Utility of Landsat 7 satellite data for continued monitoring of forest cover change in protected areas in Southeast Asia

Satellite instruments, particularly the Landsat TM (Thematic Mapper) and ETM+ (Enhanced Thematic Mapper Plus) series of sensors, are important tools in the interdisciplinary study of tropical forests that are increasingly integrated into studies that monitor changes in vegetation cover within tropical forests and tropical protected areas, and also applied with other types of data to investigate the drivers of land cover change. However, further advances in the use of Landsat to study and monitor tropical forests and protected areas are threatened by the scan line corrector failure on the ETM+ sensor, as well as uncertainty about the continuity of the Landsat mission. Given these problems, this paper illustrates how ETM+ data were used in an interdisciplinary study that effectively monitored forest cover change in Gunung Palung National Park in West Kalimantan, Indonesian Borneo. Following 31 May 2003, when the ETM+ sensor's scan line corrector failed, we analysed how this failure impedes our ability to perform a similar study from this date onwards. This analysis uses six simulated post-scan line corrector failure (SLC-off) images and reveals that data gaps caused by SLC-off introduce maximum errors of 1.47 per cent and 4.04 per cent in estimates of forest cover and rates of forest loss, respectively. The analysis also demonstrates how SLC-off has transformed ETM+ data from a complete inventory dataset to a statistical sample with variable sample fraction, and notes how this data loss will confound the use of Landsat data to model land cover change in a spatially explicit manner. We discuss potential limited uses of SLC-off data and suggest alternative sensors that may provide essential remotely sensed data for monitoring tropical forests in Southeast Asia.     

Determining hydraulic resistance in gravel‐bed rivers from the dynamics of their water surfaces

Traditionally, approaches to account for the effect of the boundary roughness of a gravel‐bed river have used a grain‐size index of the bed surface as a surrogate for hydraulic resistance. The use of a single grain‐size does not take into account the spatial heterogeneity in the bed surface and how this heterogeneity imparts resistance on the flow, nor the way in which this relationship changes with variables such as flow stage. A new technique to remotely quantify hydraulic resistance is proposed. It is based on measuring the dynamics of a river's water surface and relating this to the actual hydraulic resistance created by a rough sediment boundary. The water surface dynamics are measured using a new acoustic technique, grazing angle sound propagation (GRASP). This proposed method to measure hydraulic resistance is based on a greater degree of physical reasoning, and this is discussed in the letter. By measuring acoustically the temporal dynamics of turbulent water surfaces over a water‐worked gravel bed in a laboratory flume, a dependency is demonstrated between the temporal variation in the reflected acoustic pressure and measured hydraulic resistance. It is shown that the standard deviation in acoustic pressure decreases with increasing hydraulic resistance. This is shown to apply for a range of relative submergences and bed slopes that are typical of gravel‐bed rivers. This remote sensing technique is both rapid and inexpensive, and has the potential to be applied to natural river channels and to other environmental turbulent flows, such as overland flows. A whole new class of low‐cost, remote and non‐intrusive instruments could be developed as a result and used in a wide range of hydraulic and hydrological applications. Copyright © 2006 John Wiley & Sons, Ltd.     

Anharmonicity of inner-OH stretching modes in hydrous phyllosilicates: assessment from first-principles frozen-phonon calculations

The theoretical anharmonicity of the inner-OH stretching modes of kaolinite and lizardite is determined using a frozen-phonon approach. The anharmonicity parameter, defined as the difference between half the first overtone frequency and the frequency of the fundamental transition, is −95 and −92 cm⁻¹ for kaolinite and lizardite, respectively. These values are consistent with the experimental measurements. The very good agreement usually observed between harmonic calculations of vibrational frequencies at the density functional theory (DFT) level, using the generalized gradient approximation (GGA), and experimental positions of vibrational bands results from the fortuitous, but almost exact, cancelation of two types of errors. One is related to the GGA approximation and the other to the neglect of anharmonicity.     

Does hydrological connectivity improve modelling of coarse sediment delivery in upland environments?

Modelling the delivery of landslide-generated sediment to channel networks is challenging due to uncertainty in the magnitude–frequency distribution of failures connected to the channel network. Here, we investigate a simplified treatment of hydrological connectivity as a means for improving identification of coarse sediment delivery to upland rivers. Sediment generation from hillslopes and channel banks and its delivery to the channel network are modelled based on a modified form of SHALSTAB coupled to a network index version of TOPMODEL. The network index treatment has two important hydrological effects: (a) it only allows saturated areas to connect to the hydrological network when there is full saturation along the associated flow path; and (2) overland flow associated with unconnected but saturated zones is assumed to remain within the catchment and to contribute to a reduction in the catchment-averaged saturation deficit. We use this hydrological treatment to restrict sediment delivery to situations where there is surface hydrological connection (i.e. saturation) along the complete flow path that connects failure areas to the drainage network. This represents an extreme restriction on the possibility of connected failure as it does not allow for failed material to connect if failures are associated with partial saturation or where delivery involves runout across areas where hydrological connection is not maintained. The impact of this restriction is assessed by comparing model predictions with field mapping of connected failures and data from continuously recording coarse sediment sensors, for two storm events. The hydrological connection requirement restricted connected failures to zones closer to the drainage network and resulted in a better level of agreement with the field mapped failures. Simulations suggested that in the study catchment the majority of sediment inputs occur from hydrologically-connected areas close to the channel network during moderate sized rainstorms that occur relatively frequently.     

Examining the potential of high sampling resolution OSL dating of Chinese loess

Detailed analysis of the depositional characteristics of Chinese loess is required to determine the nature of the paleoclimate record preserved in these extensive sediments. High sampling resolution optically stimulated luminescence (OSL) dating has the potential to facilitate such an analysis. However, high-resolution dating is extremely time consuming and therefore of limited practical applicability. This study assesses the luminescence characteristics of loess from three sections on the Chinese Loess Plateau in an attempt to identify methods of increasing sample throughput without compromising data quality. Using the single-aliquot regenerative-dose technique, samples yield internally consistent results. However, dose recovery data indicate that care is required in selecting preheating regimes for different sections. The standardized growth curve approach was tested and found to be applicable within, but not between, sites. Nonetheless, the use of standardized growth curves offers increases in sample throughput that will allow more routine high-resolution dating of Chinese loess. High-resolution dose rates calculated using inductively coupled plasma (ICP) methods show relative homogeneity of radioisotope concentrations and are comparable to lower resolution field gamma-spectrometry measurements. Consequently, high-resolution OSL dating has great potential to elucidate the depositional characteristics of Chinese loess and facilitate more precise use of the paleoclimatic information it preserves.     

Measuring streambank erosion due to ground water seepage: correlation to bank pore water pressure,precipitation and stream stage

Limited information exists on one of the mechanisms governing sediment input to streams: streambank erosion by ground water seepage. The objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow/erosion with precipitation, stream stage and soil pore water pressure. The streambank site was located in Northern Mississippi in the Goodwin Creek watershed. Soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity (K_s) with depth, but differences between lateral K_s of a concretion layer and the vertical K_s of the underlying layers contributed to the propensity for lateral flow. Goodwin Creek seeps were not similar to other seeps reported in the literature, in that eroded sediment originated from layers underneath the primary seepage layer. Subsurface flow and sediment load, quantified using 50 cm wide collection pans, were dependent on the type of seep: intermittent low‐flow (LF) seeps (flow rates typically less than 0·05 L min^?1), persistent high‐flow (HF) seeps (average flow rate of 0·39 L min^?1) and buried seeps, which eroded unconsolidated bank material from previous bank failures. The timing of LF seeps correlated to river stage and precipitation. The HF seeps at Goodwin Creek began after rainfall events resulted in the adjacent streambank reaching near saturation (i.e. soil pore water pressures greater than ?5 kPa). Seep discharge from HF seeps reached a maximum of 1·0 L min^?1 and sediment concentrations commonly approached 100 g L^?1. Buried seeps were intermittent but exhibited the most significant erosion rates (738 g min^?1) and sediment concentrations (989 g L^?1). In cases where perched water table conditions exist and persistent HF seeps occur, seepage erosion and bank collapse of streambank sediment may be significant. Copyright © 2007 John Wiley & Sons, Ltd.     

The Heilongjiang Group: A Jurassic accretionary complex in the Jiamusi Massif at the western Pacific margin of northeastern China

Abstract The tectonic setting of the Eastern Asian continental margin in the Jurassic is highly controversial. In the current study, we have selected the Heilongjiang complex located at the western margin of the Jiamusi Massif in northeastern China for geochronological investigation to address this issue. Field and petrographic investigations indicate that the Heilongjiang complex is composed predominately of granitic gneiss, marble, mafic‐ultramafic rocks, blueschist, greenschist, quartzite, muscovite‐albite schist and two‐mica schist that were tectonically interleaved, indicating they represent a mélange. The marble, two‐mica schist and granitic gneiss were most probably derived from the Mashan complex, a high‐grade gneiss complex in the Jiamusi Massif with which the Heilongjiang Group is intimately associated. The ultramafic rocks, blueschist, greenschist and quartzite (chert) are similar to components in ophiolite. The sensitive high mass‐resolution ion microprobe U‐Pb zircon age of 265 ± 4 Ma for the granitic gneiss indicates that the protolith granite was emplaced coevally with Permian batholiths in the Jiamusi Massif. ⁴⁰Ar/³⁹Ar dating of biotite and phengite from the granitic gneiss and mica schist yields a late Early Jurassic metamorphic age between 184 and 174 Ma. Early components of the Jiamusi Massif, including the Mashan complex, probably formed part of an exotic block from Gondwana, affected by late Pan‐African orogenesis, and collided with the Asian continental margin during the Early Jurassic. Subduction of oceanic crust between the Jiamusi block and the eastern part of the Central Asian Orogenic Belt resulted in the formation of a huge volume of Jurassic granites in the Zhangguangcai Range. Consequently, the collision of the Jiamusi Massif with the Central Asian Orogenic Belt to the west can be considered as the result of circum‐Pacific accretion, unrelated to the Central Asian Orogenic Belt. The widespread development of Jurassic accretionary complexes along the Asian continental margin supports such an interpretation.     

Mineshaft imaging using surface and crosshole 3D electrical resistivity tomography: A case history from the East Pennine Coalfield, UK

Hidden mineshafts located in urban areas are a significant problem across much of the industrialized world. Electrical resistivity tomography (ERT) is a technique that can detect and characterize hidden mine entries by exploiting resistivity contrasts between the shaft and surrounding materials, resulting from either compositional or structural differences. A case study is presented in which both surface and crosshole 3D ERT surveys are used to image a hidden backfilled mineshaft at a built environment site, situated on Carboniferous Lower Coal Measures strata in the UK.Backfilled shafts generally present the greatest challenge for detection using geophysical methods, as contrasts between the fill and bedrock are typically low compared to air or water-filled conditions. Nevertheless, the shaft in this case was identified by both the surface and crosshole 3D surveys. The shaft appeared as a strongly resistive anomaly relative to background materials, which we interpreted as resulting from the disturbed fabric of the fill materials rather than any significant compositional differences. The study highlighted the respective strengths and weaknesses of the surface and crosshole ERT methodologies for this type of problem. The surface survey, which covered a non-rectangular area to accommodate irregular boundaries and other physical obstructions, provided a relatively rapid means of investigating the study site. However, this method had a limited depth of investigation and was constrained in its coverage by the locations of buildings. By contrast, the 3D crosshole method was able to image the shaft to the level of the deepest borehole electrodes. Although crosshole ERT is too expensive to be used for large-scale mineshaft surveys, this study clearly demonstrates its suitability for targeted investigations where surface methods cannot be deployed, such as scanning beneath surface structures or in situations where it is essential for resolution to be maintained with depth.