Audio cassettes, video tapes, credit cards and computer disks all store valuable information using very small magnetic tracks. Sometimes, these tracks are accidentally damaged or intentionally modified, and recovery of the data or verification of authenticity becomes extremely difficult—if not impossible.
Researchers at two of the Commerce Department's Boulder, Colo., laboratories have developed a new technique for recovering analog and digital data from mangled tapes or other storage media that allows for much more complete and accurate analysis.
Termed second harmonic magneto-resistive microscopy (known as SH-MRM), this technique makes use of the same high-resolution magnetic sensors developed for modern computer hard disk drives. These sensors map the microscopic magnetic fields across the damaged or distorted tracks, thereby allowing investigators to rebuild the original signal. The technique not only allows for reconstruction of the data but also gives insight into the recording process and history. To forensic analysts, this can provide critical information regarding the authenticity of evidence.
David Pappas of the National Institute of Standards and Technology and Steve Voran of the National Telecommunications and Information Administration's Institute for Telecommunication Sciences have successfully imaged a number of samples from other government laboratories. This included the recovery of audio data from a tape fragment supplied by the National Transportation Safety Board laboratory.
In addition, Pappas and Voran showed that raw digital data can be read from a very short segment of tape from a flight data recorder. This is important because small bits of tape are occasionally all that can be recovered from a major accident. While such segments may hold the key to the investigation, they are unreadable in a conventional tape deck.
Pappas and Voran also have done work for the FBI. Images from sample audio cassette recordings provided by electrical engineer Ken Marr, at the FBI Engineering Research Facility Audio Laboratory in Quantico, Va., revealed magnetic marks produced by the erase and record heads during the recording process. In the hands of experts, this information may allow for authenticity verification. Pappas and Voran also showed that the audio data from test tracks can be reconstructed and played back directly from the SH-MRM images. This information is independent of the normal inductive read process and can be critical in the evaluation of recorded evidence produced for federal criminal law cases.
As a non-regulatory agency of the U.S. Department of Commerce's Technology Administration, NIST strengthens the U.S. economy and improves the quality of life by working with industry to develop and apply technology, measurements and standards through four partnerships: the Baldrige National Quality Program, the Measurement and Standards Laboratories, the Advanced Technology Program and the Manufacturing Extension Partnership.
NTIA is the President's principal adviser on telecommunications and information policy issues and, in this role, frequently works with other Executive Branch agencies to develop and present the Administration's position on these issues. In additional, NTIA manages the Federal use of the electromagnetic spectrum.