he construction features of contemporary georadars.

All known georadars can ensure the depth of sounding into several meters only on soils with weakly absorption of radio waves (by parameters such soils close to the dry sand), which makes them unpromising for the middle area of Russia and other places where clayey soils predominate.

The basic task which we had for ourselves during the projection of the georadars of new generation was reaching of a maximally possible real potential of the device.

This goal has been achieved by two basic methods - use of a powerful transmitter and registration of signal in its own frequency spectrum without the stroboscopic transformation of the signal into the region of low frequencies. In other words, we excluded the most of the operations with the signals which can lead to the appearance of "ringing".

In order to ensure the necessary parameters for the detection of target we developed small transmitter with a pulse power of 1 megawatts. It is contemporary version of spark transmitters of A.C.Popov and G.Marconi times with the first experiments on the radio communication.

The method of registration used by us is based on the use of the high speed comparators which compare the incoming signal with a certain assigned threshold. Changing the value of threshold and the factor of amplification of receiver it is possible to record signal in the large range of its values. In the stroboscopic method the value of signal amplitude in a time moment is recorded for one radiated pulse of transmitter. In our method the moments of exceeding of threshold by the signal throughout entire time coordinates are recorded for one pulse.

The most suitable antenna both receiving and transmitting proved to be the resistor-loaded dipole in which the part of the pulse energy is absorbed on the resistors distributed along its arms. By selection the value of resistors it is possible to ensure almost absolute damping of the parasitic oscillations of the pulse.

The optimum construction of the directional antenna used under the conditions of active and passive outside interferences proved to be "anechoic chamber" without the metallic parts. It is the resist-loaded dipole covered with the dielectric box and filled with the carbonic radio-absorber which absorbs air wave.

The real potential of device is the important characteristic of georadars. The real dynamic range, which composes 40-60 dB and not practically increasing in recent years, prevented a radical increase in the depth of sounding for the georadars built according to traditional schemes. Real potential means for us the weakening of the signal in the medium with which the radar is capable to reveal underground objects. This is the critically important parameter for evaluating the possibilities of instrument. Unfortunately in the descriptions of georadars they often give the value of its potential calculated as ratio of the power of transmitter to the sensitivity of receiver. Basic technical solution for most radars developed and produced at the present time is the method of the stroboscopic transformation of the spectrum of the signal into the region of low frequencies in which occurs its registration. The collision excitation of the transmitting system is accomplished by transistors in the avalanche regime with a jump in the voltage of approximately 50-150 v. The basic technical problems connected with this circuit solution are the diificulty to provide the constancy of amplitude-frequency and linearity the phase-frequency response of stroboscopic conversion in the receiving circuit which leads to significant parasitic oscillations (ringing) of signal and masking of weak signals with stronger. This is the basic reason for the small real potential of radars of such type.

The measurement of the real potential of the georadar was accomplished as follows. Georadar was placed on the floats and was moved from the coast to the center of deep water reservoir. During the motion the depth where the reflection from the bottom disappeared due to the radio wave absorption by water was recorded. By using the records of amplitude function the linear damping was defined as the ratio of amplitude change to a difference in the depths. Real potential was defined as the product of linear damping and the depth at which the signal disappeared. For the georadars of the described construction the measured real potential composes the value not less than 120-240 dB.

ata processing methods.

Obtained data do not practically contain the parasitic oscillations ("ringing" of equipment) which are typical for the most georadars. For this reason we do not use the standard programs of georadar signals processing whose basic task to decrease the value of "ringing" and to distinguish signal against his background with the aid of the different kinds of filtration.

The method of restoring the geological profile by radar data (accepted by us at present) is based on the use of a procedure known in seismology by the name "common point of excitation" (OPV).

At the beginning the radar profile is measured by moving along the route with the device in which the distance between the receiving and transmitting antenna is fixed. Then radar data points at which it is necessary to produce sounding (in accordance with the method OPV to obtain hodographs from the layers and the objects) are determined. Hodograph is the function of signal delay from the layer (object) depending on the distance between the receiving and transmitting antennas with their symmetrical carrying to the different sides.

Hodograph makes it possible to define both the true depth of layer and wave propagation velocity in it. In order to convert radar data into the geological section it is necessary to exclude multiple reflections from the layers and to transform time axis into space by assigning wave velocity in the layer. All necessary information can be obtained from the hodograph.

The use of a quasi-seismic approach for obtaining the geological section cannot be considered satisfactory since the part of the information included in the signal amplitude, its temporary form and polarization is not used. Therefore the measurement of wave form in many cases is the only possibility to determine correctly the location of the object being investigated. The algorithms and the programs which make it possible to conduct processing of wave forms were created. The method is based on the use of a widely known algorithm it wavelet-conversion.