Abstract Low‐power, open‐path gas sensors enable eddy covariance (EC) flux measurements in remote areas without line power. However, open‐path flux measurements are sensitive to fluctuations in air temperature, pressure, and humidity. Laser‐based, open‐path sensors with the needed sensitivity for trace gases like methane (CH4) and nitrous oxide (N2O) are impacted by additional spectroscopic effects. Corrections for these effects, especially those related to temperature fluctuations, often exceed the flux of gases, leading to large uncertainties in the associated fluxes. For example, the density and spectroscopic corrections arising from temperature fluctuations can be one or two orders of magnitude greater than background N2O fluxes. Consequently, measuring background fluxes with laser‐based, open‐path sensors is extremely challenging, particularly for N2O and gases with similar high‐precision requirements. We demonstrate a new laser‐based, open‐path N2O sensor and a general approach applicable to other gases that minimizes temperature‐related corrections for EC flux measurements. The method identifies absorption lines with spectroscopic effects in the opposite direction of density effects from temperature and, thus, density and spectroscopic effects nearly cancel one another. The new open‐path N2O sensor was tested at a corn (Zea maysL.) field in Southwestern Michigan, United States. The sensor had an optimal precision of 0.1 ppbv at 10 Hz and power consumption of 50 W. Field trials showed that temperature‐related corrections were 6% of density corrections, reducing EC random errors by 20‐fold compared to previously examined lines. Measured open‐path N2O EC fluxes showed excellent agreement with those made with static chambers (m = 1.0 ± 0.3;r2 = .96). More generally, we identified absorption lines for CO2and CH4 flux measurements that can reduce the temperature‐related corrections by 10–100 times compared to existing open‐path sensors. The proposed method provides a new direction for future open‐path sensors, facilitating the expansion of accurate EC flux measurements.
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Reliability of Turbulent Fluxes Measurements Provided by a Novel Sensor on a Pistachio Orchard
Crop evapotranspiration (ETc) measurement is usually performed by sophisticated sensors that require high technical knowledge and that are not economically affordable for most end users. The objective of this work was to evaluate the performance of a novel LI-710 sensor for measuring ETc on a pistachio orchard. This simplified and easy-to-use sensor applies the Eddy Covariance (EC) method to measure water vapor flux between the surface and the atmosphere, however, it is cheaper and less complex than traditional EC heat flux system. The LI-710 sensor was installed together to an EC tower and the measurements provided by both methodologies were compared. Initial results evidenced a good agreement in terms of the evaluated meteorological variables, except for relative humidity, where higher discrepancies among sensors were observed. Regarding the sensible (H) and latent (LE) heat fluxes, the values measured by both methodologies were similar, with R2 values of 0.96 and 0.80; and RMSE values of 19 and 29 W m−2, respectively. These results suggest that LI-710 sensor can be a valid alternative to traditional EC systems for deriving ETc. However, LI-710 continues to have the fetch limitations presented in traditional methodologies, so future efforts should be paid to reduce this requirement increasing its usability in medium-small sized agricultural plots.
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- Award ID(s):
- 2120906
- PAR ID:
- 10648637
- Publisher / Repository:
- IEEE
- Date Published:
- Page Range / eLocation ID:
- 107 to 111
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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