A global statistical analysis of the first 10 months of TOPEX/POSEIDON
merged geophysical data records is presented. The global crossover an
alysis using the Cartwright and Ray (1990) (CR) tide model and Gaspar
et al. (this issue) electromagnetic bias parameterization yields a sea
level RMS crossover difference of 10.05 cm, 10.15 cm, and 10.15 cm fo
r TOPEX-TOPEX, POSEIDON-POSEIDON, and TOPEX-POSEIDON crossovers, respe
ctively, All geophysical corrections give reductions in the crossover
differences, the most significant being with respect to ocean tides, s
olid earth tide, and inverse barometer effect. Based on TOPEX-POSEIDON
crossovers and repeat-track differences, we estimate the relative bia
s between TOPEX and POSEIDON at about -15.5 +/- 1 cm. This value is de
pendent, however, to the electromagnetic bias corrections used. An orb
it error reduction method based on global minimization of crossover di
fferences over one cycle yields an orbit error of about 3 cm RMS. This
is probably an upper estimate of the orbit error since the estimation
absorbs other altimetric signals. The RMS crossover difference is red
uced to 8.8 cm after adjustment. A repeat-track analysis is then perfo
rmed using the CR tide model. In regions of high mesoscale variability
, the RMS sea level variability agrees well with the Geosat results. T
idal errors are also clearly evidenced. A recent tide model (Ma et al.
, this issue) determined from TOPEX/POSEIDON data considerably improve
s the RMS sea level variability. The reduction of sea level variance i
s (4 cm)(2) on average but can reach (8 cm)(2) in the southeast Pacifi
c, southeast Atlantic, and Indian Oceans. The RMS sea level variabilit
y thus decreases from 6 cm to only 4 cm in quiet ocean regions. The la
rge-scale sea level variations over these first 10 months most likely
show for the first time the global annual cycle of sea level. Finally,
we analyze the TOPEX and POSEIDON sea level anomaly wavenumber spectr
al characteristics. TOPEX and POSEIDON have identical spectral charact
eristics at low wavenumbers. For wavelengths shorter than 100 km, howe
ver, POSEIDON spectra are more energetic. This is probably related to
the TOPEX tracker characteristics and to the way the acceleration corr
ection is made in the geophysical data records. POSEIDON repeat-track
noise level is estimated at about 3 cm for a 1-s average. The TOPEX re
peat-track noise level is about 1.8 cm RMS but this probably correspon
ds to averages over several seconds.