Incorrect pressure reading
The AST window is set dynamically based on the pressure sensor reading from the preceding current profile. This means if the pressure sensor is damaged or with a large, incorrect offset the window may be set incorrectly. There is unfortunately no way to correct for this later or in post-processing as the listening window does not capture the surface reflection. Make sure to set the pressure offset before each deployment or contact us about returning the instrument if the pressure sensor is faulty.
Blocked centre transducer
If the AST transducer is covered by sediment/biofouling or blocked by an object, most of the energy in the pulse will be absorbed or scattered too soon. Less energy will reach the surface, and the AST readings may be missing or bad.
If the AWAC experiences tilt of greater than 10°, the AST beam can start to miss the surface due to the angle and the absorption of energy.