Papers by Giovanna Venuti
The knowledge of tropospheric water vapor distribution can significantly improve the accuracy of ... more The knowledge of tropospheric water vapor distribution can significantly improve the accuracy of Numerical Weather Prediction (NWP) models. The present work proposes an automatic and fast procedure for generating reliable water vapor products from the synergic use of Sentinel-1 Synthetic Aperture Radar (SAR) imagery and Global Navigation Satellite System (GNSS) observations. Moreover, a compression method able to drastically reduce, without significant accuracy loss, the water vapor dataset dimension has been implemented to facilitate the sharing through cloud services. The activities have been carried in the EU H2020 TWIGA project framework, aimed at providing water vapor maps at Technology Readiness Level 7. .
Applied Geomatics
The Italian official height system is defined through a high precision levelling network establis... more The Italian official height system is defined through a high precision levelling network established and maintained by the Istituto Geografico Militare - IGM. During the last 20 years, IGM has performed levelling campaigns on almost the whole peninsular area of Italy with the aim of both densifying the existing network and updating the reference heights. This paper reports about the procedure applied to correct the levelling observations for the gravity effects and the assessment on the results. The needed gravity values were predicted from the Italian gravity dataset (IGD), and both from EGM2008 and XGM2019e high resolution global gravity models. A new formulation of the normal correction as well as the standard orthometric correction were applied. The IGD derived corrections proved to be effective by reducing the misclosure error of critical loops below the tolerance level. Gravity data derived from EGM2008 and XGM2019e proved to be too poor for the correction purposes, as it was ...
EGU General Assembly Conference Abstracts, Apr 1, 2019
Living Planet Symposium, 2019
In view of the anniversary of Martin Hotine, the authors have thought to honour his memory writin... more In view of the anniversary of Martin Hotine, the authors have thought to honour his memory writing a paper on a subject related to one of his favourite items, namely the problems of map representations. The point of view which is pursued here however is non-traditional and follows some research conducted at Politecnico di Milano, joining the problems of various types of representations between different surfaces (conformal, equivalent and general maps) with the peculiar theory of the so-called inverse problems. We hope that the material presented here will be interesting enough to reach the goal that the authors have in mind.
Proceedings of the 21st EANN (Engineering Applications of Neural Networks) 2020 Conference, 2020
Real-world time series often present missing values due to sensor malfunctions or human errors. T... more Real-world time series often present missing values due to sensor malfunctions or human errors. Traditionally, missing values are simply omitted or reconstructed through imputation or interpolation methods. Omitting missing values may cause temporal discontinuity. Reconstruction methods, on the other hand, alter in some way the original time series. In this paper, we consider an application in the field of meteorological variables that exploits end-to-end machine learning. The idea is to entrust the task of dealing with missing values to a suitably trained recurrent neural network that completely by-passes the phase of reconstruction of missing values. A difficult case of reproduction of a rainfall field from five rain gauges in Northern Italy is used as an example, and the results are compared to those computed by more traditional methods. The proposed methodology is general-purpose and can be easily applied to every kind of spatial time series prediction problem, quite common in many environmental studies.
(2020), On the definition of the strategy to obtain absolute InSAR Zenith Total Delay maps for me... more (2020), On the definition of the strategy to obtain absolute InSAR Zenith Total Delay maps for meteorological applications where ν Δ is the model error, due to the observational uncertainties and the approximations introduced by the algorithm. In this way, once the ZTD map at the master epoch is know, it is enough to sum it to the differential ZTD measured by the InSAR to get the instantaneous ZTD map at high spatial resolution.
International Association of Geodesy Symposia, 2015
Spirit leveling and surface gravity observations can be expressed as orthometric height differenc... more Spirit leveling and surface gravity observations can be expressed as orthometric height differences plus corrections which require the knowledge of the Earth crust density. For leveling increments we can write observation equations in a linearized form, according to the standard Molodensky approach, i.e., intrinsic geodesy, depending on normal height differences plus a correction term. This term is a function of the gravity anomaly at the surface level, thus not requiring any assumption on the crust density, and of the curvature of the normal field force lines, which can not be neglected for leveling profiles directed along meridians. The present work shows how to derive these observation equations. An example is presented to verify the effectiveness of the new approach.
International Association of Geodesy Symposia
ABSTRACT The approximation of functionals of second order random fields from observations is a me... more ABSTRACT The approximation of functionals of second order random fields from observations is a method widely used in gravity field modelling. This procedure is known as collocation or Wiener – Kolmogorov technique. A drawback of this theory is the need to invert matrices (or solve systems) as large as the number of observations. In order to overcome this difficulty, it is common practice to decimate the data or to average them or (as in the case of this study) to produce more manageable gridded values. Gridding the data has sometimes the great advantage of stabilizing the solution. Once such a procedure is envisaged, several questions arise: how much information is lost in this operation? Is rigorous covariance propagation necessary in order to obtain consistent estimates? How do different approximation methods compare? Such questions find a clear formulation in the paper: some of them (the simplest ones) are answered from the theoretical point of view, while others are investigated numerically. From this study it results that no information is lost if the intermediate grid has the same dimension of the original data, or if the functionals to be predicted can be expressed as linear combinations of the gridded data. In the case of a band-limited signal, these linear relations can be exploited to obtain the final estimates from the gridded values without a second step of collocation. A similar result can be obtained even in the case of non-band limited signal, due to the low pass filtering of the signal, along with the noise, performed by the intermediate gridding.
Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique usefu... more Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique useful in many land applications, such as tectonic movements, landslide monitoring and digital elevation model extraction. One of its major limitation is the atmospheric effect, and in particular the high water vapour spatial and temporal variability which introduces an unknown delay in the signal propagation. This paper describes the approach and some results achieved in the framework of an ESA funded project devoted to the mapping of the water vapour with the aim to mitigate its effect in InSAR applications. Ground based (microwave radiometers, radiosoundings, GPS) and spaceborne observations (AMSR-E, MERIS, MODIS) of columnar water vapour were compared with Numerical Weather Prediction model runs in Central Italy during a 15-day experiment. The acquired experimental data and their comparison give a first idea of what can be done to gather valuable information on water vapour, which play a fundamental role in weather prediction and radio propagation studies.
International Association of Geodesy Symposia, 2015
Regional height systems are usually referred to the mean sea level at a reference tide gauge. As ... more Regional height systems are usually referred to the mean sea level at a reference tide gauge. As the mean sea level gravity potential changes from place to place, regional systems refer to different equipotential surfaces and the establishment of a unified datum requires the determination of one bias per region. This is what is referred to as the height datum problem. The possibility to solve this problem by exploiting the nowadays available satellite gravity mission data, the high resolution global gravity potential models, GNSS heights, as well as leveling and gravity data has been explored. A solution strategy and a first error budget have been presented in Gatti et al. (J Geod 87(1):15–22, 2012), showing that an accuracy of about 5 cm can be globally achieved in the bias computation. In the present work, this strategy, with refinements in the error modeling, is applied to the Italian case, where different height systems are used for the mainland and Sicily and Sardinia islands.
Riassunto Il lavoro che presentiamo ha prevalente valenza didattica e mira a precisare i concetti... more Riassunto Il lavoro che presentiamo ha prevalente valenza didattica e mira a precisare i concetti di posizionamento 3D in sistemi di riferimento e coordinate globali, come diventa sempre più necessario quando si mescolino osservazioni classiche e osservazioni GPS. La trattazione qui presentata è sintetica e limitata mentre una descrizione più approfondita ad un altro lavoro. Il software, sempre per ragioni didattiche, è sviluppato in ambiente MATLAB e per il momento è solo un prototipo.
BA.M.BA. is a new software for GPS data processing. It works following a multibase approach to pr... more BA.M.BA. is a new software for GPS data processing. It works following a multibase approach to process observations collected in static mode. The structure of the program is modular, basically constituted by three parts devoted to perform the following operations: preprocessing first processing final processing
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Papers by Giovanna Venuti