Introduction to Radar Surveillance and SOLAS Requirements
For decades, radar has played a vital role in maritime navigation, helping to prevent collisions and detect obstacles early.
The history of naval radars dates back to World War II, when they were introduced and effectively used to track and detect warships.
Since the post-war period, radar technology has advanced significantly, and the application of computers to commercial maritime radars has led to the development of the Automatic Radar Plotting Aid (ARPA) system.
ARPA provides radar users with all the necessary information and helps save significant time from target observation to data search using radar plotting and calculations. As a result, radar users can quickly obtain collision avoidance and detection data by simply clicking on a target.
How Radar and the Advanced Research Projects Agency (ARPA) Work
Before delving into radar monitoring, let’s first understand how it works:
Radar (Radio Detection and Ranging) consists of several components, primarily:
a) Transmitter
b) Receiver
c) Scanner
d) Screen
The working principle of radar begins with an oscillator called a magnetron, which has a fixed frequency. The magnetron receives an electrical signal from a power source through a modulator and generates electromagnetic energy called pulses. These pulses are sent to the scanner or antenna through a metal tube called a waveguide.
From the scanner, these pulses are transmitted into the atmosphere. The number of pulses sent through the scanner per second is called the pulse repetition rate. The pulses travel through the atmosphere at the speed of light and reflect after striking any targets in their path. The reflected echo reaches the scanner, where the receiver processes and amplifies it, then displays it as “flashes” on the screen to identify the detected target.
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Radar
The diagram above illustrates the operation of radar. The following components perform their respective functions:
- Delay line: This stores energy received from the power source.
- Modulator: Controls the switching of the magnetron and sends DC pulses from the delay line to the magnetron.
- TR unit: Blocks the receiving end of the waveguide during transmission and the transmitting end during reception.
- Mixer: Mixes the received echo with the local oscillator.
ARPA Operation
ARPA (Automatic Radar Plotting Aid) is a computer add-on to radar. ARPA records the ship’s direction and speed, as well as the direction and speed of targets, and calculates collision avoidance data, simplifying data calculations for the user. ARPA also provides many other functions and controls.
Radar and ARPA Requirements
Chapter V of the SOLAS Convention details the requirements for ships carrying radar and ARPA.
In short, these requirements are as follows:
All ships of 300 gross tonnage and above, as well as all passenger ships, must be equipped with a 9 GHz radar and electronic tracking aids.
All ships of 500 gross tonnage and above must be equipped with an automatic tracking aid to determine the range and direction of other targets.
All ships of 3,000 gross tonnage and above must be equipped with either a 3 GHz radar or a second 9 GHz radar, independent of the primary 9 GHz radar. This second automatic tracking aid (ATA) is used to determine the range and direction of other targets, independent of the primary electronic tracking aid.
SOLAS also permits the use of any other device capable of performing all the functions of radar and ARPA. However, in practice, no other device adequately serves this purpose.
After discussing radar basics, we will focus on the basics of radar surveillance and its critical applications in collision avoidance and early detection.
Radar Watchkeeping
Radar surveillance involves monitoring the radar and applying all its capabilities to fully assess any situation and immediately detect targets to avoid collision.
Radar surveillance is not limited to a single observation; multiple range and bearing observations provide a better understanding of the target’s direction and speed, as well as its course relative to the own vessel.
After a series of rapid observations, the target’s position must be determined and the data verified. Longer observations increase accuracy. The target must be located and monitored until it passes and moves away from the own vessel.
As previously mentioned, the most effective use of radar is to detect targets as early as possible (using the rangefinder) and determine their position before they approach the own vessel.
Early detection of targets makes the actions that the own vessel must take much easier. This also helps avoid close approaches and significant interference, thereby preventing collisions.
When dealing with multiple targets in situations such as fishing traffic, it is best to deal with them individually rather than all at once. Targets that pose a risk of collision must be avoided before prioritizing other targets.
Radar and ARPA must be used as auxiliary means; vessel maneuvers and course changes must be performed with excellent seamanship and following COLREGS standards.
Understanding radar and ARPA control systems is crucial. Only when radar users possess the appropriate knowledge can they fully utilize the benefits of these devices.
Therefore, a thorough understanding of radar control systems and ARPA is essential for effective operation.
Watchkeepers must be able to adjust radar settings when necessary. The most important basic radar control systems include:
a) Interference control systems: rain, gain, and sea
b) Pulse control systems, range control systems
c) Performance monitoring
d) Manual adjustments
Understanding the limitations of the equipment is also crucial in radar monitoring. Excessive reliability of radar and ARPA has contributed to many maritime accidents. Radar users must understand that these devices have limitations, and troubleshooting and data accuracy depend heavily on their performance. Promptly checking radar performance is crucial. Some of the most significant disadvantages of radar include:
- Radar may not be able to detect small vessels, ice, or other small floating objects.
- Targets are not displayed within the radar’s blind and shadowed areas.
- Range discrimination: Two small targets with the same bearing but slightly offset may appear as coincident targets.
- Direction discrimination: Two small targets with the same bearing but slightly offset may appear as a single target.
- False echoes.
We all know that every mariner relies on radar and uses it every day. However, unless we are fully familiar with and proficient in its use, we cannot be completely sure that we are using it correctly.
