The Experts below are selected from a list of 13215 Experts worldwide ranked by ideXlab platform

Riley M Duren - One of the best experts on this subject based on the ideXlab platform.

  • detection and quantification of ch 4 plumes using the wfm doas retrieval on aviris ng hyperspectral data
    Atmospheric Measurement Techniques, 2021
    Co-Authors: Jakob Borchardt, David R Thompson, Christian Frankenberg, Andrew K Thorpe, Riley M Duren, Konstantin Gerilowski, Sven Krautwurst, Heinrich Bovensmann, Charles E Miller
    Abstract:

    Abstract. Methane is the second most important anthropogenic greenhouse gas in the Earth's atmosphere. To effectively reduce these emissions, a good knowledge of source locations and strengths is required. Airborne remote sensing instruments such as the Airborne Visible InfraRed Imaging Spectrometer – Next Generation (AVIRIS-NG) with meter-scale imaging capabilities are able to yield information about the locations and magnitudes of methane sources. In this study, we successfully applied the weighting function modified differential optical absorption spectroscopy (WFM-DOAS) algorithm to AVIRIS-NG data measured in Canada and the Four Corners region. The WFM-DOAS retrieval is conceptually located between the statistical matched filter (MF) and the optimal-estimation-based iterative maximum a posteriori DOAS (IMAP-DOAS) retrieval algorithm, both of which were already applied successfully to AVIRIS-NG data. The WFM-DOAS algorithm is based on a first order Taylor series approximation of the Lambert–Beer Law using only one precalculated radiative transfer calculation per scene. This yields the fast quantitative processing of large data sets. We detected several methane plumes in the AVIRIS-NG images recorded during the Arctic-Boreal Vulnerability Experiment (ABoVE) Airborne Campaign and successfully retrieved a coal mine ventilation shaft plume observed during the Four Corners measurement campaign. The comparison between IMAP-DOAS, MF, and WFM-DOAS showed good agreement for the coal mine ventilation shaft plume. An additional comparison between MF and WFM-DOAS for a subset of plumes showed good agreement for one plume and some differences for the others. For five plumes, the emissions were estimated using a simple cross-sectional flux method. The retrieved fluxes originated from well pads, cold vents, and a coal mine ventilation shaft and ranged between (155  ±  71) kg (CH 4 ) h −1 and (1220  ±  450) kg (CH 4 ) h −1 . The wind velocity was a significant source of uncertainty in all plumes, followed by the single pixel retrieval noise and the uncertainty due to atmospheric variability. The noise of the retrieved CH 4 imagery over bright surfaces ( >1 µ W cm −2  nm −1  sr −1 at 2140 nm ) was typically ±2.3  % of the background total column of CH 4 when fitting strong absorption lines around 2300 nm but could reach over ±5  % for darker surfaces (  0.3  µ W cm −2  nm −1  sr −1 at 2140 nm ). Additionally, a worst case large-scale bias due to the assumptions made in the WFM-DOAS retrieval was estimated to be ±5.4  %. Radiance and fit quality filters were implemented to exclude the most uncertain results from further analysis mostly due to either dark surfaces or surfaces where the surface spectral reflection structures are similar to CH 4 absorption features at the spectral resolution of the AVIRIS-NG instrument.

Paul D Mannheimer - One of the best experts on this subject based on the ideXlab platform.

  • the light tissue interaction of pulse oximetry
    Anesthesia & Analgesia, 2007
    Co-Authors: Paul D Mannheimer
    Abstract:

    The underlying science of pulse oximetry is based on a simple manipulation of the Lambert–Beer Law, which describes the attenuation of light traveling through a mixture of absorbers. Signals from detected red and infrared light that has traveled through blood-perfused tissues are used to estimate th

  • the light tissue interaction of pulse oximetry
    Anesthesia & Analgesia, 2007
    Co-Authors: Paul D Mannheimer
    Abstract:

    The underlying science of pulse oximetry is based on a simple manipulation of the Lambert-Beer Law, which describes the attenuation of light traveling through a mixture of absorbers. Signals from detected red and infrared light that has traveled through blood-perfused tissues are used to estimate the underlying arterial hemoglobin oxygen saturation. However, light scatters in tissue and influences some of the simplifications made in determining this relationship. Under most clinical circumstances, the empirical process that manufacturers use to calibrate the system during its design readily accommodates this and results in accurate readings. The same tissue light scattering properties allow sensors to be configured for use on opposing or adjacent surfaces, provided that the placement sites offer sufficient signal strength and are absent factors known to influence accuracy. In this paper I review the light-tissue interaction in pulse oximetry and describe some of the assumptions made and their implications. Certain deviations from the nominal conditions, whether clinical in nature or misuse of the product, can affect system performance. Consequently, users should be cautious in modifying sensors and/or using them on tissue sites not intended by the manufacturer (off-label use). While perhaps helpful for obtaining pulsatile signals or extending the lifetime of a sensor, some practices can disrupt the optical integrity of the measurement and negatively impact the oxygen saturation reading accuracy.

Ulrich Riebel - One of the best experts on this subject based on the ideXlab platform.

  • the fundamentals of particle size analysis by transmission fluctuation spectrometry part 2 a theory on transmission fluctuations with combined spatial and temporal averaging
    Particle & Particle Systems Characterization, 2001
    Co-Authors: Marcus Breitenstein, Ulrich Riebel, Jianqi Shen
    Abstract:

    The extinction of radiation in suspensions is traditionally described by the Bouguer-Lambert-Beer Law (BLBL). Based on a quasi-continuum approach, the BLBL does not account for the discrete nature of particles or their spatial extension and arrangement. If an extinction measurement is made with a high spatial and temporal resolution, the transmitted intensity signal shows significant fluctuations. The strength of fluctuation is related to the physical properties of the suspension and the process of spatial and temporal averaging. Exploiting this connection, it is possible to calculate the particle size distribution and the particle concentration from transmission measurements. This second part provides an analytical solution for the description of transmission fluctuations in terms of the expectancy of the transmission square, including both variations of the beam diameter to particle diameter ratio and variation of the temporal resolution of the signal capture. The result also provides the basis for describing the transmission fluctuations for beams of variable diameter and allows to define a measurement volume for the case of focussed beams.

  • the fundamentals of particle size analysis by transmission fluctuation spectrometry part 1 a theory of temporal transmission fluctuations in dilute suspensions
    Particle & Particle Systems Characterization, 1999
    Co-Authors: Marcus Breitenstein, Udo Krauter, Ulrich Riebel
    Abstract:

    The extinction of radiation in suspensions is traditionally described by the Bouger-Lambert-Beer Law (BLBL). Based on a quasi-continuum approach, the BLBL does not account for the discrete nature of particles or their spatial extension and arrangement. If an extinction measurement is made with a high spatial and temporal resolution, the transmitted intensity signal shows significant fluctuations. The strength of fluctuation is related to the physical properties of the suspension and the process of spatial and temporal averaging. Exploiting this connection, it is possible to calculate the particle size distribution and the particle concentration from transmission measurements. This part of the series of papers provides a method for the temporal decomposition of the transmission's power spectrum, which permits the information on the particle size and concentration to be extracted from the seemingly irregular fluctuation of the transmission signal.

Marcus Breitenstein - One of the best experts on this subject based on the ideXlab platform.

  • the fundamentals of particle size analysis by transmission fluctuation spectrometry part 2 a theory on transmission fluctuations with combined spatial and temporal averaging
    Particle & Particle Systems Characterization, 2001
    Co-Authors: Marcus Breitenstein, Ulrich Riebel, Jianqi Shen
    Abstract:

    The extinction of radiation in suspensions is traditionally described by the Bouguer-Lambert-Beer Law (BLBL). Based on a quasi-continuum approach, the BLBL does not account for the discrete nature of particles or their spatial extension and arrangement. If an extinction measurement is made with a high spatial and temporal resolution, the transmitted intensity signal shows significant fluctuations. The strength of fluctuation is related to the physical properties of the suspension and the process of spatial and temporal averaging. Exploiting this connection, it is possible to calculate the particle size distribution and the particle concentration from transmission measurements. This second part provides an analytical solution for the description of transmission fluctuations in terms of the expectancy of the transmission square, including both variations of the beam diameter to particle diameter ratio and variation of the temporal resolution of the signal capture. The result also provides the basis for describing the transmission fluctuations for beams of variable diameter and allows to define a measurement volume for the case of focussed beams.

  • the fundamentals of particle size analysis by transmission fluctuation spectrometry part 1 a theory of temporal transmission fluctuations in dilute suspensions
    Particle & Particle Systems Characterization, 1999
    Co-Authors: Marcus Breitenstein, Udo Krauter, Ulrich Riebel
    Abstract:

    The extinction of radiation in suspensions is traditionally described by the Bouger-Lambert-Beer Law (BLBL). Based on a quasi-continuum approach, the BLBL does not account for the discrete nature of particles or their spatial extension and arrangement. If an extinction measurement is made with a high spatial and temporal resolution, the transmitted intensity signal shows significant fluctuations. The strength of fluctuation is related to the physical properties of the suspension and the process of spatial and temporal averaging. Exploiting this connection, it is possible to calculate the particle size distribution and the particle concentration from transmission measurements. This part of the series of papers provides a method for the temporal decomposition of the transmission's power spectrum, which permits the information on the particle size and concentration to be extracted from the seemingly irregular fluctuation of the transmission signal.

Erhan Deniz - One of the best experts on this subject based on the ideXlab platform.

  • uv vis absorption spectroscopy lambert Beer reloaded
    Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017
    Co-Authors: Werner Mantele, Erhan Deniz
    Abstract:

    UV-VIS absorption spectroscopy is used in almost every spectroscopy laboratory for routine analysis or research. All spectroscopists rely on the Lambert-Beer Law but many of them are less aware of its limitations. This tutorial discusses typical problems in routine spectroscopy that come along with technical limitations or careless selection of experimental parameters. Simple rules are provided to avoid these problems.