Vessel-Mounted Acoustic Doppler Profiler - VM-ADP

Vessel-Mounted Acoustic Doppler Profiler (VM-ADP)

Key Specifications

Velocity:

• Velocity range: ±10m/s
• Accuracy: 1% of measured value ±0.5cm/s
• Sampling rate: 1s to several hours
• Maximum profiling range: 50m (600kHz), depending on local conditions
• Cell size: 0.4 to 2m
• Minimum blanking distance: 0.4m

Sensors:

• Compass (flux-gate, automatic up/down detection)
• Tilt (liquid level, max 30° tilt)
• Pressure (piezoresistive, resolution better than 0.005% of full scale)
• Temperature (resistive)
• Two analog channels for use with any analog sensors.

In order to provide the true ocean currents, all vessel-mounted current profilers must subtract the ship velocity from the measured data. It is possible to use two methods. The traditional method relies on "bottom track", a technique where the Doppler profiler measures the velocity of the bottom relative to the ship. The second one relies on connecting to the gyro and the DGPS to obtain the vessel velocity. Advantages of the second solution are:

• The water depth is irrelevant and the system works equally well in shallow and deep water (bottom track does not work if the bottom is deeper than the maximum acoustic range) 
• The quality of the bottom acoustic conditions is irrelevant (bottom track fails when the bottom is acoustically indistinct) 
• High resolution data close to the surface can be collect in deep water (bottom track requires the use of low frequency acoustics because the pulse must always reach the bottom) .

The following interfaces are necessary: 

• GPS receiver: Any receiver with serial output. The accuracy of the GPS velocity should be 0.05 m/s or better (DGPS)
• Gyro: Any gyro with serial output and accuracy better than 1°. It is also possible to use combined gyro and GPS system
• Computer: The survey computer needs at least 3 serial ports and it is advisable to use an intelligent multi-port card.