Inspired by Steve Marshall's work on the springs at Silbury Hill and the Avebury region http://www.stevemarshall.org.uk/docs/Silbury Springs v2.pdf I took my FLIR C2 thermal imaging camera there this morning. The springs are "warm" in that they stay above freezing even on a day such as today where it was -4C at dawn.
The water table is not very high yet but the patches of fresh water were unfrozen whereas water that had been standing all night was frozen.
The temperature scale is to the right, the lighter the colour the warmer it is. Click to enlarge.
Of more interest was investigating if this technique could find individual springs. Below are the thermal and normal picture of part of the bank under the A4. It shows a spring glowing white, on checking water was issuing from the ground there. Without the camera I would not have noticed this spring which shows that this technique has promise and would be worth investigating further.
It does need to be done before the sun has warmed the ground and probably it needs to be a cold day as well.
I couldn't find any springs at the base of Silbury Hill itself by camera or inspection, probably the water table isn't high enough for them.