Linearity and noise in differential travel time acoustic velocity measurement

An improved constant current source for the time interval integrator in the differential travel time velocity sensor, BASS (Benthic Acoustic Stress Sensor), has extended the full scale range of velocity over which the measurement of velocity is linear from 100 cm/s to 500 cm/s/sup 1/. Slow speed response in the former constant current source introduced non-linearities of 5% to 8% for full scale ranges of 240 cm/s. When corrected, linearity is restored to 1.5% over the entire range. Electronic noise (standard deviation) is less than 0.5% of reading with a minimum noise of 0.3 mm/s equivalent velocity for a 15 cm path length.