Small Vectrino sampling volumes

After reviewing some curious Vectrino test results from Lamont-Doherty Earth Observatory, we have tested the performance of the Vectrino when using very small sampling volumes.  Our conclusion is that the smallest sampling volume with a nominal size of 1 mm is not recommended for normal operation.  Here are the results of a tank test in quiet water (very low turbulence levels).  The SNR was about 15dB at all sampling volumes and the the velocity range was 30cm/s. As can be seen, the standard deviation is quite large when the nominal sampling volume size is 1mm.   Here are the numbers: 

Vvolume height:     Std of Vx:

• 1.0mm      35.9 cm/s
• 2.5mm        0.7 cm/s
• 4.0mm        0.36 cm/s
• 5.5mm        0.30 cm/s
• 7.0mm        0.28 cm/s
  

- Marius Mathisen/Atle Lohrmann