Applying a multispectral remote sensing approach to underground electric manhole inspections

This colored panorama shows the inside of an electric manhole. Credit: Woolpert/Ameren

By Mike Battles, Qassim Abdullah and James Overton of Woolpert, and Ted Mena, Seth Bartnick, Adam Mikesch and Matthew Molitor of Ameren

Unless they are properly maintained, electric manholes can be a potential hazard to utility workers and the public. Stormwater, melting snow and de-icing salt seeps consistently into manholes and meets aging and sometimes frayed electrical infrastructure. This can lead to smoke, fire and explosions that can send 300-pound manhole covers flying. The New York City Fire Department reported that more than 4,000 manhole explosions took place between 2009 and 2018 in the city alone, injuring 57 people. These incidents also cause traffic disruptions, substantial property damage, building evacuations and power outages across the country.

City engineers and utility companies are faced with the frequent and daunting task of inspecting manholes and underground utilities to ensure safe operations and to satisfy local and federal regulations. Although mandates differ from state to state, each utility manhole must be inspected on a regular basis to make sure it does not pose a public hazard or lead to a service disruption.

Traditionally, utility manholes are either inspected by a trained technician who enters the manhole, uses a remote-controlled video camera or applies both approaches. The physical, in-person inspections potentially threaten the safety of the inspector due to his or her proximity to potentially faulty energized conductors that have been exposed to the contaminants common to city streets. These include bacteria, protozoa, viruses and parasitic worms, which enter the manhole through runoff and faulty sewage lines.

The Occupational Safety and Health Administration has recognized the hazards of these inspections and has instituted requirements for entry into manholes and vaults. These requirements call for people conducting these inspections to be “trained in the hazards of enclosed space entry, in enclosed space entry procedures and in enclosed space rescue procedures.”

Using remote-control cameras for manhole inspections also has its shortcomings. Video from these cameras does not provide spatial orientation, making it difficult for the inspector to locate the anomalies observed on video. Even when individual frames of the video are produced, locating the position of an irregularity or potential issue within a manhole is difficult, especially when dealing with hundreds of individual images that are not georeferenced. This matter becomes more complicated when dealing with large manholes.

Also, although these remote-controlled cameras can collect color imagery of visual cracks and deformations in the walls of the manhole, as well as damaged cables, they do not show if there is a cable overload or other hotspot issues. Those can only be discovered by using a thermal sensor.

Is there a safer approach?

To address this issue, Ameren and Woolpert are developing what we believe is a safer and more effective approach to utility manhole inspection through an innovative pilot program. The patent-pending approach uses a combination RGB color camera and thermal camera that are wirelessly controlled and can produce a multispectral panorama. The RGB camera provides a clear, spatially accurate inspection of the manhole floor, walls, ceiling and cables, while the thermal camera measures absolute temperature throughout the manhole, detecting overheated objects and locations.

This collaborative, multi-industry approach increases the safety of workers and the public, efficiently maps the manhole using the latest sensor technology and GIS capabilities, and minimizes traffic impacts by reducing the time required in the field to collect data.

The system was designed with the following parameters in mind:

  • Wireless operation: Wireless control and operation eliminate the need to put an inspector in a potentially hazardous situation, amid compromised infrastructure and faulty energized conductors. The field crew is provided with a wirelessly controlled interface to monitor and control the operation of the cameras within the manhole. All components of the system that enter the manhole are made from nonconductive materials.
  • Multispectral remote sensing principles: The system provides two regions of the electromagnetic spectrum: visible and thermal infrared. The visible light is captured using a digital camera, while the thermal portion is captured by a thermal camera. The four multispectral bands — three visible red, green and blue bands, and one band from the medium infrared region — provide comprehensive inspection within the manhole to detect structural anomalies and power conductors.
  • Geospatial mapping principles: Camera-based manhole inspections can produce hundreds if not thousands of images and videos. Data management becomes crucial for the inspector because he or she must weed through these images to locate an anomaly. But even if the inspector locates the image that contains the anomaly, it is challenging to determine where it is located within the manhole. Part of the data processing of this new system is the creation of a mosaic, which can be georeferenced using GIS software to provide accurate inspection and reporting per precise location.

This new system includes three subsystems:

  • A digital multispectral subsystem, which includes:
  • A three-band RGB color digital camera
  • A thermal camera
  • A GPS and IMU auxiliary subsystem
  • Remote-controlled mounting via a gimbal system

Field testing the system: A pilot project

The data acquisition process is similar to that of the remote-control camera to which the utility field staff are accustomed. Field tests in the pilot project revealed that, after a brief learning curve, members of the collection team were able to familiarize themselves with the new technology and collection sequence. Initially data collection differed by the person doing the collection but as the procedures were enhanced, the delivered data was consistent and repeatable regardless of the collector.

Field data was not only relegated to image acquisition, but attributional data also was collected. Ameren and Woolpert used their experience with traditional and RGB manhole inspections to build a conditional and logical attribute database, which enhanced efficiency while maintaining accuracy during pilot manhole inspections.  

This thermal panorama shows the inside of an electric manhole. Credit: Woolpert/Ameren

The dual data acquisition resulted in a video file for the visible colored imagery and a video file with 32 bits for the radiometric thermal data. The radiometric data provided imagery with calibrated absolute temperature of the objects inside the manhole. Once in the office, two sets of individual frames were produced from the video files.

The visible and thermal imagery was then mosaicked together to produce two panoramic views of the manhole interior: one as RGB panorama and the other thermal panorama (Figure 1 (lead image) and Figure 2, above). Woolpert utilized a proprietary software based on artificial intelligence to associate the absolute temperature reading with every pixel of the panorama.

For real-world applications, these data can be imported to GIS software for local analysis or through a web service to be shared by stakeholders at different physical locations. While viewing these data, whether through a web service or GIS software, the user can inspect the thermal mosaic to stand on thermal anomaly. Once an anomaly is detected, the colored panorama can be consulted to verify the nature of the feature or cable that is demonstrating the anomaly to address and solve the issue, improving worker and public safety, preventing property and utility damage, and decreasing the likelihood of utility failures. The user can also measure the actual temperature of features and distances to a frame of reference, as seen in Figure 3.

The GIS tool supports data analysis and reporting. Credit: Woolpert/Ameren

About the Authors

Mike Battles is a Senior Vice President and Energy Market Director at Woolpert.

Qassim Abdullah is a Vice President and Chief Scientist at Woolpert.

James Overton is a Project Manager at Woolpert.

Ted Mena is Superintendent, Contractor Services at Ameren.

Seth Bartnick is a Contractor Services Supervisor at Ameren.

Adam Mikesch is a Project Manager at Ameren.

Matthew Molitor is a Solutions Manager, Asset Management and Sensors at Ameren.

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