[GeoStL] Re: what is this?

Apparently its a base station for a GPS location reference (i.e., at a known 
latitude/longitude/altitude) associated with the Airborne Topographic Mapper. 
My guess is it probably generates highly accurate GPS position differential 
signals and sends them to these ATM aircraft - so the aircraft can correct 
their accuarcy errors in location received from GPS sattelites. Must be 
basically a system like WAAS, but "portable" and can be set up at one of about 
46 sites (in the vicinity of whereever they are mapping the terrain on a given 
day). These sites are listed at: http://aol.wff.nasa.gov/aoltm/gps_sites/

  From  http://aol.wff.nasa.gov/aoltm.html  The ATM measures topography to an 
accuracy of ten to twenty centimeters by combining measurements from an 
airborne laser altimeter and GPS (global positioning system) receivers. The ATM 
has demonstrated this accuracy at distances as great as a thousand kilometers 
from any base station. The current ATM instruments (ATM2 and ATM3) and their 
predecessors have a history going back to the mid 1970's. The instruments 
commonly fly aboard the NASA P3-B based at Wallops Flight Facility, Virginia. 
ATM2 has also flown aboard several twin-otter (DH-6) aircraft. A major task of 
the ATM over recent years has been the measurement of the Greenland ice sheet 
with the goal of determining changes in the ice sheet elevation. Other uses 
have included verification of satellite altimeters , and the measurement of 
sea-ice thickness. The altimeter often flies in conjunction with other 
instruments, and has been used to measure sea-surface elevation and ocean wave 
characteristics. 

Note there is one of these (portable) base sites in Columbia, MO 
http://aol.wff.nasa.gov/aoltm/gps_sites/colum.html
  Latitude: 38 49 6.42839 N 
  Longitude: 92 13 10.09932 W 
  Ellips. Ht.: +234.9243 m 
Thats a few more significant digits of accuracy than my GPSr has :)


John (dj&r)

  ----- Original Message ----- 
  From: Jen Guyer 
  To: geocaching@xxxxxxxxxxxxx 
  Sent: Friday, October 25, 2002 8:56 AM
  Subject: [GeoStL] what is this?



  http://aol.wff.nasa.gov/aoltm/gps_sites/capcity.html 

  I was doing a search of New Cumberland, Penn and found this. The New 
Cumberland GPS site. And of course anything GPS catches my eye. But what is it?

  Jen

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