one of the aerial methods of studying surface objects and phenomena. Aerovisual observations are carried out visually (directly or with the aid of binoculars) from aboard aircraft. Such observations are intended chiefly for the investigation of regions of difficult access, and for the facilitation and acceleration of expeditionary work in a locality. Aerovisual observations make it possible to study objects not only in their planar forms with one given reduction, as in aerial photographs or maps, but in every foreshortening and on the most advantageous scale. With aerovisual observations of open spaces, objects are distinguished at a distance of more than 500 times their size; with contrasting objects, the ratio of object to distance is 1:1,000. For aerovisual observations helicopters are predominantly used, to combine general surveying along the route with detailed examination of objects. The altitude and speed of the flight involved in aerovisual observations are determined by the purpose of the work, the nature of the objects studied (their angular measurements and optical contrast), and by the qualifications of the observer (in particular, his training, knowledge of the region, and so on). For topographical purposes, the average altitude of the flight is set at 200 to 300 m, with a speed of 60 to 80 km per hour.
The results of aerovisual observations made in the course of a flight are entered as marks on a map of the route or on the aerial photograph itself, as notes and sketches on a moving paper belt, as sound recordings on a tape recorder, or as airborne photographs on a small-format camera; they can also be entered by plotting objectives on maps with the help of sighting mechanisms. Aerovisual observations can be intended both for reconnaissance (for example, reconnoitering of ice conditions, locating game animals and fires, checking the flow of transport) and for systematic inspection of territory being mapped in the course of forest valuation surveys, geological tasks, and various engineering and topographical surveys. In topographical surveys, aerovisual observations are combined with the deciphering of aerial photographs, chiefly with the aim of studying places not discernible by the camera and of discovering essential objects that did not come out in the aerial photographs.
L. M. GOL’DMAN