Preliminary results of the Geoid Slope Validation Survey 2014 in Iowa

The National Geodetic Survey conducted a second Geoid Slope Validation Survey in the summer of 2014 (GSVS14). The survey took place in Iowa along U.S Route 30. The survey line is approximately 200 miles long (325 km), extending from Denison, IA to Cedar Rapids, IA. There are over 200 official survey bench marks. A leveling survey was performed, conforming to 1^st order, class II specifications. A GPS survey was performed using 24 to 48 hour occupations. Absolute gravity, relative gravity, and gravity gradient measurements were also collected during the survey. In addition, deflections of the vertical were acquired at 200 eccentric survey benchmarks using the Compact Digital Astrometric Camera (CODIAC) camera. This paper presents the preliminary results of the survey, including the accuracy analysis of the leveling data, GPS ellipsoidal heights, and the deflections of the vertical which serves as an independent data set in addition to the GPS/leveling implied geoid heights.