The referer is not always going to be there. The user can supply it or not, depending on how they have their setup configured. However, you can try to capture it by grabbing the HTTP_REFERER variable if it has been populated on your server.
In your case though, it sounds like you are wanting to pass it via your own redirect options and use it at that point. So, the page that is doing the redirecting simply needs to grab it's own information and pass it along.