Unit 10. The global navigation satellite system (glonass)

1. Read and translate the following text

THE GLOBAL NAVIGATION SATELLITE SYSTEM (GLONASS)

General information

The GLObal NAvigation Satellite System (GLONASS) is similar to GPS in that it is a space-based navigation system providing global, 24 hours a day, all weather access to precise position, velocity and time information to a properly equipped user. The system became fully operational in January 1996 and consists of 24 satellites in 3 orbital planes at 19,100 km altitude, corresponding to an 11 h 15 min orbital period. Orbital inclination is 648° as opposed to the 55° of GPS, this has a significant impact on operations at high latitudes. Each GLONASS satellite continuously broadcasts its own precise position as well as less precise position information for the entire constellation, but the transmitted data is in the form of Earth Centred Earth Fixed (ECEF) co-ordinates and extrapolation terms, as opposed to Keplerian parameters, as is the case for GPS. The user segment consists of the equipment necessary to track the GLONASS satellites and derive position, velocity and time from the satellite data and measurements. The GLONASS control segment is similar in purpose and function to its GPS counterpart. The Co-ordinational Scientific Informational Centre (CSIC) of the Russian Space Forces provides official information on GLONASS status and plans, information and scientific method services to increase the efficiency of GLONASS applications.

Each GLONASS satellite uses two carrier frequencies in the L band, which, contrary to the GPS implementation, are different for each satellite. The L1 band ranges from 1602-5625 MHz to 1615-5 MHz in jumps of 0-5625 MHz, while the L2 band ranges from 1246-4375 MHz to 1256-5 MHz in jumps of 0-4375 MHz. (Twenty four frequency channels are therefore generated for each of L1 and L2). Each of these signals is modulated by either or both of a 5-11 MHz precision (P) signal and/or a 0-511 MHz coarse/acquisition (C/A) signal. The binary signals are formed by a P code or a C/A code which is modulo 2 added to 50 bps data (on L1 only). The P and C/A signals are then modulo 2 added to L1 in phase quadrature (only P is present on L2). The P code is a pseudorandom sequence with a period of one second, while the C/A code is a pseudorandom sequence with a period of 1 msec. Contrary to GPS where all codes are unique to a specific satellite; a single GLONASS code is used for all satellites. GLONASS receivers duplicate the P and/or C/A codes and the transmission time is determined by measuring the offset that is to be applied to the locally generated code to synchronize it with the code received from the satellite.

In an effort to reduce the bandwidth utilized by GLONASS as well as to reduce interference in the radio astronomy band, the GLONASS operators have formulated a transitional frequency plan as follows: until 1998, frequency channels 13 through 21 will be avoided as much as possible by implementing an antipodal configuration, in which two satellites in the same plane and separated by 180 degrees broadcast on the same frequency. From 1998 to 2005, no channels above 13 will be used, with channel 13 used as little as possible. Beyond 2005, the band will be shifted from 0 to +12, to -7 to +6.

SATELLITE BASED AUGMENTATION SYSTEMS (SBAS)

SBAS are overlay systems, for the current GPS and GLONASS Global Navigation Satellite Systems (GNSS), using a suite of geostationary satellites, that will offer users more reliability through improved accuracy, availability, integrity and continuity. Though these improvements are being driven by aeronautical requirements, in practice all users, be they maritime, road, rail or surveying, will benefit.

The three major components of the SBAS are EGNOS (the European Geostationary Navigation Overlay Service), WAAS (the American Wide Area Augmentation System) and MSAS (the Japanese Multi-functional transport satellite (MTSAT) - based Satellite Augmentation System). The signals broadcast by SBAS will be totally compatible with the GPS/GLONASS signals, which means that the presence of the SBAS signal will not impair the reception of GPS/GLONASS signal in any way.

The implementation schedule for SBAS should culminate in the Advanced Operational Capability (AOC) during the period 2003 - 2005.

1. Answer the following questions

1. Why is the GLONASS similar to GPS?
2. When did the system become fully operational?
3. What does the system consist of?
4. How does each GLONASS satellite broadcast?
5. What form have the transmitted data got?
6. What is the SBAS?
7. What are the three major components of the SBAS?

1. Compare SBAS, GPS and GLONASS, discuss similar features, difference and benefits for users.
2. Translate the following words and word combinations from English into Russian. Remember them

Global Navigation Satellite System; to be similar to; space-based navigation system; global all weather access; precise position; properly equipped; operational; orbital plane; altitude; orbital inclination; broadcast; constellation; to derive position; coarse acquisition; binary signal; modulo; pseudorandom sequence.

1. Read and translate the text. Find out the subordinate clauses and define their type.

STAREC (STA tus REC ording system)

STAREC is a maritime emergency reporting system to be used by ocean going vessels in order to immediately report emergency events when such situations occur. The STAREC float-free buoy contains a Data Recorder and an INMARSAT-C communications terminal that enables the buoy to report emergency events immediately from any ocean region within the coverage of the INMARSAT system. The high capacity Data Recorder can log data from a number of sensors around the ship, including position (e.g. GPS, LORAN, DECCA, etc.), course, speed, hull motion and hull integrity, etc.; these sensors could also include equipment to monitor the status of major hull openings such as bow and stern doors in roll on/roll off ferries. The buoy has been designed to send a short message to a pre-determined point on the shore, for instance, the ship owner and/or RCC, when, in the event of an accident, it floats free from the ship, or whilst ship-borne. The shore authority can then send a message instructing the buoy to transmit all recorded data in its memory, this arrangement has the positive advantage that recorded data is available on shore and it is not necessary to engage in an extensive search to find the buoy before the data can be recovered. The initiation of the system can be done by the vessel’s crew (e.g. bridge-located push button), or automatically when the buoy’s sensors register that the buoy has been released from its normal position. A further capability enables the shipping company or shore authority to check the status of any of the sensors at any one time, simply by interrogating and requesting the buoy to send a report.

STAREC continuously records important data about the vessel in order to relay ере data to on-shore authorities if an emergency situation occurs.

STAREC was developed because many vessels disappear without any trace while “en-route” Incidents like these often generate more questions than answers and STAREC can, within minutes after an incident, be able to relay stored data which can give these answers. In addition t total disappearances, other accidents like collisions, fire black outs and involuntary groundings have revealed the need for a “neutral” recording system which can tell the story about the vessels behaviour previous (minutes/hours) to the incident.

In many ways STAREC can be compared to the “black box system” used onboard airplanes. The major advantage of STAREC over the “black box system”, however, is that the critical data do not need to be physically retrieved from the buoy, but can simply be “polled” from it whilst it is still in the water, or shipborne.