Real-time GPS and Glonass Integrity Monitoring and Reference Station Software Kees de Jong, Hans van der Marel and Niels Jonkman Delft University of Technology, Department of Geodesy, Thijsseweg 11, 2629 JA Delft, The Netherlands e-mail: K.deJong@geo.tudelft.nl Summary At the Delft University of Technology (DUT) a software suite has been developed for Continuously Operating GPS/GLONASS Reference Stations. The most important features of this software suite are a real-time GPS receiver interface, real-time integrity monitoring and communication with a computing centre. The sample rate of the receiver and the transmission rate to the computing centre can be selected independently, and the data is sent in discrete batches of several minutes up to 24 hours, or continuously. The data is stored on the local computer disk with the receiver’s sample rate. The real-time quality control and integrity monitoring is based on a single channel approach. It uses a Kalman filter based Detection, Identification and Adaptation (DIA) procedure. Presently, the AOA Turbo Rogue, Javad Positioning System, Trimble 4000SSI(E) and Trimble 4700 receivers are supported. The software includes also an interface for meteorological sensors. The software has been used since 1997 for the Dutch Permanent GPS Network and since 1999 for DUT's IGEX GPS/GLONASS reference station. 1. GPS/Glonass reference station software Already in 1993, during the definition phase of the Active GPS Reference System for The Netherlands (AGRS.NL), it was recognised that real-time applications of permanent GPS arrays would become increasingly important in the near future. Therefore, the reference station software for the AGRS.NL was developed with near real-time applications in mind. Each reference station of the AGRS.NL is equipped with a geodetic quality dual-frequency GPS receiver, meteorological sensors, a PC with multiport serial controller, modems, telephone connections, uninterruptable power supply and remote power on/off switch. The software running at the reference station, developed by DUT, performs the following tasks: - Control receiver (e.g., set observation interval, minimum elevation, data format) and collect GPS data. - Real-time integrity monitoring (or data validation) of dual-frequency GPS code and carrier data. - Control meteorological sensors (set interval) and collect temperature, pressure and relative humidity data. - Log events (time the receiver started or stopped tracking a satellite, time a new navigation message was collected, time the integrity monitoring’s was initialized, time an outlier or cycle slip was found). - Temporarily store GPS data, quality control parameters and meteorological data on the reference station’s local hard drive in a dedicated binary format. The data will be automatically removed after a user-defined period. - Transmit data, again in binary format, to the central processing facility. Before transmission, data may be decimated to a user-defined interval. Data transmission can be done continuously or in batches. When a connection is established, the reference station and central facility negotiate about the first block of data to be transmitted. This will guarantee a complete data transfer. If no connection can be established or if data transmission is interrupted, the software will try to (re-)establish the connection. - Generate alarms, e.g., when the receiver did not track any satellites for a certain interval. Recently, the software was adapted to also incorporate the validation of Glonass observations. Currently interfaces are available for the TurboRogue family of receivers, Trimble SSE/Ssi, Trimble 4700 and JPS Legacy receivers. The JPS Legacy is a GPS/Glonass receiver. Data can also be processed off-line for these receivers. In addition, an interface was developed for the off-line processing of Rinex data. For the central facility, software was developed to receive the reference station data, store it and make it available to users in Rinex format for further processing. The following tasks are performed: - Collect GPS and meteorological data from all reference stations and store this data. If no data is received within a pre-set timeout period an alarm is generated (SMS or pager).