Research on application of local oscillator power locking method to laser heterodyne radiometer

Abstract

Laser heterodyne radiometer has the advantages of low cost, small size, and high spectral resolution. It can expand the existing ground carbon measurement network, verify satellite observation results, and provide data coverage outside the satellite observation area. Using the existing laser heterodyne radiometer, is presented a prototype of near-infrared laser heterodyne radiometer based on the erbium-doped fiber amplifier that can realize local oscillator power locking. In the laser heterodyne radiometer a distributed feedback semiconductor laser with a center wavelength of 1.603 μm is used as a local oscillator light source. The erbium-doped fiber amplifier is used to enhance the local oscillator power, and the automatic power control circuit is adopted to lock the output optical power of the erbium-doped fiber amplifier. The baseline slope caused by the change of the local oscillator power is eliminated, and the whole layer atmospheric transmittance spectrum without baseline fitting is measured. The instrument performance of a highly integrated laser heterodyne radiometer based on an erbium-doped fiber amplifier is evaluated in detail, and the atmospheric CO₂ transmittance spectrum is measured in the Science Island (31.9°N, 117.2°E) of Hefei. Six groups of atmospheric CO₂ transmittance spectra are obtained during the measurement period of one day, which are compared with the simulation results from an atmospheric radiation model, showing that they are consistent with each other. The experimental results show that the application of erbium-doped fiber amplifier can improve the performance of laser heterodyne radiometer, optimize its structure, and provide equipment supplement for realizing unattended long-term atmospheric CO₂ concentration observation and building a comprehensive carbon observation network.