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PRIN 2006: Galileo and the modernized satellite positioning

the project


Dipartimento per l'Università, l'Alta Formazione Artistica, Musicale e Coreutica e per la Ricerca Scientifica e Tecnologica

Research title: Galileo and the modernized satellite positioning
Principal Investigator: Fernando SansÚ
Length: 24 months

The present proposal is a logical continuation of a Project financed in 2004 under the title "Satellite Positioning Services for the e-Government". With that project a strong impulse has been given to the regional policies concerning the satellite positioning services, to the extent that most Italian regions are on their way to construct permanent GPS networks; with this action we feel we have significantly cut the technological gap with the mean level of European nations.
Now we feel it is the right time to start looking at the new phase that will see the modernization of GPS and the birth of Galileo as new technical tools on GNSS activities. We are indeed aware we have to build on significant results, consolidated at an international level, concerning:
1.optimization of the third frequency,
2.interoperability of GPS and Galileo,
3.improvement of navigational algorithms.
However we have the feeling that typical geodetic applications of the new scenario have started only in the very last years to attract more attention. We feel therefore that working on the item of the impact of satellite positioning modernization is worth for us and may contribute, as a minimum, to avoid a further delay of Italy in such techniques and maybe to produce some novel results on specific items of e-government applications. Our targets can be classified under B) as basic items or A) as applications; we refer to:

B1) impact of Galileo in defining a unified GNSS worldwide reference frame (TRF) and study of the transformations between single techniques TRF;
B2) analysis of all possible frequency combinations, interoperability algorithms, problems of ambiguity fixing and corrections estimations towards a faster and more precise relative point positioning;
B3) study of the increased possibility of making a tropospheric tomography thanks to the augmented number of satellites in view;
B4) development of existing Italian geodetic software for future full GNSS permanent stations;
B5) development a "simulator" of a real time positioning software;

A1) definition of the new operative rules for the future GNSS permanent networks;
A2) analysis of all possible applications of modernized positioning to the e-government, cartography, cadastre, logistics etc; this point should be supported by the first practical experiments of positioning with the new systems;
A3) production of educational material for Italian world of researches and professionals.

As a consequence of the research "Satellite Positioning Services for the e-government", performed in the period 2004-2006 by more or less the same group presenting this proposal, most of Italian regional governments have today projects to develop satellite regional positioning services. On the same time the national institute IGM is organizing a new procedure to monitor and estimate the national reference service framed into IGB00. This action has prevented a completely fuzzy development of the field engaging at least regional authorities in such endeavour. The new scenario rising with the predicted modernization of GPS as well as the introduction of the Galileo system puts on us the burden of starting now to study the new dimension of services delivered by permanent GNSS networks in such a way as to avoid the birth of new technological gaps.
We are convinced in fact that although a number of operations will be directly performed in future with the unique support of the satellite segment, nevertheless the most accurate and fast services in all fields from geodynamics research down to very large scale cartography, will continue to require the support of services issued by permanent GNSS networks.
This is what we shall try to contribute at least for the Italian development and may be with some addition to the results of the international research in the field.

We shall discuss 4 different points:
1. a more detailed description of the points already presented in 1.3,
2. the time schedule of the project,
3. the list of products that can be verified a posteriori,
4. the table crossing research units and research items.

1 Detail
B1) As recalled, a reference System (RS) in 4D is basically a convention to eliminate the intrinsic deficiency of well designed systems of observation equations expressed in terms of coordinates. The very issue is to ascertain what is the time span in which we can consider as reliable a simple model of 14 parameters ( similarity transformation varying linearly in time). This has to be done by extending the IERS rules to the new techniques.
The theoretical problem has important applicative implications. If the transformation consists of a rototranslation with scale variations for space and a temporal shift for the fourth coordinate, it is necessary to try and understand how to estimate these parameters, how often and with what precision, for two different applications: post processing and in real time. The estimation of these parameters for RTK positioning with modest precision is probably already sufficient to meet the requirements for these RT applications. For precision positioning in post processing, especially for large networks, the problem must be faced rigorously. What allows these parameters and their variability to be estimated is the simultaneous tracing of various constellations.
B2) We want to study all possible combinations of the signals in different channels depending on particular purposes. For sure we shall try to identify the best combination for cycle slip detection in the single receiver and the geometry free combination that at the same time optimally annihilates the iono correction in order to get the integer ambiguity estimates in the shortest time. In this case, it is necessary to distinguish between two different approaches to use for GLONASS (R) with respect to GPS (G) and GALILEO (E). These latter satellites in fact provide and will provide fixed and assigned frequencies. The Russian constellation instead has satellite-dependent frequencies. The improvements for the three constellations however concern the possibility of having at least three fixed frequencies for the G and E satellites with relative codes that promise to be more precise and less noisy and of having new frequencies and new codes, these too being highly precise, for satellite R. For the purposes of B2) it is hoped to analyse in simulations situations that will involve the contemporaneous presence of some twenty satellites in absence of obstacles. Even though it will not be possible to consider the fixing of the phase ambiguities in real time, the problem will be, especially in urban canyons, of reconnecting satellite phase signals that are not visible with continuity: this latter operation could probably be carried out in real time. It is necessary to verify in more detail the practical results of the two current philosophies in order to arrive at a fixing of the ambiguities: the first, which can be applied to satellites (G), (E) and (R), is known as "Geometry Free" and it takes advantage of the spectral distance of the new frequencies for the precise calculation of the ionospheric bias, the second, which can only be concretely applied to the first satellites, takes advantage of the Wide Lane and the Extra Wide Lane combinations, that amplify the wavelength of the band as much as the closeness of the frequencies.
B3) The troposphere tomography which is only partially applicable nowadays with interstation distances of the order of 50 km and 10-12 satellites insight, can become much more effective with at least the double number of satellites. During the last years, some models and software were developed to perform tropospheric tomography. Now we want to investigate the improvements in spatial and temporal resolution offered by analyzing both real and simulated data from different GNSS constellations and the impact of this expected improved resolution for rainfall forecasting on critical watersheds.
B4) We would like to complete and update SW for regional networks GEOGPS, actually in a phase of implementation, to include in the new version (GeoGNSS) the modernized positioning.
B5) We intend to start writing a simulator of real time positioning, though we are aware the true real time SW has to be residing inside the instruments; this however will be the first attempt in Italy in this direction. It will be useful to assess the impact of different constellations as regards real time precision and reliability. We plan to start from the actual observations at GNSS permanent sites, to produce the network information necessary for the code and phase real time positioning and to apply them to the actual observations acquired by a GNSS rover receiver
A1) We shall study the transformation of actual GPS permanent networks into GNSS permanent networks; particular care will be given to the problem of transmission of VRS and/or FKP data.
A2) Experiments of data analysis within the new scenario will be performed, both with simulated data and with the first data available in the next two years from experimental Galileo satellites; this will be possible thanks to the support of italian industries already involved in GJU. Two major topics will be issued, which are related to the design and management of transportation infrastructures.
1. Interactions analysis during interventions on transportation infrastructures in urban areas: possible interactions are due both to different transportation infrastructure intersections (e.g. metro and roads or tram at different levels) and to transportation and other (gas, water, power, phone) infrastructures.
2. Positioning of high hazard transportations: it is a special case of fleets management with particular concern to vehicles carrying dangerous goods, whose position has to be continuously traced in order to know if they are approaching critical points (e.g. tunnels or bridges).
A3) We shall organize in 2008 a great national workshop with a 3 days school on the new GNSS positioning, for which specific educational material will be produced.

2 Time schedule
The work will be split into 2 phases:
1st year: B1), B2), B3) and definition of the algorithms for B4), B5). Study of A1)
2nd year: finalization of B) points, in particular implementation of the SW at points B4) B5); work out of A2), A3).

3 Final products
1. scientific papers on national and international qualified journals,
2. preparation of a position paper on the update of GNSS services in Italy,
3. network adjustment experimental SW,
4. user simulation SW,
5. education material.

4 Unit participation

B1: Units I, II, IV
B2: Units II, III, V
B3: Units IV, V
B4: Unit I
B5: Units I, II, V
A1: Units I, II, III, IV, V
A2: Units I, III, IV, V
A3: Units I, II, III, IV, V

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