Pressure sensor

The pressure measurements in the Nortek Aquadopp, Vector, and AWAC products are all based on the use of a piezoresistive sensor.  This sensor was favored because of its ability to pick up detailed wave action.  The resolution is close to that of expensive crystal sensors and when combined with our 16-bit low-noise A/D converter it is really great for picking up variations in the sea surface elevation. " />'>

The piezoresistive sensor is not intended for long term absolute depth measurements.  

Several limiting factors come in to play:


a) We do not measure the atmospheric pressure.  These variations give rise to changes in the pressure measurements of +/-0.3 m without any corresponding change in the sea surface elevation.

b) The sensor is non-linear, typically better than 0.5% of FS over the full range of ocean temperatures.

c) There piezoresistive sensor is temperature dependent, typically 0.25% of FS over the full range of ocean temperatures.

d) Almost all our software outputs dB instead of m.  It may still indicate otherwise in the *.hdr file but this should be ignored.

There is on exception - the DW Aquadopp software.  Because of the large correction terms that you have to contend with below 1000m, this software outputs the depth in m corrected also for the water compressibility.  This software also converts the measured frequency output to velocity using the pressure correction to the soundspeed formulas so it should be doing everything correctly  

Best regards, Atle Lohrmann

This does not mean that our pressure sensors can not be used for long term tide monitoring.  However, it is not a “sea level rise sensor” and the above elements should be included when estimating the absolute accuracy.