Range-gated viewing systems, which were at first used for object observation under poor visibility conditions, are used now also to determine distances to objects and obtain 3D images. A number of methods were suggested to determine distance. For instruments operating in real time, it is important to use fast methods. Range-intensity correlation methods are such methods because they use only two images. The methods work with rectangular-shaped illumination pulses and rectangular gate pulse shape. However, real pulses may differ from the rectangular ones that may introduce significant error into the distance measurement. To avoid the error one has to use a calibration dependence of the distance on the signal. The calibration curve depends not only on time profiles of the pulse and gate, but also on the gate duration and the difference between delay times of two images. Experimental search for optimal measurement condition through trial and error is a rather cumbersome problem. Therefore, we used numerical simulation and analytical estimates. The pulse time profile could be taken arbitrary. The gate time profile was assumed to be rectangular. The ratio of the energies received by the same pixel in two images depending on distance is used to build calibration curve. With given pulse shape, by varying gate time and delay time difference, we obtain calibration curves with different slope, different position on the distance scale and with different range of the determined distances. It appeared that the greater the slope of the curve, the narrower the range of measured distances and the lower the pixel energy. The conditions were found to get monotonous calibration curve with the highest possible return signal from all points on the distance determination interval.
It is proposed to single out two methods for observing object using range-gated vision systems (RGVS). In the first case the distance between RGVS and an object is fixed. Its observation is made by changing time delay between the leading edges of pulses of laser illumination and gate-pulses of the receiving block, i.e. neighboring layers of space are sequentially seen along the optical axis (visibility zone shifts). In the second case time delay is fixed. This corresponds either to observation of object moving along the optical axis of the system or to the study of ensemble of objects in visibility zone at different distances, including the observation on inclined path. It is shown that such a division of the observation methods has a definite physical justification. Division of the two methods for observing object will promote systematization and better understanding of the investigation results on RGVS.
The regularities were investigated of formation of range-energy profiles (REP) of visibility zone for RGVS with illuminating pulses, the shape of which differs from the rectangular (triangular or trapezoidal) one. It was established that if the illuminating pulse length ΔtL is smaller or equal to the length of gate-pulse ΔtG of the receiving block, then the expressions for characteristic distances coincide with the case of rectangular-shaped pulses and they can be used to determine distances to objects for pulses having non-rectangular shape. At ΔtL > ΔtG in a case of illuminating pulses having triangular shape REP possesses bell-like shape. For illuminating pulses having trapezoidal shape REP has either bell-like or trapezoidal shape. The last shape appears when the duration of the upper base of the illuminating pulse having trapezoidal shape exceeds the gate-pulse duration. The empirical method for determining characteristics distances to the REP maximum and boundary points of plateau area, which can be used for calculation of the distance to the object. Using calibration constants the method was proposed for calculating the distances to objects and its efficiency was experimentally proved.
The optical electronic system for far observing have been developed and tested. This system can use for detecting and tracking objects at night time at long distances. Also it can work in conditions of limited transparency of the atmosphere (the presence of atmospheric phenomena such as rain, snow, drizzle and fog). With the help of the system it is possible to distinguish details of objects with a size of 0.5 m at the maximum distance up to 7 km.
A method for distance determination with the help of range-gated viewing systems suitable for the arbitrary shape of the illumination pulse is proposed. The method is based on finding the delay time at which maximum of the return pulse energy takes place. The maximum position depends on the pulse and gate durations and, generally speaking, on the pulse shape. If the pulse length is less than or equal to the gate duration, the delay time appropriate to the maximum does not depend on the pulse shape. At equal pulse and gate durations, there is a strict local maximum, which turns into a plateau when pulse is shorter than gate duration. A delay time appropriate to the strict local maximum or the far boundary of the plateau (where non-strict maximum is) is directly related to the distance to the object. These findings are confirmed by analytical relationships for trapezoid pulses and numerical results for the real pulse shape. To verify the proposed method we used a vertical wall located at different distances from 15 to 120m as an observed object. Delay time was changing discretely in increments of 5 ns. Maximum of the signal was determined by visual observation of the object on the monitor screen. The distance defined by the proposed method coincided with the direct measurement with accuracy 1- 2m, which is comparable with the delay time step multiplied by half of the light velocity. The results can be useful in the development of 3-D vision systems.
The new scheme of the reference channel of a remote gas analyzer has been offered and realized. The use of additional reflective elements with the low reflection factor allows to receive full interception of laser radiation and to provide a linear operating mode of a photodetector even for the strongest laser lines. At the measurement of a concentration of air pollutions on a differential method the weak dependence of reflection factors for used reflecting plates from wavelength can be easy to take into account by adding corresponding factors in the formula for calculations of air pollution concentrations. The application of the new optical scheme of the reference channel for the gas analyzer and the addition new correcting temperature constants in the calculations has allowed carrying out correct measurements of air pollutants with the high accuracy.
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