Frequently Asked Questions
Night vision devices are also affected by weather related obscurants such as snow, rain, blowing sand and fog as well as smoke. Under these types of conditions, night vision devices are unable to perform. Thermal imagers can perform exceptionally well in adverse weather conditions due to the fact they do not rely on light but rather emitted energy. The infrared wavelength can penetrate smoke, rain, snow, blowing sand and most foggy conditions.
Originally, all thermal imagers were cooled. The detector on a cooled thermal imager is actually cryogenically cooled to sub zero temperatures using a very small condenser and compressor. Since the detector is so cold, its sensitivity or ability to detect emitted energy is very good. Some cooled cameras can detect human activity from 20km away. Cooled cameras are very costly and require yearly maintenance for re-calibration. They also have a mean time between failures of 2500-8000 hours.
Uncooled thermal imagers electrically stabilize the detector and do not require any cooling. Years ago uncooled detectors did not have the sensitivity or range of a cooled camera. Technology has advance with uncooled detectors so that they are almost as sensitive and are very close to the range of a cooled camera. Uncooled thermal imagers do not need periodic maintenance for re-calibration and their mean time between failure is rated at 5-10 years. Uncooled cameras are roughly 1/3 the cost of cooled thermal imagers.
A microbolometer is a “staring” array that uses an iris or shutter flag to re-calibrate the detector every few minutes. Microbolometers have a very distinct image with crisp edges on the objects in the scene.
The dynamic range of temperature for a microbolometer is somewhat limited when compared to ferroelectric arrays. This is evident when looking at a scene where a fair percentage of the viewing area is deep space, such as a desert or large body of water. Since deep space is very cold when compared to planet Earth, this presents a very large dynamic range in temperature. A microbolometer has to use very advanced histogram equalization software to accommodate this type of scene and even then the user has to be careful to not allow too much deep space or cold in the scene or the hot Earth will wash out.
Microbolometers are also adversely affected by direct or indirect sun light exposure. If the user points a microbolometer at the sun or a reflection of the sun on a window, irreversible damage can occur to the detector.
Ferroelectric arrays us a chopper mechanism to continuously calibrate the detector. Each column of pixels is calibrated every 30th of a second. This allows ferroelectric arrays to encompass a large dynamic temperature range and even look directly at the sun without incurring any damage to the detector. The image quality is not as sharp as a microbolometer but most users find it difficult to distinguish the two.
Microbolometers are also slightly more sensitive than ferroelectric arrays and allow for greater detection distances. Ferroelectric arrays are slightly less in cost and out perform microbolometers in desert or large bodies of water scenes where deep space is a factor.
HurleyIR uses either technology and chooses best suited detector for the application.
For further assistance, please call 410-875-0234 or contact us.