The accuracy of depth measurements made by a fathometer or echo sounder requires a number of corrections because of the variability of sound or acoustic velocity in water with changes in temperature, salinity, and depth of water. In addition instability of the equipment can also result in significant errors. For additional information see Practice D 5073.

Calibration of echo sounding instruments is absolutely critical in assuring the adequacy of depth measurements. When an echo sounder has been accurately calibrated, any observed (recorded) depth can be related to the true depth of water. Since the intended purpose of echo sounding is to measure the “true” depth, an independent “true” reference must be used.

A bar-check is the most wide-spread, easiest to construct, and most economical mechanical method to determine corrections for instrument and velocity errors.

This procedure explains the calibration of a fathometer or electronic depth sounder using a bar-check.

Bar-checking techniques and equipment are general in nature and may need to be modified for use in specific field conditions.

1.1 This practice provides the user with procedures used in manually calibrating the fathometer or electronic depth sounder. This narrative describes calibration terminology, describes acceptable environmental conditions for calibration, and describes the calibration procedures.

1.2 The references cited contain useful information in the construction and the correct operation of the calibration equipment.

1.3 Any references cited in this narrative to specific products or brand names are made for information only, and is intended to be descriptive, but not restrictive, of products that will perform satisfactorily.

1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.