AN INTERCOMPARISON OF 2 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 spectromet ers used to measure methane fluxes by the eddy correlation technique a t a prairie wetland site. The spectrometers were built by Unisearch As sociates Inc. of Concord, Ontario, Canada, and Campbell Scientific Inc . of Logan, Utah, and were models EMS-50 and TGA-100, respectively. Th e 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 dri fts. Most of the time, when the offset was only slowly changing (as co mpared to the eddy correlation averaging time), these drifts did not a ffect the calculated fluxes. There were times, however, when the offse t changed fast enough to have a noticeable affect on the fluxes. The E MS-50 also exhibits some drifting of the measured concentration. It wa s, however, much slower and of smaller amplitude than the drift seen i n the TGA-100.