Chirped coherent laser radar system and method
A laser radar system using collocated laser beams to unambiguously detects a range of a target and a range rate at which the target is moving relative to the laser radar system. Another aspect of various embodiments of the invention may relate to a laser radar system that uses multiple laser radar sections to obtain multiple simultaneous measurements (or substantially so), whereby both range and range rate can be determined without various temporal effects introduced by systems employing single laser sections taking sequential measurements. In addition, other aspects of various embodiments of the invention may enable faster determination of the range and rate of the target, a more accurate determination of the range and rate of the target, and/or may provide other advantages.
1 . A method for measuring motion aspects of a target, the method comprising:
directing a first laser beam at a location on the target, the first laser beam having a first frequency that varies by a first chirp rate;
directing a second laser beam at the location on the target, the second laser beam having a second frequency;
receiving a first reflected portion of the first laser beam from the location on the target and a second reflected portion of the second laser beam from the location on the target;
combining the first reflected portion and the second reflected portion; and
determining at least two motion aspects of the location on the target from the combined first reflected portion and second reflected portion, wherein the at least two motion aspects are determined independently from one another.
2 . The method of claim 1 , wherein directing the second laser beam at the location of the target comprises:
directing the second laser beam to be coincident with the first laser beam at the location of the target.
3 . The method of claim 1 , wherein the second frequency of the second laser beam varies at a second chirp rate, wherein the second chirp rate is different from the first chirp rate.
4 . The method of claim 3 , wherein the first chirp rate has the same magnitude as second chirp rate.
5 . The method of claim 3 , wherein directing a first laser beam at a location on the target where the first laser beam has a first frequency that varies by a first chirp rate comprises:
increasing, during a first time period, the first frequency of the first laser beam by the first chirp rate; and
decreasing, during a second time period, the first frequency of the first laser beam by the first chirp rate.
6 . The method of claim 5 , wherein directing a second laser beam at the location on the target where the second frequency of the second laser beam varies at a second chirp comprises:
decreasing, during the first time period, the second frequency of the second laser beam by the second chirp rate; and
increasing, during the second time period, the second frequency of the second laser beam by the second chirp rate.
7 . The method of claim 6 , wherein the first time period and the second time period have a same duration.
8 . The method of claim 1 , further comprising:
combining the first laser beam with the second laser beam prior to directing the first laser beam and the second laser beam at a location on the target.
9 . The method of claim 1 , wherein determining at least two independent motion aspects of the location on the target comprises:
determining at least a range of the location on the target.
10 . The method of claim 1 , wherein determining at least two independent motion aspects of the location on the target comprises:
unambiguously determining a range of the target and a Doppler velocity of the target.
11 . A method for determining a distance between a laser system and a target, the method comprising:
generating, from a first laser source, a first laser beam having a first frequency;
generating, from a second laser source, a second laser beam having a second frequency;
chirping up the first frequency of the first laser beam at a first chirp rate while chirping down the second frequency of the second laser beam at a second chirp rate;
directing the first laser beam and the second laser beam to a location on the target;
receiving a first reflected portion of the first laser beam from the location on the target and a second reflected portion of the second laser beam from the location on the target;
combining the first reflected portion of the first laser beam with the second reflected portion of the second laser beam; and
determining at least a range to the location on the target and a Doppler velocity of the location on the target from the combined first reflected portion of the first laser beam and second reflected portion of the second laser beam.
12 . The method of claim 11 , further comprising:
chirping down the first frequency at a third chirp rate while chirping up the second frequency at a fourth chirp rate.
13 . The method of claim 11 , wherein the first chirp rate and the second chirp rate are different from one another.
14 . The method of claim 11 , wherein the first chirp rate and the second chirp rate are substantially the same.
15 . The method of claim 12 , wherein the first chirp rate and the third chirp rate are different from one another.
16 . The method of claim 12 , wherein the first chirp rate and the third chirp rate are substantially the same.
17 . The method of claim 12 , wherein the second chirp rate and the fourth chirp rate are different from one another.
18 . The method of claim 12 , wherein the second chirp rate and the fourth chirp rate are substantially the same.
19 . The method of claim 11 , wherein directing the first laser beam and the second laser beam to a location on the target comprises combining the first laser beam with the second laser beam.
20 . The method of claim 11 , wherein combining the first reflected portion of the first laser beam with the second reflected portion of the second laser beam comprises:
electronically combining the first reflected portion of the first laser beam with the second reflected portion of the second laser beam, or
optically combining the first reflected portion of the first laser beam with the second reflected portion of the second laser beam, or
digitally combining the first reflected portion of the first laser beam with the second reflected portion of the second laser beam.