- the AWAC firmware is version 3.31 or later (March 2010)
- the ice mode is enabled.
The ice feature in firmware is available for AWACs delivered after the end of 2008 (Midlife firmware). This is indicated by a firmware version 3.xx and a hardware serial number above 1000.
The option for a temperature compensated pressure sensor is available for AWACs after spring 2011. This is an option that does not come standard with the AWAC. The error for the pressure estimate is reduced from 0.5% to 0.1% (full scale). For a 100 meter sensor this translates to a reduction in uncertainty of 50 cm to 10 cm, which can be important when estimating ice thickness.
A discussion on estimating ice thickness can be found in two relevant papers on Nortek Insight, called "Measurements of Ice Parameters in the Beaufort Sea using the Nortek AWAC Acoustic Doppler Current Profiler" (2010) and "Waves in the Summer, Ice in the Winter" (2010).
Corrections for atmospheric pressure is simply to correct for the variations during the deployment, where the zero datum is established preferably at the beginning or end when the instrument is in air, otherwise this can be done at similar points in time for a known depth.
It is worth pointing out that any pressure sensor bias can be identified and removed if the AWAC has any measurements in the air, typically at the beginning and end of the deployment.
Uncertainty from the speed of sound and density variations can be reduced by identifying ice free periods and setting the AST and pressure distance equal. This does not provide a unique solution for estimating the integrated density or speed of sound but it does allow the user to "tie" these values together and begin making limits on these values - bounding the solution.
Happy ice hunting!