Simultaneous remote sensing of multiple atmospheric gases (CO2, CH4, and H2O) based on an all-fiber laser heterodyne spectroradiometer

We report an all-fiber, near-infrared laser heterodyne radiometer (LHR) that uses two distributed feedback (DFB) diode lasers as local oscillators. This scheme allows the retrieval of the column abundances of multiple atmospheric gases of CH4, CO2, and H2O. To improve the detection efficiency, we operated the two DFB diode lasers emitting at 1653 and 1568 nm simultaneously within one scanning cycle. The duration of one scanning cycle was experimentally determined to be 2 s. An atmospheric transmission spectrum of multi-gas was observed within 20 s after averaging ten times. This approach has simplified the sensing system and reduced the probability of being affected by the rapid and random fluctuation of solar radiation due to clouds. We regulated the laser power, and hence, the amplitudes of background heterodyne signals excited by the two local oscillators, to accurately measure the transmission spectrum of each gas species. The results of the sun-tracking observations of this LHR sensor show good agreement with the data taken simultaneously by the GOSAT satellite.