Sar Interferometry And Its Applications

Satellite mounted Synthetic Aperture Radars (SAR) provide informationof the amplitude of the backscatterer its phase. This corresponds to the totaltravel time (source receiver and back), plus the phase of the scatterer itself.SAR interferometry yields the image of the differences of the phases takenin two successive passes. Or in the same pass if two receivers are availableon board; these images give a good digital elevation model of the terrain,with a vertical resolution that could be in the meter range. Millimetric motionof large areas of the terrain or of corner reflectors can also be measured withgood reliability; the system then measures subsidence, co-seismic motions andsmall motions of buildings and constructions. The coherence of t e interferometric pair, i.e., the permanence of the scattering characteristics of the terrain from one pass to the next combined with the more usual backscatterer amplitude, leads to high quality image segmentation. The possibilities and the limits of this technique are summarized.     

Imprint of Climate Variability on Mesozoic Fossil Tree Rings: Evidences of Solar Activity Signals on Environmental Records Around 200 Million Years Ago?

Evidence of the solar activity modulation of the Earth’s climate has been observed on several parameters, from decadal to millennial time scales. Several proxies have been used to reconstruct the paleoclimate as well as the solar activity. The paleoclimate reconstructions are based on direct and/or indirect effects of global and regional climate conditions. The solar activity reconstructions are based on the production of the ¹⁴C isotope due to the interaction of cosmic ray flux and the Earth’s atmosphere. Because trees respond to climate conditions and store ¹⁴C, they have been used as proxies for both for climate and solar activity reconstructions. The imprints of solar activity cycles dating back to 10,000 years ago have been observed on tree-ring samples using ¹⁴C data, and those dating back to 20 million years ago have been analyzed using fossil tree-growth rings. All this corresponds to the Cenozoic era. However, solar activity imprints on tree rings from earlier than that era have not been investigated yet. In this work, we showed that tree rings from the Mesozoic Era (of ~200 million years ago) recorded 11- and 22-year cycles, which may be related to solar activity cycles, and that were statistically significant at the 95 % confidence level. The fossil wood was collected in the southern region of Brazil. Our analysis of the fossils' tree-ring width series power spectra showed characteristics similar to the modern araucaria tree, with a noticeable decadal periodicity. Assuming that the Earth’s climate responds to solar variability and that responses did not vary significantly over the last ~200 million years, we conclude that the solar–climate connection was likely present during the Mesozoic era.