Modulated sine waves for differential absorption measurements using a CW laser system

摘要

A continuous wave Light Detection and Ranging (CW LiDAR) system utilizes two or more laser frequencies and time or range shifted pseudorandom noise (PN) codes to discriminate between the laser frequencies. The performance of these codes can be improved by subtracting out the bias before processing. The CW LiDAR system may be mounted to an artificial satellite orbiting the earth, and the relative strength of the return signal for each frequency can be utilized to determine the concentration of selected gases or other substances in the atmosphere.

主权项

1. A method of utilizing an intensity modulated laser beam to provide for measurement of differential absorption in a continuous wave lidar system, the method comprising:
utilizing a laser to provide a first light beam having a first wavelength; utilizing a laser to provide a second light beam having a second wavelength that is not equal to the first wavelength; utilizing a PN code to provide a modulation signal having an intensity modulated (IM) repeating wave form corresponding to the PN code; providing intensity modulation of the first and second light beams whereby the first and second light beams comprise first and second transmitted signals corresponding to the modulation signal, wherein the first transmitted signal is time shifted relative to the second transmitted signal; directing the first and second light beams at a target such that at least a portion of the first light beam is reflected, and at least a portion of the second light beam is reflected; receiving at least a portion of the reflected first and second light beams to form a received signal; demodulating the received signal utilizing the modulation signal to provide first and second distinct amplitude peaks; determining a magnitude of the first amplitude peak; determining a magnitude of the second amplitude peak; and utilizing the magnitudes of the first and second peaks to determine a relative absorption of the first and second light beams.