Reliable Single Frequency Dual Antenna Processing System for Marine Dredging Applications

Darren Cosandier, Koji Kittaka and Kiyoaki Soen

Abstract:	GPS real-time kinematic (RTK) has been utilized for harbor dredging applications for a number of years. Such applications require both accurate position and heading in order to obtain the location of the dredging vessel implements. The method described here involves mounting two remote GPS antennae on the vessel, denoted R1 and R2. Their distance separation is pre-calibrated and will remain constant with vessel dynamics. A base station (M) is also employed on shore. The vessel’s position is obtained by solving for the vector M-R1 or M-R2, while vessel azimuth is computed from R1-R2. Optimal accuracies are obtained using on-the-fly (OTF) techniques. Traditionally, single frequency RTK can require long initialization times to obtain reliable results—especially for base to vessel distances longer than 5 km. Times of 10 to 25 minutes are common. Nonetheless, the initialization time can be reduced significantly if the R1-R2 distance is considered. This requires specialized RTK software that solves for both M-R1 and M-R2 in a combined OTF solution. The constraints employed to achieve faster base-to-vessel initialization times include the R1-R2 distance constraint and the M-R1, M-R2 and R1-R2 ambiguity constraint. In addition, processing between R1-R2 directly allows for more accurate azimuth determination since such processing is not affected by atmospheric errors associated with a distant base. Results are presented for two field trials in Japan, including shipborne results on a dredging vessel and car based results using a much shorter antenna separation. The various modes of processing are compared along with their initialization times. For the shipborne results, on average, the distance constrained dual antenna solutions initialized in 7.8 minutes using a minimum time of 5 minutes. Of 28 tests, 27 had correct solutions. When compared to a methodology not applying the distance constraints, times were slower by 60% with one failure as well. In the car tests, the average time drops to 5.7 minutes using a minimum time of 3 minutes. The initialization time for the car results was significantly better than for the shipborne results mostly due to better satellite geometry, but a 1.0 m separation (as opposed to 12 m for the shipborne) may also play a factor.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	1281 - 1292
Cite this article:	Cosandier, Darren, Kittaka, Koji, Soen, Kiyoaki, "Reliable Single Frequency Dual Antenna Processing System for Marine Dredging Applications," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 1281-1292.
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