Airborne imagery of a disintegrating Sargassum drift line

Airborne hyperspectral and thermal infrared imagery collected over the Florida Current provide a view of the disintegration of a Sargassum drift line in 5 m s⁻¹ winds. The drift line consists mostly of rafts 20-80 m² in size, though aggregations larger than 1000 m² also occur. Rafts tend to be elongated, curved in the upwind direction, and 0.1-0.5 °C warmer than the surrounding ocean surface. Long weed ‘trails’ extending upwind from the rafts are evidence of plants dropping out and being left behind more rapidly drifting rafts. The raft line may be a remnant of an earlier Sargassum frontal band, which is detectible as an upwind thermal front and areas of submerged weed. Issues are identified that require future field measurements.     

Virtual Cities From Digital Imagery

Increasing interest is being expressed in the use of virtual cities for many fields of application, ranging from planning and simulation to business, advertising and the games industry. Currently, the extraction of buildings from imagery is costly. However, recent developments in digital photogrammetry aim to produce more rapid and efficient methods of modelling three dimensional objects in urban environments. This paper presents a semi-automatic system for the extraction of buildings from digital aerial imagery with the aid of volumetric primitives. The user is supported by automated tools, for example matching tools, in order to reach the necessary efficiency. With an extraction time of about 20 s per building primitive, this method is competitive in terms of the performance of classical photogrammetric procedures, and also offers additional features for analysis, texture mapping and Internet applications.     

The potential of Pléiades images with high angle of incidence for reconstructing the coastal cliff face in Normandy (France)

To monitor chalk cliff face along the Normandy coast (NW France) which is prone to erosion, we tested the potential of cliff face 3D reconstruction using pairs of images with high angle of incidence at different dates from the agile Pléiades satellites. The verticality aspect of the cliff face brings difficulties in the 3D reconstruction process. Furthermore, the studied area is challenging mainly because the cliff face is north-oriented (shadow). Pléiades images were acquired over several days (multi-date stereoscopic method) with requested incidence angles until 40°. 3D reconstructions of the cliff face were compared using two software: ASP® and ERDAS IMAGINE®. Our results are twofold. Firstly, despite ASP® provides denser point clouds than ERDAS IMAGINE® (an average of 1.60 points/m² from 40° incidence angle stereoscopic pairs on the whole cliff face of Varengeville-sur-Mer against 0.77 points/m² respectively), ERDAS IMAGINE® provides more reliable point clouds than ASP® (precision assessment on the Varengeville-sur-Mer cliff face of 0.31 m ± 2.53 and 0.39 m ± 4.24 respectively), with a better spatial distribution over the cliff face and a better representation of the cliff face shape. Secondly, the quality of 3D reconstructions depends mostly on the amount of noise from raw images and on the shadow intensity on the cliff face (radiometric quality of images).     

2008年“威马逊”台风期间海上大气波导时空特征

结合 MM5数值模拟结果、天气图和卫星云图,系统分析了2008年“威马逊”台风引起的大气波导特征.本次台风过程中发生的大都为悬空大气波导,位于台风涡旋之外的西北部,台风越近波导高度、强度、厚度越大;同时数值模拟表明陆地地形对海上本次大气波导形成具有一定影响.利用大气波导这一特殊大气层结可以很好的评估和预测电磁波传播和海上探测通信系统     

基于水质类型的TM图像水体信息提取

通过对一般水体、富营养化水体和严重污染水体与山体阴影在TM各波段图像上的亮度值进行分析比较可知:一般水体在TM4图像上的亮度值小于TM3波段的,而山体阴影则相反;由于富营养化水体中的浮游植物在TM4波段具有强反射特征,严重污染水体对可见光具有强吸收作用,造成了这两类水体在TM4图像上的亮度值大于TM3波段的,因而无法通...     

数字卫星云图估算面雨量的应用试验

使用云分类降水率估计的方法，有静止气象卫星数字云图进行面雨量估算。对１９９３年８月４日华北南部一次降水过程的实测雨量与估算结果的对比分析表明，这种估算方法对雨区的差别有相当高的精度，对雨量的估计有一定的参考价值。     

多暗像元大气校正方法

 针对Landsat TM影像，设计了一种适用于非均质大气的大气校正方法。该方法以暗目标减法（DOS）为基础，结合大气辐射传输模型，通过选取TM影像上多个暗像元，并计算其所对应的大气校正系数对整幅图像进行大气校正。该方法不依赖任何外部信息，并且考虑了大气的非均质性，校正精度较高。     

Morphodynamic response of a two-barred beach to a shoreface nourishment

The response to a shoreface nourishment of the two-bar system at Noordwijk (the Netherlands) is analyzed based on a daily data set of time-exposure video images collected during about 6 years, complemented with topographic and bathymetric surveys. The 1.7 Mm³ nourishment, implemented as a 3 km alongshore bump seaward of the outer bar, migrated more than 300 m onshore in 4 years before losing its integrity. Furthermore, the nourishment interrupted the autonomous seaward migration of both bars for the entire duration of the study period and, allaying earlier fears, did not intensify the three-dimensional patterns in the bars, such as the crescentic plan-shape and rip channels. The nourishment did result in clear head effects on both flanks, with the bar becoming discontinuous and the flank section decaying or becoming attached to an offshore-located bar, while the section of bar landward of the nourishment became attached to a landward-located bar. This sequence of morphologies is known as bar switching. Each switching episode took almost one year to complete and can therefore not be ascribed to individual wave events. We suspect that shoreface nourishments enhance the possibility of bar switching by creating alongshore variability in the position and depth of the outer bar and in its cross-shore migration rate and direction. The Noordwijk nourishment did not influence the shoreline position as its trend did not undergo distinctive variations after 1998. Differences in the response of the Noordwijk sandbars to the shoreface nourishment compared with other Dutch nourishments are attributed to the location and size (volume per unit length) of the nourishment with respect to the sandbars and to the median grain size of the nourished material.     

甘肃省舟曲特大泥石流的遥感影像特征及古泥石流遥感识别的地质意义

2010年舟曲特大泥石流是舟曲地区第四纪以来泥石流最新暴发期内强烈活动的体现,所造成的人员伤亡及财产损失堪称世界泥石流灾害史之最。准确分析该地区泥石流的空间分布规律及预测未来泥石流暴发时间可为泥石流的防灾救灾提供科学的依据,其首要任务就是利用一种先进技术对不同时期的泥石流堆积物的空间分布进行快速、准确的识别。遥感技术具有数据获取量大、空间分辨率高及快速等方面的独特优势,可在舟曲特大泥石流及不同时期古泥石流堆积物识别中发挥重要作用。在高分辨率的航空遥感影像上,舟曲特大泥石流具有明显的光谱特征,可用于准确圈定泥石流灾害的范围; 泥石流堆积物在沟谷两侧形成的侧碛堤及在堆积区末端形成的扇形地等形态特征也是识别泥石流的另一个重要标志。舟曲县城东南瓦厂村南及马莲坪村西南白龙江支流沟中的垄岗状堆积物和沟口处的扇形地堆积体在光学遥感影像上具有典型的古泥石流堆积的形态特征,雷达遥感的后向散射系数对比分析和对堆积物剖面的沉积特征分析也证明古泥石流的存在。研究结果表明,通过多期次、多空间分布的现代和古泥石流的对比,不仅可以揭示舟曲地区第四纪以来泥石流发育历史并间接反映地质尺度上气候变化特点,还可为未来泥石流的易发性分析提供数据支撑,因此泥石流堆积物的遥感直接识别具有重要的地质意义。