The disadvantages of thermography
The use of thermography can display images beyond the capabilities of the human eye. Wherever heat radiates, the screening will show it in colour or shades of black and white. Firefighters use it to see through the smoke in a burning building. It is used in some physiological tests and building construction.
It is safe to use because it does not produce radiation and it is noninvasive.
Thermography is used to diagnose vascular disease, neuromusculoskeletal disorders and breast tumours. It collects imaging from 5 to 8 feet away from the body and is capable of producing thousands of pictures using infrared light. Thermography can measure the heat that is given off by soft tissue. It can then be compared to another area of the body with the same structure, such as the right arm compared to the left arm. It can detect blood flow before and after exercise, showing if blockages are present. Breast cancer detection has proven to be accurate in 84 per cent of cases through the use of thermography. The problem is that images are hard to interpret and require a very well-trained professional.
The cost of the equipment is often beyond the resources of the typical medical community, such as the neighbourhood hospital. Accurate temperature is hard to measure because of emissivites, the power of a surface to emit heat by radiation. Camera accuracy is only +-2 per cent.
The National Aeronautics and Space Administration (NASA) used IR Thermography to measure surface temperature. It has been used successfully in wind and pressure tunnels. The disadvantages, according to NASA, are the difficulty to obtain accurate data from models that have less thermophysical and radiometric properties. Retrieving accurate data can require infrared-transmitting optics that are not always available. Cameras are not suited for very low temperatures below -50 degrees C. The cost of the equipment and the expertise of interpretation is a disadvantage of the practice, as it is in the medical community.
Disadvantages to using thermography in construction can be caused by errors during the collection of data. For example; if collecting data on a roof, it should be taken into consideration that the east side will cool down last as compared to the rest of the roof. This can make some areas of the roof ready for scanning moisture, while the east side will not be ready.
Debris on a roof, such as leaves and twigs, will retain heat longer than the shingles. Another item to consider is equipment on gravel roofs, such as HVAC units. These items emit heat, so the surrounding areas will maintain a higher temperature than the rest of the roof. Collecting data from electrical sources requires diligence in avoiding errors, such as those obtained from reflections. Body heat can reflect off of a transformer or light bulb.
Thermal pictures should always relate the same angle as the visual view. Failure to do so can result in a misdiagnosis of problem fixtures, such as electric boxes.