I looked at the picture a little closer and what I thought was a remote control valve is actually a hose bib in the wall that looked like it was on top of the lower pipe. My mistake. Are they just open ended pipes? If so, they are usually used to make a collar around a manual valve on the main water supply that is down below ground level, there is a tool you slide down the pipe that fits into the flow control handle, you slide it down and then use the tool to turn the water supply on and off. It might be one for the house and another for the sprinklers. Just carefully dig them up to follow them down to the shut off valves, being very careful you don't hit a plastic pipe under pressure, which makes a hell of a mess if you bust it with your shovel.

You can see where someone raised the vacum breaker - see the white pipe with the coupling? They had to raise it because they put a taller sprinkler head in - the one in the back corner it looks like to me, so it had to be raised to maintain the required 12" above the tallest head. If you want to make it less obtrusive, you can replace the sprinkler riser-pipe heads with in the ground pop up heads, and then cut the vacuum breaker down correspondingly.

In most places, you can get a pretty heavy fine if your water company discovers a vacuum breaker that is not properly installed, it is actually illegal most places to have one lower than 12" from the top of the highest head because of the danger of contaminating the city's water supply. Many jurisdictions require it be done by a licensed plumber or licensed irrigator. But as long as it is properly done, you usually will not be called out on doing the work without a permit, but if you screw it up they usually throw all those charges at you later. The guys who read the meters are trained to check for it. In Texas, it's a $1,000 fine.