Papers by Steven M. De Jong
International Journal of Applied Earth Observation and Geoinformation, 2001
The Medium Resolution Imaging Spectrometer (MERIS) is a payload component of Envisat-1. MERIS wil... more The Medium Resolution Imaging Spectrometer (MERIS) is a payload component of Envisat-1. MERIS will be operated over land with a standard 15 band setting acquiring images with a 300 m spatial resolution. The red-edge position (REP) is a promising variable for deriving foliar chlorophyll concentration, which plays an important role in ecosystem processes. The objectives of this paper are: (1) to study which factors effect the REP of vegetation,
Calibration of large-scale groundwater models is difficult due to a general lack of groundwater h... more Calibration of large-scale groundwater models is difficult due to a general lack of groundwater head measurements. The calibration becomes even more complex if the basin covers several countries with different observation systems and different base maps, or if calibration must be done in developing countries with poor data availability. In this study, we present and discuss a novel approach for
International Journal of Applied Earth Observation and Geoinformation, 2006
This paper investigates statistical relationships between land use/land cover (LULC), Landsat-7 E... more This paper investigates statistical relationships between land use/land cover (LULC), Landsat-7 ETM + imagery and landscape mosaic structure in southern Cameroon where the conversion of tropical rain forest to shifting cultivation leads to dynamic processes, acting on the spatial aggregation of various LULC types. A Global Positioning System (GPS) was used in the field to identify a total of 171 shifting cultivation patches representing eight LULC types in two sub-areas. Because of the lack of a cloudfree image for the date of field sampling, the ETM + imagery was acquired 2 months after field survey, during which it was assumed that no significant changes in LULC occurred (all dry season). Per pixel correlations were developed between spectral reflectance data, vegetation indices and LULC. As an exploratory study, several statistical methods (analysis of variance, means separations (Tukey HSD), principal component analysis (PCA), geo-statistical analysis, image classification and landscape metrics) were applied on point data and sensor images for evaluating the spatial variability within the landscape. Most variables explained 30-72% of LULC variation in the whole dataset. Those variables with high information content of LULC (infrared bands 4, 5, 7 and derived indices and PC1) also showed long ranges (6 km) spatial dependence as compared to those varying only within 1 km range. The results of these statistical analyses suggested the need to group some LULC types and the application of the Maximum Likelihood Classifier (MLC) for supervised classification provided a LULC map with the highest accuracy (81%) after consolidation of perennial LULC types, such as bush fallow, forest fallow and cocoa plantations. Landscape metrics computed from this map showed a high level of patch diversity and connectivity within the landscape and provided input data that can further be used to simulate predictive maps as substitute to cloud-covered sensor imageries. Landsat-7 ETM + imagery proved to be useful in discriminating (with about 80% accuracy) the most dynamic LULC types such cropped plots and young fallow patches (shifting every season) and the extension front of the agricultural landscape. #
Vegetation growth in semiarid, Mediterranean ecosystems is greatly dependent on moisture availabi... more Vegetation growth in semiarid, Mediterranean ecosystems is greatly dependent on moisture availability in the soil, as little precipitation is available during the growing season. Predicting the effects of climate change on vegetation development requires understanding of the exact relation between climate, moisture availability, and plant growth. Accurate moisture measurements in naturally vegetated areas are difficult because of high spatial variability and because of the coarse, shallow soils. In this study, we evaluated the possibilities of using Electrical Resistivity Tomography (ERT) to measure soil moisture availability and plant water use in a Mediterranean natural area. We found that ERT is a useful tool for measuring soil conditions, providing information on the spatial patterns within the soil and reaching depths otherwise inaccessible. In heterogeneous soils, we differentiated between lithological and moisture effects in the measurements using multitemporal data. Absolute calibration to moisture content was sometimes possible, but strongly location dependent. Based on the ERT measurements, we found that although the soils in the study area are shallow and rocky, plant roots penetrate deeply into the fractured and weathered bedrock, and vegetation subtracts water from depths down to 6 m and below. This information is important for understanding the plant–soil relations and modeling vegetation development. We conclude that ERT provides crucial information on soil moisture processes unavailable using any other currently available measurement method.
. The soil erosion model for Mediterranean regions SEMMED is presented and used to produce region... more . The soil erosion model for Mediterranean regions SEMMED is presented and used to produce regional maps of simulated soil loss for two Mediterranean test sites: one in southern Ž . France and one in Sicily. The model demonstrates the integrated use of 1 multi-temporal Landsat Ž . Ž . Thematic Mapper TM images to account for vegetation properties, 2 a digital terrain model in a GIS to account for topographical properties and to assess the transport capacity of overland flow, Ž .
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Papers by Steven M. De Jong