Airborne Spectral Imager
ASIThe NEO Airborne Spectral Imager (ASI) is a system built around a hyperspectral camera for use in aeroplanes. GPS and gyro data as well as two dimensional images are available for use during geometric correction of the data.
Basic Principle of OperationLike similar instruments in satellites, an airborne imager scans the ground line by line. The field of view is therefore a line and the imager or camera make consecutive exposures of this line while the aeroplane moves relatively to the ground. The figure below shows the basic principles of ASI.
The imager or camera system has a field of view that resembles a fan shape i.e., the camera will depict one line at the ground. By making multiple exposures while the aeroplane moves relatively to the ground the imager acquires a contnuous image of the ground. The spectrometer part splits the light from each image line into different colors or spectral channels. For each color or spectral channel a continuous image will be stored. There are 320 (or 160 optionally) spectral channels in the visible and near infra read range (VNIR) and 256 spectral channels in the short wave infra red (SWIR). This gives a lot of data!
The AeroplaneA Cessna 172 has been used for the ASI measurements. Some clips from the ASI missions are shown below.
This is the Cessna that has been used for all missions. Left: ready for action. Right, top: Gyro check before take off. Right, middle: checking the field of view. Right, bottom: Check List All OK.
ASI Image ResultsBelow are some image results from the NEO Airborne Spectral Imager. Due to turbulence and other plane movements the scanned images might be somewhat distorted. The plane, however, is equipped with gyros and GPS and therefore a rectification of the images is possible.
The image above shows ASI images before rectification. Probably not easy to play football (soccer) there.
Same image rectified.
Small village. To the left a normal RGB image and to the right an image where the vegetation has been classified using tools in ENVI. The vegetation is yellow.