Proton mag signature readings

[Francisco Xavier]

Hi Subscribers,
I have a proton mag MX500 from Planet Elect. It is a single toroidal sensor connected to a lcd control box. It can perform single mag readings as also diferential by means of time shifting readings (compare two adjacente readings - 3 seconds).
Searching an underwater field (about 45 m deep) sensor altitude of about 20 m over bottom and single sensor reading (magnetometer) and I have consistent readings a about 40 nT on same place. (2 sconds polarinzing time).
Over the same place using gradiometer readings (time shifting) I have only 5 nT and much less sharp slope signature (it is OK and consistent). The bottom is slimy/sandy and have nearly some sacrce rocks (non magnetic - it's continental shelf).
Watching the bottom with a video survey could not see anything ferrous.
The instrument manual it not very useful on this aspect. I do not know how to interpret this and if to continue searching (could be anything embedded in the mud? - but how big? without any evidences over the flat sand?).
If anybody have experience with this kind of magnetometer and such readings and situation I would like to hear from.
Thanks,

[rgecy]

Sounds like a good size hit. It would be normal for the gradiometer reading to be significantly less. Most objects eventually become covered over time and it wouldn't be unlikely to have an anchor show this kind of reading.

No telling what it is without going down to explore and move a little sand/mud.

Good Luck and be safe!

Robert in SC

[Francisco Xavier]

Thank you Robert for your reply,
It is the second place where it happens me on continental shelf (supose not exists magnetic rocks).
The first place was a moderate rocky bottom not so much sandy sockets to hide iron artifacts. I dove there and not found any vestige of magnetic material enough for the magnetic anomaly. The heavy rocky bottom around do not have any anomaly reading!
I would like to hear if it had happens to any of you the same on the field, not only on theoretical basis. Once the theoretical explanations can be presence of magnetite rocks; buried para-magnetic materials; black sand (most common on vulcanic places magnetite+ilmenite).

Best regards,

Francisco