THE RADAR

The word RADAR has been derived from the phrase "Radio Detection and Ranging". Its principle is simple. A short burst of electromagnetic energy is thrown out, bounces off a target and then returns. If we are able to time the interval between the transmission of the pulse and the return of the echo, and if the velocity of propagation is known, then, by multiplying half the time interval by the velocity, the distance to the object causing the echo can be found, the radar uses electromagnetic waves. The transmitted burst must be short. The radar receiver is blocked during the transmission period and the sooner the transmission is over, i.e. the shorter the pulse, the earlier the set is ready for reception.

The Marine radar has been designed primarily as an anti-collision aid. the radar eye — or scanner — moves with the ship, and distances and bearings are recorded with respect to this moving observation post. Echoes on the screen of moving objects are therefore subject to two movements, first the motion of own vessel reversed and secondly, the true motion of the target.

Under certain weather conditions, as for example heavy seas, rain, or snow or under certain atmospheric conditions when radar visibility is below normal, response of target can be greatly reduced. Shadow effects may confuse target interpretation. This makes the picture, especially at medium and long ranges, difficult to understand and the chance of errors can be high if a position by radar is obtained.

Plotting has two purposes: it can show us whether danger of collision exists, how close we will pass off the target and how much time there is left before this will take place.

The second purpose is connected with one of the limitations of radar which does not show up the aspect or leading edge of an isolated small target except at very close range.

The officer of the watch should use the radar when appropriate and whenever restricted visibility is encountered or expected, and of all times in congested waters, having due regard to its limitations. When radar is in use, the officer of the watch should select an appropriate range scale, observe the display carefully and plot effectively.

The officer of the watch should ensure that range scales employed are changed at sufficiently frequent intervals so that echoes are detected as early as possible and that small or poor echoes do not escape detection. Plotting or systematic analysis is commenced in ample time, remembering that sufficient time can be made available by reducing speed if necessary.

In clear weather whenever possible the officer of the watch should carry out radar practice. It is important for navigators & pilots to realise that properly - sited Shore - based Radar has a number of advantages over Shipborne radar.

Valuable information in some areas can be obtained from shore - based Radar stations by using HF R/T in case the ship's radar breaks downor develops a drop in its performance.

II.NOTES:

bounce - отскакивать, рикошетировать

propagation - распространение

multiply - умножать, множить, увеличивать

confuse - смешивать, спутывать

congested waters - перегруженные, тесные воды

plotting - прокладка курса

shipborn radar - судовой радар

leading edge - передняя кромка

ample time - достаточно времени

III. ANSWER THE FOLLOWING QUESTIONS:

1. What has the marine radar been designed for?

2. What does the radar give to seafarers?

3. When should the officer of the watch use the radar?

4. How can valuable information be obtained?

5. What are limitations of radar?

Поиск по сайту: