The Indiana High Accuracy Reference Network
Work on the Indiana High Accuracy Reference Network (HARN) is quickly coming to a close. The first phase results were accepted by the National Geodetic Survey (NGS) in early May 1998. The second phase results, submitted to the NGS by Woolpert L.L.P., have been approved and posted since early April 1999.
The first phase of the HARN established 126 stations in Indiana. The NGS, Schneider Inc., Plumb Tucket & Associates, Indiana Department of Transportation (INDOT), Indiana Department of Environmental Management (IDEM), and many others (see: contributors) made observations in the summer of 1997. Data processing was undertaken by the NGS.
For the second phase of the HARN, Woolpert was contracted, by the Office of the Indiana State Geodetic Advisor (OISGA), to observe an additional 25 stations in Indiana. Observations took place during the summer of 1998. The NGS did not make any observations in the second phase of the HARN. The phase 1 stations HONEY, G359, & GLASGOW RM 2 were resurveyed in the second phase, due to suspected monument motion.
The Indiana HARN consist of 148 A-order and B-order GPS survey stations. NGS specifications for A-order GPS survey stations require a relative baseline accuracy of 5 mm + 1:10,000,000. B-order GPS survey stations require a relative baseline accuracy of 8 mm + 1:1,000,000. Three A-order stations were established in the first phase of the Indiana HARN, including the reference markers ZID A and ZID B for the proposed Continuous Operating Reference Station (CORS) at the Indianapolis International Airport (IND). The final A-order HARN station is BLOOMINGTON NCMN 7291, a station visited by mobile Very Long Baseline Interferometry (VLBI) in 1987 as part of the NGS National Crustal Motion Network (NCMN). All other stations, first and second phases, are B-order.
Each of the Indiana counties has at least one HARN station; note that the NGS datasheet places station E 60 in Clark County, however it is believed to be north of the county line in Scott County. Porter and VanderBurgh counties have the most HARN stations with six stations each.
The NGS has designated 17 of the Indiana HARN stations as Federal Base Network (FBN) stations. These stations will be critical in the readjustment of the National Spatial Reference System (NSRS) by the NGS. They are dispersed evenly over the state, with the exception of ZID A and ZID B at IND.
To make HARN stations as usable as possible, the OISGA has built a web page with maps of the Indiana HARN and list of the HARN stations. The lists contain hyperlinks to the appropriate NGS datasheets for further site research by (Indiana) Surveyors. This new web site is located at:
http://ce.ecn.purdue.edu/~oisga
