The NASA website hosts a large number of images from the
Soviet/
Russian space agency, and other non-American space agencies. These are not necessarily in the public domain.
The
SOHO (ESA & NASA) joint project implies that all materials created by its probe are copyrighted and require permission for commercial non-educational use.
[2]
GPS determines the position of a vessel by comparing signals from several transmitting satellites in medium earth orbit (MEO). Differential GPS (DGPS) provides error correction to the GPS signals in order to increase location fix accuracy.