Intercomparison of Total Carbon Column Observing Network (TCCON) data from two Fourier transform spectrometers at Lauder, New Zealand

David F Pollard,John Robinson,Dan Smale,Hisako Shiona

doi:10.5194/amt-14-1501-2021

Abstract

Abstract. We describe the change in operational instrument for the routine measurement of column-averaged dry-air mole fraction of several greenhouse gases (denoted Xgas) at the Lauder Total Carbon Column Observing Network (TCCON) site and the steps taken to demonstrate comparability between the two observation systems following a systematic methodology. Further, we intercompare retrieved Xgas values during an intensive intercomparison period during October and November 2018, when both instruments were performing optimally, and on subsequent, less frequent occasions. The average difference between the two observing systems was found to be well below the expected level of uncertainty for TCCON retrievals for all compared species. In the case of XCO2 the average difference was 0.0264±0.0465 % (0.11±0.19 µmol mol−1).

Highlights

IntroductionThe site initially used a Bruker IFS 120HR (serial number (SN) 39, Total Carbon Column Observing Network (TCCON) identifier lh) Fourier transform spectrometer (FTS) to take both near-infrared (NIR) TCCON measurements and mid-infrared (MIR) observations for the Network for the Detection of Atmospheric Composition Change Infrared Working Group (NDACC-IRWG, De Mazière et al, 2018)
The Total Carbon Column Observing Network (TCCON; Wunch et al, 2011) coordinates globally distributed measurements of near-infrared solar absorption spectra from which high-precision retrievals of the column-averaged dryair mole fraction of several greenhouse gases, including CO2, CH4 and CO, can be made.The National Institute of Water & Atmospheric Research (NIWA) atmospheric observatory at Lauder, New Zealand, was one of the first TCCON sites and has been operating since 2004
For clarity hereafter we will refer to the instruments by their two-letter TCCON site identifier

Summary

Introduction

The site initially used a Bruker IFS 120HR (serial number (SN) 39, TCCON identifier lh) Fourier transform spectrometer (FTS) to take both near-infrared (NIR) TCCON measurements and mid-infrared (MIR) observations for the Network for the Detection of Atmospheric Composition Change Infrared Working Group (NDACC-IRWG, De Mazière et al, 2018). This meant that there were regular instrument interventions to change optical components.

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