Determining the depth of reinforcing bars in a concrete structure using electromagnetic signals

• US 6,772,091 B1
• Filed: 12/08/1999
• Issued: 08/03/2004
• Est. Priority Date: 12/08/1998
• Status: Expired due to Fees

• Current Assignee: Geophysical Survey Systems, Inc.
• Original Assignee: Geophysical Survey Systems, Inc.
• Inventors: Roberts, Roger L.
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): KIM, PAUL L
• Application Number:
  US09/457,512
• Time in Patent Office: 1,700 Days
• Field of Search: 702/166, 702/79, 702/170, 342/22, 342/118, 324/644, 324/635, 324/637, 324/645, 735/97, 736/02, 736/20
• US Class Current: 702/166
• CPC Class Codes: G01N 2223/076 X-ray fluorescence
• CPC Class Codes: G01N 23/223 by irradiating the sample with X-rays or gamma-rays and by measuring X-ray fluorescence
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005

Abstract

Ground penetrating radar (GPR) is a technique that may be used to image the inside of a structure by collecting the echoes (or reflections) resulting from electromagnetic signals such as, for example, electromagnetic waves of typically high frequency, being radiated into the structure. Typically, the rebars inside a reinforced concrete structure are strong radar wave reflectors. Locating rebars within a reinforced concrete structure and determining their depths may be accomplished by analyzing the reflections, particularly the amplitudes and arrival times of the reflections, from the rebars in the reinforced concrete structure. Provided is a method and system for determining, for a substantially concrete structure having at least a first side and containing one or more reinforcing bars, a distance of the one or more reinforcing bars from the first side of the substantially concrete structure. One or more computer-readable data signals are received, and each data signal represents an electromagnetic signal detected from an area of the concrete structure. One or more of the detected electromagnetic signals include electromagnetic energy reflected from the concrete structure as a result of an electromagnetic signal transmitted into the concrete structure. A distance of one or more of the reinforcing bars from the first side of the substantially concrete structure is determined from the one or more computer-readable data signals.

Claims

1. A method of determining, for a substantially concrete structure having at least a first side and containing at least a first reinforcing bar, a distance of the first reinforcing bar from the first side of the substantially concrete structure, the method comprising:

receiving a plurality of computer-readable data signals, wherein each data signal represents an electromagnetic signal detected from an area of the concrete structure, and wherein one or more of the detected electromagnetic signals include electromagnetic energy reflected from the concrete structure as a result of a corresponding electromagnetic signal transmitted into the concrete structure;

selecting one of the data signals, the selected data signal corresponding to the first reinforcing bar; and

determining a first distance of the first reinforcing bar from the first side of the substantially concrete structure based on the selected data signal alone from among the plurality of data signals.

2. The method of claim 1, wherein the first reinforcing bar has a longitudinal axis aligned along a first dimension, and a plurality of electromagnetic signals have been transmitted into the substantially concrete structure at different locations along a second dimension approximately orthogonal to the first dimension, and wherein the selected data signal includes electromagnetic energy reflected from the first reinforcing bar as a result of the transmission of one of the plurality of electromagnetic signals.

3. The method of claim 1, wherein each detected electromagnetic signal is detected at a different location on the first side.

4. The method of claim 3, wherein each transmitted electromagnetic signal corresponding to one of the detected electromagnetic signals is transmitted at a different location on the first side.

5. The method of claim 1, further comprising:

detecting each detected electromagnetic signal with a same receiver; and

transmitting each corresponding electromagnetic signal with a same transmitter.

6. The method of claim 1, further comprising:

temporarily storing the data signals before selecting one of the data signals.

7. The method of claim 1, wherein the selected data signal represents an electromagnetic signal detected over a detection period of time, and wherein determining the first distance includes:

determining a portion of the selected data signal during which the detected electromagnetic signal, represented by the selected data signal, includes electromagnetic energy reflected from the first reinforcing bar; and

determining, from the determined portion of the selected data signal, the first distance of the first reinforcing bar from the first side.

8. The method of claim 7, further comprising:

determining a velocity value representing a velocity at which an electromagnetic signal propagates in concrete of the substantially concrete structure,

wherein determining the first distance includes;

determining a first point in time during the detection period corresponding to a peak amplitude of the electromagnetic energy reflected from the first reinforcing bar; and

calculating the first distance using the velocity value and the first point in time.

9. The method of claim 8, wherein the detected electromagnetic signal represented by the selected data signal includes a direct-coupled portion, and the step of determining the first distance further includes:

subtracting the first point in time from a second point in time to produce a propagation time within the concrete structure for the detected electromagnetic signal represented by the selected data signal, wherein the second point in time corresponds to a peak amplitude of the direct-coupled portion; and

calculating the first distance using the velocity value and the propagation time.

10. The method of claim 9, wherein the transmitted electromagnetic signals are transmitted from a first antenna and the detected electromagnetic signals are detected by a second antenna located a second distance from the first antenna, wherein the step of calculating the first distance includes:

applying an equation;

$d=\frac{1}{2}<br><br>\sqrt{v^2<br><br>t^2-a^2},$

 

wherein d is the first distance, t is the propagation time, v is the velocity value, and a is the second distance.

11. The method of claim 8, wherein determining the first distance includes:

receiving a distance value indicative of a distance measured from the first side of the concrete structure to a second reinforcing bar contained in the substantially concrete structure; and

calculating the velocity value from the distance value.

12. The method of claim 11, wherein the transmitted electromagnetic signals are transmitted from a first antenna and the detected electromagnetic signals are detected by a second antenna located a second distance from the first antenna, wherein determining the first distance includes:

determining a propagation time within the substantially concrete structure of an electromagnetic signal transmitted into the substantially concrete structure from the first side, reflected from the second reinforcing bar and detected at the first side,

wherein the velocity value is calculated by applying an equation;

$v=\frac{2}{t}<br><br>\sqrt{{\left(a/2\right)}^2+d^2},$

 

wherein v is the velocity value, a is the second distance, t is the propagation time and d is the distance value.

13. The method of claim 7, wherein each transmitted electromagnetic signal is transmitted at a different position along the first side of the concrete structure, and the method further comprises:

for each data signal, determining a portion of the data signal during which the detected electromagnetic signal represented by the data signal includes electromagnetic energy reflected from the first reinforcing bar; and

for each data signal, determining a peak amplitude of the data signal during the determined portion,

wherein selecting one of the data signals includes selecting the selected data signal for having a peak amplitude of a highest magnitude from among the data signals corresponding to electromagnetic signals transmitted within a spatial interval of a first length along the first side of the substantially concrete structure.

14. The method of claim 13, further comprising:

migrating the data signals to facilitate determining that the selected data signal has a peak amplitude of the highest magnitude.

15. The method of claim 1, wherein the transmitted electromagnetic signals are transmitted from a first antenna and the detected electromagnetic signals are detected by a second antenna located a second distance from the first antenna, the second distance having a midpoint on an imaginary straight line between the first and second antennas, and

wherein an amplitude of each data signal is directly related to a distance between the area corresponding to the data signal and the midpoint of the second distance.

16. The method of claim 1, wherein each of the data signals represents an electromagnetic signal detected at a point along a substantially straight line along a first dimension of the first side of the concrete structure, and each detected electromagnetic signal is detected over a period of time, the method further comprising:

displaying a graph of one or more of the data signals, a first axis of the graph representing time of detection, a second axis of the graph representing a distance along the first dimension, the displaying including representing an amplitude of each of the one or more data signals over the detection time, wherein a location, with respect to the second axis, of each represented data signal corresponds to a point at which the signal was detected.

17. The method of claim 16, wherein the step of selecting the data signal includes:

selecting the data signal from the graph in accordance with the amplitudes of the represented data signals.

18. The method of claim 1, wherein the method further comprises:

adjusting the selected data signal by removing from the selected data signal data representing electromagnetic signals not reflected from the substantially concrete structure; and

determining the first distance from the adjusted data signal.

19. For a substantially concrete structure having at least a first side and containing at least a first reinforcing bar, a system for determining a distance of the first reinforcing bar from the first side of the substantially concrete structure, the system comprising:

means for receiving a plurality of computer-readable data signals, wherein each data signal represents an electromagnetic signal detected from an area within the concrete structure, and wherein one or more of the detected electromagnetic signals include electromagnetic energy reflected from the concrete structure as a result of a corresponding electromagnetic signal transmitted into the concrete structure;

means for selecting one of the data signals, the selected data signal corresponding to the first reinforcing bar; and

means for determining a first distance of the corresponding reinforcing bar from the first side of the substantially concrete structure based on the selected data signal alone from among the plurality of data signals.

20. The system of claim 19, wherein the first reinforcing bar has a longitudinal axis aligned along a first dimension, and a plurality of electromagnetic signals have been transmitted into the substantially concrete structure at different locations along a second dimension approximately orthogonal to the first dimension, and wherein the selected data signal includes electromagnetic energy reflected from the first reinforcing bar as a result of the transmission of one of the plurality of electromagnetic signals.

21. The system of claim 19, wherein each detected electromagnetic signal is detected at a different location on the first side.

22. The system of claim 21, wherein each transmitted electromagnetic signal corresponding to one of the detected electromagnetic signals is transmitted at a different location on the first side.

23. The system of claim 19, further comprising:

a receiver to detect each of the detected electromagnetic signals; and

a transmitter to transmit each of the corresponding transmitted electromagnetic signals.

24. The system of claim 19, further comprising:

a data buffer to temporarily store the data signals before selecting one of the data signals.

25. The system of claim 19, the selected data signal represents an electromagnetic signal detected over a detection period of time, and wherein the means for determining the first distance includes:

means for determining a portion of the selected data signal during which the detected electromagnetic signal, represented by the selected data signal, includes electromagnetic energy reflected from the first reinforcing bar; and

means for determining the first distance of the first reinforcing bar from the first side from the determined portion of the selected data signal.

26. The system of claim 25, further comprising:

means for determining a velocity value representing a velocity at which an electromagnetic signal propagates in concrete of the substantially concrete structure, and

wherein the means for determining the first distance includes;

means for determining a first point in time during the detection period corresponding to a peak amplitude of the electromagnetic energy reflected from the first reinforcing bar; and

means for calculating the first distance using the velocity value and the first point in time.

27. The system of claim 26, wherein, the detected electromagnetic signal corresponding to the selected data signal includes a direct-coupled portion and the means for determining the first distance further includes:

means for subtracting the first point in time from a second point in time to produce a propagation time within the concrete structure for the detected electromagnetic signal represented by the selected data signal, wherein the second point in time corresponds to a peak amplitude of the direct-coupled portion; and

means for calculating the first distance using the velocity value and the propagation time.

28. The system of claim 27, wherein the transmitted electromagnetic signals are transmitted from a first antenna and the detected electromagnetic signals are detected by a second antenna located a second distance from the first antenna, wherein the means for calculating the first distance includes:

means for applying an equation;

$d=\frac{1}{2}<br><br>\sqrt{v^2<br><br>t^2-a^2},$

 

wherein d is the first distance, t is the propagation time, v is the velocity value, and a is the second distance.

29. The system of claim 26, wherein the means for determining the first distance includes:

means for receiving a distance value indicative of a distance measured from the first side of the concrete structure to a second reinforcing bar contained in the substantially concrete structure; and

means for calculating the velocity value from the distance value.

30. The system of claim 29, wherein the transmitted electromagnetic signals are transmitted from a first antenna and the detected electromagnetic signals are detected by a second antenna located a second distance from the first antenna, wherein the means for determining the first distance includes:

means for determining a propagation time within the substantially concrete structure of an electromagnetic signal transmitted into the substantially concrete structure from the first side, reflected from the second reinforcing bar and detected at the first side,

wherein the means for calculating the velocity value includes means for applying an equation;

$v=\frac{2}{t}<br><br>\sqrt{{\left(a/2\right)}^2+d^2},$

 

wherein v is the velocity value, a is the second distance, t is the propagation time and d is the distance value.

31. The system of claim 25, wherein each transmitted electromagnetic signal was transmitted at a different position along the first side of the concrete structure, and the system further comprises:

means for determining, for each data signal, a portion of the data signal during which the detected electromagnetic signal represented by the data signal includes electromagnetic energy reflected from the first reinforcing bar; and

means for determining, for each data signal, a peak amplitude of the data signal during the determined portion,

wherein the means for selecting one of the data signals includes, for a spatial interval of a first length along the first side of the substantially concrete structure, means for selecting the selected data signal for having a peak amplitude of a highest magnitude from among the data signals corresponding to electromagnetic signals transmitted within the spatial interval.

32. The system of claim 25, wherein each transmitted electromagnetic signal was transmitted at a different position along the first side of the concrete structure, and the system further comprises:

means for determining, for each data signal, a portion of the data signal during which the detected electromagnetic signal represented by the data signal includes electromagnetic energy reflected from the first reinforcing bar; and

means for determining, for each data signal, a peak amplitude of the data signal during the determined portion,

wherein the means for selecting one of the data signals includes, for a spatial interval of a first length along the first side of the substantially concrete structure, means for selecting the selected data signal for having a peak amplitude of a highest magnitude from among the data signals corresponding to electromagnetic signals transmitted within the spatial interval.

33. The system of claim 19, wherein the transmitted electromagnetic signals were transmitted from a first antenna and the detected electromagnetic signals were detected by a second antenna located a second distance from the first antenna, the second distance having a midpoint on an imaginary straight between the first and second antennas, and wherein an amplitude of each data signal is directly related to a distance between the area corresponding to the data signal and the midpoint of the second distance.

34. The system of claim 19, wherein each of the data signals represent an electromagnetic signal detected at a point along a substantially straight line along a first dimension of the first side of the concrete structure, and each detected electromagnetic signal is detected over a period of time, the system further comprising:

means for displaying a graph of one or more of the data signals, a first axis of the graph representing time of detection, a second axis of the graph representing a distance along the first dimension, the means for displaying including means for representing an amplitude of each of the one or more data signals over the detection time, wherein a location, with respect to the second axis, of each represented data signal corresponds to a point at which the signal was detected.

35. The system of claim 19, wherein the means for selecting the data signal includes:

means for selecting the data signal from the graph in accordance with an amplitude of the detected electromagnetic signal represented by the selected data signal.

36. The method of claim 19, wherein the system further comprises:

means for adjusting the selected data signal by removing from the selected data signal data representing electromagnetic signals not reflected from the substantially concrete structure; and

means for determining the first distance from the adjusted data signal.

37. For a substantially concrete structure having at least a first side and containing at least a first reinforcing bar, a system for determining a distance of the first reinforcing bar from the first side of the substantially concrete structure, the system comprising:

a computer-readable storage medium to store a plurality of computer-readable data signals, wherein each data signal represents an electromagnetic signal detected from the concrete structure, and one or more of the detected electromagnetic signals include electromagnetic energy reflected from the concrete structure as a result of a corresponding electromagnetic signal transmitted into the concrete structure, and wherein each detected signal corresponds to an area within the concrete structure; and

a data analysis application including;

a first selection module to receive the data signals, to select one of the data signals, the selected data signal corresponding to the first reinforcing bar, and to output the selected data signal; and

a first distance determination module to receive the selected data signal, to determine a first distance of the first reinforcing bar from the first side of the substantially concrete structure based on the selected data signal alone from among the plurality of data signals, and to output the determined first distance.

38. The system of claim 37, wherein the first reinforcing bar has a longitudinal axis aligned along a first dimension, and a plurality of electromagnetic signals have been transmitted into the substantially concrete structure at different locations along a second dimension approximately orthogonal to the first dimension, and wherein the selected data signal includes electromagnetic energy reflected from the first reinforcing bar as a result of the transmission of- one of the plurality of electromagnetic signals.

39. The system of claim 37, wherein each detected electromagnetic signal is detected at a different location on the first side.

40. The system of claim 39, wherein each transmitted electromagnetic signal corresponding to one of the detected electromagnetic signals is transmitted at a different location on the first side.

41. The system of claim 37, further comprising:

a receiver to detect each of the detected electromagnetic signals; and

a transmitter to transmit each of the corresponding transmitted electromagnetic signals.

42. The system of claim 37, further comprising:

a data buffer to temporarily store the data signals before selecting one of the data signals.

43. The system of claim 37, wherein the selected data signal represents an electromagnetic signal detected over a detection period of time, and wherein the first distance determination module includes:

a signal portion determination module to receive the selected data signal, determine a portion of the selected signal during which the detected electromagnetic signal, represented by the selected data signal, includes electromagnetic energy reflected from the first reinforcing bar, and output the determined portion,

wherein the first distance of the first reinforcing bar from the first side is determined from the determined portion of the selected data signal.

44. The system of claim 43, further comprising:

a velocity determination module to determine a velocity value representing a velocity at which an electromagnetic signal propagates in concrete of the substantially concrete structure, and

wherein the first distance determination module includes;

a first time determination module to receive the selected data signal determine for the selected signal a first point in time during the detection period corresponding to a peak amplitude of the electromagnetic energy reflected from the first reinforcing bar, and output the first point in time; and

a first distance calculation module to receive the velocity value and the first point in time, calculate the first distance based on the velocity value and the first point in time, and output the calculated first distance.

45. The system of claim 44, wherein the detected electromagnetic signal represented by the selected data signal includes a direct-coupled portion, and the first distance determination further includes:

a subtraction module to receive the first point in time and a second point in time, subtract the first point in time from the second point in time to produce a propagation time within the concrete structure for the detected electromagnetic signal represented by the selected data signal, and output the propagation time, wherein the second point in time corresponds to a peak amplitude of the direct-coupled portion, and

wherein the first distance determination module receives the propagation time and calculates the first distance using the velocity value and the propagation time.

46. The system of claim 45, wherein the transmitted electromagnetic signals are transmitted from a first antenna and the detected electromagnetic signals are detected by a second antenna located a second distance from the first antenna, wherein the first distance calculation module includes:

means for applying an equation;

$d=\frac{1}{2}<br><br>\sqrt{v^2<br><br>t^2-a^2},$

 

wherein d is the first distance, t is the propagation time, v is the velocity value, and a is the second distance.

47. The system of claim 44, wherein the velocity determination module receives a distance value indicative of a distance measured from the first side of the concrete structure to a second reinforcing bar contained in the substantially concrete structure, and calculates the velocity value from the distance value.

48. The system of claim 47, wherein the transmitted electromagnetic signals were transmitted from a first antenna and the detected electromagnetic signals were detected by a second antenna located a second distance from the first antenna, wherein the first distance determination module includes:

a propagation time determination module to determine a propagation time within the substantially concrete structure of an electromagnetic signal transmitted into the substantially concrete structure from the first side, reflected from the second reinforcing bar and detected at the first side,

wherein the velocity determination module includes means for applying an equation;

$d=\frac{1}{2}<br><br>\sqrt{v^2<br><br>t^2-a^2},$

 

wherein v is the velocity value, a is the second distance, t is the propagation time and d is the distance value.

49. The system of claim 43, wherein each transmitted electromagnetic signal was transmitted at a different position along the first side of the concrete structure, and wherein the signal portion determination module is further operative to receive each data signal, to determine, for each data signal, a portion of the data signal during which the detected electromagnetic signal represented by the data signal includes electromagnetic energy reflected from the first reinforcing bar and to output the determined portions, and the system further comprises:

a peak amplitude determination module to receive the data signals, determine a peak amplitude for each data signal during the determined portion, and output the peak amplitudes,

wherein the first selection module, for a spatial interval of a first length along the first side of the substantially concrete structure, selects the selected data signal for having a peak amplitude of a highest magnitude from among the data signals corresponding to electromagnetic signals transmitted within the spatial interval.

50. The system of claim 46, further comprising:

a migration module to receive the data signals, migrate the data signals to facilitate determining that the selected data signal has a peak amplitude of the highest magnitude, and output the migrated data signals.

51. The system of claim 37, wherein the transmitted electromagnetic signals are transmitted from a first antenna and the detected electromagnetic signals are detected by a second antenna located a second distance from the first antenna, the second distance having a midpoint on an imaginary straight between the first and second antennas, and

wherein an amplitude of each data signal is directly related to a distance between the area corresponding to the data signal and the midpoint of the second distance.

52. The system of claim 37, wherein each of the data signals represent an electromagnetic signal detected at a point along a substantially straight line along a first dimension of the first side of the concrete structure, and each detected electromagnetic signal is detected over a period of time, the system further comprising:

a display device to display a graph of one or more of the data signals, a first axis of the graph representing time of detection, a second axis of the graph representing a distance along the first dimension, the displaying including representing an amplitude of each of the one or more data signals over the detection time, wherein a location, with respect to the second axis, of each represented data signal corresponds to a point at which the signal was detected.

53. The system of claim 52, wherein the data analysis application further includes:

a graphical user interface to permit a user to select the selected data signal from the graph in accordance with the amplitudes of the represented data signals.

54. The system of claim 37, wherein the data analysis application further includes:

a data adjustment module to receive the selected data signal, adjust the selected data signal by removing from the selected data signal data representing electromagnetic signals not reflected from the substantially concrete structure, and output the adjusted data signal,

wherein the first distance is determined from the adjusted data signal.

55. A method of determining a distance of an electromagnetically-reflective object from a first side of a structure containing the object, wherein a plurality of electromagnetic signals have been transmitted into the structure, each transmitted electromagnetic signal transmitted at a different location on the first side, and a plurality of electromagnetic signals have been detected from the structure, each detected electromagnetic signal detected at a different location and corresponding to a respective one of the transmitted electromagnetic signals, wherein one or more of the detected electromagnetic signals include electromagnetic energy reflected from the object as a result of the transmitted electromagnetic signal corresponding to the detected electromagnetic signal, the method comprising:

receiving a plurality of data signals, each data signal representing a respective one of the detected electromagnetic signals;

selecting one of the data signals; and

determining a distance of the object from the first side of the structure based on the selected data signal alone from among the plurality of data signals.

56. The method of claim 55, wherein the first reinforcing bar has a longitudinal axis aligned along a first dimension, and the plurality of electromagnetic signals have been transmitted into the structure at different locations along a second dimension approximately orthogonal to the first dimension.

57. The method of claim 55, wherein selecting includes selecting based on a peak amplitude of the detected electromagnetic signal, represented by the selected data signal, resulting from electromagnetic energy reflected from the object.

58. The method of claim 57, the structure is a substantially concrete structure.

59. The method of claim 58, wherein the one or more objects are reinforcing bars.

60. The method of claim 57, wherein the one or more objects are reinforcing bars.

61. The method of claim 55, wherein the structure is a substantially concrete structure.

62. The method of claim 61, wherein the one or more objects are reinforcing bars.

63. The method of claim 55, wherein the one or more objects are reinforcing bars.

64. The method of claim 55, further comprising:

detecting each detected electromagnetic signal with a same receiver; and

transmitting each corresponding electromagnetic signal with a same transmitter.

65. The method of claim 55, further comprising:

temporarily storing the data signals before selecting one of the data signals.

66. A system for determining a distance of an electromagnetically-reflective object from a first side of a structure containing the object, wherein a plurality of electromagnetic signals have been transmitted into the structure, each transmitted electromagnetic signal transmitted at a different location on the first side, and a plurality of electromagnetic signals have been detected from the structure, each detected electromagnetic signal detected at a different location on the first side and corresponding to a respective one of the transmitted electromagnetic signals, wherein one or more of the detected electromagnetic signals include electromagnetic energy reflected from the object as a result of the transmitted electromagnetic signal corresponding to the detected electromagnetic signal, the system comprising:

one or more inputs to receive a plurality of data signals, each data signals representing a respective one of the detected electromagnetic signals;

means for selecting one of the data signals; and

means for determining a distance of the object from the first side of the structure based on the selected data signal alone from among the plurality of data signals.

67. The system of claim 66, wherein the first reinforcing bar has a longitudinal axis aligned along a first dimension, and the plurality of electromagnetic signals have been transmitted into the structure at different locations along a second dimension approximately orthogonal to the first dimension.

68. The system of claim 66, wherein the means for selecting includes means for selecting based on a peak amplitude of the detected electromagnetic signal, represented by the selected data signal resulting from electromagnetic energy reflected from the object.

69. The system of claim 68, wherein the structure is a substantially concrete structure.

70. The system of claim 69, wherein the structure is a substantially concrete structure.

71. The system of claim 68, wherein the one or more objects are reinforcing bars.

72. The system of claim 66, wherein the structure is a substantially concrete structure.

73. The system of claim 72, wherein the structure is a substantially concrete structure.

74. The system of claim 66, wherein the one or more objects are reinforcing bars.

75. The system of claim 66, further comprising:

a receiver to detect each of the detected electromagnetic signals; and

a transmitter to transmit each of the corresponding transmitted electromagnetic signals.

76. The system of claim 66, further comprising:

a data buffer to temporarily store the data signals before selecting one of the data signals.

77. A computer program product, comprising:

a computer-readable medium; and

computer-readable signals stored on the computer-readable medium that define instructions that, as a result of being executed by a computer, instruct the computer to perform a process of determining a distance of an electromagnetically-reflective object from a first side of a structure containing the object, wherein a plurality of electromagnetic signals have been transmitted into the structure, each transmitted electromagnetic signal transmitted at a different location on the first side, and a plurality of electromagnetic signals have been detected from the structure, each detected electromagnetic signal detected at a different location on the first side and corresponding to a respective one of the transmitted electromagnetic signals, wherein one or more of the detected electromagnetic signals include electromagnetic energy reflected from the object as a result of the transmitted electromagnetic signal corresponding to the detected electromagnetic signal, the process comprising;

receiving a plurality of data signals, each data signals representing a respective one of the detected electromagnetic signals;

selecting one of the data signals; and

determining a distance of the object from the first side of the structure based on the selected data signal alone from among the plurality of data signals.

78. The computer-readable medium of claim 77, wherein the first reinforcing bar has a longitudinal axis aligned along a first dimension, and the plurality of electromagnetic signals have been transmitted into the structure at different locations along a second dimension approximately orthogonal to the first dimension.

79. The computer program product of claim 77, wherein selecting includes selecting based on a peak amplitude of the detected electromagnetic signal, represented by the selected data signal, resulting from electromagnetic energy reflected from the object.

80. The computer program product of claim 79, wherein the structure is a substantially concrete structure.

81. The computer program product of claim 80, wherein the one or more objects are reinforcing bars.

82. The computer program product of claim 79, wherein the one or more objects are reinforcing bars.

83. The computer program product of claim 77, wherein the structure is a substantially concrete structure.

84. The computer program product of claim 83, wherein the one or more objects are reinforcing bars.

85. The computer program product of claim 77, wherein the one or more objects are reinforcing bars.

86. The computer program product of claim 77, wherein the process further comprises:

detecting each detecte d electromagnetic signal with a same receiver; and

transmitting each corresponding electromagnetic signal with a same transmitter.

87. The computer program product of claim 77, wherein the process further comprises:

temporarily storing the data signals before selecting one of the data signals.