Comparison of dynamic height measurements from an inverted echo sounder and an island tide gauge in the central Pacific

An inverted echo sounder (IES) and deep pressure sensor were deployed within 70 km of a shallow pressure sensor at Palmyra Island (6°N, 162°W) in the central Pacific. These instruments provided yearlong records of acoustic travel time, deep pressure and sea level. Two independent time series of dynamic height are derived from travel time and sea surface elevation, respectively. The spectra of these time series are similar, and at the spectral peaks the coherence between them exceeds 99.9% confidence levels, indicating that travel time can be used to record dynamic height fluctuations. This investigation provides a frequency dependent calibration for the IES in this region. At the energetic low frequencies (periods ∼ 1 month), this calibration agrees with a calibration by the standard method using conductivity‐temperature‐depth (CTD) casts. At higher frequencies (periods of ∼3 days), using the CTD‐derived calibration may underestimate the amplitude of some processes by as much as 30%