It's the nature of the beast to be secretive. The average Sasquatch is an intelligent creature, perfectly capable of hiding out and stalking you.
Even those startled out in the open will immediately head for the tree-line.
This is their environment and they know it. They are past experts at disappearing into the foliage and behind the trees.
Thermal imaging strips away their cover; and allows you to see deep into the forest. It isn't showing you what the eye can see, but what the body emits. It's seeking out the heat, which neither Bigfoot nor any other mammal can stop radiating out.
Body heat will show up as a distinct glow on your thermal imager. Nothing will be able to sneak up on you, nor covertly watch from the shadows, as long as it's alive. The shapes may be fuzzy, but you will know if you're looking at a deer or a Sasquatch.
With most heat-seeking cameras, you will be able to transfer your images onto your computer later.
Or else you could use them to know where to approach. NB Bigfoot is bigger and stronger than you are. Bear that in mind before hurtling off after it! In fact, it might be safer all round to use that information to set up motion camera traps.