3 GBT Surveys I GI3T MEMO 223 Green Bank site survey information David H. Parker Bill Radcliff John W. Shelton April 20, 2004 This report identifies all known survey information available for the National Radio Astronomy Obser- vatory, Green Bank, West Virginia site. Most of the historical survey data, and all of the Antenna Metrol- ogy group survey data, has been incorporated into the STAR*NET least squares reduction software pack- age. Notes on the use of the STAR*NET results are included. Introduction During the construction of the Green Bank Tele- scope (GBT), the Antenna Metrology group con- ducted many surveys around the Green Bank site. We also gathered as much additional data as we could find; including a wealth of historical information, pro- vided by Sid Smith; the GBT soils report; the GBT location survey; contractor surveys; and a site survey. All of this information is far too much to be in- cluded in this report, e.g., the STAR*NET list- ing alone is 161 pages. The detailed site informa- tion is filed in the GBT Archive, under file number ST047. The latest site report is on the CD under 100302\NRAO.LST. GBT antenna surveys, and copies of the original field notes, are filed separately in the GBT Archive. 2 Surveys prior to the GBT The NRAO site drawings identify a number of bench marks established early in the history of NRAO. Un- fortunately, a number of the concrete bench marks have been disturbed or removed. It should be noted that the coordinates are in NAD27 state plane co- ordinates, in feet. The conversion from NAD27 to NAD83 is not straightforward, but the NGS provides free software (CORPSCON) to convert between co- ordinate systems. In 1960, Geonautics did an extensive survey of the 140 Foot Telescope and established a network of refer- ence bench marks around and on the telescope. Most of the ground reference bench marks have been de-. stroyed since then. Geonautics bench mark G3, lo- cated on the hill north of the 140, has survived and has been protected by a wooden fence. The south bench mark, 012, which was used to establish the telescope alignment by Polaris measurements from G12 to a mark on the south deck of the 140, also survives and is protected. In 1970, the Air Force did an extensive survey of the 140 Foot Telescope and established an additional bench mark, SITE, on the hill east of the telescope. They did many astronomical surveys from SITE and established the geodetic location and azimuth from SITE to G3, and SITE to G5. They transfered the elevation from first order bench marks in Cass to BANK (next to the school) and SITE. In 1988, NOAA established three absolute gravity bench marks on the site and measured the absolute acceleration of gravity at these bench marks. Richard Fleming generated a reference list of bench marks and coordinates. At least one of these (T-007) was found to be incorrect, so we recommend using the latest STAR*NET listing for all coordinates. Sid Smith established reference azimuth bench marks at each of the interferometer stations, in order to align the telescopes after movement. These were established by Polaris observations, and the scribe marks were made for astronomical north. In preparation for the GBT project, NRAO hired Triad engineering to do the soils report and survey the telescope location. This was where the error in Fleming's reference list was exposed, when they did not agree with the published coordinate for T-007. Unfortunately, one of the two Triad bench marks was destroyed early in the construction—which left the site without an azimuth orientation. The metrology group obtained the original Triad field notes and lo- cated several of the temporary bench marks, which allowed us to salvage the Triad survey. This survey was tied to a permanent bench mark, KING, located