The radar is used in identifying, tracking (with integrated ARPA) and positioning of vessels (including one’s own vessel) among other things in order to adhere to the COLREGs so as to safely navigate a ship from one point to another.
The marine radar is classified under the x-band (10 GHz) or S-band (3GHz) frequencies. The x-band, being of higher frequency is used for a sharper image and better resolution whereas the S-band is used especially when in rain or fog as well as for identification and tracking.
SOLAS rule
SOLAS Chapter 5, Regulation 19 states that “All ships of 3000 gross tonnages and upwards shall, in addition to meeting the requirements of paragraph 2.5, have a 3 GHz radar or where considered appropriate by the Administration a second 9 GHz radar, or other means to determine and display the range and bearing of other surface craft, obstructions, buoys, shorelines and navigational marks to assist in navigation and in collision avoidance, which are functionally independent of those referred to in paragraph.”
Main features of marine radar
- The parabolic radar antenna transmits and receives electromagnetic waves
- The frequency and the time taken by the flashes to return (reflections) to the radar receiver of the ship helps to find out whether the route of the boat can be continued with or not.
- On the PPI, the reflections can be seen so that identifying the actual distance of the objects can be even easier. The same paint on the PPI can be also be checked for determination of the bearing of the target.
How does marine radar work?
The term “Radar” is an acronym for Radio Detection and Ranging”. The radar system out electromagnetic waves as a high-speed, signal which will travel several miles in the direction of radar facing. If there are no objects in the direction of the wave, the radar screen will show blank.
Radar basically reads two things – The position of the object and the direction of the same.
Position of the object: The radar antenna is continuously rotating on top of the ship sending and receiving signals. Hence, the radar is sweeping the signals all around the ship. As the radar pulse waves are reflected by an object, it will travel in the same direction and will be received by the radar detecting the position of the object. When the pulses are received back, the computer screen will log the position.
Distance from the ship: As the radar antenna is constantly sending and receiving signals from the object on the way of the electromagnetic signal, the received signal is sent back to the computer unit, which calculates the time taken for the signal to reflect back to the radar. Once the computer knows the time, it will calculate the distance by using the speed and time formula.
Marine Radar Diagram
The basic components of marine radar are shown in the below diagram:
Uses of Marine Radar
- To calculate range and bearing of a target and thereafter use the information to determine speed, course etc
- Integration with other shipboard equipment (such as ECDIS) to derive precise data
- Navigating own vessel and her course with regard to collision avoidance
- Fixing the ship’s position using terrestrial objects such as lighthouses, buoys etc
- Differentiating between targets in high traffic density areas
- Determination of the weather, to an extent
- Use by VTS in controlling coastal traffic
- Usage of features such as parallel indexing to ensure safe navigation
- Alleviating workload on the OOW on the bridge
- Used extensively in pilotage that covers the above aspects
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Source: marineinsight
