Abstract
We have developed a laser heterodyne spectroradiometer in combination with self-calibrated wavelength modulation spectroscopy based on a software-based lock-in amplifier to observe the atmospheric carbon dioxide (CO2) column absorption near wavelength 1.57μm in solar occultation mode. This combination facilitates miniaturization of laser heterodyne radiometer. Combined with our developed retrieval algorithm, the atmospheric carbon dioxide column concentration is measured to be 413.7±1.9ppm, in agreement with GOSAT satellite observation results. This system offers high spectral signal-to-noise ratio of ~333 for the zeroth harmonic (0f) normalized second harmonic (R2f) signal of CO2 transition (R22e), with a measurement averaging time of 8s, which can be further improved by increasing averaging time in accordance to the Allan deviation analysis for the noise fluctuation. This demonstrates the feasibility of the system for atmospheric investigation and the potential of ground-based, airborne and spaceborne observations for the variation of the global greenhouse gases.
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