Methane emissions from dairy cows: Comparing open-path laser measurements to profile-based techniques

Methane emission rates from a herd of grazing dairy cows were determined from concentration measurements with four open-path lasers positioned around the fenced grazing area. The emission rates were calculated with the aid of a backward-Lagrangian stochastic model (BLS). After discarding data with insufficient laser light levels (due to technical issues discussed in the paper) and periods of light winds, four days of laser measurements were retained. Methane emission rates compared favourably to those derived from concentration measurements on a vertical-profile mast, using either BLS or the integrated horizontal flux technique. The average emission rate obtained with the laser system was 402 (±52) g day−1 cow−1.