GLOBE Data User Guide
The purpose of the GLOBE Data User Guide is to help scientists and researchers understand, access, and use available GLOBE data. The scope includes data collected by GLOBE-trained teachers, students, and citizen scientists as well as data collected from automated weather stations and data loggers.
2019-09-23 GLOBE Observer elevation data
GLOBE Observer elevation data #
23 September 2019
GLOBE's GPS protocol states that a site's elevation is in relation to mean sea level (MSL). In 1995, the thinking was that sites would be only defined over land and so the elevation would be based upon the topographic elevation difference from MSL. Most GPS devices in the 1990s and early 2000s used the elipsoid model to determine elevation, which could be as much as 100m off from the geoid height. GLOBE's former database converted the GPS elevation values to geoid heights and presented those geoid heights on the legacy Vis system. In 2014, GLOBE discontinued this practice because most newer GPS devices are capable of determining elevation using the geoid height themselves. The GLOBE Observer app does not convey GPS elevation, but instead a Google web service is used that determines the height from MSL based upon the WGS84 EGM96 geoid height. It includes both bathymetry and topography values. The consumer of GLOBE data can assume that a returned elevation value for a site is based upon the geoid height of the landform from MSL. In other words, if the coordinates are over dry land it will be the topographic height. If the coordinates are over the ocean or sea, then elevation is reported is the distance of the seafloor from MSL expressed as a negative value.