GNSS Active Network of Sao Paulo State: support to the geodesic positioning and atmospheric studies

          Currently, GNSS relative positioning is the most common method used to obtain high accuracy coordinates (few millimeters). To accomplish this kind of positioning (relative) it is necessary to use at least two receivers. One of them must remain in a reference station with know coordinates in the most appropriated reference frame (SIRGAS 2000, for example) and the other in the position to be surveyed. In this context, the use of data provided by active GNSS networks available in Brazil such as RBMC, RIBaC, and from private networks, etc., opens new perspectives. In such case, the reference station from the active GNSS network can be used as base station.

          In order to increase the number of GNSS active stations in Sao Paulo State, two research projects (process 04/09235-1 and 04/03384-5) leaded by FCT/UNESP and financed by FAPESP contributed in this sense. Currently, eleven GNSS active stations providing data in real time, constituting what has been called GNSS Active Network of Sao Paulo State (GNSS-SP Network). The PPTE station (belongs to RBMC) is also part of this network. In October 2008 was approved a Thematic Project from the FAPESP (Process 2006/04008-2) involving FCT / UNESP, USP-Poli, USP-ESALQ, INPE-CPTEC, among others, which will expand the Active GNSS Network the State of Sao Paulo. Today, xx stations are providing real time data.

           Currently, all stations installed up to 2009 already have their coordinates homologated by the IBGE. For these coordinates, click on the stations (Table) and access the descriptions of the IBGE.

                          Active reference stations homologated by IBGE
                          Active reference stations to be installed and/or homologated by the IBGE
                          Active reference stations of the RBMC (near GNSS-SP Network)

Stations of the GNSS-SP Network homologated by IBGE

          This network also can be used for atmospheric studies, specially to compute the tropospheric delay (that can be converted into precipitable water and used in Numerical Weather Predictions Models) (Sapucci 2005) and the total electron content (TEC), which is very important on ionospheric studies (Matsuoka 2003).

          The stations are providing data in real time via Internet, through the use of the NTRIP (Networked Transport of RTCM via Internet Protocol). The contribution of several units of UNESP was essential to perform the set up of the network. The installations of the new stations also require support from other institutions and organizations, which were contracted during the year 2011.

          TTwo commercial softwares (Leica - Spider and Trimble - GPSNet) are being used for monitoring the network. The station receivers are directly connected to the Internet, and the collected data are sent to a central computer that manages and storages the data, besides doing their conversion to RINEX and Hatanaka formats. Furthermore, auxiliary routines were developed to help in the automatic transference of data through the Internet and compact them hourly (1 second sample interval) and daily (15 seconds sample interval).

          This network presents a good configuration and density to accomplish investigation in São Paulo State, as well as for operational purpose. It is the densest GNSS active network in Brazil and maybe even in South America. We are performing investigations related to RTK Network and DGPS. By other hand, those users expecting to realize relative positioning have a good active GNSS network for such aim. Additionally, this network has contributed to the necessary infrastructure for the development of research in geodetic positioning and activities related to the ionosphere and troposphere. Users have available to them GNSS data to perform tasks such as monitoring surveys of the velocities of plates, Georeferencing of Rural Properties, Cadastral Surveys, Surveying, etc.

          In order to spread the use of this network data and training of the interested users, the Department of Cartography of FCT/UNESP provided a series of workshops during the year 2007/2008. They took place in ILHA SOLTEIRA, LINS and OURINHOS where reference stations were installed. Workshop with a series of lectures about the GPS system, possibility of applications and training for use of SP GNSS Network may be realized on demand.

          The interested users in obtain real time data of these stations and information about the NTRIP can access the BKG (Federal Agency for Cartography and Geodesy Germany) home-page. For the former, it is necessary to download the BKG_Ntrip_Client (BNC) or GNSS Internet Radio. The data is available in the sub-net so called GNSS Internet Radio. The data is available in the sub-net so called www.igs-ip.net (Rede BRA Misc). Furthermore, the data can also be accessed directly from FCT/UNESP, where there is an NTRIP Caster installed. But the interested user has to obtain authorization. For such case, they have to send a message gege@fct.unesp.br requesting for data and describing the main aim for using such data. Additionally, information of your institution or organization, such as name, address, main activity has to be provided. Some users have already obtained authorization for using such data.

          The data of stations ROSA, OURI and SJRP are available for investigation related to the GPS modernization, specifically the new L2C code. It is an initiative of IGS (International GNSS Service) and the data are made available to GSFC (Goddard Space Fight Center) of NASA, in ftp://cddis.gsfc.nasa.gov/gps/data/. The users can also access these data at this address.

          We would like to call to the attention of the users that such network is not totally appropriated for operational use, because it is under the administration of a university, where most of the human resources involved for running such network is mainly composed by students, who are still learning most of the details of such infra-structure. Therefore, fails may occur and we are trying to reduce it to minimum. The data are available and can be used, but so far, we can not offer reliability, availability and integrity.

João Francisco Galera Monico
GEGE leader
Department of Cartography FCT/UNESP