1.3 Types of Navigation
Methods of navigation have changed through history. Each new method has enhanced the mariner‘s ability to complete his voyage safely and expeditiously. One of the most important judgments the navigator must make involves choosing the best method to use. Commonly recognized types of navigations are listed below.
Dead Reckoning (DR) determines position by advancing a known position for courses and distances. It is accepted that only course and speed determine the DR position. Correcting the DR position for leeway, current effects, and steering error result in an estimated position (EP). An inertial navigator develops an extremely accurate EP.
Piloting involves navigating in restricted waters with frequent determination of position relative to geographic and hydrographic features.
Celestial navigation involves reducing celestial measurements to lines of position using tables, spherical trigonometry, and almanacs. It is used primarily as a backup to satellite and other electronic systems in the open ocean.
Radio navigation uses radio waves to determine position by either radio direction finding system or hyperbolic systems. Radar navigation uses radar (radio detecting and ranging) to determine the distance from or bearing of objects whose position is known. This process is separate from radar‘s use as a collision
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avoidance system (ARPA：Automatic Radar Plotting Aids) Satellite navigation uses artificial earth satellite for determination of position of vehicles.
Inertial Navigation is a totally self-contained navigation system providing vehicles‘ position in response to inertial effects on system components.
Integrated Navigation is a combination of two or more than two methods or equipment of navigation to get more accurate position, attitude and speed fixing. Integrated Bridge System (IBS) is a typical integrated navigation system that takes inputs from various ship sensors, electronically display positioning information, and provide control signals required to maintain a vessel on a preset course.
1.4 Phases Of Navigation
Four distinct phases define the navigation process. The mariner should choose the system mix that meets the accuracy requirements of each phase.
Inland Waterway Phase: Piloting in narrow canals, channels, rivers, and estuaries.
Harbor /Harbor Approach Phase: Navigating to a harbor entrance and piloting in harbor approach channels.
Coastal Phase：Navigating within 50 miles of the coast or inshore of the 200 meter depth contour.
Ocean Phase: Navigating outside the coastal area in the open
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sea.
1.5 The Earth
1.5.1 The shape of the earth
The earth is an oblate spheroid (ellipsoid)(a sphere flattened at the poles). Measurements of its dimensions and the amount of its flattening are the subject of geodesy. However for most navigational purpose, assuming a spherical earth introduces insignificant error.
The first approximation: The earth is regarded as a sphere and can be described as follows,
x2?y2?z2?R2
where
R
is
the
radius
of
the
spherical
earth,
R=6371.02?0.05km.(1964年国际天文学会通过International Astronomical Union, IAU)。
The second approximation: The earth is regarded as an ellipsoid, which can be described as:
x2a2?y2a2?z2b2?1
where a is the equatorial earth radius (or semi-major axis), b the polar earth radius (semi-minor axis).
From the above definition, we can get the concept of
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ellipticity(or Compression of the Earth).
??ellipsoid Clarke (1866) Hayford (1910) Krasov -sky (1940) Semi-major axis (km) 6378.206 6378.388 6378.245 a?b aSemi-minor Ellipticiaxis (km) ty 6356.584 6356.912 6356.863 1/295 1/297 1/298.3 Used in USA West Europe USSR Table Reference Ellipsoid Parameters The third approximation: the earth is regarded as a spheroid, which even in the parallel of latitude is not a circle, but an ellipse. 1.5.2
The point, line and plane on the earth
North Pole and South Pole: The intersection of rotation axis and the earth ellipsoid.
The earth’s axis of rotation is the line connecting the North Pole and South Pole. The
angular
speed
of
the
earth
rotation
is
??7.2921158?10?5rad/s
A great circle is the line of intersection of a sphere and a plane through its center. This is the largest circle that can be drawn on a sphere. The shortest line on the surface of a sphere between two
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points on the surface is part of a great circle.
A small circle is the line of intersection of a sphere and a plane which does not pass through the center.
The meridian is usually applied to the upper branch of the half-circle from pole to pole which passes through a given point. The opposite half is called the lower branch.
The prime meridian is used as a reference line from which longitude east and west is measured. It passes through Greenwich, England. (本初子午线通过英国格林威治的零度子午线，用作参考经线，从本初子午线开始分别向东和向西计算全世界的地理经度)
Eastern Hemisphere and Western Hemisphere Equator is the great circle which is vertical to the all meridians.
Northern Hemisphere and Southern Hemisphere A parallel or parallel latitude is a circle on the surface of the earth parallel to the plane of the equator. It connects all points of equal latitude. The equator is a great circle at latitude 0?. The poles are single points at latitude 90?. All other parallels are small circles.
1.5.3 Coordinates
Coordinates, termed latitude and longitude, can define any position on earth. Latitude (L, lat.) is angular distance from the equator, measured northward or southward along a meridian from
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