CONGO: First GPS/GIOVE Tracking Network for Science, Research

September 1, 2009 By: Uwe Hessels, Urs Hugentobler, Peter Steigenberger, Oliver Montenbruck, André Hauschild GPS World

Selected results from the COoperative Network for GIOVE Observation (CONGO) demonstrate how the global network provides early familiarization with the new Galileo signals and access to precise GIOVE orbit and clock information, to develop new processing techniques for multi-constellation, multi-frequency GNSS.

New capabilities offered by Galileo’s multiplexed binary offset carrier (MBOC) signal, including improved multipath reduction for E1 Open Service users, will create a host of novel processing techniques and applications, limited only by human creativity. Realizing the full potential of the new signals requires early familiarization with them.

Unfortunately, access to Galileo In-Orbit Validation Element (GIOVE) data is essentially restricted to European Space Agency (ESA) project partners, and GIOVE-capable GNSS receivers are not widely available in the scientific community at present. Even though the International GNSS Service (IGS) has clearly expressed its interest in incorporating Galileo into its processing, no infrastructure presently supports GIOVE observations. The lack of precise GIOVE orbit and clock information restricts the scientific community from developing new processing techniques for multi-constellation multi-frequency GNSS.

To overcome these restrictions, the German Aerospace Center (DLR) and the German Federal Agency of Cartography and Geodesy (BKG) developed a joint initiative to deploy a small global network of GNSS receivers capable of GIOVE tracking. Both institutions have long experience in GPS and GLONASS processing and already operate numerous GNSS stations within and outside Europe. All of these stations provide real-time data transmission, enabling continuous signal monitoring and processing. Most stations offer a 1-Hz measurement rate; DLR’s Experimental Verification Network (EVnet) can support up to 100 Hz for ionospheric studies and scintillation monitoring.

For the new COoperative Network for GIOVE Observation (CONGO, some of the existing BKG/DLR sites have been supplemented with GIOVE-capable receivers, and additional sites have been established with the local support of international partners. Eight stations have now been deployed at carefully selected sites around the world. This network offers global coverage with at least a dual-station visibility for most areas and serves as a starting point for routine processing of GIOVE data.

The CONGO Network

A key requirement for the CONGO network is the capability to provide continuous tracking of GIOVE satellites

irrespective of their orbital location. A visibility and coverage analysis has shown that eight stations are generally sufficient to ensure that each GIOVE satellite is always in view of at least one station. While the choice of sites is not necessarily unique and depends on many other constraints (site access, host availability, network connection, and so on), representative network layouts comprise three stations in the northern hemisphere (Europe, North America, Asia), three stations in the southern hemisphere (South Africa, South America, Australia) and two near-Equatorial sites. For CONGO, we finally selected Wettzell (Germany), Fredericton (Canada), and Chofu (Japan); Hartebeesthoek (South Africa), Concepcion (Chile), and Sydney (Australia); and Maui (U.S.) and Singapore. FIGURE 1 shows site locations with icons identifying the receivers and antennas at each station. Hardware details differ slightly from site to site, and are given later.

FIGURE 1. Overview of the CONGO network. The thumbnail pictures indicate the corresponding receivers and antennas for each site.

Depth of coverage (DOC) gives a useful performance index for assessing the quality of a tracking network. For GIOVE with an orbital altitude of 23,000 kilometers and a 15-degree elevation mask, FIGURE 2 shows that a permanent visibility from two or three stations is available for most of the time. While four areas with single-station visibility remain in the southern hemisphere and central Pacific, the existing network still offers an adequate and fully acceptable coverage for many applications.