From: Ross
Thanks for your email. I will take the opportunity to jump in here and tell you what I know about using magnetometers on UAV?s. I probably know as much as anyone.
There are 2 or 3 issues that will complicate matters for the search. First, there is typically not much ferrous material in an aircraft. Perhaps the hardened parts of the engines, landing gear other structural components. This means that the percentage of material will be small and therefore the anomaly will be small. Second, the anomaly falls off as the inverse cube with distance. This means that if say there was 1000 lbs of ferrous material, then at 100 feet altitude (if you flew right over the target) you would only get about 0.5nT of ?signal?. At 200 ft it would be 1/8th or 0.06nT! That is essentially undetectable by magnetometry when considering earth noise and platform movement noise.
The third issue has to do with UAV self-signatures In other words there are four types of magnetic effects we will see ?generated?: induced, permanent (or remanent), eddy current and electrical current. You may want to watch some movies on our Video Library called Introduction to Marine Magnetometry which discuss the first three of these.
So the issue is that on a small aircraft like a UAV, you cannot get very far away from these sources of magnetic contamination. Remember the inverse cube rule. So being close to something magnetic has a big effect on the magnetometer. Most UAV?s are not capable of towing a suspended ?bird? and thus the magnetometer will have to be hard mounted as you will see in the attached pictures. But you will notice that in standard helicopter and fixed wing installations the magnetometer is in a boom that removes the magnetometer from the immediate vicinity of the magnetic bits of the platform. This is not feasible in a UAV. Therefore we must do magnetic compensation to remove the effects of the local platform and its motion.
We are currently under contract to the US ESTCP Technology Development board to develop commercially available electrical current compensation for an AUV (autonomous underwater vehicle) to go with our standard induced, permanent and eddy current compensation software. We expect that a UAV will have on-board electronics which will generate magnetic transients which will have to be removed in order to see ?outside? the platform. This is an experimental project and although we have excellent first order results we don?t expect the project to be completed until next year.
I wish I had better information about using a UAV magnetometer for your search effort but I believe that it will not be feasible to get the kind of data you need to unequivocally (e.g., to separate the anomaly from naturally occurring geologic signal) determine that an anomaly of interest has been detected. A better method may be EM but again, this is not well suited for UAV operation due to the amount of power required for transient EM operation.
Best Regards,
Ross
Linkback: You are not allowed to view links.
Please Register or Login
http://www.thunting.com/smf/index.php/topic,21544.msg148278.html#msg148278
|
|
|
Logged
|
|
