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The new LADCP-2 system

Introduction

The LADCP-2 system employs 2 new ADCPs of the Workhorse type (WHM300) manufactured by RD Instruments. The instruments are significantly smaller and lighter than the traditional ones and operate at a frequency of 300 kHz. The range of each of the profiler is about half of one RDI BB150 system but taken together the LADCP2 system has almost twice the range as one BB300 (300 kHz) LADCP system and a similar range as one BB150 (150 kHz) instrument. Moreover at least one of the instruments will always obtain a full range profile even when approaching the sea floor or the surface. This will greatly improve the overall performance.

Pictures from the first test cruise

Many thanks to Teri Chereskin who gave me an opportunity to test the LADCP-2 system during a Revelle shakedown cruise. You can look at a few pictures taken on a test cruise on board of the research vessel Rodger Revelle.

Data from the test cruise

You can also see some first results from the cruise. A time series of depth, vertical velocity of bin 2 and the range determined by a consistent W(z) criteria shows that the WHM300 can sense the velocities up to a range of 120m close to the surface which drops down to 55m at approximately 3000m depth. The std of the vertical velocity along the beams is about 1 cm^2/s^2 and does not change much with depth. Finally the profiles computed from just one WHM300 are not unreasonable but combining two good instruments will help quite a bit.

We are concerned about the quality of the attitude sensors. The tilt does show some noise represented here by the tilt difference between each pair of the three instruments measuring the same packages behavior during a short cast. The noise in the tilt sensors will affect the compass readings and aside from a few degrees rms a residual calibration offset was present and shows up as a large residual at a particular package orientation. s