V. Zlotnicki, CORRELATED ENVIRONMENTAL CORRECTIONS IN TOPEX POSEIDON, WITH A NOTE ON IONOSPHERIC ACCURACY/, J GEO RES-O, 99(C12), 1994, pp. 24907-24914
Estimates of the effectiveness of an altimetric correction, and interp
retation of sea level variability as a response to atmospheric forcing
, both depend upon assuming that residual errors in altimetric correct
ions are uncorrelated among themselves and with residual sea level, or
knowing the correlations. Not surprisingly, many corrections are high
ly correlated since they involve atmospheric properties and the ocean
surface's response to them. The full corrections (including their geog
raphically varying time mean values), show correlations between electr
omagnetic bias (mostly the height of wind waves) and either atmospheri
c pressure or water vapor of -40%, and between atmospheric pressure an
d water vapor of 28%. In the more commonly used collinear differences
(after removal of the geographically varying time mean), atmospheric p
ressure and wave height show a -30% correlation, atmospheric pressure
and water vapor a -10% correlation, both pressure and water vapor a 7%
correlation with residual sea level, and a bit surprisingly, ionosphe
ric electron content and wave height a 15% correlation. Only the ocean
tide is totally uncorrelated with other corrections or residual sea l
evel. The effectiveness of three ionospheric corrections (TOPEX dual-f
requency, a smoothed version of the TOPEX dual-frequency, and Doppler
orbitography and radiopositioning integrated by satellite (DORIS) is a
lso evaluated in terms of their reduction in variance of residual sea
level. Smooth (90-200 km along-track) versions of the dual-frequency a
ltimeter ionosphere perform best both globally and within 20 degrees i
n latitude from the equator. The noise variance in the 1/s TOPEX ionos
pheric samples is similar to(11 mm)(2), about the same as noise in the
DORIS-based correction; however, the latter has its error over scales
of order 10(3) km. Within 20 degrees of the equator, the DORIS-based
correction adds (14 mm)(2) to the residual sea level variance.