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Laboratorio di Geomatica - PRIN
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PRIN 2008
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Abstract
Italy is now at a very initial stage in establishing its geodetic reference frame according to the modern practice, namely by a national network of permanent GNSS receivers, framed into the international IGS structure and continuously monitored in time.
As a matter of fact, the first "new" reference frame (denominated National Dynamic Network, NDN) has been established by using one month of data (last two weeks of 2007, first two weeks of 2008) of 100 national permanent GPS stations and presented and approved by the EUREF structure as complying with international standards: in the last weeks the NDN solution has been officially published in the website of Istituto Geografico Militare. This has been accomplished by IGM Institute in cooperation with the coordinator of the present project and other centres. Meanwhile permanent GNSS networks have been developed at different scales and for different purposes. Important is the development of regional networks involving at least 10 regions over 21.
Such networks have the main purpose of creating positioning services for civil applications of public interest, for applications in cartography, cadaster, road construction, mobility etc.
Also an important scientific project is being developed by INGV, for the purpose of identifying and estimating the Italian pattern of the strain tensor, aiming at a number of geodynamical applications including subsidence, bradyseism, assessment of sea level change, seismic hazard determination etc.
The present project aims at:
1) reconducting all this activity to a unitary point of view under the theoretical and practical concept of geodetic reference frame,
2) establishing the national reference frame (NDN) on the basis of a continuous time ("monitoring") solution leading in this way the Italian community to a level finally compatible with the international reality of developed countries,
3) providing a number of documents of the type "certificate", to be used by regional authorities in particular for the economically sensitive item of RTK positioning services,
4) providing the first answers to a strategic question, namely whether , how and, in case, when a homogenized structure for positioning services at national level has to be created.
A work program of this nature has naturally to be driven by the main application; namely to perform all the calculations for the monitored geodetic reference frame for a time span that might cover 1 to 2 years depending on the data availability.
Along this main road however there are a number of theoretical questions which still deserve attention and analysis. Finally the outcomes of the research program can be frozen in a number of prescriptions or standards, that might be the basis for future national developments. Accordingly we shall segment the present project into sections of applied nature, Ax, sections of basic questions, Bx and sections of standards, Sx that will be detailed in the point 12 of the Model A.
The researches will constitute a natural continuation of the previous two projects coordinated by Prof. Sansò: PRIN 2004: Satellite Positioning services for the e-government; PRIN2006: Galileo and the modernized satellite positioning; moreover, this project will strictly interact wiht the PRIN2007 Project, The geomatics in support of the actions of Government of the territory, coordinated by Prof. Maurizio Barbarella.

Targets of the research program
Hereafter we specify the four targets of the project.
1) To clarify theoretical and practical recipes aiming at unifying and homogenizing all the activities relative to the establishment of a geodetic reference system at national level; in particular solving the problem of optimal framing of the National Dynamic Network into IGS and suggesting a federate unification of existing regional networks.
2) (Main target) implementing the continuous time monitoring of National Dynamic Network assessing the overall accuracy and making visible in the deformation pattern the presence of different geophysical signals at global, national, regional, local scale.
3) Providing the prototype forms of standard certificates for permanent stations, local permanent networks and positioning services at the national scale.
4) Issuing an "expert document" to suggest the possible steps for the establishment of a federate national positioning service.

Description of the program and time table
At first we present the titles of applicative (A), methodological (B) and standards definition (S) themes; then their details are described; at least, the timetable of the project is shown.

Titles of the themes
A1. Analysis of the present status of NDN and establishing a protocol for those permanent stations that will be accepted for the NDN data analysis and creating a data base for the project.
A2. Computation of the solutions of the NDN over 1 to 2 years time span, with different SW of international relevance.
A3. Implementation of a rational experiment to prove or disprove the feasibility of an RTK positioning service at national level.

B1. Analysis and solution of the problem of framing a sub-network into a larger network, overcoming some incorrect current practices.
B2. Deep investigation of the problem of time series prediction of the coordinates of individual stations, assessing a specific stochastic prediction model for each of them.
B3. Set up of an optimal predictor of the deformation pattern accounting for the spatial correlation structure of the network.

S1. Production of a prototype certificate for standards of quality of an individual permanent station.
S2. Production of a prototype certificate for standards of quality of a permanent network framed into the NDN.
S3. Production of a prototype certificate for standards of quality of real time services.

Detailed description of the themes
A1. we hope to be able to collect data at least for 60 permanent stations over a time span covering July 2009 to July 2010; for sure this will be done over July 2009 to July 2010. The reason why we say at least 60 PS is that not all the 100 PS of NDN are delivering data that full fil criteria of continuity in time and quality criteria (e.g. signal to noise ratio, number of satellite tracked per day, absence of cycle slips, multipath effects etc.)
This data set will be pre-processed cleaned of outliers and cycle slips will be identified, at least as it can be done by quality check algorithms.
Finally a data base will be organized to be shared by all the research units.
A2. The design of the NDN will be completed by a number of international IGS stations, most probably CAGL, NOT1, SOFI, MATE, WTZR, GRASS, MEDI, ZIMM, GRAZ, PADO (IGS acronyms) that will enter into the adjustment as reference stations.
The adjustment will be independently performed by 3 different SW: Bernese, GIPSY and GAMIT.
The results will be compared to verify their congruence or explain differences.
A characteristic equation (see point B2 below) will be set up for each permanent station.
A3. The experiments carried out in the previous PRIN, 2004 and 2006, clearly showed the potentialities of near real time positioning services if geodetic class receivers are used: mean horizontal accuracies are routinely achievable, that are suited for a wide range of applications and are comparable to those achieved at an international level.
Nevertheless, two items are worth to be investigated, related 1) to the quality and potentiality of real time positioning services if low-cost receivers are used and 2) to the real time quality assessment of the services supplied by a GNSS permanent network. In details, the first item appears crucial for a wider and wider diffusion of real time positioning services, mainly for several applications asking for sub-meter accuracy. The second item is strictly related to point out criteria for the GNSS permanent network certification on the geodetic and functional point of view (correctness and reliability of the real time supplied reference frame, conservation of transmitted data and adopted procedures); proper protocols will be established in order to carry out experiments where permanent stations will be used as "rover receivers", in order to estimate the quality of real time positioning, what can be obtained thanks to the present facilities of the permanent network management software.
B1. the re-attachment of a sub-network to a reference network is a classical geodetic item which has even an exact solution when the observations used in the new network have no correlation with those in the reference one.
This is not the case for GNSS network adjustment, at least when data are analyzed in terms of double differences. Therefore the current practice of adding pieces of normal matrices is not strictly correct. We want to study the impact of this sub-optional solution with respect to others and try to find, if possible, better alternatives.
B2. The time series of the coordinates of the PS's of a network usually display a clear trend signature as well as an annual periodic signal. The residuals usually don't have a pronounced signature; yet the residual correlation should be studied station by station, also taking all three coordinates together, in order to implement a best prediction for the station analyzed, something that we could call the characteristic equation of the station.
B3. The overall pattern of geophysical signals should be also studied in a space-wise mode trying first of all to verify whether it is possible to identify geodynamical districts where the correlation between displacements is stronger. The full combination of space-time correlations should be the ultimate target where all the dynamical characteristic of the geo-system Italy are highlighted.
S1. Under this point we would like to produce a specific document, shared with scientific and the user's community, to qualify a permanent receiver as a station of a national, or of a regional network.
S2. Under this point we would like to produce a specific document to certify that a sub-network is properly working as for its own positioning within the NDN.
S3. Under this point we would like to produce a document to certify the proper function of a positioning regional network duly divided into different quality cathegorics according to the type of service provided.
As it is obvious, beyond IGM, we will ask to other important national agencies to participate to the definition of the standards for the last three points.
It has to be mentioned that, as for the points S1 and S2 they can be derived quite naturally from the work already done within the two preceding PRIN 2004 and PRIN 2006; nevertheless what we intend to produce within the present project is a true prototype of a document that could be practically used in applications

Time schedule of the project
First year: A1, A2 (part), B1, B2 (part)
Second year: A2, A3, B2, B3, S1, S2, S3

Unit work
A simple table summarizes the involvement of the different units in the project themes

A1: Milano, Perugia, Torino;
A2: Milano, Perugia, Torino, Roma, Bologna;
A3: Milano, Perugia, Torino, Roma, Bologna;

B1: Milano, Perugia, Torino, Bologna;
B2: Milano, Torino, Roma, Bologna;
B3: Milano, Roma;

S1: Milano, Perugia, Torino, Roma, Bologna;
S2: Milano, Perugia, Torino, Roma, Bologna;
S3: Milano, Perugia, Torino, Roma, Bologna.

The research units are already trained to work together because of 4 years of joint researches. The full team is summoned at least three times per year and progresses are reported. The applicative points for the NDN database of data and results analyses (A1 and A2) will be led by Politecnico di Torino and Politecnico di Milano Units; the experimental part of the project (A3) will be organized by the Roma University. The points concerning standards will be chaired by: S1: Bologna University; S2, Perugia University; S3, Politecnico di Milano; all groups trough, will participate to the final implementation. Also the methodological themes (B) will be investigated in cooperation between the Units; however, the definition of a chair for each of them doesn't seem necessary.
Yearly reports will be prepared by the coordinator and all the work in progress will be published on the website of the project.

A special mention has to be done to the full participation to the project of IGM, through a group of three persons of the Geodetic Division. The role of IGM is not of performing specific research but rather to collect the data and to participate in the adjustment of NDN and into the discussion of the results, so that its staff will be ready in future to continue the work on a routinary basis.

Final products
With respect to the themes A1/2/3, B1/2/3 and S1/2/3, the following products are foreseen.
A. A database with NDN data, the data quality check analysis, and the final adjustment results;
a document reporting the results of the experiment and a feasibility study of a positioning service at the national scale.
B. A scientific open source free software for:
1. the computation of the 3D characteristic equation of a permanent station from its daily solutions;
2. the spatial analysis of the characteristic equations of the stations belonging to the same network, in order to:
2.1. cluster the network in subnetworks characterized by homogeneous behaviour;
2.2. interpolate the velocity and velocity gradient fields within a network.
S. Three reports with the guidelines and the standards relevant to the points S1, S2 and S3.
In addition an official approval by the European Reference Frame Commission (EUREF) of the work done on NDN will be requested and published with the results.

Moreover, the results will be presented at scientific international/national Symposia and published on qualified journals. A special issue of the Bulletin of Geodesy and Geomatics on the adjustment of NDN and on the analysis of the results.
In case of success of the present project we believe that not only Italy will be aligned to the best international practice in the field but also it will give a contribution to the international discussion on the implementation of hierarchical systems of geodetic reference frames. As a matter of fact, the definition of a more rigorous approach to nesting local networks into the global one might be able to provide a more reasonable assessment of the error influences on the estimated coordinates. Clearly, also the implementation and publication of scientific software for temporal analysis of time series and spatial clustering and interpolation of displacements is an important contribution.
In addition, the standards and certification items can give a contribution to a debate that is actually ongoing worldwide.




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