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Objective: The SWOT (Surface Water and Ocean Topography) mission, planned for launch in 2022, will carry a KaRIn (Ka-band Radar Interferometer) for characterizing the ocean mesoscale and submesoscale circulation. To realize the observation target of the SWOT mission, the observation errors need to be reduced. Among the errors, the baseline inclination error caused by the inaccuracy of the baseline inclination measurement and the phase error caused by the phase mismatch in the process of interferometric imaging are hard to be removed. These two errors make the sea surface height measurement in the swath inaccurate and make it difficult to identify the characteristics of mesoscale phenomena. Therefore, to achieve the observation goal, this article is to correct phase error and baseline roll error. Method：Both errors are linear with across track distance from nadir. Under the assumption that all errors except the phase error and the roll error have met the error budget requirements, a bilateral independent cross-calibration method is proposed to detect and mitigate the two spatial coherence errors. Firstly, the errors of the left and right swaths in the experiment are calculated respectively. Secondly, the observed values in the cross region are subtracted to reduce the influence of the ocean signal. Finally, the errors are estimated based on their linear correlation with the across track distance. The orbit parameters of SWOT and Jason-2 (before October 2016) provided by AVISO (Archiving Verification and Interpretation of data of Satellites Oceanography) are used for along-track sampling. The errors of 25-day SWOT sample data are estimated by the self-crossover and crossover (with Jason-2) methods. Result: In the SWOT self-crossover, more than 90% of the error has been corrected from 8cm to 4cm, and nearly 73% of the intersection-region standard deviation has been from 6cm to 2cm. In the SWOT crossover with Jason-2, nearly 86% of the error has been corrected from 8cm to 4cm, and nearly 55% of the intersection-region standard deviation has been from 6cm to 2cm. From the absolute value and standard deviation, the error inversion effect of the self-crossover and crossover (with Jason-2) methods on the intersection point is good. The results show that the bilateral independent cross-calibration method effectively estimates the overall error, and significantly reduces the error level in the case of low instrument accuracy. Conclusion: The crossover method weakens the influence of a larger part of the ocean signal, increases the weight of the error in the calculation process, and then calculates the error through the matrix. In view of the characteristics that the phase error is different from the baseline inclination error, the left and right swaths are cross-calibrated separately to calculate the gradient slope value in the cross-track direction of the unilateral swath. The calculated gradient slope value can be directly back-calculated to get the overall error, and then remove the error. The bilateral independent cross-calibration method not only inherits the ability of the cross-calibration algorithm to correct the baseline inclination error, but also scientifically and effectively corrects the phase error. The experiment also suggests that the cross-calibration formula can be optimized based on the error characteristics to estimate other errors with gradient changes in the across track and contributes to error reduction.