Low cost “laserless” FTIR spectrometer on the farm for real-time nitrous oxide soil emission measurements

Abstract

A low-cost Fourier transform infrared (FTIR) instrument was developed where the traditional He-Ne reference laser was replaced by a low-cost linear encoder. An RMS sampling error of less than 20 nm was achieved by oversampling both the interferogram and the encoder signal and then resampling the interferogram using a correction table for the encoder. A gas calibration model was developed for the system, which was chosen to have a stroke length of 21 mm and, thereby, a resolution of 0.4 cm(-1) after apodization. The instrument was mounted on a vehicle and employed in an agricultural field test for measuring soil emissions, in particular nitrous oxide (N(2)O). The concentration of N(2)O was measured with a root mean squared error of 6 ppb. The results compared well with lab-based gas chromatography measurements.

Design and simulation of control and sampling circuits for an open-path Fourier transform infrared spectrometer based on a rotating mirror

“…By moving the reflector, this optical instrument could generate a two-beam interference effect with a continuously changing optical path difference. Despite various modifications and variants of this classic interferometer that have emerged over time [9][10][11][12], none have effectively resolved the issues of tilt and shear introduced by mirror translation [13][14][15]. However, FTIR spectrometer based on a rotating mirror [16,17] can address these aforementioned issues by changing the linear mirror movement to a rotational one [18].…”