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Bilateral independent cross-calibration method of the satellite-borne imaging altimeter

  • role： First author第一作者
  • Affiliation：

    College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

  • Email：baizhuo@stu.ouc.edu.cn
  • Introduction：白卓，研究方向为干涉成像高度计的误差处理。E-mail： baizhuo@stu.ouc.edu.cn
BAI Zhuo1,  
  • Affiliation：

    College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

ZHANG Haoxin1,  
  • role： Corresponding author通信作者
  • Affiliation：

    College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

    Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China

  • Email：chunyongma@ouc.edu.cn
  • Introduction：马纯永，研究方向为干涉成像高度计的误差处理。E-mail： chunyongma@ouc.edu.cn
MA Chunyong12*,  
  • Affiliation：

    College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

    Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China

ZHAO Chaofang12,  
  • Affiliation：

    College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

    Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China

CHEN Ge12

résumé

The Surface Water and Ocean Topography (SWOT) mission, which is scheduled to launch in 2022, will carry a Ka-band Radar Interferometer to characterize the ocean mesoscale and submesoscale circulation. The observation errors must be reduced to realize the observation target of the SWOT mission. Among the errors, the baseline inclination error caused by the inaccuracy of the baseline inclination measurement and the phase error induced by the phase mismatch in the process of interferometric imaging are difficult to eliminate. These two errors make the sea surface height measurement in the swath inaccurate and identification of the characteristics of mesoscale phenomena challenging. Therefore, the purpose of this article is to correct phase error and baseline roll error to achieve the observation goal.Both errors are linear with across track distance from nadir. Assuming that all errors, except the phase and roll errors, have met the error budget requirements, a bilateral independent cross-calibration method is proposed to detect and mitigate the two spatial coherence errors. First, the errors of the left and right swaths in the experiment are calculated. Second, 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 Archiving, Verification, and Interpretation of Satellite Oceanographic data are used for along-track sampling. The errors in the 25-day SWOT sample data are estimated by using the self-crossover and crossover (with Jason-2) methods.In the SWOT self-crossover, more than 90% of the error was corrected from 8 cm to 4 cm, and approximately 73% of the intersection-region standard deviation was adjusted from 6 cm to 2 cm.In the SWOT crossover with Jason-2, approximately 86% of the error was corrected from 8 cm to 4 cm, and approximately 55% of the intersection-region standard deviation was adjusted from 6 cm to 2 cm. Based on 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. 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.The crossover method weakens the influence of a larger portion of the ocean signal, increases the weight of the error in the calculation process, and calculates the error through the matrix. Given that 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 obtain the overall error and eliminate 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.

mots-clés

cross-calibration;Error-correction;phase error;Baseline roll error;Interferometric imaging altimeter

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