This may not be the answer your looking for on RTS. RTS is the Real Time Sonar window. It shows just the live raw signal feedback from the transducer. RTS observation can be very useful for stationary fishing directly below boat. The good news for you is that when the DI update comes out you/we will be able to have a much better understanding of whats directly under boat visually. The traditional down looking sonar is more about the strength of return than producing a visual picture like image. There is a post on here of the new DI that shows a tree in the DI view and in the down looking sonar view simultaneously. This will help illustrate what I mean by strength of signal vs picture like imaging. That's my stab at it Greg will correct whatever I may have just gotten wrong. Here is a link to the image.
If had to guess on what your pic is I would say a stump with some grass perhaps, if it's not man made object of some sort. Hit it with the SI and get a pic.
Are you wishin you were fishin? Not me......