## 1 Introduction
In most national standards, the method of coupling accelerometers or geophones to the ground is treated rather perfunctorily or is not specified at all. One of the exceptions is DIN 45669-2:2005-06 [20], which more precisely, in comparison with other standard guidelines indicates possible ways of carrying out this type of measurements using transducers:  
* Mounted on spikes (method 1);
* placed on a plate, which is laid by slurrying on a foundation of sand on the ground surface (method 2);
* buried in the ground (method 3); or
* using borehole transducers (method 4). The second of the methods (method 2) mentioned in DIN 45669-2:2005-06 [20] for measuring surface vibrations transmitted through the ground seems to be the simplest, but according to the author, in the case of more intense vibrations, the degree of coupling of transducers to the ground is insufficient, because the plate with transducers mounted on it may slipping in a horizontal plane relative to the ground surface and even temporarily have decreased contact with the ground in a vertical direction. It can lead to the recording of disturbed time history of accelerations or velocities. The last two methods of carrying out measurements (methods 3-4) may require obtaining the appropriate permit for a vertical borehole or an excavation. In both methods, the measurement is quite problematic and involves a significant risk of damage to the transducers. It can also be problematic to ensure proper orientation of the transducers in a hole or a borehole (in accordance with the adopted measuring directions). The measurements should also take into account the fact that the most of surface vibration energy is propagated in the ground medium mainly in the form of Rayleigh waves, which disappear asymptotically to zero with depth, and at a depth of 1 m it has already been reduced to a fraction [26]. In the first methods (method 1) not much equipment is required. Usually, it provides better ground coupling than measurements using a plate set up on a properly prepared ground surface covered with a thin layer of sand bedding, it is quick, and as indicated by DIN 45669-2:2005-06 [20] suitable for use in many different locations. On the other hand, DIN 45669-2 [20] indicates that the results can be influenced by: Spike geometry, spike length, the height of the transducer above the ground surface, and the position of transducer in relations to the spike's center of mass. In addition, very stiff spikes in well-compacted soil tend to register only localized motions of the upper soil layer. The lack of a clearly indicated way of carrying out this type of measurements means that in engineering practice and scientific research very diverse solutions are used--often unique only for a given region of the country, or even a scientific center dealing with the propagation of vibrations in a ground medium. Very often they are a combination of the above solutions. For example, in measurements of ground vibrations described in the report [3] seismic accelerometers (with voltage sensitivity of about 10 V/g) were fastened with screws to the measuring base in the form of a 100 mm square metal plate with a 200 mm long spike at each corner. In the case of the tests described in the [PERSON] report [5], a set of three uniaxial geophones (SENSOR SM-6 low frequency geophone A-Coil with a sensitivity of 28 V/m/s and a weight of 81 g) and additionally a set of uniaxial accelerometers (MONITRAN MTN1100/75 with a sensitivity of 100 mV/g and a weight of 120 g) was screwed to an aluminum cube and next screwed on to 200 mm long stainless steel spike previously driven fully into the ground. The cube for attaching accelerometers (KISTLER 8330A3: sensitivity 1.2 V/g, weight 28.5 g) was also used in [6]. However, in this case, the rigid steel cube with three uniaxial accelerometers mounted on its side surfaces was not anchored in the ground in any way by spikes but was pushed into the soil. A solution like the above was used in the studies [14].