(This article is part of the unmanned vessel knowledge series – Practical Applications in Lake Environmental Protection)
If you’ve ever seen a small boat gliding quietly along the river in a Z-shaped path, with various sensors mounted on its hull and a thin line trailing behind it, it’s neither lost nor sightseeing—it’s conducting an underwater health check for the river.
Unmanned boats are becoming indispensable “reconnaissance units” in the management of China’s lakes and rivers. They perform two critical tasks: identifying pollution discharge points and measuring water quality. These tasks were previously impossible, difficult, or slow to accomplish by humans; now, with underwater robots taking over, the situation has completely changed.
1. Identify the discharge outlet: Conduct an underwater CT scan of the river channel.
Traditional manual inspections rely on environmental officers conducting foot patrols along riverbanks. Many discharge outlets are not even visible above the water surface—they lie hidden beneath the riverbed, embedded within embankments, or disguised as ordinary drainage pipes. From the shore, nothing can be seen. Previous efforts to trace water quality sources often faced the dilemma of being “visible but difficult to investigate thoroughly,” with deeply buried underwater and complex underground pipelines posing significant challenges for monitoring.
The advent of unmanned boats is equivalent to equipping river channels with an “underwater CT scanner.”
Sonar Exploration: Eliminating Hidden Pipelines. In October 2025, Tongzhou District in Nantong, Jiangsu Province conducted a survey of the Shushi River, covering a total river section length of approximately 5.31 kilometers. During the operation, an SL40 unmanned vessel equipped with a customized Shark-U series side-scan sonar was deployed; survey personnel strictly maintained a speed limit of no more than 1 meter per second to ensure accuracy. Underwater images were transmitted in real time to ground-based stations, enabling repeated inspections and subsequent detailed analysis of suspected locations, ultimately identifying 21 hidden pipelines and 6 visible discharge points underwater, thereby fully mapping the extent of pollution outlets along the river.
The working principle of sonar is not complicated: the vessel emits sound waves toward the seabed; when these waves encounter different objects, they reflect back. A receiver on board captures these echoes and generates high-precision underwater images
in real time—akin to equipping a river channel with “sensitive ears” —simultaneously transmitting data and creating a “CT
scan” of the channel to accurately determine pipeline contours, materials, and burial depths. “In the past, we relied on experience for estimation and manual excavation, which was time-consuming, labor-intensive, and prone to omissions. Now sonar provides a clear picture of the subsurface conditions, enabling highly targeted remediation efforts!” remarked the head of the tracing team.
Space-ground coordination: integrated operations across water, land, and air. Along the Minsheng River in Haimen, Nantong, a technology-driven river patrol initiative involving multiple departments has been quietly launched. Unlike previous efforts, this operation features two cutting-edge technological tools—the unmanned sonar vessel and drones—as its primary assets.
The unmanned sonar vessel slowly entered the water, utilizing a high-precision sonar system to scan the riverbed topography and underwater environment. This equipment, employing multi-beam detection technology, can accurately identify concealed pollution sources such as submerged pipes and hidden discharge outlets. Simultaneously, a drone took off and conducted comprehensive scanning along the riverbank, swiftly detecting anomalies in the shoreline. Through coordinated ground-air efforts, the investigation team identified and precisely located two discharge outlets on the west bank of the Minsheng River. Using acoustic imaging technology, the unmanned sonar vessel generated three-dimensional images of the underwater structures beneath these outlets, clearly displaying key parameters including pipe diameter and inflow angles.
“Traditional manual inspection requires team members to conduct foot patrols along riverbanks, which is not only inefficient but also prone to visual blind spots and safety hazards,” stated staff at the Haimen Ecological Environment Monitoring Station. “Now, through the coordinated use of unmanned boats and drones, we have achieved integrated three-dimensional monitoring of rivers across water, land, and air, significantly enhancing both inspection efficiency and accuracy.”
AI empowerment: enabling unmanned vessels to independently “interpret” issues. In Yangzhou, the new generation of intelligent unmanned monitoring boats are equipped with AI-powered recognition cameras and side-scan sonars. Leveraging AI image recognition technology, these vessels can rapidly identify various common issues such as floating debris in waterways and abnormal discharge outlets, automatically uploading detected problems along with their locations to the system in real time. Featuring dual modes of remote control and automated patrol, operators can either perform real-time operations or pre-set inspection routes for fully automated river monitoring.
On the Xiaoqing River in Weifang, Shandong Province, a unmanned vessel over one meter long navigates the waterway. Its top-mounted 180-degree high-definition camera captures real-time images of the surrounding environment, while underwater multi-parameter sensors and side-scan sonar simultaneously transmit monitoring data to the cloud. The unmanned ship autonomously plans its route, continuously monitors key parameters—including COD, total nitrogen, total phosphorus, ammonia nitrogen, pH value, dissolved oxygen, conductivity, and turbidity—and precisely identifies abnormal readings at discharge outlets.
II. Water Quality Testing: From “Taking Photos” to “Taking Videos”
Traditional water quality monitoring involves taking “photographs” at several fixed points to determine the composition of the water at each location. In contrast, unmanned vessel-based mobile monitoring utilizes ships equipped with instruments that travel across the water surface while conducting measurements, effectively capturing “videos” of the entire aquatic area. Photographs capture a single instant, whereas videos record continuous changes over time.
One-touch water sampling with vertical suction. Traditional water quality sampling required staff to travel by boat to designated locations, submerge the sampling device underwater, retrieve it, then package, label, and refrigerate the samples—a process that was both time-consuming and labor-intensive. Unmanned boats have completely simplified this step. From shore or within a command vehicle, operators issue a one-touch sampling command via a remote control, and the sampling device on board activates immediately. Unlike conventional horizontal drag sampling methods, this system employs a vertical suction design that directly extends into the water body to collect samples. The advantages of vertical sampling include precise control over sampling locations, avoidance of water disturbance caused by vessel movement, and collection of “original” water samples from specific depths, ensuring higher representativeness. Upon completion, samples are automatically stored in the onboard refrigerated container and await subsequent laboratory analysis.
On-site testing with real-time data transmission eliminates the need to send water samples back to the laboratory for days of waiting. The unmanned vessel is equipped with a built-in detection module that can collect water samples during navigation and perform rapid on-site analysis of 13 key water quality parameters, including total phosphorus, total nitrogen, ammonia nitrogen, and COD (Chemical Oxygen Demand). Data is shared in real time with the monitoring center via a 5G network, while the electronic map on the command platform synchronously displays the concentration distribution of each parameter—any exceedances of total phosphorus or anomalies in ammonia nitrogen are clearly visible on the screen.
Microscopic-level multispectral sensing. In addition to conventional chemical parameters, unmanned vessels can also be equipped with multispectral water quality sensors. Different pollutants and algae exhibit distinct reflection, absorption, and scattering characteristics under light. By capturing spectral signals across various wavelength bands, these sensors can accurately detect subtle changes in water quality that are imperceptible to the naked eye—such as a slight increase in chlorophyll concentration or abnormal fluctuations in dissolved organic matter levels. These changes often serve as early indicators of water quality deterioration, being detected by the sensors long before visible signs like “greening of the water” or “water odor” appear.
Infrared and sonar technology: serving purposes beyond mere water quality assessment. The health of water quality depends not only on dissolved substances but also on the presence of harmful contaminants. High-definition infrared cameras installed on unmanned vessels can accurately detect abnormal heat sources at night or in low-light conditions—discreetly discharged wastewater often exhibits temperatures distinct from natural water bodies, making it invisible to infrared detection. Sonar systems conduct continuous underwater scanning to identify hidden pipes, assess sediment accumulation, and detect potential hazards in underwater structures. Water quality monitoring and hazard identification proceed concurrently, enabling a single vessel to address multiple issues simultaneously.
III. Challenges and the Future
The application of unmanned vessels in discharge outlet inspection and water quality monitoring has progressed beyond the “concept validation” phase and entered into genuine large-scale operations. However, it is not a panacea.
In complex areas with dense aquatic vegetation, the propellers of unmanned boats are prone to entanglement; in remote lake regions with weak signal coverage, remote operation and real-time data transmission may be impaired; sonar detection accuracy is significantly affected by water turbidity, leading to reduced identification performance in river sections with high sediment content. Furthermore, aligning the data collected by unmanned boats with existing environmental protection standards and utilizing it as a basis for enforcement still requires supporting technical guidelines and regulatory frameworks.
But these are not fundamental obstacles. From Nantong to Haimen, from Yangzhou to Weifang, and from Baiyangdian Lake to Taihu Lake, unmanned vessels are transforming water environment management from a reliance on manpower-intensive approaches to intelligent decision-making. What once required an entire team several days to complete water area scans can now be accomplished by a small vessel in just a few hours; the locations of discharge outlets, previously determined through empirical estimation, are now clearly visible on sonar images; and instead of waiting for pollution outbreaks to respond hastily, real-time data transmission enables proactive risk warnings.
When you stand by the river and observe a small boat moving quietly in a Z-shaped pattern on the water, it may be conducting a comprehensive health assessment of the river. Beneath the surface lies the secret of hidden pipelines, as well as the hope for a city transitioning from “passive management” to “active prevention and control.”