General Data Entry
There are small errors associated with the elevation determined by GPS satellites; therefore, the GLOBE website executes a correction factor on entered elevations based on GEODESY.
The GPS units assume that Earth is a nice ellipse when, in fact, it has an equatorial bulge and many valleys and mountains. We use a calculation to correct the elevation provided by the GPS unit based on your latitude and longitude. So, for example, even though the GPS unit says 890 meters, a closer value (based on this calculation) is 837.2.
Basically, the way the elevation is computed is by the GPS using particular ellipses to approximate Earth's surface. This is controlled by the datum setting of the GPS unit. For GLOBE GPS measurements, the datum must always be set to WGS-84. The correction factor to "improve" the elevation estimate is based on the GPS using the WGS-84 datum and a more accurate elevation data set.
While the correction factor improves the site elevations overall, individual points can suffer. Sometimes schools near sea level end up with a corrected elevation beneath sea level!
Not all users of the data on the GLOBE website use the elevation data and, if they do, it's mainly for looking at big changes in elevation (e.g., sea level vs. mountains), and the corrections won't make that much difference, since all stations in a region will be affected in the same direction.Scientists who need more refined height estimates can get elevations from independent data sources, as long as the latitude and longitude are reported accurately and with precise degrees (four or five decimal positions).