The marine radar is an essential piece of equipment used on a ship’s bridge during navigational watch to ensure safe passage. It is used to identify, track, and position vessels, including the ship it belongs to, in adherence to international maritime regulations (COLREGs). The radar operates within two frequency bands: x-band (10 GHz) and S-band (3GHz).
The x-band, known for its higher frequency, provides a clearer and more detailed image. At the same time, the S-band is especially useful in adverse weather conditions such as rain or fog, as well as for precise identification and tracking purposes.
Ship radar devices are mandatory as per COLREGS (International Regulations for Preventing Collisions at Sea).
According to 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 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 is functionally independent of those referred to in paragraph.”
The radar is instrumental in preventing sea accidents by providing various functionalities such as determining the closest point of approach (CPA) and time to the closest point of approach (TCPA), EBL, VRM, and more. Moreover, while ships are berthed in ports, the radar can be utilized by the coast guard, Vessel Traffic Service (VTS), and other authorities to monitor nearby vessel traffic. The Plan Position Indicator screen of the radar displays all detected targets, facilitating navigation and vessel monitoring.
Main Features of the Marine Radars
The main features of the marine radars can be explained as follows :
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The parabolic radar antenna transmits and receives electromagnetic waves; as far as a target being displayed is concerned, that is the wave that bounces off a certain object that paints itself on the PPI (Plan Position Indicator).
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The frequency and the time taken by the flashes to return (reflections) to the radar receiver of the ship help to find out whether the route of the boat can be continued or not. The transmission and receiving of the pulse travel twice the distance in going and hitting the target and back; therefore, the target displayed on the PPI is halved concerning its range.
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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 Works
The term “Radar” stands for Radio Detection and Ranging. The marine radar operates based on the fundamental principle of electromagnetic waves. The radar antenna transmits rapid electromagnetic waves to determine the position, including the distance, speed, and direction traveled by the waves, as well as the altitude of the object, whether it is moving or stationary.
Electromagnetic energy moves through the air at a consistently high speed, equivalent to the speed of light (300,000 kilometers per second). The object being detected can be a variety of things, such as ships, boats, terrain, weather formations, or coastlines
The radar system emits electromagnetic waves as a high-speed signal that can travel several miles in the direction the radar is facing. If there are no objects in the direction of the wave, the radar screen will be blank. If there is an object that reflects the wave to the radar, the radar’s computer will determine the distance between the ship and the object, as well as its location. Therefore, the radar essentially reads two things – the position of the object and the direction of the object.
Position of the object: The radar antenna continuously rotates on top of the ship, sending and receiving signals. This means the radar is scanning the signals all around the ship. When the radar pulse waves are reflected by an object, they travel in the same direction and are received by the radar, detecting the object’s position. When the pulses are received back, the computer screen will log the position.
Distance from the ship: Because the radar antenna is constantly sending and receiving signals from the object, the received signal is sent back to the computer unit, which calculates the time taken for the signal to reflect the radar. Once the computer knows the time, it will calculate the distance 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 about 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.
Source: marineinsight.com
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