Ghostly Image on Radar

Sarge · Posted: Tue May 22, 2007 12:54 pm Post subject: Ghostly Image on Radar

This is the first boat that I've owned with radar. I think it is really great. I have a Raymarine E80 with radar, unfortunately I don't have the manual with me so I don't know what model radar. I've only had the boat 3 weeks and the radar has worked fantastically with no problems.

Something strange happened last night...

The family and I were high-tailing it from Kingston to Edmonds in the heavy rain and partial fog, crossing the shipping lanes when my radar picked up something on the starboard side. I could see the ferry on my port side big as day, but nothing on my starboard side. It was a weird signal too..like a multi-colored fuzzy fog. Of course I moved to avoid it, but when the radar showed that it was right next to me...there was nothing there! There was lightening and thunder (all the more reason to go WOT and get home to our slip) and I'm think maybe it picked up a thunder cloud. I also got some shadowing of the ferry exactly 180 degrees opposite of where it was, but this was different.

Anyone have a guess what might have caused this ghost image on my radar? If I were to guesstimate the size of the image compared to other boats and ships which I've observed on the radar I would say it was the size of 3 freighters side by side. It was also round not long and thin like a boat or ship.

Very strange.

-Sarge/Carl

thataway · Posted: Tue May 22, 2007 1:13 pm Post subject:

You nailed it--it is a ghost image. In large targets, you will get an image on the recprocical of the primary target. I suspect it is realated to the back scatter of the beam. Some units are more susceptable than others. I have noticed it more on JVC and Ray Marine than on Furuno--but it can happen on any unit.

I have seen some technical papers on the subject.

starcrafttom · Posted: Tue May 22, 2007 2:36 pm Post subject:

it was the ghost image or the heavy rain. there is a rain adjustment on the unit. I know you dont have the book but you can down load it from the raymarine web site. you can adjust the unit to look thru or for rain showers. I once was playing with the unit while waiting on the crab pots to fill. There was a big black fire on hat island and I was able to get it to show on the radar. I had to play with the manaul adjustments but it worked for a while.

Sea Angel · Posted: Tue May 22, 2007 7:34 pm Post subject:

Would the 'wake return' adjustment also give a similiar result?

starcrafttom · Posted: Tue May 22, 2007 8:01 pm Post subject:

I have not played with that yet. so I dont know