TRMM数据在中国降雨侵蚀力计算中的应用

长时间序列降雨过程资料的获取一直是降雨侵蚀力计算中的一个难题。尝试利用地面实测站点数据分别对TRMM(Tropical Rainfall Measuring Mission)卫星的3B43和3B42数据进行回归建模和订正,并采用订正后的3 h平均降雨强度代替30 min最大降雨强度,同时基于TRMM数据的EI180的降雨侵蚀力算法,计算出了全国南北纬50°范围(TRMM覆盖区)内2013年月、季和年降雨侵蚀力;最后分别计算了省域和区域尺度下的降雨侵蚀力对全国尺度下的结果进行对比验证。结果表明:(1) TRMM降水数据比地面站点观测的降水量略大,但与实测站点数据具有很好的线性回归关系,其季尺度决定系数R²均较高,由此也说明了TRMM数据可以很好地反映全国范围内降雨的季节性变化。(2)利用订正后的TRMM3B42数据计算出研究区内的年均降雨侵蚀力为536.02 MJ·mm·hm^-2·h^-1·a^-1,其降雨侵蚀主要集中在5~8月份。(3) 2013年全国降雨侵蚀变化趋势由东南向西北方向逐渐降低,且沿海省份较内陆省份降雨侵蚀较高。(4)通过对年降雨侵蚀力结果与实测站点降雨量以及订正的TRMM降水数据分析表明,降雨侵蚀力与降水之间存在着紧密的二次非线性关系。(5)通过尺度验证,其中省域尺度验证误差为8.34%,区域尺度误差仅为0.24%,由此说明了TRMM数据在不同尺度下均具有良好的适应性,同时也验证了方法在不同尺度下的有效性。该方法为有效解决土壤侵蚀中降雨强度计算资料缺乏的瓶颈,同时也为降雨侵蚀力的计算提供了一条有效的途径。     

TRMM测雨产品3B42与台站资料在中国区域的对比分析

本文利用2004—2008年6—8月中国673个气象站逐6小时降水资料检验同期TRMM测雨产品3B42的精度。经检验得出：卫星资料日平均降水和降水频率空间分布与台站资料非常类似,相关系数分别能达到0.79和0.84,降水频率与台站资料相比偏大;从日降水相关空间分布看,卫星资料在东部地区相关性较高,日降水相关系数都在0.6～0.9之间;从日降水和逐6小时降水平均绝对误差空间分布看,卫星资料在华南地区误差最大,长江流域次之;从中国8个区域逐6小时降水总量日变化看,卫星资料与台站资料有很好的一致性,但在华南地区20时降水量偏小;按不同雨量等级对比,发现卫星资料绝对误差相对百分率空间分布有如下特点：小雨全国普遍数值偏高,中雨东部部分地区偏大,大雨和暴雨整体上数值小于1;全国平均漏演率和空演率分别为10%和14%。     

兰州市商业中心的区位格局及优势度分析

本文试图以兰州市为例,就商业中心区位的最优选择与配置、共演化动态及未来对策等进行定量分析与探讨。     

南极冰盖DEM机载测高验证与分析——以西南极Thwaites冰川为例

利用冰桥计划(IceBridge)在西南极Thwaites冰川的机载激光测高数据,对ICESat卫星测高数据和目前国际常用的4种南极DEM,包括Bamber 1km DEM、ICESat DEM、RAMPv2DEM和JLB97DEM的精度进行了验证和分析。结果表明,ICESat卫星测高数据和ICESat DEM有着较高的高程可靠性,其与冰桥计划机载测高数据的平均高程差小于5m,标准差小于15m。Bamber 1km DEM高程可靠性相比ICESat卫星测高数据和ICESat DEM低一些。JLB97DEM、RAMPv2DEM与冰桥计划机载测高数据之间的标准差超过30m,尤其在坡度较大的区域,高程可靠性低。     

Large Eddy Simulation of typical dust devil-like vortices in highly convective Martian boundary layers at the Phoenix lander site

Physical characteristics of naturally formed convective vortices in the Phoenix Mars lander environment have been investigated on a relatively hot summer Martian arctic day. For this, the NCAR LES has been adapted and developed to conduct three micro-scale simulations of the Martian Convective Boundary Layer (CBL), in situations with and without geostrophic wind, and atmospheric radiative flux divergence. Time series analysis of the vortices’ properties is discussed. The study confirms the decrease of vortex populations in windy conditions and also illustrates that intense but small vortices are expected to be observed in higher geostrophic wind situations. This may lead to more dust migration rather than dust devil formation on windy days. The background (geostrophic) wind causes the vortices to become less cyclostrophically balanced.     

Mission design for Human Outer Planet Exploration (HOPE) using a magnetoplasma spacecraft

To send humans beyond Mars, a Human Outer Planet Exploration (HOPE) mission has been studied for new spacecraft concepts and technologies. In this paper, an interplanetary trajectory and a preliminary spacecraft design are presented for the HOPE visit to Callisto, one of Jupiter's moons. To design a round-trip trajectory for the mission, the characteristics of the spacecraft and its trajectories are analyzed. A detailed optimization approach is formulated to utilize a Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine with capabilities of variable specific impulse, variable engine efficiency, and engine on-off control. It is mainly illustrated that a 30 MW powered spacecraft can make the mission possible in a 5-year round trip constraint around the year 2045. Trajectories with different power and reactor options are also discussed. The results obtained in this study can be used for formulating an overall concept for the mission.     

Sourcing and identifying andesitic tephras using major oxide titanomagnetite and hornblende chemistry,Egmont volcano and Tongariro Volcanic Centre,New Zealand

 Canonical discriminant function analysis was employed to discriminate between electron microprobe-determined titanomagnetite and hornblende analyses from Egmont volcano and Tongariro Volcanic Centre. Data sets of 436 titanomagnetite and 206 hornblende analyses from the two sources were used for the study. Titanomagnetite chemistry provided the best discrimination between these two sources with classification efficiencies of 99% for sample averages and 95% for individual analyses. The difference between sources for hornblende chemistry was less marked, but classification efficiencies of 100% for sample averages and 87% for individual analyses were achieved. Using the same methods a preliminary discrimination of individual Egmont volcano-sourced tephras was attempted. Titanomagnetite chemistry enabled the discrimination of several individual tephras or at least pairs of tephra units, but hornblende chemistry provided little discrimination. This technique provides an improvement on previous methods for chemically distinguishing distal tephra from the two sources as well as potentially identifying individual tephras from a particular source. A major advantage over previous discrimination techniques is that individual analyses can be classified with a known probability of group membership (with groups such as volcano source or an individual tephra unit). Tephras in a depositional environment where mixing is common such as within soil, loess and marine sequences, can be sourced or identified more easily with classification of individual grains. Received: 19 July 1995 / Accepted: 13 February 1996     

A practical method for SRTM DEM correction over vegetated mountain areas

Digital elevation models (DEMs) are essential to various applications in topography, geomorphology, hydrology, and ecology. The Shuttle Radar Topographic Mission (SRTM) DEM data set is one of the most complete and most widely used DEM data sets; it provides accurate information on elevations over bare land areas. However, the accuracy of SRTM data over vegetated mountain areas is relatively low as a result of the high relief and the penetration limitation of the C-band used for obtaining global DEM products. The objective of this study is to assess the performance of SRTM DEMs and correct them over vegetated mountain areas with small-footprint airborne Light Detection and Ranging (Lidar) data, which can develop elevation products and vegetation products [e.g., vegetation height, Leaf Area Index (LAI)] of high accuracy. The assessing results show that SRTM elevations are systematically higher than those of the actual land surfaces over vegetated mountain areas. The mean difference between SRTM DEM and Lidar DEM increases with vegetation height, whereas the standard deviation of the difference increases with slope. To improve the accuracy of SRTM DEM over vegetated mountain areas, a regression model between the SRTM elevation bias and vegetation height, LAI, and slope was developed based on one control site. Without changing any coefficients, this model was proved to be applicable in all the nine study sites, which have various topography and vegetation conditions. The mean bias of the corrected SRTM DEM at the nine study sites using this model (absolute value) is 89% smaller than that of the original SRTM DEM, and the standard deviation of the corrected SRTM elevation bias is 11% smaller.     

Investigating snowpack across scale in the northern Great Lakes–St. Lawrence forest region of Central Ontario,Canada

This study investigates scaling issues by evaluating snow processes and quantifying bias in snowpack properties across scale in a northern Great Lakes–St. Lawrence forest. Snow depth and density were measured along transects stratified by land cover over the 2015/2016 and 2016/2017 winters. Daily snow depth was measured using a time‐lapse (TL) camera at each transect. Semivariogram analysis of the transect data was conducted, and no autocorrelation was found, indicating little spatial structure along the transects. Pairwise differences in snow depth and snow water equivalent (SWE) between land covers were calculated and compared across scales. Differences in snowpack between forested sites at the TL points corresponded to differences in canopy cover, but this relationship was not evident at the transect scale, indicating a difference in observed process across scale. TL and transect estimates had substantial bias, but consistency in error was observed, which indicates that scaling coefficients may be derived to improve point scale estimates. TL and transect measurements were upscaled to estimate grid scale means. Upscaled estimates were compared and found to be consistent, indicating that appropriately stratified point scale measurements can be used to approximate a grid scale mean when transect data are not available. These findings are important in remote regions such as the study area, where frequent transect data may be difficult to obtain. TL, transect, and upscaled means were compared with modelled depth and SWE. Model comparisons with TL and transect data indicated that bias was dependent on land cover, measurement scale, and seasonality. Modelled means compared well with upscaled estimates, but model SWE was underestimated during spring melt. These findings highlight the importance of understanding the spatial representativeness of in situ measurements and the processes those measurements represent when validating gridded snow products or assimilating data into models.     

基于TRMM卫星降水的太行山区降水时空分布格局

基于TRMM 3B42V7数据,综合采用多元线性回归、偏最小二乘回归和地理加权回归3种方法,建立了太行山区卫星降水产品的降尺度校正模型,将遥感降水信息从0.25°×0.25°降尺度到0.05°×0.05°。在结果评估和优选的基础上,分析了"像元-集水区-全区"年、月降水的多时空尺度干湿季节分布和垂向分布特征,并从机理方面论证了研究的合理性。结果表明:①地理加权回归校正效果最优,可明显降低校正降水与实测降水系列的均方根误差和平均相对偏差且提高决定系数;偏最小二乘回归可降低两项误差,但对决定系数无提升;多元线性回归最差,各项指标均无改善。②处于夏季风迎风侧的东坡和南坡降水量普遍高于500 mm,背风侧的西坡和北坡降水量较低,最大年降水量位于东南坡海拔1 300~1 500 m的地带。③研究区7-9月降水量占全年的58.7%,干湿季节降水量之比为1:18,各集水区的变化范围为1:13~1:25。④季风风向影响降水中心的移动路径,各月降水量沿高程变化梯度区间为-5.2~6.7 mm/hm,且迎风坡降水的垂向分布更复杂。