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.     

GPS/PWV与第五代大气再分析数据的短时强降水分析

针对全球升温、极端天气增加、我国西北短时暴雨增多等现象,该文结合ERA5降水数据和气象站采集的实际降水量,利用我国西北干旱地区GPS观测数据反演的GPS/PWV对一次短时强降水过程进行分析。结果表明：(1)GPS/PWV的积累和变化与实际降水发生时刻及降水量具有密切联系,特别是GPS/PWV在陡升陡降及高位震荡与降水实际发生具有较强的对应关系,对GPS/PWV应用于我国西北干旱地区短时强降水预报及防灾减灾等具有一定的参考意义;(2)ERA5数据记录的降水事件与气象站记录的实际降水的发生存在较好的对应关系,但降水发生时刻及降水量与实际降水相比准确性较差。该研究对于增强数值同化和机器学习在短时暴雨及极端天气等预报具有重要意义。     

专业认证制度下变形观测分析与预报课程教学改革

文章从落实专业认证的现实需要出发,论述了工程教育专业认证的核心理念.并籍此对变形观测分析与预报课程的教学现状进行了深刻反思,提出了以目标导向为主的课程体系改革,以学生为中心的课堂教学改革,以内外反馈信息为导向的持续改进的课程教改方案.教学各环节中,以专业“产出”衡量专业人才培养质量,“看学不看教”,阶段性考核,确保教学改革落到实处.     

植被对潮沟发育影响的遥感研究——以崇明东滩为例

根据现场测量,通过高分辨率航空图像提取崇明东滩潮沟的空间形态、植被类型及植被盖度指数。结合多时相卫星图像及海洋数值模式,利用水边线法及宽深比法反演潮沟沟底高程并构建了研究区潮沟三维地形,分析了植被对潮沟发育的影响。结果表明:1潮沟反演的均方根误差为0.545 m,且高潮滩反演精度高于低潮滩地区;2从低潮滩到高潮滩的潮沟深度先增大再减小,主要原因是高潮滩水动力条件较弱,加之植被根系的固滩作用,下蚀作用较弱,潮沟深度较浅,低潮滩由于水域开阔,水动力条件较弱,无植被覆盖侧蚀作用增强,潮沟变宽变浅;3潮沟深度空间分布表现出南深北浅的特征,崇明东滩潮沟密度与植被盖度呈现明显的负相关(r=0.560 4,p0.02),在高盖度植被覆盖的潮滩地区潮沟大多不发育,潮沟密度较低。潮沟长度与植被类型表现出较强的相关关系,在互花米草-芦苇群落为优势的区域潮沟长度普遍比以海三棱藨草群落为优势的区域长。     

利用遗传优化LSSVR进行导航卫星钟差预报

为提高导航卫星钟差预报的精度,提出了一种最小二乘支持向量回归(LSSVR)和遗传算法(GA)相结合的导航卫星钟差预报方法。根据卫星钟差序列变化的非线性特征,选用高斯径向基函数(RBF)建立卫星钟差LSSVR预测模型。针对LSSVR模型的参数选择问题,引入GA对不同星座以及原子钟类型预测模型的参数进行搜索寻优。该方法能够在较大范围内自动确定优化参数,提高LSSVR的泛化性能。将所提出的方法用于GPS卫星钟差的短期预报,并与常规预报方法进行对比。结果表明,GA-LSSVR模型对不同星座以及原子钟类型钟差预报均表现出良好的稳健性,能够在一定程度上抑制钟差预报误差随时间延长不断增大的问题,整体预报精度优于常规方法。     

筑起一道坚固生命防线——甘肃省地质灾害防治工作纪实

防灾胜于救险,是甘肃省地质灾害防治多年实践经验的总结。甘肃地处青藏高原、黄土高原和内蒙古高原的交会地带,地质条件复杂,地貌形态多样,生态环境脆弱。据调查显示,地质灾害易发区面积占全省国土面积的一半以上。86个县（市、区）中,有62个县（市、区）位于山区丘陵,9个城市、30座县城、165个乡镇、1万多个村庄受滑坡、泥石流灾害威胁。目前,全省已查明地质灾害隐患点14591处,直接威胁226.26万人、622.5亿元财产的安全。从救险到防灾,再到相应应急体系的逐步完善,让人欣喜地看到,甘肃省地质灾害防治新理念带来的新变化,全面落实地质灾害危险性评估制度得到全面落实,地质灾害监测预警预报进一步加强,群专结合的地质灾害监测预警网络日趋完善,健全了信息共享、预警联动机制,地质灾害监测预警准确度大幅度提升。甘肃省地质灾害防治的经验和做法值得各地学习借鉴。     

立足“三移三分”全心履职尽责——湖北省孝感市孝南区构建国土资源监管新机制的经验

近年来,湖北省孝感市孝南区不断加大国土资源规范管理力度,以创新监管机制为抓手,坚持高起点谋划、高标准建设、高效能推进,构建起有自身特色的把决策权力上移,分担责任;把监督权力平移,分解责任;把执行权力下移,分化风险的“三移三分”新机制。建立起“权责明确、相互制衡、运转协调、规范高效”的权力运行体系,     

导航卫星卷积码序列MAP译码算法分析与改进

在对导航卫星卷积码序列应用MAP算法译码时,计算机会产生数值稳定性问题,输出错误的译码误码率,进而对定位结果的有效性和定位精度产生重要影响。针对该问题进行了具体分析,并对算法进行了改进,给出了一种基于最大状态度量的归一化MAP译码算法,在保持原算法最优性能的同时很好地解决了数值稳定性问题。通过仿真进一步验证了这种改进算法的有效性。     

浅析山区高速公路的设计方法

本文分析了基于运行速度的山区高速公路设计方法,对由运行速度配置技术指标的新方法运用于雅康高速公路的设计进行了具体研究,并探讨了基于运行速度的高速公路设计流程和线形指标采用的一般原则。     

没有了手机 诺基亚的未来要靠地图？

诺基亚已经将手机业务作价75亿美元卖给了微软,这一交易也于近日宣告结束。如今,诺基亚已经没有了手机业务,这种局面还是30多年来的第一次。很难想象,在今后的全球手机业务领域内,诺基亚将不再有份了。