Re: GPS USE

["Lary Martin" <larym@hotmail.com>]

All laser systems suffer from the same major shotcoming: They are 
specifically line-of-sight.  That means, if the operator accidently gets 
in front of the beam, you lose data.  If you have rooms that are not 
perfectly square, you lose data.  If the room had vertical support 
beams, you lose data.  In addition, you have laser safety 
considerations.

GPS is nice, BUT you have to remember the basic GPS program.  ALL GPS 
satellites are OWNED AND CONTROLLED by the military.  Except for 
classified, controlled military units, the GPS is intentionally degraded 
for any non-military use. Companies claiming "cenitmeter accuracy" are 
lieing.  In actuality, they use diffentental GPS or DGPS.  This system 
uses a staionary GPS antenna to establish a "known" point and a second 
antenna to establish the "difference" between the stationary antenna and 
the mobile antenna.  The problem is, because the military controls the 
satellites and the signals given off, the accuracy of the base station 
is, at best +/- 30 meters (based on major computer computation) and the 
accuracy of the mobile antenna is +/- 100 meters, the accuracy of any 
given point is VERY questionable.  IF the survey shows no area of 
concern, then the accuracy is not important.  However, if the survey 
indicates areas that require further survey or remediation, finding that 
area may be very difficult.

There are other systems that provide much better accuracy (+/- 1 ft), 
repeatability - you can go back to that EXACT spot even 10 years from 
now, 100% per cent coverage of outdoor areas (with limitation for 
terrain), over 10,000 data points per hour, and accepted by multiple 
regulatory agencies.  Indoor surveys can use the same system, and 
provide 3-D (up to 2 meters) survey maps of any room, regardless of 
supports or room configuration.

No civil surveys are required, but pre-existing surveys can be 
integrated into the survey.

We do GPS surveys when they are a vialble choice.  We also perform our 
other surveys in any area, for any isotope, to meet any regulatory 
requirement.

LARY R MARTIN
HEALTH PHYSICIST
LR MARTIN & ASSOCIATES< Inc
(757) 989-0255
(757) 989-0754 FAX
larym@hotmail.com


>From server@romulus.ehs.uiuc.edu Mon Oct 12 13:04:50 1998
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>Date: Mon, 12 Oct 1998 15:07:17 -0500 (CDT)
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>From: "Fleming, Kenneth" <knflemin@bechtel.com>
>To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
>Subject: GPS USE
>X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
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>I've been tasked with conducting a radiological survey including both
>outdoor (huge tracks of land) and indoor areas.  The client wants us to
>consider the use of GPS to locate data points; foregoing the use of 
civil
>surveys if possible.  It's been several years since I saw a system 
being
>designed for use at Kerr-McGee (West Chicago) and I don't remember the
>manufacturer.  I've seen TNutech's GPERs system (for exterior areas) 
and a
>laser ranging system (for indoor areas).
>
>If anyone has experience with any GPS type system or either of the 
above
>systems, please respond back to the E-mail address below.
>
>
>Kenny Fleming CHP CSP
>FUSRAP Radiological Control Supervisor
>knflemin@bechtel.com
>(423) 220-2306
>(423) 220-2464 FAX
>
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