2019-09-23 GLOBE Observer elevation data-1 - GLOBE Data User Guide
GLOBE Data User Guide
To discover all the various ways to use GLOBE data, download the GLOBE Data User Guide (PDF) (version 2.0, effective 30 December 2022).
Learn how to access and interpret GLOBE data with this Data User Guide. Inside, members can find appendices on GLOBE's associated metadata, the types of variables available for download, primers on our different protocols and more.
GLOBE data is collected and submitted by GLOBE-trained teachers, students and citizen scientists. GLOBE also collects additional data from automated weather stations and individual data loggers. Through the hard work of these participants, over 200 million measurements have been logged into GLOBE archives and made available for public use.
Version 1.0 of the Data User Guide is available for reference.
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.