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101.
102.
在影像匹配算法中,快速有效的匹配算法是航空摄影测量的关键.基于特征点提取的影像匹配算法具有精度高、适用性广的特点,已经逐渐成为影像匹配研究的主流.该研究分别在测试影像及航空影像中对FAST、Harris、SURF3种快速的经典特征点匹配算法进行分析比较,探讨各自的优缺点,为不同应用情况中特征点匹配方法的选取提供借鉴. 相似文献
103.
用大蒜幼嫩气生鳞茎作试材,系统研究了影响大蒜试管鳞茎形成的因素。结果表明:植物激素配比、pH值、糖源、温度、光周期和基因型都对试管鳞茎的发生有一定程度的影响。其中,无激素的MS培养基、pH值为7.5,5%的糖浓度、低温预处理、较长日照和适宜高温(25℃)有利于鳞茎的发生。 相似文献
104.
Dense infestations of a peregrine oligochaete worm, Eukerria saltensis (Beddard), have been linked to rice crop failures in southern New South Wales, Australia. The influence of E. saltensis on water quality and rice plant establishment was investigated in a series of laboratory experiments using a flooded Riverina clay soil. Worm densities of 20 and 40 per container (2548 and 5096 worms/m2, respectively) significantly increased water turbidity after 7 days incubation. Longer incubation periods led to turbidity levels of over 500 NTU being achieved (40 worms per container, 21 days incubation). Water pH was significantly reduced by densities of 10, 20, and 40 worms per container after 7 days under cyclical illumination, however in continuous darkness significant changes in pH related to worm density were only found after 21 days incubation. Nitrogen as NH4+ and total phosphorus increased significantly in the overlying water in response to increasing worm densities after 21 days incubation, however nitrogen as nitrate/nitrite and soluble phosphorus did not. Algal production (measured as extracted chlorophyll a concentration) was unaffected by the worms, reflecting the low concentrations of available phosphorus in all treatments. Rice plants grown in containers with worms produced significantly longer and heavier shoots than control plants. Root systems were unaffected, and there was no evidence of root abrasion. Evaluation of rice seed stratification in the soil profile indicates that rice seeds can be passively transported below the soil surface by the feeding and tunnelling activity of E. saltensis. Our results suggest that E. saltensis impedes the establishment of aerially-sown rice crops primarily by increasing water turbidity. Plants respond to high turbidity by partitioning more of their growth into shoot production, and consequently become vulnerable touprooting through wave action, particularly as the soil loses compaction because of worm activity. Maintaining the lowest possible water levels during rice crop establishment has helped farmers to minimize these effects. 相似文献
105.
Vanacker Veerle Govers Gerard Barros Sandra Poesen Jean Deckers Jozef 《Landscape Ecology》2003,18(1):1-15
The analysis of aerial photographs over a 33-year period (1962–1995) shows that land use in the study catchment is highly dynamic as a response to the land reform programs of the 1960s and 1970s and a strong population increase. The secondary forest is increasingly replaced by grassland while old grasslands are now used as cultivated land. Despite the increased pressure on the land, the upward movement of agricultural activity and the concurrent deforestation, the overall forest cover did not decline. The deforestation in the uplands is compensated for by a regeneration of secondary forest on abandoned rangelands and afforestation with Eucalyptus trees in the low-lying areas. The land use changes resulted in a strong decrease of the areas subject to intense soil degradation: afforestation with Eucalyptus trees on degraded lands was successful in controlling soil erosion in the lower parts of the catchment. The relationship between land use and sediment load in the river system is not straightforward. Statistical analysis of a time series of suspended sediment concentrations, which were measured at the outlet of three distinctive sub-catchments for a six-year period (1994 – 2000), revealed that the geomorphic response of the river system is not only dependent on the land use and the area affected by water erosion, but also on the spatial connectivity between sediment producing areas and the river network.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
106.
Indigenous and spontaneous vegetation: their relationship to urban development in the city of Leeds, UK 总被引:1,自引:2,他引:1
The concepts of indigenous and spontaneous vegetation are considered as subsets of the broader category, semi-natural vegetation. Indigenous vegetation is conceptualised as that which has originated in a rural landscape and developed over a time period of several centuries or more, either naturally or as a result of traditional management methods, together with the environmental conditions supporting it. In contrast, spontaneous vegetation is that which has naturally colonised derelict urban sites, mainly within the last century. An investigation, using map and aerial photographic data, examined the relative proportions of potentially indigenous and spontaneous vegetation on proposed development sites in Leeds, a large industrial city in the UK. Results suggested that spontaneous vegetation occupied approximately 13% by area of the development sites while possible indigenous vegetation occupied as little as 5%. However, further analysis suggested that approximately 25% of the proposed development sites were within 0.5 km of a designated site containing indigenous vegetation. It is argued that both types of semi-natural vegetation can make positive contributions to the urban environment but that public perception of spontaneous vegetation and, in particular, the locations where it occurs, are often negative. Further research into public perceptions of semi-natural vegetation and ways of incorporating it into urban development are required. 相似文献
107.
108.
对11年生飞播马尾松林进行综合抚育间伐试验的结果表明,不同的间伐强度和次数均产生不同的效果。胸径生长以间伐强度大和2次间伐为好;树干形质以间伐强度小为好;间伐对树高、冠幅、林木分化等均有影响。 相似文献
109.
110.
Estimation of yield zones using aerial images and yield data from a few tracks of a combine harvester 总被引:1,自引:0,他引:1
Yield maps derived from yield mapping systems are often erroneous not only due to limitations in measuring the yield precisely
but due to insufficient consideration of the requirements of yield mapping systems in practice as well. Aerial images of cultivated
crop fields at an advanced growth stage frequently provide a spatial pattern similar to that of yield maps. Therefore, the
possibility of generating a yield map using aerial images and measured yield data of a few tracks was examined for a period
of 2 years in two fields grown with cereals. Yield zones based on Visible Atmospherically Resistant Index (VARI) values were
compared with yield zones based on measured yield data of the whole field. About half of the grid cells of a field were allocated
to the same yield zones irrespective of the mode of yield determination. Using the Kruskal–Wallis test, the data sub-sets
of measured yield within the yield zones based on the VARI values differed significantly for all tested yield zones. As a
result, the approach was successful in the case of these experimental sites. 相似文献