What does “ephemeris” mean?
This refers to a list or table of positions of a celestial body as a function of time. The word comes from the latin word for diary. In GPS, ephemeris refers to a set of numeric parameters that can be used to determine a satellite’s position. Satellite image distribution files from earth observing satellites like Landsat or ERS-1 usually have ephemeris or orbital data included in the file header; this information is ignored when using the “rubber-sheeting” method of geometric correction, but is essential when the more accurate georeferencing method called orthorectification is used.
