| CPC G01S 7/4913 (2013.01) [G01S 7/4915 (2013.01); G01S 7/4917 (2013.01); G01S 17/50 (2013.01)] | 18 Claims |
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1. A method of determining a range to one or more targets, the method comprising:
generating a reference signal having a reference optical spectrum and a transmission signal having a transmission optical spectrum,
the reference optical spectrum having at least a first reference frequency component and the transmission optical spectrum having at least a first transmission frequency component and a second transmission frequency component, different from the first transmission frequency component;
directing the transmission signal to at least one target;
receiving a reflection signal from the at least one target, the reflection signal having a reflection optical spectrum having at least a first and a second reflection frequency components that correspond to the first and second transmission frequency components;
mixing the reflection signal with the reference signal, thereby generating a mixed signal;
detecting the mixed signal, thereby producing an electrical return signal corresponding to an intensity of the mixed signal, the electrical return signal having frequency components corresponding to the frequency components of the reflected signal;
based on the electrical return signal, estimating the reflection optical spectrum, wherein estimating the reflection optical spectrum comprises applying a spectral estimation method to the electrical return signal to identify phases of the frequency components in the electrical return signal, wherein the spectral estimation method is a Fourier transform, a time-frequency transform, a finite impulse response filter, or a Kalman filter; and
either one or both of (i) and (ii):
(i)
based on the estimated reflection optical spectrum, determining a time-of-flight delay of the reflection signal, wherein determining the time-of-flight delay of the reflection signal further comprises:
determining a representation of phase difference of frequency components in the electrical return signal, said frequency components corresponding to interference of the first and the second reflection frequency components with the first reference frequency component; and
based on the representation of phase difference of frequency components in the electrical return signal and on a difference of the frequencies of the first and second reflection frequency components, determining the time-of-flight delay of the reflection signal,
(ii)
based on the estimated reflection optical spectrum and the reference optical spectrum, determining a frequency shift of the reflection optical spectrum, the frequency shift having a Doppler shift component and a range shift component, wherein:
at least one of the transmission optical spectrum and the reference optical spectrum comprises a first component having a first frequency, and a second component having a second frequency, different from the first frequency, and wherein the at least one of the transmission optical spectrum and the reference optical spectrum is asymmetric about the midpoint of the reference optical spectra,
wherein determining a frequency shift of the reflection optical spectrum, the frequency shift having a Doppler shift component and a range shift component comprises:
determining the range shift component of the frequency shift; and
based on the estimated reflection optical spectrum, the reference optical spectrum and the range shift component of the frequency shift, determining a signed Doppler shift component of the reflection optical spectrum.
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