelength from 400 to 1,100 nm. The outputs of the four cameras are multiplexed for real-time transmission so that the single video transmitter suffices for sending the image data to the ground station for real-time monitoring and recording: this aspect of the design reduces the cost and weight below what they would otherwise be.
The airplane carries an attitude reference sensor that measures absolute heading, roll, and pitch. This sensor comprises a three-axis magnetometer and a two-axis electrolytic clinometer. The position and reference data acquired by the GPS receiver and the attitude reference sensor can be used to register the multispectral image data with geographical coordinates, without need for predetermined ground reference targets.
The multiplexing of camera outputs is synchronized with, and performed in conjunction with, other functions that include triggering of the cameras, reading and storage of data from the GPS receiver and the attitude reference sensor, and the overlay of time, position, and attitude information on the image data. These functions are performed by a circuit that includes five micro- controllers, a video multiplexer, and a video synchronization separator, all mounted on a prototype circuit board.
The ground subsystem includes a receiver for video and digital data signals, a laptop computer that displays a moving map, a digital video cassette recorder, and a monitor that displays the video images in real time. Both the airborne and the ground subsystems were constructed mostly from commercial off-the-shelf components. Most of the development effort was expended on the airborne subsystem because of the need for miniaturization, minimization of weight, and minimization of the effects of airplane-engine vibrations.
This work was done by Robert Lahnemann and Todd McNamee of Air-O-Space International, LLC for Stennis Space Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to the Intellectual Property Manager, Stennis Space Center; (228) 688-1929. Refer to SSC-00089.