Research Highlights - CRE

2013-04-11T14:28:00+08:00

A Generalised Split-Window Algorithm for Land Surface Temperature Estimation from MSG-2/SEVIRI Data

Author: Caixia Gao, Bohui Tang, Hua Wu, Xiaoguang Jiang,and Zhaoliang Li

This study aims to determine the land surface temperature (LST) using data from a spinning enhanced visible and infrared imager (SEVIRI) onboard MSG-2 using the generalised split-window (GSW) algorithm. Coefficients in the GSW algorithm are pre-determined for several overlapping sub-ranges of the LST, land surface emissivity (LSE) and atmospheric water vapour content (WVC) using the data simulated with the atmospheric radiative transfer model MODTRAN 4.0 under various surface and atmospheric conditions for 11 view zenith angles (VZAs) ranging from 0º to 67º. The results show that the root mean square error (RMSE) varies with VZA and atmospheric WVC and that the RMSEs are within 1.0 K for the sub-ranges in which the VZA is less than 30º and the atmospheric WVC is less than 4.25 g/cm². A sensitivity analysis of LSE uncertainty, atmospheric WVC uncertainty and instrumental noise (NEΔT) is also performed, and the results demonstrate that LSE uncertainty can result in a larger LST error than other uncertainties and that the total error for the LST is approximately 1.21 K and 1.45 K for dry atmosphere, 0.86 K and2.91 K for wet atmosphere at VZA=0° and at VZA=67°, respectively, if the uncertainty of the LSE is 1% and that of the WVC is 20%.The GSW algorithm is then applied to the MSG-2/SEVIRI data with the LSE determined using the temperature-independent spectral indices methodand the WVC either determined using the measurements in two split-window channels or interpolated temporally and spatially using the ECMWF data. Finally, the SEVIRI LST (SEVIRI LST1) derived in this study is evaluated through thecomparisonswith SEVIRI LST (SEVIRI LST2) provided by the land surface analysis satellite applications facility and MODISLST product, respectively. The results show that more than 80% of the differences between the SEVIRI LST1 and SEVIRI LST2 are within 2 K, and approximately 70% of the differences between SEVIRI LST1 and MODIS LST are within 4 K. Furthermore, compared to the MODIS LST, for four specific areas with different land surfaces, our GSW algorithm overestimates the LST within 1 K for vegetated surfaces and at 1.3 K for bare soil.

Comparison of land surface temperatures from MSG-2/SEVIRI and Terra/MODIS

2013-04-11T14:26:00+08:00

Comparison of land surface temperatures from MSG-2/SEVIRI and Terra/MODIS

Author: CaixiaGao,XiaoguangJiang,HuaWu,BohuiTang,ZiyangLi,and Zhao Liang Li

Land surface temperature (LST) is an important parameter in climatological and environmental research and can be derived from satellite thermal infrared data using various LST retrieval methods. Due to the differences in retrieval methods and input data sources, the LST generated from the Spinning Enhanced Visibleand Infrared Imager (SEVIRI)onboardthe MSG-2 satellite is different from that retrieved from the MODIS onboard Terra satellite. This study aims toevaluate the SEVIRI LST retrieved using the generalised split-window method with the land surface emissivity (LSE) estimated using the day/night Temperature-Independent Spectral Indices based method against the MODIS-derived LST extracted from theMOD11B1 V5 product during 7 clear-sky days. The results show that (1) discrepancies exist between the two LST products, with a maximum of 4.9 K on average; (2) these differences are considered to be time-dependent, i.e., higher discrepancies are observed during the daytime;(3) these differences are land-cover dependent, i.e., bare areas generally present larger differences than vegetated areas; (4) these differences depend on the view zenith angle (VZA) differences, inversely proportional to VZA differences. Finally, the main sources of LST differences are investigated and identified in terms of LSE, instrumental noise equivalent temperature difference (NEΔT) and mis-registration ofthe two LST products. These discrepancies may mainly result from errors in LSE, which are caused primarily by the atmospheric correction error for the SEVIRI-derived LST;the LST differences arising from NEΔT andmis-registration are within 0.4 K.

Sensitivity and effectiveness of landscape metric scalograms in determining the characteristic scale of a hierarchically structured landscape

2013-04-10T14:07:00+08:00

Sensitivity and effectiveness of landscape metric scalograms in determining the characteristic scale of a hierarchically structured landscape

Author: Na Zhang, Harbin Li

Landscape metric scalograms (the response curves of landscape metrics to changing grain size) have been used to illustrate the scale effects of metrics for real landscapes. However, whether they detect the characteristic scale of hierarchically structured landscapes remains uncertain. To address this question, the scalograms of 26 class-level metrics were systematically examined for a simple random landscape, seven hierarchical neutral landscapes, and the real landscape of the Xilin River Basin of Inner Mongolia, China. The results show that when the fraction of the focal patch type (P) is below a critical value (P_c), most metric scalograms are sensitive to change in single-scale and lower-level hierarchical structure and insensitive to change in higher-level hierarchical structure. The scalograms of only a few metrics measuring spatial aggregation and connectedness are sensitive to change in intermediate-level hierarchical structure. Most metric scalograms explicitly identify the characteristic scale of a single-scale landscape and fine or intermediate characteristic scales of a multi-scale landscape for both simulated and real landscapes. When P exceeds P_c, only some metrics detect scale and change in structure. The scalograms of total class area and Euclidean nearest-neighbor distance cannot detect scale or change in structure in either case. Landscape metric scalograms are useful for addressing scale issues, including illustrating the scale effects of spatial patterns, detecting multi-scale patterns, and developing possible scaling relations.

Na Zhang, Harbin Li. 2013. Sensitivity and effectiveness of landscape metric scalograms in determining the characteristic scale of a hierarchically structured landscape. Landscape Ecology, 28: 343-363. DOI 10.1007/s10980-012-9837-x.

“A Pilot-scale Demonstration of Reverse Osmosis Unit for Treatment of Coal-bed Methane Produced Water and Its Modeling”

2012-06-07T08:54:00+08:00

Prof. ZHANG Hongxun, Associate Prof. YU zhisheng and LIU Xinchun are responsible for this project funded by the national science and technology major projects. This work presents the first demonstration project in China for treatment of coal-bed methane (CBM) produced water and recycling to provide a research and innovation base for solving the pollution problem of CBM extraction water. The below is on-site photograph of the pilot-scale demonstration with reverse osmosis unit.

The total dissolved solids (TDS) in the CBM produced water are removed to meet the "drinking water standards" and "groundwater quality standards" of China and can be used as drinking water, irrigation water, and livestock watering. The cost for treatment of CBM produced water is also assessed, and the RO technology is an efficient and cost-effective treatment method to remove pollutants.

Furthermore, a model for the RO membrane separation process is developed to describe the quantitative relationship between key physical quantities - membrane length, flow velocity, salt concentration, driving pressure and water recovery rate, and the water recovery restriction equation based on mass balance is developed. This model provides a theoretical support for the RO system design and optimization.

Novel Aerosol Sampler Developed by GUCAS

2012-04-28T18:03:00+08:00

Exposure of atmospheric aerosol is associated with many adverse health impacts, such as asthma, allergy and cardiovascular diseases. Fine particles, also called PM_2.5 due to their aerodynamic diameter are not larger than 2.5 um, are more dangerous because they can deeply arrive at alveolus thus directly induce toxicant to respiratory and circulatory systems. However, ambient aerosol sample collection is usually a long haul because most aerosol samplers are designed with heavy and big outlines, and don’t have adjustable flow rate thus don’t have applicability in different research regions.

A dual-channel aerosol sampler was recently designed and manufactured by Dr. ZHANG Yang in Professor ZHANG YuanXun's Group in the Division of Atmospheric Environmental Sciences, CRE, GUCAS. It is characterized by small volume, slight weight, easy carrying, simple and friendly operation, convenient observation and high precision. The application of advanced single chip microcomputer control and LCD Panel technique greatly optimized its operation interface making its function control and parameter display panel conveniently. The flow rate of each channel is accurately controlled by proportional valve and automatically corrected by pressure and temperature compensating. In addition, this sampler is available to collecting the aerosol sample of TSP, PM₁₀, and PM_2.5 via switching the particle size selector easily. Thus, it is very suitable for field sampling.

This sampler has already been applied in a sampling campaign during and after the 2011 Shenzhen UNIVERSIADE. Results shows that our aerosol sampler has stable and reliable performance.

Operation Panel Display

GUCAS1.0 Aerosol Sampler (Taken in 2011 Shenzhen UNIVERSIADE Campaign)

Effects of Spatial Aggregation of Soil Spatial Information on Watershed Hydrological Modeling

2012-04-26T21:34:00+08:00

LI Runkui, a postdoctoral researcher of CRE major in remote sensing application, studied on the effects of spatial aggregation of soil spatial information on watershed hydrological modeling and fruited his conclusions recently. His findings has been published on Hydrological Processes in a recent issue.

Many researchers have examined the impact of detailed soil spatial information on hydrological modelling due to the fact that such information serves as important input to hydrological modelling, yet is difficult and expensive to obtain. Most research has focused on the effects at single scales; however, the effects in the context of spatial aggregation across different scales are largely missing. This paper examines such effects by comparing the simulated runoffs across scales from watershed models based on two different levels of soil spatial information: the 10-m-resolution soil data derived from the Soil-Land Inference Model (SoLIM) and the 1:24000 scale Soil Survey Geographic (SSURGO) database in the United States. The study was conducted at three different spatial scales: two at different watershed size levels (referred to as full watershed and sub-basin, respectively) and one at the model minimum simulation unit level. A fully distributed hydrologic model (WetSpa) and a semi-distributed model (SWAT) were used to assess the effects. The results show that at the minimum simulation unit level the differences in simulated runoff are large, but the differences gradually decrease as the spatial scale of the simulation units increases. For sub-basins larger than 10 km² in the study area, stream flows simulated by spatially detailed SoLIM soil data do not significantly vary from those by SSURGO. The effects of spatial scale are shown to correlate with aggregation effect of the watershed routing process. The unique findings of this paper provide an important and unified perspective on the different views reported in the literature concerning how spatial detail of soil data affects watershed modelling. Different views result from different scales at which those studies were conducted. In addition, the findings offer a potentially useful basis for selecting details of soil spatial information appropriate for watershed modelling at a given scale.

Difference between R-MAE and RD for different sub-basin sizes, SWAT-simulated water yields: (a) default parameter set; (b) parameter set calibrated with SoLIM; (c) parameter set calibrated with SSURGO

Diversity of Bacteria and Mycobacteria in Biofilms of Two Urban Drinking Water Distribution

2012-04-26T20:28:00+08:00

To give an insight into the bacterial diversity of biofilms from full-scale drinking water distribution systems (DWDSs), the bacterial community compositions of biofilms from two urban DWDSs were determined using a 16S rRNA gene library technique. Meanwhile, the occurrence and diversity of mycobacteria were also analyzed by a Mycobacterium-specific hsp gene assay. The biofilms from the full-scale DWDSs have complex bacterial populations. Proteobacteria was the common and predominant group in all biofilm samples, in agreement with previous reports. The community structures of bacteria at the three sites in the south urban DWDS were significantly different, despite the similar physicochemical properties of portable water. Some abundant and peculiar bacterial phylotypes were noteworthy, including Methylophilus, Massilia, and Planomicrobium, members of which are rarely found in DWDSs and their roles in DWDS biofilms are still unclear. The diversity of Mycobacterium species in biofilm samples was rather low. Mycobacterium arupense and Mycobacterium gordonae were the primary Mycobacterium species in the south and north urban DWDS biofilms, respectively, indicating that M. arupense may be more resistant to chloride than M. gordonae.

Those findings were observed by Dr. LIU Ruyin, assistant professor of CRE, who has spent almost two years on this research. He, as well as his group, will continue their research and are expected to identify some key factors associated with drinking water security.

Phylogenetic analysis of hsp gene sequences of Mycobacterium spp.

Environmental Health Study: How does Household Air Pollution Affect Human Body?

2012-04-25T22:25:00+08:00

Environmental Health Study: How does Household Air Pollution Affect Human Body?

Author: ZHANG YuanXun

Ambient air pollution is associated with impaired vascular health, oxidative stress and systemic inflammation in Children. However, a recent study has demonstrated that increased PM_2.5 (aerosols with aerodynamic diameter not more than 2.5 um) and black carbon (BC) exposures were not associated with higher blood pressure (BP) among children in households cooking with biomass.

Those findings will be published on Epidemiology, a famous journal for epidemiologic research. The associated project, Air Pollution and Its Health Outcomes in Rural Western-China, is cooperated by University of Minnesota (lead by Dr. Jill BAUMGARTNER) and GUCAS (lead by Dr. ZHANG YuanXun), as well as some other scientists from the United States and the United Kingdom. Early in 2006, Dr. BAUMGARTNER and Dr. ZHANG have started their exploration in rural Yunnan. They recruited school-aged children from 180 rural households cooking with biomass in Yunnan, China. The associations between personal PM_2.5 and BC exposures and BP were investigated using one- and two- pollutant multivariate regression models. Interestingly, their new findings do not support their previous study of older women in this setting, showing a positive relationship between PM exposure and BP. How does household air pollution affect human body? Dr. BAUMGARTNER and Dr. ZHANG will continue their collaborations in this field over a span of years, and expected to find more implications.

This international collaboration was supported by the Robert Wood Johnson Foundation, American Philosophical Society and “100-Talents Projects” of CAS.

Measurements of Blood Pressure and Air Pollution Exposures

Research Progress: Dechlorination of p,p'-DDTs coupled with sulfate reduction by novel sulfate-reducing bacterium Clostridium sp. BXM

2012-04-13T18:28:00+08:00

The latest research results supported by NSFC hosted by Prof. HU Zhengyi show that RSC (sulfate-reducing bacterium)-induced natural dechlorination may play an important role in the fate of organochlorines. Those findings has been published on Environmental Pollution recently.

A novel non-dsrAB (without dissimilatory sulfite reductase genes) sulfate-reducing bacterium (SRB) Clostridium sp. BXM was isolated from a paddy soil. Incubation experiments were then performed to investigate the formation of reduced sulfur compounds (RSC) by Clostridium sp. BXM, and RSC-induced dechlorination of p,p'-DDT in medium and soil solution. The RSCs produced were 5.8 mM and 4.5 mM in 28 mM sulfate amended medium and soil solution respectively after 28-day cultivation. The p,p'-DDT dechlorination ratios were 74% and 45.8% for 5.8 mM and 4.5 mM RSCs respectively at 6 hours. The metabolites of p,p'-DDT found in the two reaction systems were identified as p,p'-DDD and p,p'-DDE. The dechlorination pathways of p,p'-DDT to p,p'-DDD and p,p'-DDE were proposed, based on mass balance and dechlorination time-courses. The results indicated that RSC-induced natural dechlorination may play an important role in the fate of organochlorines.

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