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

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 (N2O). The concentration of N2O was measured with a root mean squared error of 6 ppb. The results compared well with lab-based gas chromatography measurements.