The following graphic shows the area of the measured surface in square meters as a function of the angle of beam spread a of the ultrasonic lobe and the distance r between the survey tool and the cavern wall.

• The larger the measured surface on the cavern wall, the greater the probability that reflections originating from different distances within this measured surface are contained in the signal response. The following examples indicate various possibilities:
  

  	Uniform flat surface: all distances in the measured surface are approximately the same (optimum). The maximum in the signal response definitely represents the distance looked for.
  	Irregular rough surface: the distances in the measured surface are scattered. The maximum in the signal response very probably represents the distance looked for.
  	Inclined structured and rough surface: the distances in the measured surface are greatly scattered. The signal response is extended in length because the ultrasonic lobe grazes along a wall. In this case the maximum in the signal response cannot simply be accepted as the distance looked for. Often it is necessary to make a separate interpretation referring to the adjacent sections and the signals in the vicinity and also considering the interpretation of the vertical sections!

  
   
• Owing to the energy distribution within the emitted ultrasonic lobe, which is at its maximum at the center, the greatest reflection density under normal circumstances is expected from the central area of the measured surface on the cavern wall.
• In rough-walled caverns the distances measured are normally shorter than they should be (blue wall surface instead of grey surface). In this case a measuring error occurs because reflections from different distances within the measured surface are contained in the signal response. This error can be minimized only by optimizing and adapting the survey beam to the prevailing conditions.







• The measuring frequency together with the acoustic velocity in the surrounding medium determines the wavelength and consequently also the angle of beam spread of the ultrasonic lobe.
  
  The constant measuring frequency of 620 kHz, which is used by all our competitors, covers only a limited part of the frequency range necessary for optimizing the survey results.
  
  The same is true for the measuring frequency of 250 kHz, as used in the USA.
  
  
• The survey beam can be optimized only if the measuring frequency is adapted to the physical conditions.
• Inappropriate adjustment of the ultrasonic ceramic unit, which is also affected by the temperature and pressure, leads to "squinting" and consequently to errors in the direction.
• The SOCON systems, and only these, remain fixed at each measuring point firstly to optimize the ultrasonic lobe, secondly to record the survey value several times for a plausibility check, and thirdly to correlate the survey signal. This technique is certainly more complicated, but it is essential in order to achieve optimum and high quality data acquisition.
• The shape and general development of the survey beam have a significant effect on the survey results. For this reason it is necessary to record the echogram. A correct and proper procedure is essential for performing interpretation and evaluation and for obtaining results that can be referred to and checked over the long term. Survey systems that supply solely distance information make it impossible to perform a correct interpretation. "Interpretation" in such cases simply means filtering out the data that do not fit in the picture and replacing them by interpolated data.