After the distance to the surface is measured, the thickness of the ice draft itself can be calculated by subtracting the location of the leading edge of the altimeter peak from the mean depth determined from the high accuracy, temperature-compensated pressure sensor. These are calculations the user has to do in post processing and is not done internally by the instrument.
| \( \text{Ice draft(keel)} = \text{Water depth} - \text{Distance to ice} \) | (1) |
In post-processing it is necessary to convert the pressure measurements to an equivalent height of the free water surface, and to apply various corrections (see below) to both types of data.
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