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- Author or Editor: B. Pinty x
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Abstract
The inference of surface reflectance from satellite observations requires the knowledge of the double-way transmittance through the atmosphere. Since the existing pyranometer networks routinely provide measurements of the incident transmittance over sensitive climatic regions, it would be useful for subsequent applications to relate this ground-based measurement to the corresponding double-way transmittance. A variety of satellite radiance simulations corresponding to clear sky conditions has been made in order to derive a suitable parameterized expression between the two quantities. The accuracy of this expression when making use of additional meteorological observations is shown and discussed. Finally, the derived expression is used to improve a method recently proposed by Pinty et al. for retrieving surface albedo over the African Sahel from METEOSAT radiances.
Abstract
The inference of surface reflectance from satellite observations requires the knowledge of the double-way transmittance through the atmosphere. Since the existing pyranometer networks routinely provide measurements of the incident transmittance over sensitive climatic regions, it would be useful for subsequent applications to relate this ground-based measurement to the corresponding double-way transmittance. A variety of satellite radiance simulations corresponding to clear sky conditions has been made in order to derive a suitable parameterized expression between the two quantities. The accuracy of this expression when making use of additional meteorological observations is shown and discussed. Finally, the derived expression is used to improve a method recently proposed by Pinty et al. for retrieving surface albedo over the African Sahel from METEOSAT radiances.
Abstract
Surface albedo can be inferred from geostationary satellite measurements as long as the effects due to the atmosphere, the spectral response of the sensor, and the angular anisotropy of the reflected field are corrected. In this paper, we developed a method which includes ad hoc correction procedures for the three categories of effects. An application of the method is conducted over the Sahara and the African Sahel using METEOSAT radiances together with auxiliary data derived from other satellites (Tiros-N and Nimbus-7) and standard meteorological observations. The surface albedo maps are estimated over this region, at a spatial resolution compatible with one used in climate models, for 2 days representative of the dry and the wet seasons, respectively. The observed seasonal surface albedo change and the relationships between the surface and the planetary albedos are discussed in order to examine the validity of the method and the correction procedures.
Abstract
Surface albedo can be inferred from geostationary satellite measurements as long as the effects due to the atmosphere, the spectral response of the sensor, and the angular anisotropy of the reflected field are corrected. In this paper, we developed a method which includes ad hoc correction procedures for the three categories of effects. An application of the method is conducted over the Sahara and the African Sahel using METEOSAT radiances together with auxiliary data derived from other satellites (Tiros-N and Nimbus-7) and standard meteorological observations. The surface albedo maps are estimated over this region, at a spatial resolution compatible with one used in climate models, for 2 days representative of the dry and the wet seasons, respectively. The observed seasonal surface albedo change and the relationships between the surface and the planetary albedos are discussed in order to examine the validity of the method and the correction procedures.
Abstract
A technique for inferring the spatial and seasonal albodo changes over a whole climatic region from satellite data is developed. This technique uses the diurnal variation of radiances which is measured by geostationary satellites and requires the knowledge of a surface albedo value over at least one reference site. The proposed method is tested over western Africa, using METEOSAT data; and surface albedo maps representative of the wet and dry seasons are derived. With regard to the considered scales and to the achievable accuracies, the technique is shown to be relevant for climatological studies.
Abstract
A technique for inferring the spatial and seasonal albodo changes over a whole climatic region from satellite data is developed. This technique uses the diurnal variation of radiances which is measured by geostationary satellites and requires the knowledge of a surface albedo value over at least one reference site. The proposed method is tested over western Africa, using METEOSAT data; and surface albedo maps representative of the wet and dry seasons are derived. With regard to the considered scales and to the achievable accuracies, the technique is shown to be relevant for climatological studies.
Abstract
This note describes low-level observations obtained during WAMEX from an instrumented DC 7 aircraft. These data give a detailed description of the dynamical and thermodynamical structure of the layer 0.5–3 km over a zonal and a meridional cross section. The results indicate that a large and variable northerly wind occurs down to the Equator in the monsoon layer.
Abstract
This note describes low-level observations obtained during WAMEX from an instrumented DC 7 aircraft. These data give a detailed description of the dynamical and thermodynamical structure of the layer 0.5–3 km over a zonal and a meridional cross section. The results indicate that a large and variable northerly wind occurs down to the Equator in the monsoon layer.
Abstract
The conversion of radiances measured by the METEOSAT visible channel into broadband radiances can be performed as long as the appropriate conversion factors are known. A simple model allowing a spectral description of the optical properties of cloud free atmospheres and land surfaces is used to estimate these conversion factors. A sensitivity study of these factors indicates that a knowledge of the optical properties of the surfaces (described through spectrally averaged albedos and spectral band ratios) is decisive for retrieving broadband conversion factors. A parameterization is proposed which permits estimation of METEOSAT conversion factors for radiation budget calculations.
Abstract
The conversion of radiances measured by the METEOSAT visible channel into broadband radiances can be performed as long as the appropriate conversion factors are known. A simple model allowing a spectral description of the optical properties of cloud free atmospheres and land surfaces is used to estimate these conversion factors. A sensitivity study of these factors indicates that a knowledge of the optical properties of the surfaces (described through spectrally averaged albedos and spectral band ratios) is decisive for retrieving broadband conversion factors. A parameterization is proposed which permits estimation of METEOSAT conversion factors for radiation budget calculations.
The physical interpretation of simultaneous multiangle observations represents a relatively new approach to remote sensing of terrestrial geophysical and biophysical parameters. Multiangle measurements enable retrieval of physical scene characteristics, such as aerosol type, cloud morphology and height, and land cover (e.g., vegetation canopy type), providing improved albedo accuracies as well as compositional, morphological, and structural information that facilitates addressing many key climate, environmental, and ecological issues. While multiangle data from wide field-of-view scanners have traditionally been used to build up directional “signatures” of terrestrial scenes through multitemporal compositing, these approaches either treat the multiangle variation as a problem requiring correction or normalization or invoke statistical assumptions that may not apply to specific scenes. With the advent of a new generation of global imaging spectroradiometers capable of acquiring simultaneous visible/near-IR multiangle observations, namely, the Along-Track Scanning Radiometer-2, the Polarization and Directionality of the Earth's Reflectances instrument, and the Multiangle Imaging SpectroRadiometer, both qualitatively new approaches as well as quantitative improvements in accuracy are achievable that exploit the multiangle signals as unique and rich sources of diagnostic information. This paper discusses several applications of this technique to scientific problems in terrestrial atmospheric and surface geophysics and biophysics.
The physical interpretation of simultaneous multiangle observations represents a relatively new approach to remote sensing of terrestrial geophysical and biophysical parameters. Multiangle measurements enable retrieval of physical scene characteristics, such as aerosol type, cloud morphology and height, and land cover (e.g., vegetation canopy type), providing improved albedo accuracies as well as compositional, morphological, and structural information that facilitates addressing many key climate, environmental, and ecological issues. While multiangle data from wide field-of-view scanners have traditionally been used to build up directional “signatures” of terrestrial scenes through multitemporal compositing, these approaches either treat the multiangle variation as a problem requiring correction or normalization or invoke statistical assumptions that may not apply to specific scenes. With the advent of a new generation of global imaging spectroradiometers capable of acquiring simultaneous visible/near-IR multiangle observations, namely, the Along-Track Scanning Radiometer-2, the Polarization and Directionality of the Earth's Reflectances instrument, and the Multiangle Imaging SpectroRadiometer, both qualitatively new approaches as well as quantitative improvements in accuracy are achievable that exploit the multiangle signals as unique and rich sources of diagnostic information. This paper discusses several applications of this technique to scientific problems in terrestrial atmospheric and surface geophysics and biophysics.
Abstract
Under the Paris Agreement (PA), progress of emission reduction efforts is tracked on the basis of regular updates to national greenhouse gas (GHG) inventories, referred to as bottom-up estimates. However, only top-down atmospheric measurements can provide observation-based evidence of emission trends. Today, there is no internationally agreed, operational capacity to monitor anthropogenic GHG emission trends using atmospheric measurements to complement national bottom-up inventories. The European Commission (EC), the European Space Agency, the European Centre for Medium-Range Weather Forecasts, the European Organisation for the Exploitation of Meteorological Satellites, and international experts are joining forces to develop such an operational capacity for monitoring anthropogenic CO2 emissions as a new CO2 service under the EC’s Copernicus program. Design studies have been used to translate identified needs into defined requirements and functionalities of this anthropogenic CO2 emissions Monitoring and Verification Support (CO2MVS) capacity. It adopts a holistic view and includes components such as atmospheric spaceborne and in situ measurements, bottom-up CO2 emission maps, improved modeling of the carbon cycle, an operational data-assimilation system integrating top-down and bottom-up information, and a policy-relevant decision support tool. The CO2MVS capacity with operational capabilities by 2026 is expected to visualize regular updates of global CO2 emissions, likely at 0.05° x 0.05°. This will complement the PA’s enhanced transparency framework, providing actionable information on anthropogenic CO2 emissions that are the main driver of climate change. This information will be available to all stakeholders, including governments and citizens, allowing them to reflect on trends and effectiveness of reduction measures. The new EC gave the green light to pass the CO2MVS from exploratory to implementing phase.
Abstract
Under the Paris Agreement (PA), progress of emission reduction efforts is tracked on the basis of regular updates to national greenhouse gas (GHG) inventories, referred to as bottom-up estimates. However, only top-down atmospheric measurements can provide observation-based evidence of emission trends. Today, there is no internationally agreed, operational capacity to monitor anthropogenic GHG emission trends using atmospheric measurements to complement national bottom-up inventories. The European Commission (EC), the European Space Agency, the European Centre for Medium-Range Weather Forecasts, the European Organisation for the Exploitation of Meteorological Satellites, and international experts are joining forces to develop such an operational capacity for monitoring anthropogenic CO2 emissions as a new CO2 service under the EC’s Copernicus program. Design studies have been used to translate identified needs into defined requirements and functionalities of this anthropogenic CO2 emissions Monitoring and Verification Support (CO2MVS) capacity. It adopts a holistic view and includes components such as atmospheric spaceborne and in situ measurements, bottom-up CO2 emission maps, improved modeling of the carbon cycle, an operational data-assimilation system integrating top-down and bottom-up information, and a policy-relevant decision support tool. The CO2MVS capacity with operational capabilities by 2026 is expected to visualize regular updates of global CO2 emissions, likely at 0.05° x 0.05°. This will complement the PA’s enhanced transparency framework, providing actionable information on anthropogenic CO2 emissions that are the main driver of climate change. This information will be available to all stakeholders, including governments and citizens, allowing them to reflect on trends and effectiveness of reduction measures. The new EC gave the green light to pass the CO2MVS from exploratory to implementing phase.
