YSI SonTek ADVField, Техническая документация инструкция

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SonTek/YSI
Acoustic Doppler Velocimeter Principles of Operation (September 1, 2001) 8
lation values will affect the short-term variability in velocity data (e.g., increase the noise), but
will not bias the mean velocity measurements. For mean velocity measurements, correlation val-
ues as low as about 30% can be used.
The description given above is intended to provide general guidelines when using the correlation
coefficient as a data quality parameter. To understand the exact meaning of the correlation coef-
ficient, and all factors affecting it, requires an in-depth discussion of pulse-coherent Doppler
processing. Additional information and references are available from SonTek.
7. Special Considerations
This section addresses several aspects of the ADV that require special attention. Section 7.1 de-
scribes the different 16-MHz and 10-MHz ADV probe configurations, and the environments in
which they are used. Section 7.2 discusses the effect of sound speed on ADV velocity data. Sec-
tion 7.3 describes concerns related to near boundary measurements, and the type of performance
that can be expected. Section 7.4 discusses software modifications to reduce the size of the sam-
pling volume. Section 7.5 discusses the use of the ADV for low flow applications.
7.1. Alternate Probe Configurations
The 16-MHz and 10-MHz ADV probes, used in a variety of laboratory and field experiments, are
available in several configurations for different measurement needs. These variations are divided
into four areas: location of the sampling volume, acoustic sensor mounting, sensor orientation,
and coordinate resolution. Probes can be configured with almost any combination of these. The
5-MHz ADVOcean probe uses a single, rugged configuration: 3D sensor, oriented looking
down, with an 18-cm distance to the sampling volume.
Sampling volume location
. The sampling volume can be located either 5 or 10 cm from the tip of
the acoustic sensor. The 5-cm sensor can be used in shallower water and gives a stronger return
signal by about 6 dB. The 10-cm sensor has less potential for flow interference in oscillatory
flow.
Sensor mounting
. The sensor can be mounted on a 25 or 40-cm long stainless steel stem, or on a
100-cm flexible cable. The 40-cm stem is used in laboratory applications to reduce the amount of
equipment in the water. The 25-cm stem is used in field applications where a more rigid mount-
ing is required. The 100-cm cable allows increased flexibility in the sensor orientation, but re-
quires more complicated mounting arrangements.
Sensor orientation
. The ADV acoustic sensor can be oriented looking up, down, or to the side.
Down is most common as it allows for easy mounting and measurements close to the bottom
boundary. Side-looking is typically used in wave tanks with the sensor mounted looking across
the direction of propagation, reducing the chance of flow interference. Up-looking is typically
used for measurements near the surface, under a layer of ice, or near the bottom of a vessel or
structure.
Coordinate resolution
. The ADV can be built to measure either 2D or 3D fluid flow, using two
or three acoustic receivers respectively. 3D is the most common configuration; 2D is most com-
monly used for very shallow water (minimum 3 cm) with a side-looking sensor, or for very nar-
row channels using a down-looking sensor.