Improving the efficiency of night vision device development.

Increasing the efficiency of night vision device development..

INCREASING THE EFFICIENCY OF NIGHT VISION DEVICE DEVELOPMENT

As is known, night vision devices (NVD) are widely used in special equipment for observation and aiming at dusk and at night. However, their domestic element base still lags behind foreign ones in its parameters. Therefore, the only way to create competitive NVD is to develop original rational circuit solutions that compensate for the shortcomings of the element base.

Currently, there are a significant number of types of NVD based on image intensifier tubes (IITs), active-pulse NVDs, low-level television (LTV) systems, thermal imaging (TIV) devices (photo 1) [1].

a – NVD based on IITs;

б – NTV-system;

в – AI NV;

г – AI TV NV;

d – TPV device;

e – laser rangefinder
Photo 1. Appearance of typical NVDs:

To design rational NVD schemes, it is necessary to determine from what positions the rationality of constructing these schemes should be assessed. The main feature of the scheme rationality is, first of all, the degree of satisfaction of the customer's requirements, i.e. the main requirements of the technical specifications for NVD. Another important feature is the cost, which should not exceed the funds allocated by the customer. Such features should also include the time required for development, preparation of production and the production itself, the degree of its readiness to master NVD schemes, the possibility of creating a simple and technological design in accordance with these schemes, the possibility of metrological support, operational reliability, the degree of satisfaction of operational requirements, ergonomics, maintainability, trainability of service personnel, the degree of use of foreign element base. The main requirements of the technical specifications include the recognition (detection) range when the night vision device operates in passive, active or active-pulse modes, the detection range of the object of observation by glare, the angle of the field of view in passive, active or active-pulse modes, the accuracy of range measurement, the degree of protection against light interference, dimensions (volume), weight, power consumption, and continuous operation time in various operating modes.

In accordance with the above, the degree of rationality of the scheme (DR) can be determined by the formula

DR = RTZa x Sb x VRv x VPPg x VPd x SGPe x VTKzh x VMOz x SETi x SENk x SERl x SRMm x SON x SIZBO, (1)

where RTZ is the rationality of the scheme from the point of view of fulfilling the requirements of the technical specifications;
C is the cost;
VR is the time for developing the PNV;
VPP is the time for preparing for production;
VP is the time for production;
SGP – degree of production readiness for mastering the NVD scheme;
VTK – possibility of creating a technological and simple design based on the NVD scheme;
VMO – possibility of metrological support;
SET – degree of satisfaction of operational requirements for resistance to mechanical, climatic and special influences;
SEN – degree of operational reliability;
SER – degree of ergonomics;
SRM – degree of maintainability;
SO – degree of training of service personnel;
SIZB – the degree of use of foreign element base.

RTZ is determined by the formula

RTZ = DRRPp x DRAr x DOPs x DOAt x DOBu x UPZPf x UPZAx x TIDts x Pch x Osh x Mshch x Ee VPyu x VAya, (2)

where DR is the recognition range when the NVD is operating in passive mode;
DRA is the recognition range when the NVD is operating in active (active-pulse) mode;
DOP is the detection range when the NVD is operating in passive mode;
DOA – detection range when the NVD is operating in active (active-pulse) mode;
DOB – detection range of the observed object by glare;
UPZP – field of view angle when the NVD is operating in passive mode;
UPZA – field of view angle when the NVD is operating in active (active-pulse) mode;
TID – range measurement accuracy;
P – degree of protection against light interference;
O – volume (dimensions) of the NVD;
M – weight of the NVD;
E – power consumption of the NVD;
VP – time of continuous operation of the NVD in passive mode;
VA – time of continuous operation of the NVD in active (active-pulse) mode.

The exponents for all components of formulas (1, 2) are assigned in a point system based on the results of the analysis of customer requirements and processing of statistical data from an expert survey. Depending on the nature of the NVD application, individual components of formulas (1, 2) can be combined or omitted.

The possibility of rational creation and application of the basic element base of the NVD logically follows from the possibility of creation and application of a rationally constructed NVD scheme. In this case, the degree of rationality of the element base used in the NVD AI can be estimated by the formula

RE = ФДа x ФВЭб x ОДв x ВОг x ВЗд x ОТе x ВУж x ВРз x СХТи x Вк x Эл x СЭм, (3)

where ФД – physical availability of the element base;
ФВЭ – actual possibility of its operation in the modes permitted by the TU;
ОД – absence of scarce elements and materials;
VO – the possibility of using domestic element base;
VZ – the possibility of quick replacement of the spent element base;
OT – absence of toxicity, leading to the complication of manufacturing and installation technology, adjustment, operation, storage and disposal;
VU – the possibility of simple disposal of spent elements;
SHT – complexity of storage and transportation;
V – the possibility of eliminating the risk of theft and vandalism;
E – aesthetics and ergonomics;
SE – the cost of the element base.

The exponents of the formula components are assigned according to a point system based on the results of the analysis of the rational scheme of the PNV and the statistics of the expert survey.

However, to ensure round-the-clock and all-weather operation and multifunctionality, the capabilities of one NVD are not enough. In this regard, it is necessary to create multi-channel NVDs. They will allow solving problems of increased complexity in various external conditions, where the capabilities of single-channel NVDs are limited, and in multi-channel NVDs the disadvantages of one channel are compensated by the advantages of another [1]. Let us first consider the capabilities of single-channel NVDs.

Passive and passive-active NVDs based on EOP and low-level TV systems are quite simple, relatively cheap, but are unable to operate at a reduced level of natural night illumination (ENI), deteriorated atmospheric transparency and under the influence of light interference, and do not provide accurate measurement of the distance to the object.

Low-level television (LTV) systems provide remote transmission of images and their duplication, allow digital image processing in real time, the introduction of text, symbolic and digital information in an electronic channel, provide ease of observation, but have a shorter range than NVDs based on an EOP, and have all their disadvantages.

Active-pulse NVDs (AI NVDs) are free from the above mentioned disadvantages, provide noise immunity and precise range measurement, can include a TV channel, but do not work in all types of fog, are inoperative in smoke, have a limited field of view in the active-pulse mode, do not provide search in it and reveal the location of the NVD, are more expensive than passive NVD and NTV systems.

Thermal imaging (TI) devices operate at any level of ENO, at reduced atmospheric transparency, in smoke and in the presence of many light interferences, but they do not function in all fogs and are not protected from all interferences, do not provide accurate range measurement, their capabilities depend on the level of natural temperature contrasts, the devices are more complex and expensive than all the devices listed above, and often require cryogenic cooling.

In multichannel NVDs, unlike single-channel ones, the main disadvantages of the latter must be overcome or minimized. Due to this, multichannel NVDs must provide increased ranges of action (detection and recognition) with a field of view angle acceptable for effective search and detection, all-weather and round-the-clock operation, functioning under conditions of exposure to light and dust and smoke interference, measuring the range, coordinates, and speed of movement of the observed object. The design of a multichannel NVD must be modular, provide for its adaptability in terms of the ability to operate in a wide range of changing external conditions.

The ultimate goal of developing such NVDs is to create a fully integrated system in which the image is synthesized based on the analysis of signals from various channels. This is the basis for creating a fully automated system as a component of a robotic complex.

The main methods for developing multi-channel NVDs can be summarized as follows.

1. The number of individual channels included in the multichannel system should be minimal, their number and type are determined by specific system requirements.

2. The channels should be selected according to their physical design principle in such a way that the disadvantages of one channel are compensated by the advantages of another.

3. The design of the multichannel system should allow for autonomous operation of individual channels.

4. The image generation process should be carried out in real time.

5. Individual channels should not create electrical, electromagnetic, mechanical, optical or acoustic interference with each other, or mutual structural inconveniences.

6. The final image from the output of all channels, as well as alphanumeric information and symbols, should be displayed on a single indicator and presented in an ergonomically convenient form; if necessary, duplication of information should be provided.

7. In the interests of ensuring high image quality, the input optics of channels with different spectral regions should be separate, if possible (with the exception of the input protective glass and the head mirror); if this is not possible, then the multispectral optical system common to these channels should not reduce the image quality to a level at which the technical requirements for the system are not met.

8. It is necessary to carefully match the optical axes (in most cases with an accuracy of no less than 0.1 mrad), the angles of the fields of view and the magnifications of individual channels.

9. If the channels operate alternately, their switching must be carried out quickly and must not interfere with the operation of the system; the time it takes to enter the system mode and its individual channels is determined by the specific technical requirements for the system and can be reduced by operating individual units in standby mode (for example, cooling systems for the photodetector of the TPV channel).

10. Work on the creation of multi-channel night vision devices should be carried out in the direction of automating the process of searching, detecting and recognizing objects.

11. The advantage of a specific multichannel system design over a prototype or an alternative technical solution is determined based on the results of calculating its probability characteristics and the efficiency/cost ratio; in this case, the cost must be determined for comparable stages of sample development and the level of its production. The efficiency criterion of a multichannel system is an increase in the information content of the image, leading to an increase in the range while maintaining the required probability of detection and recognition, or an increase in the said probabilities, or a decrease in the time it takes to solve a problem using this system while maintaining the required probabilities and range.

A generalized characteristic of any system is the probability of visualizing an object PS [2]:

PS = Рор Боб Рр, (4)

where Рор, Ри, Рр are the probabilities of orientation, detection and recognition of an object, respectively.

Рор = Рор1 (E, t, П) + Рор2 (DT, t, П) — Рор1,2, (5)
Ри = Ри1 (D, E, t, t, П) + Ри2 (DT, D, t, t, П) — Ри1,2,
Рр = Рр1 (D, E, t, t, П) + Рр2 (DT, D, t, t, П) — Рр1,2,

where Рор1, Рор2 – probability of orientation on the terrain for short-wave (1) channel (for example, channel on EOP, low-level TV, AI TV, etc.) and, accordingly, (2) – long-wave channel (for example, TPV). In most cases, the channels operate independently, and therefore:

Р1,2 = Р1Р2. (6)

Probability Рор depends on the set of parameters of night vision devices P, level of ENO E, transparency of the atmosphere t, time t for solving a specific problem, search sector, characteristics of backgrounds and other factors. For long-wave channels, the energy characteristic is the temperature contrast DT.

The value of PS is determined by the visibility of specific objects on the ground (groups of trees, buildings, hills, etc.) and the horizon line. The value of PS is calculated using the formula:

PS = Р1 + Р2 > Р1 Р2 (7)

The differential and integral laws of recognition range distribution have the following form [2]:

where D0.5 is the range corresponding to the probability Рр = 0,
sa – standard deviation of the angular size resolved by the system,
a – size of the element resolved on the observed surface of the object.

sD = D D0.5sa, (9)

where a – angular size of the test object, ensuring detection with probability P = 0.5 under the condition of observation corresponding to the recognition of objects;
sD standard deviation of the value of the system's range.

For example, if each channel has D = 900 m with PS = 0.5, then the two-channel system has D = 1150 m. When using a set of secondary features and supplementing one image with others, the range D increases by at least 1.5 times.

The specificity of calculating multichannel systems consists in choosing the angular resolution of individual channels that provide a smaller reduction in RP and Pp for each channel separately compared to the required one, if the channels have close ranges. The probability of orientation is always higher when using a multichannel NVD. If the channels have too large a difference in range, then the functions are redistributed between them by the magnitude of the angle of the field of view. The channel with a greater range is usually narrower, and the channel with a shorter range is wide-field.

The advantage is in simplifying the system as a whole, in increasing RP and Pp, and, consequently, in reducing the time to solve the problem.

The issue of the absolute increase in the cost of a multi-channel system compared to the cost of individual channels is not as acute as it seems at first glance. For example, the use of a TPV channel in the system, which solves only search and detection problems at extreme ranges, requires the use of a FPU with lower sensitivity and a coarser resolution, simpler optics, a less complex electronic channel, etc. All this reduces the cost, which can be further reduced by unifying the channels, the modular principle of their construction, and creating specialized adapters that provide functional communication between individual modules and channels.

The most successful combination is the use of both TV and AI TV channels in a multichannel system. This combination ensures round-the-clock and all-weather operation, which continues even in the presence of light and dust and smoke interference, and allows for high-precision measurement of distances to observed objects, as well as such important parameters as their speed and coordinates. In such a system, its adaptability, the possibility of automated control of its parameters, and the modular design principle can be implemented relatively easily. Using images of NTV and TPV channels from a single TV monitor allows us to move to an integrated system, and using an additional computer allows us to move to a fully automated device.

Thus, there are real opportunities to increase the efficiency of NVD development through the rational construction of their circuits.

Photo 2. Typical multi-channel device,
containing NTV, TPV and laser rangefinder channels

Literature

1. Geykhman I.L., Volkov V.G. Fundamentals of improving visibility in difficult conditions. M.,: Nedra, 1999.
2. Aleshin B.S., Bondarenko A.B., Volkov V.G., Drab E.S., Tsibulkin L.M. Optical devices for observation, processing and recognition of objects in difficult conditions. M.:, GNIIAS, 1999, 139 p.