Investigating the use of UAV systems for photogrammetric applications : a case study of Ramla Bay (Gozo, Malta)

In this study, we present the 3D digital model of Ramla Bay (Gozo) obtained by using photograms taken from drones. The high-resolution 3D model of Ramla Bay allowed the construction of a detailed Digital Elevation Model (DEM). Comparison of an earlier LIDAR data derived DEM (ERDF 156 Data, 2013) and the photogrammetric DEM developed in this study allowed to make preliminary observations regarding the potential evolution of the coastal area over the last 5 years. This study serves as a proof of concept to demonstrate that coastal evolution can be quantitatively analysed in terms of changes of the sand dune systems. Furthermore, the technique used in this paper represents a good compromise in terms of cost effectiveness and a valid substitute for laser scanner survey. It is also useful for monitoring the dynamics of the beach-dune system and the characterization of the coast for the mitigation of coastal erosion.peer-reviewe

EFFICACY OF PNEUMATIC DILATATION FOR THE TREATMENT OF IDIOPATIC ACHALASIA: A SINGLE-CENTRE EXPERIENCE

Pneumatic dilatation (PD) and surgical miotomy (SM) are presentely the best treastments for untreated achalasia, with similar efficacy. There is no information on the relative efficacy of PD in younger compared to older patients. Aim of our study was to compare success rate and safety of PD patients under fifty years old in our Unit with graded PD under fluoroscopic view. Five male and 15 female with a median age of 47 years were treated. Twelve patients were less than fifthy years old (group I) while 8 were older (group II). Median dysphagia questionnaire score was 14 and 13 in group I and II respectively. Technical success was achieved in all patients. Seven patients were previously treated through other techniques. In group I all patients achieved a complete remission of symptoms with significant decrease of the dysphagia questionnaire (3). in group II all patients achieved a complete remissionof symptoms with significant decrease of the dysphagia questionnaire score (4,5) but 3 of them repeated the procedure. In boths groups the efficacy of the dilation was radiologically confirmed. Neither early nor late complications were reported in either groups. In our experience PD was an effective and safe procedure both in young and old patients although the older group had more recurrences, all successfully re-dilated

Land cover change and fast soil degradation in the East African Rift Valley, Kenya

The Kerio Valley (Elgeyo-Marakwet and Baringo county, Kenya) is part of the East African Rift Valley system; it is characterized by steep slopes and a large elevation gradient between the plateau and the valley floor. The study area is the Kimwarer river basin, between 2838 and 1202 m a.s.l.. The summit plateau is above 2500-2700 m a.s.sl., characterized by rolling hills and a cool/humid climate; potential vegetation is montane rainforest; most of it has been transformed into corn, tea and hay fields. Below the plateau, the Elgeyo Escarpment is steep and dissected by V-shaped valleys and active/inactive landslide scars, descending to 1300-1400 m a.s.l.. The potential vegetation is montane rainforest above ~2000 m, deciduous Acacia woods/shrublands below. Cultivations are increasingly substituting forests even in the steepest slopes. The Kerio Valley floor includes floodplains and low-steepness alluvial fans; the potential Acacia savannah has been mostly substituted by corn crops, later abandoned because of extreme soil erosion, resulting in a semi-desert habitat. The soil types follow elevation and topography: organic carbon-rich Ferralsols are common on the high plateau, stony Umbrisols, Cambisols, Phaeozems are common in the high slopes of the escarpment, while Kastanozems are common in the low slopes; shallow remnants of Plinthosols and Vertisols are common in the valley floor. Land-use change in the Kerio Valley floor happened during the ‘80s, when local people moved from pastoralism to agriculture; original Acacia savannah was disrupted by ploughing to permit cropping during the rainy seasons. Soil maps performed during that period describe soils as Ferralsols, with rooting depth limitations by lateritic crusts below 1-2 m. At present, the lateritic crust outcrops over large surfaces, and 2-5 m deep, 10-20 m large gullies cover >50% of the surface. The cultivations are thus being abandoned. The soil loss might be estimated conservatively ~100 t/ha/y; this is an extremely high value considering the almost flat surface. The average soil loss calculated by an adapted RUSLE method is 51 t/ha/y; there is an important underestimation by the model. The erosion is much weaker in the upland Ferralsols, where soil is protected by high organic matter content and by the high productivity of the vegetation, helped by the absence of a truly dry season and the smaller evapotranspiration. On the slopes of the escarpment, deforestation happened mostly after 2010, as visible from aerial photos. Umbrisols with thick A horizons are dominant under natural vegetation, but are not observed in deforested areas, evidencing a fast loss of the 30-50 cm A horizon (>320 t/ha/y). Deeper, less resistant horizons are exposed, and rills, gullies and mudflows develop after most rainstorms, with variations depending on soil type. The RUSLE model predicts average losses ~350 t/ha/y, with much higher values on the steep slopes

Accumulation of cross-channel non-linear interference in dispersion-managed and disaggregated optical network segment

We evaluate the generation of the cross-channel interference (XCI) for coherent transmission through a variety of dispersion-managed segments in a disaggregated optical network framework, using split-step Fourier method (SSFM) simulations and an implementation of the Gaussian noise (GN) model. We observe that the small inline residual dispersion remaining after each span affects the accumulation of the XCI, causing GN model predictions to no longer be conservative. We find an asymptotic upper bound to this additional accumulation, providing a worst-case prediction, and observe that this depends upon the residual dispersion within the link. This upper bound scales similarly to the self-channel interference (SCI) accumulation, and is well characterized by the parameters of the underlying fiber spans and the transmitted signals.Comment: 11 pages, 5 figure

Quality of Transmission Estimation for Planning of Disaggregated Optical Networks

Modern optical networks depend upon advanced software-defined networking (SDN) technologies, which in turn rely on a network abstraction to infer the quality of transmission (QoT). In general, the QoT estimation is based upon the generalized signal-to-noise ratio (GSNR), which takes into account the ASE noise, cross-phase modulation (XPM) and self-phase modulation (SPM) components of the nonlinear interference (NLI). Uniquely, the SPM accumulates coherently, causing the total amount of SNR degradation to depend upon the physical lightpath (LP) history, preventing a fully disaggregated GSNR degradation evaluation. As the current signal symbol rate are increasing, the SPM will provide a progressively more significant contribution to the SNR degradation. We propose a method to evaluate the equivalent SPM component of the NLI that is generated in each fiber span within an optical line system (OLS), independent of the history or configuration of the optical network

Modelling non-linear interference in non-periodic and disaggregated optical network segments

We investigate the generation of nonlinear interference (NLI) within two disaggregated transmission scenarios, each considering a chain of three distinct optical line systems that contain fibers with different dispersion values, with 400G-ZR+ 64 GBd transmission simulated using the split-step Fourier method. Firstly, by separating the NLI into its main constituents: the self- and cross-phase modulations, we investigate the impact of accumulated dispersion upon NLI generation and compensate for the coherent accumulation of the former to produce a model that is fully spectrally and spatially separable, including for alien wavelengths. Considering ideal and optimized in-line amplification, we calculate the amplified spontaneous emission noise and combine this value with the recovered NLI to obtain the generalized signal-to-noise ratio. We show that this disaggregated model provides accurate and conservative results for both transmission scenarios, showing that abstracting these signals with a Gaussian noise approximation always results in a conservative prediction, even for non-uniform fiber dispersion scenarios

Simulative assessment of non-linear interference generation within disaggregated optical line systems

Lightpaths within optical line systems (OLS)s that deploy coherent optical technologies are mainly impaired by two additive Gaussian disturbances: the amplified spontaneous emission (ASE) noise from the optical amplifiers and the non-linear interference (NLI) from fiber propagation, together with some amount of phase noise, typically compensated for bythe carrier phase estimator module within the digital signal processing (DSP) unit. The main obstacle in accurately modelling the physical layer of a disaggregated optical network arises from the spatially-coherent and spectrally-aggregated general behavior of the NLI generation.Within this paper, we perform an accurate split-step Fourier method (SSFM) physical layer simulation campaign over a wide range of fiber chromatic dispersion values that range from 2to 16.7 ps / (nm·km) and channel symbol rates from 32 GBd to 85 GBd. For all the explored scenarios, we first show that the NLI generation in an OLS can be spectrally disaggregated in a practical manner by considering a superposition of self-channel (SC) and cross-channel (XC) NLI components only. Secondly, by considering the span-by-span generalized signal-to-noise ratio (GSNR) deterioration, we show that the XC-NLI accumulation components can also be considered as spatially disaggregated, leaving the SC-NLI as the only spatial coherency contribution. Consequently, by appropriately managing these coherent NLI contributions, we find that it is possible to produce a conservative physical layer model that is both spectrally and spatially disaggregated