Signature Assessment

Assessment of camouflage materials and analysis of construction material for thermographical inspections, verification and validation of thermal simulations.

The rendition of an object in a thermal image (signature) is decisively influenced by its environment. In order to make a statement about the visibility of an object in a certain environment, it is therefore necessary to determine the influence of decisive environmental factors on the thermal appearance.
 

Procedure

A method for characterizing distinctive features of textiles worn on a thermal image has been realized.

For this purpose, a textile is placed on a heating plate with a temperature control in the environmental simulation laboratory. The temperature is set to 34 °C, which corresponds to the skin temperature of the human body. Afterwards, a sequence of thermal images is recorded at different wind speeds for 5 min at a defined air temperature in four different environmental scenarios with an image frequency of 1 Hz under the following conditions:

• Without any radiation sources
  
• Artificial sun as source of radiation
  
• Artificial sun and cold sky as source of radiation
  
• Cold sky as source of radiation

The measurements are performed for an angle of incline of the sample of 30° and 45° to the vertical axis in order to achieve different reflective conditions vis-à-vis the radiation sources.

The mean temperature of the textile surface investigated is then determined and averaged over time throughout the sequence.

To determine the conspicuity of a person, who wears the textile examined, in a natural environment the air temperature is used for comparison as the air temperature dominates the temperature of green vegetation in a thermal image.

Based on the behavior caused by different influences, conclusions can be made about the behavior of the textile in a wide variety of different scenarios, which were not investigated themselves.

The reproducibility of the measurement procedure returns a maximum deviation of 0.3 °C in the worst case scenario. The results of the validation of the measurement method can be provided on  request.

As the heating plate can be heated stably to temperatures of up to 80 °C, it is also possible to use the method for analyzing covers of technical devices like generators or the like.