Project Description

Database to simulate spectro-directional reflectance of the Earth surface

The ADAM climatological database and toolkit developed by NOVELTIS enable the calculation of realistic narrow-band reflectance values over the spectral 240-4000 nm range (at 1 nm spectral resolution) and in any observation geometry, at 0.1° x 0.1° (≈10 x 10km) spatial resolution.

In the optical spectral range, remotely sensed observations by satellite sensors are used to estimate several geophysical parameters characterizing the state of the atmosphere, ocean, and land surfaces. These observations are expressed in terms of “reflectance” of the target medium.
Earth surface reflectances are, to the first order, shaped by the absorbing properties of the surface constituents (e.g. photosynthetic and non-photosynthetic pigments for plant canopies and water surfaces, mineral composition for soils, water content, etc.). The surface reflectance also varies with the illumination and view geometry depending on the scattering generated by different “geometrical” factors of the medium considered (wave slopes for ocean surfaces which lead to a departure of the maximum reflectance from the “pure” specular direction surface roughness and canopy structure (e.g. volume and spatial distribution of leaves and crowns) which shape the directional signature of soil and vegetation reflectance. Indeed, the reflectance of most natural surfaces is largely anisotropic in the solar spectral range.
However, the directionality of the surface reflectance is often neglected in operational algorithms dedicated to atmospheric correction or characterization of atmospheric properties. There is therefore a need for accurate information on typical surface (Top-of-Canopy/Bottom-of-Atmosphere) reflectances, representing realistically the spectral and directional signatures of the Earth surfaces, in order to quantify the sensitivity of the retrievals to surface reflectance variability and to develop adaptation measures accounting for surface anisotropy.

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Database to simulate spectro-directional reflectance of the Earth surface

The ADAM climatological database and toolkit developed by NOVELTIS enable the calculation of realistic narrow-band reflectance values over the spectral 240-4000 nm range (at 1 nm spectral resolution) and in any observation geometry, at 0.1° x 0.1° (≈10 x 10km) spatial resolution.

Project details

Website

Catégories:

Share this project:

Contact-us
In the optical spectral range, remotely sensed observations by satellite sensors are used to estimate several geophysical parameters characterizing the state of the atmosphere, ocean, and land surfaces. These observations are expressed in terms of “reflectance” of the target medium.
Earth surface reflectances are, to the first order, shaped by the absorbing properties of the surface constituents (e.g. photosynthetic and non-photosynthetic pigments for plant canopies and water surfaces, mineral composition for soils, water content, etc.). The surface reflectance also varies with the illumination and view geometry depending on the scattering generated by different “geometrical” factors of the medium considered (wave slopes for ocean surfaces which lead to a departure of the maximum reflectance from the “pure” specular direction surface roughness and canopy structure (e.g. volume and spatial distribution of leaves and crowns) which shape the directional signature of soil and vegetation reflectance. Indeed, the reflectance of most natural surfaces is largely anisotropic in the solar spectral range.
However, the directionality of the surface reflectance is often neglected in operational algorithms dedicated to atmospheric correction or characterization of atmospheric properties. There is therefore a need for accurate information on typical surface (Top-of-Canopy/Bottom-of-Atmosphere) reflectances, representing realistically the spectral and directional signatures of the Earth surfaces, in order to quantify the sensitivity of the retrievals to surface reflectance variability and to develop adaptation measures accounting for surface anisotropy.
NOVELTIS - ADAM website
To be useful, a database of the Earth surface spectro-directional reflectance must cover wide spectral and directional ranges, whilst being of small size to facilitate manipulation.
In order to address these constraints, the approach relied on the development of a calculation toolbox which, for each Earth pixel, simulates the spectro-directional reflectance from a limited number of gridded satellite products,which are the basis of the ADAM database.

Means used

  • For land surfaces (sol, vegetation, snow), the data consist in a monthly climatology (for a typical year) of normalized reflectances (i.e. corrected from the directional effects) derived from MODIS observations in seven bands (visible to near infrared). Specific algorithms have been developed to interpolate/extrapolate the reflectance data over the wide 240-4000 nm spectral range at 1 nm resolution, and then to simulate the surface directional signature.

  • Over oceans and lakes, the algorithms relies on chlorophyll products (from the SeaWiFS instrument) to simulate the spectral variation of water reflectance, and on wind speed data (from the QuikScat instrument) to simulate the directional variations.

  • A dedicated web site (https://adam.noveltis.fr/) has been designed by NOVELTIS to provide access to the database and toolbox, while also enabling online calculations and display.

Results

  • ADAM climatological database, representative of year 2005 over land and 1999-2009 over ocean provided at monthly / 0.1° resolutions in netCDF-4 files

  • • ADAM calculation toolkit enabling calculation of the spectro-directional variation of Earth surface reflectance over the 240-4000 nm spectral range (1 nm resolution) and in any observation geometry depending on user’s choices.

  • ADAM web portal offers user-friendly functionalities, including the possibility to visualize monthly reflectance maps and to perform online calculations.

  • Assessment of the ADAM products against PARASOL multispectral/multidirectional observations over several land surface classes over year 2008.

  • It will help support the design of processing chains for atmospheric parameter retrievals (concentrations of aerosol, trace gaz, etc.) from remotely sensed observations in the UV to near infrared.

Clients / Partners

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