We modeled crustal and lithospheric thickness variation as well as the variations in temperature, composition, S wave seismic velocity, and density of the lithosphere beneath the Saharan Metacraton (SMC) applying an interdisciplinary 3‐D modeling. Regardless of the limited data set, we aimed at consistent imaging of the SMC lithospheric structure by combining independent data sets to better understand the evolution of the metacraton. We considered that the SMC was once an intact Archean‐Paleoproterozoic craton but was metacratonized during the Neoproterozoic due to partial loss of its subcontinental lithospheric mantle (SCLM) during collisional processes along its margin. This has permitted the preservation of three cratonic remnants (Murzuq, Al‐Kufrah, and Chad) within the metacraton. These cratonic remnants are overlain by Paleozoic‐Mesozoic sedimentary basins (Murzuq, Al‐Kufrah, and Chad), which are separated by topographic swells associated with the Hoggar Swell, Tibesti Massif, and Darfur Dome Cenozoic volcanism. The three cratonic remnants are underlain by a relatively thicker lithosphere compared to the surrounding SMC, with the thickest located beneath Al‐Kufrah reaching 200 km. Also, the SCLM beneath Al‐Kufrah cratonic remnant is significantly colder and denser. Modeling of the lithosphere beneath the Chad and Murzuq Basins yielded a complex density and temperature distribution pattern, with lower values than beneath the Tibesti Massif. Further, our modeling indicated a uniform and moderately depleted mantle composition beneath the SMC. The presence of a relatively thinner lithosphere beneath the noncratonic regions of the SMC is attributed with several tectonic events, including partial SCLM delamination during the Neoproterozoic, Mesozoic‐Cenozoic rifting, and Cenozoic volcanism.
Regional gravity field modelling by means of remove-compute-restore procedure is nowadays widely applied in different contexts: it is the most used technique for regional gravimetric geoid determination, and it is also used in exploration geophysics to predict grids of gravity anomalies (Bouguer, free-air, isostatic, etc.), which are useful to understand and map geological structures in a specific region. Considering this last application, due to the required accuracy and resolution, airborne gravity observations are usually adopted. However, due to the relatively high acquisition velocity, presence of atmospheric turbulence, aircraft vibration, instrumental drift, etc., airborne data are usually contaminated by a very high observation error. For this reason, a proper procedure to filter the raw observations in both the low and high frequencies should be applied to recover valuable information. In this work, a software to filter and grid raw airborne observations is presented: the proposed solution consists in a combination of an along-track Wiener filter and a classical Least Squares Collocation technique. Basically, the proposed procedure is an adaptation to airborne gravimetry of the Space-Wise approach, developed by Politecnico di Milano to process data coming from the ESA satellite mission GOCE. Among the main differences with respect to the satellite application of this approach, there is the fact that, while in processing GOCE data the stochastic characteristics of the observation error can be considered a-priori well known, in airborne gravimetry, due to the complex environment in which the observations are acquired, these characteristics are unknown and should be retrieved from the dataset itself. The presented solution is suited for airborne data analysis in order to be able to quickly filter and grid gravity observations in an easy way. Some innovative theoretical aspects focusing in particular on the theoretical covariance modelling are presented too. In the end, the goodness of the procedure is evaluated by means of a test on real data retrieving the gravitational signal with a predicted accuracy of about 0.4 mGal
In this work, a record of 16 channels, with future channel spacing in the telecommunication standardization sector of the International Telecommunications Union G.694.1 (ITU-T G.694.1) for Dense Wavelength Division Multiplexing (DWDM) (i.e., 12.5 GHz), is simulated and tested. This work is done to realize a proposed high capacity DWDM-Passive Optical Network (DWDM-PON) system. These specifications are associated with enhancing the upstream (US) capacity to 2.5 Gb/s over a 25 km Single-Mode Fiber (SMF) transmission and producing a noteworthy average Bit Error Rate (BER) of 10 −12 during the system's evaluation process. These performance indicators are achieved through design optimization of the cross-seeding Rayleigh Backscattering (RB) elimination technique. This optimization has successfully reduced (compared to the cross-seeding related literature) the simulated DWDM-PON components and maintained an effective Rayleigh Backscattering elimination with the aforementioned system's performance enhancement and capacity enlargement.(1) injection-locked Fabry-Perot Lasers (FP-Ls) [5,6], (2) Reflective Semiconductor Optical Amplifiers (RSOAs) [7], and (3) Semiconductor Optical Amplifier (SOAs) with Reflective Electro-Absorption Modulators (R-EAMs) [8]. However, reflective transmitters that utilize FP-L require polarization and temperature control, which add complexity [5]. Those that use RSOAs suffer from a limited bit ratẽ 1.25 Gb/s due to internal noises and nonlinearities [9]. Finally, any colorless ONU that uses SOA with R-EAM (SOA-REAM) suffers from chromatic dispersion and high interference in the signal due to the wide bandwidth of R-EAM [10]. As a result, the reflective transmitter technique generates a high level of Rayleigh Backscattering (RB), which affects the signal received at the CO [11]. Before reviewing the DWDM-PON system's key requirements, it is useful to conduct a review of the origins and effects of RB. Rayleigh Scattering is a dominant intrinsic loss mechanism in the low-absorption window between the ultraviolet and infrared absorption tails. It results from random inhomogeneities occurring on a small scale compared to the operating wavelength. These inhomogeneities act as refractive index fluctuations (or induced dipole moment) within the fiber and arise from density and compositional variations, which are frozen into the glass lattice upon cooling [12,13].Optical losses, due to RB in optical fibers, have caused considerable problems. Some examples of these problems include lowering the allowable bit rate, increasing the system's noise levels, and minimizing the transmission distances [14][15][16][17]. Detailed examples and deeper analyses can be found for bi-directional wavelength-reuse fiber systems and WDM-PON Systems in [14][15][16][17]. To the author's best knowledge, this work is one of the rare studies that considers RB for DWDM-PON systems with remarkable operating conditions. Now, methods for satisfying the most critical requirements for DWDM-PON systems (i.e., a low-cost ONU colorless o...
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