Argonaut-SL Principles of Operation

The Argonaut-SL (Side-Looking) belongs 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 (three transducers) and a 2D Argonaut (two transducers) are 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-MD and Argonaut-XR measure the 3D velocity. In the same manner, the Argonaut-SL measures 2D velocity in the plane defined by its two acoustic beams.

Doppler technology has a number of 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.

The 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.

More details about the Argonaut-SL can be found at:

• Argonaut-SL Overview
• Argonaut-SL Description
• Argonaut-SL Applications
• Argonaut-SL Specifications

• Argonaut-SL Webinar Training Sessions and Podcasts
• Instruments for Hydrology Training Course
• Ask questions or request Argonaut-SL literature
• Listing of all SonTek/YSI products