Thermography in the rain

This blog post is in response to something that I came across recently. I put off a thermographic survey of a building due to a weather forecast for rain. The client then came back and said that he found someone else, and they said that their camera works in the rain.

Hmmm, where to start.

Most cameras will of course work in light rain, and they are fairly resistant to at least some damage by water. I will not in any way dispute that someone’s camera works in the rain. However, this is not the same as saying that surveys can be successfully carried out in the rain. It is not advisable to carry out thermography externally on a building when it is, or has recently been raining. In this case the external images were very important to the client, as he wanted to use them for a number of purposes. You must remember that rain is made up of water droplets which are opaque to a thermal camera. Rain will reduce the amount of radiation reaching the camera, and will render temperature measurements inaccurate. The rain may cause the surface to be damp, and therefore cold due to evaporative cooling. This will mask any problems that may otherwise be visible.

My advice to anyone looking at having thermography done on a building is to wait until the conditions are suitable. If it has rained, wait for a sufficient time for the effects of the rain to be insignificant. A good thermographer, will limit his scope of works during or after rain to internal images only. His report will also state when it last rained, and should note any surfaces that are visibly wet.

Does anyone reading this do thermography in the rain?

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