DEM 网格间距对重力近区地形改正精度影响及验证

利用分形随机算法建立平地、丘陵和山地3种精细地形仿真场景,将DEM逐级重采样为不同网格间距,分析不同DEM网格间距对3种地形的重力近区地形改正误差影响。发现随着DEM网格间距的增加,近区地形改正误差随之增大。对于平地,使用1∶10 000的DEM,网格间距为5m仍能够满足规范要求;对于丘陵地,使用1∶5 000的DEM,网格间距为2.5m能够满足规范要求;对于山地,使用1∶1 000的DEM,网格间距1m能够满足规范要求。通过消费级无人机获取丘陵地精细地形,验证地形仿真的结论,同时说明消费级无人机能够应用于重力近区地形改正。     

海洋磁力测量多站日变改正基值归算方法研究

海洋磁力测量多站日变改正中,为了使整个测区磁场水平统一,必须以主站为基准对分站日变基值进行归算。对多站日变改正中日变基值的归算方法进行了研究,给出了多站日变改正基值归算公式。结论表明:当主站和分站日变基值都采用平均值法时,分站日变基值不需要向主站进行归算;而采用其他方法时(如基时刻或基时段法),为了使整个测区磁场水平统一,必须对分站日变基值进行归算。     

Using inverse theory and seabeam bathymetry to improve seismic refraction data corrections

An array consisting of ocean bottom seismometer and on-bottom hydrophones, was used to conduct a seismic experiment on 0.4 Ma crust east of the Juan de Fuca Ridge. Seismic sources were large (>50 kg) explosive charges detonated by SUS devices set to explode at 1829 or 2438 m nominal depth. The objectives of the experiment were to determine the compressional wave velocity and attenuation structures of the uppermost 500 m depth. The relative positions of shots and receivers were originally determined by treating each shot-receiver pair independently, via raytracing of various water waves. Due to the reflection of some of these water waves by the rough bottom, significant scatter resulted, preventing a determination of a physically realizable velocity-depth function. A new method is described that co-locates shot and receiver positions, including receiver depths consistent withseabeam bathymetry, using only the water waves that do not interact with the bottom. Several potential pitfalls are outlined using this method. A stable solution could only be achieved by discarding shots located well outside the array. The water path corrections were applied to the refracted arrivals, again using theseabeam bathymetry. The joint inversion location procedure, along with the use of precise gridded bathymetry, reduced the travel time scatter to a level whereby a velocity-depth function could be determined. The results, using only the hydrophone data, indicate an initial velocity at the seafloor of 2.7 km s^-1 with gradients from 4.6 s^-1 slowly decreasing to 4.1 s^-1 at 679 m depth. This velocity is similar to others conducted over very young oceanic crust, and can be interpreted as being due to a high porosity at the surface, due to cracks, fissures, and open pores, which rapidly diminish with depth.     

水色遥感大气校正方程的研究进展

大气校正是水色遥感研究中必不可少的一步,文中概括总结了对于一类水体、二类水体的大气校正以及在每类水体中对气溶胶单散射、复散射两种情况下的大气校正方法,列出了比较实用的计算流程。     

太湖水质参数的遥感监测研究

以太湖为研究对象,对TM各波段辐射率与水质参数进行拟合,分析了TM各波段经6S模型大气校正和未经校正直接拟合在监测内陆湖泊水质中的可行性。结果表明:TM波段经6S模型校正后能与太湖水质参教进行较好的匹配,同时通过实验得到了太湖地区水质参数的实用性回归公式。     

Correction for water depth variations of marine crustal reflection seismic data using refraction statics

Water depth variations in marine reflection seismic profiling cause velocity push-down and, in regions of rapid fluctuations of the water-bottom slope, stack degradation. Static corrections are a very satisfactory and practical solution to these problems under typical survey conditions with water depths not exceeding a few hundred metres and relatively hard water bottoms. Static time shifts are best derived from a refraction analysis of first arrivals rather than from fathometer data, especially over underwater valleys where unconsolidated sediment of velocity close to that of water has been deposited unconformably onto the underlying lithified rocks. These points are illustrated by a field example from the GLIMPCE survey in Lake Superior. The availability of computer-effective algorithms such as the generalized linear inversion method allows the implementation of refraction statics during the initial processing of regional marine crustal surveys.LITHOPROBE Publication No. 263.     

Wave Transformation and Breaking in Diagonal Opposing Current

- When waves propagate into diagonal opposing current from non-current area, not only the wave parameters but also the direction of wave propagation will change, that is, wave refraction will occur. The authors have calculated the changes of wave parameters, including wave refraction, by Linear Wave Theory, and have also done systematic study on wave transformation and breaking in opposing current by means of experimental analysis and theoretical calculation. In order to know the effect of wave refraction, computation is done in this paper about wave transformation and breaking on gentle slopes in diagonal opposing current.     

大洋底质调查钢丝绳的倾斜校正

根据“东方红 2”调查船 3次大洋底质调查获得的实放钢丝绳长度、钢丝绳倾斜角度、船舶漂移速度等数 1 0个实测数据 ,通过统计分析得到了放钢丝绳长度与钢丝绳倾斜角度之间的经验关系公式。依据该经验公式进行倾斜校正比用余弦法进行校正少放钢丝绳数百至一千多米。该公式适用条件 :水深 2 0 0 0～ 6 0 0 0 m,钢丝绳倾角 0～ 5 5°     

Influence of Energy Directional Spread on Wave Spectral Refraction

Pierson- Moskowitz Spectrum, JONSWAP Spectrum as well as Bretschneider- Mitsuyasu Spectrum are used in this paper for analyzing the influence of wave energy directional spread on refraction of wave spectrum due to both current and topography of sea bed. The author's calculation indicates that such kind influence on the characteristic value of wave height as well as the average direction of wave energy propagation can not be ignored.     

An Analytic-Numerical Solution of Wave Transformation

An analytic-numerical solution of wave transformation in shoaling water is presented in this paper. The analytical expression for wave heights along the wave rays is derived in consideration of the combined effect of water depth shoaling, the wave refraction and the sea bottom friction. The wave rays (orthogonals) are calculated by a fourth order Runge-Kutta algorithm and the wave crest lines are computed by an iteration procedure. The numerical results are compared with analytical solution for a special case of parallel- straight contour shore and field data, and comparisons show that the proposed mathematical model and computation method are very useful and convenient for engineering application.