Gap filling strategies for long term energy flux data sets

Falge, Eva; Baldocchi, Dennis; Olson, Richard J.; Anthoni, Peter; Aubinet, Marc; Bernhofer, Christian; Burba, George; Ceulemans, R.; Clement, Robert; Dolman, A. J.; Granier, André; Gross, Patrick; Grünwald, Thomas; Hollinger, David Y.; Jensen, N. O.; Katul, Gabriel G.; Keronen, Petri; Kowalski, Andrew S.; Lai, Chun‐Ta; Law, B. E.; Meyers, Tilden P.; Moncrieff, John; Moors, E.J.; Munger, J. William; Pilegaard, Kim; Rannik, Üllar; Rebmann, Corinna; Suyker, Andrew E.; Tenhunen, John; Tu, Kevin; Verma, Shashi B.; Vesala, Timo; Wilson, K.; Wofsy, S. C.

doi:10.1016/s0168-1923(00)00235-5

Cited by 519 publications

(327 citation statements)

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“…Half-hourly gross primary productivity (GPP) values were obtained based on the calculated daytime Re and the filled half-hourly daytime CO 2 fluxes. For the two layer H 2 O fluxes, data gaps were filled by the look-up table method (Falge et al, 2001a;Reichstein et al, 2005) based on T a , vapor pressure deficit (VPD), and R n .…”

Section: Data Preparingmentioning

confidence: 99%

Spatiotemporal variations of T/ET (the ratio of transpiration to evapotranspiration) in three forests of Eastern China

Zhu

et al. 2015

Ecological Indicators

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The ratio of transpiration to evapotranspiration (T/ET) Forest a b s t r a c t Evapotranspiration (ET), which is comprised by evaporation from soil surface (E), transpiration (T) and evaporation from the intercepted water by canopy (EI), plays an important role in maintaining global energy balance and regulating climate. Quantifying the spatiotemporal variations of T/ET (the ratio of T to ET) can improve our understandings on the role of vegetation ecophysiological processes in climate regulation. Using eddy covariance measurements at three forest ecosystems (Changbaishan temperate broad-leaved Korean pine mixed forest (CBS), Qianyanzhou subtropical coniferous plantation (QYZ) and Dinghushan subtropical evergreen mixed forest (DHS)) in north-south transect of Eastern China (NSTEC), we run the revised Shuttleworth-Wallace model (S-W model), validated its performance with the water vapor fluxes measured at two layers, and quantified the spatiotemporal variations of T/ET. The S-W model performed well in simulating ET and T/ET. The mean value of annual T/ET at three forests during the observation period all exceeded 0.6. The diurnal variation of canopy stomal conductance (G c ) dominated that of T/ET. The seasonal dynamics of T/ET was mainly shaped by that of leaf area index (LAI), vapor pressure deficit (VPD) and air temperature (T a ) through altering G c and the portion that the energy absorbed by canopy (P EC ) at temperate forest (CBS), while the seasonal dynamics of T/ET at subtropical forests (QYZ and DHS) were mainly affected by T a , net radiation, VPD, and soil water content through altering G c and soil surface conductance (G s ). The variation of mean annual G c governed the interannual varaition and spatial variation of T/ET. Therefore, forests in Eastern China played an important role in regulating climate through T and G c primarily affected the spatial and temproal variations of the role of forest T in regulating climate.

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Section: Data Preparingmentioning

confidence: 99%

Spatiotemporal variations of T/ET (the ratio of transpiration to evapotranspiration) in three forests of Eastern China

Zhu

et al. 2015

Ecological Indicators

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“…We filled data gaps with the mean diurnal average method (Falge, 2001). The diurnal means were computed for consecutive 26-day windows to account for seasonal trends in phenology and soil moisture.…”

Section: Data Quality and Assurancementioning

confidence: 99%

How plant functional-type, weather, seasonal drought, and soil physical properties alter water and energy fluxes of an oak–grass savanna and an annual grassland

Baldocchi

Kiang

2004

Agricultural and Forest Meteorology

523

414

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Savannas and open grasslands often co-exist in semi-arid regions. Questions that remain unanswered and are of interest to biometeorologists include: how do these contrasting landscapes affect the exchanges of energy on seasonal and annual time scales; and, do biophysical constraints imposed by water supply and water demand affect whether the land is occupied by open grasslands or savanna? To address these questions, and others, we examine how a number of abiotic, biotic and edaphic factors modulate water and energy flux densities over an oak-grass savanna and an annual grassland that coexist in the same climate but on soils with different hydraulic properties.The net radiation balance was greater over the oak woodland than the grassland, despite the fact that both canopies received similar sums of incoming short and long wave radiation. The lower albedo and lower radiative surface temperature of the transpiring woodland caused it to intercept and retain more long and shortwave energy over the course of the year, and particularly during the summer dry period.The partitioning of available energy into sensible and latent heat exchanged over the two canopies differed markedly. The annual sum of sensible heat exchange over the woodland was 40% greater than that over the grassland (2.05 GJ m −2 per year versus 1.46 GJ m −2 per year). With regards to evaporation, the oak woodland evaporated about 380 mm of water per year and the grassland evaporated about 300 mm per year. Differences in available energy, canopy roughness, the timing of physiological functioning, water holding capacity of the soil and rooting depth of the vegetation explained the observed differences in sensible and latent heat exchange of the contrasting vegetation surfaces.The response of canopy evaporation to diminishing soil moisture was quantified by comparing normalized evaporation rates (in terms of equilibrium evaporation) with soil water potential and volumetric water content measurements. When soil moisture was ample normalized values of latent heat flux density were greater for the grassland (1.1-1.2) than for the oak savanna (0.7-0.8) and independent of moisture content. Normalized rates of evaporation over the grassland declined as volumetric water content dropped below 0.15 m 3 m −3 , which corresponded with a soil water potential of −1.5 MPa. The grassland senesced and quit transpiring when the volumetric water content of the soil dropped below −2.0 MPa. The oak trees, on the other hand, were able to transpire, albeit at low rates, under very dry soil conditions (soil water potentials below −4.0 MPa). The trees were able to endure such low water potentials and maintain basal levels of metabolism because * Corresponding author. Baldocchi et al. / Agricultural and Forest Meteorology 123 (2004) ecological forcings kept the tree density and leaf area index of the woodland low, physiological factors forced the stomata to close progressively and the trees were able to tap deeper water sources (below 0.6 m) than the grasses.

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“…The commonly used methods for filling gaps in water vapour (or latent heat flux) measurements include: the mean diurnal variation method (Falge et al, 2001a,b), regression methods (Greco and Baldocchi, 1996;Berbigier et al, 2001), evaluation of a 2-week average Priestley-Taylor coefficient (Wilson and Baldocchi, 2000;Wilson et al, 2001), look-up tables (Falge et al, 2001b) and multiple imputation (Hui et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

“…Falge et al (2001b) filled gaps in annual ET using mean diurnal variation and look-up tables for 28 data sets from 18 FluxNet sites and found that the differences in annual ET among methods ranged from À48 to +86 mm per year. Although several gap-filling techniques have been evaluated in replacing missing half hour data (Falge et al, 2001a, b), they have not been evaluated for longer gaps of order of days.…”

Section: Introductionmentioning

confidence: 99%

Filling gaps in evapotranspiration measurements for water budget studies: Evaluation of a Kalman filtering approach

Alavi

Warland

Berg

2006

Agricultural and Forest Meteorology

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Missing data in long-term eddy covariance measurements of latent heat flux produce errors in the estimation of evapotranspiration and the water budget. Because no standard method of gap filling has been widely accepted, identification of optimal filling methods for gaps is crucial for determining total evapotranspiration. In this study we evaluate the application of a Kalman filter for filling gaps in latent heat flux data collected from an agricultural research station. The filtering approach was compared with several gap-filling methods including mean diurnal variation, multiple regressions, 2-week average Priestley-Taylor coefficient, and multiple imputation. The results demonstrated that a Kalman filtering approach developed using the relationship between latent heat flux, available energy, and vapour pressure deficit provides a closer approximation of the original data and introduces smaller errors than the other methods evaluated. Evaluation of the Kalman filter approach demonstrates the efficiency of this technique in replacing data in both small and large gaps of up to several days. #

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Gap filling strategies for long term energy flux data sets

Cited by 519 publications

References 10 publications

Spatiotemporal variations of T/ET (the ratio of transpiration to evapotranspiration) in three forests of Eastern China

Spatiotemporal variations of T/ET (the ratio of transpiration to evapotranspiration) in three forests of Eastern China

How plant functional-type, weather, seasonal drought, and soil physical properties alter water and energy fluxes of an oak–grass savanna and an annual grassland

Filling gaps in evapotranspiration measurements for water budget studies: Evaluation of a Kalman filtering approach

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