YSI ADV6600 - Manual (Page 83)

Section 5. Mounting and Installation
ADV6600
Y S I
Environmental
Page 73
Some points to keep in mind regarding non-fixed (tethered) deployments either free or in a PVC
pipe:
• The compass is sampled once per second, so rapid or abrupt movement of the system can yield
inaccurate compass measurements, and therefore inaccurate velocity measurements.
• Some slight and regular movements of the system are acceptable and will be averaged out
during the collection time period (averaging interval). How much of this environmental “white
noise” that will be average out is a function of the amount of movement the system is
experiencing and the length of time the ADV6600 is averaging. In all cases the longer the
average the more of the regular movements will be removed (averaged out)
• The variation in the three rotations (heading, pitch, and roll) is recorded to the system as
Heading Standard Deviation, Pitch Standard Deviation, and Roll Standard Deviation,
respectively and can be used to determine how “active” the movement of the ADV6600 was
during the deployment.
5-2. Mounting Cautions
In order to assure a successful deployment of your ADV6600, users should be aware of several
situations to avoid when selecting a site or deployment method. Critical considerations are detailed
below.
5-2.1. Bottom Interference
When deploying the ADV6600, it is critical to be certain that the sampling volume of the Doppler
sensor extends approximately 7 cm (2.8 inches) from the bottom of the sensor transducer which is
shown in the diagram below. This sampling volume MUST be well above the bottom of the body of
water being monitored. Therefore, when considering a deployment site, assure that there is
sufficient water depth present to allow the transducer to be at least 6 inches above the bottom (or
other boundary) and still cover all of the water quality sensors. In practice, this means that the
water at the deployment site must be at least 15 inches deep. By running a Beam Check at the site,
you will be able to determine if the ADV sensor is too close to the bottom. For example, the beam
check below shows a strong signal for all three receivers at a lower x-axis value than the sampling
bottom indicating that the Doppler sensor is closer to the boundary (bottom of the body of water)
than the sampling volume of the sensor which resides about 7 cm below the transmit transducer.
Clearly, the ADV6600 would have to be raised until the boundary peak shifted to greater x-axis
values than the sampling volume in order to be able to acquire useful velocity data.