Caesium Magnetometers. When Sales and Science Collide.

Modern Mag has created a backpack that can replace the standard backpack that ships with a prominent American Caesium magnetometer. To design this backpack I had to study and understand the Caesium magnetometer specifications. I have used this magnetometer many times in the past (my university owned one), but still wanted to check the latest specifications. So I downloaded a brochure and was fairly shocked at the claims being made. Look – I am not going to name and shame here, but I really urge customers to try to separate the science from the marketing hype. The claims being made about this common magnetometer and my comments are as follows:

  1. “Best sensitivity in the industry at 0.008nT/Hz.” FALSE. Best is 0.0003nT/Hz from the GSMP-35
  2. “Very fast sampling at 5 samples per second.” Yeah that’s OK, but most optically pumped magnetometers I have used can sample twice as fast at 10 samples per second (10 Hz).
  3. “Low AC field interference. Best in the industry for rejecting AC power line grid noise.” What? This is digital signal processing 101. Just sample the magnetic field at greater than twice the multiple of the AC signal you want to reject and the job is done. There are no tricks to efficiently removing powerline noise. It is easy and effective.
  4. “Reliability -our Cesium sensors never need calibration or factory realignment.” What? I have never seen or used an optically pumped magnetometer in the last 15 years that needed calibration. This is irrelevant.
  5. “Designed for extreme ruggedness and reliability.” Hmmm, last time I hired one from a prominent Australian renter, it had a faulty sensor cable that was adding a LOT of noise to the data. Also, we were only looking for mineral sands in very low magnetic gradient fields, but the sensor kept loosing lock all the time. Could have been the faulty cable of course, but I wondered about the size of the sensor dead zones. All those cables hanging out look pretty vulnerable to me. Would not call it “rugged”.
  6. “Designed for large area surveys with 8-hour data storage capacity and two 6 hour battery packs.” Memory and data storage is not an issue these days, with Modern Magnetometers shipping with oodles of cheap memory. Besides the files captured from a days data are pretty small. Modern Mag samples most surveys at 1Hz for 8-10 hours a day and the ASCII files are only 1MB in size. Regarding the “6 hours battery packs”, they are large heavy lead acid batteries. Modern Mag has one k-mag with a large Li-ion battery that lasts all day that is lighter than a 12v 7.2 Ah SLA battery!
  7. “Comes with a two year warranty.” Most do.
  8.  “This low cost Cesium vapor magnetometer system offers the mining/oil/gas survey companies the best total field magnetic survey tool available. Based on items 1-7 I would have to say that no geophysicist in their right mind would conclude this having compared data from all the magnetometers out there.

To further counter this spin, what i don’t like about this Caesium magnetometer is:

  1. It is heavy because of its lead acid batteries.
  2. It is big and has an external frame. Thus it is difficult to manoeuvre through trees.
  3. It has a high heading error. This puts stripes in the data easily seen in the 1VD and quiet areas of the data.
  4. The case is HUGE. Operators call it the coffin!
  5. The GPS electronics are too close to the sensor which probably contributes to the high heading error.
  6. It does NOT have GPS navigation. This is a big, big, BIG omission. The GPS can tell you where you have been, but not where to go.
  7. It costs the same (last I heard) as other superior magnetometers from several manufacturers.

It is probably a good thing that marketing material is not peer reviewed by scientists! In defense of this company, I suspect that the marketing material (and the magnetometer) has not been updated in a very very long time. Much of the information would have been accurate 10 years ago, but modern magnetometers are much improved.

So shop around. Think like a scientist and do your own research and comparisons when purchasing an optically pumped magnetometer. There is a clear winner when you do this. (Hint – it is not a Caesium magnetometer!).

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