XCO<sub>2</sub>-measurements with a tabletop FTS using solar absorption spectroscopy

Abstract

A commercial low-resolution (0.5 cm⁻¹) Fourier-Transform-Spectrometer (FTS) has been modified and is used for determining the total column XCO₂ of the atmosphere by analyzing direct solar radiation. The spectrometer has a small home-built solar tracker attached, so that it is a ready-to-use instrument. The results are validated with temporally coinciding on-site measurements taken with a high-resolution Total Carbon Column Observing Network (TCCON) FTIR-spectrometer. For the whole comparison period of 5 months (26 measurement days) an agreement with TCCON-results of (0.12 ± 0.08)% is achieved. This makes the spectrometer a promising candidate for a low-cost addition to the TCCON core FTIR sites, especially suitable for locations with limited infrastructure. An impressive mechanical and thermal stability is proved, enabling the spectrometer for use in field campaigns and for the monitoring of local sources

Intercomparability of X<sub>CO<sub>2</sub></sub> and X<sub>CH<sub>4</sub></sub> from the United States TCCON sites

“…Because of different spectral resolutions between the TC-CON instruments (0.02 cm −1 ) and the traveling spectrometers (0.5 cm −1 ), we anticipate systematic differences in their X gas retrievals (Gisi et al, 2012;Petri et al, 2012). Even in the absence of instrumental problems, spectroscopic inadequacies can cause systematic differences that correlate with T (temperature) errors, surface pressure errors, and solar zenith angle (SZA; Wunch et al, 2011b).…”

“…One EM27/SUN instrument is operated by Caltech and one by Los Alamos National Laboratory (LANL). These instruments have been described in detail elsewhere (Gisi et al, 2012). Briefly, similar to the TC-CON spectrometers, they measure direct solar near IR spectra, albeit at a lower resolution (0.5 cm −1 versus 0.02 cm −1 ).…”

“…These factors were based on the TCCON and mFTS data at all sites and were used in combination with the TCCON to in situ profiles bias correction . An additional scaling factor is used because retrievals from lower-resolution spectra are biased compared to higher-resolution spectra due to errors in a priori profiles and spectroscopy (Gisi et al, 2012;Hedelius et al, 2016;Petri et al, 2012). For the box plots, we use the convention that the whiskers are 90 % CI.…”

“…These sites were at (1) the California Institute of Technology (Caltech), Pasadena, California (CA); (2) Armstrong Flight Research Center (AFRC), Edwards, CA; (3) Lamont, Oklahoma (OK); and (4) Park Falls, Wisconsin (WI). Bias quantification was accomplished by comparisons with two mobile EM27/SUN spectrometers (Gisi et al, 2012). A map of the US 2015 TCCON sites is shown in Fig.…”

A Singular Value Decomposition framework for retrievals with vertical distribution information from greenhouse gas column absorption spectroscopy measurements

“…Carbon Observatory (OCO-2, Boesch et al (2011)), ground-based spectrometers such as the Total Column Carbon Observing Network (TCCON, Wunch et al (2011) and other instruments (Gisi et al, 2012). Atmospheric measurements have also been made using airborne integrated path differential absorption (IPDA) lidar instruments (Abshire et al, 2014;Lin et al, 2015;Menzies et al, 2014;Refaat et al, 2016).…”