Standard values

Table 5 provides a list of common standard values for calibration.  The calibration sphere TS is dependent on the water temperature and salinity (i.e., sound speed dependent).  The copper spheres specified for each frequency have been shown to be “optimal” in that the TS of the specified spheres vary minimally for a normal range of temperatures and salinities (Foote et al. 1987).  However, many groups use a single tungsten carbide sphere to calibrate multiple frequencies (Foote 1990).

 

Table 5.  Calibration standard values.  Calibration sphere measurements are the sphere diameter.  ‘Cu’ denotes copper and ‘WC’ denotes tungsten carbide. Calculations for the WC spheres are from Foote (1990) (38.1 mm, bandwidth about 3 kHz) or from the manufacturer’s data sheet (Biosonics and Simrad). 

Frequency [kHz]	Calibration Sphere	Nominal TS [dB]
38	60.0 mm Cu	-33.60
38	38.1 mm WC	-42.04
70	32.1 mm Cu	-39.10
70	38.1 mm WC	-40.56
120	23.0 mm Cu	-40.40
120	38.1 mm WC	-39.83
200	13.7 mm Cu	-45.00
200	38.1 mm WC	-39.45
420	23.0 mm WC	-43.60