How Close is Close Enough When Measuring Scalar Fluxes with Displaced Sensors?

Kristensen, Leif; Mann, Jakob; Oncley, Steven; Wyngaard, J. C.

doi:10.1175/1520-0426(1997)014<0814:hcicew>2.0.co;2

Cited by 105 publications

(71 citation statements)

References 11 publications

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“…Equation (12) provides a reasonable fit to the data of Kristensen et al (1997), Fig. 5, for scalar flux attenuation due to horizontal sensor displacement.…”

Section: Spatial Separationmentioning

confidence: 86%

“…This displacement reduces the correlation between the measurements of vertical velocity and scalar concentration. Kristensen et al (1997) found that the corresponding reduction of the measured flux is minimized if the scalar sensor is placed below the anemometer. However, Wyngaard (1988) showed that "cross talk" error caused by flow distortion is eliminated if the sensor configuration has reflection symmetry about a horizontal plane through the measuring point, which requires a horizontal displacement of the scalar sensor.…”

Section: Spatial Separationmentioning

confidence: 99%

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The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance

Oncley

Foken

Vogt

et al. 2007

Boundary-Layer Meteorol

334

272

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An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause this imbalance, though our estimates of

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“…Equation (12) provides a reasonable fit to the data of Kristensen et al (1997), Fig. 5, for scalar flux attenuation due to horizontal sensor displacement.…”

Section: Spatial Separationmentioning

confidence: 86%

Section: Spatial Separationmentioning

confidence: 99%

The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance

Oncley

Foken

Vogt

et al. 2007

Boundary-Layer Meteorol

334

272

View full text Add to dashboard Cite

show abstract

“…Care was taken to minimise high-frequency attenuation (Lenschow and Raupach, 1991;Moore, 1986) with the use of a small measurement cell, short tube length (1.0 m) and high flow rate (12 L min −1 ). To minimise flux loss due to sensor separation, the intake tube was attached underneath the sensing volume of the sonic anemometer (Kristensen et al, 1997). Initially, the tube was made of 3/8 Dekabon, with an inner diameter of 5.8 mm.…”

Section: Carbon Dioxide and Water Vapour Flux Measurementsmentioning

confidence: 99%

Carbon budgets for an irrigated intensively grazed dairy pasture and an unirrigated winter-grazed pasture

et al. 2016

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Abstract. Intensification of pastoral agriculture is occurring rapidly across New Zealand, including increasing use of irrigation and fertiliser application in some regions. While this enables greater gross primary production (GPP) and livestock grazing intensity, the consequences for the net ecosystem carbon budget (NECB) of the pastures are poorly known. Here, we determined the NECB over one year for an irrigated, fertilised and rotationally grazed dairy pasture and a neighbouring unirrigated, unfertilised, wintergrazed pasture. Primary terms in the NECB calculation were: net ecosystem production (NEP), biomass carbon removed by grazing cows and carbon (C) input from their excreta. Annual NEP was measured using the eddy-covariance method. Carbon removal was estimated with plate-meter measurements calibrated against biomass collections, preand post-grazing. Excreta deposition was calculated from animal feed intake. The intensively managed pasture gained C (NECB = 103 ± 42 g C m −2 yr −1 ) but would have been subject to a non-significant C loss if cattle excreta had not been returned to the pasture. The unirrigated pasture was C-neutral (NECB = −13 ± 23 g C m −2 yr −1 ). While annual GPP of the former was almost twice that of the latter (2679 vs. 1372 g C m −2 yr −1 ), ecosystem respiration differed by only 68 % between the two pastures (2271 vs. 1352 g C m −2 yr −1 ). The ratio of GPP to the total annual water input of the irrigated pasture was 37 % greater than that of the unirrigated pasture, i.e. the former used the water input more efficiently than the latter to produce biomass. The NECB results agree qualitatively with those from many other eddy-covariance studies of grazed grasslands, but they seem to be at odds with long-term carbon-stock studies of other New Zealand pastures.

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“…The open sides of the asymmetric sonic anemometers were exposed to the north-west at the experimental plot. The open-path infrared gas analyzer were mounted 0.2 m below the sonic anemometer and displaced 0.3 m laterally and perpendicular to the predominating wind direction in order to minimize flux loss due to vertical (Kristensen et al, 1997) and longitudinal (Massman, 2000) sensor separation, respectively. Data were recorded on a personal computer inside of a small hut 50 m from the site.…”

Section: Field Measurementsmentioning

confidence: 99%

“…The former relates the canopy resistance to environmental variables at an atmospheric reference height (Javis, 1976;Noilhan and Planton, 1989); the latter correlates canopy resistance to the assimilation rate (Ball et al, 1987;Leuning, 1995;Jacobs and De Bruin, 1997). Although these two types of models have been applied to various canopies and plants (Niyogi and Raman 1997;Ronda et al, 2001), there has been no comparison of the two types of models in terms of their application to the P-M model to simulate the actual ET of crop fields, especially in the arid area of northwest China.…”

mentioning

confidence: 99%

Evaluation of Penman-Monteith model applied to a maize field in the arid area of northwest China

Zhao

Ersi

et al. 2010

Hydrol. Earth Syst. Sci.

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Abstract. The Penman-Monteith (P-M) model has been applied to estimate evapotranspiration in terrestrial ecosystem throughout the world. As shown in many studies, bulk canopy resistance is an especially important factor in the application of the P-M model. In this study, the authors used the Noilhan and Planton (N-P) approach and the Jacobs and De Bruin (J-D) approach to express the bulk canopy resistance. The P-M model was applied to a maize field using the two approaches in an arid area of northwest China and evaluated on the basis of measured half-hourly values from the eddy covariance system. The results indicate that the N-P approach slightly underestimates the bulk canopy resistance, while the J-D approach overestimates it. Over the entire maize growing season, the N-P approach yielded a more consistent estimate of bulk canopy resistance than did the J-D approach. Correspondingly, the P-M model with J-D bulk canopy resistance slightly underestimated the latent heat flux throughout the maize growing season, but overestimated the latent heat flux during the dry season as compared to the N-P approach results. The good fit between the simulated latent heat flux estimated by the P-M model using the N-P approach and the data measured at half-hour time steps demonstrates that the application of this approach is reasonable in relatively homogenous maize fields that are not drought-stressed. Further research to improve the performance of P-M model to simulate evapotranspiration in the cropped fields is discussed.

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How Close is Close Enough When Measuring Scalar Fluxes with Displaced Sensors?

Cited by 105 publications

References 11 publications

The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance

The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance

Carbon budgets for an irrigated intensively grazed dairy pasture and an unirrigated winter-grazed pasture

Evaluation of Penman-Monteith model applied to a maize field in the arid area of northwest China

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