Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/023—Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/88—Radar or analogous systems specially adapted for specific applications
  • G01S13/885—Radar or analogous systems specially adapted for specific applications for ground probing
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
  • G01V3/12—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with electromagnetic waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
  • G01S13/06—Systems determining position data of a target
  • G01S13/08—Systems for measuring distance only
  • G01S13/32—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
  • G01S13/34—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
  • G01S13/347—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal using more than one modulation frequency

Definitions

• the technical field of the invention relates to a method of suppressing interfering signals in the processing of data from a step-frequency georadar, and a step-frequency georadar with means to carry out said method.
• a georadar is a type of radar that sends electromagnetic waves (radio waves) down into the ground and measures reflections from objects or stratifications. In order to achieve a good distance resolution, a georadar must have a very large bandwidth.
• a step-frequency georadar provides this bandwidth by sending out signals with a stepwise increasing frequency, and measures the ground response for each individual frequency.
• the signals reflected from the surface of the ground are very weak, and since the georadar covers a large frequency area, the probability of interfering signals from other sources is large.
• Base stations for mobile communication, broadcasting senders, and communication radio all fall within the frequency area of the georadar, and may thus interfere with the georadar.
• the manner of operation of the step-frequency georadar where only a small frequency area is received at one time, will make it so that the georadar is only interfered with when the step-frequency radars sending frequency is relatively concurrent with the interfering frequency.
• the object of the invention is to suppress interfering signals in order for other, nearby senders to influence the georadar to a smaller extent. This is achieved by taking advantage of the step-frequency radars narrow band receiver system, and adaptively removing the interfering signals. Short description of the figures
• Figure 1 shows the received signal with the interference given as a function of the frequency, as well as a filtered approximation of the same signal where a robust estimation is used in order to filter said signal.
• Figure 2 shows a received signal where the method for removing interference is utilized.
• Figure 3 shows a radargram where the interference form the nearby sender is clear.
• Figure 4 shows a radargram based on the same signal as figure 2, where the interference from the nearby sender is considerably reduced.
• a step-frequency georadar works by sending a continual signal at a given frequency over a short period of time.
• the receiver of the radar is adjusted to the exact same frequency, and will therefore receive a signal with the above mentioned frequency which is the sum of all the signals reflected from different parts of the ground.
• the signal is measured by the receiver as signal strength and relative phase.
• the sender and receiver change frequency, and the same process is repeated for the new frequency. This is repeated with small frequency steps until the entire bandwidth of the georadar is covered.
• the receiver is now left with a signal strength and relative phase for all the frequency steps. Since the total reflected signal is measured for each frequency, this comprises the grounds frequency response (1 ) as shown in figure 1 .
• this frequency response In order to establish a radargram this frequency response must be transformed to a time response, e.g. by the aid of a Fourier transformation. This process is repeated while the radar is moved along the ground in order to form a radargram as shown in figures 3 and 4.
• the signal strength (1 ) is shown for a signal received with a step-frequency georadar.
• the frequency area of the radar is from about 100 MHz to about 2900 MHz, in other words a total bandwidth of close to 3 GHz.
• the signal also comprises interference from two other sources.
• An interference signal (2) is situated at around 900 MHz, and another interference signal (3) at around 2100 MHz.
• Figure 3 shows the resulting radargram with these interference sources.
• the step-frequency radar is basically relatively robust towards interference, since the interference will only disturb a small fraction of the received signal. Still, the interference from the two senders is clearly evident in the radargram.
• the interference is displayed as vertical bands.
• the method for removing interference adaptively consists of the following steps: a) determination of a criteria (5) for when a measured signal (1 ) for a frequency is to be replaced by a filtered signal (4) for the same frequency, where said criteria is based on a deviation calculated as the absolute value of the complex differential between the measured (1 ) and filtered (4) signal for the given frequency, where said criteria (5) is at least one of the following:
• the deviation is larger than a median deviation multiplied by a factor K, where the median deviation is the median of the deviations;
• P may have value in the range of 90-95 %.
• K may have a value in the range of 3-5.
• the robust estimator may comprise a sliding median filter. This sliding median filter may preferably have a bandwidth in the range of 50-100 MHz.
• the method in accordance with the present invention may in addition comprise calculation of the time response by transforming the modified frequency response form the frequency domains to the time domains.
• Said transformation from the frequency domain to the time domain may e.g. be accomplished by an inverse Fourier transformation.
• the invention also relates to a step-frequency georadar comprising an antenna system, data processing equipment, and other means, which are arranged to accomplish the method as described above.
• a lower limit is set for how large the deviation must be for the signal to be replaced by the filtered values.
• Figure 2 shows the received signal after the data points with the largest deviation have been replaced by the filtered values (6,7).
• Figure 4 reproduces the diagram after the signals have been filtered in accordance with this method. The vertical bands are gone, without notably affecting important details. In these figures a combination of the criterion suggested in c) are used.

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• Engineering & Computer Science (AREA)
• Remote Sensing (AREA)
• Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Computer Networks & Wireless Communication (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Life Sciences & Earth Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Geology (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geophysics (AREA)
• Radar Systems Or Details Thereof (AREA)
• Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Priority Applications (4)

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Publications (1)

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Cited By (3)

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Citations (3)

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• 2011
  • 2011-10-07 NO NO20111362A patent/NO335171B1/no not_active IP Right Cessation
• 2012
  • 2012-10-04 AU AU2012319273A patent/AU2012319273B2/en not_active Expired - Fee Related
  • 2012-10-04 WO PCT/NO2012/050192 patent/WO2013051944A1/en active Application Filing
  • 2012-10-04 JP JP2014534508A patent/JP5926389B2/ja not_active Expired - Fee Related
  • 2012-10-04 CN CN201280044699.0A patent/CN103959087B/zh not_active Expired - Fee Related
  • 2012-10-04 EP EP12837687.8A patent/EP2764379A4/en not_active Withdrawn

Patent Citations (3)

Non-Patent Citations (1)

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