A guide to identifying and elevating AIS data quality

Originally designed as an anti-collision tool, the Automatic Identification System (AIS) has, over the past two decades, evolved into a comprehensive data collection and analysis system. It is integral to modern maritime operations, providing real-time information about vessel movements, identification, and navigation.

High-quality AIS data is crucial for:

·       Ensuring maritime safety: Errors or gaps in data, such as inaccurate positioning or missing vessel identification, can lead to increased risk of accidents or delayed decision-making in high-traffic areas.

·       Improving operational efficiency: Poor data quality can lead to inefficiencies in scheduling and resource allocation, longer transit times, and increased operational costs.

·       Supporting regulatory compliance: Regulatory authorities use AIS data to monitor vessel compliance with maritime laws, such as IMO and SOLAS regulations and emission controls.

·       Enhancing Search and Rescue Operations: Low-quality data, such as outdated positions or corrupted messages, can delay rescue efforts and increase the risk to human lives and cargo.

The collection and use of quality data are essential for any organization, whether commercial or governmental. Making significant decisions without quality data is like shooting in the dark, and this is no different for the maritime industry.

As data-driven decisions move to the forefront of any organization, understanding how to assess and ensure the quality of AIS data becomes paramount. Let’s discover how we can do that.

Balancing quantity (Unique MMSI counts) with quality (global coverage)

Global AIS coverage is essential for maintaining continuous and comprehensive maritime situational awareness. While the volume of AIS messages and vessels tracked might seem like indicators of data quality, they are not always reliable. For instance, Terrestrial AIS may capture the majority of messages, but these signals typically represent vessels within 40 nautical miles of the coastline, leaving those farther out undetected.

The count of unique MMSI numbers detected, representing the number of distinct vessels tracked over a given time period, is a key metric that reflects the breadth of coverage. However, this metric can be inflated by MMSI misuse or errors, potentially distorting the actual coverage extent. This means relying solely on a single source of AIS data like Terrestrial AIS for vessel tracking can be problematic.

Going beyond Terrestrial AIS:

 Leveraging Satellite AIS data can avoid gaps in AIS coverage and blind spots, empowering you to track vessels accurately and better managing risks to navigation safety, security, and operational efficiency.

Taking it one step further, Enhanced Satellite AIS utilizes advanced satellite technology to expand coverage beyond the capabilities of traditional Satellite and Terrestrial AIS systems. It effectively captures AIS signals from highly congested High Traffic Zones (HTZs), such as the South China Sea, the North and Baltic Seas, the Gulf of Mexico, and busy ports, ensuring that no vessel goes untracked and significantly reducing undetected AIS messages. In dense shipping areas, such as HTZs, where signal congestion and message collisions often impact data quality, Enhanced Satellite AIS excels by delivering up to 115,000 unique MMSIs and providing an additional 65 million AIS messages daily, thereby overcoming the limitations of traditional AIS data collection methods.

Measuring and improving AIS data latency

Latency refers to the delay measured as the difference between the message’s reception and the time it is available to users.

Terrestrial AIS provides near-instantaneous updates; however, this speed is limited by its restricted coverage. Consequently, vessels traveling farther from the coast remain untracked, leading to incomplete and potentially misleading data. Satellite AIS, however, overcomes this limitation by offering consistent, global coverage. This means that, unlike terrestrial systems, Satellite AIS ensures that updates are not only timely but also encompass the entirety of a vessel’s journey. Therefore, the reliability of AIS data is more accurately reflected in its comprehensive global reach rather than just its latency.

Ensuring speed with global coverage:

Real-time AIS from Spire Maritime provides continuous vessel positions with a median latency of under one minute regardless of location. This immediacy, made possible by an interconnected satellite architecture that ensures real-time coverage, enables stakeholders to maintain an accurate and current understanding of maritime activities, which is crucial for timely decision-making, especially in dynamic environments.

For major shipping lanes, the Enhanced Satellite AIS coverage provides a median latency of 11 minutes. While this latency is higher than Terrestrial and Real-time Satellite systems, it offers a significant advantage by covering high-traffic zones where accurate and timely AIS data is essential.

Redetection rate factoring in AIS quality

The Redetection Rate per Time Interval (RRpTI) measures how effectively a system can consistently detect the same vessels over time. RRpTI calculates the percentage of vessels detected within a specific time interval (e.g. 15 minutes) that are redetected in the subsequent interval, expressed as the ratio of vessels redetected to the total number initially detected.

For instance, if a vessel is detected between 0:00 and 0:15 and is again detected in the subsequent interval from 0:15 to 0:30, it is considered a successful redetection, contributing to the RRpTI. A high RRpTI ensures consistent vessel monitoring, enabling real-time tracking and reducing the risk of losing a vessel’s location due to signal gaps. Conversely, a low RRpTI can lead to blind spots, making it challenging to maintain an accurate picture of vessel movements, which can compromise decision-making and response times in critical situations.

A significant improvement in consistent tracking and redetection is observed when Satellite AIS is added to the data feed, compared to using Terrestrial AIS alone. Real-time Satellite AIS leads to an even more substantial increase in reliability and redetection accuracy than relying solely on Terrestrial AIS.

Assessing port coverage

Port coverage refers to the ability to track vessels within port areas, a critical aspect for effective port operations and logistics management. This metric is typically measured as the percentage of baseline port traffic captured, providing insight into how well the system monitors vessel movements within these crucial zones. However, a key limitation is that the baseline for port traffic could be set too low, potentially leading to inflated results and an overestimation of actual coverage. Ensuring an accurate baseline is essential for reliable port coverage assessments and maintaining the integrity of operational and logistical planning.

When considering port coverage, the quality of AIS data depends on the sources used. Relying solely on Terrestrial AIS offers the lowest coverage for both ports and MMSIs. Adding Satellite AIS data enhances coverage, while combining Terrestrial, Satellite, and Real-time AIS achieves the highest percentage of MMSI coverage reported in ports. This underscores the importance of using multiple AIS sources to enhance data accuracy and extend port coverage in maritime operations.

Leveraging flexible delivery methods and tailored data-cleansing services

While high-quality AIS data is crucial, the manner in which this data is delivered plays an equally vital role. Flexible API solutions ensure that users can access both real-time, near real-time, and historical AIS data in the format that best suits their needs, whether it be JSON, CSV, or NMEA format AIS messages as transmitted. Spire Maritime offers a range of delivery methods tailored to diverse use cases, including TCP streaming, GraphQL APIs, and REST APIs with OGC-compliant WFS and WMS standards. This versatility in delivery not only enhances the accessibility of high-quality data but also supports its effective integration into various applications, ensuring that users receive timely and actionable information to make informed decisions.