Calculation of vector winds from spaceborne fan-beam scatterometers require
s that backscatter measurements from different antennas be relatively calib
rated to high accuracy. A method is developed to perform postlaunch antenna
calibration using global mean ocean backscatter measurements in conjunctio
n with estimates of the statistical distribution of near-surface wind veloc
ity and the model function relating backscatter to winds. Substantial analy
tic simplifications result from assuming that the wind speed and azimuth di
stributions are separable and that the upwind-downwind asymmetry term in th
e model function is small. The analytic model allows quantitative examinati
on of the sensitivity of the technique to errors in the approximate wind di
stributions and empirical model function. The approach and its assumptions
are tested using 13 months of ERS-1 backscatter data, surface wind estimate
s from two operational weather analyses, and three empirical C-band model f
unctions. It is shown that the ERS-1 antennas are relatively calibrated to
within 0.2 dB, which is consistent with other published results obtained us
ing ground receiving stations and Amazon forest data. The results are nearl
y insensitive to realistic errors in the estimated wind velocity distributi
ons and model function. Analysis suggests that the ocean antenna calibratio
n technique should be accurate to about 0.2 dB using as little as 3 weeks o
f scatterometer data.