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.

In October and November of 1997 the Galileo Solid State Imager (SSI) detected lightning from 26 storms on the night side of Jupiter. More than half the surface area of the planet was surveyed. The data include images of lightning against moonlit clouds (illuminated by light from Io) and images of the same storm on the day and night sides. The spatial resolution ranged from 23 to 134 km per pixel, while the storms ranged in size up to ∼1500 km. Most storms were imaged more than once, and they typically exhibit many flashes per minute. The storms occur only in areas of cyclonic shear and near the centers of westward jets. Latitudes near 50° in both hemispheres are particularly active, although the northern hemisphere has more lightning overall. The greatest optical energy observed in a single flash was 1.6×10^(10) J, which is several times larger than terrestrial superbolts. The average optical power per unit area is 3× 10^(−7) W m^(−2), which is close to the terrestrial value. The limited color information is consistent with line and continuum emission from atomic hydrogen and helium. The intensity profiles of resolved lightning strikes are bell-shaped, with the half-width at half-maximum ranging from ∼45 to 80 km. We used these widths to infer the depth of the strikes, assuming that the appearance of each is the result of light scattering from a point source below the cloudtops. We conclude that lightning must be occurring within or below the jovian water cloud. The occurrence of lightning in regions of cyclonic shear has important implications for the dynamics of Jupiter's atmosphere.

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.

RÉSUMÉLe spectromètre-imageur à raie de fluorescence FLI (Fluorescence Line Imager) a été conçu et fabriqué pour le ministère des Pêches et Océans (en 1981) dans le cadre de la phase 1 d'un projet visant la mise au point d'un capteur satellitaire perfectionné équipé de détecteurs à transfert de charge (D.T.C.) pour l'étude de la surface terrestre. Une version plus compacte constituée d'une seule caméra existe sur le marché depuis 1990: il s'agit du spectromètre-imageur CASI (Compact Airborne Spectral Imager). Les deux instruments offrent la souplesse de fonctionnement permise par la conception d'un spectromètre-imageur pourvu de détecteurs en peigne qui assurent un pouvoir élevé de résolution spatiale dans le visible et le proche-infrarouge selon des modes spectraux contrôlés par ordinateur. Ils permettent également l'obtention de spectres complets le long du même intervalle spectral avec un pouvoir de résolution spatiale plus faible. Depuis 1983, ils survolent une grande variété de cibles situées tant sur terre que sur mer et génèrent des images dont la limite de résolution spectrale et la sensibilité sont supérieures à celles obtenues avec d'autres capteurs comparables.

Three images of Venus have been returned so far by the Galileo spacecraft following an encounter with the planet on UT February 10, 1990. The images, taken at effective wavelengths of 4200 and 9900 Å, characterize the global motions and distribution of haze near the Venus cloud tops and, at the latter wavelength, deep within the main cloud. Previously undetected markings are clearly seen in the near-infrared image. The global distribution of these features, which have maximum contrasts of 3%, is different from that recorded at short wavelengths. In particular, the “polar collar,” which is omnipresent in short wavelength images, is absent at 9900 Å. The maximum contrast in the features at 4200 Å is about 20%.

Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not the mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts. The inside of the far side South Pole—Aitken basin (>2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta.

Images of Venus taken at 418 (violet) and 986 [near-infrared (NIR)] nanometers show that the morphology and motions of large-scale features change with depth in the cloud deck. Poleward meridional velocities, seen in both spectral regions, are much reduced in the NIR. In the south polar region the markings in the two wavelength bands are strongly anticorrelated. The images follow the changing state of the upper cloud layer downwind of the subsolar point, and the zonal flow field shows a longitudinal periodicity that may be coupled to the formation of large-scale planetary waves. No optical lightning was detected.

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.