This Content Originally Published by a land surveyor to Land Surveyors United Network
It is a simple questions with complex answers. the constelations move during the day on an approximate 12 hour schedule. the trees are never a good place to trust satellite positions. Perhaps at one time they contained more moisture than the other. Under cover simply moving a few feet can make a tremendous difference.
Two words... Satellite Orbits .....
Have you ever done what we "old school" GPS users had to do? Mission Plan? There are (or were) typically two times a day when you should be getting a coffee and a doughnut (short break) and getting a steak and a beer (loong break). The orbits are shifting all the time and even with multiple constellations of GPS satellites we have today, you can have periods of "bad" GPS coverage.
Check with your GPS equipment supplier or manufacturer and ask to be shown how to do this with your GPS post processing software...