How do we utilise radar for normal navigation purposes under normal conditions of visibility? There are four basic ways: Fix by radar range and visual bearing. This is used when there are few recognisable navigation marks ashore for visual bearings. Fix using radar ranges as position arcs. This is the most accurate method of obtaining…
Radar is referred to as an aid to navigation because it has certain shortcomings that could result in a collision or grounding if it is relied on exclusively. These shortcomings are: Size of target. Radio waves reflect very well from large objects but sometimes small objects are missed because of their size, shape or freeboard…
What is the nature of the transmission and how does it affect the performance of the radar? There are a number of parameters which we can look at: Power Output. Obviously, the power output of the different radars will differ from one another, but to give one an idea of the power required, navigation radars…
Although radars have become more sophisticated with the advances in technology, it is intended to give a very basic description of the components and workings of a typical radar system. The block diagram that follows is a very simplified version of a radar and must be seen as such. The process begins in the Master…
Most marine radars operate in the 10 GHz (3 cm wavelength) and 3 GHz (10 cm wavelength) frequency bands. Although a bit outdated, these bands are still referred to as X band (10GHz) and S band (3 GHz). Radars operating in the 10 GHz band (3 cm wavelength) provide much better definition (more detailed picture)…
Introduction Radar is an acronym derived from RAdio Detection And Ranging. It is an electronic detection system making use of super high frequency radio signals which are reflected off objects in their path. By utilising specially designed antennas and control equipment, it is possible to obtain reasonably accurate bearings of objects and with a super…
An amplitude is the “azimuth” of a heavenly body when it is on the observer’s rational horizon. The angle at the zenith between the prime vertical circle (the vertical circle passing through the east and west points) and the vertical circle passing through the body is called the amplitude of the body. Amplitude formula To…
In order to determine the error of the gyro or magnetic compass by astronomical observation, one must be able to find the true bearing of a celestial body from the observer at any time. By comparing the compass bearing with the bearing calculated at a specific time, one can determine the error of the compass.…
When using the observation of heavenly bodies to determine geographical position, a “day’s work” for a navigator comprises five sets of astro sights (provided the weather is cooperative): During morning nautical twilight the navigator will take the sextant altitudes of at least three or four heavenly bodies and using this will be able to put…
In sub-paragraphs h to k of the procedure, the true bearing is obtained through the use of the A, B, C tables in Nories. There is an alternative method of determining true bearing, namely by calculation. There are two formulas that could be used: Sine formula. In order to convert the azimuth angle to a…