Remotely operable compact instruments for measuring atmospheric CO₂ and CH₄ column densities at surface monitoring sites

Abstract. Remotely operable compact instruments for measuring atmospheric CO₂ and CH₄ column densities were developed in two independent systems: one utilizing a grating-based desktop optical spectrum analyzer (OSA) with a resolution enough to resolve rotational lines of CO₂ and CH₄ in the regions of 1565–1585 and 1674–1682 nm, respectively; the other is an application of an optical fiber Fabry-Perot interferometer (FFPI) to obtain the CO₂ column density. Direct sunlight was collimated via a small telescope installed on a portable sun tracker and then transmitted through an optical fiber into the OSA or the FFPI for optical analysis. The near infrared spectra of the OSA were retrieved by a least squares spectral fitting algorithm. The CO₂ and CH₄ column densities deduced were in excellent agreement with those measured by a Fourier transform spectrometer with high resolution. The rovibronic lines in the wavelength region of 1570–1575 nm were analyzed by the FFPI. The I₀ and I values in the Beer-Lambert law equation to obtain CO₂ column density were deduced by modulating temperature of the FFPI, which offered column CO₂ with the statistical error less than 0.2% for six hours measurement.