Search

The study aims to evaluate ground deformations in a vast area characterized by the coexistence of intense anthropic activities and offshore natural gas production. Onshore subsidence can be studied by GNSS, InSAR, high precision leveling and extensometers that provide broad datasets for a fully integrated description of the phenomenon. At present, seafloor subsidence monitoring cannot be carried out by high precision leveling, and GNSS is the only reliable method, implemented by means of permanent stations installed on offshore hydrocarbon production facilities. In the Northern/Central Adriatic Sea gas production platforms, GNSS data are recorded since more than 15 years, allowing to estimate not only the average subsidence of the platform/seafloor, but also possible velocity variations due to underground fluids withdrawal. This study shows the comparison of 22 offshore GNSS permanent stations located in the study area. Raw data have been processed with two different software packages (GIPSY-OASIS and GAMIT-GLOBK) based on different approaches and considering different boundary conditions of geodetic and/or modeling nature. Main results point out the high accuracy of the GNSS technology considering also the impact of data processing. Finally, at selected permanent stations we also performed a comparison of results obtained by GNSS, InSAR and high precision leveling.

GNSS technology has become widely used for monitoring purposes. The high precisions nowadays available have made the technique suitable also for the monitoring of structures that are usually affected by very small displacements. In this work we investigate the issue concerning the monitoring of a tall structure such as the Garisenda tower, which lay in the Bologna city centre, by using GNSS data gathered by a permanent station placed on its top. We consider the need to investigate the variations in the leaning of the structure, therefore also the position of the ground at the bottom of the structure should be known. Unfortunately it is not possible to place a GNSS receiver under a tall structure in urban context because of the too poor sky visibility. A solution would be to choose another permanent station located as close as possible assuming its behaviour coherent with the ground under the monitored structure. This hypothesis has proven not to be verified in the analysed case, where four permanent stations located within few kilometres far from the Garisenda tower were available. Therefore a strategy to combine data from the five permanent stations using a uniform strain model was developed in order to define a reference to which compare the positions given by the GNSS sensor placed on the top of the tower. The impact of such strategy will be shown and discussed in terms of mean variation of the leaning of the tower over a period of about four years.

GNSS real-time techniques and UAV photogrammetry can be alternative methods for the monitoring of sand beaches. This activity is particularly important in environments such as the Emilia-Romagna coastline. In this paper, two couples of surveys (year 2019 and 2020) performed using GNSS or a low-cost UAV equipment over a common area were compared in order to analyse: point-wise height differences, profile shapes along defined sections, and volumes variations over time. Both surveys were aligned to the same reference benchmark through GNSS measurements. The highest discrepancies between the two surveying methods (tens of cm) were found in vegetated areas and along the shoreline, otherwise, the height differences are mainly within the 10 cm level. In terms of volumes, excluding the most critical areas, differences close to zero can be found. Obtained results show that GNSS and UAV photogrammetry provides similar results, at least for quite flat terrains and when decimetre-level accuracy is required.

The relatively poor spatial resolution of thermal images is a limitation for many thermal remote sensing applications. A possible solution to mitigate this problem is super-resolution, which should preserve the radiometric content of the original data and should be applied to both the cases where a single image or multiple images of the target surface are available. In this perspective, we propose a new super-resolution algorithm, which can handle either single or multiple images. It is based on a total variation regularization approach and implements a fully automated choice of all the parameters, without any training dataset nor a priori information. Through simulations, the accuracy of the generated super-resolution images was assessed, in terms of both global statistical indicators and analysis of temperature errors at hot and cold spots. The algorithm was tested and applied to aerial and terrestrial thermal images. Results and comparisons with state-of-the-art methods confirmed an excellent compromise between the quality of the high-resolution images obtained and the required computational time.

Emilia-Romagna coast consists of 110km of low and sandy beaches, which are particularly exposed to coastal erosion. Among different defence projects, the current trend is going towards soft interventions, such as beach nourishment. In 2016, the third intervention of “Security projects through submarine sand nourishment for critical areas of the regional coastline” was completed. This paper concerns the analysis of the eight coastal stretches involved by this project. A Monitoring Plan for the years 2017 and 2018 has been arranged to evaluate the evolution of each beach and the intervention effectiveness. Morphological variations in terms of shoreline, height, beach profiles and accumulated or eroded volumes have been evaluated by comparing surveys performed on each beach at different times. In the specific case of this project, the presence of a new geodetic infrastructure along Emilia-Romagna coast, the Coastal Geodetic Network (RGC), ensured advantages to surveys’ realization. All the observed results show good evolutions from a general point of view, even if it is difficult to deduce a single trend for the eight beaches. On the other hand, the increasing availability and spatial coverage of data from monitoring surveys could provide powerful instruments for coastal studies. This paper confirms monitoring activities as an efficient way to evaluate beaches’ morphological changes and coastal defence intervention effectiveness.

The Garisenda tower in Bologna is a symbol of the city and one of the most valuable heritages of the medieval age. The tower is leaning markedly since the XIV century because of a foundation failure and its stability is nowadays under constant monitoring through many sensors. In 2013 a GNSS permanent station was installed on the top of the tower with the aim to test the satellite technology for this particular kind of structural monitoring. Being the leaning of the Garisenda the subject of the investigation and being the sensor placed on its top, one fundamental hypothesis is the stationarity of the ground under the tower with respect to the reference system used for the GNSS measures. This hypothesis has demonstrated to be unreliable considered the high precision of the survey and the Earth crust dynamics, therefore opening interesting issues concerning the reference to be used in such kind of monitoring. The proposed solution rely on a strain model of the area surrounding the Garisenda tower, estimated using data from four other GNSS permanent stations already present in Bologna. The method is described and results are shown in terms of trend over time of the Garisenda's leaning. Nevertheless, the methodology can be generalized for every kind of structural monitoring based on GNSS data for which millimetre level of precision is needed.

GNSS technology is still not considered as a suitable method for structural monitoring because of its relatively low precision, despite the increase in acquisition frequencies. This paper aims to evaluate a strategy for filtering a daily kinematic GNSS solution using a movement smoothing model based on the observations of previous days, so as to obtain a less scattered solution. A test was conducted with a permanent GNSS station located on top of the medieval Garisenda tower in Bologna (Italy), as it is an important part of the city’s cultural heritage and a reliable test site. Because of the presence of the adjacent Asinelli tower, which is taller than the Garisenda, sky visibility is not optimal here, and for this reason a particular sequential filtering can be adopted in order to obtain more accurate solutions. The test was performed using RTKLIB software to calculate 1 Hz baselines between the test station and a master one located on a stable area about one kilometer away from the tower. In order to obtain reliable results, several variables were considered both in the data processing phase and in defining the filter. All results are reported and discussed in detail in the paper. The test results reveal a reduction in scatter of about 20% in the filtered kinematic time series, especially in weaker geodetic components.

GNSS is one of the most used technique to monitor Reference Frame, Plate motion, Landslides, Structures, etc... Data acquired by GNSS satellites have to be processed considering models, approaches and strategies which are influencing the final results and, if wrongly done, may introduce biases. In this work the Precise Point Positioning (PPP) approach for GNSS data processing has been considered and investigated. As well-known PPP is faster and more flexible compared to the carrier phase differenced approach. On the other hand the differenced approach has been generally characterized by a better repeatability, especially for quite small baselines. Until few years ago one of the major limits of PPP was the impossibility to resolve the ambiguity as integer but nowadays some methods are available to resolve this aspect expecting an increasing of the precision. Starting from two subsets of the IGS Tracking network (one located in Europe and composed by 16 stations around Italy and another one, composed by 9 stations and located in Antarctica) processed respectively for 11 and 3 years, the impact of some data processing strategies has been considered. For both the networks different kind of solutions has been obtained, each one using more refined strategies, considering the ambiguity phase resolution, the possibility to frame the solution using global transformation parameters (provided by JPL), or framing the solution using regional transformation parameters. Furthermore, with the aim to evaluate in polar regions the impact of different tropospheric models in GNSS solutions the Antarctica network has been processed also considering the Vienna Mapping function instead of the Niell MF. The results will be synthetized by two parameters which are accuracy and precision: accuracy has been obtained comparing each solution with the reference ITRF2008 solution (ITRF2008-TRF-IGS.SNX.gz) and precision has been estimated considering the scattering of the solutions (time series) around a straight line obtained by a least square approach.