Argonaut-MD Expanded Description
Designed with state-of-the-art surface mount electronics and proven Doppler technology,
SonTek's Argonaut series of acoustic current meters offers unsurpassed accuracy in
velocity measurements. Argonauts are available in several configurations for a wide range
of applications. A few of the most common are described below.
1.1. Open-Ocean Moorings - The Argonaut-MD
The Argonaut-MD (Mooring Deployments) is designed for current monitoring in the open
ocean. The Argonaut-MD uses a fixed measurement volume centered 1.25 m from the instrument
for 3-MHz systems (2.0 m for 1.5-MHz systems) and is housed in a single canister with internal memory and batteries. The Argonaut-MD can
be clamped to the mooring line or mounted within a mooring cage. Low power consumption and
flexible sampling strategies allow multiple year deployments using alkaline batteries. |
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1.2. Shallow-Water Deployments - The Argonaut-XR
The Argonaut-XR (Extended Range) is ideal for shallow water current monitoring in areas
such as rivers, irrigation channels, estuaries, and ports. Designed for bottom-mounting,
the Argonaut-XR has a measurement volume programmable over a vertical range up to
40 m.
With the integrated pressure sensor, the Argonaut-XR can adjust the measurement volume
height to report depth-averaged velocity over the entire water column or over a
user-programmable range (even with tide or stage variation). The Argonaut-XR can be used
for real-time monitoring (cable lengths up to 1500 m) or autonomous deployments with the
external battery pack. |
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1.3. Underwater Structures - The Argonaut-SL
The Argonaut-SL (Side-Looking) is designed for horizontal operation, making a remote
velocity measurement from an underwater structure (pier, bridge, channel, etc.) while
allowing a simple and secure instrument mounting. The Argonaut-SL measures 2D currents in
an adjustable measurement volume located at a range up to 22 m. Like the Argonaut-XR, the
Argonaut-SL can be used for real-time or autonomous applications. |
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The Argonauts belong to a class of instruments known as monostatic Doppler current
meters. Monostatic refers to the fact that the same transducer is used as transmitter and
receiver. A monostatic Doppler uses a set of acoustic transducers with precisely known
relative orientations. Each transducer produces a narrow beam of sound perpendicular to
the transducer face. The operation of a 3D Argonaut (with three transducers) is shown here.
| During operation, each transducer produces a short pulse of
sound at a known frequency that propagates along the axis of the acoustic beam. Sound from
the outgoing pulse is reflected ("scattered") in all directions by particulate
matter in the water. Some portion of the scattered energy travels back along the beam axis
to the transducer. This return signal has a frequency shift proportional to the velocity
of the scattering material. This frequency change (Doppler shift), as measured by the
Argonaut, is proportional to the projection of the water velocity onto the axis of the
acoustic beam. By combining data from three beams, and knowing the relative orientation of
those beams, the Argonaut measures the 3D velocity. In the same manner, the Argonaut-SL
measures 2D velocity in the plane defined by its two acoustic beams. |
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Doppler technology has several inherent advantages that make it the preferred method
for current measurement. Combining this with SonTek’s proven ability to develop
instruments that are both powerful and easy to use, the Argonaut is the ideal choice for a
wide range of applications. Argonaut advantages include:
- Measurements are made in a remote sampling volume free from flow distortion.
- Velocity data are free from drift; the Argonaut never requires calibration.
- Doppler technology has no inherent minimum detectable velocity, giving excellent
performance at low flows.
- The Argonaut has no moving parts, is immune to biofouling contamination, and the user
can directly apply anti-fouling paint to prevent growth.
- The same robust computational algorithms are used for velocities from 1 cm/s to 10 m/s.
SonTek's user interface allows easy operation with minimal training and experience.
First time users can collect test data within minutes of receiving the Argonaut.
Deployments require only a few minutes to configure the Argonaut and start collecting
data. The basic operating parameters include the following: averaging time, time between
samples, and start time. The Argonaut provides the highest quality Doppler velocity data
without requiring the user to become an expert on Doppler technology.
Argonaut velocity data has a specified accuracy of ±1% of
measured velocity and ±0.5 cm/s. These specifications have
been verified using laboratory simulations, tow-carriage testing, and field comparisons
with other meters. Results from one tow-carriage test are presented here.
An Argonaut was mounted from the bottom of a moving carriage at the Offshore Model
Basin (OMB) tow facility in Escondido, California. The meter was towed over a working tank
length of 45 m at eight speeds in both directions. Two different mounting orientations
were used with no effect on velocity performance. Tow carriage speed at OMB has been
independently verified to ±0.5%. Results from all runs are
shown in the plot below. A least squares linear fit of the velocity data to the carriage
speed gives a slope of 0.996 with an offset of 0.1 cm/s.
The Argonaut-MD is designed for autonomous deployment and is most commonly mounted as
part of a multiple-instrument mooring. It comes standard with internal battery power,
4-MB
memory, compass/tilt sensor, and a temperature sensor. Optional features include a
pressure sensor and an integrated CTD.
For deployment, the Argonaut-MD can be clamped directly to a mooring line without
acoustic or flow interference. This allows the meter to be installed without a break in
the mooring line. When required, an in-line load cage is available.
5.1. Physical Parameters
- Dimensions: 10.2-cm (4.0-in) diameter by 65.5-cm (25.8-in) length
- Weight in air (with alkaline batteries): 6.4 kg (14.0 lb)
- Weight in water (with alkaline batteries): 1.4 kg (3.1 lb)
- Pressure rating (Delrin housing): 600 m
- Pressure rating (Titanium housing): 6000 m
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5.2. Standard Features
- Fixed measurement volume located 0.5 m to 2.0 m vertically from sensor
- Alkaline batteries sufficient for 120 days continuous operation
- Flexible sampling strategies for reduced duty cycle operation and extended deployments
- 4-MB internal memory (over 200,000 samples)
- Beam angle 45° for optimal 3D velocity performance
- Temperature sensor for automatic sound speed compensation
- Compass/tilt sensor to report velocity in Earth (East-North-Up) coordinates
5.3. Optional Features
- Lithium batteries sufficient for 180 days continuous operation
- Integrated pressure sensor
- Integrated CTD
- Clamps for mounting to mooring line
- In-line mooring load cage
Details about this SonTek/YSI product can be found at:
