Patent ID: 8605262

Claim:
A method of measuring absorption utilizing a transmitted optical signal, the method comprising: providing a first laser that produces light having a first wavelength; providing a second laser that produces light having a second wavelength that is not equal to the first wavelength; generating at least one PN code; modulating light produced by the first laser utilizing the PN code to provide a first outgoing optical signal comprising light at the first wavelength, the first outgoing optical signal including first PN code data; modulating light produced by the second laser utilizing the PN code to provide a second outgoing optical signal comprising light at the second wavelength, the second outgoing optical signal including second PN code data that is time shifted relative to the first PN code data of the first outgoing optical signal; directing the first and second outgoing optical signals towards a target to thereby cause at least a portion of the first optical signal and a portion of the second optical signal to be reflected from the target to provide return signal data; detecting a return signal comprising at least a portion of the first signal that has been reflected from the target and a portion of the second signal that has been reflected from the target; correlating the return signal data with the first and second PN code data to provide first and second distinct amplitude peaks corresponding to the portions of the first and second signals that have been reflected from the target, respectively; determining a magnitude of the first amplitude peak; determining a magnitude of the second amplitude peak; utilizing the magnitudes of the first and second amplitude peaks to determine a relative absorption of the first and second signals.