Pressure sensor calibrations of acoustic telemetry transmitters

Table 1 Error rates of acoustic transmitter pressure sensor output associated with three external effects (i.e., water temperature, salinity, and atmospheric pressure)

External effect	Constant variables	Range of external effect	Estimated depth (m)	Error (m) at a depth of 68 m compared to actual depth
Water temperature (°C)	Salinity: fresh water	ρ of 4 °C fresh water = 999.9720 kg/m³	67.88	0.12 shallower
	Atmospheric pressure: standard	ρ of 20 °C fresh water = 998.2072 kg/m³	68
		ρ of 40 °C fresh water = 992.2164 kg/m³	68.41	0.41 deeper
Salinity (kg/m³)	Water temperature: room temperature	ρ of fresh water = 998.2072 kg/m³	68
Salinity (kg/m³)	Atmospheric pressure: standard	Salt water ρ = 1024.8103 kg/m³	66.23	1.77 shallower
Atmospheric pressure (Pa)	Water temperature: room temperature	Low P = 87,000 Pa	69.46	1.46 deeper
	Salinity: fresh water	Standard P = 101,325 Pa	68
		High P = 108,000 Pa	67.32	0.68 shallower

The estimated depths were calculated based on the hydrostatic pressure for fresh water at 20 °C and standard atmospheric pressure with the following formula: P _total = P _atmosphere + P _fluid, (P _fluid = ρgh), where ρ = water density (kg/m³), g = gravitational acceleration (9.8 m/s²), and h = depth (m). For all evaluations of external effects on depth estimates, depths of 68 m (maximum depth of V16 transmitters) were used because errors would be most pronounced here (i.e., because changes in water density are cumulative with depth)

ISSN: 2050-3385