Event statistic generation method and apparatus for intrusion detection

1. A computer-implemented event statistic generation method for intrusion detection comprising:

processing a plurality of return signals from a coherent optical time domain reflectometer into time domain signals for each of a plurality of sensor bins, the plurality of return signals corresponding to a plurality of stimulation pulses injected into an optical sensor fiber during a time period; and

for each sensor bin:

transforming the respective time-domain signal into a corresponding frequency-domain signal;

calculating, from the respective frequency-domain signal, a first signal power area of a first frequency band expected to contain system noise;

calculating, from the respective frequency-domain signal, a second signal power area of a second frequency band expected to contain energy related to at least a first event; and

generating an event statistic proportional to the ratio of the second signal power area to the first signal power area at least in part by dividing the second signal power area by the first signal power area.

2. The method as claimed in claim 1 , comprising processing a plurality of return signals for each of a plurality of time periods to obtain, for each sensor bin, a plurality of event statistics.

3. The method as claimed in claim 1 , comprising converting each event statistic to a visual representation indicative of the relative size of the event statistic an outputting a matrix of the respective visual representations on a display.

4. The method of claim 3 , wherein each visual representation is a grey-scale value.

5. The method of claim 3 , wherein each visual representation is a colour-scale value.

6. The method of claim 1 , wherein generating an event statistic comprises applying a scaling factor derived from the number of frequency bins in the first and second frequency band.

7. The method of claim 1 , further comprising calculating, from the frequency-domain signal, a third signal power area of a third frequency band expected to contain energy related to at least a second event, and generating a further event statistic proportional to the ratio of the third signal power area to the first signal power area at least in part by dividing the third signal power area by the first signal power area.

8. The method of claim 1 , further comprising injecting the plurality of stimulation pulses and receiving the return signals.

9. A computer-implemented intrusion detection method comprising detecting an intrusion from one or more event statistics generated by the method of claim 1 .

10. An event statistic generation apparatus comprising:

a processor; and

a memory storing instructions which when executed by the processor, cause the processor to:

process a plurality of return signals from a coherent optical time domain reflectometer into time domain signals for each of a plurality of sensor bins, the plurality of return signals corresponding to a plurality of stimulation pulses injected into an optical sensor fiber during a time period; and

for each sensor bin:

transform the respective time-domain signal into a corresponding frequency-domain signal;

calculate, from the respective frequency-domain signal, a first signal power area of a first frequency band expected to contain system noise;

calculate, from the frequency-domain signal, a second signal power area of a second frequency band expected to contain energy related to at least a first event; and

generate an event statistic proportional to the ratio of the second signal power area to the first signal power area at least in part by dividing the second signal power area by the first signal power area.

11. The apparatus as claimed in claim 10 , wherein when the instructions are executed by the processor they cause the processor to process a plurality of return signals for each of a plurality of time periods to obtain, for each sensor bin, a plurality of event statistics.

12. The apparatus as claimed in claim 10 , wherein the instructions, when executed by the processor, cause the processor to convert each event statistic to a visual representation indicative of the relative size of the event statistic an outputting a matrix of the respective visual representations on a display.

13. The apparatus of claim 12 , wherein each visual representation is a grey-scale value.

14. The apparatus of claim 12 , wherein each visual representation is a colour-scale value.

15. The apparatus of claim 10 , wherein the processor generating an event statistic comprises applying a scaling factor derived from the number of frequency bins in the first and second frequency band.

16. The apparatus of claim 10 , wherein the instructions, when executed by the processor, cause the processor to calculate, from the frequency-domain signal, a third signal power area of a third frequency band expected to contain energy related to at least a second event, and generating a further event statistic proportional to the ratio of the third signal power area to the first signal power area at least in part by dividing the third signal power area by the first signal power area.

17. The apparatus of claim 10 , further comprising the optical fibre sensor and wherein the processor forms part of a controller that implements the coherent optical time domain reflectometer.