Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment mon...Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment monitoring.Given the weak scattering characteristics of the ocean,the system thermal noise superimposed on SAR images has significant interference,especially in cross-polarization channels.Noise-Equivalent Sigma-Zero(NESZ)is a measure of the sensitivity of the radar to areas of low backscatter.The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level.For TOPSAR,NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range.Therefore,the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data.This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm.A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths.According to assessment with wide-swath TOPSAR cross-polarization data,the GF3-02 TOPSAR mode has a very low thermal noise level,which is better than−33 dB at the edge of each beam,and controlled below−38 dB at the center of the beam.The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users.After discussing the relationship between normalized radar cross section(NRCS)and wind speed,we provide a formula for NRCS related to wind speed and radar incidence angle.Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images,the bias is−0.0048 dB,the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.展开更多
给出了一个词共现改进的向量空间模型(Word Co-Occurrence Mode Based On VSM,WCBVSM)与模拟退火交叉覆盖算法(Cross Cover Algorithm Based On Simulated Annealing Algorithm,SACA)相结合的文本分类新模型。传统的向量空间模型(VSM)...给出了一个词共现改进的向量空间模型(Word Co-Occurrence Mode Based On VSM,WCBVSM)与模拟退火交叉覆盖算法(Cross Cover Algorithm Based On Simulated Annealing Algorithm,SACA)相结合的文本分类新模型。传统的向量空间模型(VSM)采用词条作为文档的语义载体,没有考虑文本上下文词语之间的语义隐含信息,在词共现模型的启发下,提出WCBVSM,它通过统计文本中的词共现信息,加入VSM,以获得文档隐含的语义信息。针对交叉覆盖算法中识别精度与泛化能力之间的一对矛盾,结合模拟退火算法的思想,提出了SACA,改进了传统交叉覆盖在覆盖初始点选取时的随机性,并通过增加每个覆盖所包含的样本点来减少覆盖数,从而增强了覆盖的泛化能力。实验结果表明提出的文本分类新模型在加快识别速度的基础上,提高了分类的精度。展开更多
基金The National Natural Science Foundation of China under contract No.41976169.
文摘Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment monitoring.Given the weak scattering characteristics of the ocean,the system thermal noise superimposed on SAR images has significant interference,especially in cross-polarization channels.Noise-Equivalent Sigma-Zero(NESZ)is a measure of the sensitivity of the radar to areas of low backscatter.The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level.For TOPSAR,NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range.Therefore,the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data.This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm.A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths.According to assessment with wide-swath TOPSAR cross-polarization data,the GF3-02 TOPSAR mode has a very low thermal noise level,which is better than−33 dB at the edge of each beam,and controlled below−38 dB at the center of the beam.The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users.After discussing the relationship between normalized radar cross section(NRCS)and wind speed,we provide a formula for NRCS related to wind speed and radar incidence angle.Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images,the bias is−0.0048 dB,the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.
文摘给出了一个词共现改进的向量空间模型(Word Co-Occurrence Mode Based On VSM,WCBVSM)与模拟退火交叉覆盖算法(Cross Cover Algorithm Based On Simulated Annealing Algorithm,SACA)相结合的文本分类新模型。传统的向量空间模型(VSM)采用词条作为文档的语义载体,没有考虑文本上下文词语之间的语义隐含信息,在词共现模型的启发下,提出WCBVSM,它通过统计文本中的词共现信息,加入VSM,以获得文档隐含的语义信息。针对交叉覆盖算法中识别精度与泛化能力之间的一对矛盾,结合模拟退火算法的思想,提出了SACA,改进了传统交叉覆盖在覆盖初始点选取时的随机性,并通过增加每个覆盖所包含的样本点来减少覆盖数,从而增强了覆盖的泛化能力。实验结果表明提出的文本分类新模型在加快识别速度的基础上,提高了分类的精度。
