2008 Alum


Cynthia Boshell

Cynthia Boshell


Years participated in RESESS:
2007 →
2008


An Overview

Uplift, subsidence, or systematic error? Measuring elevation in the Longmont-Denver corridor

Academic Affiliation: Junior, University of Colorado at Boulder, Mathematics
Science Research Mentors: Pamela Fromhertz – NOAA; Curt Smith – NOAA; Ronnie Taylor – NOAA
Writing and Communication Mentor:Shelly Olds – UNAVCO


Abstract

The Colorado Department of Transportation (CDOT) and National Geodetic Survey (NGS) conducted a 119 km leveling project that extended from Longmont to Denver International Airport. Up to10 cm elevation differences were observed in the area of Denver International Airport, raising questions about data collection procedures and benchmark stability. A detailed examination of data was conducted to identify possible systematic error. Field notes and the field abstract (a report that summarized recorded observations) were examined to determine how observations were made. Observation times, progression of observation activities, and time lapses between observations were identified as the main sources of systematic error. Data analysis was performed using elevation differences, published values, and loop closures. These provided further evidence that elevation differences were the result of systematic error. This research concluded that systematic error was responsible for the overall observed elevation difference of approximately10 cm and provided a basis for the National Geodetic Survey to finalize and publish elevation data for the benchmarks included in this leveling project. Future impacts of this research will include improvements in field crew training, revised data analysis procedures, and continued monitoring of possible uplift and subsidence through the National Geodetic Survey’s Height Modernization program.