KUP 19: Have knowledge of the fundamentals of radar and automatic radar plotting aids (ARPA)

Learning objective:
The learning objective is to equip learners with a solid understanding of the fundamental principles of radar systems and automatic radar plotting aids (ARPA). This includes gaining knowledge of radar operations, understanding how ARPA assists in tracking and predicting the movement of vessels, and ensuring navigational safety through the effective use of radar technology in various maritime contexts

Content

1. Introduction

Electronic navigation systems have revolutionized the way mariners navigate at sea, providing accurate and real-time information to enhance safety, efficiency, and situational awareness. Over the years, significant advancements in technology have led to the development of sophisticated electronic navigation systems that have transformed the maritime industry. Let’s explore some of the key advances in electronic navigation systems and their impact on maritime navigation.

1). Electronic Chart Display and Information Systems (ECDIS):
ECDIS has replaced traditional paper charts in many vessels, offering digital navigation capabilities. These systems integrate electronic charts, GPS positioning, and sensor data to provide a comprehensive and interactive display of the vessel’s position, surrounding objects, and navigational information. ECDIS enhances situational awareness, enables precise route planning, and facilitates automatic alerts for potential dangers or deviations from planned routes [1].

2). Automatic Identification System (AIS):
AIS is a transponder-based system that allows vessels to exchange vital information, such as vessel identity, position, course, and speed, with other AIS-equipped vessels and shore-based stations. AIS enhances collision avoidance, vessel tracking, and traffic management, enabling mariners to identify and monitor nearby vessels in real-time. This technology significantly improves situational awareness, particularly in congested waterways or areas with limited visibility [2].

3). Radar and Automatic Radar Plotting Aid (ARPA):
Radar systems have been a fundamental tool for maritime navigation, providing essential information about surrounding vessels, land masses, and weather conditions. Advanced radar systems, coupled with ARPA, offer enhanced target tracking capabilities, automatic plotting of target movements, and alarms for potential collision risks. These systems assist mariners in monitoring vessel traffic, detecting potential hazards, and making timely navigational decisions [3].

4). Global Navigation Satellite Systems (GNSS):
Global Navigation Satellite Systems (GNSS) are integral to modern navigation, providing position data through a constellation of satellites orbiting the Earth. The first and most widely known of these systems, or constellations, is the Global Positioning System (GPS), developed and operated by the United States. Other constellations include Galileo (European Union), BeiDou (China), and GLONASS (Russia) [4].

GNSS satellites broadcast their location and time. The receiver calculates its distance to each satellite by comparing the sent and received times. Using signals from three satellites, the receiver determines its position via trilateration. A fourth satellite is needed to correct the receiver’s clock error. Combining signals from multiple constellations enhances accuracy and performance. GNSS signals consist of three main parts: the navigation message, code, and carrier. The navigation message provides satellite orbit data and a timestamp. The code, or pseudorandom noise (PRN), uniquely identifies each satellite and helps calculate the distance (pseudo range). The carrier is the sinusoidal wave that transmits the code, operating in the L-Band radio spectrum.

5). Integration and Connectivity:
Modern electronic navigation systems offer increased integration and connectivity, allowing seamless exchange of information between different onboard systems. Integration with other bridge systems, such as radar, ECDIS, and AIS, enables data sharing and enhances the overall functionality of the systems. Furthermore, connectivity with shore-based systems and access to real-time weather and navigation information further improves decision-making and voyage planning.

These advances in electronic navigation systems have transformed maritime navigation, offering mariners unprecedented capabilities to navigate safely and efficiently. The integration of these systems has significantly improved situational awareness, collision avoidance, and route optimization. However, it is crucial for mariners to receive proper training and remain proficient in using these technologies to ensure their effective and responsible use.

As technology continues to advance, electronic navigation systems will likely evolve further, incorporating artificial intelligence, machine learning, and enhanced connectivity. These advancements will continue to empower mariners with sophisticated tools to navigate with precision, reduce risks, and optimize their voyages. Embracing these advancements and staying up-to-date with the latest electronic navigation systems are crucial for mariners to navigate confidently and safely in today’s maritime environment.

2. Fundamentals of RADAR and APPA

RADAR

RAdio Detection And Ranging

Developed just before WWII [5]

The basic principle behind radar is simple – extremely short bursts of radio energy (travelling at the speed of light) are transmitted, reflected off a target and then returned as an echo. Radar makes use of a phenomenon we have all observed, that of the ECHO PRINCIPLE.

Radar operates by generating a microwave radio frequency pulse and directing it in a narrow beam from a rotating antenna. After the pulse is transmitted, the receiver detects the echoes and amplifies them to produce bright spots or areas on the indicator. The time between the transmitted pulse and echoes is interpreted as distance (range) from own ship. 

As used aboard ships and other surface craft, radar data are displayed on a plan position indicator, a map-like display with its own ship in the center. Other vessels, buoys, and land masses show up as bright spots or areas on a dark background. 

Using a reflection plotter and plotter pencil (similar to a grease pencil), the radar observer can, by successive plots of other vessels, track and calculate the movements of other vessels and assess any risk of collision

ARPA

Automatic Radar Plotting Aid

Developed for marine usage in the 1970’s

Fittings aboard tankers were made mandatory in 1982, or other classes of ships soon after. On an ARPA the radar observer can designate a “target” ship of interest and the ARPA calculates the speed and course of the ship and assesses the risk of collision. Targets may also be “acquired” automatically and tracked. A number of targets can be tracked simultaneously. A “dangerous” target (one having a risk of collision) will be highlighted and an alarm will sound. On any target being tracked, the closest point of approach (CPA) and time to closest point of approach (TCPA) are calculated and displayed.

• Primary items on the radar screen:

Information display on ARPA radars was simple, including ship position, course, speed, bearing, distance, CPA and TCPA. Except for position, course and speed, there were some others in AIS display, such as ship MMSI, name, type and navigational status.

• Fundamental operations of radar and ARPA:

Radar operates by generating a microwave radio frequency pulse and directing it in a narrow beam from a rotating antenna. After the pulse is transmitted, the receiver detects the echoes and amplifies them to produce bright spots or areas on the indicator.

A radar system consists of a transmitter that produces electromagnetic waves, a transmitting and receiving antenna (often the same antenna is used for both), and a receiver and processor to determine the properties of the objects.

3. Principles of chart work

Chart work is an essential skill for mariners, enabling them to plot courses, determine positions, and navigate accurately across vast oceans and waterways. By applying the principles of chart work, mariners can confidently navigate their vessels, avoid hazards, and reach their destinations safely. Let’s explore the key principles that underpin this critical aspect of maritime navigation.

Scale and Measurement:
Charts are scaled-down representations of larger areas, allowing mariners to visualize and plan their routes. Understanding the scale of a chart is crucial for accurate measurements and calculations. Mariners use various navigational tools, such as dividers, parallel rules, and compasses, to measure distances, plot courses, and determine positions on the chart accurately.

Chart Datum and Soundings:
Chart datum provides a reference point for measuring water depths on nautical charts. Mariners must account for the tidal variations and apply appropriate corrections to ensure the accuracy of soundings (water depth measurements) on the chart. By using the correct chart datum and applying tidal corrections, mariners can navigate safely and avoid shallow areas or submerged hazards.

Magnetic Variation and Compass Rose:
Magnetic variation is the angular difference between true north and magnetic north. It is important for mariners to apply the appropriate magnetic variation correction to ensure accurate compass readings. The compass rose on the chart helps mariners align their compasses and determine magnetic bearings, enabling them to navigate along desired courses with precision.

Bearings and Fixes:
Bearings are the directions measured in degrees relative to a reference point, such as a navigational aid or landmark. By taking bearings of visible objects from their vessel and plotting them on the chart, mariners can determine their positions or obtain visual fixes. Fixes are positions determined by intersecting lines of bearings, providing mariners with accurate location information on the chart.

Dead Reckoning and Estimated Position:
Dead reckoning (DR) is a method of estimating a vessel’s position by calculating its speed, course, and time. Mariners use their vessel’s course and speed, combined with elapsed time, to project their position on the chart. Estimated positions (EPs) are based on the DR calculations and provide a continuous reference for navigating between fixes or when visibility is limited.

Danger Bearings and Clearing Bearings:
Danger bearings and clearing bearings are used to navigate safely around hazards or obstructions. A danger bearing is a line drawn on the chart that represents the direction in which a vessel should steer to avoid a hazard. Clearing bearings, on the other hand, are lines drawn to ensure safe clearance of an object or a specific area.

Great Circle and Rhumb Line:
When planning long-distance voyages, mariners can choose between great circle routes and rhumb lines. Great circle routes follow the shortest distance along the surface of a sphere, while rhumb lines represent constant compass directions. Mariners consider factors such as time, distance, weather, and navigational hazards to determine the most suitable route for their voyage.

By applying these principles of chart work, mariners can confidently navigate the seas, make informed decisions, and ensure the safety of their vessels and crew. It is crucial for mariners to stay updated with the latest charts, utilize accurate navigational tools, and rely on proper techniques to maintain accuracy and precision in their chart work. With a solid foundation in chart work principles, mariners can navigate with accuracy, confidence, and efficiency in the ever-changing marine environment.

Recommendation

References

1. Hecht, H. (2006). The electronic chart: functions, potential and limitations of a new marine navigation system. Geomares publishing.
2. AIS transponders. https://www.imo.org/en/OurWork/Safety/Pages/AIS.aspx
3. ATEX MARINE. “ARPA RADAR”. https://atex.ae/arpa-radar/
4. Marwan Ramadan. © 2024 Swift Navigation, Inc. “What is GNSS Positioning?”. https://www.swiftnav.com/resource/blog/what-is-gnss-positioning
5. Whiton, R. C., Smith, P. L., Bigler, S. G., Wilk, K. E., & Harbuck, A. C. (1998). History of operational use of weather radar by US weather services. Part I: The pre-NEXRAD era. Weather and Forecasting, 13(2), 219-243.