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1. WO2010076037 - METHOD FOR INTERFEROMETRIC RADAR MEASUREMENTS

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

CLAIMS

1. A method for estimating a displacement of a remote object in a radar scenario by means of an interferometric radar, said method comprising the steps of: - transmitting from said radar a first emitted signal at a first instant and a second emitted signal at a second instant, said first emitted signal and said second emitted signal having an emission frequency and an emission amplitude;

- receiving at said remote object said first emitted signal and said second emitted signal;

- receiving at said radar a first response signal and a second response signal from said radar scenario, said first response signal and said second response signal comprising respectively a first remote object response signal portion and a second remote object response signal portion;

- demodulating said first response signal and said second response signal, said step of demodulating creating a first demodulated response signal and a second demodulated response signal comprising respectively a first demodulated frequency-shifted signal and a second demodulated frequency-shifted signal;

- extracting a first phase and a second phase respectively from said first demodulated frequency-shifted signal and from said second demodulated frequency-shifted signal;

- computing a difference between said first phase and said second phase;

- computing a displacement of said remote object, said displacement responsive to said difference between said first phase and said second phase, characterized in that said method comprises furthermore the steps of: - prearranging a transponder at said remote object; frequency-shifting, at said transponder, said first emitted signal and said second emitted signal as received at said remote object, said frequency-shifting step creating a first frequency-shifted signal and a second frequency-shifted signal that have a shifted frequency that differs from said emission frequency by a predetermined frequency-shift, and retransmitting from said transponder said first frequency-shifted signal and said second frequency-shifted signal, such that said first remote object response signal portion and said second remote object response signal portion respectively comprise said first frequency-shifted signal and said second frequency-shifted signal, such that said first and said second demodulated frequency-shifted signal have a frequency that differs from said emission frequency responsive to said frequency shift.

2. The method according to claim 1 , wherein said frequency shift is selected such that the wavelength of said first and said second emitted signal differs from said the wavelength of said first and said second frequency- shifted signals less than a predetermined frequency shift fd, in order to univocally establish said displacement of said remote object with respect to said difference between said first phase and said second phase.

3. The method according to claim 2, wherein said predetermined frequency- shift fd is at least six orders of magnitude (106) lower than said emitted frequency. 4. The method according to claim 1 , wherein said step of demodulating is a coherent demodulation that provides multiplying said first response signal and said second response signal respectively by said first emitted signal and by said second emitted signal.

5. The method according to claim 1 , wherein said phase-extracting step comprises:

- multiplying said first demodulated response signal and said second demodulated response signal by a phasor, said phasor being a periodic signal having a frequency equal to said frequency-shift, said multiplying step creating a first baseband signal and a second baseband signal which respectively comprise a first baseband demodulated frequency- shifted signal and a second baseband demodulated frequency-shifted signal; filtering said first baseband signal and said second baseband signal, said filtering step suppressing portions of signals whose frequency is in absolute value greater than an unilateral filter bandwidth, said filtering step producing a first baseband filtered signal and a second baseband filtered signal; - computing said first phase and said second phase respectively from said first baseband filtered signal and from said second baseband filtered signal, wherein said predetermined frequency-shift is greater than said unilateral filter bandwidth.

6. The method according to claim 1 , wherein a further remote object is present in said radar scenario, and said method provides the steps of:

- prearranging a further transponder at said further remote object;

- further frequency-shifting, in said transponder, said first emitted signal and said second emitted signal as received at said further remote object, said further frequency-shifting step creating a further first frequency-shifted signal and a further second frequency-shifted signal that have a further shifted frequency that differs from said emission frequency by a further predetermined frequency-shift, and retransmitting from said further transponder said further first frequency-shifted signal and said further second frequency-shifted signal; - further phase-extracting, said further phase-extracting step extracting a further first phase and a further second phase respectively of said further first demodulated frequency-shifted signal and of said further second demodulated frequency-shifted signal;

- computing a difference between said further first phase and said further second phase; computing a displacement of said further remote object, said displacement responsive to said difference between said further first phase and said further second phase.

7. The method according to claim 1 , wherein said first emitted signal and said second emitted signal comprise a repeated sequence of tones that have:

- a predetermined duration of said tones, such that a tone reflected by a remote object that is located at a predetermined distance from said radar is received at said radar before that said radar stops transmitting said tone, such that a coherent demodulation of said tone is carried out at said radar, said predetermined distance being called the maximum radar range of said radar; - respective different frequencies, said frequencies differing by a predetermined frequency pitch , such that an unambiguous range limit is defined, i.e. a distance is defined that is related to said frequency pitch, and within which the displacement of a remote object may be established without ambiguity by said radar; such that said radar scenario set between said radar and said unambiguous range limit is subdivided in a plurality of resolution cells that are equal in number to said tones of said sequence of tones, and said radar measures a displacement of said remote object in a predetermined cell selected among said plurality of resolution cells, said predetermined cell called an observed resolution cell,

- wherein said frequency pitch is set such that said unambiguous range limit is greater than said maximum radar range, wherein said step of extracting comprises the steps of:

- acquiring a first sequence of sample values of said first demodulated response signal and a second sequence of sample values of said second demodulated response signal, each sample value of said first sequence and each sample value of said second sequence corresponding to a tone of said sequence of tones, each of said sample values comprising a signal portion related to a respective demodulated frequency-shifted signal;

- applying an inverse discrete Fourier transform (IDFT) to said first sequence of sample values and to said second sequence of sample values, such that a first transformed sequence of sample values of said first demodulated response signal and a second transformed sequence of sample values of said first demodulated response signal are obtained, each sample value of said first transformed sequence and each sample value of said second transformed sequence associated to one resolution cell, wherein said signal portion relative to a respective demodulated frequency-shifted signal is migrated from said observed resolution cell into one of said migrated resolution cells responsive to the value of said frequency shift. - extracting from said first transformed sequence and from said second transformed sequence a first sample value and a second sample value which are associated to said migrated resolution cell; - computing said first phase and said second phase of respective sample values which are associated to said migrated resolution cell. 8. A method according to claim 7, wherein said predetermined frequency pitch is a positive pitch.

9. A method according to claim 7, wherein said frequency pitch is set such that said unambiguous range limit is substantially double of said maximum radar range, and said resolution cells, whose diameter is less or equal to said maximum radar range, are equal in number to said resolution cells, which are called displaced resolution cells, that have a diameter set between said maximum radar range and said unambiguous range limit,

10. The method according to claims 6 and 7, wherein said remote object and said further remote object are located in said observed resolution cell, and said further frequency-shift is set such that said signal portion which is associated to a respective further demodulated frequency-shifted signal is migrated from said observed resolution cell into a further migrated resolution cell that is different from said migrated resolution cell. 11. The method according to claim 1 , comprising the steps of: prearranging an amplifier at said remote object; amplifying, at said amplifier, said first and said second emitted signal as received at said transponder, or said first and said second frequency-shifted signal, such that said first frequency-shifted signal and said second frequency-shifted signal have an amplified amplitude that is greater than said emission amplitude.

12. The method according to claim 1 , wherein said method provides a step of fixing said frequency-shift and/or said further frequency-shift from a remote position, in particular by means of wireless communication techniques, in particular by means of WIFI communication techniques.

13. The use of a transponder for estimating a displacement of a remote object in a radar scenario by means of an interferometric radar, - wherein said transponder is prearranged at said remote object; and wherein said transponder is associated with a radar system that operates with the method according to any of the previous claims.

14. The use of a transponder according to claim 13, wherein said object is a ground-based object selected among. - landslides,

- subsidence and bradyseism,

- civil works such as buildings, bridges, off-shore structures,

- river banks, open pits.