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721.
BRDF大气影响订正环的收敛性研究 总被引:3,自引:0,他引:3
定量遥感要求对星载或机载遥感数据进行大气影响订正。精确的大气订正则需要知道下垫面的方向性反射(或辐射)特征,而这正是定量遥感所要知道的。这就形成了一个死循环。为了解开这个死结,MODIS可见/近红外产品采用了考虑地表BRDF的迭代订正。然而迭代订正的收敛性是有待研究的问题。胡宝新等用大量的模拟来表明该算法的收敛性,但模拟很难耗尽各式各样的可能情况。本文旨在从理论上研究该订正环的收敛性并阐明收敛的条件。 相似文献
722.
2010年太原空气污染物特征及环流形势 总被引:1,自引:0,他引:1
利用太原市2010年6个环境监测站SO2、NO2、PM10的逐日监测资料和MICAPS、自动站逐日资料,应用统计方法分析了太原市污染物的时空分布特征,并分析了污染严重时期的大气环流形势特点。结果表明:随着城市工业结构变化、集中供暖布局改变、以及住宅小区建设,PM10。已不再是首要污染物,3种污染物的时空分布特征均发生了明显变化;大气结构对污染物扩散的影响也呈现复杂化的特点。 相似文献
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Barnaby Clark Juha Suomalainen Petri Pellikka 《International Journal of Applied Earth Observation and Geoinformation》2011
SPOT satellites have been imaging Earth's surface since SPOT 1 was launched in 1986. It is argued that absolute atmospheric correction is a prerequisite for quantitative remote sensing. Areas where land cover changes are occurring rapidly are also often areas most lacking in situ data which would allow full use of radiative transfer models for reflectance factor retrieval (RFR). Consequently, this study details the proposed historical empirical line method (HELM) for RFR from multi-temporal SPOT imagery. HELM is designed for use in landscape level studies in circumstances where no detailed overpass concurrent atmospheric or meteorological data are available, but where there is field access to the research site(s) and a goniometer or spectrometer is available. SPOT data are complicated by the ±27° off-nadir cross track viewing. Calibration to nadir only surface reflectance factor (ρs) is denoted as HELM-1, whilst calibration to ρs modelling imagery illumination and view geometries is termed HELM-2. Comparisons of field measured ρs with those derived from HELM corrected SPOT imagery, covering Helsinki, Finland, and Taita Hills, Kenya, indicated HELM-1 RFR absolute accuracy was ±0.02ρs in the visible and near infrared (VIS/NIR) bands and ±0.03ρs in the shortwave infrared (SWIR), whilst HELM-2 performance was ±0.03ρs in the VIS/NIR and ±0.04ρs in the SWIR. This represented band specific relative errors of 10–15%. HELM-1 and HELM-2 RFR were significantly better than at-satellite reflectance (ρSAT), indicating HELM was effective in reducing atmospheric effects. However, neither HELM approach reduced variability in mean ρs between multi-temporal images, compared to ρSAT. HELM-1 calibration error is dependent on surface characteristics and scene illumination and view geometry. Based on multiangular ρs measurements of vegetation-free ground targets, calibration error was negligible in the forward scattering direction, even at maximum off-nadir view. However, error exceeds 0.02ρs where off-nadir viewing was ≥20° in the backscattering direction within ±55° azimuth of the principal plane. Overall, HELM-1 results were commensurate with an identified VIS/NIR 0.02ρs accuracy benchmark. HELM thus increases applicability of SPOT data to quantitative remote sensing studies. 相似文献
725.
Atmospheric Infrared Sounder (AIRS) data show that the Saharan air layer (SAL) is a dry, warm, and well-mixed layer between 950 and 500 hPa over the tropical Atlantic, extending westward from the African coast to the Caribbean Sea. The formations of both Hurricane Isabel and Tropical Depression 14 (TD14) were accompanied with outbreaks of SAL air during the period 1-12 September 2003, although TD14 failed to develop into a named tropical cyclone. The influence of the SAL on their formations is investigated by examining data from satellite observations and numerical simulations, in which AIRS data are incorporated into the MM5 model through the nudging technique. Analyses of the AIRS and simulation data suggest that the SAL may have played two roles in the formation of tropical cyclones during the period 1-12 September 2003. First, the outbreaks of SAL air on 3 and 8 September enhanced the transverse-vertical circulation with the rising motion along the southern edge of the SAL and the sinking motion inside the SAL, triggering the development of two tropical disturbances associated with Hurricane Isabel and TD14. Second, in addition to the reduced environmental humidity and enhanced static stability in the lower troposphere, the SAL dry air intruded into the inner region of these tropical disturbances as their cyclonic ?ows became strong. This effect may have slowed down the formation of Isabel and inhibited TD14 becoming a named tropical cyclone, while the enhanced vertical shear contributed little to tropical cyclone formation during this period. The 48-h trajectory calculations confirm that the parcels from the SAL can be transported into the inner region of an incipient tropical cyclone. 相似文献
726.
The networking status of journals reflects their academic influence among peer journals. This paper analyzes the cited and citing environments of this journal, Advances in Atmospheric Sciences (Adv. Atmos. Sci.), using methods from social network analysis. Since its initial publication, Adv. Atmos. Sci. has been actively participating in the international journal environment and international journals are frequently cited in Adv. Atmos. Sci. Particularly, this journal is intensely interrelated with its international peer journals in terms of their similar citing patterns. The international influence of Adv. Atmos. Sci. is comparatively bigger than other Chinese SCI journals in atmospheric sciences as reffected by total cites to Adv. Atmos. Sci. and the total number of international journals citing it. The academic visibility of Adv. Atmos. Sci. is continuing to improve in the international research community as the number of reference citation it receives in its peer journals internationally increases over time. 相似文献
727.
Tide-induced airflow is commonly seen in coastal lands and affects ground stability especially with a less permeable pavement on the ground surface. A tide-induced airflow model in a two-layered unsaturated zone consisting of a highly permeable layer underneath a less permeable layer was established by Li and Jiao [Li HL, JJ Jiao. One-dimensional airflow in unsaturated zone induced by periodic water table fluctuation. Water Resour Res 2005;41:W04007. doi:10.1029/2004WR003916] to describe the one-dimensional airflow with constant atmospheric pressure at the ground surface. In this study, we expand the Li and Jiao model by considering the realistic atmospheric pressure fluctuations and the initial condition. A new transient solution to the airflow model is developed for an initial boundary value problem (IBVP). The transient solution can be used not only to calculate the subsurface air pressure at a future time with a known initial condition, but also to evaluate the asymptotic air pressure variations when time becomes long. The amplitude ratio and phase lag of the subsurface air pressure relative to the tide-induced hydraulic head variations inside the unconfined aquifer below the unsaturated zone are investigated. The results reveal that effect on the subsurface pressure due to changes of atmospheric pressure amplitude depends on the configurations of air resistance in the less permeable layer and the air-filled porosity difference in the two layers. The introduction of atmospheric pressure fluctuations into the airflow model leads to insignificant influence on water table level. A field application of the new solution at Hong Kong International Airport in Hong Kong, China is demonstrated. It indicates that the new transient solution can be conveniently used to evaluate the subsurface air pressure with discrete atmospheric pressure data at the ground surface. 相似文献
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