引潮位的Doodson规格化展开及其精度评定

基于引潮位Doodson规格化展开的基本原理以及ELP/MPP02月球历表、Newcomb太阳历表的结构,设计了一个用以代表三角函数的数据结构;并由此自定义了三角函数的乘法与加法算法,将月球、太阳引潮位分别展开至5阶、3阶,振幅绝对值截断阈值为10-7,在展开过程中对"伪波"进行"滤波"处理后,最终得到包含4 686项展开式的引潮位展开表(其中振幅绝对值超过10-6的展开式有2 441项)。以德国BFO(Black Forest Observatory)测站为例,基于DE431历表,通过天球参考系变换计算得到1950—2050年间时间间隔为1 h的法向引潮力基准序列BFDE431;并根据各个引潮位展开表计算得到相应的法向引潮力序列;通过与BFDE431基准序列求差,得到各个差值序列的统计值。计算结果表明,文中给出的展开表对应的差值序列数值在±58×10~(-11)m·s~(-2)(nGal)以内,均方差为12.5×10~(-11)m·s~(-2),与XI89展开表的精度相当。但由于没有考虑行星及地球扁率的影响,仍未达到HW95和RATGP95展开表的精度水平。     

新型FMCW地基合成孔径雷达在大桥变形监测中的应用

地基合成孔径雷达（GB-SAR）是一种新型的建筑变形监测技术,相较于传统的监测手段,该方法拥有高精度,覆盖面大等优点。基于FMCW技术的Fast-GBSAR系统采用调频连续波技术,相较于国内已有的基于步进连续波技术的类似系统,该系统处理速度提高30倍,并拥有更高的可靠性。Fast-GBSAR在国内已对多座大桥进行了公开测试,监测结果表明Fast-GBSAR测量精度能达到0.01 mm,在变形监测领域极具潜力。     

高频地波雷达电离层杂波抑制研究

基于高频地波雷达中的电离层杂波特性,提出了一种基于时频分析结合自适应旁瓣对消来抑制电离层杂波的方法。该方法首先通过时频分析合理地选择扫频脉冲时段和多普勒频率区间,然后对选定的时频域区间利用特征分解法分别进行阵元-脉冲域和阵元-多普勒域抑制电离层杂波,最后利用阵列结构特点采用分段处理的自适应旁瓣对消继续对电离层杂波进行抑制。实测数据表明,该处理方法对电离层杂波的抑制效果很好。     

北极海域SAR海浪方向谱反演及其与中法海洋卫星CFOSAT/SWIM数据的比较

The interaction between ocean waves and sea ice in the Arctic ocean has received significant attention. However, the study on this issue is significantly limited due to the lack of observation data. Synthetic Aperture Radar (SAR) plays an important role in the research of ocean wave and sea-ice interaction because of its unique capability of imaging sea surface in two dimensions. Sentinel-1 (S1), which consists of Sentinel-1A (S1A) and Sentine-1B (S1B), can cover the entire Arctic Area within 2 days. The Interferometric Wide Swath (IW) mode, one of the main imaging modes of S1 in the Arctic, has been providing SAR images with a high resolution of 10 m. The ocean wave spectra are derived using the S1 IW data. The spectra are likely to provide vital observation for studying the interaction between sea-ice and waves as they present the distribution of wave energy and their variations in different frequencies and directions. Meanwhile, the retrieved ocean wave spectra are an excellent validation data source for SWIM, which is onboard the China-France Oceanography Satellite and provides measurements of ocean wave spectra in the global ocean.In this study, we use the sub-images from the S1 IW image with a size of 1024 pixels × 1024 pixels (10.24 km × 10.24 km) to retrieve ocean wave spectra by using a nonlinear retrieval method (i.e., MPI scheme). The retrieved ocean wave spectra and wave parameters are compared with SWIM measurements acquired at an incidence angle of 10°, and the Significant Wave Height (SWH) is measured at nadir. The SWIM spectrum covers a large area by approximately 70 km × 90 km. To make a comparison, all the SAR sub-image spectra within a SWIM beam coverage are averaged to calculate a new observed SAR spectrum, which is inputted into the MPI inversion scheme. Then, the retrieved SAR ocean wave spectrum is compared with the SWIM spectrum. The footprint size of the SWIM nadir beam is 18 km, which is comparable to the S1 sub-image size. Accordingly, a SAR sub-image is extracted at SWIM nadir, and the corresponding ocean wave spectrum is retrieved. The SWH is calculated by integrating the retrieved wave spectra to compare with the SWIM nadir measurements of SWH. The experiment was carried out using the data acquired in September 2020 in the Greenland Sea and Norwegian Sea, where the ocean waves generated in the North Atlantic and propagating vast distances to the ice-covered area in the Arctic ocean can be frequently observed. Fifty-four ocean wave spectra were retrieved from 25 IW data and are compared with the SWIM slope spectra. The comparison shows that the SAR-retrieved spectra are consistent with SWIM spectra in terms of structure and energy distribution. Good agreements are also found between the integral parameters of the SAR ocean wave spectra and SWIM slope spectra. The comparison yields a bias and an RMSE of 0.11 and 0.71 m for SWH and a bias and an RMSE of -0.52 s and 0.62 s for mean wave period. The comparison of the dominant wave parameters yield a bias of -7.74° and an RMSE of 15.75° for the dominant wave direction and a bias of -0.56 m and an RMSE of 52.73 m for the dominant wavelength. Furthermore, 5075 data pairs of S1-retrieved SWH and SWIM nadir SWH were collocated and compared. The comparison result yields a bias of 0.03 m, an RMSE of 0.48 m, and a correlation of 0.95. The comparison between the S1 retrieved results and the SWIM measurements suggests that ocean wave information can be effectively retrieved from S1 IW data by using the MPI method in the Arctic ocean. Although the MPI method relies on prior information, it is still an effective method for obtaining ocean wave spectra in high resolution. The spectra retrieved from S1 are likely to show the energy attenuation of ocean waves in different frequencies and directions when propagating toward an ice-covered area. This finding will be of great support for the further study on the interaction between sea ice and ocean waves. © 2023 National Remote Sensing Bulletin. All rights reserved.     

Development of a 3-D urbanization index using digital terrain models for surface urban heat island effects

This study assesses surface urban heat island (SUHI) effects during heat waves in subtropical areas. Two cities in northern Taiwan, Taipei metropolis and its adjacent medium-sized city, Yilan, were selected for this empirical study. Daytime and night time surface temperature and SUHI intensity of both cities in five heat wave cases were obtained from MODIS Land-Surface Temperature (LST) and compared. In order to assess SUHI in finer spatial scale, an innovated three-dimensional Urbanization Index (3DUI) with a 5-m spatial resolution was developed to quantify urbanization from a 3-D perspective using Digital Terrain Models (DTMs). The correlation between 3DUI and surface temperatures were also assessed. The results obtained showed that the highest SUHI intensity in daytime was 10.2 °C in Taipei and 7.5 °C in Yilan. The SUHI intensity was also higher than that in non-heat-wave days (about 5 °C) in Taipei. The difference in SUHI intensity of both cities could be as small as only 1.0 °C, suggesting that SUHI intensity was enhanced in both large and medium-sized cities during heat waves. Moreover, the surface temperatures of rural areas in Taipei and Yilan were elevated in the intense heat wave cases, suggesting that the SUHI may reach a plateau when the heat waves get stronger and last longer. In addition, the correlation coefficient between 3DUI and surface temperature was greater than 0.6. The innovative 3DUI can be employed to assess the spatial variation of temperatures and SUHI intensity in much finer spatial resolutions than measurements obtained from remote sensing and weather stations. In summary, the empirical results demonstrated intensified SUHI in large and medium-sized cities in subtropical areas during heat waves which could result in heat stress risks of residents. The innovative 3DUI can be employed to identify vulnerable areas in fine spatial resolutions for formulation of heat wave adaptation strategies.     

略论珠穆朗玛峰重力值的推估

仅根据邻近点的重力与高程资料,采用了4种有关公式,有效地推估了珠穆朗玛峰顶上的重力值,该值为(976970±7)×10^-5m·s^-2。这一结果为精确推求珠峰大地水准面和正高提供了必要的数据     

遥感解译在南京市生活垃圾填埋场识别中的应用

运用遥感技术对南京市航空影像进行了解译工作,提取了面积大于10 000 m2的垃圾场位置并进行了实地查证和分析比对,绘制出南京市垃圾填埋场分布图,为南京市垃圾场的适宜性评价工作奠定了基础。     

机载激光测深中的波浪改正技术

基于我国新研制的机载激光测深系统基本配置,提出了3种可供选择的波浪改正计算方案(也称为深度值归算方案),具体分析了3种方案的适用条件和应用范围,并从理论上对3种改正模型的计算精度进行了估算。     

利用MATLAB实现图像处理与分析

本文通过对图像的均衡操作、二值图像的处理、小波去噪等实例，介绍了MATLAB进行图像处理和分析的实用方法与技巧，它对各种软钉包、进行图像处理和分析等，提供了高效便捷的方法。     

SAR海洋内波表层流反演方法探讨

基于海洋内波SAR成像机理与M4S海面微波散射成像模型,提出SAR海洋内波表层流反演新方法。首先从SAR图像上获得内波剖面的海面后向散射强度,利用AH理论的线性近似关系得到猜测表层流,通过海面微波散射成像模型仿真海洋内波的SAR海面后向散射强度,利用二分法不断地修改风速和流速梯度等参数,使仿真信号最大程度的逼近实际SAR图像上的海面后向散射强度,输出最终海表层流。以中国南海海区3景海洋内波SAR图像为例,对该方法进行了探讨。结果表明,仿真的海洋内波SAR海面后向散射强度剖面和实际SAR图像上的信号剖面吻合,两者的相关系数达90%以上,说明该反演方法是收敛与可行的。