Assessment of freely available CartoDEM V1 and V1.1R1 with respect to high resolution aerial photogrammetric DEM in high mountains

The accuracy of DEMs shows wide variations from one terrain to another and it needs to be determined. This study evaluates NRSC (National Remote Sensing Centre, Hyderabad, India) CartoDEM V1 and V1.1R1 with respect to resampled ADS80 DEM for parts of the Himalayas. Both the test DEMs were properly registered with reference to resampled ADS80 DEM and then individually subtracted to get the difference DEMs. Visual and statistical analyses were performed to assess the quality of the tested DEMs in terms of visible terrain and vertical accuracy. For calculating the accuracies in different terrain classes, slope and aspect maps were generated from the ADS80 DEM. Properly registered Landsat5 TM data were used for the development of the land cover map with four classes. The overall vertical accuracy measured for CartoDEM V1 was 269.9 m (LE90), while CartoDEM V1.1R1 showed huge improvement in the accuracy with 68.5 m (LE90).     

夏季草原与戈壁地表能量分析

利用野外试验资料，比较分析了夏季祁连山区草原和河西走廊张掖戈壁地表能量特征，并探讨了环境因素与地表能量特征的关系。结果表明，在夏季典型晴天，山区草原的净辐射、潜热通量大于戈壁，而感热、土壤热通量小于戈壁；山区草原净辐射、潜热通量的日变化大于戈壁；而感热、土壤热通量的日变化小于戈壁。在山区草原，晴天潜热通量是土壤热通量的三倍多，感热通量与土壤热通量差异很小，净辐射主要用于蒸发、蒸腾；在戈壁，晴天土壤热通量和感热通量是潜热通量的近两倍，净辐射主要用于加热地表，并通过地表加热下层土壤和地面大气。两地均存在能量不平衡现象，草原感热、潜热、土壤热通量之和小于净辐射，戈壁感热、潜热、土壤热通量之和大于净辐射，戈壁能量不平衡大于草原。导致山区草原和戈壁地表净辐射特征差异的主要因素是太阳辐射，导致山区草原和戈壁地表能量分量特征差异的主要因素是陆面植被和水分，根本因素是陆面水分。      

Computational properties of a new horizontal staggered grid

On variable configuration in the horizontal direction, Winninghoff[1] had some discussions in the 1960s. Subsequently, according to the thoughts of Winning- hoff, Liu Yudi[2―9] has widely and deeply studied al- most all the existing horizontal grids from the fre- quency and group velocity of inertia gravity and Rossby waves. Results show that although Arakawa C grid is the best one among all existing horizontal grids, it also has some shortcomings. For example, there is still an “average…     

一种新水平网格的Rossby波计算特性

提出了一个新的水平跳点网格（LE网格），这种网格将h放置在格点上，u,v同时放置在x方向和y方向格点中间.并采用一种推导频散关系的通用方法，研究在该LE网格上与Arakawa A E网格上描述Rossby波产生误差的情况，分可分辨和不可分辨两种情况.采用二阶中央差或四阶紧致差分格式从频率和群速度两个方面进行对比分析，结果表明不论在可分辨或不可分辨情况下，还是采用二阶中央差或四阶紧致差分格式，在频率和群速度两方面，LE网格在描述Rossby波产生的误差均较Arakawa A E网格要小，同时也表明不论在可分辨还是不可分辨的情况下，采用高精度的四阶紧致差分格式，LE网格和Arakawa A_E网格在描述Rossby波时产生的频率误差和x、y方向群速度误差并非必然减少.