5-1
5
5.
CALIBRATION
This chapter contains the procedures for calibrating the system.
5.1
Overview
Calibration is mandatory for acoustic resource surveys. In order to improve data ac-
curacy, calibrate the unit with a standard sphere. The purpose of the standard sphere
is to calibrate the TX and RX sensitivity of the entire system. The sensitivity correction
value is found by measuring the target strength (TS) and theoretical TS of a known
target (standard sphere) on the open sea. The difference between the target strength
and TS is the sensitivity correction value. Defining TX and RX sensitivity as the sum
of the source level and the receiver sensitivity (in dB), the sensitivity correction value
is equal to the TX and RX sensitivity minus its default value. Sensitivity measurements
taken during the Calibration mode (hereafter referred to as "CAL mode") are stored,
along with the source level and decibels, as a sonar data file. These measurements
allow you to ascertain the TX and RX sensitivity at the time of data recording.
5.2
Preparation
5.2.1
Necessary parts
A minimum of four persons (control the fishing line; operate the PC software) are re-
quired for the calibration. In addition, persons for anchorage and ship handling are
also necessary.
Name
Qty
Remarks
Standard sphere
1
Fishing rod
3
Rod mount
3
Fishing reel
3
With fishing line capacity of approx. 100 m
Fishing line
1
Nylon mono-filament, line weight 15
Weight
2
Fishing type, #150
Rope for passing fishing
line under hull
Approx.
40 m*
φ
8 - 10
* Approx. length for 400 ton vessel
Surface-activating
agent
Suitable
quantity
Dishwashing liquid can also be used.
Bucket
1
CTD (Conductivity Tem-
perature Depth) profiler
1
Water temperature gauge can be used.
Walkie-talkie
1
Ship's public address system can also be used.
