Zhangyu Dong

Quantifying changes in multiple ecosystem services during 1992–2012 in the Sanjiang Plain of China

Rapid and periodic assessment of the impact of land cover changes on ecosystem services at regional levels is essential to understanding services and sustainability of ecosystems. This study focused on quantifying and assessing changes of multiple ecosystem services in the Sanjiang Plain of China as a result of land cover changes over the period of 1992-2012. This region is important for its large area of natural wetlands and intensive agriculture. The ecosystem services that were assessed for this region included its regulating services (water yield and ecosystem carbon stocks), supporting services (suitable waterbird habitats), and provisioning services (food production), and the approach to the assessment was composed of the surface energy balance algorithms for land (SEBAL), soil survey re-sampling method and an empirical waterbird habitat suitability model. This large scale and integrated investigation represents the first systematic evaluation on the status of ecosystem carbon stocks in the Sanjiang Plain in addition to the development of an effective model for analysis of waterbird habitat suitability with the use of both remote sensing and geographic information systems (GIS). More importantly, the result from this study has confirmed trade-offs between ecosystem services and negative consequences to environment in this region. The trade-offs were typically manifested by increased water yield and significantly grown food production, which is in contrast with significant losses in ecosystem carbon stocks (-14%) and suitable waterbird habitats (-23%) mainly due to the conversion of land cover from wetland to farmland. This finding implies that land use planning and policy making for this economically important region should take ecosystem service losses into account in order to preserve its natural ecosystems in the best interest of society.

SPOT5 multi-spectral (MS) and panchromatic (PAN) image fusion using an improved wavelet method based on local algorithm

Remote sensing image fusion is an effective way to extract a large volume of data from multi-source images. However, traditional image fusion methods cannot meet the requirements of applications because they can lose spatial information or distort spectral characteristics. In this paper, a new wavelet method based on a local algorithm is presented. The proposed method fuses multi-spectral (MS) and panchromatic (PAN) images to improve spatial information and preserve spectral characteristics. The main advantage of the new fusion method is the exploitation of the dependency between neighboring pixels. SPOT5 MS and PAN images were employed to execute the fusion methods. To compare with the new method, the principal component analysis (PCA), wavelet transformation, and PCA-based wavelet (PCA+W) image fusion methods were selected. Qualitative and quantitative analyses and classification accuracy assessment were conducted to evaluate the performance of the fusion methods. The results demonstrate that the new wavelet method based on a local algorithm is better than traditional image fusion methods. The new fusion method can achieve a wide range of balance between high spatial resolution retention and spectral characteristic preservation; thus, the new method is suitable for different applications.

Monitoring Loss and Recovery of Salt Marshes in the Liao River Delta, China

ABSTRACT Jia, M.; Wang, Z.; Liu, D.; Ren, C.; Tang, X., and Dong, Z., 2015. Monitoring loss and recovery of salt marsh in the Liao River Delta, China. Coastal salt marsh plays an important role in the aquatic food web and the export of nutrients to coastal waters. The salt marshes in the Liao River Delta of China, dominated by Suaeda heteroptera, experienced a dramatic loss in the 1990s and then recovered in the 2000s. This study investigates these changes of salt marsh using a time series of Landsat Thematic Mapper (TM) images acquired in 1988, 1995, 2000, 2004, 2007, and 2009. The classification tree method was used on these TM images to extract S. heteroptera, and an interactive self-organizing data analysis algorithm was used to determine other land cover types. The conversions between salt marsh and other land cover types were described with conversion matrices. The classification results show that, during 1998–2004, salt marsh decreased dramatically at an average rate of 662.68 ha/y. However, during the period 2004–2009, salt marsh recovered gradually at a rate of 115.51 ha/y. The conversion matrix indicates that, from 1988 to 2004, a large area of former salt marsh was directly replaced by man-made landscape types, such as reed field (5111 ha), aquaculture pond (2655 ha), reservoir (1720 ha), and paddy field (729 ha). In contrast, the result for the period from 2004 to 2009 shows that salt marshes were recovered by the conversion of some areas of former barren beaches and river back to salt marsh. Driving forces analysis suggests that salt marsh dynamics were mainly caused by human activities, with the secondary drivers being climatic warming and dry conditions.

Influence of vegetation phenology on modelling carbon fluxes in temperate deciduous forest by exclusive use of MODIS time-series data

Understanding the influence of vegetation phenology on modelling primary productivity, biomass, and natural carbon dynamics, as well as the underlying mechanisms, is crucial for assessing the vulnerability of terrestrial carbon pools under future changing climate conditions. Considering that the component fluxes of carbon sequestration, gross primary production (GPP) and ecosystem respiration (Re), are dominant alternately during the course of the year, here we propose a new model for estimating the carbon sequestration of temperate deciduous forest exclusively based on Moderate Resolution Imaging Spectroradiometer (MODIS) time-series data, including land-surface temperature (LST), Terra night-time LST (LST′), enhanced vegetation index (EVI), land-surface water index (LSWI), fraction of absorbed photosynthetically active radiation (FPAR), and leaf area index (LAI). This study aims to reveal the main environmental control variables that contribute to the net ecosystem exchange (NEE) variations and to develop an improved model that accurately predicts NEE according to the growing and dormant seasons. The seasonality information was extracted from time series of MODIS NDVI data based on nonlinear least squares fits of asymmetric Gaussian model functions in the computer program, TIMESAT. The results suggest that the improved model could provide substantially better NEE estimates and well reflect the seasonal dynamics of the temperate deciduous forest. In addition, because both ecosystem photosynthesis and respiration are powerful during the growing season, all variables are strongly correlated with NEE at the 0.01 p-level, whereas only some parameters (temperature and water) are significant during the non-growing period due to dominant respiration and limited photosynthesis.

A Method on Decreasing Magnetic Moment of Halbach Cylinder Magnets

Halbach cylinder magnet has been widely used as field source due to its great features. However, the existence of the magnetic moment in the Halbach cylinder magnet limits its application in some fields. To eliminate the dipole moment of the whole magnet system, a method is presented here that incorporates permanent magnets to provide an opposite dipole moment. Both the FEM simulation and the experimental results demonstrate that this method is effective.

Changes in habitat suitability for waterbirds of the Momoge Nature Reserve of China during 1990–2014

AbstractThere is increasing empirical evidence that changes in habitat quality play an important role in determining species distributions and biodiversity. However, most research has focused on habitat quality, and we still lack approaches for tracking habitat quality dynamics. In this paper, by establishing qualitative and quantitative relationships between waterbird populations and key habitat indicators such as water abundance, food, shelter conditions and disturbance, we developed an object-oriented classification method, in conjunction with a geographic information systems (GIS) based centroid moving method, to assess habitat suitability dynamics for waterbirds at the Momoge Nature Reserve, China. Our results showed that habitat suitability improved during 1990–2000 and declined during 2000– 2014. Habitats with very good and good grades increased by 71.47 km2 (4.88%) during 1990–2000 and decreased by 200.66 km2 (13.78%) during 2000–2014. The habitat area with a good grade moved to the north, while t...

High Field Superconducting Magnet Technologies for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) has become one of the most powerful tools in modern medical diagnosis and interventional therapy. It can achieve very fast scanning due to the synchronization in time and space under the high field with high homogeneity. High field with high stability in time can improve the ratio of signal to noise and the imaging resolution. It has become an important diagnostic tool in the early stages of cancer, and the evaluation of the efficacy of treatment and high-risk surgery, neuroscience, and molecular imaging. On the other hand, in recent years, the development of openness in high field magnets can combine the MRI with positron emission tomography and/or accelerator, which contributes to form more excellent medical diagnosis tools. The high-field superconducting has been widely used in medical imaging. The superconducting magnet technology depends on the development of material and cryogenic technology. In this paper, the superconducting MRI systems applied in the medical diagnosis and interventional therapy in China were reviewed.

Coastline Changes in Hangzhou Bay Based on Object-oriented Method Using Multi-source Remote Sensing Data

The coastline is defined as the line of contact between land and a body of water.Coastline change detection is critical issues for coastal resource management,coastal environmental protection,and sustainable development and planning.Changes of coastline may be caused by natural processes and/or human activities.Over the past 30 years,the coastal sites in Hangzhou Bay have been under an intensive restraint associated with population growth and economic development.This study introduced object-oriented classification method to monitor coastline changes in Hangzhou Bay using multi-source remote sensing data,i.e.,Landsat Multispectral Scanner(MSS) image in 1983,Landsat Thematic Mapper(TM) image in 1993,Landsat Enhanced Thematic Mapper Plus(ETM+) image in 2002,and Environment Satellite Charge Coupled Device(CCD) image in 2011.Results showed that,from 1983 to 1993,there was 60.2 km northern coastline moved landward with the maximum distance of 0.6 km and a lost area of 23.5 km2,because of the coastal erosion.And from 1993 to 2011,the northern coastline moved seaward because of land reclamation and construction.From 1993 to 2002,this part of coastline moved seaward with the maximum distance of 3.6 km and 42.5 km2 filled up areas.From 2002 to 2011,it moved seaward with the maximum distance of 2.7km and 61.0 km2 filled up areas.From 1983 to 1993,natural processes were the main reasons for northern coastline recession.During the study periods,southern coastline of Hangzhou Bay moved seaward caused by sedimentation and land reclamation.From 1983 to 1993,1993 to 2002,and 2002 to 2011,this coastline moved seaward with the maximum distance of 1.8km,2.7 km and 5.1 km,respectively,and with area of 34.3 km2,230.2 km2 and 331.7km2 sea surfaces turned into mainland,respectively.Southern coastline moved seaward was the result of natural processes and human activities.From 1983 to 2011,the filled up areas were growing faster and larger.The result of this study can provide valuable information for Hangzhou Bay coastline dynamics and may assistant to the coastal land management and sustainable development and planning.