Hyperspectral imaging has demonstrated impressive capabilities in airborne surveys, particularly for mineral and biomass characterisations. 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 customised 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.

Research to assess the feasibility of developing a standoff active or passive optical tripwire detector is discussed. Reflectivities of typical tripwires and background materials were measured for UV, VNIR and SWIR wavelengths. A breadboard testbed was developed to obtain images of tripwires against various backgrounds for various geometries and a wide range of UV and VNIR wavelengths. Sample images of simulated and real tripwires in uncluttered environments and against typical cluttered backgrounds were acquired and analyzed. Line detection algorithms were applied to the images to detect tripwires. Although detection was not attempted in real-time, analysis showed that available, cost-effective DSPs could potentially execute those algorithms on the images in real-time. The algorithms successfully detected tripwires in a heavily cluttered background and even have the capability to detect partially obscured wires. To complement the measurements, a spreadsheet model was developed to evaluate the merits of different detectors, sources of illumination, wavebands and geometries for different scenarios. Acceptable signal-to-clutter ratios were found for a number of reasonable passive and active illumination scenarios. The study demonstrated that an optical tripwire detector is feasible in principle.

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.

The compact airborne spectrographic imager (casi) is a pushbroom imaging spectrograph intended for acquisition of VNIR multispectral imagery from light aircraft. An ongoing development program has resulted in improvements to the radiometric calibration procedures, and the capability for roll correction and geocorrection of imagery acquired with casi. A variety of monitoring and research missions have been undertaken for aquatic and terrestrial applications and development of remote sensing methodologies.

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.

The V5 ultraviolet auroral imager is one of a complement of experiments launched into polar orbit aboard the Swedish spacecraft Viking in February of 1986. The imager consists of two intensified wide‐angle f/1 cameras, identical except in passband, with electronic despinning providing exposure times of one second. Critical to electronic despinning is the use of tapered fiber optic bundles to remove distortions generated when the spherical focal surface of the Burch configuration camera is projected onto the plane of the charge coupled detector. Data acquired by V5 are telemetered to a ground station in Kiruna, Sweden for archiving and real time display using a VAX11/750 system.

A 100 X100 pixel charge-coupled-device (CCD) area detector combined with an image intensifier, all-sky optics, and a filter wheel has been developed to provide quantitative monochromatic images of the aurora. The design of the instrument provides for a variable exposure rate to accommodate the large dynamic range of auroral intensities, from a minimum of 20 ms up to several minutes. Standard auroral emission features are monitored by four selectable filters, normally at 6300, 5577, 3914, and 4278 A. Depending on the filter utilized, sensitivity can be from 180 to 250 R ADU-1 s-1. The instrument has been used successfully in support of balloon, rocket, and satellite campaigns.

The features of two-dimensional CCD imaging arrays have led to widespread use of these devices as quantitative optical and x-ray image sensors. In this paper we discuss the desirable attributes that a general purpose digital CCD camera system should have to exploit these capabilities and provide applications flexibility. These include wide dynamic range, flexible readout format and high speed clocking and data acquisition. The ability to digitally sum a number of successive image frames increases the dynamic range and reduces array cooling requirements in intensified-CCD and x-ray applications. We discuss the ways in which these goals have been achieved through the architecture of the DCS-2 Digital Camera System. The system consists of a camera head and controller connected by a datalink over which control information and image data are transmitted. Camera operation is controlled by a Micro-programmable Control Unit (MCU) in response to commands received from the controller over the serial channel in the datalink. The MCU controls all aspects of the CCD readout including integration time and generation of clock signals. The CCD video signal undergoes correlated double sampling and is digitized and transmitted to the controller over the parallel channel in the datalink on a pixel-sequential basis. The instrument controller is based around a microcomputer system with floppy and Winchester disk storage. Successive image frames received from the camera head are summed directly into the Summation Video Memory (SVM). The SVM is a novel three-port design which provides ports for the camera and computer and which also provides an output signal to drive a real-time display monitor. A menu-driven software package provides an interactive environment for control of the CCD readout configuration and image acquisition.

A versatile optical instrument capable of all-sky auroral imaging at low light levels is described. The All-Sky Imaging Photometer uses as a detector an image dissector photomultiplier tube operating in a photon-counting mode. A miniprocessor interprets commands entered interactively by the operator through a terminal, and controls data acquisition and display. A motorized filter wheel holding up to six interference filters permits monitoring of auroral emis-sions at monochromatic wavelengths.

A method is proposed for recovery of some of the events which occur during the dead time of a paralysable event counter. A practical implementation of the technique is presented, along with a simple method for calibrating the circuit.

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.