Estimating slope from raster data – a test of eight algorithms at different resolutions in flat and steep terrain

Different slope algorithms can result in totally different estimates. In the worst case, this may lead to inappropriate and useless modelling estimates. A frequent lack of awareness when choosing algorithms justifies a thorough comparison of their characteristics, making it possible for researchers to select an algorithm which is optimal for their purpose. In this study, eight frequently used slope algorithms applied to Digital Elevation Models (DEMs) are compared. The influences of the resolution of the DEM (0.5, 1, 2, and 5 metres), as well as the terrain form (flat and steep terrain), are considered. It should be noted that the focus of the study is not to compare estimates with ‘ground truth’ data, but on the comparisons between the algorithms, and the ways in which they might differ depending on resolution and terrain. Descriptive statistics are calculated in order to characterize the general characteristics of the eight tested algorithms. Eight combinations of DEM resolution and terrain form are analysed. The results show that the Maximum and Simple Difference algorithms always yield higher mean slope values than the other algorithms, while the Constrained Quadratic Surface algorithm produces the lowest values compared to the others. It is concluded that the estimated slope values are heavily dependent on the number of neighbouring cells included in the estimation. An Analysis of Variance (ANOVA) of estimated slope values strongly indicates (at the significance level of 0.01) that the tested algorithms yield statistically different results. The eight algorithms produce different estimates for all tested resolutions and terrain forms but one. The differences are more pronounced in steep terrain and at a higher resolution. More detailed pairwise comparisons between estimated slope values are also carried out. It is concluded that the smoothing effects associated with the Constrained Quadratic Surface algorithm are greater in steeper terrain, showing significantly lower estimates than other algorithms. On the other hand, the Maximum and Simple Difference algorithms show significantly higher estimates in almost all cases, except the combination of steep terrain and low resolution. With an increase in grid cell size, the loss of information contents in DEMs leads to lower estimated slope values as well as smaller relative differences between algorithms. Based on the results of this study it is concluded that the choice of algorithm results in different estimated slope values, and that resolution and terrain influences these differences significantly

On generating digital elevation models from liDAR data – resolution versus accuracy and topographic wetness index indices in northern peatlands

Global change and GHG emission modelling are dependent on accurate wetness estimations for predictions of e.g. methane emissions. This study aims to quantify how the slope, drainage area and the TWI vary with the resolution of DEMs for a flat peatland area. Six DEMs with spatial resolutions from 0.5 to 90 m were interpolated with four different search radiuses. The relationship between accuracy of the DEM and the slope was tested. The LiDAR elevation data was divided into two data sets. The number of data points facilitated an evaluation dataset with data points not more than 10 mm away from the cell centre points in the interpolation dataset. The DEM was evaluated using a quantile-quantile test and the normalized median absolute deviation. It showed independence of the resolution when using the same search radius. The accuracy of the estimated elevation for different slopes was tested using the 0.5 meter DEM and it showed a higher deviation from evaluation data for steep areas. The slope estimations between resolutions showed differences with values that exceeded 50%. Drainage areas were tested for three resolutions, with coinciding evaluation points. The model ability to generate drainage area at each resolution was tested by pair wise comparison of three data subsets and showed differences of more than 50% in 25% of the evaluated points. The results show that consideration of DEM resolution is a necessity for the use of slope, drainage area and TWI data in large scale modelling

Cropland changes in times of conflict, reconstruction, and economic development in Iraqi Kurdistan

The destruction of land and forced migration during the Anfal attacks against the Kurds in Iraq in the late 1980s has been reported to have severe consequences for agricultural development. A reconstruction program to aid people in returning to their lands was launched in 1991. To assess the agricultural situation in the Duhok governorate during the pre-Anfal (A), post-Anfal (B), reconstruction (C), and present (D) periods, we mapped winter crops by focusing on inter-annual variability in vegetation greenness, using satellite images. The results indicate a decrease in cultivated area between period A and B, and a small increase between period B and C. This supports reports of a decline in cultivated area related to the Anfal campaign, and indicates increased activity during the reconstruction program. Period D showed a potential recovery with a cropland area similar to period A

Skyddsombudets roll i små byggföretag

Problem What is the role of the safety representative? What training does the safety representative have and in what areas do they want to increase their knowledge? How can a safety representative be proactive? • What affect do the party organizations have in small enterprises? Purpose The purpose of the study is to investigate how safety representatives are working in small construction enterprises and what it is that controls the preventive health and safety work. Methodology Based on the study purpose, an open approach has been used where the collected data is the result of literary studies, quantitative survey and interviews. Conclusions Safety representatives have an important role in small enterprises. Since the employer itself often does not have the necessary resources, the representative gets a greater role. A safety representative shall represent its colleagues in questions about the work environment witch requires a commitment from both the elected and its colleagues. Training, time and expertise in health and safety are key factors to be able to influence and interact with the employer. Some safety representatives are lacking in basic knowledge and routines and unionized representatives generally have basic training. The joint training program by the party organizations is addressing the issues that are important to the industry. Risk awareness is key to a good preventive work and it is important that the safety representative is involved in the procurement of occupational health and safety. Small enterprises represent a large part of the construction industry. Authorities and external actors should adapt their work methods and communication channels to reach out to the group. Regional safety representatives should not be seen as an alternative, but rather as a complement. Keyword Safety representatives, occupational health, small enterprises, construction, collaboration

Bismuth(III) Forms Exceptionally Strong Complexes with Natural Organic Matter

The use of bismuth in the society has steadily increased during the last decades, both as a substitute for lead in hunting ammunition and various metallurgical applications, as well as in a range of consumer products. At the same time, the environmental behavior of bismuth is largely unknown. Here, the binding of bismuth(III) to organic soil material was investigated using extended X-ray absorption spectroscopy (EXAFS) and batch experiments. Moreover, the capacity of suwannee river fulvic acid (SRFA) to enhance the solubility of metallic bismuth was studied in a long-term (2 years) equilibration experiment. Bismuth(III) formed exceptionally strong complexes with the organic soil material, where >99% of the added bismuth(III) was bound by the solid phase, even at pH 1.2. EXAFS data suggest that bismuth(III) was bound to soil organic matter as a dimeric Bi3+ complex where one carboxylate bridges two Bi3+ ions, resulting in a unique structural stability. The strong binding to natural organic matter was verified for SRFA, dissolving 16.5 mmol Bi per gram carbon, which largely exceeds the carboxylic acid group density of this compound. Our study shows that bismuth(III) will most likely be associated with natural organic matter in soils, sediments, and waters

Multireference calculations of the phosphorescence and photodissociation of chlorobenzene

Multireference complete active space self-consistent-field (CASSCF) and multireference CASSF second-order perturbation theory (MSCASPT2) calculations were performed on the ground state and a number of low-lying excited singlet and triplet states of chlorobenzene. The dual phosphorescence observed experimentally is clearly explained by the MSCASPT2 potential-energy curves. Experimental findings regarding the dissociation channels of chlorobenzene at 193, 248, and 266 nm are clarified from extensive theoretical information including all low-energy potential-energy curves

Borylation in the Second Coordination Sphere of Fe(II) Cyanido Complexes and Its Impact on Their Electronic Structures and Excited-State Dynamics

Second coordination sphere interactions of cyanido complexes with hydrogen-bonding solvents and Lewis acids are known to influence their electronic structures, whereby the non-labile attachment of B(C6F5)3 resulted in several particularly interesting new compounds lately. Here, we investigate the effects of borylation on the properties of two FeII cyanido complexes in a systematic manner by comparing five different compounds and using a range of experimental techniques. Electrochemical measurements indicate that borylation entails a stabilization of the FeII-based t2g-like orbitals by up to 1.65 eV, and this finding was confirmed by Mössbauer spectroscopy. This change in the electronic structure has a profound impact on the UV–vis absorption properties of the borylated complexes compared to the non-borylated ones, shifting their metal-to-ligand charge transfer (MLCT) absorption bands over a wide range. Ultrafast UV–vis transient absorption spectroscopy provides insight into how borylation affects the excited-state dynamics. The lowest metal-centered (MC) excited states become shorter-lived in the borylated complexes compared to their cyanido analogues by a factor of ∼10, possibly due to changes in outer-sphere reorganization energies associated with their decay to the electronic ground state as a result of B(C6F5)3 attachment at the cyanido N lone pair

Development and Application of a ReaxFF Reactive Force Field for Oxidative Dehydrogenation on Vanadium Oxide Catalysts

We have developed a new ReaxFF reactive force field to describe accurately reactions of hydrocarbons with vanadium oxide catalysts. The ReaxFF force field parameters have been fit to a large quantum mechanics (QM) training set containing over 700 structures and energetics related to bond dissociations, angle and dihedral distortions, and reactions between hydrocarbons and vanadium oxide clusters. In addition, the training set contains charge distributions for small vanadium oxide clusters and the stabilities of condensed-phase systems. We find that ReaxFF reproduces accurately the QM training set for structures and energetics of small clusters. Most important is that ReaxFF describes accurately the energetics for various oxidation states of the condensed phases, including V_2O_5, VO_2, and V_2O_3 in addition to metallic V(V^0). To demonstrate the capability of the ReaxFF force field for describing catalytic processes involving vanadium oxides, we performed molecular dynamics (MD) simulation for reactions of a gas of methanol exposed to the (001) surface of V_2O_5. We find that formaldehyde is the major product, in agreement with experiment. These studies find that water desorption from surface VIII sites is facilitated by interlayer bonding