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991.
992.
Impact of orthorectification and spatial sampling on maximum NDVI composite data in mountain regions 总被引:1,自引:0,他引:1
Fabio M.A. Fontana Alexander P. Trishchenko Yi Luo Stefan Wunderle 《Remote sensing of environment》2009,113(12):2701-2712
Topography and accuracy of image geometric registration significantly affect the quality of satellite data, since pixels are displaced depending on surface elevation and viewing geometry. This effect should be corrected for through the process of accurate image navigation and orthorectification in order to meet the geolocation accuracy for systematic observations specified by the Global Climate Observing System (GCOS) requirements for satellite climate data records. We investigated the impact of orthorectification on the accuracy of maximum Normalized Difference Vegetation Index (NDVI) composite data for a mountain region in north-western Canada at various spatial resolutions (1 km, 4 km, 5 km, and 8 km). Data from AVHRR on board NOAA-11 (1989 and 1990) and NOAA-16 (2001, 2002, and 2003) processed using a system called CAPS (Canadian AVHRR Processing System) for the month of August were considered. Results demonstrate the significant impact of orthorectification on the quality of composite NDVI data in mountainous terrain. Differences between orthorectified and non-orthorectified NDVI composites (ΔNDVI) adopted both large positive and negative values, with the 1% and 99% percentiles of ΔNDVI at 1 km resolution spanning values between − 0.16 < ΔNDVI < 0.09. Differences were generally reduced to smaller numbers for coarser resolution data, but systematic positive biases for non-orthorectified composites were obtained at all spatial resolutions, ranging from 0.02 (1 km) to 0.004 (8 km). Analyzing the power spectra of maximum NDVI composites at 1 km resolution, large differences between orthorectified and non-orthorectified AVHRR data were identified at spatial scales between 4 km and 10 km. Validation of NOAA-16 AVHRR NDVI with MODIS NDVI composites revealed higher correlation coefficients (by up to 0.1) for orthorectified composites relative to the non-orthorectified case. Uncertainties due to the AVHRR Global Area Coverage (GAC) sampling scheme introduce an average positive bias of 0.02 ± 0.03 at maximum NDVI composite level that translates into an average relative bias of 10.6% ± 19.1 for sparsely vegetated mountain regions. This can at least partially explain the systematic average positive biases we observed relative to our results in AVHRR GAC-based composites from the Global Inventory Modeling and Mapping Studies (GIMMS) and Polar Pathfinder (PPF) datasets (0.19 and 0.05, respectively). With regard to the generation of AVHRR long-term climate data records, results suggest that orthorectification should be an integral part of AVHRR pre-processing, since neglecting the terrain displacement effect may lead to important biases and additional noise in time series at various spatial scales. 相似文献
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To achieve size preserving tracking, in addition to controlling the camera’s pan and tilt motions to keep the object of interest
in the camera’s field of view (FOV), the camera’s focal length is adjusted automatically to compensate for the changes in
the target’s image size caused by the relative motion between the camera and the target. The estimation accuracy of these
changes determines the effectiveness of the resulting zoom control. The existing method of choice for real-time target scale
estimation applies structure from motion (SFM) based on the weak perspective projection model. In this paper we propose a
target scale estimation algorithm with a linear solution based on the more advanced paraperspective projection model, which
improves the accuracy of scale estimation by considering center offset. Another key issue in SFM based algorithms is the separation
of target and background features, especially when composite camera (pan/tilt/zoom) and target motions are involved. This
paper designs a fast target feature separation/grouping algorithm, the 3D affine shape method. The resulting separation automatically
adapts to the target’s 3D geometry and motion and is able to accommodate a large amount of off-plane rotation, which most
existing separation/grouping algorithms find difficult to achieve. Experimental results illustrate the effectiveness of the
proposed scale estimation and feature separation algorithms in tracking translating and rotating objects with a PTZ camera
while preserving their sizes. In comparison with the leading size preserving tracking algorithm described by Tordoff and Murray,
our algorithm is able to reduce the cumulative tracking error significantly from 17.4% to 3.3%. 相似文献
995.
Wei-Hung Lin Yuh-Rau Wang Shi-Jinn Horng Tzong-Wann Kao Yi Pan 《Expert systems with applications》2009,36(9):11509-11516
This paper proposes a blind watermarking algorithm based on maximum wavelet coefficient quantization for copyright protection. The wavelet coefficients are grouped into different block size and blocks are randomly selected from different subbands. We add different energies to the maximum wavelet coefficient under the constraint that the maximum wavelet coefficient is always maximum in a block. The watermark is embedded the local maximum coefficient which can effectively resist attacks. Also, using the block-based watermarking, we can extract the watermark without using the original image or watermark. Experimental results show that the proposed method is quite robust under either non-geometry or geometry attacks. 相似文献
996.
针对三维图形的无线网络环境下的传输的安全需求,提出一种可信的无线网络图形处理系统.该系统以leon3 SOC为开发平台,结合无线网络、加密认证、图形加速技术,可以较好的解决三维图形数据的安全传输和实时渲染问题.文中对基于AES和MD5算法的安全认证系统和图形加速硬件系统进行了研究与实现.最后对无线网络可信图形处理系统的软硬件性能进行了测试. 相似文献
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