Abstract
The National Laboratory for Marine Science and Technology of China proposed the Guanlan ocean science satellite project in order to observe mesoscale and submesoscale ocean phenomena more effectively. In the project, the interferometric radar altimeter (IRA) is a main payload to be used to retrieve sea surface height (SSH) by means of interferometric imaging technology. Sea state is one of the important factors that affect the accuracy of the SSH that is retrieved by IRA. In the present work, the effects of velocity bunching and layover induced by sea waves are numerically simulated. The results demonstrate that the SSH would be significantly underestimated due to velocity bunching. On the other hand, the layover effect of sea waves along range direction would decrease (destroy) the coherence between the master-slave IRA images and then increase the random altimetry noise. Spatial smoothing is one of the main methods for reducing the residual error of sea waves. Here, we propose a theoretical formula to evaluate the residual error of sea waves for different wavelength, significant wave height and wave direction. The conclusions obtained in this work are helpful for better understanding the influence of sea state on the SSH retrieved by IRA.
Highlights
Since the advent of ocean radar satellite in the 1970s [1], altimeter and synthetic aperture radar (SAR) are two important microwave sensors for sea surface measurement
The results show that the layover mainly affects the correlation of master-slave images and the effect of interference imaging, while the velocity bunching more affects the mean sea surface height (SSH) inversion
In the actual height smoothing, we hope to choose the rectangular smoothing window of the magnitude of kilometers to reduce the impact of waves, while the mean SSH deviation that is caused by the velocity bunching and layover cannot be eliminated
Summary
Since the advent of ocean radar satellite in the 1970s [1], altimeter and synthetic aperture radar (SAR) are two important microwave sensors for sea surface measurement. In the general process of SAR observation, since the significance wave height (SWH) is small and the incident angle is large, the main factor that affects the SSH measurement is velocity bunching; the layover effect of ocean wave can be ignored. We can see that the impact of ocean waves on the IRA height measurement results is mainly caused by the velocity bunching effect [23,24,25], the layover effect [26,27,28,29,30] caused by the small incident angle and the spatial resolution. The final measurement results need to be smoothed, so that the spatial resolution reaches the magnitude of kilometers, in order to reduce the influence of random noise to effectively observe mesoscale and submesoscale ocean phenomena.
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