Pseudo Invariant Calibration Sites
Pseudo Invariant Calibration Sites (PICS) are terrestrial sites used for the in-flight radiometric monitoring of Earth Observation optical sensors. Due to their difficult access and large size, the methodologies developed to exploit these sites can only rely on partial characterisation of the optical properties of their surface and atmospheric conditions. The company NOVELTIS (FR) supported by ONERA (Office National d'Etudes et de Recherches Aérospatiales) and LSCE (Le Laboratoire des Sciences du Climat et de l'Environnement) carried out a study under ESA contract to improve the surface and atmosphere characterisation of the PICS. Such characterisation data are made public to support the reduction of uncertainties in radiometric monitoring methodologies. The study consisted in:
- Revisiting the list of Pseudo-Invariant Calibration Sites (PICS) over desert areas defined by Cosnefroy et al. (1997) based on recent multi-spectral remotely sensed data with enhanced temporal and spatial coverages and resolutions, focusing on site scales of 20 km and 100 km spatial resolutions.
- Collecting sand samples from an ensemble of identified sites.
- Analysing in laboratory their physical (mineralogy and grain size analysis) and optical (spectro-directional reflectance) properties.
- Assessing the performance of several BRDF models to fit sand spectro-directional measurements don in laboratory as well as surface reflectance derived from the POLDER/PARASOL space-borne instrument over the PICS.
- Building a database combining the sand spectro-directional measurements of the samples collected in this study and other similar measurements available in the literature.
- Determining a climatology of aerosol and atmosphere conditions over the PICS supporting modelling studies of the top-of-atmosphere (TOA) signal over the PICS.
In the frame of the ESA-PICS study, the PICSAND database of sand optical properties has been built and made available online on the PICSAND portal
The final reports of this study are available here: PICS Reports