Is there a way to boost GPS signal?

[Meta4]

200 yards has nothing to do with it.

Nothing to do with being 200 yards from anything.

The OP explained he launched 200 metres from the waterfall.

I was referring to him taking off with zero GPS signal which could have meant the drone switching into ATTI mode, with the potential consequence of it drifting in turbulent air.

In situations with restricted GPS it can be a perfectly safe technique to launch and climb to get GPS.
It's up to the flyer to decide if there are obstacles too close or if there is enough breeze to cause a problem.
But he had GPS and the air would not have been "turbulent" 200 metres from the waterfall.