The performance limits were explored for an X-ray Diffraction based explosives detection system for baggage scanning. This XDi system offers 4D imaging that comprises three spatial dimensions with voxel sizes in the order of ~(0.5cm)3, and one spectral dimension for material discrimination. Because only a very small number of photons are observed for an individual voxel, material discrimination cannot work reliably at the voxel level. Therefore, an initial 3D reconstruction is performed, which allows the identification of objects of interest. Combining all the measured photons that scattered within an object, more reliable spectra are determined on the object-level. As a case study we looked at two liquid materials, one threat and one innocuous, with very similar spectral characteristics, but with 15% difference in electron density. Simulations showed that Poisson statistics alone reduce the material discrimination performance to undesirable levels when the photon counts drop to 250. When additional, uncontrolled variation sources are considered, the photon count plays a less dominant role in detection performance, but limits the performance also for photon counts of 500 and higher. Experimental data confirmed the presence of such non-Poisson variation sources also in the XDi prototype system, which suggests that the present system can still be improved without necessarily increasing the photon flux, but by better controlling and accounting for these variation sources. When the classification algorithm was allowed to use spectral differences in the experimental data, the discrimination between the two materials improved significantly, proving the potential of X-ray diffraction also for liquid materials.
Accurate information about land use patterns is crucial for a sustainable and economical use of water in agricultural systems. Water demand estimation, yield modeling and agrarian policy are only a few applications addressed by land use classifications based on remote sensing imagery. In Central Asia, where fields are traditionally large and state order crops dominate the area, small units of fields are often separated for the additional cultivation of income crops for the farmers. Traditional object based land use classifications on multi-temporal satellite imagery using field boundaries show low classification accuracies on these separated fields, expressed by a high uncertainty of the final class labels. Although segmentation of smaller subfields was shown to be suitable for improving the classification result, the extraction of subfields is still a time-consuming and error-prone process. In this study, energy based Graph-Cut segmentation technique is used to enhance the segmentation process and finally to improve the classification result. The interactive segmentation technique was successfully adopted from bio-medical image analysis to fit remote sensing imagery in the spatial and in the temporal domain. A set of rules was developed to perform the image segmentation procedure on pixels of single satellite datasets and on objects representing time series of a vegetation index. An ensemble classifier based on Random Forest and Support Vector Machines was used to receive information about classification uncertainty before and after applying the segmentation. It is demonstrated that subfield extraction based on Graph Cuts outperforms traditional image segmentation approaches in simplicity and reduces the risk of under- and over-segmentation significantly. Classification uncertainty decreased using the derived subfields as object boundaries instead of original field boundaries. The segmentation technique performs well on several multi-temporal satellite images without changing parameters and may be used to refine object based land use classifications to subfield level.
In Central Asia, more than eight Million ha of agricultural land are under irrigation. But severe degradation problems and
unreliable water distribution have caused declining yields during the past decades. Reliable and area-wide information
about crops can be seen as important step to elaborate options for sustainable land and water management. Experiences
from RapidEye classifications of crop in Central Asia are exemplarily shown during a classification of eight crop classes
including three rotations with winter wheat, cotton, rice, and fallow land in the Khorezm region of Uzbekistan covering
230,000 ha of irrigated land. A random forest generated by using 1215 field samples was applied to multitemporal
RapidEye data acquired during the vegetation period 2010. But RapidEye coverage varied and did not allow for
generating temporally consistent mosaics covering the entire region. To classify all 55,188 agricultural parcels in the
region three classification zones were classified separately. The zoning allowed for including at least three observation
periods into classification. Overall accuracy exceeded 85 % for all classification zones. Highest accuracies of 87.4 %
were achieved by including five spatiotemporal composites of RapidEye. Class-wise accuracy assessments showed the
usefulness of selecting time steps which represent relevant phenological phases of the vegetation period. The presented
approach can support regional crop inventory. Accurate classification results in early stages of the cropping season
permit recalculation of crop water demands and reallocation of irrigation water. The high temporal and spatial resolution
of RapidEye can be concluded highly beneficial for agricultural land use classifications in entire Central Asia.
The Moderate Imaging Spectroradiometer (MODIS) provides operational products of the Normalized Difference
Vegetation Index (NDVI), the Enhanced Vegetation Index (EVI), and the fraction of photosynthetic active radiation
(fPAR). FPAR can be used in productivity models, but agricultural applications depend on sub-pixel heterogeneity.
Examples for heterogeneous areas are the irrigation systems of the inner Aral Sea Basin, where the 1 km fPAR product
proved less suited. An alternative can be to upscale fPAR to the 250 m scale, but there are few studies evaluating this
approach. In this study, the use of MODIS 250 m NDVI and EVI for this approach was investigated in an irrigation
system in western Uzbekistan. The analysis was based on high resolution fPAR maps and a crop map for the growing
season 2009, derived from ground measurements and multitemporal RapidEye data. The data was used to explore
statistical relationships between RapidEye fPAR and MODIS NDVI/EVI with respect to spatial heterogeneity. The
correlations varied between products (daily NDVI, 8-day NDVI, 16-day NDVI/EVI), with results suggesting that 8-day
NDVI performed best. The analyses and the compiled fPAR maps show that, compared to 1 km MODIS fPAR, the 250 m
scale is more homogeneous, allows for crop-specific analyses, and better captures the spatial patterns in the study region.
Land surface biophysical parameters such as the fraction of photosynthetic active radiation (fPAR) and leaf area
index (LAI) are keys for monitoring vegetation dynamics and in particular for biomass and carbon flux simulation.
This study aimed at deriving accurate regression equations from the newly available RapidEye satellite sensor
to be able to map regional fPAR and LAI which could be used as inputs for crop growth simulations. Therefore,
multi-temporal geo- and atmospherically corrected RapidEye scenes were segmented to derive homogeneous
patches within the experimental fields. Various vegetation indices (VI) were calculated for each patch focusing
on indices that include RapidEye's red edge band and further correlated with in situ measured fPAR and LAI
values of cotton and rice. Resulting coefficients of determination ranged from 0.55 to 0.95 depending on the
indices analysed, object scale, crop type and regression function type. The general relationships between VI and
fPAR were found to be linear. Nonlinear models gave a better fit for VI-LAI relation. VIs derived from the red
edge channel did not prove to be generally superior to other VIs.
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