A simulation of the Chilean Coastal Current and associated topographic upwelling near Valparaíso, Chile

A 4-year simulation of the surface circulation driven by the local wind on a section of the central Chilean coast is presented. The model is shown to reproduce the major observed features of the circulation. Comparison to observations of sea-surface temperature (SST) taken within the study area suggests that the model captures well coastal upwelling processes in the region. The circulation is shown to have two distinct modes corresponding to spring/summer and autumn/winter. During spring/summer sustained strong south-westerly wind forcing drives an equatorward coastal jet consistent with the Chile Coastal Current (CCC) and coastal upwelling at previously identified locations of intense upwelling at Topocalma Point and Curaumilla Point. Weaker winds during autumn/winter produce a slower CCC and a more homogenous SST field. Upwelling/relaxation and topographic eddies provide the main sources of variability on sub-seasonal time-scales in the model. The mechanisms responsible for each of these are discussed. Upwelling at Topocalma and Curaumilla Points is shown to be produced through generation of an upwelling Ekman bottom boundary layer following acceleration of the CCC close to the coast, reinforced by secondary circulation due to flow curvature around the headlands. Additional upwelling occurs north of Curaumilla Point due to development of shallow wind-driven overturning flow. Wind-sheltering is shown to be an important factor for explaining the fact that Valparaíso Bay is typically an upwelling shadow. Flow separation and eddy formation within Valparaíso Bay is seen to occur on the order of 10 times per year during relaxation after strong wind events and may persist for a number of weeks. Shorter lived topographic eddies are also seen to occur commonly at Topocalma and Toro Points. These eddies are shown to form in response to the surface elevation minima produced at each of these locations during upwelling.     

On A Low Cloud Phenomenon At The Breidamerkurjökull Glacier, Iceland

An impressive cloud wall has frequently been observed on the southern slopes of the Vatnajökull ice sheet, which is located in south-eastern Iceland. Its optical and dynamic features suggest a delicate balance of the atmospheric agents involved. This has been confirmed by a thorough analysis of a well documented event and by statistics covering a whole summer season. As an exemplary event, the regional development of the associated cloud has basically been documented with synchronous surface data along a suitable transect of the glacier. Data from tethered balloons, radiosoundings and routine synoptic data have also been exploited extensively. Cloud development was generally aided by a high moisture potential because of proximity to the open seas and the remnants of a frontal system. Furthermore the occurrence of the cloud phenomenon was associated with onshore (southerly) surface winds, assisting advection and lifting of the associated air masses above the slopes of the ice sheet. Northward protrusion of the associated cloud was apparently opposed by continuous katabatic winds and topographically induced lee effects.     

一种新的控制点采集方法

控制点采集是遥感应用中的一项重要工作,由于通常所采用的地形图出版时间较早,为采集控制点带来困难。本文介绍的控制点采集方法是:首先,通过Coreldraw作图软件,充分利用河流、道路等地物特征,将遥感影像与地形图调配吻合,然后,在地形图上选取公里网格点作为控制点,同时注明坐标值。利用该方法采集的控制点进行几何校正,其精度可以控制在0.5个像元内,可以满足TM影像图几何纠正的精度要求.     

正压模式中大地形作用下的低频波

利用包含大地形和常数纬向基本气流的正压模式方程组,研究了大地形对低频波激发的作用,结果表明：起作用的地形因子主要是地形的最大高度和地形坡度,地形最大高度的作用主要是使Ｒｏｓｓｂｙ波趋向低频,而地形坡度的作用主要是对Ｒｏｓｓｂｙ波的稳定性决定作用。同时,适当地形坡度也可导致低频波的形成。     

浅谈错视及其纠正与地质制图

本文侧重论述了错视,错视的表现及其利用与纠正,同时举例论述了正确运用错视对提高地质制图质量的重要性。     

Development in Precision Seafloor Survey and Mapping in China

This article presents a general introduction to the development in China since 1980s in precision seafloor survey and mapping. Emphasis is given to the processing and integration of data from the acquisition system centered on the multibeam bathymetric survey equipment, and to the interactive map generation systems, MBChart, SeaMap, and SeaGIIS. Application of these systems will also be described.     

Identification of the affected areas by mass movement through a physically based model of landslide hazard combined with an empirical model of debris flow

In tropical areas, mass movements are common phenomena, especially during periods of heavy rainfall, which frequently take place in the summer season. These phenomena have caused loss of life and serious damage to infrastructure and properties. The most prominent of these phenomena are landslides that can produce debris flows. Thus, this article aims at determining affected areas using a model to predict landslide prone areas (SHALSTAB) combined with an empirical model designed to define the debris flow travel distance and area of deposition. The methodology of this work consists of the following steps: (a) elaboration of a digital elevation model (DEM), (b) application of the deterministic SHALSTAB model to locate the landslide prone areas, (c) identification of the debris flow travel distance and area of deposition, and (d) mapping of the affected areas (landslides and debris flows). This work was developed in an area in which many mass movements occurred after intense rainfall during the summer season (February 1996) in the state of Rio de Janeiro, southeast Brazil. All of the scars produced by that event were mapped, allowing for validation of the applied models. The model results show that the mapped landslide locations can adequately be simulated by the model.     

无人机摄影测量技术的探索与应用研究

阐述了应用无人机摄影测量技术建立航空摄影测量系统的关键技术与方法。介绍了无人机摄影平台的设计与研制,通过对外业控制点布设、解析空三、内判测图等航测生产工序中技术要点的研究,以及试验成果的精度检验与分析,论证了采用该系统进行航空摄影测量的可行性。     

Topographic modeling of Phoebe using Cassini images

High-resolution Cassini stereo images of Saturn's moon Phoebe have been used to derive a regional digital terrain model (DTM) and an orthoimage mosaic of the surface. For DTM-control a network of 130 points measured in 14 images (70-390 m/pixel resolution) was established which was simultaneously used to determine the orientation of the spin-axis. The J2000 spin-axis was found at Dec=78.0°±0.1° and RA=356.6°±0.3°, substantially different from the former Voyager solution. The control points yield a mean figure radius of 107.2 km with RMS residuals of 6.2 km demonstrating the irregular shape of this body. The DTM was computed from densely spaced conjugate image points determined by methods of digital image correlation. It has a horizontal resolution of 1-2 km and vertical accuracies in the range 50-100 m. It is limited in coverage, but higher in resolution than the previously derived global shape model of Phoebe [Porco et al., 2005. Cassini imaging science: initial results on Phoebe and Iapetus. Science 307, 1237-1242] and allows us to study the morphology of the surface in more detail. There is evidence for unconsolidated material from a steep and smooth slope at the rim of a 100 km impact feature. There are several conically shaped craters on Phoebe, which may hint at highly porous and low compaction material on the surface.     

Assessment of radargrammetric DSMs from TerraSAR-X Stripmap images in a mountainous relief area of the Amazon region

The Brazilian Amazon is a vast territory with an enormous need for mapping and monitoring of renewable and non-renewable resources. Due to the adverse environmental condition (rain, cloud, dense vegetation) and difficult access, topographic information is still poor, and when available needs to be updated or re-mapped. In this paper, the feasibility of using Digital Surface Models (DSMs) extracted from TerraSAR-X Stripmap stereo-pair images for detailed topographic mapping was investigated for a mountainous area in the Carajás Mineral Province, located on the easternmost border of the Brazilian Amazon. The quality of the radargrammetric DSMs was evaluated regarding field altimetric measurements. Precise topographic field information acquired from a Global Positioning System (GPS) was used as Ground Control Points (GCPs) for the modeling of the stereoscopic DSMs and as Independent Check Points (ICPs) for the calculation of elevation accuracies. The analysis was performed following two ways: (1) the use of Root Mean Square Error (RMSE) and (2) calculations of systematic error (bias) and precision. The test for significant systematic error was based on the Student’s-t distribution and the test of precision was based on the Chi-squared distribution. The investigation has shown that the accuracy of the TerraSAR-X Stripmap DSMs met the requirements for 1:50,000 map (Class A) as requested by the Brazilian Standard for Cartographic Accuracy. Thus, the use of TerraSAR-X Stripmap images can be considered a promising alternative for detailed topographic mapping in similar environments of the Amazon region, where available topographic information is rare or presents low quality.