Retrieval of the photochemical reflectance index for assessing xanthophyll cycle activity: a comparison of near-surface optical sensors

Abstract. Unattended optical sensors are increasingly being deployed on eddy covariance flux towers and are often used to complement existing vegetation and micrometeorological measurements to enable assessment of biophysical states and biogeochemical processes over a range of spatial scales. Of particular interest are sensors that can measure the photochemical reflectance index (PRI), which can provide information pertaining to leaf pigments and photosynthetic activity. This interest has facilitated the production of a new range of lower-cost multispectral sensors specifically designed to measure temporal changes in the PRI signal. However, little is known about the characteristics (spectral, radiometric and temporal) of many of these PRI sensors, making it difficult to compare data obtained from these sensors across time, geographical locations and instruments. Furthermore, direct testing of the capability of these sensors to actually detect the conversion of the xanthophyll cycle, which is the original biological basis of the PRI diurnal signal, is largely absent, often resulting in an unclear interpretation of the signal, particularly given the wide range of factors now known to influence PRI. Through a series of experiments, we assess the sensitivity of one of the leading brands of PRI sensor (Skye SKR 1800) to changes in vegetation photosynthetic activity in response to changing irradiance. We compare the results with those obtained using a more expensive industry-standard visible to near-infrared hyperspectral spectrometer (PP Systems UniSpec) and determine the radiometric compatibility of measurements made by the different instruments. Results suggest that the SKR 1800 instrument is able to track rapid (seconds to minutes) and more gradual diurnal changes in photosynthetic activity associated with xanthophyll cycle pigment conversion. Measurements obtained from both the high and lower cost instrument were significantly linearly correlated but were subject to a large systematic bias, illustrating that differences in instrument configuration (e.g. spectral response functions and band positions) can have a large impact on the PRI measurement values obtained. Despite differences in absolute PRI values, significant correlations were observed between the canopy PRI derived from both the SKR 1800 and the UniSpec instruments, and the epoxidation state of the xanthophyll cycle (r2 = 0.46 p < 0.05 and r2 = 0.76 p < 0.01, respectively). However, the dynamic range of the SKR 1800 PRI signal was often lower than more expensive instruments and thus the lower cost multispectral instrument may be less sensitive to pigment dynamics related to photosynthetic activity. Based on our findings, we make a series of recommendations for the effective use of such sensors under field conditions and advocate that sensors should be fully characterized prior to their field deployment.

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Retrieval of the photochemical reflectance index for assessing xanthophyll cycle activity: a comparison of near-surface optical sensors

Biogeosciences Discussions ◽

10.5194/bgd-11-11903-2014 ◽

2014 ◽

Vol 11 (8) ◽

pp. 11903-11942 ◽

Cited By ~ 1

Author(s):

A. Harris ◽

J. Gamon ◽

G. Z. Pastorello ◽

C. Wong

Keyword(s):

Optical Sensors ◽

Xanthophyll Cycle ◽

Lower Cost ◽

Photosynthetic Activity ◽

Spatial Scales ◽

Systematic Bias ◽

Diurnal Changes ◽

Near Surface ◽

Photochemical Reflectance Index ◽

Wide Range

Abstract. Unattended optical sensors are increasingly being deployed on eddy covariance flux towers and are often used to complement existing vegetation and micrometeorological measurements to enable assessment of biophysical states and biogeochemical processes over a range of spatial scales. Of particular interest are sensors that can measure the photochemical reflectance index (PRI), which can provide information pertaining to leaf pigments and photosynthetic activity. This interest has facilitated the production of a new range of lower-cost sensors specifically designed to measure temporal changes in the PRI signal. However, little is known about the characteristics (spectral, radiometric and temporal) of many of these PRI sensors, making it difficult to compare data obtained from these sensors across time, geographical locations and instruments. Furthermore, direct testing of the capability of these sensors to actually detect the conversion of the xanthophyll cycle, which is the original biological basis of the PRI diurnal signal, is largely absent, which often results in an unclear interpretation of the signal, particularly given the wide range of factors now known to influence PRI. Through a series of experiments, we assess the sensitivity of one of the leading brands of PRI sensor (Skye SKR 1800) to changes in vegetation photosynthetic activity in response to changing irradiance. We compare the results with those obtained using a more expensive industry-standard spectrometer (PP-systems UniSpec) and determine the radiometric compatibility of measurements made by the different instruments. Results suggest that the lower cost SKR 1800 instrument is able to track rapid (seconds to minutes) and more gradual diurnal changes in photosynthetic activity associated with xanthophyll cycle pigment conversion. Measurements obtained from both the high and lower cost instrument were significantly linearly correlated but were subject to a large systematic bias, illustrating that small differences in instrument configuration can have a large impact on the PRI measurement values obtained. Despite differences in absolute PRI values, significant correlations were observed between the PRI derived from the SKR 1800 and the epoxidation state of the xanthophyll cycle (r2 = 0.46, p < 0.05), although the dynamic range of the SKR 1800 PRI signal was often lower than more expensive instruments and thus the lower cost instrument may be less sensitive to pigment dynamics related to photosynthetic activity. Based on our findings, we make a series of recommendations for the effective use of such sensors under field conditions.

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A Short Review of Cavity-Enhanced Raman Spectroscopy for Gas Analysis

Sensors ◽

10.3390/s21051698 ◽

2021 ◽

Vol 21 (5) ◽

pp. 1698

Author(s):

Christian Niklas ◽

Hainer Wackerbarth ◽

Georgios Ctistis

Keyword(s):

Raman Spectroscopy ◽

Laser Beam ◽

Gas Sensors ◽

Optical Sensors ◽

Lower Cost ◽

Short Review ◽

Gas Analysis ◽

Beam Power ◽

Laser Beam Power ◽

Wide Range

The market of gas sensors is mainly governed by electrochemical, semiconductor, and non-dispersive infrared absorption (NDIR)-based optical sensors. Despite offering a wide range of detectable gases, unknown gas mixtures can be challenging to these sensor types, as appropriate combinations of sensors need to be chosen beforehand, also reducing cross-talk between them. As an optical alternative, Raman spectroscopy can be used, as, in principle, no prior knowledge is needed, covering nearly all gas compounds. Yet, it has the disadvantage of a low quantum yield through a low scattering cross section for gases. There have been various efforts to circumvent this issue by enhancing the Raman yield through different methods. For gases, in particular, cavity-enhanced Raman spectroscopy shows promising results. Here, cavities can be used to enhance the laser beam power, allowing higher laser beam-analyte interaction lengths, while also providing the opportunity to utilize lower cost equipment. In this work, we review cavity-enhanced Raman spectroscopy, particularly the general research interest into this topic, common setups, and already achieved resolutions.

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Gamma models for estimating the odds ratio for a skewed biomarker measured in pools and subject to errors

Biostatistics ◽

10.1093/biostatistics/kxz028 ◽

2019 ◽

Author(s):

Dane R Van Domelen ◽

Emily M Mitchell ◽

Neil J Perkins ◽

Enrique F Schisterman ◽

Amita K Manatunga ◽

...

Keyword(s):

Odds Ratio ◽

Adjusted Odds Ratio ◽

Lower Cost ◽

Cost Effective ◽

Ratio Estimation ◽

Statistical Efficiency ◽

Function Model ◽

Processing Error ◽

Wide Range ◽

Pooled Samples

SUMMARYMeasuring a biomarker in pooled samples from multiple cases or controls can lead to cost-effective estimation of a covariate-adjusted odds ratio, particularly for expensive assays. But pooled measurements may be affected by assay-related measurement error (ME) and/or pooling-related processing error (PE), which can induce bias if ignored. Building on recently developed methods for a normal biomarker subject to additive errors, we present two related estimators for a right-skewed biomarker subject to multiplicative errors: one based on logistic regression and the other based on a Gamma discriminant function model. Applied to a reproductive health dataset with a right-skewed cytokine measured in pools of size 1 and 2, both methods suggest no association with spontaneous abortion. The fitted models indicate little ME but fairly severe PE, the latter of which is much too large to ignore. Simulations mimicking these data with a non-unity odds ratio confirm validity of the estimators and illustrate how PE can detract from pooling-related gains in statistical efficiency. These methods address a key issue associated with the homogeneous pools study design and should facilitate valid odds ratio estimation at a lower cost in a wide range of scenarios.

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Low-energy optical switching of SO2 linkage isomerisation in single crystals of a ruthenium-based coordination complex

RSC Advances ◽

10.1039/d1ra01696b ◽

2021 ◽

Vol 11 (22) ◽

pp. 13183-13192

Author(s):

Jacqueline M. Cole ◽

David J. Gosztola ◽

Sven O. Sylvester

Keyword(s):

Single Crystals ◽

Optical Sensors ◽

Optical Switching ◽

Optical Switches ◽

Low Energy ◽

Coordination Complex ◽

Wide Range

Single crystals that behave as optical switches are desirable for a wide range of applications, from optical sensors to read–write memory media.

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Triazole, Benzotriazole, and Naphthotriazole as Corrosion Inhibitors for Brass

CORROSION ◽

10.5006/0010-9312-32.10.414 ◽

1976 ◽

Vol 32 (10) ◽

pp. 414-417 ◽

Cited By ~ 15

Author(s):

R. WALKER

Keyword(s):

Corrosion Inhibitors ◽

Lower Cost ◽

Solution Ph ◽

Inhibitor Efficiency ◽

Wide Range ◽

Better Than

Abstract The use of triazole, benzotriazole, and naphthotriazole as corrosion inhibitors for brass is briefly reviewed. The corrosion of 70/30 brass immersed in a wide range of solutions is reported both with and without the inhibitors. The inhibitor efficiency of benzotriazole is given as a function of the solution pH and the concentration used. Triazole was only effective in mildly corrosive solutions and benzotriazole and naphthotriazole were much better. Generally naphthotriazole was better than benzotriazole but is much more expensive and a higher concentration of benzotriazole can give the same protection as naphthotriazole at a much lower cost.

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Future trends in diagnosis using laboratory-on-a-chip technologies

Parasitology ◽

10.1017/s0031182099004126 ◽

1999 ◽

Vol 117 (7) ◽

pp. 191-203 ◽

Cited By ~ 16

Author(s):

M. S. TALARY ◽

J. P. H. BURT ◽

R. PETHIG

Keyword(s):

Gene Expression ◽

Lower Cost ◽

Building Blocks ◽

Cancer Diagnostics ◽

Future Trends ◽

Biotechnological Applications ◽

Environmental Testing ◽

Current State ◽

Microelectronic Fabrication ◽

Wide Range

There has been an enormous growth in the development of biotechnological applications, where advances in the techniques of microelectronic fabrication and the technologies of miniaturization and integration in semiconductor industries are being applied to the production of Laboratory-on-a-Chip devices. The aim of this development is to create devices that will perform the same processes that are currently carried out in the laboratory in reduced timescales, at a lower cost, requiring less reagents, and with a greater resolution of detection and specificity. The expectations of this Laboratory-on-a-Chip revolution is that this technology will facilitate rapid advances in gene discovery, genetic mapping and gene expression with broader applications ranging from infectious diseases and cancer diagnostics to food quality and environmental testing. A review of the current state of development in this field reveals the scale of the ongoing revolution and serves to highlight the advances that can be perceived in the development of Laboratory-on-a-Chip technologies. Since miniaturization can be applied to such a wide range of laboratory processes, some of the sub-units that can be used as building blocks in these devices are described, with a brief description of some of the fabrication processes that can be used to create them.

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MAX-DOAS observations of aerosols, formaldehyde and nitrogen dioxide in the Beijing area: comparison of two profile retrieval approaches

Atmospheric Measurement Techniques ◽

10.5194/amt-8-941-2015 ◽

2015 ◽

Vol 8 (2) ◽

pp. 941-963 ◽

Cited By ~ 47

Author(s):

T. Vlemmix ◽

F. Hendrick ◽

G. Pinardi ◽

I. De Smedt ◽

C. Fayt ◽

...

Keyword(s):

Standard Deviation ◽

A Priori ◽

Systematic Bias ◽

Aerosol Extinction ◽

Data Set ◽

Near Surface ◽

Beijing Area ◽

Least Squares Fit ◽

Relative Differences ◽

Good Agreement

Abstract. A 4-year data set of MAX-DOAS observations in the Beijing area (2008–2012) is analysed with a focus on NO2, HCHO and aerosols. Two very different retrieval methods are applied. Method A describes the tropospheric profile with 13 layers and makes use of the optimal estimation method. Method B uses 2–4 parameters to describe the tropospheric profile and an inversion based on a least-squares fit. For each constituent (NO2, HCHO and aerosols) the retrieval outcomes are compared in terms of tropospheric column densities, surface concentrations and "characteristic profile heights" (i.e. the height below which 75% of the vertically integrated tropospheric column density resides). We find best agreement between the two methods for tropospheric NO2 column densities, with a standard deviation of relative differences below 10%, a correlation of 0.99 and a linear regression with a slope of 1.03. For tropospheric HCHO column densities we find a similar slope, but also a systematic bias of almost 10% which is likely related to differences in profile height. Aerosol optical depths (AODs) retrieved with method B are 20% high compared to method A. They are more in agreement with AERONET measurements, which are on average only 5% lower, however with considerable relative differences (standard deviation ~ 25%). With respect to near-surface volume mixing ratios and aerosol extinction we find considerably larger relative differences: 10 ± 30, −23 ± 28 and −8 ± 33% for aerosols, HCHO and NO2 respectively. The frequency distributions of these near-surface concentrations show however a quite good agreement, and this indicates that near-surface concentrations derived from MAX-DOAS are certainly useful in a climatological sense. A major difference between the two methods is the dynamic range of retrieved characteristic profile heights which is larger for method B than for method A. This effect is most pronounced for HCHO, where retrieved profile shapes with method A are very close to the a priori, and moderate for NO2 and aerosol extinction which on average show quite good agreement for characteristic profile heights below 1.5 km. One of the main advantages of method A is the stability, even under suboptimal conditions (e.g. in the presence of clouds). Method B is generally more unstable and this explains probably a substantial part of the quite large relative differences between the two methods. However, despite a relatively low precision for individual profile retrievals it appears as if seasonally averaged profile heights retrieved with method B are less biased towards a priori assumptions than those retrieved with method A. This gives confidence in the result obtained with method B, namely that aerosol extinction profiles tend on average to be higher than NO2 profiles in spring and summer, whereas they seem on average to be of the same height in winter, a result which is especially relevant in relation to the validation of satellite retrievals.

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Structural interpretation using refraction velocities from marine seismic surveys

Geophysics ◽

10.1190/1.1442026 ◽

1986 ◽

Vol 51 (1) ◽

pp. 12-19 ◽

Cited By ~ 3

Author(s):

James F. Mitchell ◽

Richard J. Bolander

Keyword(s):

Sedimentary Rock ◽

Seismic Energy ◽

Seismic Survey ◽

Subsurface Structure ◽

Seismic Reflection Data ◽

Near Surface ◽

Reflection Data ◽

Wide Range ◽

Streamer Length ◽

Set Up

Subsurface structure can be mapped using refraction information from marine multichannel seismic data. The method uses velocities and thicknesses of shallow sedimentary rock layers computed from refraction first arrivals recorded along the streamer. A two‐step exploration scheme is described which can be set up on a personal computer and used routinely in any office. It is straightforward and requires only a basic understanding of refraction principles. Two case histories from offshore Peru exploration demonstrate the scheme. The basic scheme is: step (1) shallow sedimentary rock velocities are computed and mapped over an area. Step (2) structure is interpreted from the contoured velocity patterns. Structural highs, for instance, exhibit relatively high velocities, “retained” by buried, compacted, sedimentary rocks that are uplifted to the near‐surface. This method requires that subsurface structure be relatively shallow because the refracted waves probe to depths of one hundred to over one thousand meters, depending upon the seismic energy source, streamer length, and the subsurface velocity distribution. With this one requirement met, we used the refraction method over a wide range of sedimentary rock velocities, water depths, and seismic survey types. The method is particularly valuable because it works well in areas with poor seismic reflection data.

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Preparation of ZnO-Zn2TiO4Sol Composite Films and Its Photocatalytic Activities

Journal of Nanomaterials ◽

10.1155/2013/428419 ◽

2013 ◽

Vol 2013 ◽

pp. 1-5 ◽

Cited By ~ 10

Author(s):

Xiujuan Qin ◽

Li Cui ◽

Guangjie Shao

Keyword(s):

Methyl Orange ◽

Photocatalytic Oxidation ◽

Spectral Response ◽

Sol Gel ◽

Composite Films ◽

Visible Region ◽

Performance Testing ◽

Structure Characterization ◽

Semiconductor Oxides ◽

Wide Range

Ti-doped ZnO sol-composite films were prepared on the glass substrate by the two-step sol-gel technique. X-ray diffraction, Uv-Vis spectrophotometer, and FS spectrum of composite films were used to help make structure characterization and optical performance testing. The results showed that the composite was a mixture of ZnO + Zn2TiO4. Because of synergistic effect of both semiconductor oxides, composite films had a wide range of spectral response in the visible region, and the absorption band edge was about 510 nm, and the Green Belt of composite films luminous significantly enhanced. Photocatalytic oxidation experiments showed that using the composite films treatment (16.5 ml, l0 mg/L methyl orange aqueous solution)/cm2, the decolorization rate of methyl-orange was 90% after 3 hours irradiation.

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Empirical Correlation between Inelastic and Elastic Spectral Displacement Demands

Earthquake Spectra ◽

10.1193/020515eqs021m ◽

2016 ◽

Vol 32 (3) ◽

pp. 1419-1448 ◽

Cited By ~ 3

Author(s):

Peter J. Stafford ◽

Timothy J. Sullivan ◽

Domenico Pennucci

Keyword(s):

Seismic Hazard ◽

Hazard Assessment ◽

Spectral Response ◽

Seismic Hazard Assessment ◽

Assessment Process ◽

Earthquake Intensity ◽

Empirical Relationships ◽

Wide Range ◽

Performance Based Seismic Design ◽

Displacement Demand

Inelastic spectral displacement demand is arguably one of the most effective, simplified means of relating earthquake intensity to building damage. However, seismic hazard assessment is typically conducted using empirical ground-motion prediction equations (GMPEs) that only provide indications of elastic spectral response quantities, which an engineer subsequently relates to inelastic demands using empirical relationships such as the equal-displacement rule. An alternative approach is to utilize relationships for the inelastic spectral displacement demand directly within the seismic hazard assessment process. Such empirical relationships are developed in this work, as a function of magnitude, distance, building period, and yield strength coefficient, for four different hysteretic models that are representative of a wide range of possible structural typologies found in practice. The new relationships are likely to be particularly useful for performance-based seismic design and assessment.

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