465 research outputs found
Morphological Analysis of the Polarized Synchrotron Emission with WMAP and Planck
The bright polarized synchrotron emission, away from the Galactic plane,
originates mostly from filamentary structures. We implement a filament finder
algorithm which allows the detection of bright elongated structures in
polarized intensity maps. We analyse the sky at 23 and 30 GHz as observed
respectively by WMAP and Planck. We identify 19 filaments, 13 of which have
been previously observed. For each filament, we study the polarization
fraction, finding values typically larger than for the areas outside the
filaments, excluding the Galactic plane, and a fraction of about 30% is reached
in two filaments. We study the polarization spectral indices of the filaments,
and find a spectral index consistent with the values found in previous analysis
(about -3.1) for more diffuse regions. Decomposing the polarization signals
into the and families, we find that most of the filaments are detected
in , but not in . We then focus on understanding the statistical
properties of the diffuse regions of the synchrotron emission at 23 GHz. Using
Minkowski functionals and tensors, we analyse the non-Gaussianity and
statistical isotropy of the polarized intensity maps. For a sky coverage
corresponding to 80% of the fainter emission, and on scales smaller than 6
degrees (), the deviations from Gaussianity and isotropy are
significantly higher than 3. The level of deviation decreases for
smaller scales, however, it remains significantly high for the lowest analised
scale (). When 60% sky coverage is analysed, we find that the
deviations never exceed 3. Finally, we present a simple data-driven
model to generate non-Gaussian and anisotropic simulations of the synchrotron
polarized emission. The simulations are fitted in order to match the spectral
and statistical properties of the faintest 80% sky coverage of the data maps.Comment: 35 pages, 17 figure
25 years of satellite InSAR monitoring of ground instability and coastal geohazards in the archaeological site of Capo Colonna, Italy
For centuries the promontory of Capo Colonna in Calabria region, southern Italy, experienced land subsidence and coastline retreat to an extent that the archaeological ruins of the ancient Greek sanctuary are currently under threat of cliff failure, toppling and irreversible loss. Gas extraction in nearby wells is a further anthropogenic element to account for at the regional scale. Exploiting an unprecedented satellite Synthetic Aperture Radar (SAR) time series including ERS-1/2, ENVISAT, TerraSAR-X, COSMO-SkyMed and Sentinel-1A data stacks acquired between 1992 and 2016, this paper presents the first and most complete Interferometric SAR (InSAR) baseline assessment of land subsidence and coastal processes affecting Capo Colonna. We analyse the regional displacement trends, the correlation between vertical displacements with gas extraction volumes, the impact on stability of the archaeological heritage, and the coastal geohazard susceptibility. In the last 25 years, the land has subsided uninterruptedly, with highest annual line-of-sight deformation rates ranging between -15 and -20 mm/year in 2011-2014. The installation of 40 pairs of corner reflectors along the northern coastline and within the archaeological park resulted in an improved imaging capability and higher density of measurement points. This proved to be beneficial for the ground stability assessment of recent archaeological excavations, in an area where field surveying in November 2015 highlighted new events of cliff failure. The conceptual model developed suggests that combining InSAR results, geomorphological assessments and inventorying of wave-storms will contribute to unveil the complexity of coastal geohazards in Capo Colonna. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
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