In these formulae: H0(1) - Hankel function; λn, Ψn - eigen-values and eigen-function depending on distance; N - the number of propagating modes.
Calculation times of group delay for the first three modes in relation to the arrival time of water wave run as high as 0.0242, 0.0975, 0.2227 sec respectively.
3. Experimental results
Marine experiment was performed under winter isotermia conditions by using acoustic independent mobile receiving and transmitting system to measure and monitoring the oceanological parameters of enviroument. This complex consist of transmitting, receiving systems and that of processing and collection data.
The transmitting system is an independent electromagnetic transducer having a transmission control subsystem. It provides according to the study scheme transmitting various signals of transmission frequency being 200-300 Hz, bandwidth being 50 Hz, and is intended for multiple fixing at a depth up to 300 m. The system can be equipped with monitoring hydrophone transmitting data through radio-communication channel or with the UWT system. Power supply maintain the continuity of system from a few twenty-four hours to a few weeks, depending on time transmission diagram.
Under real conditions the transducer operated at a depth of zs on a carrier frequency close to 250 Hz and provided a band of 50 Hz. As the sounding signal, 255-symbol M-code with a symbol duration of 0.04 sec was used. The code was transmitted in series with a repeat period of 20 sec and that of series being 60 sec, partially compensating the absence of the UWT system in the experiment conducted, and it permitted to secure a per-init time scale graduated to 0.0004 sec while selecting a discret of quantization frequency of 2500 Hz. The property of partial orthogonality and peculiarities of M-code uncertainty function offered scope for resolving signals in time and amplitude that arrived at the point of reception with different time delays. The transducer was operated by computer.
Receiving system consist of independent hydrophones with data transmition through radio-communication channel, data collection and processing system on the basis of Pentium class computer. Coordination of fixing the systems is carried out using satellite navigation system GPS.
Used during the experiment were two independent hydrophones at a depth z, at a distance of 20000 m from the source and that of 1000 m from one to another. They provided unprocessing data communication through radio channel to the receiving post where they were collected and primarily processed. Software capabilities made it possible to record synchronously the signals arrived from two independent hydrophones and monitoring one during the period of 2 min each in 16-bit format. Tranmission of the series was produced in 15-30 min during the period of 12 hours, the total data amount run around 27 Mb.
Figure 1 shows amplitude spectra of the transmitted signal (from the monitoring hydrophone) and the signal from a receiving hydrophone, and Figure 2 illustrates the result of cross-correlative processing of those signals. The point set to zero with the axis of time of the correlative function complies with distance given in computing model.
