The GEOSAT Follow-on (GFO) Altimeter

The NAVY GEOSAT Mission (1985-1990) demonstrated the ability of an altimeter equipped satellite to provide global measurements of mesoscale ocean features with 3 centimeter precision. The GEOSAT radar altimeter, developed by JHU/APL, was an enormous success. Built with early 1980's technology, the GEOSAT altimeter weighed 191 pounds and consumed 146 watts. The GFO radar altimeter, under development by E-Systems Inc., will achieve the GEOSAT measurement capability, but at one-third the weight and one-half the power (48 pounds, excluding antenna, and 76 watts). The GFO altimeter uses the same proven linear FM waveform, pulse repetition frequency (PRF), pulse compression technique, and alpha-beta tracker design as the GEOSAT radar altimeter, but takes advantage of current RF and digital signal processing technologies to produce an instrument that is both light-weight and reliable. Also, thanks to a cooperative working relationship with JHU/APL, the GFO radar altimeter design encompasses "lessons learned" from both the GEOSAT and TOPEX programs. Analysis of the range, waveheight, and back-scattering cross section performance indicates that the GFO altimeter will achieve the GEOSAT performance in all areas. Finally, the GFO altimeter design encompasses features allowing economical expansion; including a C-band channel for improved range accuracy, and a 33% higher PRF for improved instrument noise performance. The GFO dual-channel altimeter would weigh 107 pounds and consume 156 watts.