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  • Copernicus GmbH  (3)
  • 1
    Online Resource
    Online Resource
    Response time correction of slow-response sensor data by deconvolution of the growth-law equation
    Copernicus GmbH ; 2022
    In:  Geoscientific Instrumentation, Methods and Data Systems Vol. 11, No. 2 ( 2022-08-11), p. 293-306
    Details
    In: Geoscientific Instrumentation, Methods and Data Systems, Copernicus GmbH, Vol. 11, No. 2 ( 2022-08-11), p. 293-306
    Abstract: Abstract. Accurate high-resolution measurements are essential to improve our understanding of environmental processes. Several chemical sensors relying on membrane separation extraction techniques have slow response times due to a dependence on equilibrium partitioning across the membrane separating the measured medium (i.e., a measuring chamber) and the medium of interest (i.e., a solvent). We present a new technique for deconvolving slow-sensor-response signals using statistical inverse theory; applying a weighted linear least-squares estimator with the growth law as a measurement model. The solution is regularized using model sparsity, assuming changes in the measured quantity occur with a certain time step, which can be selected based on domain-specific knowledge or L-curve analysis. The advantage of this method is that it (1) models error propagation, providing an explicit uncertainty estimate of the response-time-corrected signal; (2) enables evaluation of the solution self consistency; and (3) only requires instrument accuracy, response time, and data as input parameters. Functionality of the technique is demonstrated using simulated, laboratory, and field measurements. In the field experiment, the coefficient of determination (R2) of a slow-response methane sensor in comparison with an alternative fast-response sensor significantly improved from 0.18 to 0.91 after signal deconvolution. This shows how the proposed method can open up a considerably wider set of applications for sensors and methods suffering from slow response times due to a reliance on the efficacy of diffusion processes.
    Type of Medium: Online Resource
    ISSN: 2193-0864
    URL: Article
    DOI: 10.5194/gi-11-293-2022
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2022
    detail.hit.zdb_id: 2690575-9
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  • 2
    Online Resource
    Online Resource
    Continuous in situ measurement of dissolved methane in Lake Kivu using a membrane inlet laser spectrometer
    Copernicus GmbH ; 2020
    In:  Geoscientific Instrumentation, Methods and Data Systems Vol. 9, No. 1 ( 2020-04-20), p. 141-151
    Details
    In: Geoscientific Instrumentation, Methods and Data Systems, Copernicus GmbH, Vol. 9, No. 1 ( 2020-04-20), p. 141-151
    Abstract: Abstract. We report the first high-resolution continuous profile of dissolved methane in the shallow water of Lake Kivu, Rwanda. The measurements were performed using an in situ dissolved gas sensor, called Sub-Ocean, based on a patented membrane-based extraction technique coupled with a highly sensitive optical spectrometer. The sensor was originally designed for ocean settings, but both the spectrometer and the extraction system were modified to extend the dynamical range up to 6 orders of magnitude with respect to the original prototype (from nmol L−1 to mmol L−1 detection) to fit the range of concentrations at Lake Kivu. The accuracy of the instrument was estimated to ±22 % (2σ) from the standard deviation of eight profiles at 80 m depth, corresponding to ±0.112 mbar of CH4 in water or ±160 nmol L−1 at 25 ∘C and 1 atm. The instrument was able to continuously profile the top 150 m of the water column within only 25 min. The maximum observed mixing ratio of CH4 in the gas phase concentration was 77 %, which at 150 m depth and under thermal conditions of the lake corresponds to 3.5 mmol L−1. Deeper down, dissolved CH4 concentrations were too large for the methane absorption spectrum to be correctly retrieved. Results are in good agreement with discrete in situ measurements conducted with the commercial HydroC® sensor. This fast-profiling feature is highly useful for studying the transport, production and consumption of CH4 and other dissolved gases in aquatic systems. While the sensor is well adapted for investigating most environments with a concentration of CH4 up to a few millimoles per liter, in the future the spectrometer could be replaced with a less sensitive analytical technique possibly including simultaneous detection of dissolved CO2 and total dissolved gas pressure, for exploring settings with very high concentrations of CH4 such as the bottom waters of Lake Kivu.
    Type of Medium: Online Resource
    ISSN: 2193-0864
    URL: Article
    DOI: 10.5194/gi-9-141-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2690575-9
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  • 3
    Online Resource
    Online Resource
    High-resolution underwater laser spectrometer sensing provides new insights into methane distribution at an Arctic seepage site
    Copernicus GmbH ; 2019
    In:  Ocean Science Vol. 15, No. 4 ( 2019-08-13), p. 1055-1069
    Details
    In: Ocean Science, Copernicus GmbH, Vol. 15, No. 4 ( 2019-08-13), p. 1055-1069
    Abstract: Abstract. Methane (CH4) in marine sediments has the potential to contribute to changes in the ocean and climate system. Physical and biochemical processes that are difficult to quantify with current standard methods such as acoustic surveys and discrete sampling govern the distribution of dissolved CH4 in oceans and lakes. Detailed observations of aquatic CH4 concentrations are required for a better understanding of CH4 dynamics in the water column, how it can affect lake and ocean acidification, the chemosynthetic ecosystem, and mixing ratios of atmospheric climate gases. Here we present pioneering high-resolution in situ measurements of dissolved CH4 throughout the water column over a 400 m deep CH4 seepage area at the continental slope west of Svalbard. A new fast-response underwater membrane-inlet laser spectrometer sensor demonstrates technological advances and breakthroughs for ocean measurements. We reveal decametre-scale variations in dissolved CH4 concentrations over the CH4 seepage zone. Previous studies could not resolve such heterogeneity in the area, assumed a smoother distribution, and therefore lacked both details on and insights into ongoing processes. We show good repeatability of the instrument measurements, which are also in agreement with discrete sampling. New numerical models, based on acoustically evidenced free gas emissions from the seafloor, support the observed heterogeneity and CH4 inventory. We identified sources of CH4, undetectable with echo sounder, and rapid diffusion of dissolved CH4 away from the sources. Results from the continuous ocean laser-spectrometer measurements, supported by modelling, improve our understanding of CH4 fluxes and related physical processes over Arctic CH4 degassing regions.
    Type of Medium: Online Resource
    ISSN: 1812-0792
    URL: Article
    URL: Article
    DOI: 10.5194/os-15-1055-2019
    DOI: 10.5194/os-15-1055-2019-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2183769-7
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