Effect of overtopping discharges on accessibility, maintenance and costs of dikes

Civil Engineering and GeosciencesHydraulic Engineerin

The uncertainty of MODIS C6 aerosol optical depth product over land

Geoscience & Remote SensingCivil Engineering and Geoscience

Improved MODIS Dark Target aerosol optical depth algorithm over land: Angular effect correction

Aerosol optical depth (AOD) product retrieved from MODerate Resolution Imaging Spectroradiometer (MODIS) measurements has greatly benefited scientific research in climate change and air quality due to its high quality and large coverage over the globe. However, the current product (e.g., Collection 6) over land needs to be further improved. The is because AOD retrieval still suffers large uncertainty from the surface reflectance (e.g., anisotropic reflection) although the impacts of the surface reflectance have been largely reduced using the Dark Target (DT) algorithm. It has been shown that the AOD retrieval over dark surface can be improved by considering surface bidirectional distribution reflectance function (BRDF) effects in previous study. However, the relationship of the surface reflectance between visible and shortwave infrared band that applied in the previous study can lead to an angular dependence of the AOD retrieval. This has at least two reasons. The relationship based on the assumption of isotropic reflection or Lambertian surface is not suitable for the surface bidirectional reflectance factor (BRF). However, although the relationship varies with the surface cover type by considering the vegetation index NDVISWIR, this index itself has a directional effect and affects the estimation of the surface reflection, and it can lead to some errors in the AOD retrieval. To improve this situation, we derived a new relationship for the spectral surface BRF in this study, using 3 years of data from AERONET-based Surface Reflectance Validation Network (ASRVN). To test the performance of the new algorithm, two case studies were used: 2 years of data from North America and 4 months of data from the global land. The results show that the angular effects of the AOD retrieval are largely reduced in most cases, including fewer occurrences of negative retrievals. Particularly, for the global land case, the AOD retrieval was improved by the new algorithm compared to the previous study and MODIS Collection 6 DT algorithm, with the increase of 2.0 and 4.5 % AOD retrievals falling within the expected accuracy envelope ±(0.05 + 15 %), respectively. This implies that the users can get more accurate data without angular bias, i.e., more meaningful AOD data.Optical and Laser Remote SensingAtmospheric Remote Sensin

The Sensitivity of AOD Retrieval to Aerosol Type and Vertical Distribution over Land with MODIS Data

This study is to evaluate the sensitivity of Aerosol Optical Depth (AOD τ) to aerosol vertical profile and type, using the Moderate Resolution Imaging Spectroradiometer (MODIS) collection 6 algorithm over land. Four experiments were performed, using different aerosol properties including 3 possible non-dust aerosol models and 14 vertical distributions. The algorithm intrinsic uncertainty was investigated as well as the interplay effect of aerosol vertical profile and type on the retrieval. The results show that the AOD retrieval is highly sensitive to aerosol vertical profile and type. With 4 aerosol vertical distributions, the algorithm with a fixed vertical distribution gives about 5% error in the AOD retrieval with aerosol loading τ≤0.5 . With pure aerosols (smoke and dust), the retrieval of AOD shows errors ranging from 2% to 30% for a series of vertical distributions. Errors in aerosol type assumption in the algorithm can lead to errors of up to 8% in the AOD retrieval. The interplay effect can give the AOD retrieval errors by over 6%. In addition, intrinsic algorithm errors were found, with a value of >3% when τ> 3.0. This is due to the incorrect estimation of the surface reflectance. The results suggest that the MODIS algorithm can be improved by considering a realistic aerosol model and its vertical profile, and even further improved by reducing the algorithm intrinsic errors.Optical and Laser Remote SensingAtmospheric Remote Sensin

In search of a better sediment mixing coefficient model

Results of sediment transport calculations are often necessary in solving practical coastal engineering problems. (Sediment transport due to waves and currents). Many transport formulae have been proposed in literature in the past. Selection of the proper one while solving a particular problem, is a difficult task for a coastal engineer. In considering sediment transport under wave-current conditions it is worthwhile to make a distinction between two situations, viz.: The fluctuations in the orbital motion have to be fully taken into account in order to find the resulting sediment transport (intra-wave type of description; often: cross-shore sediment transport); - It is sufficient to take time-averaged effects of the waves into account in order to find the resulting sediment transport rate (intra-wave type of description is not required; often: longshore sediment transport). For the longshore sediment transport mode, transport formulae based on time-averaged velocity distributions and time-averaged sediment concentration distributions over the water depth can often be used. The present paper is restricted to this type of formula.Civil Engineering and Geoscience

Twomey effect in subtropical stratocumulus clouds from UV depolarization lidar

Marine stratocumulus clouds are important climate regulators, reflecting sunlight over a dark ocean background. A UV-depolarization lidar on Ascension, a small remote island in the south Atlantic, measured cloud droplet sizes and number concentration using an inversion method based on Monte Carlo (MC) modelling of multiple scattering in idealised semiadiabatic clouds. The droplet size and number concentration weremodulated due to smoke from the African continent, measured by the same instrument.Atmospheric Remote Sensin

Methanolsynthese in een slurryreactor

Document(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science

Pin/hole joint construction and laminate therefor

A pin/hole joint construction in a laminate (1) comprises layers (9) of fibres and resin bonded to one another. At least one hole (2) extends transversely completely through the layers in the laminate, in which hole a pin (3) is accommodated that bears against the inner surface of the hole for transferring forces between the laminate and the pin. In the laminate a first region (13) is defined in which the layers are directly on top of one another and a second region (14) in which at least one reinforcing layer (5) is provided that is bonded to the adjacent layers of fibres and resin, in which second region the at least one hole is located. All layers of fibres and resin are continued into the second region.Aerospace Engineerin

Effect drijvende constructies op waterkwaliteit

Water ManagementCivil Engineering and Geoscience