In the 3rd episode of Terra Nova (counting the 2 hour pilot as 2 episodes), Instinct, they used infrared cameras on balloons to see how many of the pterosaurs were in the area. Why can't they just start floating more balloons and use them to scan for humans to find where the Sixers are encamped?
Because the plot doesn't want it to happen (yet?).
I see 2 possible reasons:
- It only worked with the pterosaurs because they were above the canopy, and the 6ers knew how to hide.
- It only worked with the pterosaurs because there were so many, and their heat bled through the canopy to make the signature visible.
In the 4th episode (by your same count), the heat signature from the human was blocked by the nearby plants, so it took them a bit of time to see the person.