Thermal Imaging and Law Enforcement

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Thermal Imaging and Law Enforcement

• Ashraf Wilsily

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A Brief Introduction

• Can you see? Minority Report
• What is thermal imaging?
• See heat as it radiates from object
• All objects above 0K emit thermal IR energy
• Is it the same as the green images from James
  Bond movies?
• IR theory
• How and why does it work?
• Limitations
• Application to Law Enforcement

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Radiation IR Theory

• Three methods by which heat flows from one object
  to another radiation, convection, conduction
• IR radiation, beyond red, or beyond visible
• Near IR (from .7mm to 1.3mm)
• Mid IR (from 1.3mm to 3mm)
• Thermal IR (beyond 3mm to microwave)
• Only one related to sensation of heat
• Every body emits energy from its surface as
  electromagnetic waves

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Heat transmittance between objects
Thermal profiles show false color (left). Night
vision characterized by green color (above).
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How thermal imagers (IR cameras) work

• Lens focuses IR light emitted by objects in view
• Focused light is scanned by a phased array of
  IR-detector elements
• Translation of data into electric impulses
• Impulses sent to a signal-processing unit to
  translate the info from elements into data for
  display
• Signal processing unit sends info to the display,
  where it appears as various false colors
  depending on intensity of IR emission
• The combination of all impulses from all elements
  creates the image thermal profile

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Basic Components of Thermal-Imaging System
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Examples of thermal imagers
Daylight
Thermal profiles show false color
At Night
IR imager
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Limitations

• Cannot see through walls, or glass
• Exterior heat loss is measured first
• Cannot see through clothing
• If one is carrying a gun, the exterior of the
  coat would appear cooler to the camera
  indicating a possible gun possession
• Parameters important in thermal imaging may not
  achieve desired performance
• Temperature range, spectral range, accuracy,
  resolution, maximum frame rate, etc.

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Law Enforcement

• Thermal Building Profiles
• Used in US to conduct thermal profiles of
  buildings suspected of harboring illegal growing
  operations
• An airborne forward-looking IR unit or handheld
  thermal imaging camera is needed for such audits
• Relative temperature to other buildings
• Marijuana processing generates lots of heat from
  high-voltage bulbs that simulate sunlight
• Does it always work? Can account to this by using
  extra insulation

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Law Enforcement

• Locating fugitives
• Can locate an escapee, an armed robber on foot or
  in a backyard at a distance
• Vehicle pursuit
• Vehicle engines, tires, and brakes all emit heat
• Speeding increases this heat, making fugitives
  car easier to distinguish among other vehicles on
  road
• Advantages? Endangering citizens less and police
  still able to track fleeing vehicle

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More on Law Enforcement

• Disturbed surface scenario
• Find large amounts of cash, drugs, and bodies
  buried in the ground or hidden in structure walls
  or flooring
• Differences in temp and moisture content are
  critical factors in their discoveries
• Can detect temp differences to 0.01C recognize
  disturbed ground and patched wallboard even when
  surface is camouflaged well
• Surveillance of marine and aerial suspects
• Perimeter surveillance

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Suspect Marijuana grow house
Locating fugitives at a distance
Surveillance of marine and aerial suspects
Vehicle pursuit
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Summary

• New set of eyes to see heat
• Going beyond the visible
• Many applications but extensively used in law
  enforcement
• Accepted in the US as evidence in courts