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991.
S. Manthira Moorthi Raja Kayal R. Rama Krishnan P.K. Srivastava 《International Journal of Applied Earth Observation and Geoinformation》2008,10(2):140-1
RESOURCESAT-1 satellite was launched in October of 2003. Since then it has been consistently providing high quality 5 m monochromatic and multispectral images of same resolution. LISS-4 MX sensor has complex acquisition geometry. It operates in three spectral bands imaged by 3 CCD arrays, which are separated by a finite time in imaging along the satellite track direction. Individual band data is acquired at different times while the satellite is driven by a pre-determined yaw profile. In addition, the odd–even pixels are too shifted by a small fixed delay in time. A unique challenge in LISS-4 MX Level-2 data processing sub-system is to autonomously rectify and additionally co-register the three bands data because of the influence of orbit and attitude in the time gap in the imaging sequence. In this paper, authors bring out details of in-flight calibration arrived for LISS-4 MX sensor. It addresses parameterization of co-registration problem by doing sensitivity analysis of the geometric model parameters to achieve co-registration among all bands. This approach can also be used for other sensor system having similar imaging geometry to achieve improved image co-registration among bands. 相似文献
992.
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994.
Diofantos G Hadjimitsis 《Transactions in GIS》2008,12(5):633-644
Satellite sensors have provided new datasets for monitoring regional and urban air quality. Satellite sensors provide comprehensive geospatial information on air quality with both qualitative remotely sensed imagery and quantitative data, such as aerosol optical depth which is the basic unknown parameter for any atmospheric correction method in the pre‐processing of satellite imagery. This article presents a new method for retrieving aerosol optical thickness directly from satellite remotely sensed imagery for short wavelength bands in which atmospheric scattering is the dominant contribution to the at‐satellite recorded signal. The method is based on the determination of the aerosol optical thickness through the application of the contrast tool (maximum contrast value), the radiative transfer calculations and the ‘tracking’ of the suitable darkest pixel in the scene. The proposed method that needs no a‐priori information has been applied to LANDSAT‐5 TM, LANDSAT‐7 ETM+, SPOT‐5 and IKONOS data of two different geographical areas: West London and Cyprus. The retrieved aerosol optical thickness values show high correlations with in‐situ visibility data acquired during the satellite overpass. Indeed, for the West London area a logarithmic regression was fitted for relating the determined aerosol optical thickness with the in‐situ visibility values. A high correlation coefficient (r2= 0.82; p= 0.2) was found. Plots obtained from Tanre et al. (1979, 1990) and Forster (1984 ) were reproduced and estimates for these areas were generated with the proposed method so as to compare the results. The author's results show good agreement with Forster's aerosol optical thickness vs. visibility results and a small deviation from Tanre's model estimates. 相似文献
995.
一次“梅中返春”稳定性持续暴雨过程的预报失误分析 总被引:1,自引:1,他引:0
使用NCEP-FNL资料对杭州湾一次稳定性持续暴雨过程进行分析,发现冷暖气流在浙江不断交绥形成持续降雨,低层冷空气和东南暖湿气流的不断增强,使大气斜压扰动发展,锋区降雨增强,暴雨发生。此次过程,由于数值模式预报出现偏差而导致杭州湾24h大雨、暴雨预报出现较大失误。检验结果,GFS模式36h预报时效内对冷暖系统预报较好,但对低层锋区的风场预报有偏差,从而对中低层辐合、水平锋生和水汽输送产生影响,大雨、暴雨落区出现偏差。另外,模式对杭州湾南岸冷空气影响预报偏弱也是暴雨漏报的一个重要因素。稳定性降雨预报中,预报员需重视模式在预报临近时刻的调整,根据实况监测和雨带的移动、演变对冷暖气流影响作甄别,从而及时调整降雨落区和影响时间,对预报做出有益修正。 相似文献
996.
风电功率预测中最重要的因子是风速,准确的风速预测是风电功率预测的前提和基础。为了提高短期风速预测的准确性,本研究采用WRF模式,对我国上海崇明吕四风电场的风速进行预报。在此基础上,利用PCA-RBF算法结合WRF模式预报风向、气温、气压等气象要素对预报风速进一步订正。实验结果表明,利用PCA-RBF算法对WRF模式预报风速进行订正后,预报风速的误差进一步减小,相对均方根误差降低20%~30%,相对平均绝对误差降低15%~20%。与其他智能算法(BP算法、LSSVM算法)对比分析后得出,PCA-RBF算法对WRF模式预报风速具有较好的订正效果,能够有效提高风速预报准确率。 相似文献
997.
考虑到北斗卫星导航系统(BDS)的B1B2,B1B3及B2B3之间硬件延迟(DCB)值存在一个闭合差,分析BDS卫星端DCB改正公式不同表示方法在3种采样率下对定位精度的影响,分别进行了伪距定位和精密定位解算。结果表明,不同采样率的DCB改正后SPP下精度改善在m级,提高10%~80%;动态PPP下精度改善在dm~m级,提高50%~90%。改正公式的不同DCB表示方法对精度影响在cm量级,在SPP中可忽略该误差,动态PPP中建议取DCB改正均值作为最终改正值。 相似文献
998.
Donghai Zhang Xiang Chen Zhoutao Zheng Xiafei Zhou Tao Jiang 《International Journal of Digital Earth》2016,9(10):1021-1034
The false topographic perception phenomenon (FTPP) refers to the visual misperception in remote-sensing images that certain types of terrains are visually interpreted as other types in rugged lands, for example, valleys as ridges and troughs as peaks. For this reason, the FTPP can influence the visualization and interpretation of images to a great extent. To scrutinize this problem, the paper firstly reviews and tests the existing FTPP-correction techniques and identifies the inverse slope-matching technique as an effective approach to visually enhance remote-sensing images and retain the colour information. The paper then proposes an improved FTPP-correction procedure that incorporates other image-processing techniques (e.g. linear stretch, histogram matching, and flat-area replacement) to enhance the performance of this technique. A further evaluation of the proposed technique is conducted by applying the technique to various study areas and using different types of remote-sensing images. The result indicates the method is relatively robust and will be a significant extension to geovisual analytics in digital earth research. 相似文献
999.
气象台站的迁移常导致气候序列的非均一性。本文对互助站迁站前后气温序列作均一性检验及订正。采用t检验和SNHT法,对互助站迁站前后的气温序列进行均一性检验,结果表明站址迁移对互助站温度序列均一性的影响非常显著。对差值法、一元线性回归、逐步多元线性回归以及确立订正方程式的参考站平行资料年限对互助站气温序列订正效果进行分析,结果表明用参考站15年平行观测资料建立的逐步多元线性回归订正效果较好。用逐步多元线性回归法对互助站迁站前的气温序列进行订正,经订正后互助站气候倾向率为0.31℃/10a,消除了序列的不均一现象。 相似文献
1000.
We conducted reconnaissance experiments to synthesize aqueous and hydrocarbon inclusions trapped in calcite at conditions relevant to petroleum basins, and characterize the microthermometric properties of such inclusions. Fluid inclusions (FIs) were synthesized in a system of saline aqueous solution (5 or 20 wt% NaCl) coexisting with either heavy crude oil or gasoline under gas-undersaturated conditions, from 90 to 210 °C and 200–550 bar. The synthetic inclusions are not representative of gas-bearing systems, and methane (CH4) was not detected in any aqueous inclusions. The FIs are mainly distributed along planar healed cracks, indicating that the inclusions formed by fracture healing in the calcite crystal. Microthermometric measurements were conducted on coeval aqueous and hydrocarbon inclusions, and Raman spectroscopic analyses were done on aqueous inclusions, to determine the properties of FIs trapped at these conditions.Homogenization temperatures of synthetic FIs are mostly lower than the experimental trapping temperature, although the FIs show high variability in measured homogenization temperature. Results allow comparison of Th values for each sample with the expected Th, isochores and pressure corrections calculated for the system H2ONaCl. The latter parameters are broadly consistent with the known PVTX properties of H2ONaCl fluids, suggesting little effect of hydrocarbons on the homogenization behavior, although the low precision of the Th data limits this assessment. Nevertheless, this result is not unexpected considering that light hydrocarbons (gas) is not present in the experiments (as corroborated by Raman spectroscopy), a consequence of using “dead” oil in the experiments. Simulation of gas-bearing petroleum basins will require additional protocols for producing gas, either by in-situ cracking of the starting hydrocarbon material, or by other means. The reconnaissance experiments documented here provide a basis for such future experiments. 相似文献