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51.
Scaling Gross Primary Production (GPP) over boreal and deciduous forest landscapes in support of MODIS GPP product validation 总被引:1,自引:0,他引:1
David P. Turner William D. RittsWarren B. Cohen Stith T. GowerMaosheng Zhao Steve W. RunningSteven C. Wofsy Shawn UrbanskiAllison L. Dunn J.W. Munger 《Remote sensing of environment》2003,88(3):256-270
The Moderate Resolution Imaging Radiometer (MODIS) is the primary instrument in the NASA Earth Observing System for monitoring the seasonality of global terrestrial vegetation. Estimates of 8-day mean daily gross primary production (GPP) at the 1 km spatial resolution are now operationally produced by the MODIS Land Science Team for the global terrestrial surface using a production efficiency approach. In this study, the 2001 MODIS GPP product was compared with scaled GPP estimates (25 km2) based on ground measurements at two forested sites. The ground-based GPP scaling approach relied on a carbon cycle process model run in a spatially distributed mode. Land cover classification and maximum annual leaf area index, as derived from Landsat ETM+ imagery, were used in model initiation. The model was driven by daily meteorological observations from an eddy covariance flux tower situated at the center of each site. Model simulated GPPs were corroborated with daily GPP estimates from the flux tower. At the hardwood forest site, the MODIS GPP phenology started earlier than was indicated by the scaled GPP, and the summertime GPP from MODIS was generally lower than the scaled GPP values. The fall-off in production at the end of the growing season was similar to the validation data. At the boreal forest site, the GPP phenologies generally agreed because both responded to the strong signal associated with minimum temperature. The midsummer MODIS GPP there was generally higher than the ground-based GPP. The differences between the MODIS GPP products and the ground-based GPPs were driven by differences in the timing of FPAR and the magnitude of light use efficiency as well as by differences in other inputs to the MODIS GPP algorithm—daily incident PAR, minimum temperature, and vapor pressure deficit. Ground-based scaling of GPP has the potential to improve the parameterization of light use efficiency in satellite-based GPP monitoring algorithms. 相似文献
52.
Steve Greenbaum 《Journal of Automated Reasoning》1997,18(2):259-264
Violet is an easy-to-use theorem prover based on locking resolution, with integrated equality extensions that use term rewriting and Knuth–Bendix completion. Violet participated in the CADE-13 ATP System Competition. 相似文献
53.
Boundary cell-based acceleration for volume ray casting 总被引:4,自引:0,他引:4
Several effective acceleration techniques for volume rendering offer efficient means to skip over empty space, providing significant speedup without affecting image quality. The effectiveness of such an approach depends on its ability to accurately estimate the object boundary inside a volume with minimal computational overhead. We propose a novel boundary cell-based acceleration technique for ray casting which skips over empty space by accurately calculating the intersection distance for each ray. Very short distance estimation time is achieved by exploiting a projection template to calculate the parallel-projection values of each boundary cell and the coherency of adjacent cells. Since no hardware acceleration is used, the projection procedure can also be efficiently parallelized. Experimental results are provided to demonstrate the performance of our new algorithm. 相似文献
54.
A review of the various models of New Product Development (NPD) process shows that although different approaches have been proposed, they are in fact all variants on a linear theme: some may include feedback loops, but they all essentially advocate that certain steps precede, or are preceded by, others. An inevitable consequence on the Internet/World Wide Web (WWW or Web) is that such models are no longer applicable. Based on the lessons learned from the development of a new financial service offered via the Internet, we show how such assumptions of linearity need no longer be a constraint. In addition, innovativeness is not related to firm size. But the fact that the Web allows for the real-time development of new financial services based on on-going feedback from potential and current customers raises a new set of managerial issues that have to be tackled. The objective of this paper is to use the context of the recent launch of an innovative financial service product via the Web to explore the managerial changes that are starting to affect the banking industry. 相似文献
55.
Abstract: This paper describes the application of Artificial Intelligence techniques for plan generation, plan execution, and plan monitoring to automate a Deep Space Communication Station. This automation allows a communication station to respond to a set of tracking goals by appropriately reconfiguring the communications hardware and software to provide the requested communications services. In particular this paper describes: (1) the overall automation architecture, (2) the plan generation and execution monitoring AI technologies used and implemented software components, and (3) the knowledge engineering process and effort required for automation. This automation was demonstrated in February 1995, at the DSS13 Antenna Station in Goldstone, CA on a series of Voyager tracks and the technologies demonstrated are being transferred to the operational Deep Space Network stations. 相似文献
56.
在计算机视觉研究领域,如何检测和消除图像中的高光(specular)一直是个热点问题,有关的研究结果对于提高计算机视觉算法性能有着重要的影响.针对这一问题,提出了一种检测和消除高光的方法.首先,通过比较高光和漫反射光(diffuse)的色度特性的不同,给出了一种交互检测单色物体表面高光区域的方法;然后,引入补色(inpainting)方法并结合光照约束条件,设计了一种去除单张图像中高光并还原出漫反射分量的新的补色算法.与一般补色方法不同,该算法充分利用了高光区域含有的信息来指导补色过程.通过综合利用观测到的像素值、光源的色度分析(illumination chromaticity analysis)、光源颜色的平滑性等来约束补色过程,保证了算法能够克服一般的补色方法无法保持物体表面细微明暗变化的缺点.实验结果表明,与以往的去除单张图像高光的方法相比,该算法能够提供更好的光源色度估计,从而得到更准确的结果. 相似文献
57.
In this reply, the authors explore several issues raised by I. Kirsch (2004; see record 2004-11156-008) concerning their original article (S. Stewart-Williams & J. Podd, 2004; see record 2004-11156-007), which dealt with the roles of expectancy and classical conditioning in the placebo effect. The only notable disagreement concerns a definitional issue, namely, Stewart-Williams and Podd's claim that the placebo concept can be extended to inert psychotherapies. The authors defend this claim against the criticisms Kirsch raised. In addition, they comment on the suggestion that nonconscious learning processes play only a small role in human placebo effects, arguing that there are theoretical reasons to expect these processes to be more important than has previously been recognized. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
58.
Satellite radar remote sensing of seasonal growing seasons for boreal and subalpine evergreen forests 总被引:2,自引:0,他引:2
John S. Kimball Kyle C. McDonald Steve E. Frolking 《Remote sensing of environment》2004,90(2):243-258
We evaluated whether satellite radar remote sensing of landscape seasonal freeze-thaw cycles provides an effective measure of active growing season timing and duration for boreal and subalpine evergreen forests. Landscape daily radar backscatter measurements from the SeaWinds scatterometer on-board the QuikSCAT satellite were evaluated across a regional network of North American coniferous forest sites for 2000 and 2001. Radar remote sensing measurements of the initiation and length of the growing season corresponded closely with both site measurements and ecosystem process model (BIOME-BGC) simulations of these parameters because of the sensitivity of the Ku-band scatterometer to snow cover freeze-thaw dynamics and associated linkages between growing season initiation and the timing of seasonal snowmelt. In contrast, remote sensing estimates of the timing of growing season termination were either weakly or not significantly associated with site measurements and model simulation results, due to the relative importance of light availability and other environmental controls on stand phenology in the fall. Regional patterns of estimated annual net primary production (NPP) and component photosynthetic and autotrophic respiration rates for the evergreen forest sites also corresponded favorably with remote sensing estimates of the seasonal timing of spring thaw and associated growing season length, indicating the importance of these parameters in determining spatial and temporal patterns of NPP and the potential utility of satellite radar remote sensing for regional monitoring of the terrestrial biosphere. 相似文献
59.
The increasing gap in performance between processors and main memory has made effective instructions prefetching techniques more important than ever. A major deficiency of existing prefetching methods is that most of them require an extra port to I-cache. A recent study by Rivers et al. [19] shows that this factor alone explains why most modern microprocessors do not use such hardware-based I-cache prefetch schemes. The contribution of this paper is two-fold. First, we present a method that does not require an extra port to I-cache. Second, the performance improvement for our method is greater than the best competing method BHGP [23] even disregarding the improvement from not having an extra port. The three key features of our method that prevent the above deficiencies are as follows. First, late prefetching is prevented by correlating misses to dynamically preceding instructions. For example, if the I-cache miss latency is 12 cycles, then the instruction that was fetched 12 cycles prior to the miss is used as the prefetch trigger. Second, the miss history table is kept to a reasonable size by grouping contiguous cache misses together and associated them with one preceding instruction, and therefore, one table entry. Third, the extra I-cache port is avoided through efficient prefetch filtering methods. Experiments show that for our benchmarks, chosen for their poor I-cache performance, an average improvement of 9.2% in runtime is achieved versus the BHGP methods [23], while the hardware cost is also reduced. The improvement will be greater if the runtime impact of avoiding an extra port is considered. When compared to the original machine without prefetching, our method improves performance by about 35% for our benchmarks. 相似文献
60.