Investigating the relationship between ground‐measured LAI and vegetation indices in an alpine meadow,north‐west China

A field campaign was carried out in the alpine meadow of Heihe River Basin, north‐west China on 11–15 July 2002. Several bio‐geophysical parameters such as leaf area index (LAI) were measured according to VALERI sampling procedures within 38 elementary sampling units (ESUs) in the 3 km×3 km ‘VALERI’ site. A quarter scene of Landsat 7 ETM+ with acquisition times close to the field campaign time was atmospherically and geographically corrected. Three kinds of spectral vegetation index maps including NDVI, SR and MSAVI in the sampling area were derived from the corrected ETM+ image. The two sets of LAI data measured with LAI‐2000 and TRAC instrument at the same site were inter‐compared. This is particularly meaningful for assessing the accuracy of LAI measurements. The relationships between the measured LAI and the three kinds of vegetation indices were also investigated. These comparisons found good relationships between the measured LAI and the different vegetation indices in most cases. Among them, NDVI seems the most promising estimator for extraction of LAI for the alpine meadow. In addition, the LAI‐2000 seems to perform better for LAI measurement in the alpine meadow than the TRAC instrument.     

River bed identification for check‐dam engineering using SPOT‐5 image in the HongShiMao watershed of the Loess Plateau,China

The Loess Plateau located in the upper and middle reaches of the Yellow River is the most serious soil erosion region in China. Check‐dams (also known as silt trappers) have been demonstrated to be an effective soil and water conservation measure in the region and a traditional workflow for check‐dam planning and engineering is time‐consuming and cannot meet the requirement of efficiently locating optimal check‐dam sites. Fine resolution satellite imagery and analysis can play a key role in screening and determining special river bed segments that can be candidates for check‐dam sites. In this research, HongShiMao watershed of the Loess Plateau was selected as our case study area. Based on a detailed analysis of spectral characteristics of a fused SPOT‐5 imagery for dominant land covers and geomorphological features of a constructed digital elevation model, the river bed of key channels within the watershed was automatically identified. Then we selected four check‐dam sites on the river bed and four orientations of a check‐dam site to explore locational and directional profiles. Such profile information is most useful for locating optimal check‐dam sites in a cost‐effective manner and reducing associated expenditures surrounding check‐dam constructions. This remote sensing application demonstrates the latest spatial information technologies such as fine resolution satellite imagery and 3D geospatial visualisation hold promises for changing traditional workflows and advancing scientific decision making of environmental conservation projects.     

Estimate of net primary productivity of aquatic vegetation of the Amazon floodplain using Radarsat and JERS‐1

Synthetic aperture radar images, combined with field measurements, were used to estimate net primary productivity (NPP) of aquatic vegetation in the lower Amazon. Input data for a NPP model are (i) the total biomass of aquatic vegetation, determined by radar imagery and field measurements and (ii) the area occupied by aquatic vegetation, determined from radar imagery. After correction for monthly biomass losses, the NPP of one growth cycle of aquatic vegetation was calculated in the image domain. The total net primary productivity of Hymenachne amplexicaules, the dominant aquatic vegetation in the area, was on average 19×10¹¹ g C yr^?1 for the entire area. Spatially, lower values of produced organic carbon (<900 g C m^?2 yr^?1) are confined to regions where the plants developed only in the beginning of the rising phase of the hydrological cycle. In general, values are higher (>5000 g C m^?2 yr^?1) in areas closer to the Amazon River where the availability and influence of nutrient‐rich water is greater.     

Mapping mineralogical alteration using principal‐component analysis and matched filter processing in the Takab area,north‐west Iran,from ASTER data

The Takab area, located in north‐west Iran, is an important gold mineralized region with a long history of gold mining. The gold is associated with toxic metals/metalloids. In this study, Advanced Space Borne Thermal Emission and Reflection Radiometer data are evaluated for mapping gold and base‐metal mineralization through alteration mapping. Two different methods are used for argillic and silicic alteration mapping: selective principal‐component analysis and matched filter processing (MF). Running a selective principal‐component analysis using the main spectral characteristics of key alteration minerals enhanced the altered areas in PC2. MF using spectral library and laboratory spectra of the study area samples gave similar results. However, MF, using the image reference spectra from principal component (PC) images, produced the best results and indicated the advantage of using image spectra rather than library spectra in spectral mapping techniques. It seems that argillic alteration is more effective than silicic alteration for exploration purposes. It is suggested that alteration mapping can also be used to delineate areas contaminated by potentially toxic metals.     

Coral spawn and bathymetric slicks in Synthetic Aperture Radar (SAR) data from the Timor Sea,north‐west Australia

Annular‐ to crescent‐shaped low backscatter SAR slicks over carbonate reefs and shoals in the Timor Sea that exhibit ‘feathering’, and within the coral spawning period for the region, are interpreted to be caused by a coral spawn event. This represents the first time that such an event has been interpreted through satellite remote sensing. Additionally, ocean current data and detailed swath bathymetry of the sea floor to the south‐east of the coral spawn slicks suggest that elongate repeating slicks in this area are related to current flow over submarine channels. Assessment of these slicks in association with ancillary data, such as bathymetry, current velocities, weather, and timing of SAR acquisition allow a more robust interpretation of their origins. Through differentiating coral spawn and bathymetric slicks from oil and other biological slicks in shallow carbonate systems, such as the Timor Sea, petroleum and environmental assessments for these areas can be improved.     

Vegetation cover changes and their relationship to climate variation in the source region of the Yellow River,China, 1990–2000

The change history of vegetation cover and its relations to growing season precipitation (GSP) and average growing season temperature (AGST) in the source region of the Yellow River (SRYR) during 1990–2000 was retrieved based on the 1 km Advanced Very High‐Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) data and meteorological records. The results show an overall warming and drying trend of the climate and a common degradation tendency of the ecosystem, with a greening trend in higher rugged regions. The pixel‐by‐pixel correlations between NDVI and climate factors indicate that a decrease in GSP mainly affects ecosystems with low precipitation and worse vegetation condition, and superimposes on the effects of increasing AGST which further deteriorate the climate background of these ecosystems. However, the positive correlations between AGST and NDVI in some higher/rugged regions suggest that the raising temperature can ameliorate vegetation growth conditions in these areas. Comparison and combination of the results of three change detection algorithms, i.e. post‐classification comparison (PCC), principal components analysis (PCA) and a newly developed multi‐temporal image difference (MTID) method, show that the integration of different methods can give a more comprehensive understanding of vegetation changes than any single method.     

Relationships between tree growth and NDVI of grassland in the semi‐arid grassland of north China

This study explores the relationships between the Normalized Difference Vegetation Index (NDVI), recorded above‐ground grass biomass and tree‐ring width index of relict Meyer spruce (Picea meyeri Rehd. et Wils.) forest in the typical steppe, north China. The average NDVI in May, June and August derived from an area of 0.5°×0.5° shows a large correlation with measured above‐ground production, indicating that NDVI can reflect the approximate variability of above‐ground biomass in the typical steppe. The integrated NDVI from 20 May to 10 July also exhibits high agreement with tree‐ring width series of Meyer spruce from 1982 to 1994, which is attributed to their common response to precipitation in the previous August–October and current May. This study provides a basis for linking remotely sensed NDVI of grassland to tree growth in semi‐arid grassland.     

ASTER‐derived emissivity and coal‐fire related surface temperature anomaly: a case study in Wuda,north China

Subsurface and surface coal fires form serious environmental, economic and safety problems in coal‐producing countries like China and India. Remote sensing offers the possibility of detecting and studying thermal anomalies due to coal fires. Emissivity plays an important role in determining the surface temperature of a body using remotely sensed data. In the present study an attempt is made to use satellite‐derived emissivity to estimate the surface temperature in Wuda, north China. With the use of multispectral thermal Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data (five bands in 8.125–11.65 µm region) in combination with a Temperature/Emissivity Separation (TES) algorithm, the anomalous pixels due to coal fires can be extracted from the background to achieve a qualitative study of coal fires. In the present study, during night‐time overpass of ASTER, satellite images have been recorded and simultaneous field measurements were collected. These field measurements were used to process the satellite thermal data and to validate the results obtained. Using the TES approach, satellite‐based temperature corresponded well with actual field measurements at selected locations.     

The Spatial Transformation and Hotspot Detection of Land Use and Cover in Arid Basin：A Case of the Middle Reaches of Heihe River

Based on the data of land use/cover change in the middle reaches of the Heihe River in 1987,2001 and 2016,with the support of remote sensing technology,the Markov transfer matrix and land use dynamic estimation model were used to simulate the land use transformation direction and spatial distribution characteristics,detect hotspots of land use/cover change,analyze the relevant driving factors,and propose the countermeasures for development bottlenecks during the study period in the middle reaches of the Heihe River between 1987~2001 and 2001~2016.Its main findings are as follows：the main changes of land use in the middle reaches of Heihe River as the land of human activities gradually increasing,the ecological land decreasing continuously.The areas with sharp changes in land use are mainly concentrated on both sides of the river,the types of transformation are mainly in the conversion of waters into grassland,grassland into cultivated land,and the unused land to construction land;The scope of land use transformation in the study area have obvious spatial differences,the frequency and expansion are significantly higher than the previous period;as a whole,the hot region are located in the oasis area of agriculture in Zhangye,but the early hot region is more dispersed,small,no benefit,the later is concentrated,and has more central tendency in the larger space.     

Spatial–temporal dynamics of gross primary productivity,evapotranspiration, and water-use efficiency in the terrestrial ecosystems of the Yangtze River Delta region and their relations to climatic variables

Moderate Resolution Imaging Spectroradiometer (MODIS) products and climate data collected from meteorological stations were used to characterize the spatial–temporal dynamics of gross primary productivity (GPP), evapotranspiration (ET), and water-use efficiency (WUE) in the Yangtze River Delta (YRD) region and the response of these three variables to meteorological factors. The seasonal patterns of GPP and WUE showed a bimodal distribution, with their peak values occurring in May and August, and April and October, respectively. By contrast, the seasonal variation of ET presented a unimodal pattern with its maximum in July or August. The spatial distribution of ET and GPP was similar to higher values occurring in the south. From 2001 to 2012, GPP in the eastern YRD decreased, while GPP in the western part increased. In comparison, over the 12 years, ET in the northern part of YRD decreased, while ET in the southern part increased. The spatial distribution and spatial variation of WUE were both similar to those of GPP. This implies that the changes in WUE are primarily controlled by the variations in GPP. The annual average WUE over vegetation types followed the order of: evergreen broadleaf forest (1.95 g C kg^?1 H₂O) > deciduous broadleaf forest (1.87 g C kg^?1 H₂O) > evergreen needle leaf forest (1.70 g C kg^?1 H₂O) > deciduous needle leaf forest (1.68 g C kg^?1 H₂O) > grassland (1.66 g C kg^?1 H₂O) > cropland (1.61 g C kg^?1 H₂O). Both GPP and ET increased with increasing annual mean temperature (T_a) and annual mean precipitation across all of the plant function types. WUE decreased as vapour pressure deficit (VPD) increased in all of the biomes. Interestingly, the relationship between WUE and VPD was the most significant in broadleaf forest. Whether this phenomenon is universal should be investigated in future studies.     

Use of RADARSAT‐1 data and a digital elevation model to assess flood damage and improve rice production in the lower part of the Chi River Basin,Thailand

In Thailand, flooding due to seasonal monsoon conditions frequently destroys a substantial amount of rice production, the most important agricultural activity of the country. Taking the 2001 monsoon flooding that hit the Lower Chi River Basin as an example, we developed a new method for accurately assessing damage to flood‐affected paddies. A RADARSAT‐1 image acquired during peak flooding was combined with a 30‐m digital elevation model (DEM) to develop a ‘flood‐level‐determination’ algorithm for estimating floodwater depth. Based on the elongation capability of the rice varieties, a water depth of 80 cm was used to separate ‘non‐damaged’ from ‘damaged’ paddy areas, indicating that about 60% of the paddy fields in the flooded areas were non‐damaged paddies. To minimize the loss of rice and maximize farmers' incomes, a map of rice varieties appropriate for the damaged paddy areas was produced, combining the flood‐affected paddy map with the flood frequency map. Our results demonstrate the potential of using single‐date RADARSAT‐1 data and a DEM to provide accurate and economic means of assessing flood damage to rice fields that can be used to improve rice production.     

DEM‐optical‐radar data integration for palaeohydrological mapping in the northern Darfur,Sudan: implication for groundwater exploration

North‐western Sudan, as a part of the eastern Sahara, is among the driest places on earth. However, the region underwent drastic climatic changes through the alternation of dry and wet conditions in the past. During humid phases, when the rain was plentiful over a prolonged time period, the surface was veined by rivers and dotted by large lakes. The new Shuttle Radar Topography Mission data (SRTM ～90 m) revealed a large endorheic drainage basin, which is centred by a large terminal palaeolake, in the northern Darfur State. The use of GIS methods allowed the delineation of the drainage basin and its associated palaeorivers. The SRTM data along with the Landsat (ETM+) and Radarsat‐1 images corroborate the presence of segments of palaeoshorelines associated with the palaeolake highstands. These constitute a convincing argument of the long‐term existence of a possible pre‐Holocene large water body in the region in the past. The remains of the highest palaeoshoreline have a constant altitude of 573±3 m asl. At its maximum extent, the mega Lake occupied an area of about 30 750 km² (the same size as the Great Bear Lake, Canada's largest lake), which would have contained approximately 2530 km³ of water. This, ancestral lake, which we named the Northern Darfur Megalake (ND Megalake), represents indisputable evidence of the past pluvial conditions in the eastern Sahara. The discovered palaeoshorelines will have significant consequences for improving our knowledge of continental climate change and regional palaeohydorology, and should be taken into consideration in studies of past human habitation in the region. Much of the water carried by the Northern Darfur palaeorivers and the ND Megalake would have percolated into the underlying rocks feeding the Nubian Sandston aquifer. These findings show that the used approach of space‐data integration can help significantly in the groundwater exploration efforts in the Darfur region, where freshwater access is essential for refugee survival, and can be successfully adopted in other parts of Sudan and arid lands in general.     

Mapping the concentrations of total suspended matter in Lake Taihu,China, using Landsat‐5 TM data

Remote sensing techniques can be used to estimate and map the concentrations of suspended matter in inland water, providing both spatial and temporal information. Although an empirical approach to remote sensing of inland waters has been carried out frequently, satellite imagery has not been incorporated into routine lake monitoring programmes due in part to the lack of a standard prediction equation with multi‐temporal capacity for suspended matter. Empirical and physical models must be developed for each lake and its corresponding turbidity composition if they are to be compared over time, or with other bodies of water.

This study aimed to develop and apply multi‐temporal models to estimate and map the concentrations of total suspended matter (TSM) in Lake Taihu, China. Two Landsat‐5 Thematic Mapper (TM) images and nearly contemporaneous in situ measurements of TSM were used. A modified Dark‐Object Subtraction (DOS) method was used, and appeared to be adequate for atmospheric correction. The relationships were examined between TSM concentrations and atmospherically corrected TM band and band ratios. Results of this study show that the ratio TM4/TM1 has a strong relationship with TSM concentrations for lake waters with relatively low concentrations of phytoplankton algae. However, TM3 provided a strong predictive relationship with TSM concentrations despite varied water quality conditions. Different prediction models were developed and compared using multiple regression analysis. The Akaike Information Criteria (AIC) approach was used to choose the best models. The validation of the multi‐temporal capability of the best models indicated that it is feasible to apply the linear regression model using TM3 to estimate TSM concentrations across time in Lake Taihu, even if no in situ data were available.     

Broad‐scale increase in NPP quantified for the African Sahel, 1982–1999

In association with a recently discovered greening trend in the Sahel, several interesting new perspectives have appeared in the literature regarding its climate and ecology. In this Letter, satellite data from 1982 to 1999 and a light use efficiency model are used to map net primary production (NPP) increases throughout the Sahel (total area of 1.13×10¹³ m²). A patchy, east‐west band of increasing NPP is identified, with several hotspots showing large increases. The total rate of NPP change for the Sahel is estimated to be 51.0 Mt C year^?1 over the 18‐year period, yielding an absolute net gain of 918.0 Mt C. This increase is associated with a decrease in the inter‐annual variability of NPP for the 1990s compared to the 1980s. These results lay the groundwork for untangling the effects of direct, localised human impact and climate forcing on land cover by conducting model intercomparison experiments, contextualizing the role the Sahel may play in the tropical carbon cycle, and for reducing the uncertainty regarding Sahelian carbon sequestration.     

Classifying depth‐layered geological structures on Landsat TM images by gravity data: a case study of the western slope of Songliao Basin,northeast China

Geological structures on remotely sensed images, Landsat Thematic Mapper (TM) images in this case, can be classified by quantitative depth information on the basis of the comparison of results from Landsat TM images and geophysical data. Although the lineaments with different depths can be visually interpreted together on Landsat TM images, the depth information and geological significance of these lineaments are however hard to obtain solely from the Landsat TM images of a study area under a thick cover, and it is of much importance for hydrocarbon exploration in the Western Slope Belt of Songliao Basin, northeast China. During the present study, the 3‐dimensional field source information, including location and depth information, is derived from 3‐dimensional Euler deconvolution of gravity data in particular. As an example, it may be quantitatively classified into four groups of depth range: <100?m, 100–500?m, 500–1000?m, >1000?m. It is then superimposed onto the lineaments map from Landsat TM images using a geographical information system (GIS). With a comprehensive analysis of the superimposed maps, we obtain validation and quantitative depth information of the geological structures delineated on the Landsat TM images. Four depth‐layered maps of geological structures with different depths are presented here. It is concluded that the number of structures with depth greater than 1000?m on the Landsat TM images is fewer than those at the other three depth ranges. The detection of geological structures on Landsat TM images attributed to depth information derived from the geophysical data may also be possible by this approach.     

The use of digital aerial photography and CORINE‐derived methodology for monitoring recent and historic changes in land cover near UK Natura 2000 sites for the BIOPRESS project

BIOPRESS – Linking pan‐European land cover change to pressures on biodiversity – is a European Community Framework 5 project, which aims to develop a standardised product that will link quantified historical (1950–2000) land cover change to pressures on biodiversity. It exploits archived historic and recent aerial photographs (a data source that has remained consistent over the last 60 years) to assess land cover change around Natura 2000 sites within 30×30 km windows and 15×2 km transects. The CORINE (Coordination of Information on the Environment) land cover mapping methodology has been adapted for use with aerial photographs. Sample sites are mapped to CORINE Land Cover (CLC) classes, and then backdated to assess change. Results from eight UK transects (and associated windows) are presented. Changes in land cover classes are interpreted as pressures: urbanisation, intensification, abandonment, afforestation, deforestation and drainage. Urbanisation was the major pressure in all but two transects (both in the uplands), and intensification was of similar importance in most transects. Afforestation was a significant pressure in two transects. In six out of the eight transects, annual change was greater in the 1990–2000 period than in the 1950–1990 period. The methodology has been demonstrated to provide quantitative results of long‐term land cover change in the UK rural landscape at a spatial scale that is relevant to management decisions. The methods are transferable and applicable to a wide range of landscape studies.     

Assessment of land‐cover changes related to shrimp aquaculture using remote sensing data: a case study in the Giao Thuy District,Vietnam

Shrimp culture is a sector of aquaculture that has a high potential for poverty alleviation and rural development in Vietnam. However, the development of this activity induces changes that potentially have negative impacts on the environment, one of which is wetland deterioration. This paper describes the use of a proposed change detection methodology in the assessment of mangrove forest alterations caused by aquaculture development, as well as the effectiveness of the measures taken to mitigate deforestation in the district of Giao Thuy, Vietnam, between 1986, 1992 and 2001. Geometric and radiometric corrections were applied to Landsat images prior to identifying changes through comparison of unsupervised classifications. Changes were afterwards validated using a thresholding method based on Tasselled Cap feature image differencing and a rule‐based feature selection matrix. The matrix is used to identify the feature that is most efficient at detecting the presence of change between given land‐cover classes. The proposed approach aims to minimize commission errors in the post‐classification change detection process. The results suggest that 63% of mangrove areas apparent in 1986 had been replaced by shrimp ponds in 2001. Between 1986 and 1992, 440 ha of adult mangrove trees had disappeared, whereas the mangrove extent increased by 441 ha between 1992 and 2001. This recovery is attributed to reforestation projects and conservation efforts that promoted natural regeneration.     

A monitoring indicator system for remote sensing of grassland vegetation growth and suitability evaluation – a case study of the Xilingol Grassland in Inner Mongolia,China

Grassland vegetation growth directly reflects plant growth conditions, and growth processes are an important component of ecological status assessments of grasslands and can provide timely guidance for agricultural production. In this study, the Xilingol Grassland in Inner Mongolia was used as the study area, and a monitoring indicator system for the remote sensing of grassland vegetation growth was established based on 16 days of Moderate Resolution Imaging Spectroradiometer (MODIS) data and ground sampling data, which were used to assess the suitability of the indicator system. A monitoring indicator system for the remote sensing of grassland vegetation that included the modified growth index (MGI)-normalized difference vegetation index (NDVI), MGI-enhanced vegetation index (EVI), growth index (GI)-NDVI, and GI-EVI was established by using the year 2000 as the base year, two vegetation indices and difference and normalized difference methods. A model for estimating the ground growth (g) was then constructed by using expert opinion scoring and the Analytic Hierarchy Process (AHP) to determine the weights of vegetation coverage (c), height (h), and yield (y) in the ground plots, with the model calculated as follows: g = 0.2543c + 0.1848 h + 0.5609y. Additionally, the ground growth value was calculated according to the ground growth model, and the values obtained from the remote-sensing indicators in the corresponding region were subjected to a correlation analysis based on this partition. The remote-sensing growth indices suitable for temperate steppe, meadow steppe, and desert steppe regions were GI-EVI, MGI-NDVI, and GI-NDVI, respectively. Finally, vegetation growth in the Xilingol Grassland was evaluated using the optimal remote-sensing GI for each area, and the results indicated that the areas with the greatest growth improvement occurred in the temperate steppe region followed by the meadow steppe region, whereas vegetation growth improvement was insignificant in the desert steppe region. The results of this study have important significance for the economic development and ecological environmental improvement of pastoral and semi-pastoral regions and can be used to determine the optimal use and scientific management of grasslands.