Abstract:
The present invention refers to a positioning system, in particular for carrying out Georadar acquisitions, and more in particular of a 3-dimension type. In one embodiment, the positioning system for data acquisition using a data acquisition system includes at least one antenna that is passed over a surface to be surveyed. The positioning system includes a plurality of guides side by side that can be coupled to the surface and a structure having a surface with at least one guide that engages the plurality of guides and which is suitable for being conducted along the plurality of guides. The structure includes the at least one antenna of the data acquisition system (FIG.  1 ).

Description:
BACKGROUND OF THE INVENTION 
   The present invention refers to a positioning system, in particular for acquiring Georadar type data, and more particularly of the 3-dimension type. 
   The laying of new technological networks (optical fibers) and the new lines for conveying electricity is based on no-dig or trenchless technologies. This technology is characterized by the possibility of laying the plants without having to dig a trench. A remote-control drill drags the cable along a preset path. The intensive laying of cables and tubes in the first meters underground and the lack of maps of the technological plants quite often make surveys necessary prior to the laying phases. 
   The Georadar surveys are up to now the only ones capable of identifying any technological plant or construction present underground. 
   During the laying of a cable without digging a trench, the more dangerous portions of the trench are the drill immersion and surfacing areas, that have a plan extension of about 4 m*4 m for a depth of a few meters, where the majority of the subservices can be found. The drill is immersed to the preset depth and then advances horizontally parallel to the plane (surface) of the ground. 
   In addition, this laying technique is suggested for laying the new technological networks (Directive dated 3 Mar. 1999 art.5). 
   The geophysical radar or Georadar uses the reflection of electromagnetic waves for exploring underground. The technique is based on the insertion in the ground, by means of a transmitting antenna, of electromagnetic waves with extremely brief impulses (a few nanoseconds), whose central frequency is between 10 and 2000 MHz. The signal reflected from the surfaces of any discontinuity present underground is received by a receiving antenna and recorded after sampling at suitable frequency. This type of survey enables high resolution measurements to be carried out with graphic return of an underground continual section (time-distance) in real time 
   To analyse an area of ground, the transmission and reception antennas have to be passed over the entire area concerned. The depth to be surveyed and the resolution required are determined through the choice of the antenna. High frequency antennas have good resolution but low penetration. To conduct Georadar surveys to locate the subservices the resolution needed is a few centimeters and the survey depth required is a few meters. Antennas with a frequency of the central band around 400 MHz are generally used. 
   The processing of the data received can be made by means of a bidimensional analysis, supplying in output the data relating to the various vertical planes analyzed. It can also be made by means of a three-dimension analysis. For three-dimension analyses the data received have to meet the theorem of the spatial sampling. In addition, good contact has to be kept and therefore good coupling between the ground and the antenna, as if there is air between the antenna and the ground the quality of the data deteriorates because of the reduced penetration of the signals. 
   Normally, for acquiring data, the lines that will indicate the path that the antennas will have to follow are traced on the portion of ground to be analyzed, by means of paint or chalk, or theodolites are used. 
   In addition, the majority of times, the Georadar surveys have to be carried out in heavily urbanized areas where it is very difficult to interrupt the traffic of vehicles, pedestrians or commercial activities. Therefore, they are operations that have to be carried out quickly minimizing as much as possible the disturbance to the road traffic and the surface activities. 
   SUMMARY OF THE INVENTION 
   In view of the state of the technique described, an object of the present invention is to provide a positioning system, in particular for achieving Georadar acquisitions that is simple to carry out and apply, has low cost, and enables data acquisition to be carried out rapidly and with precision. 
   In accordance with the present invention, this and other objects are achieved by a positioning system for acquiring data using a data acquisition system including at least one antenna that is passed over a surface to be surveyed. The positioning system includes a plurality of guides side by side, that can be coupled to the surface; and a structure having a surface with at least one guide that engages the plurality of guides and is suitable for being conducted along the plurality of guides. The structure includes the at least one antenna of the data acquisition system. 
   Thanks to the present invention, the most precise low cost data acquisition possible can be carried out. In addition, it can be carried out in limited space and on irregular surfaces because of its innate flexibility. It is simple, reliable, has a very limited weight and is extremely easy to apply. It guarantees very good coupling between the antenna and the means surveyed because the antenna can follow any possible sinking. 
   In addition, the system presented herein can be applied and can be adapted to any Georadar acquisition system. 
   It can be used without interrupting the traffic of vehicles or pedestrians as its dimensions are small and it does not move even if a vehicle passes over it. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The characteristics and advantages of the present invention will appear evident from the following detailed description of an embodiment thereof, illustrated as non-limiting example in the enclosed drawings, in which: 
       FIG. 1  represents a positioning system for carrying out Georadar acquisitions in accordance with the present invention, seen in axonometry; 
       FIG. 2  represents a positioning system for carrying out Georadar acquisitions in accordance with the present invention, seen in profile; 
       FIG. 3  represents a variant of a positioning system for carrying out Georadar acquisitions in accordance with the present invention, seen in profile. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The inventive idea of the present invention is based on arranging some guides on the surface to be surveyed to use as tracks for the movements of the Georadar antenna on the ground. 
   In  FIG. 1  which is an axonometric view and in  FIG. 2  which is a profile view of the positioning system for carrying out Georadar acquisitions in accordance with the present invention, base guides  10  are shown positioned on a supporting layer  11 , all in the form of a mat  12  placed on top of a surface to be surveyed  17 . 
   A support structure  13  for supporting the antenna Georadar (not shown) is placed on the mat  12 . This support structure  13  has some support guides  14  provided on its lower surface, preferably at least two, that engage the recesses  15  left by the base guides  10  on the supporting layer  11 . Only one support guide can be enough if it is capable of ensuring alignment with the base guides  10 . The base guides  10  are preferably positioned on the supporting layer  11  equally spaced out and parallel. 
   The support structure  13 , in particular its upper part, can be made in any manner to support and hold the transmission and reception system (not shown in the Figure) placed over it while the support structure  13  is being pulled. In the alternative, the support structure  13  can support even only one or more antennas connected to the system by means of suitable cables. 
   Once the Georadar antenna has been positioned over the support structure  13  itself, it is pulled with the support structure  13 , either manually or mechanically, along the base guides  10  to guarantee the area to be investigated is covered. Preferably, making unidirectional, parallel and progressive profiles. For example, starting from one corner of the mat  12  and running along the entire length of the guide. At the end of the base guide, the support structure  13  is moved with the antenna to the adjacent base guide, and the support structure  13  is passed along the new base guide. Adjacent base guides can be passed over in the same direction or in opposite directions. 
   The mat  12 , with the base guides  10 , is preferably composed of a soft material, so that it can follow the unevenness of the ground, such as rubber, PVC, cardboard, etc. 
   In an embodiment of the present invention, with a working frequency of 500 MHZ, (one antenna with the dimensions of about 60×30×21 cm.), a mat  12  with the dimensions of about 4×4 m having a height of about 0.3 mm, the distance D 1  between two guides is about 5 cm, the height H of the guide is about 0.3 mm, the distance D 2  of the guide is about 2.45 cm. The measurements of the guides  14  are the same as the guides  10  so that they can easily engage with each other. In this embodiment, the support guides  14 , 2.45 cm wide, engage the recesses  15  with a width of 2.55 mm. Thus a clearance of 1 mm has been created between the support guides  14  and the recesses  15  so that the support structure  13  can be easily pulled. According to the materials and the tolerances required, the dimensions given above can vary according to specific needs. 
   Normally different working frequencies are used in accordance with the resolution and depth required for the surveys. For example, frequencies commonly used are 125, 250, 500, 1000 MHz. 
   With the aim of limiting the number of mats  12  to the variation of the frequency, the mat  12  can have the base guides  10  with a close pitch and dimensions such that they meet the sampling theorem for a higher frequency antenna. For acquisitions with a lower frequency antenna, the same mat is used but the number of parallel profiles to be carried out is reduced passing along profiles spaced out between each other according to multiples of the minimum distance that exists between two parallel guides. To reduce the passage errors between one passage of the antenna and the other, the guides have been fitted with an identification (for example, with suitable colors) so as to indicate the different steps for the different frequencies, or with suitable reference symbols. 
   The measurements of the guides are determined for the highest use frequency (lowest wavelength) and the base guides  10  are highlighted so that the structure  13  will have to use as a reference for the lower frequencies, for example, a color or a symbol for each frequency that can be utilized. 
   Preferably, to align the sections made by pulling the support structure  13  and in particular to facilitate the departure or the arrival (or both) of the passage along the guides, the guides themselves have been provided with a stopping device  16  (only partly shown for simplicity, but which can be extended for all the base guides  10  and the corresponding recesses  15 ). This permits precise reference points to be achieved for the beginning and the end of the data acquisition. Alternatively, a profile can be used as the stopping device  16 . For example, a profile can be applied to the extremity of the guides, such as a mechanical stop or any other retainer. 
   The supporting layer  11  (as well as the guides  10  and  14 ) preferably has a smooth upper surface so that the support structure  13  can advance without problems, and has a lower abrasive or rough surface so that once the mat  12  has been placed on the ground it has no movement. As an alternative or in combination, the lower surface of the mat  12  can be provided with glue for greater adherence. 
   In addition, the base guides  10  can also be directly fixed to the ground (for example with glue) with manual or mechanical systems without the presence or the need for the supporting layer  11 . 
   Other variations to the above arrangement are possible for the adjustment to the specific working conditions and considering the different needs that can arise, such as when the surface surveyed is not horizontal ground but a vertical wall. 
     FIG. 3  represents a variant of the system in accordance with the present invention, seen in profile. The guides  10  and  14  have been described previously as having a substantially rectangular shape, but they can also be shaped differently, for example triangular, trapezoidal or with a sinusoidal form. Advantageously, a sinusoidal form is that of the corrugated type of cardboard, normally used for packaging. Thus a mat  12  can be created with a piece of corrugated cardboard, with the dimensions desired. As the support structure  13 , another piece can be used, with the dimensions desired, to apply suitable directly or indirectly to the Georadar antenna. Alternatively, a structure in a plastic material (more resistant) with the same shape as the cardboard. 
   The present invention developed for Georadar acquisitions can naturally also be used for all those applications in which a structure has to follow particular references suitably spaced out, such as a scanner, sounding, ultrasonic surveys, and other non-destructive surveys. 
   The positioning system in accordance with the present invention guarantees the supply of data that enables a success rate of 98% to be reached during the calculation phase in determining the positioning of structures within the surveyed area. 
   The acquisition time is also reduced considerably (up to ⅕–⅙ in relation to the systems normally used), as the preparation of the area surveyed no longer has to be prepared for the following survey.