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The Topex/Poseidon ground track maintenance manuever targeting strategy was changed following launch due to the observation of unexpected, and hence, anomalous accelerations.
Estimates of the effectiveness of an altimetric correction, and interpretation of sea level variability as a response to atmospheric forcing, both depend upon assuming that residual errors in altimetric corrections are uncorrelated among themselves and with residual sea level, or knowing the correlations.
TOPEX/Poseidon (T/P) is a joint mission of US NASA and French CNES design launched August 10, 1992. It carries two radar altimeters which alternately share a common antenna. There are two project designated verification sites, a NASA site off the coast at Pt. Conception, CA, and a CNES site near Lampedusa Island in the Mediterranean Sea. Altimeter calibration and validation for T/P is performed over these highly instrumented sites by comparing the spacecraft's altimeter radar range to computed range based on in situ measurements which include the estimated orbit position. This paper presents selected results of orbit determination over each of these sites to support altimeter verification. A short arc orbit determination technique is used to estimate a locally accurate position determination of T/P from less than one revolution of satellite laser ranging (SLR) data. This technique is relatively insensitive to gravitational and nongravitational force modeling errors and is therefore essentially geometrical. The quality of these short arc orbits is demonstrated by covariance analysis and by comparison to orbits determined from longer arcs of data and other tracking data types, such as DORIS and Global Positioning System Demonstration Receiver (GPSDR) data.
The TOPEX/POSEIDON altimeter measurement system is evaluated over the Great Lakes. Using in situ lake level measurements, the temporal variations in lake level are removed from the altimeter measurements, thus permitting the performance of the altimeter system to be assessed.
There is considerable controversy as to whether flares are the sole producers of energetic protons or whether coronal mass ejections play a central role. We note that the system described in this paper is presently capable of computing flux predictions only for protons associated with solar-flare activity.