Thermal imaging: much heat but little light - legal aspects of the thermal imager

FBI Law Enforcement Bulletin,The, Dec, 1997 by Thomas D. Colbridge

IMPLICATIONS FOR LAW ENFORCEMENT

It is impossible to predict when, or even if, the U.S. Supreme Court will resolve this debate. In light of the disagreement over the warrantless use of thermal imagers, the following general guidelines for police officers using thermal imagers should ensure the lawful use of this technology.

Search Warrants

Law enforcement officers should consult their legal advisors to determine whether a search warrant is required to use a thermal imager in their jurisdictions. Of course, search warrants are always preferred. Given the current debate over thermal imagery, a warrant should be obtained whenever possible before using the thermal imager.

Probable Cause

None of the cases reviewed advocate that a thermal scan alone provides probable cause for a search. Heat is generated by many different activities, both legal and illegal. The results of a thermal scan provide but one of many facts the officer must combine into the mix of probable cause to obtain a search warrant and search the scanned building.

Placement of the Thermal Imager

The courts that have upheld the warrantless use of thermal imagers have stressed that officers using the device did not physically intrude upon the area scanned. Scanners were aimed at the target by officers standing outside the curtilage of the home or business or from aircraft flying within navigable airspace above the area. Thermal scanning conducted from within the curtilage of a home or from a helicopter flying below navigable airspace is plainly more intrusive. Officers should ensure that any scan is conducted from a location where they have authority to be.

The Capability of the Thermal Imager

One of the most important factors in this ongoing debate is the nature of the information the thermal imager provides. The Supreme Court has acknowledged that police may use new technology to enforce the laws(34) but has cautioned that there are limits: "An electronic device to penetrate walls or windows so as to hear and record confidential discussions...would raise very different and far more serious questions...."(35)

Does the thermal imager penetrate walls and reveal such "intimate details"(36) so as to implicate the Fourth Amendment? One federal court has noted that infrared photographs of a mobile home revealed rafters inside and that the home appeared to be split into two rooms.(37) If FLIR devices do reveal such intimate detail, either directly or through interpretation of the images, the argument against warrantless use of the device is stronger. If, on the other hand, the device merely reveals whether one structure is emitting more heat than another, the argument against warrantless use is weaker.

Officers using thermal imagers should document clearly the capabilities of their machines. A reviewing court certainly will inquire whether the particular imager can distinguish intimate details within the targeted building. Videotapes or still photographs of any thermal images should be made and retained for the court to see. Interpretation of the thermal images should be limited to the question of whether the targeted structure is emitting substantially more infrared radiation than similar structures in the area.