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Abstract
Improving the altimetric precision under the requirement of ensuring the along-track resolution is of great significance to the application of iGNSS-R satellite ocean altimetry. The results obtained by using the empirical integration time need to be improved. Optimizing the integration time can suppress the noise interference from different sources to the greatest extent, thereby improving the altimetric precision. The inverse relationship between along-track resolution and signal integration time leads to the latter not being infinite. To obtain the optimal combination of integral parameters, this study first constructs an analytical model whose precision varies with coherent integration time. Second, the model is verified using airborne experimental data. The result shows that the average deviation between the model and the measured precision is about 0.16 m. The two are consistent. Third, we apply the model to obtain the optimal coherent integration time of the airborne experimental scenario. Compared with the empirical coherent integration parameters, the measured precision is improved by about 0.1 m. Fourth, the verified model is extrapolated to different spaceborne scenarios. Then, the optimal coherent integration time and the improvement of measured precision under various conditions are estimated. It was found that the optimal coherent integration time of the spaceborne scene is shorter than that of the airborne scene. Depending on the orbital altitude and the roughness of the sea surface, its value may also vary. Moreover, the model can significantly improve the precision for low signal-to-noise ratios. The coherent integration time optimization model proposed in this paper can enhance the altimetric precision. It would provide theoretical support for the signal optimization processing and sea surface height retrieval of iGNSS-R altimetry satellites with high precision and high along-track resolution in the future.
Highlights
Measured sea surface height (SSH) is one of the critical parameters of marine ecosystem monitoring, which is of paramount significance to applications such as fishery, oil drilling, and commercial navigation
The research mainly involves three aspects: the processing of intermediate frequency (IF) data and the extraction of precision information; the derivation and verification of the coherent integration time optimization model; and the application of the validated model to airborne and spaceborne altimetry mission scenarios to predict the optimal solution for precision
(2) For the purpose of optimizing the precision performance, we consider the influence of the correlation between waveforms on the covariance of the power waveform, and derive the coherent integration time optimization model from the statistical properties of the waveform
Summary
Measured sea surface height (SSH) is one of the critical parameters of marine ecosystem monitoring, which is of paramount significance to applications such as fishery, oil drilling, and commercial navigation. The previous study has shown that in the spaceborne iGNSS-R altimetry scenario, in order to achieve an altimetric precision better than 20 cm, the signal processing time required for a single height retrieval is approximately 10 s, and the along-track spatial resolution is about 65 km [8]. For signal post-processing, one method to improve the altimetric precision is to increase the signal’s coherent integration time and incoherent average number. Both methods inhibit the noise introduced in different ways. Different from previous studies, in order to improve the precision of iGNSS-R ocean altimetry, this study constructs a coherent integration time optimization model by deducing the conversion relationship among coherent integration time, waveform correlation, and altimetric precision. The model can more accurately estimate the variation of precision with coherent integration time in different iGNSS-R altimetry applications so as to optimize the final precision result
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