Jump to content

Recommended Posts

Posted

Anyone care to guess what caused the return at the 8 o'clock position on this commercial marine radar display?  

It's on a 12-mile range setting, so each ring represents 3 miles across.  That places the target 4.5-5 nm out from the vessel carrying the radar.  

Now, I know what it is, from its track (relative to the antenna's sweep period), and by having encountered such targets before.

 

SUkHM7I.jpg

Posted

Skyviper, you are correct in one respect.  You are looking at a heavy rain storm approaching from the vessel's port side. I happen to know that this boat is tied up at its slip in a small marina.  

Notice the diagonal line near the center of the display ?  That's the land and docks in that marina, and in the surrounding area.  The target at 8 o'clock traces back from a thin line and then gets "thicker" as it goes along. The antenna sweeps every 3-4 seconds.  To make a line like that at that distance (given the sweep interval) requires a bit of headway.  Hint: It's not another vessel.

 

Posted

An airliner from the size of the return.  Too bad it wasn't a video, as opposed to a still, then you'd appreciate how fast the return traverses the display.

 

Posted
1 hour ago, Skyviper said:

Well. That makes sense.

So how high or low was it?

To figure that out, one must know the height of the radar, how its mounted (savvy installers place a wedge under the mounting flange to compensate for a boat's running angle), and the vertical beam width (large span open array radar antennas usually have a narrower beam width, than smaller, enclosed dome antennas).

One boat that I used to run had a 72-mile radar mounted on it's bridge top.  The antenna was about 20 feet above the waterline.  On its 12-mile range setting, I used to see smaller, private aircraft departing from a local airport about 6-7 nautical miles away, and at the 36-mile range setting, military transports climbing out of  joint base McGuire -Dix-Lakehurst (once they cleared the ground clutter).

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use, Privacy Policy, and We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue..