Two levels here.

1. Is it legal?

2. Is it ethical?

The first is easy to answer.

If it's on private property just trespassing is going to be an issue. Best to try to talk to the owner if you can get ahold of them.

The second question is more subjective. It sounds harmless to me personally, but I'd put myself in the land owners shoes. If I found out someone was doing that without asking me I might understand, but I wouldn't be happy.