Side-looking Airborne Radar Research Articles

Unique radar system used for mapping uncharted regions in South America

A sophisticated airborne radar system that can ‘see’ at night and through clouds is being used by the Aero Service Division of Litton Industries to map and create photo‐like images of uncharted jungle regions of South America.An aerial search for natural resources over 80,000 square miles of the cloud‐covered Orinoco basin in Venezuela using a Side‐Looking Airborne Radar (SLAR) system installed aboard a high‐altitude jetliner is being conducted by Litton Aero Service in association with Goodyear Aerospace Corp. Plans for a second SLAR survey will begin in May and cover 600,000 square miles of the Brazilian Amazon basin, an area onefifth the size of the United States. This project will be conducted in association with LASA, Brazil's leading civil engineering and resources firm. The two contracts amount to about $6.5 million.

Use of side-looking air-borne radar for sea ice identification

An experiment was conducted to assess the performance of side-looking air-borne radar (SLAR) in mapping and identifying sea ice parameters. A Philco-Ford AN/DPD-2 (Modified) SLAR was installed on a Coast Guard C-130 aircraft and flown on an experimental basis during September 1969 in conjunction with the S.S. MANHATTAN's transit of the Northwest Passage. In addition to the research effort to determine its feasibility as an ice observational technique, the SLAR was also used as a routing aid to the MANHATTAN. The results of this experiment indicate that SLAR can readily be used to detect ice concentrations, floe size and number, and water openings, and to identify through careful image interpretation, ice age, ice drift, surface topography, fractures, and pressure characteristics. SLAR's broad areal coverage, all weather, day and night capability make it an effective means of observing sea ice and for many purposes it provides observations superior to information obtained by a visual ice observer. SLAR imagery can be used in research efforts to study the formation, growth, and decay of sea ice and can be used operationally for ship routing and ice forecasting. It will be necessary to conduct similar experiments during other seasons of the year to determine whether there is a seasonal influence on the imaged appearance of sea ice. (Author)

Comparison of SLAR Images and Small-Scale, Low-Sun Aerial Photographs

A comparison of side-looking airborne radar (SLAR) images and black and white aerial photos of similar scale and illumination of an area in the Mojave Desert of California shows that aerial photos yield far more information about geology than do SLAR images because of greater resolution, tonal range, and geometric fidelity, and easier use in stereo. Nevertheless, radar can differentiate some materials or surfaces that aerial photos cannot; thus, they should be considered as complementary, rather than competing tools in geologic investigations. The most significant advantage of SLAR, however, is its freedom from the stringent conditions of weather, date, and time that are required by small-scale aerial photos taken with a specified direction and angle of illumination. Indeed, in low latitudes, SLAR is the only way to obtain small-scale images with low illumination from certain directions; moreover, in areas of nearly continuous cloudiness, radar may be the only practical source of small-scale images.

A New Approach to Preliminary Site Surveillance

Optimum deployment of deep submersibles to dive sites requires rapid collection of topographic information, intermediate in precision between conventional depth sounding and direct visual observation. The area and depth resolution of conventional depth sounding systems operating from the surface does not provide the detail necessary for submersible operations. High resolution deep-towed side-looking sonar, television, and camera systems require too much pre-dive survey time. The synthetic aperture array technique, originally developed for side-looking airborne radar, provides a potential solution for this problem. Application of this technique to side-looking sonar involves unique problems in the areas of medium stability, vehicle motion compensation, reverberation limitations, and the range-azimuth ambiguities resulting from the relatively low propagation velocity. An investigation of these problems has revealed that the technology required to develop a synthetic aperture side-looking sonar is available. Swath coverage on the order of 10 km with a resolution cell of 10 meters in water depths of 7000 m appears to be feasible, from a surface ship operating at a speed of 10 knots. The synthetic aperture approach appears to offer considerable savings in cost and complexity compared to conventional side-looking sonar arrays of similar performance.

Applications of Airborne Remote Sensing Technology

Aerial photography has been used for nearly a century. Recent developments in aerial photography, such as color film, color infrared film, and multiband photographic systems, have greatly increased the amount of useful information obtainable from aerial photographs. Remote sensing instruments that operate in different parts of the electromagnetic spectrum from the human eye and photographic sensors can detect many things beyond the scope of human and photographic sensors. Thermal imagery can detect thermal pollution entering streams. Side-looking airborne radar can map terrain day or night, almost without regard for weather conditions. Remote sensing instruments having civil engineering applications are described herein. The emphasis is on photography, thermal imagery, multispectral imagery, and side-looking airborne radar. Applications of airborne remote sensing technology to soils mapping, water pollution detection and monitoring, and urban and regional planning are illustrated.

Radar Expression of Virginia Dale Precambrian Ring-Dike Complex, Wyoming/Colorado

The Virginia Dale Precambrian ring-dike complex, at the extreme south end of the Laramie Range, was first recognized by W. A. Braddock in 1962 from high-altitude air photos. This roughly circular feature is well expressed on 1957 early side-looking airborne radar (SLAR) imagery, from which in 1965 it was independently noted as a striking geomorphic (domal) anomaly. This particular imagery example illustrates the notable potential of radar imagery in general for delineation of larger scale elements, especially lineament patterns. The Virginia Dale complex is believed by the current authors to be of particular significance, not only for its relevance to Precambrian history, but also for possible influence on Phanerozoic events here, and in particular for its possible bearing on location of the Ferris-Aultman and other associated Paleozoic diatremes.

Structural Geologic Interpretations from Radar Imagery

Certain structural geologic features may be more readily recognized on sidelooking airborne radar (SLAR) images than on conventional aerial photographs, other remote sensor imagery, or by ground observations. SLAR systems look obliquely to one or both sides and their images resemble aerial photographs taken at low sun angle with the sun directly behind the camera. They differ from air photos in geometry, resolution, and information content. Radar operates at much lower frequencies than the human eye, camera, or infrared sensors, and thus “sees” differently. The lower frequency enables it to penetrate most clouds and some precipitation, haze, dust, and some vegetation. Radar provides its own illumination, which can be closely controlled in intensity and frequency. It is narrow band, or essentially monochromatic. Low relief and subdued features are accentuated when viewed from the proper direction. Runs over the same area in significantly different directions (more than 45° from each other), show that images taken in one direction may emphasize features that are not emphasized on those taken in the other direction; optimum direction is determined by those features which need to be emphasized for study purposes. Lineaments interpreted as faults stand out on radar imagery of central and western Nevada; folded sedimentary rocks cut by faults can be clearly seen on radar imagery of northern Alabama. In these areas, certain structural and stratigraphic features are more pronounced on radar images than on conventional photographs; thus radar imagery materially aids structural interpretation.

Radar Remote Sensing in Biology

Radar's potential as a sensor for surveys of natural and cultivated vegetation has recently been demonstrated in a preliminary way. Its combination of fine resolution from long distances with a virtual independence of weather and time of day makes radar particularly attractive for wide area surveys that must be performed quickly. Aircraft radar can effectively image a much wider swath of territory than other aircraft-borne sensors. This advantage, however, does not carry over into spacecraft radar, where the swath possible with optical sensors is much more than it is at aircraft altitudes. Radars with characteristics suitable for vegetation surveys have been developed for military reconnaissance in the past two decades. Because most of the images produced in the past by these radars have not been available to the scientific community, their potential for vegetation surveys is not recognized widely. Recently, however, many such images have been released and a few research programs have begun to document the potential of radar for vegetation studies. The kind of radar that will undoubtedly receive most application in plant geography (and perhaps even ecology) studies is side-looking airborne radar (SLAR). Such radar produces a continuous-strip image that looks much like a continuous strip photograph taken from a very high altitude. Unlike the photograph, however, the area imaged is not beneath the aircraft, but rather extends from a short distance out to the

RADAR, GEOGRAPHIC TOOL

Examination of representative and recently declassified samples of imagery from the type of radar developed especially for reconnaissance and mapping purposes by the military, the Side-Looking Airborne Radar (“SLAR”), indicates that SLAR images look very much like medium-grade aerial photos and will serve the following types of geographic tasks even better: 1) Tasks which require an overview of subcontinental magnitude. 2) Tasks which require an overview in which careful timing is critical. 3) Tasks which require an overview with maximum economy of time and money.

An Automatic Sensitivity Time Control System

A completely transistorized automatic sensitivity time control (ASTC) circuit was designed and developed to operate in conjunction with a side-looking airborne radar surveillance set. The ASTC technique is a closed loop system which automatically controls the radar receiver gain vs range function in accordance with the average signal return. The addition of ASTC substantially improved the imagery of a side-looking airborne radar recorded during low altitude flights.