An Intercomparison of Two Tunable Diode Laser Spectrometers Used for Eddy Correlation Measurements of Methane Flux in a Prairie Wetland

An intercomparison was made between two tunable diode laser spectrometers used to measure methane fluxes by the eddy correlation technique at a prairie wetland site. The spectrometers were built by Unisearch Associates Inc. of Concord, Ontario, Canada, and Campbell Scientific Inc. of Logan, Utah, and were models EMS-50 and TGA-100, respectively. The fluxes were found to agree very well with each other in the range of 0 to 42 mg m-2 h-1. The TGA-100 was observed to exhibit offset drifts. Most of the time, when the offset was only slowly changing (as compared to the eddy correlation averaging time), these drifts did not affect the calculated fluxes. There were times, however, when the offset changed fast enough to have a noticeable affect on the fluxes. The EMS-50 also exhibits some drifting of the measured concentration. It was, however, much slower and of smaller amplitude than the drift seen in the TGA-100