Search

Hyperspectral imaging has demonstrated impressive capabilities in airborne surveys, particularly for mineral and biomass characterizations. Based on this success, it is believed that other applications like search and rescue operations, and detection/identification of various ground military targets could greatly benefit from this technology. The strength of hyperspectral imaging comes from the access to another dimension of information: the spectral content of the detected return signal for each spatial pixel. In the case of conventional hyperspectral imaging, the return signal depicts the spectral reflectance of the day irradiance from the scene within the field of view of each pixel. However, by inserting a range-gated intensifier into a hyperspectral camera and by combining the camera with selected pulsed lasers, it becomes possible to relate the returned spectral information to specific light/matter interactions like induced fluorescence. This new technique may be referred to as 'active hyperspectral imaging.' Among its advantages, this approach is independent of the ambient lighting conditions and can be customized in excitation wavelengths. Moreover, by using a range-gated intensified camera, it is possible to survey limited area with a significant increase in signal-to-noise ratio. A camera of this type has been built by our group in collaboration with private industry and is described in this paper. The internal design of the camera is discussed, new issues concerning the calibration of the camera are depicted and a model based on signal-to-noise ratio analysis is presented. From the fluorescent characteristics of surrogate land mines measured in the laboratory, this model is used to predict the capabilities of detecting surface-laid mines from an aerial platform based scenario.

Airborne optical remote sensing has recently seen an evolution from limited spectral discrimination into high spectral resolution imagery. Hyperspectral imagers now have the ability to sample a scene at both high spatial and high spectral resolution, permitting optimal selection from the available information to meet specific applications. Techniques have been developed which provide for high speed acquisition, radiometric calibration, conversion to spectral reflectances, geometric correction and interpretation of airborne hyperspectral data. The same technology currently in use for discrimination of subtle features in airborne scenes is available for industrial inspection applications which can benefit from combined spectral reflectance and imaging information.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A very flexible, sophisticated, low-cost and powerful commercial imaging spectrograph has been designed and developed that can provide resolutions from under one meter to several meters depending upon aircraft altitude and ground speed. The instrument uses a two-dimensional frame transfer CCD array to image a line beneath the aircraft and to sense the spectrum for each point in the scene. To keep data rates compatible with the built-in digital cassette recorder, a flexible scheme allows the operator to select the spectral bands and spatial information to be recorded. This compact airborne spectrographic imager can be employed to examine water quality, vegetation stress, fish schools, and to distinguish camouflage from vegetation.

Many event detector-counter systems have dead times associated with them during which events are not detected and are lost. A method is proposed for recovery of some of the events occurring during the dead times of a paralyzable event counter. Simulation and theoretical results are presented. As the event recovery method relies on a knowledge of the dead time, a method, using only the event recovery technique, through which this knowledge can be obtained is indicated. Several possible cases in which this result could be used to improve an event counting system are also stated.