Sensor apparatus and method

Abstract

A multi component seismic sensor which utilises orthogonal accelerometers to determine its orientation. The accelerometers may be used to measure seismic signals directly, or the system may include geophones for this purpose.

1. A method of conducting a seismic survey comprising the steps of:
 positioning at least one sensor apparatus comprising three orthogonally arranged accelerometers in terrain of interest;   using the accelerometers of the apparatus to detect steady state acceleration;   collecting seismic data produced by seismic events;   transferring data to a central location for analysis;   analysing the steady state acceleration data to determine the orientation of the apparatus; and   analysing the seismic data to measure the seismic vibrations.   
     
     
       2. A method of conducting a seismic survey according to  claim 1  comprising the step of using the accelerometers to collect seismic data. 
     
     
       3. A method of conducting a seismic survey according to  claim 1  comprising the step of using geophones to collect seismic data. 
     
     
       4. A method of conducting a seismic survey according to  claim 3  comprising the step of fixing a geophone in the same axis as each accelerometer. 
     
     
       5. A method of conducting a seismic survey according to  claim 1  comprising the step of inputting signals received to data processing software. 
     
     
       6. A method of conducting a seismic survey according to  claim 1  comprising the further steps of providing orthogonally disposed magnetic sensors adjacent the accelerometers, and using the output of the magnetic sensors to determine the orientation of the sensor apparatus relative to North. 
     
     
       7. A method of conducting a seismic survey according to  claim 1  comprising the step of transposing the three signals to the required vertically referenced axes, based on the measured orientation of the apparatus. 
     
     
       8. A sensor apparatus for use in seismic surveys, comprising three accelerometers disposed in fixed positions relative to one another in an orthogonal array wherein each accelerometer is sensitive only to accelerations applied along the axis of the sensor apparatus in which the accelerometer is disposed; and wherein each accelerometer is sensitive both to accelerations with frequencies representative of seismic movement of the earth's surface, and to steady state accelerations representative of the effect of gravity. 
     
     
       9. A sensor apparatus according to claim S comprising three analog geophones each associated with a respective one of the accelerometers for measuring vibration, the geophones being coupled to an analog-to-digital converter. 
     
     
       10. A sensor apparatus according to  claim 9  wherein each said geophone is fixed in the same axis as a respective accelerometer. 
     
     
       11. A sensor apparatus according to  claim 8  comprising means to communicate data such as seismic signals to data processing software in a data processing unit remote from the sensor apparatus. 
     
     
       12. A sensor apparatus according to  claim 8  further comprising data processing means. 
     
     
       13. A sensor apparatus according to  claim 11  wherein said means to communicate data is selected from an electric transmission cable and a fibre optic link. 
     
     
       14. A seismic survey apparatus for seabed use, the apparatus comprising a cable and at least one watertight container along the length of the cable and adapted to be lowered by said cable to contact the seabed; each container containing a sensor apparatus comprising three accelerometers disposed in fixed positions relative to one another in an orthogonal array wherein each accelerometer is sensitive only to accelerations applied along the axis of the sensor apparatus in which the accelerometer is disposed, and wherein each accelerometer is sensitive both to accelerations with frequencies representative of seismic movement of the earth's surface, and to steady state accelerations representative of the effect of gravity; and means to communicate seismic signals to a data processing unit. 
     
     
       15. A seismic survey apparatus according to  claim 14  wherein said data processing unit is at a remote location and said cable provides a communication path for data between the watertight container and the remote location. 
     
     
       16. A seismic survey apparatus, comprising:
 a sensor unit including a housing having a housing axis;   a first accelerometer disposed in the housing, the first accelerometer measuring acceleration along a first axis;   a second accelerometer disposed in the housing, the second accelerometer measuring acceleration along a second axis;   a third accelerometer disposed in the housing, the third accelerometer measuring acceleration along a third axis, wherein the first axis, the second axis, and the third axis are substantially orthogonal to each other and form a sensor reference frame relative to the housing axis; and   a processor configured to process an output of each of said first accelerometer second accelerometer and third accelerometer to determine a transposition matrix, the transposition matrix being used at least in part to transpose measured seismic vibrations to a second reference frame.   
     
     
       17. The apparatus of claim 16, wherein the first accelerometer, the second accelerometer and the third accelerometer measure steady state acceleration. 
     
     
       18. The apparatus of claim 16, wherein the processor is disposed within the housing. 
     
     
       19. The apparatus of claim 17, wherein an output of the sensor unit is indicative of measured seismic vibrations transposed to the second reference frame. 
     
     
       20. The apparatus of claim 16, wherein the first accelerometer, the second accelerometer and the third accelerometer measure steady state acceleration in real time.