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  • 2020-2023  (29)
  • 2020-2022  (40)
  • 1955-1959  (165)
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  • 1
    Book
    Book
    London [u.a.] : Oxford Univ. Press
    Type of Medium: Book
    Pages: XI, 244 S , Ill.
    Language: English
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  • 2
    Keywords: Chemistry. ; Electronic books.
    Type of Medium: Online Resource
    Pages: 1 online resource (561 pages)
    Edition: 1st ed.
    ISBN: 9783709171660
    Series Statement: Fortschritte der Chemie Organischer Naturstoffe Progress in the Chemistry of Organic Natural Products Series ; v.12
    Language: English
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  • 3
    Type of Medium: Book
    Pages: Seite 1-58, Blatt Tafel 1 , Illustrationen
    Series Statement: Philosophical transactions of the Royal Society of London no. 686 = vol. 242 (1960)
    Language: English
    Note: Umschlagtitel
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  • 4
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    In:  http://aquaticcommons.org/id/eprint/14426 | 8 | 2014-02-05 23:15:21 | 14426
    Publication Date: 2021-07-10
    Description: EXTRACT (SEE PDF FOR FULL ABSTRACT):The 1000 year records of particulate deposition (soluble and insoluble), oxygen isotopic ratios, and net accumulation from the Quelccaya ice cap are presented. The net accumulation record from Quelccaya is shown to serve as a reasonable proxy for the water levels in Lake Titicaca. ... The ice core record from the Dunde ice cap offers the potential to reconstruct a very detailed history of environmental conditions on theTibetan Plateau for the last 3000 years.
    Keywords: Atmospheric Sciences ; Earth Sciences ; PACLIM
    Repository Name: AquaDocs
    Type: conference_item
    Format: application/pdf
    Format: application/pdf
    Format: 13-14
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  • 5
    Publication Date: 2020-12-10
    Description: Airborne and orbital imaging spectroscopy can facilitate the quantification of chemical and physical attributes of surface materials through analysis of spectral signatures. Prior to analysis, estimates of surface reflectance must be inferred from radiance measurements in a process known as atmospheric correction, which compensates for the distortion of the electromagnetic signal by the atmosphere. Inaccuracies in the correction process can alter characteristic spectral signatures, leading to subsequent mischaracterization of surface properties. Global observations pose new challenges for mapping surface composition, as varied atmospheric conditions and surface biomes challenge traditional atmospheric correction methods. Recent work adopted an optimal estimation (OE) approach for retrieving surface reflectance from observed radiance measurements, providing the reflectance estimates with a posterior probability. This work incorporates these input probabilities to improve the accuracy of surface feature measurements. We demonstrate this using a generic feature-fitting method that is applicable to a wide range of Earth surface studies including geology, ecosystem studies, hydrology and urban studies. Specifically, we use a probabilistic framework based on generalized Tikhonov-regularized least squares, a rigorous formulation for appropriate weighting of features by their observation uncertainty and leveraging of prior knowledge of material abundance for improving estimation accuracy. We demonstrate the validity of this procedure and quantify the increase in model performance by simulating expected accuracies in the reflectance estimation. To evaluate global uncertainties in mineral estimation, we simulate observations representative of the expected global range of atmospheric water vapor and aerosol levels, and characterize the sensitivity of our procedure to those quantities.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 6
    Publication Date: 2021-06-14
    Description: In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 7
    Publication Date: 2022-05-16
    Description: Remote imaging spectroscopy, also known as hyperspectral imaging, uses Radiative Transfer Models (RTMs) to predict the measured radiance spectrum for a specific surface and atmospheric state. Discrepancies between RTM assumptions and physical reality can cause systematic errors in surface property estimates. We present a statistical method to quantify these model errors without invoking ground reference data. Our approach exploits scene invariants — properties of the environment which are stable over space or time — to estimate RTM discrepancies. We describe techniques for discovering these features opportunistically in flight data. We then demonstrate data-driven methods that estimate the aggregate errors due to model discrepancies without having to explicitly identify the underlying physical mechanisms. The resulting distributions can improve posterior uncertainty predictions in operational retrievals.
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 8
    Publication Date: 2020-09-21
    Description: Remote imaging spectroscopy's role in Earth science will grow in the coming decade as a series of globe-spanning spectroscopy missions launch from NASA, ESA, and other agencies. The nature of remote imaging spectroscopy will change, advancing from short regional studies to address global multi-year questions. The diversity of data will also grow with exposure to a wider range of biomes and atmospheric conditions. To execute these new investigations we must reconcile diverse observing conditions to derive consistent global maps. To this end, rigorous uncertainty quantification and propagation enables an optimal synthesis of data accounting for observing conditions and data quality. Understanding data uncertainties is also important for principled hypothesis testing, information content assessment, and informed decision making by end users. We survey prior efforts in uncertainty quantification for imaging spectroscopy, and describe methods for validating the accuracy of uncertainty predictions. We conclude with a discussion of remaining challenges and promising avenues for future research. © (2020) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 9
    Publication Date: 2022-01-10
    Description: Changes in electron flux in Earth's outer radiation belt can be modeled using a diffusion‐based framework. Diffusion coefficients D for such models are often constructed from statistical averages of observed inputs. Here, we use stochastic parameterization to investigate the consequences of temporal variability in D. Variability time scales are constrained using Van Allen Probe observations. Results from stochastic parameterization experiments are compared with experiments using D constructed from averaged inputs and an average of observation‐specific D. We find that the evolution and final state of the numerical experiment depends upon the variability time scale of D; experiments with longer variability time scales differ from those with shorter time scales, even when the time‐integrated diffusion is the same. Short variability time scale experiments converge with solutions obtained using an averaged observation‐specific D, and both exhibit greater diffusion than experiments using the averaged‐input D. These experiments reveal the importance of temporal variability in radiation belt diffusion.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 10
    Publication Date: 2022-07-25
    Description: Future global Visible Shortwave Infrared Imaging Spectrometers, such as the Surface Biology and Geology (SBG) mission, will regularly cover the Earth's entire terrestrial land area. These missions need high fidelity atmospheric correction to produce consistent maps of terrestrial and aquatic ecosystem traits. However, estimation of surface reflectance and atmospheric state is computationally challenging, and the terabyte data volumes of global missions will exceed available processing capacity. This article describes how missions can overcome this bottleneck using the spatial continuity of atmospheric fields. Contemporary imaging spectrometers oversample atmospheric spatial variability, so it is not necessary to invert every pixel. Spatially sparse solutions can train local linear emulators that provide fast, exact inversions in their vicinity. We find that estimating the atmosphere at 200 m scales can outperform traditional atmospheric correction, improving speed by one to two orders of magnitude with no measurable penalty to accuracy. We validate performance with an airborne field campaign, showing reflectance accuracies with RMSE of 1.1% or better compared to ground measurements of diverse targets. These errors are statistically consistent with retrieval uncertainty budgets. Local emulators can close the efficiency gap and make rigorous model inversion algorithms feasible for global missions such as SBG.
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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