1,720,991 research outputs found
Improved PPP performance in regional networks
No full textIt has been demonstrated that precise point positioning (PPP) is a powerful tool in geodetic and geodynamic applications. As is known, it provides solutions in the reference system of the satellite orbits. We focuses on the strategy to transform PPP solutions into the International Terrestrial Reference System (ITRS) by applying a set of local Helmert transformation parameters obtained from a regional network rather than using global parameters.
In order to carry out this test, a regional network composed of 14 stations was analyzed using GIPSYOASIS II software, over a period of 6 years. Two solutions differently aligned to the ITRS were compared in terms of accuracy, scattering, frequency content and local movements.
One solution is aligned to IGb08 through the X-files provided by JPL, while the other is aligned to the European reference frame densification of IGb08 using customized regional X-files. Therefore, both are updated realizations of the ITRS. The test shows that a regional, instead of a
global, alignment to the ITRS can significantly improve the repeatability of the solutions. A small improvement can also be found in terms of agreement with the regional densification of IGb08. The analysis of the signal content in the differently aligned time series allowed some differences to be found, in terms of both frequency and magnitude. These differences are mainly due to an evident common signal that is defined for the whole area and which is removed when using regional alignment. Finally, residual scattering was calculated after removing the modeled signals from each time series, which results in a scatter being significantly smaller for the regional solution than for the global solution. In order to obtain these results, the choice of the reference stations is a major question and therefore discussed in detail
A multi-image super-resolution algorithm applied to thermal imagery
No full textAlthough thermal imaging is a widely used technique in many applications and is under continuous development, one of its limits is the relatively coarse spatial resolution. Nevertheless, in the last years, a number of super-resolution algorithms have been developed which allow to enhance the resolution of the images. They can be divided in two main different categories: single-image or multiple image-based algorithms. In this work, a multiple image-based algorithm for the super-resolution was implemented, tested and applied to terrestrial thermal imaging with the aim to overcome the limitation of the low resolution. In particular, the method relies on the use of many images acquired from slightly different positions to obtain, thanks to the redundancy of observations, a super-resolution frame having an upsampling factor of four. Several tests were performed on synthetic datasets, and the accuracy of the obtained super-resolution images was investigated. Moreover, an original algorithm capable to identify gross errors during the image registration phase, which is one of the crucial phases, is presented and its reliability assessed. Results showed the effectiveness of the proposed method on both common visible images and thermal infrared ones, since discrepancies between reconstructed and reference values are reduced by 18 and 25% respectively, when compared with a conventional bicubic algorithm. Finally, the proposed method was tested on a case study concerning the thermal survey of the façade of a historical building in Bologna (Palazzo D’Accursio). A dataset of real thermal frames was acquired and a super-resolution image of the subject was generated through the developed algorithm. Strengths and weaknesses of the method were analysed and discussed in the paper
Study on the accuracy of Multi-GNSS PPP for different observing sessions time spans using PRIDE PPP-AR open-source software package
Full text linkThe Precise Point Positioning (PPP) approach to GNSS observables is widely used for processing data from permanent stations, providing highly precise coordinates. However, the performance of PPP for observation sessions shorter than 24 h has not yet been thoroughly investigated in the case of multi-constellation acquisitions. In recent years, the PRIDE PPP-AR software package has been made freely available. Since it includes a graphical user interface (GUI) version that runs under Windows, it can also be easily used by technical surveyors aiming to process data acquired from a single GNSS receiver. This is particularly valuable for surveys conducted in areas lacking dense geodetic infrastructures or reliable augmentation services. In this paper, based on a wide and consistent dataset, the coordinate precision obtained from observation sessions ranging from 30 min to 24 h processed with PRIDE PPP-AR is analyzed. In addition to multi-constellation GNSS data (GPS + Galileo + GLONASS + BeiDou), independent GPS-only and Galileo-only processing was also evaluated. Furthermore, the reliability of the formal errors provided by the software was examined, as these represent the only available information for assessing coordinate quality in surveys that lack geometric redundancy. While several online PPP services already exist, PRIDE PPP-AR overcomes common limitations related to the number of processed files and the choice of GNSS constellations. The results show that two-hour observation sessions can reliably achieve horizontal coordinate accuracy within 2 cm and vertical accuracy within 5 cm, whereas 30-minute sessions are suitable for applications requiring 5–10 cm accuracy
Monitoring of the Garisenda Tower through GNSS using advanced approaches toward the frame of reference stations.
Full text linkLow-cost GNSS sensors for monitoring applications
Full text linkAmong several instruments and techniques that can be used for monitoring purposes, GNSS technology has undergone a fast evolution and provides a large choice of solutions. Despite the best performances can be achieved by using double frequency geodetic receivers, capable to maintain high precisions even for wide-scale monitoring, in the recent years, several interesting solutions were presented in the low-cost market. In this work, a monitoring system based on a couple of low-cost GNSS receivers has been developed and tested in the field (Ponte Motta in Cavezzo - Modena, Italy). The two receivers were positioned about 50 m from each other and data were acquired at 1-Hz frequency. The position solutions were calculated both in post processing, through two different free and open-source software packages, and using an embedded RTK processor. The analysis aims to assess on one hand the capability of the system to perform the monitoring of slow displacements with the best possible precision, and, on the other hand, the performances of the real-time solutions that can be used for early warning purposes. The precisions evidenced by the tests show that such low-cost instrumentation can be used for many monitoring purposes, especially considering the cost that is about a tenth of geodetic instruments
A priori estimation of radar satellite interferometry’s sensitivity for landslide monitoring in the Italian Emilia-Romagna region
Full text linkThe InSAR technique is known to be a powerful tool for precise monitoring of wide areas in terms of displacements. It is conceivable to also use this technique to monitor landslide areas, but geometrical distortions due to ground morphology and land cover could make InSAR processing ineffective for such applications. Because of the computational burden of InSAR processing, it is important to have preliminary knowledge about the possible suitability of the technique for the inspected area before acquiring and processing the data. This paper aims to perform a preliminary analysis of the InSAR sensitivity for the specific case of landslide monitoring. A new approach is proposed considering aspects specific to landslide displacements, which are basically tangent to the slope direction. Pre-processed coherence maps were used to account for the impact of land cover. The whole analysis can be carried out without acquiring cumbersome SAR datasets and can be used as a preliminary step. The Italian Emilia-Romagna region has been considered as the study area, with landslide areas accounting for more than 12% of its territory. The outcomes show that the inspected area has favourable morphological conditions, mainly thanks to its mild slopes and the limited number of landslides facing north, but the land cover has a strong negative impact on the InSAR sensitivity. Nevertheless, 7.5% of the landslide areas have promising conditions for monitoring using radar interferometry
Precision of PPP as a Function of the Observing-Session Duration
No full textOver the past decade, precise point positioning (PPP) has become a tool widely used in many Global Navigation Satellite Syste applications and the performance levels of the method are often close to those that can be achieved through a differenced approach. The aim of this paper is to analyze the dependency of the precision of a PPP solution output from the GIPSY-OASIS II software on the observing-session durations. In detail, starting from real data acquisitions spanning 24, 12, 6, 3 h, 1 h, and 1⁄2 an hour, all processed through the PPP, a continuous function has been defined and the related coefficients have been estimated. The original dataset consists of daily RINEX files provided from 44 sites of both International GNSS Service (IGS) and European Permanent Network (EPN) permanent networks acquired over one year. Each RINEX file was split into several shorter files according to the above listed time spans and processed by using GIPSY-OASIS II together with jet propulsion laboratory (JPL) precise post-processed products. The uncertainty of the proposed function was also estimated and a complete analysis of its compliance with the data sample has been provided. The estimated model is demonstrated to reach a millimeter accuracy level within a statistical confidence level of 99% using the experimental data
Georeferenced 3D model of the rock pinnacle "Campanile di Val Montanaia" from Structure from Motion
No full textWe produced a high-quality 3D model of a rocky pinnacle in the Dolomites (Italy), the "Campanile di Val Montanaia". The survey was performed by means of a lightweight Unmanned Aerial Vehicle (UAV) and by climbing the pinnacle to collect Ground Control Points (GCPs) coordinates. All data has been processed using Structure from Motion (SfM) technique. We share a georeferenced 3D mesh of the pinnacle aligned to ITRF2014 and delivered using projected coordinates UTM zone 33N (EPSG:32633). The dataset is associated with the following publication submitted to Remote Sensing: A Laboratory for the Integration of Geomatic and Geomechanical Data: The Rock Pinnacle "Campanile di Val Montanaia". Remote Sens. 2023, 15, 4854. https://doi.org/10.3390/rs1519485
A PPP kinematic application on historical GPS data: the reprocessing of the ITASE98-99 Antarctica mission height profiles
Full text linkThe analysis of altimetric profiles in Antarctica and their evolution over the years is a sensitive topic for the scientific community since it helps understand the effects of climate change that the continent undergoes. Different geomatic techniques, including the GNSS technology, can be employed to obtain altimetric profiles. However, the GNSS differenced approaches, such as the Post Processing Kinematic, are hardly usable to define long profiles in Antarctica because of the low number of CORS stations. In these conditions, the Precise Point Positioning (PPP) approach is a valid alternative to avoid processing very long baselines. The aim of this article is to define a standard procedure for the processing of historical GPS data, thanks to the availability of a dataset from the International Trans-Antarctic Scientific Expedition, which took place between 1998 and 1999 (ITASE98-99). This expedition focused on mapping the Antarctic territory, subdividing it by nations of influence, using geophysical and geodetic technologies, including GPS. The altimetric profiles had already been calculated in 2002 by the Geomatics group of the University of Bologna using the Gipsy-OASIS II software. In this work, the new version of the JPL software, GipsyX, is used to apply the newly implemented models and reprocessed products. The calibration of the processing parameters leading to the final PPP solution is described in the paper, including details on the implementation of a post-processing filtering procedure. The average a posteriori elevation error is 4.6 cm, while 99% of them are within 27 cm. The comparison of the new results to both the previous processing and the REMA elevation model shown that about double the number of solutions are now available, meter-level elevation spikes have been avoided, and a half meter bias is now reduced to a few centimeters. Given the almost 15 years difference between the 1999.0 expedition epoch and the REMA reference epoch, the obtained results can be used to study accumulation/erosion effects on the Antarctica ice sheet
Monitoring of the Italian GNSS Geodetic Reference Frame
No full textIn 2011, Italy established a new geodetic reference system, the European Terrestrial Reference System 1989 (ETRS89),
which was based upon the ETRF2000 reference frame at epoch 2008.0. In order to maintain this reference, the IGMI
defined a permanent GNSS network within the EPN densification project, known as the “Rete Dinamica Nazionale”
(RDN) and composed of 99 tracking stations located in and around Italy. Eight years of data are now available and the
aim of this work is to estimate the velocities of the official RDN sites. It was necessary to pre-analyze the data
accurately because of the incomplete maintenance of the associated repository. The network was calculated using a PPP
approach and applying the GIPSY-OASIS II software package, and the solutions were aligned to ITRS using a
customized procedure. After they were transformed into ETRF2000, the time series of the solutions were properly
analyzed to find discontinuities and solve jumps caused by earthquakes and instrumental changes. Results highlighted
the residual velocities with respect to ETRS89, which can reach 5 mm/year in some areas. The velocity field is shown
to be very inhomogeneous, with clusters of sites presenting very different behaviours
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