Objective
The aim of this project is to develop a commercial Doppler Sonar for measuring current speed and direction within the ocean to a depth of one thousand meters and beyond.
Signal processing techniques and acoustic research already developed for atmospheric measurements with the same kind of instrument will be used to produce a so-called "Second generation Doppler Sonar". The innovations are an electronically steerable transducer and very sophisticated signal processing. This will improve measurement reliability and accuracy in "hostile" environments and the sensitivity to increase the range of measurement.
Intermediate results of this project will be available at the end of 1989.
The work has included the following phases :
2.1 Computer simulations of the transducer :
A deep-range capability corresponds to operating frequencies which are lower than used by the usual commercial systems. We have chosen a nominal central frequency of 40 kHz.
Different phase-array transducers have been modelled, both from the technical point of view (eg. the size and directivity pattern, transient response, sensitivity, etc.) and from the cost and maintainability point of view.
2.2 Manufacturing and test of the transducer which has been chosen after the computer simulations :
The tests conducted in a water tank have been in perfect agreement with the expected characteristics. Although using a relatively low frequency, the transducer's sophisticated design made possible its very small size (a cylinder of 20 cm height and 20 cm diameter). This unique transducer generates 5 beams through an electronic steering technique.
2.3 Software design :
The other original feature of the Remtech Doppler Currentmeter lies in the signal processing. To begin with, the received signal is pre-processed using a Fast Fourrier Transform. This allows an extremely accurate frequency analysis, compared to the usual commercially employed method. So with the Fast Fourrier method, one can take into consideration an ambient noise whose energy depends on the frequency, as well as distinguish between spurious signals and the useful signal itself.
Moreover, the emitted pulse is frequency coded, which allows the use of a consensus method applied to the received signal. This enables us to work with signal-to-noise ratios which are much weaker than with standard sonars.
2. 4 Tests on board a ship :
Tests have been conducted in the Mediterranean Sea and have shown that the 1000 m depth range capability was reached and even exceeded.
Programme(s)
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
78143 Velizy
France