基于量化区间跃迁模型的星载SAR原始数据压缩误差机理研究

A study of spaceborne SAR raw data compression error based on a statistical model of quantization interval transfer probability

星载合成孔径雷达(SAR)压缩后的原始数据信噪比是SAR系统设计时原始数据压缩比选取以及应用分析的重要理论依据,前人常用的量化信噪比并不能完全表征压缩后信号与噪声的关系.本文提出了量化区间跃迁的统计概率模型,旨在得出考虑系统噪声情况下,饱和度全集上星载SAR原始数据信噪比在ADC前与BAQ后的映射关系:当回波信号功率较小,输入信噪比较低时,4bit,3bit,2bit,1bitBAQ压缩后信噪比区别不大;当回波为中等功率信号且信噪比较高时,压缩比特数每减少1bit,信噪比恶化约5dB;当回波功率较大,ADC饱和时,量化后原始数据信噪比呈阶跃性下降,饱和度越高,信噪比恶化越严重.本文采用模拟高斯数据和实测SAR原始数据验证了理论结果的正确性,为星载SAR系统设计时BAQ压缩比的选取以及后续的应用分析提供了理论依据.

SAR raw data signal to noise ratio（SNR） after compression is of great importance since the choice of compression ratio is dependent on it during SAR system design and application analysis.The signal to quantization noise ratio（SQNR） generally used may not precisely indicate the relationship between signal and noise.Considering the thermal noise,a statistical model of quantization interval transfer probability is proposed in this paper.SNR mapping between SAR raw data before analog to digital converter（ADC） and after block adaptive quantization（BAQ） over the whole set of saturation degree is obtained using this model.When the power of echo is small with low SNR,after 1,2,3 or 4 bits BAQ compression,SNR has tiny dierence among the four compression levels.When the power of the echo is medium with higher SNR,the SNR degradation after BAQ is about 5 dB with each bit decreasing from 4 bits.If voltage of the echo is higher than the clipping point of ADC,SNR after ADC and BAQ degrades stepwise.The higher the saturation degree of SAR raw data,the worse the SNR is.Simulated Gaussian data and real SAR raw data are used to verify the theoretical results,which are useful in the choice of BAQ compression ratio and further application analysis.