EUROSPEC: at the interface between remote-sensing and ecosystem CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;  flux measurements in Europe

Porcar‐Castell, Albert; Arthur, Alasdair Mac; Rossini, Micol; Eklundh, Lars; Pacheco‐Labrador, Javier; Anderson, Karen; Balzarolo, Manuela; Martín, M. Pilar; Jin, Hongxiao; Tomelleri, Enrico; Cerasoli, Sofia; Sakowska, Karolina; Hueni, Andreas; Julitta, Tommaso; Nichol, Caroline; Vescovo, L.

doi:10.5194/bg-12-6103-2015

Cited by 52 publications

(56 citation statements)

References 143 publications

(170 reference statements)

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“…More recently, techniques for the measurement of the top of canopy Sun-Induced comparisons [28]. To the best of our knowledge, only one study [22] quantified the expected impacts of sensor characteristics, such as spectral resolution (SR), spectral sampling interval (SSI), stability, and signal to noise ratio (SNR) on the accuracy of SIF retrieval.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Sun-Induced Chlorophyll Fluorescence Estimates Obtained from Four Portable Field Spectroradiometers

et al. 2016

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Remote Sensing of Sun-Induced Chlorophyll Fluorescence (SIF) is a research field of growing interest because it offers the potential to quantify actual photosynthesis and to monitor plant status. New satellite missions from the European Space Agency, such as the Earth Explorer 8 FLuorescence EXplorer (FLEX) mission-scheduled to launch in 2022 and aiming at SIF mapping-and from the National Aeronautics and Space Administration (NASA) such as the Orbiting Carbon Observatory-2 (OCO-2) sampling mission launched in July 2014, provide the capability to estimate SIF from space. The detection of the SIF signal from airborne and satellite platform is difficult and reliable ground level data are needed for calibration/validation. Several commercially available spectroradiometers are currently used to retrieve SIF in the field. This study presents a comparison exercise for evaluating the capability of four spectroradiometers to retrieve SIF. The results show that an accurate far-red SIF estimation can be achieved using spectroradiometers with an ultrafine resolution (less than 1 nm), while the red SIF estimation requires even higher spectral resolution (less than 0.5 nm). Moreover, it is shown that the Signal to Noise Ratio (SNR) plays a significant role in the precision of the far-red SIF measurements.

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Section: Introductionmentioning

confidence: 99%

Comparison of Sun-Induced Chlorophyll Fluorescence Estimates Obtained from Four Portable Field Spectroradiometers

et al. 2016

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“…For continuous global monitoring of carbon exchange, satellite remote sensing is needed. However, the data from EC observations and satellite remote sensing cannot be linked directly due to the mismatch of spatial scales [9,10]. To deal with this problem, continuous tower-based spectral observations in coordination with EC measurements is an efficient solution and can serve as a bridge between the eddy covariance (EC) measurements and satellite-based remote sensing data [9,10,11,12].…”

Section: Introductionmentioning

confidence: 99%

“…However, the mismatch between the footprints of different spectral flux observations is a key problem [10,13]. Since the goal of the tower-based observations is to provide spectral signals in coordination with the flux data, the footprints of the two systems should match.…”

Section: Introductionmentioning

confidence: 99%

“…Tower-based spectral measurements involve the measurement of the down-welling (incoming) and up-welling (both reflected and emitted) radiation fluxes from the canopy. Three main instrument configurations have been applied to in situ optical observations to quantify incoming and reflected radiation: bi-conical, hemispherical-conical and bi-hemispherical [10,26]. The bi-hemispherical and hemispherical-conical configurations are the most commonly used for tower-based and long-term spectral observation [11].…”

Section: Introductionmentioning

confidence: 99%

“…For the up-welling measurements, hemispherical-conical configurations use a conical fore-optic (bare fiber) at nadir or off-nadir with a small field of view (FOV) (such as 25°) whereas bi-hemispherical configurations use a cosine-corrected foreoptic view at nadir with a large FOV of 180°. Obviously, compared to the conical observations, the hemispherical observations of the up-welling radiation have the advantage of sampling a wider area [10] and hence provide a footprint that is more similar to that of the EC measurements.…”

Section: Introductionmentioning

confidence: 99%

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Modeling the Footprint and Equivalent Radiance Transfer Path Length for Tower-Based Hemispherical Observations of Chlorophyll Fluorescence

Liu

et al. 2017

Sensors

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The measurement of solar-induced chlorophyll fluorescence (SIF) is a new tool for estimating gross primary production (GPP). Continuous tower-based spectral observations together with flux measurements are an efficient way of linking the SIF to the GPP. Compared to conical observations, hemispherical observations made with cosine-corrected foreoptic have a much larger field of view and can better match the footprint of the tower-based flux measurements. However, estimating the equivalent radiation transfer path length (ERTPL) for hemispherical observations is more complex than for conical observations and this is a key problem that needs to be addressed before accurate retrieval of SIF can be made. In this paper, we first modeled the footprint of hemispherical spectral measurements and found that, under convective conditions with light winds, 90% of the total radiation came from an FOV of width 72°, which in turn covered 75.68% of the source area of the flux measurements. In contrast, conical spectral observations covered only 1.93% of the flux footprint. Secondly, using theoretical considerations, we modeled the ERTPL of the hemispherical spectral observations made with cosine-corrected foreoptic and found that the ERTPL was approximately equal to twice the sensor height above the canopy. Finally, the modeled ERTPL was evaluated using a simulated dataset. The ERTPL calculated using the simulated data was about 1.89 times the sensor’s height above the target surface, which was quite close to the results for the modeled ERTPL. Furthermore, the SIF retrieved from atmospherically corrected spectra using the modeled ERTPL fitted well with the reference values, giving a relative root mean square error of 18.22%. These results show that the modeled ERTPL was reasonable and that this method is applicable to tower-based hemispherical observations of SIF.

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Temporal Variability of CO2 and N2O Flux Spatial Patterns at a Mowed and a Grazed Grassland

et al. 2017

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Spatial patterns of ecosystem processes constitute significant sources of uncertainty in greenhouse gas flux estimations partly because the patterns are temporally dynamic. The aim of this study was to describe temporal variability in the spatial patterns of grassland CO 2 and N 2 O flux under varying environmental conditions and to assess effects of the grassland management (grazing and mowing) on flux patterns. We made spatially explicit measurements of variables including soil respiration, aboveground biomass, N 2 O flux, soil water content, and soil temperature during a four-year study in the vegetation periods at grazed and mowed grasslands. Sampling was conducted in 80×60 m grids of 10 m resolution with 78 sampling points in both study plots. Soil respiration was monitored nine times, and N 2 O flux was monitored twice during the study period. Altitude, soil organic carbon, and total soil nitrogen were used as background factors at each sampling position, while aboveground biomass, soil water content, and soil temperature were considered as covariates in the spatial analysis. Data were analyzed using variography and kriging. Altitude was autocorrelated over distances of 40-50 m in both plots and influenced spatial patterns of soil organic carbon, total soil nitrogen, and the covariates. Altitude was inversely related to soil water content and aboveground biomass and positively related to soil temperature. Autocorrelation lengths for soil respiration were similar on both plots (about 30 m), whereas autocorrelation lengths of N 2 O flux differed between plots (39 m in the grazed plot vs. 18 m in the mowed plot). Grazing appeared to increase heterogeneity and linkage of the spatial patterns, whereas mowing had a homogenizing effect. Spatial patterns of soil water content, soil respiration, and aboveground biomass were temporally variable especially in the first 2 years of the experiment, whereas spatial patterns were more persistent (mostly significant correlation at p<0.05 between location ranks) in the second 2 years, following a wet year. Increased persistence of spatial patterns after a wet year indicated the recovery potential of grasslands following drought and suggested that adequate water supply could have a homogenizing effect on CO 2 and N 2 O fluxes.

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EUROSPEC: at the interface between remote-sensing and ecosystem CO<sub>2</sub> flux measurements in Europe

Cited by 52 publications

References 143 publications

Comparison of Sun-Induced Chlorophyll Fluorescence Estimates Obtained from Four Portable Field Spectroradiometers

Comparison of Sun-Induced Chlorophyll Fluorescence Estimates Obtained from Four Portable Field Spectroradiometers

Modeling the Footprint and Equivalent Radiance Transfer Path Length for Tower-Based Hemispherical Observations of Chlorophyll Fluorescence

Temporal Variability of CO2 and N2O Flux Spatial Patterns at a Mowed and a Grazed Grassland

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