Interferometric attitude and direction sensor using GPS carrier phase data

• Autorzy: Caporali A. , Dalla Torre A. , Praticelli N.
• Konferencja: 7th Bilateral Geodetic Meeting Italy-Poland (7; 22-24.05.2003; Bressanone, Italy)
• Języki publikacji: EN

Abstrakty

EN

A prototype attitude sensor suitable for navigation on the Earth surface or for platforms in Low Earth Orbit has been implemented using pairs of GPS receivers. The attitude sensor provides two or three attitude angles depending on its configuration and provides aIso information on the deformation of the platform on which the GPS antenna are mounted. The basic measurement performed by the GPS Attitude Sensor consists in comparing the down-converted carrier phases from a pair of receivers. The fringe phase for each visible satellite is further differenced between satellites, to remove the drift of one receiver cIock relative to the other. The baseline joining a pair of antennas defines bodyfixed angles, which are estimated in real time using a two step procedure: a coarse estimation is first mad e with the Ambiguity Resolution Function (ARF) algorithm, and, second, the refined estimate is made by least squares. Assuming baselines ranging from 0.2 meters to 1 meter, the r.m.s. (root mean square) of the repeatability at 1 Hz varies from 1° to 0.25° for the horizontal angle (e.g. azimuth), and a factor of 2 larger for the vertical angle (e.g. elevation). For greater accuracy a longer baseline must be used, but it will be more difficult to select the correct integer ambiguities. To solve this problem compatibly with the requirement of real time processing, we use one intermediate antenna in a bootstrap mode: a 200 mm baseline is used to put for a first estimate of the solution; then the data from a 1000 mm baseline are used, in combination with the constraints coming from the 200 mm baseline, to obtain a refined solution. This approach yields a stable and accurate solution. AItematively, we have configured the three antennas at the corners of a triangle, to estimate the three body-fixed angles, the independent baseline lengths and of the angle in-between. The estimate is again made epoch-wise, i.e. regardless the value the parameters had at previous epochs. Alternatively, a limited memory filter can be used, to smooth the noise. The estimated angles are 'absolute' , that is geographicaIly unbiased, as they refer to the true geographic pole. The Software module allows the operator to communicate with the receivers through a serial interface to a PC, to perform and to display the orientation solution. The Software tool has been created in order to deal with receivers of different manufacturers and with different configurations. Considering the frame in which the GPS attitude sensor has been developed the following S/W environment was used: Borland Visual C++ selected to create the communication interface with the user to extract the raw data from the receivers and to display the results. Lahey FORTRAN90 selected to perform the attitude solution. The F90 module is mad e available to the C++ module as a Dynamically Link Library (DLL) and it's caIIed for each observation epoch. Complementary use of the GLONASS and GALILEO navigation sateIlites has the potential to improve epoch-wise on the geometry and, hence, on the r.m.s. Figure. A possible application for a long baseline configuration (e.g. 10 m) is to provide a reference for mapping the magnetic declination, for cartographic use. The sensor has the capability to measure relatively small (>0.005 m) changes in the baseline, simultaneously with the angles. As such, it can work as a strain gauge, e.g. to monitor large deformable structures in orbit or on the ground. If the angles are known in advance, like in the case of fixed GPS receivers on known coordinates, the sensor can be used for the determination of the variation of the distance between the antennas for long baselines (0.1-10km) in Real Time with high accuracy. A network of antennas spread in a large area can provide useful information for seismic studies. Having no moving parts, the sensor can withstand the shocks of the launch and is immune from thermal and mechanical drifts, but is sensitive to the occultation of the navigation sateIlites produced by nearby obstacles or structures.

Słowa kluczowe

EN

GPS system; satellite geodesy

PL

geodezja satelitarna; GPS system

• Wydawca: Wydział Geodezji i Kartografii Politechniki Warszawskiej
• Czasopismo: Reports on Geodesy
• Rocznik: 2003
• Tom: z. 2/65
• Strony: 173--193
• Opis fizyczny: tab., fot., schem.

Twórcy

autor

Caporali A.

• Centro Interdipartimentale di Studi e Attivitá Spaziali CISAS'G. Colombo', and Dipartimento di Geologia, Paleontologia e Geofisica, University of Padova, Italy

autor

Dalla Torre A.

• Centro Interdipartimentale di Studi e Attivitá Spaziali CISAS'G. Colombo', and Dipartimento di Geologia, Paleontologia e Geofisica, University of Padova, Italy

autor

Praticelli N.

• Centro Interdipartimentale di Studi e Attivitá Spaziali CISAS'G. Colombo', and Dipartimento di Geologia, Paleontologia e Geofisica, University of Padova, Italy