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

79Citations
Citations of this article
82Readers
Mendeley users who have this article in their library.

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 H2O 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 XCO2 and XCH4, 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 XCO2 and XCH4 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 O2 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 XCO2 and XCH4 products, which ensures that the records are traceable to the WMO in situ scale.

Figures

  • Figure 1. Setup of the lamp system. The bulb is tilted against the optical axis to avoid channeling. The lamp system is mounted on a height-adjustable tripod for the fine adjustment of the light beam.
  • Figure 3. ILS results obtained with LINEFIT for two different ways of performing the analysis. The simple analysis assumes a uniform path between lamp and detector, whereas the more refined approach divides the observed absorption into one contribution from inside and one from outside the spectrometer. Results are in agreement within 0.15 %.
  • Figure 2. Transmission spectrum of 4 m lab air (black curve) in the 7000–7400 cm−1 region. Overlying is the LINEFIT calculation (red curve), the residuum multiplied by a factor of 10 is shown in blue. For clarity reasons, an offset of −0.1 was added to the residuum.
  • Table 1. Compilation of ILS modulation efficiencies measured at maximum OPD= 1.8 cm. Measurements were performed in Karlsruhe in June and July 2014, in between the spectrometers were transported for campaign measurements by road thus experiencing a lot of mechanical impacts and vibrations.
  • Figure 5. Total columns of O2, CO2 and CH4 for the different spectrometers on 4 days of the calibration measurements in Karlsruhe. Solar observations were performed in June and July 2014, in between the spectrometers were transported for campaign measurements. One data point consists of 10 interferograms, the measurement time being 58 s each.
  • Figure 4. Spectral windows used during the retrieval for the different species. The fit is in accordance with the measurement, the residual, which has been multiplied with a factor of 10 for H2O and 20 for the other species, is small.
  • Table 2. Calibration factors for O2 column for the different instruments. Measurements were performed in June and July 2014, in between the spectrometers were transported for campaign measurements. Instrument 1 has been scaled to one, which is an arbitrary choice.
  • Figure 6. In situ pressure data from the Karlsruhe tall tower (http: //imkbemu.physik.uni-karlsruhe.de/~fzkmast/) together with pressure data calculated from total column amounts of O2 and H2O. The column data is scaled with an in situ factor of 0.9700 for better comparability.

Cited by Powered by Scopus

76Citations
80Readers

Register to see more suggestions

Mendeley helps you to discover research relevant for your work.

Already have an account?

Cite

CITATION STYLE

APA

Frey, M., Hase, F., Blumenstock, T., Groß, J., Kiel, M., Mengistu Tsidu, G., … Orphal, J. (2015). Calibration and instrumental line shape characterization of a set of portable FTIR spectrometers for detecting greenhouse gas emissions. Atmospheric Measurement Techniques, 8(7), 3047–3057. https://doi.org/10.5194/amt-8-3047-2015

Readers over time

‘15‘16‘17‘18‘19‘20‘21‘22‘23‘24‘2505101520

Readers' Seniority

Tooltip

Researcher 26

46%

PhD / Post grad / Masters / Doc 25

44%

Professor / Associate Prof. 6

11%

Readers' Discipline

Tooltip

Earth and Planetary Sciences 23

45%

Environmental Science 15

29%

Physics and Astronomy 7

14%

Chemistry 6

12%

Save time finding and organizing research with Mendeley

Sign up for free
0