SonTek/YSI Argonaut-XR Technical Manual - HydroScientific West

SonTek/YSI
4.2. Argonaut XR
The XR is most commonly mounted on the bottom looking up, but can also be installed from a
surface buoy or other structure looking down. The measurement volume is a cone with sides
sloped 25° off the vertical axis of the instrument. The diameter of the measurement volume cone
is 0.93 times the range from the transducer head (e.g., at 4 m, the cone has a diameter of 3.7 m).
The vertical extent of the measurement volume for the XR is set by the user and may be modified
by the instrument using dynamic boundary adjustment (see §6.1). The vertical range of the
measurement volume is defined by two parameters – Cell Begin and Cell End. Both are given in
vertical distances from the transducers up to a maximum range of 15 m. The minimum difference
between the two, and hence the minimum height of the measurement volume, is 0.5 m.
The precise vertical weighting within the measurement volume is determined by the convolution
of the acoustic pulse with the receive window during which the return signal is sampled. For the
XR, the acoustic pulse is 0.5-m long. The receive window is based on the settings of Cell Begin
(CB) and Cell End (CE). The length of the receive window is equal to the measurement volume
height (the difference between CB and CE). Figure 4 shows the weighting function and location
of the XR measurement volume relative to the user-specified values of CB and CE.
Some portion of the measurement volume extends beyond the limits set by CB and CE. For
typical operating parameters, more than 95% of the weighting function is contained within the
specified cell limits. The area outside the specified cell limit has minimal affect, and is not
normally considered part of the measurement volume.
4.3. Argonaut SL
The SL is designed for horizontal side-looking operation from underwater structures, but can also
be used for vertical up or down-looking installations in narrow channels. The measurement
volume is a V-shaped wedge in the plane defined by the two acoustic beams. The sides of the V
are sloped 25° off the horizontal axis of the instrument. The width of the V is equal to 0.93 times
the range from the transducer head (e.g., at 4 m, the width is 3.7 m).
The limits of the measurement volume are determined by user-selected parameters (see §6.2 for
guidelines). This range is defined by two parameters – Cell Begin (CB) and Cell End (CE). Both
are given in distance from the transducers along the axis of the instrument. The minimum difference
between the two, and hence the minimum length of the measurement volume, is 0.5 m.
The precise weighting within the measurement volume is determined by the convolution of the
acoustic pulse with the receive window during which the return signal is sampled. For the SL, the
6
1.0
Weigh
Functio 0.5
0.0
0.25
m 0.25
m
Cell
Range 0.5 to 14.5
Min. 0.5
0.25
m
0.25
m
Cell
Range 1.0 to 15.0
Figure 4 – Argonaut XR and SL Measurement Volume Weighting Function
Range
(m)
Argonaut Principles of Operation (March 1, 2001)