Meaning of Surname?

Ok, I've been going absolutely crazy trying to figure out what my surname means in Norwegian. It's originally spelled "Sætre" in Norway, but when my grandpa came here to America they changed it to "Sather". I just found out actually, that these surnames actually have meaning and I was wondering if anyone could help me out? That would be great and I thank you for your help! -Andrea (If you need anymore information, I'd be more than happy to assist)