Raman spectroscopy as a tool to determine the thermal maturity of organic matter : application to sedimentary, metamorphic and structural geology

Raman spectrometry is a rapid, non-destructive alternative to conventional tools employed to assess the thermal alteration of organic matter (OM). Raman may be used to determine vitrinite reflectance equivalent OM maturity values for petroleum exploration, to provide temperature data for metamorphic studies, and to determine the maximum temperatures reached in fault zones. To achieve the wider utilisation of Raman, the spectrum processing method, and the positions and nomenclature of Raman bands and parameters, all need to be standardized. We assess the most widely used Raman parameters as well as the best analytical practices that have been proposed. Raman band separation and G-band full-width at half-maximum are the best parameters to estimate the maturity for rocks following diagenesis–metagenesis. For metamorphic studies, the ratios of band areas after performing deconvolution are generally used. Further work is needed on the second-order region, as well as assessing the potential of using integrated areas on the whole spectrum, to increase the calibrated temperature range of Raman parameters. Applying Raman spectroscopy on faults has potential to be able to infer both temperature and deformation processes. We propose a unified terminology for OM Raman bands and parameters that should be adopted in the future. The popular method of fitting several functions to a spectrum is generally unnecessary, as Raman parameters determined from an un-deconvoluted spectrum can track the maturity of OM. To progress the Raman application as a geothermometer a standardized approach must be developed and tested by means of an interlaboratory calibration exercise using reference materials

HYPERNETS : a network of automated hyperspectral radiometers to validate water and land surface reflectance (380-1680 nm) from all satellite missions

Satellites are now routinely used for measuring water and land surface reflectance and hence environmentally relevant parameters such as aquatic chlorophyll a concentration and terrestrial vegetation indices. For each satellite mission, radiometric validation is needed at bottom of atmosphere for all spectral bands and covering all typical conditions where the satellite data will be used. Existing networks such as AERONET-OC for water and RadCalNet for land provide vital information for validation, but (AERONET-OC) do not cover all spectral bands or (RadCalNet) do not cover all surface types and viewing angles. In this Perspective Article we discuss recent advances in instrumentation, measurement methods and uncertainty estimation in the field of optical radiometry and put forward the viewpoint that a new network of automated hyperspectral radiometers is needed for multi-mission radiometric validation of water and land surface reflectance. The HYPERNETS federated network concept is described, providing a context for research papers on specific aspects of the network. This network is unique in its common approach to both land and water surfaces. The common aspects and the differences between land and water measurements are explained. Based on early enthusiasm for HYPERNETS data from validation-oriented workshops, it is our viewpoint that this new network of automated hyperspectral radiometers will be useful for multi-mission radiometric validation of water and multi-angle land surface reflectance. The HYPERNETS network has strong synergy with other measurement networks (AERONET, AERONET-OC, RadCalNet, FLUXNET, ICOS, skycam, etc.) and with optional supplementary measurements, e.g., water turbidity and fluorescence, land surface temperature and soil moisture, etc

The MERIS water products: Performance, current issues and potential future improvements

MERIS Level 1 and Level 2 water products will be improved in the 3rd MERIS reprocessing which is planned to take place before the end of 2009. The instrument radiometric degradation model will be updated. Improvements to the atmospheric correction in both case 1 and case 2 waters will be implemented. A vicarious adjustment strategy to remove residual biases in the Level 2 marine signals will be put in place. In addition, a cloud screening scheme with improved detection capabilities will improve the cirrus detection capability. In parallel, long term algorithmic improvements are being pursued and are partially covered by three exploratory ongoing studies. The first study addresses the limitation of the current MERIS atmospheric correction scheme in sun glint conditions. The second aims at defining an operational adjacency effect correction. The third study makes use of the ability of MERIS to measure transmission in the O2-A oxygen band to better identify and characterize clouds and aerosols

HYPERNETS: a network of automated hyperspectral radiometers to validate water and land surface reflectance (380–1680 nm) from all satellite missions

International audienceSatellites are now routinely used for measuring water and land surface reflectance and hence environmentally relevant parameters such as aquatic chlorophyll a concentration and terrestrial vegetation indices. For each satellite mission, radiometric validation is needed at bottom of atmosphere for all spectral bands and covering all typical conditions where the satellite data will be used. Existing networks such as AERONET-OC for water and RadCalNet for land provide vital information for validation, but (AERONET-OC) do not cover all spectral bands or (RadCalNet) do not cover all surface types and viewing angles. In this Perspective Article we discuss recent advances in instrumentation, measurement methods and uncertainty estimation in the field of optical radiometry and put forward the viewpoint that a new network of automated hyperspectral radiometers is needed for multi-mission radiometric validation of water and land surface reflectance. The HYPERNETS federated network concept is described, providing a context for research papers on specific aspects of the network. This network is unique in its common approach to both land and water surfaces. The common aspects and the differences between land and water measurements are explained. Based on early enthusiasm for HYPERNETS data from validation-oriented workshops, it is our viewpoint that this new network of automated hyperspectral radiometers will be useful for multi-mission radiometric validation of water and multi-angle land surface reflectance. The HYPERNETS network has strong synergy with other measurement networks (AERONET, AERONET-OC, RadCalNet, FLUXNET, ICOS, skycam, etc.) and with optional supplementary measurements, e.g., water turbidity and fluorescence, land surface temperature and soil moisture, etc

Applying uncertainties to ocean colour data

Remote sensing is a powerful tool for studying the marine environment; however, many images are contaminated by sun glint, the specular reflection of light from the water surface. Improved radiative transfer modelling could lead to better methods for estimating and correcting sunglint. This thesis explores the effect of using detailed numerical models of the sea surface when investigating the transfer of light through the atmosphere-ocean system. New numerical realisations that model both the shape and slope of the sea surface have been created; these contrast with existing radiative transfer models, where the air-water interface has slope but not elevation. Surface realisations including features on a scale from 3 mm to 200 m were created by a Fourier synthesis method, using up to date spectra of the wind-blown sea surface. The surfaces had mean square slopes and elevation variances in line with those of observed seas, for wind speeds up to 15 m/s. Ray-tracing using the new surfaces gave estimates of reflected radiance that were similar to those made using slope statistics methods, but significantly different in 41% of cases tested. The mean difference in the reflected radiance at these points was 19%, median 7%. Elevation-based surfaces give increased sideways scattering and reduced forward scattering of light incident on the sea surface. The elevation-based models have been applied to estimate pixel-pixel variation in ocean colour imagery and to simulate scenes viewed by three types of sensor. The simulations correctly estimated the size and position of the glint zone. Simulations of two ocean colour images gave a lower peak reflectance than the original values, but higher reflectance at the edge of the glint zone. The use of the simulation to test glint correction methods has been demonstrated, as have global Monte Carlo techniques for investigating sensitivity and uncertainty in sun glint correction. This work has shown that elevation-based sea surface models can be created and tested using readily-available computer hardware. The new model can be used to simulate glint in a variety of situations, giving a tool for testing glint correction methods. It could also be used for glint correction directly, by predicting the level of sun glint in a given set of conditions.Great Western Research; ARGANS Lt