Navigation and Seamanship (1+1)

3.1.8.4.1. Paper recorder

                                                                         

Though paper recording is very old technique, it is reliable and recordings could be saved for future reference. Such recordings will be much useful in fish biomass estimation studies. Paper used for echo recording could be of two types , wet paper and dry paper. The wet paper contains a chemical solution which is coloured black/brown when an electric current is passed through it. The amount of colouring is proportional to the current strength which in turn is made proportional to the strength of echo form either the bottom or from fish. Care must be taken when storing unused wet paper so that its humidity, and thereby its sensitivity is not reduced. On dry paper, the echo traces are produced by electric sparks from the styles burning off a light grey surface layer, and this can be stored for long period of time. Dry paper has a smaller dynamic range for recording echo strength than has wet paper. The visual record of the reflected echoes of sound transmitted by an echo sounder is known as Echo gram.