Intercomparison of TCCON data from two Fourier transform spectrometers at Lauder, New Zealand

Abstract. We describe the change of operational instrument for the routine measurement of column-averaged dry-air mole fraction of several greenhouse gases (denoted X_gas) 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 X_gas 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 X_CO2 the average difference was 0.0264 ± 0.0465 % (0.11 ± 0.19 μmol mol⁻¹).