천문항해를 이용한 방위산출 알고리즘 및 임베디드 장치의 구현

Abstract

The celestial navigation uses the sun and stars to determine the position of the vessel and to know the bearing for the voyage. After observing the sun and stars in the sky, the navigators of the ship found their position through a complicated calculation process and sailed to the destination. The celestial navigation was a major task to the navigators and was considered the most important in the voyage.

The compass is used to find the bearing of the vessel and there are the Magnetic compass and Gyro Compass. THD is an electronic device that provides the ship's true heading and is installed on ships of 300GT(Gross Tonnage) and upwards less than 500GT/passenger craft certified to carry 100 passenger or less, which do not carry a Gyro Compass in accordance with IMO regulations. Most ships satisfy the THD of the IMO regulations as Standard Magnetic Compass. The static error limit of THD is set within ± 1.0 °.

The navigational triangle consists of three points that are the pole, the zenith, and the celestial body, three sides that are Colatitude, Polar -distance and Coaltitude and three angles are the Meridian angle, Azimuth angle, and Parallactic angle. In order to calculate the ship's position using the navigational triangle, it is necessary to know the exact time and position of the sun.

Most of the sun's geographical position calculation is using the Nautical Almanac. Also, the planetary theories VSOP 82 and VSOP 87 can be used for obtaining more precise celestial coordinates. By deriving the cycles of the celestial bodies with mathematical calculation, it is possible to obtain the celestial coordinates and rectangular coordinates exactly, and the accuracy of bearing calculation can be further improved. Observation time, the position of the vessel, and celestial body, that is the geographic position of the sun, are required to calculate bearing using an observation. Also, time errors should be minimized to increase the accuracy of the observations. If you know the position of the ship and the geographic position of the sun, it is possible to find the bearing using the algorithm about calculating the bearing of the navigational triangle.

In this paper, we propose the One Body Fix position calculation algorithm that shortens the time for calculating the position using the navigational triangle and simplifies the calculation process. This algorithm derives its position using the sun the Azimuth angle(z), Declination(Dec), and observed altitude. Based on the derived location, we can correct the error by calculating the heading of the ship and true north using Azimuths of the sun and Sight Reduction Tables.

We used the computer and IT technology to computerize the bearing calculation method used in astronomical navigation and the calculation processes that people performed directly. The implemented embedded device has the convenience and accuracy to be used in real ship, and it implemented SW and HW in embedded form. By automating an observation and calculation processes, the operator can reduce the time of bearing calculation.

Experiments have been performed several times to test the accuracy and the result showed an error within 0.2°. These results were within the margin of error about devices by IMO regulations, THD and compass, etc. The implemented embedded device is expected to be very useful for the ship as the convenience and high accuracy.