Calibration and instrumental line shape characterization of a set of portable FTIR spectrometers for detecting greenhouse gas emissions

Abstract

Abstract.A comprehensive calibration procedure for mobile, low-resolution, solar-absorption FTIR spectrometers, used for greenhouse gases observations, is developed. These instruments commend themselves for campaign use and deployment at remote sites. The instrumental line shape (ILS) of each spectrometer has been thoroughly characterized by analyzing the shape of H 2 O signatures in open path spectra. A setup for the external source is suggested and the invariance of derived ILS parameters with regard to chosen path length is demonstrated. The instrumental line shape characteristics of all spectrometers were found to be close to nominal. Side-by-side solar observations before and after a campaign, which involved shipping of all spectrometers to a selected target site and back, are applied for verifying the temporal invariability of instrumental characteristics and for deriving intercalibration factors for XCO 2 and XCH 4 , which take into account residual differences of instrumental characteristics. An excellent level of agreement and stability was found between the different spectrometers: the uncorrected biases in XCO 2 and XCH 4 are smaller than 0.01 and 0.15 %, respectively, and the drifts are smaller than 0.005 and 0.035 %. As an additional sensitive demonstration of the instrumental performance we show the excellent agreement of ground pressure values obtained from the total column measurements of O 2 and barometric records. We find a calibration factor of 0.9700 for the spectroscopic measurements in comparison to the barometric records and a very small scatter between the individual spectrometers (0.02 %). As a final calibration step, using a co-located TCCON (Total Carbon Column Observation Network) spectrometer as a reference, a common scaling factor has been derived for the XCO 2 and XCH 4 products, which ensures that the records are traceable to the WMO in situ scale.

Intercomparison of open-path trace gas measurements with two dual-frequency-comb spectrometers

“…Here, we find agreement between two DCS instruments that is an order of magnitude better and is comparable to that achieved with highly calibrated, state-of-the-art solar-looking FTS systems that retrieve vertical column measurements (Messerschmidt et al, 2011;Frey et al, 2015;Hedelius et al, 2016); how-ever, open-path DCS does not require instrument-specific calibrations (e.g., of the instrument line shape) and provides a very different capability by retrieving the dry mole fractions across regional, kilometer-scale paths over day and night on a mobile platform. Moreover, as the agreement between openpath DCS instruments is below the level of natural background fluctuations, future measurements can facilitate accurate inverse modeling to identify sources and sinks of carbon emission over regions.…”

Addition of a channel for XCO observations to a portable FTIR spectrometer for greenhouse gas measurements

“…PROFFIT is in wide use in the NDACC (e.g. Sepúlveda et al, 2014;Virolainen et al, 2014;Mengistu Tsidu et al, 2015), is in very good agreement with the official TCCON analysis (Dohe, 2013), and is also successfully applied for the analysis of spectra recorded with the EM27/SUN (Gisi et al, 2012;Frey et al, 2015). For the analysis of the low-resolution spectra, the methane, water vapour, HDO, and CO a priori profiles were adopted from the TC-CON processor.…”

“…model studies of greenhouse gases sources (Messerschmidt et al, 2013) and observation of local sources (Lindenmaier et al, 2014). Recently, several investigators demonstrated that portable low-resolution FTIR spectrometers still allow surprisingly precise and accurate measurements of column-averaged greenhouse gas abundances (Petri et al, 2012;Gisi et al, 2012;Frey et al, 2015). Such devices are a promising supplement to the TCCON, for performing measurements at remote sites, for mobile applications (Klappenbach et al, 2015), and for observations of dedicated sources and sinks on regional and smaller scales .…”

Comparison of XCO abundances from the Total Carbon Column Observing Network and the Network for the Detection of Atmospheric Composition Change measured in Karlsruhe

“…For the analysis of spectra recorded in the MIR, we use the retrieval algorithm PROFFIT (Hase et al, 2004), which is widely used within NDACC and for analyses of lowresolution spectra as recorded with EM27/SUN spectrometers (Bruker Optics GmbH, Germany; Gisi et al, 2012;Hase et al, 2015;Frey et al, 2015; Klappenbach et al, Figure 1. A priori VMR profiles used for the TCCON retrieval of NIR spectra (daily varying profile) and for the NDACC retrieval of MIR spectra (one fixed profile).…”