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Seeing below the surface to advance safety

Researchers at Northeastern University are developing technologies to protect the United States from a variety of external threats. Professor of Electrical and Computer Engineering Carey Rappaport is the associate director of both the ALERT (Awareness and Localization of Explosive-Related Threats) Center and Gordon-CenSSIS (Bernard M. Gordon Center for Subsurface Sensing and Imaging Systems). Rappaport is also working on the VOTERS (Versatile Onboard Traffic Embedded Roaming Sensors) project as a lead researcher on the use of radar to monitor the condition of roads, bridges and monuments. All three centers were founded with significant federal funding support.

Here, Rappaport discusses the work he and his colleagues have been doing to fortify the nation’s security.

Can you explain what subsurface sensing and imaging means?

It means using various types of non-invasive methods to see below surfaces or inside hidden regions. At the Gordon-CenSSIS and ALERT centers, we use radar, ultrasound, x-rays, visible light and other wave-based probes to identify or detect things under a surface, such as tumors in the body, explosives under clothing, buried pollutants or damaged coral reefs underwater. Although sensing waves have always been able to penetrate below the surface, the challenge we’ve focused on is how best to make sense of the data that scatters back to us.

What areas of research is the ALERT Center currently investigating?

ALERT, a seven-university partnership, is currently investigating the use of chemical, electrical, and electromagnetic modalities to spot suicide bombers, warn people about suspicious bags that have been abandoned and determine whether vehicles are carrying bombs. There are so many ways to hide things, and we want to identify the threats with the least amount of public disruption. Everyone dislikes having to unpack and undress at airport security checks. Wouldn’t it be great if we could develop technology that would effectively sense hidden threats without a passenger even having to slow down? That is one of the center’s goals.

How would the ideal suicide bomber detection system work?

We’re working on a multi-modality, layered-sensor approach, with optical, radar, terahertz and x-ray sensors observing pedestrians as they walk toward and then past a nondescript sensing platform. The various sensors look for different aspects of the pedestrian: his movement, the reflection from radar-scattering objects on his skin under his clothing, the presence of trace explosive chemicals on his clothing and the x-ray density of foreign objects he has on his person. The goal would be to identify any suspicious activity and send a warning to the operator.

You are also researching ways to make roads, tunnels and bridges safer. How are you doing that?

The same concepts for sensing through clothing or within the body can be applied to looking through the road surface to find subsurface damage. The VOTERS program builds on work that we have pursued for years under the Gordon-CenSSIS SoilBED project. We are using radar and acoustic sensing techniques to quickly and inexpensively determine bridge deck and roadway health. If we can identify differences in concrete strength at one location relative to another, we can inform construction crews exactly when and where to do spot repairs before they become multi-week lane-closing traffic nightmares. We intend to outfit fleets of commercial trucks, buses, or cars with a suite of sensors that will continuously report on road health, and save cities and towns significant inspection and repair money.

What made you decide to focus your efforts on this area of research?

I like working on important research problems that everyone can understand, employing technology that many people are familiar with. But I try using these technologies in innovative and inexpensive ways. I started down this path a dozen years ago when I led a project on humanitarian land mine detection. Our guiding principle was to configure existing technology into systems that a Cambodian farmer might be able to afford. Although radar has been around for more than half a century, it has only recently been used for imaging tumors or sensing concealed pipe bombs or identifying hidden pavement problems.

My ultimate goal is to find cost-effective and relatively painless ways of seeing and interpreting obscured regions more effectively.