Surface roughness signatures of summer arctic snow-covered sea ice in X-band dual-polarimetric SAR

ABSTRACT

Surface roughness of sea ice is primary information for understanding sea ice dynamics and air–ice–ocean interactions. Synthetic aperture radar (SAR) is a powerful tool for investigating sea ice surface roughness owing to the high sensitivity of its signal to surface structures. In this study, we explored the surface roughness signatures of the summer Arctic snow-covered first-year sea ice in X-band dual-polarimetric SAR in terms of the root mean square (RMS) height. Two ice campaigns were conducted for the first-year sea ice with dry snow cover in the marginal ice zone of the Chukchi Sea in August 2017 and August 2018, from which high-resolution (4 cm) digital surface models (DSMs) of the sea ice were derived with the help of a terrestrial laser scanner to obtain the in situ RMS height. X-band dual-polarimetric (HH and VV) SAR data (3 m spatial resolution) were obtained for the 2017 campaign, at a high incidence angle (49.5°) of TerraSAR-X, and for the 2018 campaign, at a mid-incidence angle (36.1°) of TanDEM-X 1–2 days after the acquisition of the DSMs. The sea ice drifted during the time between the SAR and DSM acquisitions. As it is difficult to directly co-register the DSM to SAR owing to the difference in spatial resolution, the two datasets were geometrically matched using unmanned aerial vehicle (4 cm resolution) and helicopter-borne (30 cm resolution) photographs acquired as part of the ice campaigns. A total of five dual-polarimetric SAR features―backscattering coefficients at HH and VV polarizations, co-polarization ratio, co-polarization phase difference, and co-polarization correlation coefficient ―were computed from the dual-polarimetric SAR data and compared to the RMS height of the sea ice, which showed macroscale surface roughness. All the SAR features obtained at the high incidence angle were statistically weakly correlated with the RMS height of the sea ice, possibly influenced by the low backscattering close to the noise level that is attributed to the high incidence angle. The SAR features at the mid-incidence angle showed a statistically significant correlation with the RMS height of the sea ice, with Spearman’s correlation coefficient being higher than 0.7, except for the co-polarization ratio. Among the intensity-based and polarimetry-based SAR features, HH-polarized backscattering and co-polarization phase difference were analyzed to be the most sensitive to the macroscale RMS height of the sea ice. Our results show that the X-band dual-polarimetric SAR at mid-incidence angle exhibits potential for estimation of the macroscale surface roughness of the first-year sea ice with dry snow cover in summer.     

脉冲星平均脉冲不对称性的研究

本文讨论了光线的狭义相对论性偏折、光行时间差和磁场拖曳对脉冲到达相位的综合影响。在辐射束中的核、内锥以及外锥的辐射高度有差别时,观测得到的平均脉冲中的各个成份的位置也会发生改变,导致平均脉冲的不对称。分析了脉冲星ＰＳＲ１４５１６８ 和ＰＳＲＪ０４３７４７１５ 资料,发现它们的平均脉冲属于两种不同的不对称性。用相位综合漂移理论解释了这两种不对称性。     

我国单点动态垂直基准的建立

确定基准是研究地壳垂直运动的重要内容之一,在讨论均衡基准特点的同时,指出了在其研究我国大陆现今地壳垂直运动中可能带来的不适用性,从而提出了单点动态垂直基准。该基准在多次重合点变动情况下,能够保持前后基准一致,易于维护,与基本验潮站相联系,速率结果具有绝对性质,可以较好地适应未来,特别是具有适应采用空间技术手段的特点。全面叙述了利用国家高精度重复水准测量资料研究我国大陆现今地壳垂直运动过程中,建立单点动态垂直基准的情况。     

《建筑地基基础设计规范》承载力的确定方法研究

《建筑地基基础设计规范》GBJ7－89中给出了根据土的物理、力学指标查表确定承载力的方法,该方法在将实验获得的基本物理力学数据回归分析的基础上,由承载力基本值计算得到承载力标准值,但实际计算中,由于取值位数不同,会得出不同的解答,甚至出现无解的状况。研究发现其根本原因是回归分析中均方差计算公式不合适。通过采用《港口工程地基规范》推荐的均方差计算公式计算表明,该公式较合理,建议《建筑地基基础设计规范》在修订时加以修正。     

应用最优化订正法制作长江上游面雨量预报

利用最优化订正法，通过对MAPS数值降水预报进行订正，制作长江上游六大流域短期面雨量预报。2002年6－10月业务试验表明，长江上游六大流域平均的常规降水面雨量预报准确率比MAPS高19％左右，强降水天气过程的击中率为48％左右，取得了较好的效果。     

面雨量计算方法及其在海河流域的应用

参考我国水文部门和省气象台的方法，比较客观地确定了华北地区海河流域及其支流域(七条河系：滦河河系、北三河河系、永定河河系、大清河河系、子牙河河系、南运河河系、徒骇马颊河河系；一个区；海河下游区)的边界，实现了在各支流域内计算机自动选取代表测站，计算各支流域的实况和预报面雨量，对2001年汛期面雨量做了集成预报试验。另外，将2000年6～8月及2001年6～7月滦河的面雨量与潘家口水库的入库流量进行了对比分析。     

在煤田地震勘探中与速度无关的DMO技术探讨

由于煤田地质条件的局限性,与速度无关DMO的技术,在实际应用中只能用均方根速度来近似地震反射波的速度,而在速度分析中,较好的办法是在DMO后得的道集上作DMO速度分析,同时注意数据处理参数的合理选择,与速度无关的技术才能在煤田地震勘探中取得很好的应用效果。     

平均经圈环流质量流函数简化计算方案的应用

用一个简化计算方案，求得了1948-1999年52a逐月平均经圈环流质量流函数。用它分析了平均经圈环流的气候态及20世纪80年代和90年代最强El Nino事件的气候异常态。结果表明：它很好地给出了平均经圈环流的气候态的季节变化及气候异常态与SSTA的物理联系。上述结果与通常迭代法计算结果基本一致。     

中国飞机积冰的气候特征

本文利用美国国家环境预报中心（NCP）和国家大气研究中心（NCAR）联合处理的全球大气40年（1958－1997）资料，对近40年中国飞机积冰的气候特征进行了分析，通过功率谱及交叉谱分析的方法对南京地区的飞机积冰发生频率进行了周期变化的分析，并利用k均值法进行了飞机积冰的航空气候区划，给出了飞机积冰的时空分布特征。