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## Publications

Publications (74)

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...

High‐resolution numerical weather prediction (NWP) simulations of heavy rainfall events are known to be strongly sensitive to the choice of the sub‐grid scale parameterization schemes. In the African continent, studies on such a choice at the convective‐resolving scales are not numerous. By exploiting a state‐of‐theart NWP model, the Weather Resear...

In the last decades, the great availability of data and computing power drove the development of powerful machine learning techniques in many research areas, including the ones, as the meteorology, where traditional conceptual models were usually adopted. In this work, we analyze the performance obtained by different techniques in the forecasting o...

The availability of atmospheric water vapor content observations, with high temporal and spatial resolution, proved to have a high impact in the prediction of heavy rain events obtained from numerical weather prediction models. Several techniques can be applied to derive such observations. Some of them are well consolidated, some others are still u...

The use of low-cost GNSS stations for meteorological applications requires the modeling of ionospheric errors. Although low-cost dual-frequency receivers are now available, current ones are still missing the L2 frequency and this prevents the availability of iono-free observations. This second frequency can be predicted by exploiting dual-frequency...

Atmospheric Phase Screens (APSs) derived from Interferometric Synthetic Aperture Radar (InSAR) observations contain the difference between the tropospheric water vapor induced delay of two acquisition epochs, i.e. the slave and the master (or reference) epochs. Using estimates of the atmospheric state coming from independent sources, for example nu...

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...

A Synthetic Aperture Radar can offer not only an accurate monitoring of the earth surface deformation, but also information on the troposphere, such as the total path delay or the columnar water vapor at high horizontal resolution. This can be achieved by a proper interferometric processing and post-processing of the radar interferograms. The fine...

This paper proposes a simple and fast method to estimate Atmospheric Phase Screens (APSs) by jointly exploit a stack of Synthetic Aperture Radar (SAR) images and a dataset of GNSS-derived atmospheric product. The output of this processing is conceived to be ingested by Numerical Weather Prediction Models (NWPMs) to improve weather forecasts. In ord...

The Mediterranean region is frequently struck by severe rainfall events causing numerous casualties and several million euros of damages every year. Thus, improving the forecast accuracy is a fundamental goal to limit social and economic damages. Numerical Weather Prediction (NWP) models are currently able to produce forecasts at the km scale grid...

In the last few years, many studies claimed that machine learning tools would soon overperform the classical conceptual models in extreme rainfall events forecasting. In order to better investigate this statement, we implement advanced deep learning predictors, such as the deep neural nets, for the forecasting of the occurrence of extreme rainfalls...

This paper presents the first experimental results of a study on the ingestion in the Weather Research and Forecasting (WRF) model, of Sentinel satellites and Global Navigation Satellite Systems (GNSS) derived products. The experiments concern a flash-floodevent occurred in Tuscany (Central Italy) in September 2017. The rationale is that numerical...

Goal of the project was to investigate whether the assimilation of high resolution Earth Observation variables improve the forecast of heavy rain events. Several experiments were conducted assimilating soil moisture, surface wind, sea surface temperature, land surface temperature and zenith total delay. The assimilation of wind and water vapor cont...

The activities carried out within the WP2 of the TWIGA-H2020 project are described. In particular, the following topics are covered: the definition of a new low-cost GNSS receiver network to be soon installed in Uganda, a new algorithm for the retrieval of water vapor maps from Sentinel-1 data and the ongoing numerical weather prediction experiment...

GNSS atmospheric water vapor monitoring is not yet routinely performed in Italy, particularly at the regional scale. However, in order to support the activities of regional environmental protection agencies, there is a widespread need to improve forecasting of heavy rainfall events. Localized convective rain forecasts are often misplaced in space a...

The STEAM (SaTellite Earth observation for Atmospheric Modelling) project, funded by the European Space Agency,
aims at investigating new areas of synergy between high-resolution numerical weather prediction (NWP) models and
data from spaceborne remote sensing sensors. An example of synergy is the incorporation of high-resolution remote
sensing dat...

Since many years, the GNSS has been regarded by the meteorological community as one of the systems for atmospheric water vapour remote sensing. Time series of wet delays, estimated as by-products of accurate positioning, have been assimilated into numerical weather prediction models. However, a dedicated use the system for water vapour monitoring i...

The European Space Agency (ESA) STEAM (SaTellite Earth
observation for Atmospheric Modelling) project aims at
investigating new areas of synergy between high-resolution
numerical atmosphere models and data from spaceborne
remote sensing sensors, with focus on Copernicus Sentinels
1, 2 and 3 satellites. An example of synergy is the ingestion
of surf...

We study the impact of atmospheric turbulence, specifically the wet tropospheric delay, in that synthetic aperture radar (SAR) with very long integration time, from minutes to hours, and wide swaths, such as the geosynchronous or geostationary SAR. In such systems, the atmospheric phase screen (APS) cannot be assumed frozen in time as for Low Earth...

From 2001 to 2008, the National Geographic Institute of Spain (IGN) carried out the REDNAP project to the establishment of a National High Precision Levelling Network in the whole Spanish territory. Within REDNAP, spirit levelling and gravity observations were complemented by GNSS data. The levelling network of the continental area and those of the...

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 h...

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 heig...

Discontinuity detection is of great relevance at different stages of the processing and analysis of geodetic time-series of data. This paper is essentially a review of two possible methods. The first method follows a stochastic approach and exploits the Bayesian theory to compute the posterior distributions of the discontinuity parameters. The epoc...

When monitoring deformations by means of different sensors, one has to be sure that the various observations do see the same variations in time of the earth surface. As an example one can think of a deformation as seen by the SAR technique and the deformation of the same surface as seen by GPS. To this aim a hypothesis testing procedure has to be s...

The global height datum problem, that is the determination of biases of
different height systems at global scale, is revised and two solutions
are proposed. As it is well known, biased heights enter into the
computation of terrestrial gravity anomalies, which in turn are used for
geoid determination. Hence, these biases enter as secondary or indire...

Regional height systems do not refer to a common equipotential surface, such as the geoid. They are usually referred to the mean sea level at a reference tide gauge. As mean sea level varies (by ±1 to 2 m) from place to place and from continent to continent each tide gauge has an unknown bias with respect to a common reference surface, whose determ...

When monitoring deformations by means of different sensors, one has to be sure that the various observations do see the same variations in time of the earth surface. As an example one can think of a deformation as seen by the SAR technique and the deformation of the same surface as seen by GPS. To this aim a hypothesis testing procedure has to be s...

The problem of the convergence of the collocation solution to the true gravity field was defined long ago (Tscherning in Boll Geod Sci Affini 39:221–252, 1978) and some results were derived, in particular by Krarup (Boll Geod Sci Affini 40:225–240, 1981). The problem is taken up again in the context of the stochastic interpretation of collocation t...

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 i...

In this work we report the main conclusions of the European Space Agency (ESA) Metawave project (Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects) for what concerns the Synthetic Aperture Radar Interferometry (InSAR) viewpoint. The Atmospheric Phase Screen (APS) estimated with the Permanent Scatterers (P...

One of the most attractive scientific issues in the use of GNSS (Global Navigation Satellite System) signals, from a meteorological point of view, is the retrieval of high resolution tropospheric water vapour maps. The real-time (or quasi real-time) knowledge of such distributions could be very useful for several applications, from operative meteor...

The problem of the convergence of the collocation solution to the true gravity field was defined long ago (Tscherning in Boll Geod Sci Affini 39:221–252, 1978) and some results were derived, in particular by Krarup (Boll Geod Sci Affini 40:225–240, 1981). The problem is taken up again in the context of the stochastic interpretation of collocation t...

A method based on neural networks is proposed to retrieve precipitable water vapor (IPWV) over land from brightness temperatures measured by the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). Water vapor values provided by European Centre for Medium-Range Weather Forecasts (ECMWF) were used to train the network. The perfo...

Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique useful in many land applications, such as monitoring tectonic movements and landslides or extracting digital elevation models. One of its major limitations is the atmospheric variability, and in particular the high water vapor spatial and temporal variabilit...

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 limitations is the atmospheric effect, and in particular the high water vapour spatial and temporal variability which...

The theory of GBVPs provide the basis to the approximate methods used to compute global gravity models. A standard approximation procedure is least squares, which implicitly assumes that data, e.g. gravity disturbance and gravity anomaly, are given functions in L2(S). We know that solutions in these cases exist, but uniqueness (and coerciveness whi...

This paper deals with the problem of detecting and correcting cycle-slips in Global Navigation Satellite System (GNSS) phase
data by exploiting the Bayesian theory. The method is here applied to undifferenced observations, because repairing cycle-slips
already at this stage could be a useful pre-processing tool, especially for a network of permanen...

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 di...

The determination of local and regional geoid models has been the topic of extensive research in
physical geodesy for the last decades. From the initial realizations of astrogeodetic geoid models and
combination solutions with few gravity observations, we have sailed through the era of satellite geodesy and the exploitation of altimetric observat...

The computation of the vertical at- traction due to masses above the mean topogra- phy (Residual Terrain Correction, RTC) is still a matter of study in the high precision geoid estimation by remove-restore technique. This topographical efiect can be evaluated from the knowledge of a Digital Terrain Model (DTM) in two difierent ways: numerical integ...

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 appro...

Two techniques are commonly used to predict values of a random field u(t) from a vector of observations Y; one, mainly used in geodesy, is collocation, the other, mainly used in hydrology and geology, is kriging. Both techniques are based on the same optimization principle, that is minimizing the mean square prediction error, and use the same class...

Many problems in physical geodesy can be formulated in terms of boundary-value problems (BVPs) for the gravitational potential; many of them can be ultimately formulated as a Dirichlet problem. For this reason, there is a flourishing literature of geodetic contributions to potential theory. In this paper, the authors pick up some classical argument...

The paper first reviews the existing mathematical theory for the estimation of a random field T, with known covariance C, from a finite vector of observations, related to T by linear functionals, in the framework of a Bayesian approach.
In particular in Section 2 and Section 3 the equivalence between ordinary collocation formulas, their explainatio...

The application of the collocation theory to the prediction of some random field functional depends on the knowledge of the covariance function. Whether we include the estimation of the covariance into a unique theoretical set up with the prediction of the signal, or we do it separately in a more traditional way, this step can be performed only und...

A typical remote sensing data clustering is the maximum likelihood supervised procedure. It consists of the estimation of a suitable mixture of distributions, based on training samples only, and in the subsequent pixel-by-pixel classification, performed by maximizing the likelihood ratio. In this way all the information on the parameters of the dis...

this paper we refer to the first case, the polynomial interpolation. The GRASS user can fix the degree of the polynomial interpolation surface or apply the "optimized polynomial interpolation" command which, taking into account the feature of the grid observations layer, chooses, for a fixed significance level, both the optimal k dimension of the m...

In GPS phase data processing for high precision static positioning, the
problem of the cycle slip detection has to be faced. The differences
between the two-phases observations or between phase and range
observations of a single GPS receiver and a single satellite, all
expressed in metric form, are completely free from the geometry and
depend only...

The Wiener–Kolmogorov principle of minimizing the mean square estimation error is discussed in the framework of prediction
theory, from both theoretical and practical points of view. Alternatives for suboptimal solutions, more easily computable
and not requiring the explicit knowledge of the covariance function, are proposed. A robust version of t...

Working Group on Measurements and Methods of Hight Precision Space Geodesy - ASI Research (1998-1999-2000)

The height datum problem is present in the geodetic literature since the times of Pizzetti, when it was realized that as only differences of the gravity potential can be derived from measurements, there was still one global parameter to be settled in order to determine a global model.
Several more realistic formulations of the problem have been int...

The analysis of the Molodensky problem in spherical approximation can be reduced to the simple Dirichlet problem. If the boundary
data are noisy (white noise), it is requested to explain what is the meaning of the solution of a B.V.P. with data of this
kind. This can be correctly done in the framework of generalized random field theory and an equiv...

SOMMARIO L'analisi di dati laser scanning si basa in primo luogo sui metodi standard di rappresentazione dei modelli digitali del terreno, seguite poi dall'uso di strumenti statistico-analitici opportuni per la soluzione di alcuni problemi che sono specifici di tale tecnica; ad esempio, la separazione degli oggetti che insistono sul suolo rispetto...

SOMMARIO L'elaborazione delle osservazioni laser scanning conduce ad un modello digitale di superfi-cie, DSM, della zona in esame; ovvero, laddove sul terreno sono presenti manufatti o vege-tazione, il modello fornisce la quota di questi ultimi. Può tuttavia essere necessario cono-scere l'andamento morfologico del terreno, il DTM, sottostante a man...

The collocation approach to the estimation of a field from observed functionals, is known, by examples and simulations, to display a not very strong dependence from the choice of the specific reproducing kernel-covariance function. In. fact the situation is similar to the case of the dependence of least squares parameters on the weight of observati...

The collocation method can be fruitfully applied in SST estimation on repeated mission tracks. Some applications have been carried out in the western Mediterranean Sea using ERS1-ERM and TOPEX/POSEIDON data. In this work some refinements of the method are analyzed to obtain improvements in the estimates of the stationary component of the SST in the...

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 proble...

In geodesy as well as in geophysics there are a number of examples where the unknown parameters are partly constrained to be integer numbers, while other parameters have a continuous range of possible values. In all such situations the ordinary least square principle, with integer variates fixed to the most probable integer value, can lead to parad...