VISION

Compute the wind and temperature fields in a region, by measuring parameters of acoustic sound propagation

SCIENTIFIC TOPICS

Vector and scalar tomography, acoustics in moving inhomogeneous media

1) Experimental setup

2) Simulation model

3) Wind reconstruction

4) Temperature reconstruction

APPLICATIONS

Meteorology, wind tunnels

RESULTS

Tomography methods aim at recovering an unknown multi-dimensional field based on the interactions between the considered medium and radiations emitted by measuring devices. They offer an attractive alternative to classical methods employed in sensor networks, since they allow non-invasive measurements with a significantly smaller number of sensing devices. In this project, we focus on the use of acoustic tomography for measuring temperature and wind flow fields. A new technique based solely on acoustic waves propagation is presented. In contrast to the usual straight ray assumption, a bent ray model is considered in order to achieve higher accuracy. Under this assumption, we propose an iterative reconstruction algorithm that allows to entirely recover the considered fields. Simulation results confirm the effectiveness and fast convergence of our scheme.

We also developed a laboratory size experiment, where we focus only on estimating the temperature from the time of flight measurements. The experiment aims at showing the feasibility of our acoustic tomography method, identifying the practical problems and providing the bounds on the achievable accuracy. It consists of 12 ultrasound emmiters and 12 receivers placed on the ring with the radius of 1m. The signal is generated and acquired by Motu 24I/O audio card, operated by a computer. The card provides 24, 24-bit/96 kHz analog inputs and outputs, and the possibility to connect 4 cards together and thus, extend the number of input and output channels to 96. This option is very favorable when we want to increase spatial resolution. To compensate for relatively modest power levels of input and output signals arrays of amplifiers and preamplifiers are used. Both the amplifiers and preamplifiers are built in our laboratory in order to meet the tight specifications of bandwidth and SNR. To avoid mechanical distance calibration we use the time delay estimates to compute the positions and the delays of the transducers. In this way the positions are determined up to the precision of 5mm, for the distances of 1m, and the delays of the transducers are within the accuracy of 15us. Since the error is mainly systematic its influence can be canceled when estimating only the temperature variation from a fixed known temperature value. We estimated the temperature distribution around a hot plate placed inside the ring. In Figures, we show the experimental setup and the experimental result.

MAIN PUBLICATIONS

I.Jovanovic, L. Sbaiz and M. Vetterli, "Acoustic tomography method for measuring temperature and wind velocity", IEEE International Conference on Acoustics, Speech, and Signal Processing, May 2006.

I. Jovanovic, L. Sbaiz and M. Vetterli, "Acoustic tomography for estimating temperature and wind flow", 13th International Symposium for the Advancement of Boundary Layer Remote Sensing, ISARS, pp. 69-71, 2006.