Visual-optical channel of information leakage.

Visual-optical channel of information leakage.

Visual-optical channel of information leakage

Dmitry Khalyapin

Obtaining visual characteristics of an object is constantly being improved thanks to new observation equipment (television, infrared viewing, visual-optoelectric, photographic) and its placement on various carriers (ship, car, plane, satellite). The human eye is the final device for perceiving visual information. Its capabilities are significantly increased by using various observation devices both in the visible range (binoculars, monoculars, periscopes, telescopes) and devices for visualizing images of an object in the IR range, radar images, thermal and X-ray images (night vision devices, thermal imagers, X-ray machines, side-view radars, etc.)

The objects of obtaining visual information are very diverse, determined by the customer of the information — from scenes of infidelity of spouses, images of new technology and its components to global observation of the entire surface of the Earth in order to obtain data on the possible harvest of this year or the location of troops and means of delivery of nuclear weapons.

For the owner of the information (an individual, a company, a state), its loss can have the most disastrous consequences. For example, a photo shoot of new models at a fashion show in Paris to determine the public's reaction to the «revolutionary change in the waistline» led to the fact that by the time the French designers took their products overseas, they saw thousands of dresses made according to their new styles. And instead of the planned profits, they suffered huge losses.

The received images of the positions of Soviet military missiles in Cuba with the help of aircraft and spy satellites allowed American military analysts to determine that they belonged to offensive nuclear missile weapons, which almost led the world to a new world war.

The species characteristics of an object make it possible to describe and classify detected objects by shape and contours, and to determine their details from a photograph or observed characteristics.

Obtaining the species characteristics of an object is the result of solving three problems:

• detection — this is the stage of visual perception when the observer selects an object from the surrounding background, the nature of which remains unclear to him;

• distinction —when the observer is able to determine large details of an object, to perceive two objects located nearby separately;

• recognition (identification) — when the observer, distinguishing individual small details, identifies the essential features of an object and can distinguish this object from others in his field of vision.

The visual characteristics of the objects of observation can be obtained either directly in the light range, or by visualizing images in the IR range, radar range, due to thermal radiation of objects.

The possibility of forming a visual channel of information leakage depends on certain psychophysiological features of the observer's perception of the object, such as:

• angular dimensions of the object;
• levels of adaptation brightness;
• contrast object/background;
• perception time;
• image noise.

Any image is characterized by brightness contrast K— direct or inverse.

With direct — the background brightness Вф is greater than the object brightness Во:

The contrast can be expressed in relative units or percentages. Contrast up to 20% is considered low, up to 50% — medium and more than 50% — high.

The optimal image contrast for long-term observation is 85-90%. Minimum meaning K, at which the eye distinguishes an object (the threshold of contrast sensitivity), is 2-3% in the case when the direction to the object is precisely known, and 7-9% during non-fixed observation.

Significant limitations may be imposed by the conditions of the temporal characteristics of perception, which is associated with the inertial properties of vision and is of great importance when observing moving objects or objects that briefly enter the operator's field of view. In such observation, the effect of short duration is enhanced by the effective brightness of the object, which, with short stimuli, may be significantly less than the actual brightness. In this case, the brightness contrast of a moving object may be significantly less than a stationary one.

The angular dimensions of the object of observation are also determining factors in visual characteristics

a = 2arctg (L/2I),

where L— is the linear size of the object image, and I is the distance from the observer's eye to the observation plane. These characteristics are related to the physiological data of the observer.

The absolute threshold for detecting apor in most people is 0.5″ (a thin black line on a light background).

Another observation parameter is related to this indicator — visual acuity (the resolving power of the eye), equal to 1/apor. Visual acuity depends on the distance between adjacent light-sensitive elements of the retina. It is maximum in the central part of the retina (in the angle of view ~7°).

The range of background and object brightness perceived by the eye is very wide and lies within 10-7 — 105 cd/m2.

However, it should be taken into account that in real conditions this range significantly depends on the average brightness of the field of view — the adaptation level. So for a high adaptation level (daylight) it is 1000: 1, and for a low one — 10: 1. The transition from one adaptation level to another requires a certain amount of time, which must be taken into account, for example, when an observer moves from a dark to a lighted (or vice versa) room.

The state of the observation route has a significant impact on obtaining visual information — from clean air to very heavy fog, corresponding to a meteorological code from 10 to 0, which determines the meteorological range of possible detection and observation of objects.

Many legends have appeared about the capabilities of video reconnaissance satellites. For example, during the American-Iraqi crisis, the American press wrote a lot about the characteristics of their latest video reconnaissance satellites such as Keyhope 11, 12, which make it possible to distinguish members of the Iraqi government by the shape of their beards. However, in reality, the maximum resolution of such systems is limited by the fact that filming is conducted through the Earth's atmosphere, with its dustiness and turbulence, and therefore the physical limit of resolution is 10-15 cm (with a «good» atmosphere) and 30 cm (with a «bad» atmosphere).

Despite these limitations, the possibility of unauthorized receipt of information via a visual-optical channel is extremely important. For example, long-focus cameras allow you to take pictures of documents located on an office wall or table at a distance of up to 5 km.

The RK 6500 telescope, made according to the Schmidt scheme, allows identifying a car at a distance of 10 km. Devices with electronic image stabilization allow hand-held observation from moving cars and helicopters.

Miniature cameras in standard design and camouflaged as various household items — wristwatches, lighters, etc., including remote-controlled cameras — have appeared in large quantities on the market of technical intelligence equipment. These devices allow making copies of A4 — A6 documents and allow re-photographing up to 800 documents.

Such a significant number of technical means for obtaining visual characteristics of objects and information carriers located on various media, from a jacket button to multi-ton spy satellites, requires specialists to use a set of protective measures to eliminate the possibility of leakage of visual information.

The emergence and widespread practical use of optical fibers has made it possible to obtain fundamentally new visual observation devices. When using them, observation devices depart from the traditional «line of sight» scheme, i.e. observation only of those objects that are in the line of sight of the eye or the optical axis of the device. It has become possible to obtain information from closed spaces — the probe is passed through a keyhole or a hole in the wall, and its rotation provides a visual overview of the interior of the room.

The equipment located on reconnaissance satellites provides an overview and receipt of information contained in images of various objects with a resolution of 15-30 cm to 1.0 m, depending on the type of equipment used (photographic, optical-electronic, including television, infrared imaging, etc.). With a resolution of about 1 — 2 m, it is possible to distinguish types of aircraft, ships, cars from space. Providing a resolution of 30 cm allows us to read the aircraft's side numbers and examine the weapons suspended from them, and count the number of soldiers in formation.

Significantly new possibilities are revealed by using zonal photography in various parts of the spectrum (both visible and infrared). It becomes possible to identify camouflaged objects in forests.

World of Security. July 1998.