Physical Heights Realized Through GNSS and Geopotential Models
21/09/2016 | 17:00 | Session 5: Height systems and vertical datum unification
Author(s): Daniel Roman and Xiaopeng Li
Daniel Roman and Xiaopeng Li
This paper will discuss the determination of both orthometric and dynamic heights using geopotential models and GNSS-derived coordinates. The U.S.A. will be adopting this approach to definition of official coordinates within the National Spatial Reference System (NSRS) in 2022. The Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project has been underway for the past eight years with the specific goal of providing the geopotential model that will serve as the basis for geoid model development and height determination in that new datum. Exemplar models developed using updated techniques and data sets are available on an annual basis online for examination. This year’s release will be the xGEOID15 models. The ‘A’ model will incorporate available satellite and terrestrial data, whereas the ‘B’ model will use that data and aerogravity from GRAV-D. Currently, these models are only to degree and order 2160 – five arcminute resolution. This is insufficient for the task of developing cm-level accurate heights as the omission error itself is greater than that as determined from previous studies. As such, the signal must be augmented from geoid height models at one arcminute intervals. Comparisons are made at bench marks and water level stations near tidal bench marks for the purposes of evaluating the performance of this approach. Geometric coordinates were derived using primarily the GPS signal and processing using both traditional “bluebook” procedures and Online Positioning User Service (OPUS). The OPUS suite of tools are being evaluated as an automated means for deriving geometric coordinates from the GPS (and eventually GNSS) data in a streamlined fashion. The GNSS-derived coordinates and the geopotential transformation are expected to achieve a cm-level accuracy at least in coastal, flat regions based on previous comparisons in Geoid Slope Validation Studies in 2011 and 2014.