General Sampling Expansion Reconstruction Method (GSERM) and Digital Spectrum Reconstruction Method (DSRM), which prove effective to reconstruct azimuth signal of Displaced Phase Center Apertures (DPCA) Synthetic Aper...General Sampling Expansion Reconstruction Method (GSERM) and Digital Spectrum Reconstruction Method (DSRM), which prove effective to reconstruct azimuth signal of Displaced Phase Center Apertures (DPCA) Synthetic Aperture Radar (SAR) system from its Periodic Non-Uniform Sampling (PNUS) data sequences, would amplify the noise and sidelobe clutter simultaneously in the reconstruction. This paper formulates the relation of the system transfer matrixes of the above two methods, gives the properties, such as periodicity, symmetry, and time-shift property, of their Noise and Sidelobe Clutter Amplification Factor (NSCAF), and discovers that DSRM is more sensitive than GSERM in the white noise environment. In addition, criteria based on initial sampling point analysis for the robust PRF selection are suggested. Computer simulation results support these con-clusions.展开更多
Combining ecological niche modeling with phylogeography has become a popular approach to understand how historical climate changes have created and maintained population structure. However, methodological choices in g...Combining ecological niche modeling with phylogeography has become a popular approach to understand how historical climate changes have created and maintained population structure. However, methodological choices in geographic extents and environmental layer sets employed in modeling may affect results and interpretations profoundly. Here, we infer range-wide phylogeographic structure and model ecological niches of Cyanoderrna ruficeps, and compare results to previous studies that examined this species across China's Mainland and Taiwan only. Use of dense taxon sampling of closely related species as outgroups question C. ruficeps monophyly. Furthermore, previously unsampled C. ruficeps populations from central Vietnam were closely related to disjunct western populations （Nepal, Tibet, Myanmar, Yunnan）, rather than to geographically proximate populations in northern Vietnam and eastern China. Phylogeographic structure is more complex than previously appreciated; niche model projections to Last Glacial Maximum climate scenarios identified larger areas of suitable conditions than previous studies, but potential distributional limits differed markedly between climate models employed and were dependent upon interpretation of non-analogous historical climate scenarios. Previously identified population expansion across central China may result from colonization from refugial distributions during the Last Interglacial, rather than the Last Glacial Maximum, as previously understood [Current Zoology 61 （5）： 901-909, 2015].展开更多
文摘General Sampling Expansion Reconstruction Method (GSERM) and Digital Spectrum Reconstruction Method (DSRM), which prove effective to reconstruct azimuth signal of Displaced Phase Center Apertures (DPCA) Synthetic Aperture Radar (SAR) system from its Periodic Non-Uniform Sampling (PNUS) data sequences, would amplify the noise and sidelobe clutter simultaneously in the reconstruction. This paper formulates the relation of the system transfer matrixes of the above two methods, gives the properties, such as periodicity, symmetry, and time-shift property, of their Noise and Sidelobe Clutter Amplification Factor (NSCAF), and discovers that DSRM is more sensitive than GSERM in the white noise environment. In addition, criteria based on initial sampling point analysis for the robust PRF selection are suggested. Computer simulation results support these con-clusions.
基金We thank Nikki Boggess, who assisted in labwork. Fieldwork in Vietnam was facilitated by Dr. Le Mahn Hung, and supported by the National Geographic Committee for Research and Exploration. Fieldwork in China was supported by the National Science Foundation （DEB-0344430 to ATP）. The laboratory portions of this work were supported by the National Science Foundation （DEB-0743576 to RGM）. We thank recordists who shared their Stachyris/Cyanoderma recordings on Xeno-canto.
文摘Combining ecological niche modeling with phylogeography has become a popular approach to understand how historical climate changes have created and maintained population structure. However, methodological choices in geographic extents and environmental layer sets employed in modeling may affect results and interpretations profoundly. Here, we infer range-wide phylogeographic structure and model ecological niches of Cyanoderrna ruficeps, and compare results to previous studies that examined this species across China's Mainland and Taiwan only. Use of dense taxon sampling of closely related species as outgroups question C. ruficeps monophyly. Furthermore, previously unsampled C. ruficeps populations from central Vietnam were closely related to disjunct western populations （Nepal, Tibet, Myanmar, Yunnan）, rather than to geographically proximate populations in northern Vietnam and eastern China. Phylogeographic structure is more complex than previously appreciated; niche model projections to Last Glacial Maximum climate scenarios identified larger areas of suitable conditions than previous studies, but potential distributional limits differed markedly between climate models employed and were dependent upon interpretation of non-analogous historical climate scenarios. Previously identified population expansion across central China may result from colonization from refugial distributions during the Last Interglacial, rather than the Last Glacial Maximum, as previously understood [Current Zoology 61 （5）： 901-909, 2015].
