GB1359298A - Integrated navigation systems for ships - Google Patents

Abstract

1359298 Radio navigation ESSO RESEARCH & ENG CO 20 Aug 1971 [1 Sept 1970] 41715/70 Heading H4D A shipborne navigation system has a number of sensors giving position information and computer means for determining the best estimate of position by considering appropriate sensors. The system determines the error in the estimated position from a knowledge of the sensor accuracies and decides if the error is acceptable for the general area in which the vessel is located, e.g. a greater accuracy is preferred if the vessel is in coastal waters than oceanic. In addition the system decides if the error is acceptable for the vessel to proceed to the next area of the voyage. The system utilizes a computer performing the algorithm of Fig. 1. The availability of sensors is determined by the vessel's position, e.g. the oceanic sensors may not be suitable or available for coastal areas. The computer decides at 3 which of the available sensors is most accurate and reads the output. At 5 the availability of other comparably accurate sensors is determined. If there are any available then the most accurate one is read at 7. This process continues until no more comparably accurate sensors are available, in which case the readings are combined at 9 and the vessel's position given an initial estimate at 11. However, the initial estimate may indicate that one of the sensors is unsuitable for the vessel's general area, e.g. if in coastal waters and an oceanic sensor is giving an output. If so, that sensor is discounted at 15 and the whole process repeated from 5. Eventually, all such spurious sensors are discounted and the output from each used sensor compared at 17 to the combined or averaged outputs at 11. If the output of any sensor is seriously different from the output at 11 then that sensor is in error, a warning is given at 18 and the sensor discarded. The whole process is repeated until all erroneous sensors are discarded and the output at 11 gives the best estimated position. From a knowledge of the accuracies of the used sensors the error E 0 in position is determined at 19. The output from 11 is used at 21 to determine the present phase P 1 of the voyage, i.e. the vessel's general area. The error E 1 in position acceptable in phase P 1 is determined at 23 and at 25 it is decided if E 0 >E 1 . If so, then an alarm is given at 27 indicating that the vessel's position is not known to sufficient accuracy. In addition, the error in position is displayed. If E 0 < E 1 then the course to be made good is calculated at 28. The next phase P 2 of the voyage is determined at 29 and the error E Z allowable in P 2 determined at 31. If E 0 > E 2 it is not safe to proceed to P 2 and a warning is given at 35. If E 0 < E 2 then the algorithm finishes at 37.