共查询到20条相似文献，搜索用时 31 毫秒
1.
Modeling crop gross primary production (GPP) is critical to understanding the carbon dynamics of agro-ecosystems. Satellite-based studies have widely used production efficiency models (PEM) to estimate cropland GPP, wherein light use efficiency (LUE) is a key model parameter. One factor that has not been well considered in many PEMs is that canopy LUE could vary with illumination conditions. This study investigates how the partitioning of diffuse and direct solar radiation influences cropland GPP using both flux tower and satellite data. The field-measured hourly LUE under cloudy conditions was 1.50 and 1.70 times higher than that under near clear-sky conditions for irrigated corn and soybean, respectively. We applied a two-leaf model to simulate the canopy radiative transfer process, where modeled photosynthetically active radiation (PAR) absorbed by canopy agreed with tower measurements (R2 = 0.959 and 0.914 for corn and soybean, respectively). Derived canopy LUE became similar after accounting for the impact of light saturation on leaf photosynthetic capacity under varied illumination conditions. The impacts of solar radiation partitioning on satellite-based modeling of crop GPP was examined using vegetation indices (VI) derived from MODIS data. Consistent with the field modeling results, the relationship between daily GPP and PAR × VI under varied illumination conditions showed different patterns in terms of regression slope and intercept. We proposed a function to correct the influences of direct and diffuse radiation partitioning and the explained variance of flux tower GPP increased in all experiments. Our results suggest that the non-linear response of leaf photosynthesis to light absorption contributes to higher canopy LUE on cloudy days than on clear days. We conclude that accounting for the impacts of solar radiation partitioning is necessary for modeling crop GPP on a daily or shorter basis. 相似文献
2.
《International Journal of Digital Earth》2013,6(7):843-857
ABSTRACTIncreasing attention has been paid to the deterioration of air quality in China during the past decade. This study presents the spatiotemporal variations of aerosol concentration across China during 2000–2016 using aerosol optical depth (AOD) from the atmospheric product of Moderate Resolution Imaging Spectroradiometer. Percentile thresholds are applied to define AOD days with different loadings. Temporally, aerosol concentration has increased since 2000 and reached the highest level in 2011; then it has declined from 2011 to 2016. Seasonally, aerosol concentration is the highest in summer and the lowest in winter. Spatially, North China and Sichuan Basin are featured by high aerosol concentration with increasing trends in North China and decreasing trends in Sichuan Basin. North, Southeast and Southwest China have been through increasing days with low AOD loading; however, Northeast China has experienced increasing days with high AOD loading. It is likely that air quality influenced by aerosols has notably improved over North China in spring and summer, over Southwest and Southeast China in autumn, but has degraded over Northeast China in autumn. 相似文献
3.
Minna Ma Jie Dong Fawei Zhang Wenwen Cai Hongqin Li 《International Journal of Digital Earth》2018,11(11):1166-1183
Vegetation gross primary production (GPP) is an important variable for the carbon cycle on the Qinghai-Tibetan Plateau (QTP). Based on the measurements from 12 eddy covariance flux sites, we validated a light use efficiency model (i.e. EC-LUE) to evaluate the spatial-temporal patterns of GPP and the effect of environmental variables on QTP. In general, EC-LUE model performed well in predicting GPP at different time scale over QTP. Annual GPP over the entire QTP ranged from 575 to 703 Tg C, and showed a significantly increasing trend from 1982 to 2013. However, there were large spatial heterogeneities in long-term trends of GPP. Throughout the entire QTP, air temperature increase had a greater influence than solar radiation and precipitation (PREC) changes on productivity. Moreover, our results highlight the large uncertainties of previous GPP estimates due to insufficient parameterization and validations. When compared with GPP estimates of the EC-LUE model, most Coupled Model Intercomparison Project (CMIP5) GPP products overestimate the magnitude and increasing trends of regional GPP, which potentially impact the feedback of ecosystems to regional climate changes. 相似文献
4.
定量分析气溶胶与痕量气体之间的时空变化关系有助于进一步研究气粒转化。本文采用2006年—2015年MODIS气溶胶光学厚度(AOD)、细粒子模态比(FMF)和OMI痕量气体(SO_2、NO_2和HCHO)数据,对黄海、东海和南海区域上空的细粒子气溶胶与痕量气体进行定量分析。先对气溶胶和痕量气体作均值分析发现:AOD_(fine)、SO_2、NO_2和HCHO的均值在黄海、南海、东海均依次减小;再对气溶胶对痕量气体的敏感度分析发现:黄海地区的AOD_(fine)对SO_2最敏感,敏感度为0.424,这与中国东部沿海城市的人为排放有关;而东海和南海地区对HCHO的敏感度较高,依次为0.664和0.545,主要受东南亚和中国南方地区生物质燃烧影响。最后,对3个区域的气溶胶与痕量气体按季节作相关性分析发现:黄海地区AOD_(fine)在夏秋两季与SO_2的相关性较强(R0.5),主要由于夏秋两季的温湿度大,利于发生气—粒转化;东海地区夏季HCHO与AOD_(fine)相关性较明显(R=0.57);南海春季HCHO与AOD_(fine)相关性较好(R=0.57),呈现出区域与季节性的变化。最终发现,气溶胶与痕量气体随着时空变化存在相关关系。 相似文献
5.
陆地总初级生产力遥感估算精度分析 总被引：1，自引：0，他引：1
准确估算陆地总初级生产力GPP(Gross Primary Productivity)数值对碳循环过程模拟有重要影响。本文介绍了多种基于植被指数以及基于光能利用率的遥感GPP算法,综述了不同算法在其研究区域的估算精度;并分析了MODIS/GPP以及BESS/GPP两种遥感GPP产品在不同植被类型的估算精度。通过对比全球碳通量站网络GPP数据表明,MODIS/GPP产品在全球估算结果具显著相关性(R2=0.59)及中等标准误差(RMSE=2.86 g C/m2/day),估算精度较高的植被类型有落叶阔叶林,草地等;估算精度较低类型包括常绿阔叶林,稀树草原等。本文对GPP产品中存在的不确定性进行分析,通过综述前人研究中发现的遥感估算GPP方法中存在的问题,指出可能的提高卫星遥感GPP产品估算精度的方法及发展趋势。 相似文献
6.
Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM) has been used for the blending of Landsat and MODIS data. Specifically, the 30 m Landsat-7 ETM+ (Enhanced Thematic Mapper plus) surface reflectance was predicted for a period of 10 years (2000–2009) as the product of observed ETM+ and MODIS surface reflectance (MOD09A1) on the predicted and observed ETM+ dates. A pixel based analysis for six observed ETM+ dates covering winter and summer crops showed that the prediction method was more accurate for NIR band (mean r2 = 0.71, p ≤ 0.01) compared to green band (mean r2 = 0.53; p ≤ 0.01). A recently proposed chlorophyll index (CI), which involves NIR and green spectral bands, was used to retrieve gross primary productivity (GPP) as the product of CI and photosynthetic active radiation (PAR). The regression analysis of GPP derived from closet observed and synthetic ETM+ showed a good agreement (r2 = 0.85, p ≤ 0.01 and r2 = 0.86, p ≤ 0.01) for wheat and sugarcane crops, respectively. The difference between the GPP derived from synthetic and observed ETM+ (prediction residual) was compared with the difference in GPP values from observed ETM+ on the two dates (temporal residual). The prediction residuals (mean value of 1.97 g C/m2 in 8 days) was found to be significantly lower than the temporal residuals (mean value of 4.46 g C/m2 in 8 days) that correspondence to 12% and 27%, respectively, of GPP values (mean value of 16.53 g C/m2 in 8 days) from observed ETM+ data, implying that the prediction method was better than temporal pixel substitution. Investigating the trend in synthetic ETM+ GPP values over a growing season revealed that phenological patterns were well captured for wheat and sugarcane crops. A direct comparison between the GPP values derived from MODIS and synthetic ETM+ data showed a good consistency of the temporal dynamics but a systematic error that can be read as bias (MODIS GPP over estimation). Further, the regression analysis between observed evapotranspiration and synthetic ETM+ GPP showed good agreement (r2 = 0.66, p ≤ 0.01). 相似文献
7.
Southwestern China experienced a period of severe drought from September 2009 to May 2010. It led to widespread decline in the enhanced vegetation index (EVI) and gross primary productivity (GPP) in the springtime of 2010 (March to May). However, this study observed a spatial inconsistency between drought-impacted vegetation decline and the precipitation deficit. Significant aerosol loads that correspond to inconsistent areas were also observed during the drought period. After analyzing both MODIS GPP/NPP Collection 5 (C5) and the newer Collection 5.5 (C55) data, a large area observed to be experiencing GPP decline in the eastern part of the study area proved to be unreliable. Based on EVI data, after atmospherically contaminated data were screened from analysis, approximately 20% of the study area exhibited browning whereas 33% displayed no change or greening and the remaining area (approximately 47%) lacked sufficient data to document changing conditions. Correlation analysis showed that fire occurrences, aerosol optical depth, and precipitation anomalies during the two drought periods (from September to February and from March to May) all contributed to a decrease in GPP. C55 data remains vulnerable to aerosol contamination due to a much higher correlation coefficient with aerosol optical depth compared to C5 data. In the future, users of remotely sensed data should be cautious of and take into account impacts related to atmospheric contamination, even during drought periods. 相似文献
8.
结合地基激光雷达和太阳辐射计的气溶胶垂直分布观测 总被引：4，自引：1，他引：3
选取2013年1月灰霾和2月晴好天进行气溶胶垂直分布的雷达观测研究,并对不同高度气溶胶消光系数进行对比分析。结果显示在研究时间段内,晴好天时气溶胶的垂直分布不均匀,易出现垂直分层现象,而灰霾天时气溶胶主要集中在垂直高度1km以下,基本无分层现象。对比分析显示,严重灰霾天时气溶胶消光系数较大,在400米高度可达到中度污染天的5倍,以及晴好天的50倍。此外,整层大气的气溶胶光学厚度与400米处消光具有较好的相关性。 相似文献
9.
N. R. Patel V. K. Dadhwal S. K. Saha 《Journal of the Indian Society of Remote Sensing》2011,39(3):383-391
The present study investigates the characteristics of CO2 exchange (photosynthesis and respiration) over agricultural site dominated by wheat crop and their relationship with ecosystem
parameters derived from MODIS. Eddy covariance measurement of CO2 and H2O exchanges was carried out at 10 Hz interval and fluxes of CO2 were computed at half-hourly time steps. The net ecosystem exchange (NEE) was partitioned into gross primary productivity
(GPP) and ecosystem respiration (R
e) by taking difference between day-time NEE and respiration. Time-series of daily reflectance and surface temperature products
at varying resolution (250–1000 m) were used to derive ecosystem variables (EVI, NDVI, LST). Diurnal pattern in Net ecosystem
exchange reveals negative NEE during day-time representing CO2 uptake and positive during night as release of CO2. The amplitude of the diurnal variation in NEE increased as LAI crop growth advances and reached its peak around the anthesis
stage. The mid-day uptake during this stage was around 1.15 mg CO2 m−2 s−1 and night-time release was around 0.15 mg CO2 m−2 s−1. Linear and non-linear least square regression procedures were employed to develop phenomenological models and empirical
fits between flux tower based GPP and NEE with satellite derived variables and environmental parameters. Enhanced vegetation
index was found significantly related to both GPP and NEE. However, NDVI showed little less significant relationship with
both GPP and NEE. Furthemore, temperature-greenness (TG) model combining scaled EVI and LST was parameterized to estimate
daily GPP over dominantly wheat crop site. (R
2 = 0.77). Multi-variate analysis shows that inclusion of LST or air temperature with EVI marginally improves variance explained
in daily NEE and GPP. 相似文献
10.
Accurate estimation of ecosystem carbon fluxes is crucial for understanding the feedbacks between the terrestrial biosphere and the atmosphere and for making climate-policy decisions. A statistical model is developed to estimate the gross primary production (GPP) of coniferous forests of northeastern USA using remotely sensed (RS) radiation (land surface temperature and near-infra red albedo) and ecosystem variables (enhanced vegetation index and global vegetation moisture index) acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. This GPP model (called R-GPP-Coni), based only on remotely sensed data, was first calibrated with GPP estimates derived from the eddy covariance flux tower of the Howland forest main tower site and then successfully transferred and validated at three other coniferous sites: the Howland forest west tower site, Duke pine forest and North Carolina loblolly pine site, which demonstrate its transferability to other coniferous ecoregions of northeastern USA. The proposed model captured the seasonal dynamics of the observed 8-day GPP successfully by explaining 84–94% of the observed variations with a root mean squared error (RMSE) ranging from 1.10 to 1.64 g C/m2/day over the 4 study sites and outperformed the primary RS-based GPP algorithm of MODIS. 相似文献
11.
太阳光入射与地表、大气相互作用,会在天空中出现较为稳定的天空偏振模式图,即以太阳为中心,天空中的偏振信号呈现一定的规律分布。影响天空偏振模式图的强度及形态主要由地表反射性质、空气分子散射性质及气溶胶光学性质共同影响。本研究利用矢量辐射传输模型,以海洋下垫面为例,在获取沙尘非球形与煤烟非球型气溶胶单次散射性质的基础上,模拟了不同气溶胶光学厚度情况下的全天空偏振模式图。结果表明,天空以太阳入射方向为中心呈现一个较为稳定的天空偏振模式图。沙尘型散射气溶胶光学厚度的增大会减弱该模式图的强度,而煤烟型吸收气溶胶光学厚度的增大会增大该模式图的强度。利用双模态(沙尘型与煤烟型混合)气溶胶模型,系统分析不同气溶胶比例情况下的天空偏振模式图,结果表明全天空偏振模式图的基本模态依旧存在,但是其强度受气溶胶模型与光学厚度双重影响。因此在利用全天空偏振模式图进行气溶胶光学性质反演时需要注意气溶胶模态信息的选择。 相似文献
12.
气溶胶单次散射反照率SSA（Single Scattering Albedo）的卫星定量遥感对气候评估和大气污染治理均具有重要意义。搭载于S5P（Sentinel-5 Precursor）上的对流层监测仪（TROPOMI）具有目前同类卫星传感器中最优的空间分辨率。本文基于S5P/TROPOMI数据开展了中国东部地区的SSA反演研究。首先利用中国东部地区AERONET（Aerosol Robotic Network）站点数据对OPAC（Optical Properties of Aerosols and Clouds）气溶胶模型进行约束改进,构建了更为合适的气溶胶类型,并使用地基激光雷达（Lidar）预设相应气溶胶类型的垂直结构。然后使用辐射传输模型SCIATRAN构建查找表LUT（Look-Up Table）,将TROPOMI UVAI（Ultraviolet Absorbing Index）和MODIS AOD（Aerosol Optical Depth）数据联合输入反演气溶胶SSA数据。反演结果与地基站点数据对比,相关系数R2为0.61,均方根误差为0.05;和OMI SSA产品相比,总体趋势一致且具有空间连续性更好。基于TROPOMI的高分辨率SSA算法和数据将有助于中小尺度下气溶胶时空分布、光学特性等研究。 相似文献
13.
Aerosol and water vapour are very important element in the Earth’s climate system which has direct role in the Earth’s radiation budget. In this paper the seasonality, latitudinal distribution and the relationship of aerosol optical thickness (AOD) and water vapour (WV) using MODIS Level 3 monthly data from 2001 to 2008 are analysed. The analysis shows that AOD (0.55 μm) values reach maximum during southwest monsoon and remain minimum during northeast monsoon period. The Equatorial Indian Ocean shows minimum AOD (0.115 to 0.153) throughout the year compared to Arabian Sea (0.208 to 0.613) and Bay of Bengal (0.214 to 0.351). Arabian Sea shows high variation and maximum value of AOD compared to Bay of Bengal and Equatorial Indian Ocean. During southwest monsoon WV over Bay of Bengal was found higher in concentration compared to Arabian Sea and Equitorial Indian Ocean throughout the study period. Comparison between Arabian Sea (2.98 cm to 5.07 cm) and Bay of Bengal (3.49 cm to 5.94 cm) shows that WV concentration is less in Arabian Sea throughout the year. The analysis of correlation between WV and AOD was found to be inconsistent. However, AOD and WV shows a strong positive correlation for whole year (Mean R2 =0.90) in the Equitorial Indian Ocean region except in the months of January, February and March. In general, the correlation between WV and AOD is found to be strongly positive for oceanic aerosol (sea salt) in low water vapour condition. 相似文献
14.
查找表方法确定气溶胶类型 总被引：2，自引：0，他引：2
针对传统气溶胶类型确定方法的局限性以及当前气溶胶类型确定存在的困难,提出一种使用多波段气溶胶光学厚度数据确定气溶胶类型的方法。基于大气颗粒物的散射与吸收特性分析,通过构建查找表的方法实现气溶胶类型的确定。该方法利用Mie散射理论通过正向模拟不同类型气溶胶粒子数量与多波段光学厚度之间的关系来构建查找表,基于该查找表,使用440 nm、670 nm、870 nm及1020 nm 4个波段的气溶胶光学厚度确定气溶胶类型。使用模拟的多波段气溶胶光学厚度数据开展了气溶胶类型的确定实验,分析了不同波段气溶胶光学厚度误差对气溶胶类型确定结果的影响。结果表明,该方法可根据4个波段的气溶胶光学厚度以较高的精度确定出沙尘性、水溶性和煤烟3种气溶胶粒子的数量,从而确定气溶胶类型。 相似文献
15.
T. M. Midhuna Biswadip Gharai Subin Jose P. V. N Rao 《Journal of the Indian Society of Remote Sensing》2017,45(4):685-697
Satellite-based measurements of aerosols are one of the most effective ways to understand the role of aerosols in climate in terms of spatial and temporal variability. In the present study, we attempted to analyse spatial and temporal variations of satellite derived aerosol optical depth (AOD) over Indian region using moderate resolution imaging spectrometer over a period of 2001–2011. Due to its vast spatial extent, Indian region and adjacent oceanic regions are divided into different zones for analysis. The land mass is sub divided into five different zones such as Indo Gangetic Plain (IGP), Indian mainland, North Eastern India (NE), South India-1 (SI-1), South India-2 (SI-2). Oceanic areas are divided into Arabian Sea and Bay of Bengal. Arabian Sea is further divided as three zones viz. Northern AS (NAS), Central AS (CAS) and Eastern AS (EAS) zones. Bay of Bengal is divided as North BoB (NBoB), West BoB (WBoB), Central BoB (CBoB), and East BoB (EBoB). The study revealed that among all the land regions, IGP showed the highest peak AOD value (0.52 ± 0.17) while SI-2 showed the lower values of AOD in all the months compared to all India average. The maximum AOD is observed during premonsoon season for all regions. During the winter, average AOD levels were substantially lower than the summer averages. Peak of aerosol loading (0.35 ± 0.159) is observed in March over NE region, whereas in all other regions, peak is observed during May. Frequency distribution of long term AOD (<0.2, 0.3–0.5, >0.5) shows a shift of frequency distribution of AOD from <0.3 to 0.3–0.5 during the study period in all regions except IGP. In IGP shift of frequency of AOD values occurs from 0.3–0.5 to >0.5. Oceanic areas also shows seasonal variation of AOD. Over Arabian Sea, high AOD values with greater variations were observed in summer monsoon season while in Bay of Bengal it is observed during winter monsoon. This is due to the high wind speed prevailing in Arabian Sea during monsoon season which results in production of more sea salt aerosol. Highest AOD values are observed over NAS during monsoon season and over NBOB during winter season. Lowest AOD values with its lower variations observed in both the central region of Arabian Sea and Bay of Bengal. 相似文献
16.
基于遥感和美国碳通量观测数据的GPP模型比较研究 总被引：1，自引：0，他引：1
基于遥感和碳通量观测数据,本文采用VPM、EC-LUE、TG、GR、VI和MOD17六个模型估算了五种主要植被类型站点尺度的总初级生产力(GPP)。利用线性相关和定量分析方法评价并比较了上述模型在不同时间尺度上(8天、生长季和年际)的GPP模拟精度。结果表明:1)EC-LUE和VPM模型总体估算精度最高(R20.78);2)森林生态系统中,GPP估算值和实测值在季节和年累积总量上相对误差较小,而在草地和农田系统中,相对误差较大;3)GR、VI和TG模型在森林生态系统GPP估算中模拟精度较高,因其在形式上相对简单,需要的参数和输入数据相对较少,因而适用于大尺度的森林生态系统GPP估算。 相似文献
17.
《International Journal of Digital Earth》2013,6(6):623-638
ABSTRACTThe capacity of six water stress factors (ε′i) to track daily light use efficiency (ε) of water-limited ecosystems was evaluated. These factors are computed with remote sensing operational products and a limited amount of ground data: ε′1 uses ground precipitation and air temperature, and satellite incoming global solar radiation; ε′2 uses ground air temperature, and satellite actual evapotranspiration and incoming global solar radiation; ε′3 uses satellite actual and potential evapotranspiration; ε′4 uses satellite soil moisture; ε′5 uses satellite-derived photochemical reflectance index; and ε′6 uses ground vapor pressure deficit. These factors were implemented in a production efficiency model based on Monteith’s approach in order to assess their performance for modeling gross primary production (GPP). Estimated GPP was compared to reference GPP from eddy covariance (EC) measurements (GPPEC) in three sites placed in the Iberian Peninsula (two open shrublands and one savanna). ε′i were correlated to ε, which was calculated by dividing GPPEC by ground measured photosynthetically active radiation (PAR) and satellite-derived fraction of absorbed PAR. Best results were achieved by ε′1, ε′2, ε′3 and ε′4 explaining around 40% and 50% of ε variance in open shurblands and savanna, respectively. In terms of GPP, R2?≈?0.70 were obtained in these cases. 相似文献
18.
气候模式对气溶胶光学厚度AOD的合理模拟,是模拟研究气溶胶气候效应的前提。利用在线耦合的区域气候—大气化学—气溶胶耦合模式系统RIEMS-Chem,模拟研究了2010年中国东部地区AOD的季节变化情况。模拟结果与卫星搭载的中分辨率成像光谱仪(MODIS)的反演资料和地基气溶胶观测网(AERONET)的站点观测资料分别进行了一年四季的详细对比,检验结果显示尽管模拟值有所低估,模式仍然能够合理地反映AOD的季节变化情况和空间分布特征,与AERONET站点观测值相比,整体相关系数为0.6。MODIS反演和相应模拟结果均显示,中国东部地区AOD整体水平夏季最大,春季次之,秋、冬季最小,华北平原、四川盆地和华中地区是AOD的主要大值区。只考虑日间AOD时,其季节分布特征略有不同,在华北平原地区,日间AOD夏季最大(1.1—1.5),在长江中下游流域地区,日间AOD则在春季最大(1.1—1.7);在中国东部,日间AOD的大值在夏、冬两季分别主要分布在长江以北、以南地区,而在春、秋两季则主要位于长江中下游流域。 相似文献
19.
为提高风云三号气象卫星(FY-3)紫外臭氧总量探测仪(TOU)观测数据得到的吸收性气溶胶指数AAI(Absorbing Aerosol Index)或AI(Aerosol Index)的可靠性,需要了解AAI指数与相对湿度之间的内在关系。本研究利用大气辐射传输模型DAK(Doubling-Adding KNMI)分别模拟了在城市气溶胶和乡村气溶胶模式下AAI同相对湿度之间的关系,并将结果同已观测到的实际结果进行对比。结果发现,在相对湿度呈高值时AAI指数出现很大的变化,但相对湿度对两种气溶胶模型的影响具有相反的效应,分析显示当大气中含有吸收性气溶胶如含碳类气溶胶(在中国北部的污染过程中很常见)时,AAI结果对RH(Relative Humidity)有很强的依赖。在应用AAI指数产品检测污染过程中需要注意气溶胶的具体类型和相对湿度的影响,必要时在高相对湿度过程中进行数据校正或剔除。 相似文献
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基于6S传输模型,本文利用中分辨率成像光谱仪（MODIS）数据并结合较新的NASA的V5．2气溶胶业务反演算法,以上海市MODIS数据为研究数据源,结合晴朗天气（晴朗且无云或云稀薄）与AERONET发布的探测日（即发布AOD探测值日期）选取8组MODISLIB数据集,对其进行气溶胶厚度反演。同时将反演结果与AERONET架设在太湖区域点（31N,120E）的太阳光度观测的光学厚度进行验证。结果表明：V5．2反演算法结果与观测值呈现相同的变化趋势,反演值与观测值误差不大,在气溶胶光学厚度反演中具有较好的应用。 相似文献