That’s NYPD Commissioner Ray Kelly touting a new technology called “terahertz imaging detection” to a local news outlet.
Terahertz radiation is electromagnetic waves at the high end of the infrared band, just below the microwave band. The waves can penetrate a wide variety of non-conducting materials, such as clothing, paper, cardboard, wood, masonry, plastic, and ceramics, but they can’t penetrate metal or water. Thus, directing terahertz radiation at a person and capturing the waves that bounce off them can reveal what is under their clothes without the discomfort and danger of going “hands-on” in a search for weapons. Many materials have unique spectral “fingerprints” in the terahertz range, so terahertz imaging can be tuned to reveal only certain materials. (In case you’re wondering, I got this information off the top of my head…)
Will the machines be tuned to display only particular materials? Or will they display images of breasts, buttocks, and crotches? The TSA’s “strip-search machines” got the moniker they have because they did the latter—until the agency tardily re-configured them.
Then there’s the flip-side of not going “hands-on.” Terahertz imaging detection doesn’t natively reveal to the person being searched that law enforcement has picked him or her out for scrutiny. A pat-down certainly lets the individual know he or she is being searched, positioning one to observe and challenge one’s treatment as a suspect. Terahertz imaging lacks this natural—if insufficient—check on abuse.
So terahertz imaging is not just a “hi-tech pat-down.” Its potential takes what would be a pat-down and makes it into a secret, but intimate, visual examination—a surreptitious strip-search. Pat-downs and secret strip-searches are very different things, and it is not necessarily reasonable, where a pat-down might be called for, to use terahertz imaging.
And that brings us to the fundamental problem with Commissioner Kelly’s proffer to use this technology at a “specific event” or at a “shooting-prone location.” These contexts do not create the individualized suspicion that Fourth Amendment law demands when government agents are going to examine intimate details of a person’s body and concealed possessions.
It is certainly possible to devise a terahertz imaging device and a set of use protocols that are constitutional and appropriate for routine, domestic law enforcement, but Commissioner Kelly hasn’t thought of one, and I can’t either.
Consider the dollar costs and potential health effects of terahertz imaging detection, it might just be that the pat-downs pass muster far better than the high-tech gadgetry.