RU2167434C2 - Method determining density of concentration of fish - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: method determining density of concentration of fish includes survey with use of laser underwater TV system with range gating, visual or computer counting of number of fishes observed in frame. Counting registers not only fishes illuminated by laser pulse but as well those present at this moment in space between TV camera and illuminated zone and observed in the form of silhouettes. Density of concentration of fishes is computed by division of number of observed fishes by value of volume of spherical sector whose radius equals product of light velocity in water by half-time of delay of gate of opening of detector of laser underwater TV system relative to pulse of laser radiator. In this case angles correspond to angle of view of detector of laser underwater TV system. EFFECT: raised authenticity of results of counting of fishes most distant but still visible, present on boundary of underwater. 4 dwg

Description

 The invention relates to fisheries, in particular to methods for assessing the number and stocks of commercial fish.

 Known pulsed laser-television system, working on the principle of spatial gating (Gryazin N.G. Optoelectronic systems for viewing space: Television systems. - L .: Engineering, Leningrad Branch, 1988, p. 141-146, Fig. 8.5) .

 The method of spatial gating consists in locking the photodetector of the system for all the time, except for the time of direct exposure of the photosensitive element reflected from a given section of space to a photosensitive element. Gating allows transmission of light to the receiver only from objects located at a distance from the camera, which is determined by the delay time, while light from other objects, including scattered water, does not pass to the receiver. At the same time, the influence of scattering haze on the photoconverter drive decreases in time of exposure and the contrast of the input image increases.

 Underwater television systems are used for filming the coastal shelf of the seabed. Filming is carried out using systems that are installed on submarine or surface ships, in bathyscaphes and bathyspheres.

 Known methods for measuring the density of fish concentration carried out using underwater television do not always allow reliable results due to incomplete accounting of fish located at the border of underwater vision, the most distant, but still visible.

 The proposed method allows to eliminate this drawback.

 To implement the method, a laser underwater television system is used, which contains a laser emitter 1, a light receiver (high-sensitivity TV camera) 2, cable or cableless communication channel 3, on-board equipment 4.

 In FIG. 1 shows a diagram of a device for implementing the method for determining the concentration density of fish; in FIG. 2 is a pulse diagram in a laser gating system; in FIG. 3 is an example of a photograph of a fish cluster by a laser TV camera; in FIG. 4 is a diagram for example of calculating the density of fish concentrations.

 The method for determining the concentration density of fish is carried out using a laser underwater television system, which works as follows (Fig. 1 and 2).

The laser 1 emits short pulses of light 5, which are reflected from objects 6, 7, 8, the reflected pulses 9, 10 and 11 are returned to the light receiver 2 at intervals corresponding to the distance to the objects. The receiver opens for a short time (strobe) 12 with an adjustable time delay 13 relative to the laser pulse 5. During the strobe period, only light reflected from the object 7 located in a thin spherical layer 14 whose radius R is equal to
R = C • t / 2,
where C is the speed of light in water; t is the delay time.

 This system allows you to increase the range of underwater vision by eliminating the scattering of light between the camera and objects located at a distance determined by the delay time of the strobe. Light from objects 8 located farther than this layer is not perceived.

 As shown by experiments with an underwater laser system, objects 7 located between the camera and the specified layer are depicted in the form of dark silhouettes (Fig. 3). In this case, the ability to observe all objects located within the inspected space can be simultaneously preserving the positive qualities of laser television in terms of eliminating scattered light and increasing the range of underwater vision.

 The received video signal via a communication cable 3 is transmitted to the on-board equipment 4, comprising a monitor 15 and a computer 16 for monitoring and video-grammatical processing. The operation of the laser 1 and receiver 2 is controlled from the control panel 17, which can be combined with computer 16, using the appropriate software.

 The determination of the density of the accumulation of fish by the described method is as follows.

 After turning on the submerged device submerged in water, using the delay line available in the equipment, the delay time of the strobe 13 relative to the laser emitter pulse is set (Fig. 2), which determines the distant boundary and the magnitude of the volume of water being examined. Visually or automatically using a computer, fish are counted in the inspected volume (observed in the frame at the time of shooting). For the convenience of counting, the frame can be stopped ("frozen") on the display screen by known methods, and, if necessary, recorded on a disc. When counting, not only the fish illuminated by the laser pulse are visible, but also located at that moment in the zone between the TV camera and the perceived layer of water and observed in the form of dark silhouettes (Fig. 3).

 Thus, when counting, all fish located within the spherical sector-shaped space, whose radius is equal to half the path that the light passes during the delay time of the opening strobe of the receiver of the laser underwater television system, and the angles correspond to the viewing angles of the receiver of the laser underwater television, are taken into account. system.

 The calculation of the density of the cluster (the number of fish per unit volume of water) is made according to the values of this radius (time delay of the strobe), the angles of view of the TV camera and the number of fish in the inspected space.

 Density calculation example.

где C = 2,24 • 10 м/с - скорость света в воде.Suppose a TV camera has horizontal and vertical viewing angles of 2α and 2β, respectively (Fig. 4). During shooting, we determine the value of the delay time t (Fig. 2, item 3) so that the radius of the water layer R perceived by the TV camera does not exceed the range of underwater visibility, i.e. so that objects (fish) are visible in the illuminated layer. If the number of fish per frame at the time of measurement is N, then the density is

where C = 2.24 • 10 m / s is the speed of light in water.

 For convenience, the delay time controller can be graduated in units not of time, but of distance in meters.

 The amount of water viewed by the TV camera can be determined with high accuracy due to the fact that the boundary of this volume is very clear and is determined by the delay value of the strobe of opening the shutter of the receiver relative to the laser pulse. Calculation of the number of fish is also very accurate, since there is no uncertainty about the position of the fish relative to the border of vision - all the fish observed belong to the volume of water examined by the camera. This is a great advantage of the proposed method.

 As shown by sea trials of a laser television system, the proposed method will allow to obtain the most reliable data on the number of fish in the considered volume of water and, as a consequence, the final result, on the size of its stocks.

 An additional increase in the reliability of estimates of the density of fish clusters takes place in this method due to the fact that the laser television system has a significantly increased range of underwater vision: according to the results of recent experiments, there is 3.2 times more transparency of water according to a standard white disk. This significantly weakens or completely eliminates the influence of the camera on the behavior of fish, which also positively affects the accuracy of estimates of the density of fish concentration in natural conditions.

 The implementation of the proposed method, which became possible as a result of the use of laser television, made it possible to obtain the most reliable data on the concentration density of fish due to a more accurate determination of the magnitude of the volume being examined and taking into account all the fish in it.

Claims (1)

 A method for determining the concentration density of fish, including shooting using a laser underwater television system with range gating, characterized in that they count visually or using a computer the number of fish observed in the frame, taking into account not only the fish illuminated by the laser pulse, but also located at this moment in the volume between the TV camera and the illuminated zone and observed in the form of silhouettes, and the calculation of the fish concentration density is carried out by dividing the number of fish observed by the volume of the spherical sector, the radius of which is the product of the speed of light in water by half the delay time of the strobe of opening the receiver of the laser underwater television system relative to the pulse of the laser emitter, while the angles correspond to the viewing angles of the receiver of the laser underwater television system.

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