Researchers from the Hefei Institutes of Physical Science, Chinese Academy of Sciences, have developed new technologies to improve the accuracy and spectral resolution of laser heterodyne radiometers (LHRs) for atmospheric greenhouse gas measurements.
Their findings have been published in Optics and Laser Technology, Optics Express, and Optics Letters.
Laser heterodyne radiometers are widely used for remote sensing of atmospheric greenhouse gases due to their high spectral resolution, compact design, and suitability for field observations. However, their performance is limited by challenges such as inaccurate instrument calibration, wavelength instability, and spectral distortion in conventional double-sideband detection.
In this study, the team developed a series of improvements in calibration methods, optical systems, and detection technologies.
For instrument calibration, the researchers proposed a new method combining gas absorption measurements with a deconvolution algorithm, enabling more accurate characterization of the instrument response. The improved calibration reduced spectral errors and enhanced the accuracy of methane concentration retrieval.
They also developed a real-time wavelength calibration system based on an all-fiber Mach–Zehnder interferometer, providing a stable frequency reference for LHR measurements. The system was successfully applied to atmospheric carbon dioxide observations on Science Island in Hefei.
In addition, the researchers designed a single-sideband laser heterodyne spectrometer to overcome spectral distortion caused by conventional double-sideband systems. The new design eliminates central dip distortion and improves spectral resolution, enabling more accurate measurements of greenhouse gas absorption signals.
These advances improve greenhouse gas monitoring and atmospheric observations with laser heterodyne spectroscopy.
Schematic diagram of an all-fiber laser heterodyne radiometer with real-time wavelength calibration. （Image by TAN Tu）