Alan, Roger, Geological Survey of Finland used the transverse gradient system for the country-wide AM mapping program, from mid 1970s to early 2000s (over two million line kms total). I recall Sheldon Breiner visited us in late 1970s to see the system in operation. Yes there was a Geometrics TN, but our work was originally inspired by the aircraft (DC-3 first, then DHC Twin Otter) characteristics. Sheldon made a comment that it was nice to see that it works before the company/group trying it goes bust - he had tried to advocate the system without any success.
The brains behind the system design and implementation were late Maunu Puranen (inventor of the Dual-Frequency AEM system) and Juha Korhonen, whose review paper on the subject is freely accessible at http://tupa.gtk.fi/julkaisu/specialpaper/sp_039_pages_077_102.pdf <http://tupa.gtk.fi/julkaisu/specialpaper/sp_039_pages_077_102.pdf> Best (personal) regards and greetings, Markku Peltoniemi > [email protected] kirjoitti 20.2.2019 kello 16.02: > > > > > Today's Topics: > > 1. Re: Cross-line magnetic field measurements - an enquiry (and > a challenge?) (Roger Henderson) > 2. Re: Cross-line magnetic field measurements - an enquiry (and > a challenge?) (Alan Reid) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 20 Feb 2019 12:10:04 +1100 > From: Roger Henderson <[email protected]> > To: [email protected] > Subject: Re: [SEGMIN] Cross-line magnetic field measurements - an > enquiry (and a challenge?) > Message-ID: <[email protected]> > Content-Type: text/plain; charset="utf-8" > > Alan, > I was intrigued to see Rich?s name again after I have just included it in a > review I am doing on data processing in Australia. > As I ran Geometrics in Australia I know we certainly used the reduction in > spacing that appeared to be the case, as a selling point for horizontal > gradient flying but I don?t know about the proof that it was exactly halved. > It did seem to be true in reality. > Because I just had correspondence with Ian Lilly who worked for Geometrics > and liased with Rich and was much closer to the processing than I was, below > is Ian?s reply to my asking if he knew the whereabouts of the proof. (The > 'pencil and paper' seems right for Rich) > > I remember Rich doing the proof in pencil on a yellow pad during one of my > visits to Sunnyvale. I have a very vague and possibly faulty recollection > that geoMetrics published a simplified version in something like a tech note > when they were trying to garner interest in gradiometers. > > I am not aware of the ?tech note? (anymore, at least!). > Maybe someone in Geometrics or Dick Wold, who was involved at the time, knows > more. > > I hope you can track it down. > Regards > Roger Henderson > >> On 19 Feb 2019, at 7:45 pm, Alan Reid via SEGMIN <[email protected]> >> wrote: >> >> Dear GrvMag and SEGMin listers >> >> I?m addressing both lists because the matter concerns both? >> >> Years ago, the late great Richard Hansen told me he?d proved that, for a >> conventional airborne magnetic total field survey, cross-line gradient >> measurements gave you the equivalent of halving the line spacing. The proof >> was for noise-free data, but hey, it's an indication of a usefulness that?s >> widely recognised and exploited. >> >> I subsequently asked Richard for his proof and he?d lost it, but he >> re-proved it another way. Regrettably, I?ve now also lost that proof. And >> Richard is no longer available to ask?? Hence the enquiry and the challenge. >> >> 1. Does anyone know of a published proof? If so, please may we have the >> reference (and even maybe a link to a pdf? >> >> 2. If not, does anyone have a proof they?d be prepared to offer for >> publication. I?d happily welcome it to ?Geophysical Prospecting?, and I?m >> sure ?Geophysics? and some other journals would be equally welcoming. >> >> 3. If neither of the above, the challenge is to produce a proof. It?d make a >> decent basis for an MSc, a pretty chapter in a PhD, and/or a worthwhile >> paper. From a personal perspective, it?d also ?complete? the survey design >> criteria I published in 1980. >> >> Regards >> >> Alan B Reid PhD >> Reid Geophysics Ltd >> 7 Keymer House >> Michel Grove >> Eastbourne BN21 1JZ >> UK >>
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