Code-space optical electronic distance meter
First Claim
1. An electronic distance meter (EDM), comprising:
- a first light emitter providing for the illumination of a first distant target with a first beam of light;
a first light detector providing for the reception and detection of light reflected from said first distant target;
a satellite navigation receiver connected to provide a one-pulse-per-second (1-PPS) output for a derivative clock synchronized to an atomic clock in conventional orbiting global positioning system (GPS) satellites, and outputting a precision timing base;
a first modulator connected to the first light emitter providing for modulation of said first beam of light with a first pseudo-random number (PRN) modulation signal having a first characteristic PRN code sequence; and
a first digital signal processor (DSP) connected to receive both said precision timing base and a first detected-light input signal from the first light detector and having range computer means for code correlation and code-phase locking onto said first detected-light input signal and for determining a first distance to said first target based on the difference in phase of said first detected-light input signal and said first PRN modulation signal, given the speed of light through an interim medium to said target object;
wherein, the first modulator drives the first light emitter according to a pseudo-random number (PRN) code sequence that mimics one of the PRN codes transmitted by conventional orbiting global positioning system (GPS) satellites and includes at least one of a coarse acquisition (C/A) code having a code length of 1023 chips transmitted at a rate of 1.023 Mbits/sec., and a precision (P) code having a code length of 510 chips transmitted at a rate of 10.23 Mbits/sec; and
wherein, the first digital signal processor (DSP) resolves a time-of-flight delay "t" to said first distant target to within tens of picoseconds.
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Accused Products
Abstract
An electronic distance meter comprises an integrated circuit from a GPS navigation receiver having a local pseudo-random number code generator for code demodulation that is connected to modulate either a polychromatic or a monochromatic light source. An optical system focuses the light on a distant target with an unknown range. Reflections from the distant target are focused on a light detector that produces a phase-delayed copy of the original pseudo-random number code. The time-of-flight to and back from the distant target is a function of the distance. The GPS receiver integrated circuit computes the range based on the code-phase delay to a precision better than one centimeter. The position of a remote target can be triangulated from several electronic distance meters each having known positions, e.g., determined by included GPS navigation receivers. Conversely, the position of a single electronic distance meter can be determined by triangulation by ranging to several remote targets each having known positions.
113 Citations
6 Claims
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1. An electronic distance meter (EDM), comprising:
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a first light emitter providing for the illumination of a first distant target with a first beam of light; a first light detector providing for the reception and detection of light reflected from said first distant target; a satellite navigation receiver connected to provide a one-pulse-per-second (1-PPS) output for a derivative clock synchronized to an atomic clock in conventional orbiting global positioning system (GPS) satellites, and outputting a precision timing base; a first modulator connected to the first light emitter providing for modulation of said first beam of light with a first pseudo-random number (PRN) modulation signal having a first characteristic PRN code sequence; and a first digital signal processor (DSP) connected to receive both said precision timing base and a first detected-light input signal from the first light detector and having range computer means for code correlation and code-phase locking onto said first detected-light input signal and for determining a first distance to said first target based on the difference in phase of said first detected-light input signal and said first PRN modulation signal, given the speed of light through an interim medium to said target object; wherein, the first modulator drives the first light emitter according to a pseudo-random number (PRN) code sequence that mimics one of the PRN codes transmitted by conventional orbiting global positioning system (GPS) satellites and includes at least one of a coarse acquisition (C/A) code having a code length of 1023 chips transmitted at a rate of 1.023 Mbits/sec., and a precision (P) code having a code length of 510 chips transmitted at a rate of 10.23 Mbits/sec; and wherein, the first digital signal processor (DSP) resolves a time-of-flight delay "t" to said first distant target to within tens of picoseconds. - View Dependent Claims (2, 3, 4, 5)
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6. An electronic distance meter (EDM), comprising:
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a laser light source for directing an incident beam of light on a reflective target; an optical detector for detecting any reflected light that may be returned from said reflective target; a laser-light modulator connected to impress a pseudo-random number (PRN) sequence on said incident beam of light using a direct sequence spread spectrum (DSSS) method; a DSSS despreader and correlator for detecting said PRN sequence in said reflected light and for determining an amount of PRN code phase delay that occurred during a round-trip to said reflective target; a precision reference clock used to pace said PRN sequence and to measure said PRN code phase delay; and a satellite navigation receiver connected to discipline the precision reference clock, wherein a basic measurement accuracy of said PRN code phase delay is based on atomic clocks in orbiting navigation satellites.
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Specification