In-situ UV-Visible spectrometry as an alternative to determine solute concentrations at high temporal frequency in organic-rich stream waters

<p>In-situ monitoring of the temporal variation of solutes&#8217; (nutrients and metals) concentrations as tracers can enhance knowledge of the hydrological and biogeochemical behavior of catchments. UV-Visible spectrometry represents a relatively inexpensive and easily used tool to explore how those concentrations vary in time at high temporal frequency. However, it is not yet clear which are the best calibration methods and which solutes can be modeled with this approach. In this investigation we explored the relationship between solutes&#8217; concentrations and wavelength absorbance in the UV-Visible range to find the best calibration method and to identify solutes that could be effectively predicted. To this end, we installed a UV&#8211;Visible spectrometer probe in a high-altitude and organic-rich tropical Andean (P&#225;ramo) stream to record the wavelength absorbance at a 5-min temporal resolution from December 2017 to March 2019. Simultaneously, we sampled stream water at 4-hour frequency for subsequent determination of solutes via ICP-MS in the laboratory. Our results show that multivariate statistical methods outperformed simpler calibration strategies to model the solutes&#8217; concentrations that could be effectively predicted using calibration and validation datasets. Eleven out of 21 evaluated solutes (Al, DOC, Ca, Cu, K, Mg, N, Na, Rb, Si and Sr) were successfully calibrated (NSE > 0.50). This finding suggests the possibility of calibrating solutes (i.e., metals) that had not previously been calibrated through UV-Visible spectrometry in the field. Interestingly, the calibration was feasible for all solutes that presented a statistically significant correlation with dissolved organic carbon. The findings of this research provide insights into the value of in-situ operation of spectrometers to monitor water quality in organic-rich streams (e.g., peatlands). This research contributes to our understanding of aquatic ecosystems alongside assessing catchment hydrological functioning and also can enhance the protection of human water supplies.</p>

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Six-Axis Force Torque Sensor Model-Based In Situ Calibration Method and Its Impact in Floating-Based Robot Dynamic Performance

Sensors ◽

10.3390/s19245521 ◽

2019 ◽

Vol 19 (24) ◽

pp. 5521

Author(s):

Francisco Javier Andrade Chavez ◽

Silvio Traversaro ◽

Daniele Pucci

Keyword(s):

Dynamic Performance ◽

Calibration Method ◽

Full Description ◽

Temperature Drift ◽

Model Based ◽

Floating Base ◽

In Situ Calibration ◽

Calibration Methods ◽

The Impact

A crucial part of dynamic motions is the interaction with other objects or the environment. Floating base robots have yet to perform these motions repeatably and reliably. Force torque sensors are able to provide the full description of a contact. Despite that, their use beyond a simple threshold logic is not widespread in floating base robots. Force torque sensors might change performance when mounted, which is why in situ calibration methods can improve the performance of robots by ensuring better force torque measurements. The Model-Based in situ calibration method with temperature compensation has shown promising results in improving FT sensor measurements. There are two main goals for this paper. The first is to facilitate the use and understanding of the method by providing guidelines that show their usefulness through experimental results. Then the impact of having better FT measurements with no temperature drift are demonstrated by proving that the offset estimated with this method is still useful days and even a month from the time of estimation. The effect of this is showcased by comparing the sensor response with different offsets simultaneously during real robot experiments. Furthermore, quantitative results of the improvement in dynamic behaviors due to the in situ calibration are shown. Finally, we show how using better FT measurements as feedback in low and high level controllers can impact the performance of floating base robots during dynamic motions. Experiments were performed on the floating base robot iCub.

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First report of a novel multiplexer pumping system coupled to a water quality probe to collect high temporal frequency in situ water chemistry measurements at multiple sites

Limnology and Oceanography Methods ◽

10.1002/lom3.10122 ◽

2016 ◽

Vol 14 (12) ◽

pp. 767-783 ◽

Cited By ~ 16

Author(s):

François Birgand ◽

Kyle Aveni-Deforge ◽

Brad Smith ◽

Bryan Maxwell ◽

Marc Horstman ◽

...

Keyword(s):

Water Quality ◽

Water Chemistry ◽

Temporal Frequency ◽

First Report ◽

High Temporal Frequency ◽

Pumping System

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Partial Least Squares local calibration of a UV–visible spectrometer used for in situ measurements of COD and TSS concentrations in urban drainage systems

Water Science & Technology ◽

10.2166/wst.2008.131 ◽

2008 ◽

Vol 57 (4) ◽

pp. 581-588 ◽

Cited By ~ 32

Author(s):

A. Torres ◽

J.-L. Bertrand-Krajewski

Keyword(s):

Least Squares ◽

Partial Least Squares ◽

Urban Drainage ◽

Local Calibration ◽

Data Set ◽

Drainage Systems ◽

Calibration Methods ◽

Urban Drainage Systems ◽

Uv Visible

Recent UV–visible spectrometers deliver on line and in situ absorbance spectra in wastewater or stormwater transported in urban drainage systems. After calibration with local data sets, spectra can be used to estimate pollutant concentrations. Calibration methods are usually based on PLS (Partial Least Squares) regression. Their most important difficulty lies in the identification of the number of both i) the latent vectors and ii) the independent variables. A method is proposed to identify these variables, based on an exhaustive tests procedure (Jackknife cross validation and matrix of prediction indicator). It was applied to estimate TSS (total suspended solids) or COD (chemical oxygen demand) concentrations at the inlet of a storage-settling tank in a stormwater separate sewer system, and compared to three other calibration methods used either for turbidity meters or UV–visible spectrometers. With the available calibration data set: i) the spectrometer gives results with better prediction quality than the turbidity meter, ii) for the spectrometer, local calibration gives better results than global calibration, iii) the proposed PLS method gives results with a similar order of magnitude in uncertainties as the manufacturer local calibration method, but is more open and transparent for the user. Similar results were obtained for a second data set.

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Comparison of UV–VIS and FDOM sensors for in situ monitoring of stream DOC concentrations

Biogeosciences ◽

10.5194/bg-12-3109-2015 ◽

2015 ◽

Vol 12 (10) ◽

pp. 3109-3118 ◽

Cited By ~ 31

Author(s):

E.-J. Lee ◽

G.-Y. Yoo ◽

Y. Jeong ◽

K.-U. Kim ◽

J.-H. Park ◽

...

Keyword(s):

Laboratory Experiments ◽

Stream Water ◽

Temperature Correction ◽

In Situ Monitoring ◽

Optical Measurements ◽

High Temporal Resolution ◽

Storm Events ◽

Fluorescent Dissolved Organic Matter ◽

Forest Stream

Abstract. Optical measurements using ultraviolet–visible (UV–VIS) spectrophotometric sensors and fluorescent dissolved organic matter (FDOM) sensors have recently been used as proxies of dissolved organic carbon (DOC) concentrations in streams and rivers at a high temporal resolution. Despite the merits of the sensors, temperature changes and particulate matter in water can interfere with the sensor readings, over- or underestimating DOC concentrations. However, little efforts have been made to compare responses of the two types of the sensors to critical interferences such as temperature and turbidity. The performance of a UV–VIS sensor and an FDOM sensor was compared in both laboratory experiments and in situ monitoring in a forest stream in Korea during three storm events. Although the UV–VIS sensor did not require temperature correction in laboratory experiments using the forest stream water, the deviations of its values from the DOC concentrations measured with a TOC analyzer increased linearly as turbidity increased. In contrast, the FDOM sensor outputs decreased significantly as temperature or turbidity increased, requiring temperature and turbidity correction for in situ monitoring of DOC concentrations. The results suggest that temperature correction is relatively straightforward but turbidity correction may not be simple because the attenuation of light by particles can significantly reduce the sensitivity of the sensors in highly turbid waters. Shifts in composition of fluorophores also need to be carefully tracked using periodically collected samples since light absorbance and fluorescence can vary as the concentrations of dominant fluorophores change.

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High frequency un-mixing of soil samples using a submerged spectrophotometer in a laboratory setting—implications for sediment fingerprinting

Journal of Soils and Sediments ◽

10.1007/s11368-021-03107-6 ◽

2021 ◽

Author(s):

Niels F. Lake ◽

Núria Martínez-Carreras ◽

Peter J. Shaw ◽

Adrian L. Collins

Keyword(s):

Particle Size ◽

Soil Sample ◽

Suspended Sediment ◽

Temporal Frequency ◽

Soil Samples ◽

Sediment Sources ◽

High Temporal Frequency ◽

Novel Method ◽

The Relationship

Abstract Purpose This study tests the feasibility of using a submersible spectrophotometer as a novel method to trace and apportion suspended sediment sources in situ and at high temporal frequency. Methods Laboratory experiments were designed to identify how absorbance at different wavelengths can be used to un-mix artificial mixtures of soil samples (i.e. sediment sources). The experiment consists of a tank containing 40 L of water, to which the soil samples and soil mixtures of known proportions were added in suspension. Absorbance measurements made using the submersible spectrophotometer were used to elucidate: (i) the effects of concentrations on absorbance, (ii) the relationship between absorbance and particle size and (iii) the linear additivity of absorbance as a prerequisite for un-mixing. Results The observed relationships between soil sample concentrations and absorbance in the ultraviolet visible (UV–VIS) wavelength range (200–730 nm) indicated that differences in absorbance patterns are caused by soil-specific properties and particle size. Absorbance was found to be linearly additive and could be used to predict the known soil sample proportions in mixtures using the MixSIAR Bayesian tracer mixing model. Model results indicate that dominant contributions to mixtures containing two and three soil samples could be predicted well, whilst accuracy for four-soil sample mixtures was lower (with respective mean absolute errors of 15.4%, 12.9% and 17.0%). Conclusion The results demonstrate the potential for using in situ submersible spectrophotometer sensors to trace suspended sediment sources at high temporal frequency.

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Intercomparison of Spectroradiometers for Global and Direct Solar Irradiance in the Visible Range

Journal of Atmospheric and Oceanic Technology ◽

10.1175/1457.1 ◽

2003 ◽

Vol 20 (7) ◽

pp. 997-1010 ◽

Cited By ~ 15

Author(s):

José A. Martínez-Lozano ◽

Maria P. Utrillas ◽

Roberto Pedrós ◽

Fernando Tena ◽

Juan P. Díaz ◽

...

Keyword(s):

Solar Irradiance ◽

Visible Range ◽

Correction Factors ◽

Absolute Deviation ◽

Solar Elevation ◽

In Situ Calibration ◽

Laboratory Reference ◽

Uv Visible ◽

Made In

Abstract This paper presents the results of the analysis of the spectral, global, and direct solar irradiance measurements in the visible range (400–700 nm) that were made in the framework of the first Iberian UV–visible (VIS) instruments intercomparison. The instruments used in this spectral range were four spectroradiometers: three Licor 1800s equipped with different receiver optics and one Optronic 754. For the direct solar irradiance measurements the spectroradiometers were equipped with collimators with different fields of view. Parallel studies have been carried out with the data given by the spectroradiometers with their original calibration file and with the same data that is corrected, following in situ calibration of the instruments using a laboratory reference lamp. To compare the series of spectral data the relative values of mean absolute deviation (MAD) and root-mean-square deviation (rmsd) have been used. The results obtained from the measurements of global irradiance show that the Licor 1800s presented very significant differences at the beginning and at the end of the day due to the deviation from ideal cosine response of the collection optics (i.e., cosine errors). This forced the analysis to be limited to the measurements corresponding to solar elevations higher than 30°. For this solar elevation range, the results of the intercomparison between the Licor instruments, before their in situ calibration, showed differences of about 5% in the visible range. The results from the measurements of direct irradiance show that, if correction factors are considered, these deviations are reduced to 3%, and when the Licors are compared with the Optronic, the deviations are less than 2%.

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