Tracking Plastic Waste from City Rivers to Island Beaches: Continuing an Experiment on Remote Sensing of Marine Litter in the Philippines

by Francis Capistrano, Head of Experimentation and Elmerei Cuevas, Social Innovation Analyst, UNDP Accelerator Lab Philippines

June 25, 2025

A plastic bag floats in a polluted ocean, surrounded by debris and trash.

Imagine: you are on an island beach resort. You are lying relaxed on powdery white sand as the gentle warm breeze ruffles your hair and the playful tropical waves tickle your toes. Suddenly, something wet and slimy slaps your face. It’s a piece of plastic. Someone carelessly littered it somewhere, and now it’s getting in the way of your paradise mood.

Irritating, isn’t it?

But the proliferation of plastic waste in pristine waters isn’t just an irritation. In the Island Garden City of Samal in the Davao Region of the Philippines, the matter is not merely about aesthetics but about the viability of their tourism industry as well as the livelihood and health of their communities. The problem, as locals claim, is that the trash—which washes up on their shores, clogs up their mangrove forests, or dirties up their dive sites—came not from their island, but from nearby cities as well.

How does one solve this transboundary issue of marine plastic pollution? And in the first place, how can marine plastic pollution be systematically monitored so it can be better addressed? The United Nations Development Programme (UNDP) Philippines Accelerator Lab (ALab PH) recently conducted an experiment to see if satellite remote sensing technology would be useful in helping to improve the monitoring and surveillance of plastic and other litter in the water. Here’s our story.

Plastic bottles and a trash bag floating in water under a sunny sky.

People on a boat observing a group of dolphins swimming in the blue ocean.

Identifying and monitoring marine litter to better build a circular economy

Since it was set up in 2019, ALab PH has been promoting innovative solutions to help address the problem of marine plastic waste, as the Philippines is tagged among the top global contributors. The Lab treats the problem as a systemic issue that goes beyond waste management, as it is rooted in a “take-make-waste,” a linear economic system. Change requires a shift towards a circular economy, which requires a multiplicity of solutions that address economic, institutional, behavioral, and cultural factors.

Among the experiments pursued by ALab PH to help strengthen enforcement is the use of satellite remote sensing to detect and monitor plastic and other waste that leak into waterways. It first tested the remote sensing technology in Pasig River and nearby tributaries in Metro Manila, in partnership with Pasig City where UNDP Philippines pioneered the systemic approach to promote circular economy at the city level. The first two phases of the experiment were supported by the Japan SDGs Innovation Challenge (JSIC), backed by the Japan Cabinet Office, the Japan Innovation Network, and the global Accelerator Labs Network.

The JSIC grant enabled ALab PH to partner with the Japan Manned Space Systems (JAMSS) Corp. The first salvo succeeded in detecting the waste in water using spectral image sensing, i.e., analyzing available satellite imagery to detect light spectra that correspond to the abundance of waste. Phase 2 of the project was implemented to represent the remote sensing model on a dashboard alongside data gathered by volunteers through citizen science. Learn more about the experiment via this blog and this short video by our late friend Rex Lor, former Head of Solutions Mapping, who led this initiative.

Aerial view of a tropical beach with turquoise water and palm trees.

A remote sensing model in an island paradise

Can the technology work in the context of island tourism destinations such as Samal?

In 2024, ALab PH once again received a grant from JSIC to test if the same or better results can be achieved by the remote sensing model in a different context: from urban waterways to shores and beaches. The Lab picked Samal, whose local government has partnered with UNDP on several projects. It is among the local governments where the European Union-funded Green Economy Partnership with the Philippines will be implemented and has been involved in the Ending Plastic Pollution Innovation Challenge.

Fortunately, the partners from Samal local government were open to experiment with ALab PH on extending the application of marine litter. Jointly, we agreed to test the technology to see if it can work in Samal's context and if the findings will be useful. The local government partners wanted to see if it can detect patterns, including potentially the flow and source of the waste, as well as the composition.

Map outline showing the location of islands, labeled with names and boundaries. — The Island Garden City of Samal is composed of two islands—Samal Island and Talicud Island—that lie within the Davao Gulf. The Gulf opens southward into the Celebes Sea north of Malaysia and Indonesia. Davao City—the economic center of mainland Mindanao—and other urbanized localities of the Davao Region line up the north of the Davao Gulf.

This phase 3 of the remote sensing experiment application in Samal was conducted over a five-month sprint or short implementation period. The team engaged Dr. Yuichi Ito, a Japanese remote sensing and astrophysics expert, to help implement the experiment. Ito-san previously led the JAMSS team which supported the first two phases but has since spun off his own company, Alpha Space Design Lab. Like in the previous two phases, Phase 3 entailed the gathering and analysis of available satellite imagery from Copernicus Sentinel and the presentation of marine litter analytics through an online dashboard.

As previously learned from Phases 1 and 2, the remote sensing model could only work well if it is validated with good ground truth data. In October, the ALab PH team and Ito-san headed over to Samal to engage local stakeholders and collaborate with them for the ground truth validation. Colleagues from the global Accelerator Lab team also joined to take video documentation of the process as well as to gather stories from the ground (see photos). The four-day mission included field inspections of marine litter hotspots around Samal and Talicud islands; meetings with the local government as well as with the Department of Science and Technology regional office in nearby Davao City; and a consultation workshop with local stakeholders.

During the consultation workshop, the team met with 36 participants which included fisherfolk, tourism leaders, hotel managers, as well as officials from the local government (representatives from the environment, engineering, and tourism offices) and local police and coast guard. After the ALab PH team and Ito-san gave an overview of the experiment, the stakeholders were asked to identify where the litter hotspots were. The group also brainstormed ways that the local stakeholders can contribute photos and information about the location of waste. This led to a quick-and-dirty crowdsourcing campaign where citizens were incentivized to contribute photos through social media.

Three people are discussing a map on a whiteboard in a well-lit room.

Conclusion: Multiplicity of Solutions Needed

After the mission, the team got back to work to develop the solutions. While Ito-san calibrated the remote sensing model and built the dashboard (visit it at https://bit.ly/samalmarineplasticdashboard), the local government and other local stakeholders helped to promote the crowdsourcing campaign. Fast-forward to January 2025, the experiment was concluded and presented back to the Samal stakeholders for feedback.

As the ALab PH Team and Ito-san reported, the model was successful to a limited extent in detecting waste. What made the detection difficult was that unlike in the case of Metro Manila where the trash was abundant, the trash seen in Samal tended to be more scattered and mixed with organic waste such as driftwood. The waste was nevertheless found to be floating in clusters and along the tidal lines within the Davao Gulf. As the waste drifts inland into the island from mainland Davao, the trash tends to be trapped in mangrove roots, rocky sand, and other rough surfaces. As the results of the analysis only covered the last quarter of the year, the stakeholders expressed the need to extend the detection to a full year to account for changes in season and thus tidal patterns.

Dashboard displaying data visualizations, maps, and charts for monitoring a water body. — The dashboard showcases the model estimates derived from the spectral analysis conducted on satellite images to detect the presence of plastic pollution. It also features findings from citizen scientists who volunteered their time to contribute photos of waste.

Results also showed that the satellite remote sensing technology works, but under certain conditions. Detection, after all, was limited to the type of satellite sensing used, which was spectral analysis of available optical satellite data. Apart from the lower resolution of the public data, the remote sensing was hampered by high cloud cover during the time. Ito-san also explored the potential of other technologies, such as synthetic aperture radar (which makes use of radar waves, hopefully to address the issue of cloud cover), and recommended other sources of higher-quality, albeit more expensive, data and methodologies.

In terms of complementary approaches, one that could be developed further is by involving the citizens themselves. The quick-and-dirty crowdsourcing run helped to generate photos to calibrate the remote sensing model. However, most photos provided were on the shore, as it was difficult for citizens to capture marine litter on the water itself on an ordinary day. One missed opportunity was involving the fisherfolk more in the exercise by finding ways to address their lack of mobile phones to join in on the crowdsourcing. Some photos, such as those taken under mangrove trees, were also difficult to use as ground-truth data. Juan Daray—former ALab PH Social Innovation Analyst who helped to manage the crowdsourcing run—recommended steps to not only improve the quality of photos gathered but also to more intently involve communities under systematic citizen science initiatives. Nevertheless, the photos contributed by citizen scientists are also incorporated by Ito-san in the dashboard.

From the experiment, it was clear that multiple tools and methods are needed to adequately monitor waste leakage, its source and flows, and patterns across time. But apart from the multiplicity of monitoring tools, how do we as a collective act on the findings to reduce marine litter? Who do we need to engage and get on board?

We look forward to future collaborations on addressing the marine litter challenge and on confronting the bigger challenge of transitioning to a circular economy: not only in Samal but also beyond. As we speak, we are collaborating with universities in the Davao region to engage students in creating potential solutions to improving the monitoring and management of waste in the Davao Gulf. Under the Green Economy Programme, UNDP also recently called out for proposals for community-led circular economy initiatives.

We look forward to co-creating innovative solutions with you! Interested in the work we do or other experiments? Reach out to us via acceleratorlab.ph@undp.org.