DEVICE FOR FISH SEARCH INSTRUMENT

Abstract: A device for fish search instrument (1) and operatively adapted for generating signals corresponding to the strength of echos from reflecting objects, e.g. fish in the sea, comprises an echo strength discriminator (3) connected with the fish search instrument (1) and operative to display the echos according to strength in at least two strength categories, echo counting means (4) connected with the discriminator (3) for counting the number of echos within each strength category, and display means (5) associated with the echo counting means (4) and operatively adapted for providing an indication of the counted echos in each strength category.

Description: Device for Fish Search Instrument. During the later years increasing importance has been attached to selective fishing. In order to preserve the stock of fish, preferably only fish of the correct kind and size should be cought in restricted quantities according to stipulated quotas. Up to now it has been difficult to form a well founded opinion as to kind and size before the catch is made. The fish search equipments us ' ed, i.e. sonar sounding systems, include inherent characteristics which make the estimates less accurate than desired. Even though dispersion and attenuation of the sound waves have been compensated by time variable gain, the strength of the finally presented signals on screen or printer have been dependent on the direction of the incident sound wave. In other words, the strength of the fish echo is dependent on the location of the fish in the sound beam. The echo from an object or target in the sea is dependent on the reflection characteristics of the object, i.e. the target strength. For fish the target strength is different for different species. Such difference is particularly large between species with and without swimming bladder. Furthermore, the target strength of a fish is dependent on its size and how it is situated in the sound beam. Thus, a fish gives a stronger echo seen from its broad side than seen from the front. The present invention is a contribution to the art of making selective fishing possible by displaying the size distribution of the fish. In the exemplified embodiment illustrated in figure 1 is schematically shown an echo sounding system 1 with a signal output 2 for echo signals representing the target strength of objects in the sea. Said signals are transferred to a target strength detector 3, in which the signals are compared with selected limit values for the target strength categories to be processed. Such categories may imply a simple indication of "big" or "small" fish, or a more accurate subdivision into target strength ranges as : -50 to -40 dB -40 to -30 dB -30 to -20 dB -20 to ' -10 dB -10 to 0 dB stronger than 0 dB The accuracy of such gradation into categories is dependent on how correctly the signals delivered by the echo sounding system represent the target strengths. The target strength detector 3 is connected to an echo counter 4, which is operative to count the number of echos detected by the detector 3 within each category, here illustrated by three categories A, B and C. The echo counter 4 is connected tc display means which indicates the number of echos within each size category. Such indication may be presented in digital form, as histogram on screen or in any other suitable manner. Another embodiment of the invention is shown in " figure 2. Between the first output 2 of the echo sounding system 1 and the target strength detector 3 is inserted a single fish detector 6. This detector consists of a signal amplitude detector 7 and a signal duration detector 8. In order that a signal may be considered an echo from a single fish, it must (should) have an amplitude above a certain level and a duration of the same order of magnitude as a transmitter pulse. If the duration is too short, the signal is probably noise, and if it is too long, the echo is probably due to more than one single fish. Furthermore, a signal processing unit 9 is preferably connected to the output of the echo counter 4. In this signal processing unit 9 the number of echos in each category A, B, C is multiplied by a factor representing the weight of a fish having the corresponding target strength. Thus, the total weight of the fish is derived for each size category and may be presented to the operator of the equipment. Further, the percentual distribution"C-f the size or weight όTf the fish within a certain period of time, e.g. the last half hour, may be calculated. As indicated in figure 2, the size distribution is advantageously shown as additional information on the screen or printer of the echo sounding system..

Claims: Patent Claim. A device for fish search instrument and operatively adapted for generating signals which represent the strength of echos from reflecting objects, e.g. fish in the sea, c h a r a c t e r i z e d b y an echo strength discriminator connected with the fish search instrument and operative to display the echos according to strength in at least two strength categories, echo counting means connected to the echo strength discriminator for counting the number of echos within each strength category, and display means connected to the echo counting means for providing an indication of the number of echos in each category.

Inventors: KRISTENSEN HOGNE FINN, SOLLI HAAKON, KRISTENSEN, HOGNE, FINN, SOLLI, HAAKON
Applicants: SIMRAD SUBSEA A S, SIMRAD SUBSEA A/S
Application year: 1985
Main classification: G01S15
IPC codes: G01S15