What About the Oceans? Mapping Offshore Infrastructure

Mapping stationary structures in the ocean helps us track fishing vessels and monitor pollution more effectively.

We’re all accustomed to seeing maps of the terrestrial spaces we occupy. We expect to see cities, roads and more well labeled, whether in an atlas on our coffee table or Google Maps on our smartphone. SkyTruthers even expect to access information about where coal mines are located or where forests are experiencing regrowth. We can now see incredibly detailed satellite imagery of our planet. Try looking for your house in Google Earth. Can you see your car in the driveway?

In comparison, our oceans are much more mysterious places. Over seventy percent of our planet is ocean, yet vast areas are described with only a handful of labels: the Pacific Ocean, Coral Sea, Strait of Hormuz, or Chukchi Sea for example. And while we do have imagery of our oceans, its resolution decreases drastically the farther out from shore you look. It can be easy to forget that humans have a permanent and substantial footprint across the waters of our planet. At SkyTruth, we’re working to change that.

Former SkyTruth senior intern Brian Wong and I are working to create a dataset of offshore infrastructure to help SkyTruth and others more effectively monitor our oceans. If we know where oil platforms, aquaculture facilities, wind farms and more are located, we can keep an eye on them more easily. As technological improvements fuel the growth of the ocean economy, allowing industry to extract resources far out at sea, this dataset will become increasingly valuable. It can help researchers examine the effects of humanity’s expanding presence in marine spaces, and allow activists, the media, and other watchdogs to hold industry accountable for activities taking place beyond the horizon.

What We’re Doing

Brian is now an employee at the Marine Geospatial Ecology Lab (MGEL) at Duke University. But nearly two years ago, at a Global Fishing Watch research workshop in Oakland, he and I discussed the feasibility of creating an algorithm that could identify vessel locations using Synthetic Aperture Radar (SAR) imagery. It was something I’d been working on on-and-off for a few weeks, and the approach seemed fairly simple.

Image 1. SkyTruth and Global Fishing Watch team members meet for a brainstorming session at the Global Fishing Watch Research Workshop, September 2017. Photo credit: David Kroodsma, Global Fishing Watch.

Readers who have been following SkyTruth’s work are probably used to seeing SAR images from the European Space Agency’s Sentinel-1 satellites in our posts. They are our go-to tools for monitoring marine pollution events, thanks to SAR’s ability to pierce clouds and provide high contrast between slicks and sea water. SAR imagery provides data about the relative roughness of surfaces. With radar imagery, the satellite sends pulses to the earth’s surface. Flat surfaces, like calm water (or oil slicks), reflect less of this data back to the satellite sensor than vessels or structures do, and appear dark. Vessels and infrastructure appear bright in SAR imagery because they experience a double-bounce effect. This means that — because such structures are three-dimensional — they typically reflect back to the satellite more than once as the radar pulse bounces off multiple surfaces. If you’re interested in reading more about how to interpret SAR imagery this tutorial is an excellent starting point.

Image 2. The long, dark line bisecting this image is a likely bilge dump from a vessel captured by Sentinel-1 on July 2, 2019. The bright point at its end is the suspected source. Read more here.

Image 3. The bright area located in the center of this Sentinel-1 image is Neft Daşları, a massive collection of offshore oil platforms and related infrastructure in the Caspian Sea.

Given the high contrast between water and the bright areas that correspond to land, vessels, and structures (see the vessel at the end of the slick in Image 2 and Neft Daşları in Image 3), we thought that if we could mask out the land, picking out the bright spots should be relatively straightforward. But in order to determine which points were vessels, we first needed to identify the location of all the world’s stationary offshore infrastructure, since it is virtually impossible to differentiate structures from vessels when looking at a single SAR image. Our simple task was turning out to be not so simple.

While the United States has publicly available data detailing the locations of offshore oil platforms (see Image 4), this is not the case for other countries around the world. Even when data is available, it is often hosted across multiple webpages, hidden behind paywalls, or provided in formats which are not broadly accessible or useable. To our knowledge, no one has ever published a comprehensive, global dataset of offshore infrastructure that is publicly available (or affordable).

Image 4. Two versions of a single Sentinel-1 image collected over the Gulf of Mexico, in which both oil platforms and vessels are visible. On the left, an unlabelled version which illustrates how similar infrastructure and vessels appear. On the right, oil platforms have been identified using the BOEM Platform dataset.

As we began to explore the potential of SAR imagery for automated vessel and infrastructure detection, we quickly realized that methods existed to create the data we desired. The Constant False Alarm Rate algorithm has been used to detect vessels in SAR imagery since at least 1988, but thanks to Google Earth Engine we are able to scale up the analysis and run it across every Sentinel-1 scene collected to date (something which simply would not have been possible even 10 years ago). To apply the algorithm to our dataset, we, among other things, had to mask out the land, and then set the threshold level of brightness that indicated the presence of a structure or vessel. Both structures and vessels will have high levels of reflectance. So we then had to separate the stationary structures from vessels. We did this by compiling a composite of all images for the year 2017. Infrastructure remains stationary throughout the year, while vessels move. This allowed us to clearly identify the infrastructure.

Image 5. An early version of our workflow for processing radar imagery to identify vessel locations. While the project shifted to focus on infrastructure detection first, many of the processing steps remained.

Where We Are Now

Our next step in creating the infrastructure dataset was testing the approach in areas where infrastructure locations were known. We tested the algorithm’s ability to detect oil platforms in the Gulf of Mexico, where the US Bureau of Ocean Energy Management (BOEM) maintains a dataset. We also tested the algorithm’s ability to identify wind turbines. We used a wind farm boundary dataset provided by the United Kingdom Hydrographic Office to validate our dataset, as well as information about offshore wind farms in Chinese waters verified in media reports, with their latitude and longitude available on Wikipedia.

Image 6. Wind farms in the Irish Sea, west of Liverpool.

Our results in these test areas have been very promising, with an overall accuracy of 96.1%. The methodology and data have been published by the journal Remote Sensing of Environment. Moving beyond these areas, we are continuing to work with our colleagues at MGEL to develop a full global dataset. What started as a project to identify vessels for GFW has turned into an entirely different, yet complementary, project identifying offshore infrastructure around the world.

Image 7. This animated map shows the output of our offshore infrastructure detection algorithm results (red) compared to the publicly available BOEM Platform dataset (yellow).

In addition to helping our partners at Global Fishing Watch identify fishing vessels, mapping the world’s offshore infrastructure will help SkyTruth more effectively target our daily oil pollution monitoring work on areas throughout the ocean that are at high risk for pollution events from oil and gas drilling and shipping (such as bilge dumping). This is also the first step towards one of SkyTruth’s major multi-year goals: automating the detection of marine oil pollution, so we can create and publish a global map of offshore pollution events, updated on a routine basis.

Be sure to keep an eye out for more updates, as we will be publishing the full datasets once we complete the publication cycles.

More oil pollution in southeast Asia: suspected bilge dumping off Indonesia and The Philippines

[This analysis of oil pollution in the waters of southeast Asia was written as part of a collaborative effort between SkyTruth team members Lucy Meyer and Brendan Jarrell.]

Our routine monitoring of the world’s oceans has led to some extraordinary findings. For example, in previous updates, we’ve identified oil slicks in traffic-heavy locations like the Strait of Malacca. But as you’ll see in this post, bilge dumps occur elsewhere in southeast Asia. 

Those who follow our posts are probably familiar with how we identify vessels at sea. To new readers, let us explain what bilge dumping is and how we identify potentially responsible vessels. Bilge dumping is the disposal of waste water from a ship’s lower hull. Bilge water is supposed to be treated before it’s discharged, but sometimes vessel operators will bypass the pollution control equipment and flush oily, untreated bilge into the ocean – in direct violation of marine pollution law. We use images from satellites to monitor for illegal bilge dumping. In satellite imagery, oily bilge dumps usually form distinctive linear slicks. By matching the time of the imagery to broadcasts from a vessel tracking service called automatic identification system (AIS), we can determine the identity of vessels that appear to be causing the slicks. We used this process to identify the vessel associated with a long bilge slick in Figure 1 below.


Figure 1: A vessel shown passing through the Sunda Strait, identified as the Sungai Gerong, apparently trailing a long oily bilge slick.


This Sentinel-1 radar satellite image from July 2nd shows a slick about 177 kilometers long around the southwest tip of Banten Province, Island of Java, Indonesia (Figure 1). In the yellow box, you can see a vessel at the head of the slick. By investigating AIS broadcasts from exactEarth’s ShipView service, we identified an Indonesian oil products tanker named the Sungai Gerong as the likely vessel. The satellite scene, captured at 22:33 UTC (Coordinated Universal Time), shows a slick that closely aligns to the AIS broadcasts from the Sungai Gerong.

You’ll probably notice that the tail-end of the slick is a bit contorted and offset from the track of the Sungai Gerong. The slick’s appearance was likely influenced by ocean currents and local weather conditions between the time of the ship’s passing and when the image was taken. Global wind maps show that there were 10-15 knot winds blowing northwest up to six hours before the image was acquired. This data suggests that wind likely impacted the slick’s appearance. As a result, we believe that the Sungai Gerong is the likely source of this slick.

Using AIS, we tracked the Sungai Gerong as it traveled north through the Sunda Strait — the body of water between the Indonesian islands of Java and Sumatra — to the port of Jakarta. Similar to the Strait of Malacca, the Sunda is an important waterway that connects the Indian Ocean to the Java Sea. Though not as dense with marine traffic as the Malacca Strait, the Sunda is still subjected to pollution from vessels. 

We also recently identified two suspected bilge dumps in the Philippines (Figure 2). Occurring on July 6th in the South China Sea, a 238 kilometer long slick behind the vessel in this Sentinel-1 radar image looks like a bilge dump. The Philippine island of Palawan, a popular tourist destination for its beautiful natural landscape, appears on the right side of the map frame. Another smaller slick without a known source is visible to the left of the larger slick.


Figure 2: The Ulaya makes its way through the South China Sea. Palawan Island, a part of the Philippines, can be seen to the right.


Using AIS broadcasts from ShipView, we identified the Ulaya, a Thai oil tanker, as a possible source of the slick. The last AIS broadcast from the Ulaya (seen directly above the ship) was transmitted fifteen minutes before the image was captured. These AIS broadcasts give us reason to believe that the Ulaya could be responsible for this slick. Moreover, ShipView shows that the vessel was headed towards the Port of Belawan in the Strait of Malacca with a shipment of  Dangerous Goods. According to the International Maritime Organization, a United Nations agency that regulates global shipping, chemicals falling under this classification are “hazardous to marine environments.” Thus, a slick from this ship could be of greater concern than usual.

These examples show that bilge dumping continues to be a problem in the waters of southeast Asia. But with satellite imagery, anyone, anywhere can see what’s happening on the water and help to raise the alarm. We hope that our persistent and careful surveillance will inspire others to pressure policy makers, government regulators, and the shipping industry to take strong, coordinated action to stop bilge dumping.

“Well Kick” Causes Spill in Java Sea

Following up on recent reports of oil in the water off the north coast of Karawang Regency, West Java, Indonesia, SkyTruth has picked up a slick in Sentinel-1 radar imagery. In the image from July 18th, an unidentified platform (circled in red) located roughly 12 km north of the Karawang shore is shown emitting a 34.7 km-long slick into the Java Sea. A story written by the local Jakarta Post on July 18th describes state-owned energy firm Pertamina’s decision to evacuate personnel and halt operations at an offshore production rig in their Offshore Northwest Java (ONWJ) block. The evacuation was ordered after a dangerous “well kick”, or unplanned release of gas caused by low pressure in a wellbore, initiated a large slick on the 16th of July. A separate report released by the Jakarta Post five days later indicated that the Indonesian Transportation Ministry teamed up with Pertamina in response to the oil-related event, along with several other smaller entities in the area. The response vessels were able to set up a boom around the perimeter of the offshore platform. Unfortunately, this didn’t stop oil from reaching villages and beaches on West Java’s coast. Given the fact that several vessels surround the unidentified object in the Sentinel-1 image, we believe that this could be the affected drilling platform. Pertamina’s upstream director Dharmawan Samsu estimated that it will take approximately eight weeks for the oil and gas leakage to be plugged.

The unidentified platform (circled in red) can be seen leaking oil into the Java Sea. Several small vessels are in the platform’s proximity.

Bilge slick detail

PERKASA Caught Bilge-Dumping?

Possible Bilge Dumping by Indonesian Cement Carrier in the Strait of Malacca

By Lucy Meyer

On February 15, 2019, a vessel that appeared to be releasing oily waste was captured by satellite almost 10 kilometers offshore Peureulak, a small town in Aceh Province, on the northern tip of the Indonesian island of Sumatra. Radar imagery from the European Space Agency’s Sentinel-1 satellite shows an 18-kilometer slick trailing a northbound ship, visible as a bright spot at the end of the dark slick.

Bilge slick detail
Figure 1. Sentinel-1 radar satellite image showing suspected bilge-dumping (dark, linear slick) off Sumatra on February 15, 2019.

The ship is traveling through the Strait of Malacca, a narrow strip of water between Sumatra and the Malay Peninsula. The Strait is one of the world’s busiest shipping lanes as it is both the shortest and most convenient path between the Indian and Pacific Oceans. Due to the Strait’s high density of marine traffic of all types, oil spills — accidental and intentional — are likely to occur. Figure 1 illustrates suspected bilge dumping, a typically intentional discharge of oily waste from ships to reduce ballast water or free up space in the cargo holds. Typically, bilge-dumps form distinctive linear slicks visible on satellite imagery.

While radar satellite images are very useful tools for detecting slicks, they are typically not detailed enough to allow identification of the responsible vessel. However, many vessels broadcast their identity and other information using the radio-frequency Automatic Identification System (AIS). AIS use is required for all large cargo vessels and tankers. By studying the AIS broadcasts in this area using exactEarth’s ShipView service, which collects the signals using satellites and ground-based receivers, SkyTruth analyst Bjorn Bergman determined the Indonesian cement carrier PERKASA (Figure 2) was at this location when the Sentinel-1 radar image was acquired. Formerly known as KOEI MARU NO 7, the vessel was built in 1981 by Ube Industries, Ltd., a Japanese chemical manufacturing company. Today, the ship is operated by PT Indobaruna Bulk Transport (IBT), an Indonesian shipping company based in Jakarta.

Figure 2. MV PERKASA [source: IBT].
Figure 3. PERKASA’s AIS broadcast track overlain on Sentinel-1 image.

Figure 3 shows the PERKASA’s  AIS-derived track overlain on the Sentinel-1 image, revealing a very close match between the vessel’s path and the suspected bilge slick. The AIS signal immediately to the south of the vessel location on the image indicates it was traveling 11 knots (~20.4 km/h) at 11:17 UTC;  the signal immediately following at 12:10 UTC indicate the vessel was traveling 10.8 knots (~20.0 km/h). Using the location data encoded with these AIS signals, we calculated the likely position of PERKASA at the instant the image was acquired (11:43 UTC). The ship’s predicted location closely matches the vessel’s position in the Sentinel-1 image, and no other vessels broadcasting AIS were likely candidates for a match. This leads us to infer that PERKASA is the vessel seen apparently discharging oily bilge waste in the satellite image.

Slicks to the south
Figure 4. Zoomed-out view of Sentinel-1 image showing a series of patchy slicks along the coast of Aceh Province, Indonesia. Dark, linear slick at upper left is the suspected bilge slick from PERKASA shown in Figures 1 and 3.

To the south, a chain of less-distinctive slicks along the coast are roughly aligned with PERKASA’s track (Figure 4). These slicks are broad and striated as opposed to the slender 18-kilometer long slick, which could be a result of wind and current blowing apart what had originally been a series of discharges from the vessel. The AIS transmissions from PERKASA are infrequent in this region (Figure 5), making us somewhat less confident that this vessel was also the source of these patchy slicks.

Slicks to the south + AIS
Figure 5. PERKASA’s AIS-derived track overlain on Figure 4.

The operator of PERKASA, IBT, claims “we put high priority in safety by adhering to policies, practices, and procedures in our Safety Management System to ensure the safety of crews, staffs, cargoes, vessels, as well as environment.” In addition nearly all of IBT’s fleet is registered with classification societies. According to The International Association of Classification Societies (IACS), the purpose of a classification society is “to provide classification and statutory services and assistance to the maritime industry and regulatory bodies as regards maritime safety and pollution prevention.” IACS is a non-governmental organization composed of twelve classification societies.  PERKASA is registered with Biro Klasifikasi Indonesia (BKI) and Nippon Kaiji Kyokai (ClassNK), which is a member of IACS.  

One of the certification services provided by ClassNK is the Verification for Clean Shipping Index (CSI). The objective of CSI is to verify the environmental performance of a vessel’s operations in five areas, including water and wastes. Ballast water, sewage/black water, garbage, sludge oils, and bilge water are covered under this category.

Bilge dumping — intentional or otherwise — would seem to violate the principles touted by the vessel operator, and call into question the effectiveness of the classification societies.  


Possible Bilge-dumping Offshore Indonesia

Near the northern tip of Indonesia’s Bangka Belitung Islands (located directly below the yellow box within the inset map of image 1), I spotted a slick that resembles clock hands pointing to the hours 4 and 11. Captured by radar satellite, Sentinel-1, on the evening of January 8, 2019 (22:40 GMT), the slick stretches at least 117 kilometers. Due to the slick’s narrowness and distinct sharp turn in track, it is likely a bilge dump. To the right, the slick trails beyond the edge of available imagery. Though we cannot see the responsible vessel on this image, the sharp linear impression of the slick indicates that it probably passed through the area within 24 hours of the scene’s capture.

Image 1. Sentinel-1 scene of slick approximately 50 km north of Bangka Belitung Islands. See text for explanation.

SkyTruth analyst Bjorn Bergman verified this presumption. To look for similarities in timing and trajectory, Bergman used ExactEarth’s ShipView, a web-based platform that provides access to automatic identification system broadcasts (a global vessel tracking system commonly abbreviated to ‘AIS’), and identified the Indonesian crude oil tanker GAMSUNORO as a possible source.

Image 2. ExactEarth ShipView displaying AIS signal of tanker GAMSUNORO.
Credit: Includes material © 2019 exactEarth Ltd. All Rights Reserved.

Image 3 juxtaposes the slick and GAMSUNORO’s AIS signal. Traversing southeast, the ship’s first signal was recorded at 12:59 GMT. Close to 14:00 GMT, the vessel encountered the area with the slick. From this information, we know the tanker’s predicted track occurred approximately 8 ½ hours before the scene was captured. In addition, the vessel’s path imitates the shape of the slick. However, the ship’s track is slightly displaced to the northeast. It is possible that the slick may have drifted due to steady winds blowing from the NE (~6-13 knots) at least seven hours prior to the image’s capture. There appears to be a strong correlation in the temporal and spatial attributes of slick and ship, indicating that the GAMSUNORO is a likely source. To corroborate our findings, we followed the ship as it sailed southbound.

Image 3. GAMSUNORO’s AIS signal superimposed onto the Sentinel-1 scene

Initially, we anticipated the ship would journey to Jakarta; however, image 2 displays the vessel’s latest position (January 14, 2019 at 10:55 GMT) anchored about 6 miles offshore near the town of Indramayu. With an updated version of the vessel’s track, we may be able to find evidence of a continued slick either on their way south or at their current anchorage. Whether or not we are able to positively ID the perpetrator, this is one of many examples displaying the temporal challenges of using satellite imagery to capture not just illegal activity but any short-lived phenomena.