Small Targets, Serious Threats: Why They Pose a Major Navigational Risk

Some of the most serious threats to safe navigation are small targets that can easily be overlooked. These may include small fishing vessels or pleasure craft without active AIS signals, workboats operating close to the vessel, or buoys and floating objects moving with the waves.

Detecting these targets early and maintaining stable tracks in complex conditions remains a critical navigational safety challenge. BOTIX addresses this challenge with its in-house-developed 4D Imaging Small-Target Radar, which can detect slow-moving floating objects as well as high-speed small craft.

Detection Alone Is Not Enough

Small targets that cannot be detected and tracked continuously can develop into serious collision risks within a very short time.

• In 2016, the bulk carrier CATALINA collided with the fishing vessel Lu Rong Yu 58398 in fog with visibility of approximately 200 metres. The fishing vessel sank, resulting in 14 fatalities and five missing persons.

• In November 2025, a merchant vessel and a fishing vessel collided in waters near Weihai, Shandong Province. The fishing vessel sank, leaving nine persons missing.

These accidents highlight a critical challenge: maintaining continuous, stable and reliable detection and tracking of small targets under complex operating conditions.

Small targets are inherently difficult to track because they are low-profile, physically small and subject to irregular motion.

• Their low height above the water makes their returns particularly susceptible to sea clutter.

• Their small size results in weak reflected radar signals.

• Their unstable motion makes it difficult to maintain continuous tracks.

Together, these characteristics can increase false alarms and missed detections on conventional navigational radar. The challenge becomes more pronounced in high sea states, when stronger sea clutter can further obscure weak target returns.

On a radar display, these returns may appear intermittently or disappear entirely. Their size and intensity may also resemble surrounding clutter, making it difficult to determine whether a return represents a genuine target or environmental interference.

The challenge of small-target detection is therefore no longer simply about seeing a return. It is about continuously and accurately separating potentially hazardous targets from a complex, dynamic and interference-heavy background.

From Detecting Signals to Understanding the Scene

To address the challenge of small-target perception in complex marine environments, BOTIX has developed an integrated solution spanning low-level signal processing and higher-level perception algorithms.

The BOTIX 4D Imaging Small-Target Radar offers a strong inherent signal-to-clutter ratio.

Its narrow beams, short wavelength, wide bandwidth and Doppler-processing capabilities concentrate target-return energy within the range-Doppler domain, while distributing clutter more broadly. This helps suppress fluctuations caused by sea and rain clutter and produces a more stable background against which weak targets can be detected.

This improved signal foundation enables the radar to detect small targets earlier and maintain more stable tracks. To translate this advantage into reliable performance in dynamic marine environments, BOTIX has also developed an algorithm architecture that adapts continuously to changing conditions.

BOTIX’s integrated scene-adaptive algorithms go beyond a conventional sequential detection-and-tracking process by introducing adaptive mechanisms at multiple processing stages.

Designed around the characteristics of maritime radar targets, the system analyzes multiple features in real time, including noise, point-cloud, clustering and tracking data. The results are fed dynamically into subsequent processing stages, allowing parameters to be adjusted throughout the perception pipeline.

For weak small targets whose signal levels fluctuate significantly and are therefore susceptible to missed detections, BOTIX combines regional parameter estimation with two-dimensional spatial detection. In BOTIX testing, this approach improved the probability of detecting weak small targets by approximately 30% under the relevant test conditions.

Making Small Targets Clearly Visible

BOTIX compared the detection performance of its 4D Imaging Small-Target Radar with that of an X-band navigational radar using a 16-metre pilot boat as the target.

Under the test conditions, the pilot boat appeared comparatively indistinct and unstable on the conventional navigational radar display. Its return began to disappear intermittently as the target approached approximately 300 metres and was completely lost at a range of around 100 metres.

By comparison, the BOTIX 4D Imaging Small-Target Radar maintained clearer and more stable imaging under the same conditions. Within the tested 300-metre range, the target return remained stable and the system continued to provide clear perception output.

In complex waters, navigational safety depends heavily on whether a perception system can detect and continuously track small targets, while maintaining reliable situational awareness in fog, at night, under strong clutter and in high sea states.

The BOTIX 4D Imaging Small-Target Radar addresses the challenge of small targets that are difficult to detect or resolve at close range. It combines strong raw-return signal quality, scene-adaptive perception algorithms and stable target output within an integrated capability chain.

By making overlooked targets clearer, more distinguishable and easier to track, BOTIX is helping strengthen navigational safety one detail at a time.