Carlos Henrique Grohmann

Multiscale Analysis of Topographic Surface Roughness in the Midland Valley, Scotland

Surface roughness is an important geomorphological variable which has been used in the Earth and planetary sciences to infer material properties, current/past processes, and the time elapsed since formation. No single definition exists; however, within the context of geomorphometry, we use surface roughness as an expression of the variability of a topographic surface at a given scale, where the scale of analysis is determined by the size of the landforms or geomorphic features of interest. Six techniques for the calculation of surface roughness were selected for an assessment of the parameters behavior at different spatial scales and data-set resolutions. Area ratio operated independently of scale, providing consistent results across spatial resolutions. Vector dispersion produced results with increasing roughness and homogenization of terrain at coarser resolutions and larger window sizes. Standard deviation of residual topography highlighted local features and did not detect regional relief. Standard deviation of elevation correctly identified breaks of slope and was good at detecting regional relief. Standard deviation of slope (SDslope) also correctly identified smooth sloping areas and breaks of slope, providing the best results for geomorphological analysis. Standard deviation of profile curvature identified the breaks of slope, although not as strongly as SDslope, and it is sensitive to noise and spurious data. In general, SDslope offered good performance at a variety of scales, while the simplicity of calculation is perhaps its single greatest benefit.

Morphometric analysis in geographic information systems: applications of free software GRASS and R

Development and interpretation of morphometric maps are important tools in studies related to neotectonics and geomorphology; Geographic Information Systems (GIS) allows speed and precision to this process, but applied methodology will vary according to available tools and degree of knowledge of each researcher about involved software. A methodology to integrate GIS and statistics in morphometric analysis is presented for the most usual morphometric parameters-hypsometry, slope, aspect, swath profiles, lineaments and drainage density, surface roughness, isobase and hydraulic gradient. The GIS used was the Geographic Resources Analysis Support System (GRASS-GIS), an open-source project that offers an integrated environment for raster and vector analysis, image processing and maps/graphics creation. Statistical analysis of parameters can be carried out on R, a system for statistical computation and graphics, through an interface with GRASS that allows raster maps and points files to be treated as variables for analysis. The basic element for deriving morphometric maps is the digital elevation model (DEM). It can be interpolated from scattered points or contours, either in raster or vector format; it is also possible to use DEMs from NASAs Shuttle Radar Topographic Mission, with 30m of ground resolution for the USA and 90m for other countries. Proposed methodology can be adapted according to necessities and available tools. The use of free and open-source tools guarantees access to everyone, and its increasing popularization opens new development perspectives in this research field.

Short Note: Comparison of roving-window and search-window techniques for characterising landscape morphometry

Neighbourhood analysis in a Geographical Information System (GIS) calculates the value of a given raster cell from the values of its neighbouring cells. Common operations include filtering (highpass, low-pass, etc.) and smoothing (mean, mode) of data, operations that can be done by means of roving-windows or search-windows. Digital terrain analysis (or geomorphometry) relies on neighbourhood operations to calculate morphometric variables such as slope, aspect, local relief or surface roughness (among many others) at scales ranging from local (i.e., single landforms) to regional (entire mountain chains). The intent of this paper is to compare both techniques in a multi-scale study of geomorphometry, in central-eastern Brazil. The study area is limited by coordinates 0 and 26 S latitude and 34 W and 56 W longitude, with approximately 4:900:000km. The roving-window approach can be considered the standard filter technique in raster GIS operations and in image processing (Demers, 2004; Lillesand et al., 2004). It determines the new value for a given cell in a raster map using a mathematical function (mean, mode, standard deviation, etc.) of the cells values inside a n n neighbourhood (with odd n) centred in the cell of interest U 93

SRTM resample with short distance-low nugget kriging

The shuttle radar topography mission (SRTM), was flow on the space shuttle Endeavour in February 2000, with the objective of acquiring a digital elevation model of all land between 60° north latitude and 56° south latitude, using interferometric synthetic aperture radar (InSAR) techniques. The SRTM data are distributed at horizontal resolution of 1 arc‐second (∼30 m) for areas within the USA and at 3 arc‐second (∼90 m) resolution for the rest of the world. A resolution of 90 m can be considered suitable for the small or medium‐scale analysis, but it is too coarse for more detailed purposes. One alternative is to interpolate the SRTM data at a finer resolution; it will not increase the level of detail of the original digital elevation model (DEM), but it will lead to a surface where there is the coherence of angular properties (i.e. slope, aspect) between neighbouring pixels, which is an important characteristic when dealing with terrain analysis. This work intents to show how the proper adjustment of variogram and kriging parameters, namely the nugget effect and the maximum distance within which values are used in interpolation, can be set to achieve quality results on resampling SRTM data from 3” to 1”. We present for a test area in western USA, which includes different adjustment schemes (changes in nugget effect value and in the interpolation radius) and comparisons with the original 1” model of the area, with the national elevation dataset (NED) DEMs, and with other interpolation methods (splines and inverse distance weighted (IDW)). The basic concepts for using kriging to resample terrain data are: (i) working only with the immediate neighbourhood of the predicted point, due to the high spatial correlation of the topographic surface and omnidirectional behaviour of variogram in short distances; (ii) adding a very small random variation to the coordinates of the points prior to interpolation, to avoid punctual artifacts generated by predicted points with the same location than original data points and; (iii) using a small value of nugget effect, to avoid smoothing that can obliterate terrain features. Drainages derived from the surfaces interpolated by kriging and by splines have a good agreement with streams derived from the 1” NED, with correct identification of watersheds, even though a few differences occur in the positions of some rivers in flat areas. Although the 1” surfaces resampled by kriging and splines are very similar, we consider the results produced by kriging as superior, since the spline‐interpolated surface still presented some noise and linear artifacts, which were removed by kriging.

Effects of spatial resolution on slope and aspect derivation for regional-scale analysis

This paper investigates differences between morphometric parameters (slope and aspect) derived from a resampled DEM and resampled morphometric data derived from a medium resolution DEM, with examples for three study areas in South America selected to represent flatlands, hilly terrain, and mountain ranges. Using a low resolution DEM for regional scale morphometric analysis is not an optimal choice, since attenuation of elevation will strongly affect the distribution of calculated parameters. Unless bounded by computational constraints, one should choose to derive basic morphometric parameters from higher resolution data, and resample it to a coarser resolution as needed. HighlightsAveraging higher-resolution elevation data will strongly affect the distribution of calculated morphometric parameters.It is best to derive basic morphometry from higher resolution data, and resample it to a coarser resolution as needed.Slope derived from resampled elevation show a strong decrease in maximum values with coarser resolutions.Resampled slopes are more correlated to the original ones, with less decrease in maximum values and with similar mean values.Aspect changes less with resampling, but peaks and valleys in the density curve are intensified as resolution decreases.

Trend-surface analysis of morphometric parameters: A case study in southeastern Brazil

Trend-surface analysis was carried out on data from morphometric parameters isobase and hydraulic gradient. The study area, located in the eastern border of Quadrilatero Ferrifero, southeastern Brazil, presents four main geomorphological units, one characterized by fluvial dissection, two of mountainous relief, with a scarp of hundreds of meters of fall between them, and a flat plateau in the central portion of the fluvially dissected terrains. Morphometric maps were evaluated in GRASS-GIS and statistics were made on R statistical language, using the spatial package. Analysis of variance (ANOVA) was made to test the significance of each surface and the significance of increasing polynomial degree. The best results were achieved with sixth-order surface for isobase and second-order surface for hydraulic gradient. Shape and orientation of residual maps contours for selected trends were compared with structures inferred from several morphometric maps, and a good correlation is present.

Permian non-marine bivalves of the Falkland Islands and their palaeoenvironmental significance

Simões, M.G., Quaglio, F., Warren, L., Anelli, L.E., Stone, P., Riccomini, C., Grohmann, C.H. & Chamani, M.A.C. December 2012. Permian non-marine bivalves of the Falkland Islands and their palaeoenvironmental significance. Alcheringa 36, 543–554. ISSN 0311-5518. We describe the occurrence of non-marine bivalves in exposures of the Middle Permian (Capitanian) Brenton Loch Formation on the southern shore of Choiseul Sound, East Falklands. The bivalves are associated with ichnofossils and were collected from a bed in the upper part of the formation, within a 25 cm thick interval of dark siltstones and mudstones with planar lamination, overlain by massive sandstones. The shells are articulated, with the valves either splayed open or closed. At the top of the succession, mudstone beds nearly 1.5 m above the bivalve-bearing layers yielded well-preserved Glossopteris sp. cf. G. communis leaf fossils. The closed articulated condition of some shells indicates preservation under high sedimentation rates with low residence time of bioclasts at the sediment/water interface. However, the presence of specimens with splayed shells is usually correlated to the slow decay of the shell ligament in oxygen-deficient bottom waters. The presence of complete carbonized leaves of Glossopteris associated with the bivalve-bearing levels also suggests a possibly dysoxic-anoxic bottom environment. Overall, our data suggest that the bivalves were preserved by abrupt burial, possibly by distal sediment flows into a Brenton Loch lake, and may represent autochthonous to parautochthonous fossil accumulations. The shells resemble those of anthracosiids and are herein assigned to Palaeanodonta sp. aff. P. dubia, a species also found in the Permian succession of the Karoo Basin, South Africa. Our results confirm that (a) the true distributions in space and time of all Permian non-marine (freshwater) bivalves are not yet well known, and (b) there is no evidence for marine conditions in the upper part of the Brenton Loch Formation.

Análise digital de terreno e evolução de longo-termo de relevo do centro-leste brasileiro

As diversas teorias geomorfologicas para evolucao do relevo em longo-termo (da ordem de dezenas de milhoes de anos) contemplam a existencia de superficies de aplainamento, formadas pela acao continua dos agentes erosivos/deposicionais em periodos de quiescencia tectonica e reconheciveis como extensas areas de relevo muito suave perturbadas localmente por elevacoes residuais, ou pela aparente concordância altimetrica dos divisores de aguas de uma regiao. Apesar de passadas varias decadas desde a publicacao das principais teorias sobre evolucao das formas de relevo, a validade desses modelos ainda e palco de discussao. Neste trabalho sao apresentados estudos relativos a compartimentacao do relevo, em escala regional, da regiao centro-leste brasileira. As analises foram focadas em analise digital de terreno, com processamento e integracao de dados em Sistema de Informacoes Geograficas, visando a extracao e caracterizacao de variaveis relativas a superficie topografica e a compilacao e tratamento matematico de dados termocronologicos e geofisicos. Os resultados obtidos foram interpretados tendo em vista o contexto geologico e as teorias de evolucao do relevo em longo-termo. A integracao entre dados morfometricos, termocronologicos e geofisicos nao suporta a validade do uso de superficies aplainadas em correlacoes estratigraficas de âmbito regional.

Algorithms for extraction of structural attitudes from 3D outcrop models

The acquisition of geological attitudes on rock cuts using traditional field compass survey can be a time consuming, dangerous, or even impossible task depending on the conditions and location of outcrops. The importance of this type of data in rock-mass classifications and structural geology has led to the development of new techniques, in which the application of photogrammetric 3D digital models has had an increasing use. In this paper we present two algorithms for extraction of attitudes of geological discontinuities from virtual outcrop models: ply2atti and scanline, implemented with the Python programming language. The ply2atti algorithm allows for the virtual sampling of planar discontinuities appearing on the 3D model as individual exposed surfaces, while the scanline algorithm allows the sampling of discontinuities (surfaces and traces) along a virtual scanline. Application to digital models of a simplified test setup and a rock cut demonstrated a good correlation between the surveys undertaken using traditional field compass reading and virtual sampling on 3D digital models. HighlightsWe present two algorithms for attitude calculation from photogrammetric 3D models.We test the algorithms on a simplified setup and a rock cut.The sampling methods demonstrate a good correlation with traditional measures.Virtual sampling must be carried out carefully to avoid errors.

Integrated geological map of the São Roque Domain, North of São Paulo City - Brazil

The São Roque Domain has an extensive geological cartographic base that began in the nineteenth century with the works performed by the Geographic and Geological Commission of São Paulo Province. The first more detailed geological maps of geological substrate of the São Paulo city and neighboring areas were executed in the decades of 1940–1950, and culminated in the integrated maps by José Moacyr Vianna Coutinho published in the 1970s. As part of a systematic geological mapping campaign led by PRÓ-MINÉRIO, most of the São Roque Domain was mapped at 1:50,000 scales; these maps, and others at the same or more detailed scale published mostly in the 1980s, are only available in unpublished academic theses and reports. This article presents an integrated map of most of the São Roque Domain based on all the available maps and some new stratigraphic and geochronological data that appeared in recent local literature.