1. Two New Applications of Time Reversal Mirrors: Seismic Radio and Seismic Radar
Sherif M. Hanafy
September 2010

2. Outline Introduction Seismic Radio Seismic Radar
Methodology
Field Examples
Seismic Radar
Summary and Conclusions

3. Finding trapped miner(s) using seismic data is a three steps process
Introduction
Finding trapped miner(s) using seismic data is a three steps process
First step; before the collapse. Record a group of calibration records (Band-limited Green’s Functions)
Second step; after the collapse. Record a SOS call from the trapped miner(s).
Third step. Use the ‘one’ SOS call and the ‘many’ calibration records (GF) to find the location of the trapped miner(s).

4. First Step; before the collapse
Introduction
First Step; before the collapse
Geophones are planted on the ground surface above the mine.
Select some communication points inside the mine
Receiver Line
Ground Surface
Subsurface Mine
…………… G1 G2 G3 Gn

5. First Step; before the collapse
Introduction
First Step; before the collapse
From each communication point (Gx) we will record the earth’s natural band-limited Green’s function
Direct Waves
Receiver Line
Ground Surface
Subsurface Mine Gx

6. Second step; get the SOS call
Introduction
Second step; get the SOS call
After a collapse occurs,
trapped miners should go to the nearest communication point and hit the mine wall at this point
This (SOS) call will be recorded by the geophones on the ground surface
Receiver Line
Ground Surface
Subsurface Mine G1 G2 G3

7. Introduction Now, the problem is:
We have many reference GFs (calibration records)
We have only one SOS (with low signal-to-noise ratio)
Where are the trapped miners?
Where did the SOS come from?

8. We use a gather-to-gather no-shift
Intorduction
We use a gather-to-gather no-shift
crosscorrelation
Crosscorrelation results
Recorded SOS call
Band-limited Green’s function

9. Third step; where are the trapped miner(s)?
Introduction
Third step; where are the trapped miner(s)?
Does the recorded SOS looks like one of our previously recorded band-limited calibration Green’s functions? NO NO NO
Yes G1 G2 G3
………. Gn
The location of the trapped miners is the location of the calibration Green’s functions that best match the recorded SOS
Recorded SOS

10. Results of Trapped Miners (U of U)
Steam-Tunnel Test
Results of Trapped Miners (U of U)
Normalized m(x,0)
X (m)
X (m)
X (m)

11. Examples of the Results
Tucson, Arizona Test
Examples of the Results
Tunnel 2
Tunnel 3
Normalized m(x,0)
Normalized m(x,0)
X (m)
X (m)

12. Results with Random Noise
Results without adding noise
Results with adding noise
Normalized m(x,0)
X (m)
Normalized m(x,0)
X (m)
New S/N =
1:1738
Normalized m(x,0)
X (m)
Normalized m(x,0)
X (m)
New S/N =
1:2670

13. Unknown SOS Excitation Time1
Excitation Time
Location of Trapped Miner
Normalized Amplitude -1
-0.25 45
Time Shift (ms)
X (m)
0.25

14. Re-phrase the problem Find trapped miners in collapsed mines
Find seismic source with unknown location and excitation time

15. For more details, see
Hanafy et al.: Using super-stack and super-resolution properties of time reversal mirrors to locate trapped miners. TLE, March 2009, P

16. Part 1 Seismic Radio

17. Coding Data Binary coding Telegrams Seismic TRM
S = ( )Bin = (83)Dec
Morse Code
None zero stat
Seismic TRM
Seismic Radio
Zero state

18. Unknown SOS Excitation Time1
Excitation Time
Location of Trapped Miner
Normalized Amplitude -1
-0.25 45
Time Shift (ms)
X (m)
0.25

19. Cross Section

20. More Than One Shot

21. Sending Seismic Coded message
Step 1: Calibration record
Record a Green’s function with high signal-to-noise ratio.
Step 2: Coded Message
Turn on all receivers at the receiving line. Listen to any seismic signal coming from the transmitting station.
Step 3: Decode the message
Use GF from step 1 to decode message recorded in step 2.
Transmitting station
Receiving line

22. Decode Principles Six elements are used to decode the message:
Signal is interpreted as "1“.
No-signal is interpreted as "0“.
(111111) for the beginning of the message.
(000000) for spaces between words.
(110110) for end of message.
Each group of 6-successive bits will represent one letter.

23. Suggested Code Book Beginning 111111 7 000111 H 010001 R 011011 Space
000000 8
001000 I
010010 S
011100
End
110110 9
001001 J
010011 T
011101
101010 A
001010 K
010100 U
011110 1
000001 B
001011 L
010101 V
011111 2
000010 C
001100 M
010110 W
100001 3
000011 D
001101 N
010111 X
100010 4
000100 E
001110 O
011000 Y
100011 5
000101 F
001111 P
011001 Z
100100 6
000110 G
010000 Q
011010

24. Part 1 Seismic Radio Field Example

25. Field Example Data are collected at Tucson, AZ., USA.
One Green’s function is recorded with 30 stacks.
Couple of messages were send using a sledge hammer.
Line of receivers consisted of 72 receivers with 5 m receiver interval

26. Field Example

27. Site Sketch

28. Data Samples Reference Green’s Function
Coded Message – No Noises are Added
Same Coded Message – Noise are Added
X (m)
355
Time (s)
0.5
X (m)
355
Time (s) 15
X (m)
355
Time (s) 15
Signal-to-noise ration lowered by a factor of 340

29. Decoding Messages Decoding Original Message
Decoding Message with Noise

30. Another Example

31. Part 2 Seismic Radar

32. Unknown SOS Excitation Time1
Excitation Time
Location of Trapped Miner
Normalized Amplitude -1
-0.25 45
Time Shift (ms)
X (m)
0.25

33. Sources/Receivers Layout
If the source location is known, we can find excitation time (Radio application).
For many possible source locations distributed in 1D, finding the right location is easy (trapped miners application).
What about 2D source matrix? It is also possible (radar application).
Transmitting station
Receiving line
Using 2D receiver matrix will improve the results, since the extra receivers will help enhancing the final results.

34. Field Example Data are collected at Tucson, AZ., USA.
120 Green’s functions are recorded
5 receiver/shot lines are used with inline offset = 5 m and crossline offset = 15 m.
Each line contains 24 shots/receivers.

35. Field Example

36. Field Example

37. Four Different Routes

38. Four Different Routes

39. Four Different Routes

40. Four Different Routes

41. Field Example Green’s Function Passive Data Receiver No. 120 Time (s)
120
Time (s)
0.5
Receiver No.
120
Time (s) 5

42. Results of Route 2

43. Results of Route 2

44. Results of Route 2 (Velocity)
Stations 2 to 11 is 45 m
Time is 17.7 s
Velocity = 45/17.7 = 2.5 m/s.
Stations 108 to 98 is 50 m
Time is 17.5 s
Velocity = 50/17.5 = 2.9 m/s.

45. Results of Route 3

46. Results of Route 3 (Velocity)
Stations 25 to 46 is 105 m
Time is 21.1 s
Velocity = 105/21.2 = 5 m/s.
Stations 87 to 74 is 65 m
Time is 11.9 s
Velocity = 65/11.9 = 5.5 m/s.

47. Sensitivity Test

48. Implication
This concept can be used to track moving objects, find movement speed, and get an idea about the moving object (human, cars, etc.)
Secure important areas and buildings is the main applications.
Remotely monitoring activity in an area of interest is another application

49. When it does not work?
If the area of interest has many activities, such as in cities, near road; simply where many moving objects are expected.

50. Summary and Conclusion
Time reversal mirrors can be used to send coded messages with seismic waves.
Time reversal mirrors can also be used to track moving objects for location and speed.
Two field tests are made to test the accuracy of each proposed method.

51. Thank You