On the Temperature Correction of the Aquatrak Acoustic Tide Gauge

Temperature corrections for the Aquatrak acoustic tide gauge are derived. These account for variable temperature (and hence sound velocity) along the sounding tube, thermal expansion of the calibration tube, and the thermal response of the transducer/controller combination. When averaged over long periods (e.g., seasonal), the corrections are typically several millimeters in magnitude, with short-period (e.g.. diurnal) variations as large as several centimeters. The correction associated with thermal expansion of the calibration tube is of the same order as the correction for variable sound velocity, which is already applied at some Aquatrak installations. The corrections derived here relate to the situation in which an initial adjustment has been made by the manufacturer (making the calibration tube a fixed known length under factory conditions), and a subsequent calibration is performed to define a single zero offset for the instrument.