Comparing spaceborne ERS-SAR and airbone geophysical data: application to geology in the French Guiana rainforest landscapes

Schematically French Guiana geological setting comprises essentially Palaeoproterozoic terrains, which are deeply altered under a humid tropical climate.
In July and December 1996 the French Geological Survey (BRGM) working for the French Ministry of Industry supervised an airborne geophysical survey combining magnetism and spectrometry measurements, practically flown by CGG (Compagnie Générale de Géophysique).

The objectives were :

    (i) the realisation of a global geophysical mapping to consolidate the geological background,
    (ii) an aid to the elaboration of a strategy for the mineral exploration of French Guiana, especially for gold,
    (iii) the synthesis and the amalgamation of former geophysical surveys realized in the 70’s.

Magnetism and SAR data provide information about the basaltic veins, which cut through the Palaeoproterozoic terranes. Those veins reveal the onset of the Atlantic Ocean, about 200 Ma ago.
For Palaeoproterozoic series, magnetism provides better arguments to highlight structural features, while radiometry undoubtedly provides more accurate contrasts for plutonic varieties.

Indeed the contribution of three different elements has been distinguished : on the one hand, uranium (U) and thorium (Th) abundant in the granites especially in the eastern part of French Guiana, and on the other hand potassium (K) highly concentrated in more pelitic terms of sedimentary units.
Some geophysical features could be compared with the ERS-SAR lineaments revealing faulting, schistosity or lithology, for example by alignment of the hydrographic network.
The remote sensing backscattering mainly due to the shape of the canopy (C-band) modulated by regional morphology and surface roughness, and the geophysical data corresponding to characteristics of the rocks themselves are highly complementary.