Abstract
GEOID12 Model Overview
Track: Geodesy
Authors: Daniel Roman, Yan Wang, Xiaopeng Li
The recently released GEOID12 model provides an update for surveying and engineering applications requiring transformations between the North American Datum of 1983 (NAD 83) and the North American Vertical Datum of 1988 (NAVD 88). GEOID12 incorporates a number of recently completed adjustments to the NGS Database. The National Adjustment of 2011 (NA2011) was completed and released at the same time as GEOID12 and represents the most recent realization of ellipsoidal or geometric coordinates for bench marks. This complements recent adjustments to the leveled heights in several states particularly those in the central Gulf Coast region where subsidence is an issue. Underpinning this is the United States Gravimetric Geoid for 2012 (USGG2012) that incorporates gravity field observations from multiple satellite gravity missions (GRACE, GOCE). USGG2012 provides the fine detail that fills in the information in between the control data represented by both the GPS on leveled Bench Marks for 2012 (GPSBM2012) and archived values in the OPUS-DB on leveled Bench Marks for 2012 (OPUSDDBM12). The preponderance of these control points derive from GPSBM2012 (around 23,000) but the OPUSDBBM12 provides additional coverage to reduce interpolation across gaps in the GPSBM2012 coverage. The control data were used to develop a conversion surface with Least Squares Collocation following the same techniques used for GEOID03 and GEOID09. This surface provides the transformation necessary to change USGG2012 into GEOID12. It also provides insight into the expected shift between NAVD 88 and the future vertical datum of the United States to be implemented in 2022.