SonTek Argonaut SW series of acoustic current meters

Designed with surface-mount electronics and Doppler technology, SonTek’s Argonaut series of acoustic current meters is designed for accuracy in velocity measurements. The meters are available in several configurations, making them suitable for a wide range of applications.

In a number of small, low head-loss channels (usually irrigation, though there are many others), hydrometrists have tried several methods to obtain continuous or near-continuous flow measurements. This includes the use of flumes and weirs often being installed in applications where discharge is very low. While trapezoidal flumes allow for better measurements throughout a range of flows without introducing large head losses, they are difficult and costly to build. Weirs have often been of the thin plate variety. The thin-plated weirs can create large areas of backwater and have the ever-present threat of lost accuracy (and further backwater effects) by becoming clogged with debris.

With a side-mounted Doppler velocity sensor (such as our Argonaut- SL), there is no need to be concerned with head-loss or backwater effects. However, the difficulty of maintaining water depth or mounting a relatively large sensor in a small channel played a major part in the development of the Argonaut-SW velocity sensor. The SW is a bottom-mounted system intended for complex index velocity sites (those with large-stage variation or stratified flow) and for sites where purely theoretical discharge calculations are desired.

The SW has three acoustic beams. When properly bottom mounted (usually in a channel), one of these beams points straight up, and the other two point up/downstream at a 45° angle. The upward-looking beam measures water level. The two slanted beams measure the water velocity in two dimensions via the Doppler method. This level and velocity information is then used (together with the geometry of the channel) to compute flow, mean velocity and area. A key technical innovation in the Argonaut-SW, which separates it from other Doppler sensors, is that velocity measurements are made all the way to the water’s surface without any of the contamination normally associated with side-lobe interference. This enables it to take full advantage of the vertically integrated velocity in its internal flow calculations.