Total Station Survey Research Articles

Measuring Beach Profiles along a Low-Wave Energy Microtidal Coast, West-Central Florida, USA

Monitoring storm-induced dramatic beach morphology changes and long-term beach evolution provides crucial data for coastal management. Beach-profile measurement using total station has been conducted along the coast of west-central Florida over the last decade. This paper reviews several case studies of beach morphology changes based on total-station survey along this coast. The advantage of flexible and low-cost total-station surveys is discussed in comparison to LIDAR (light detection and ranging) method. In an attempt to introduce total-station survey from a practical prospective, measurement of cross-shore beach profile in various scenarios are discussed, including: (1) establishing a beach profile line with known instrument and benchmark locations; (2) surveying multiple beach profiles with one instrument setup; (3) implementation of coordinate rotation to convert local system to real-earth system. Total-station survey is a highly effective and accurate method in documenting beach profile changes along low-energy coasts.

Total station survey monitoring through an observation window: a systematic error correction to remove the effects of glass properties

Total stations are used extensively for taking geodetic and engineering survey measurements. These measurements are made possible by accurate observation of targeted points. One example is deformation surveys, slope stability monitoring, in mines. Continuous monitoring necessitates sheltering or housing the instrument to protect it against harsh weather conditions that are characteristic of mining environments. Previous studies carried out by Afeni and Cawood (2012) revealed that the properties of the glass material matters when using a total station to take observations through a glass window of a structure that houses the total station at a mine. This study briefly discusses total station survey monitoring and developed systematic error correction formula to reduce the effect of glass properties, such as thickness and colour, on distance measurements through a shelter window glass in a surface mine environment. Each developed formula is combined with the atmospheric corrections formula given by Leica Geosystem, who is the manufacturer of the total station used in this research, to form a combined atmospheric and glass correction formula. The formula performed well when tested on two sets of observations.

Investigation of the Accuracy of Google Earth Elevation Data

Abstract Digital Elevation Models (DEMs) comprise valuable source of elevation data required for many engineering applications. Contour lines, slope - aspect maps are part of their many uses. Moreover, DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally-produced relief maps. This paper proposes a method of generating DEM by using Google Earth elevation data which is easier and free. The case study consisted of three different small regions in the northern beach in Egypt. The accuracy of the Google earth derived elevation data are reported using root mean square error (RMSE), mean error (ME) and maximum absolute error (MAE). All these accuracy statistics were computed using the ground coordinates of 200 reference points for each region of the case study. The reference data was collected with total station survey. The results showed that the accuracies for the prepared DEMs are suitable for some certain engineering applications but inadequate to meet the standard required for fine/small scale DEM for very precise engineering study. The obtained accuracies for terrain with small height difference can be used for preparing large area cadastral, city planning, or land classification maps. In general, Google Earth elevation data can be used only for investigation and preliminary studies with low cost. It is strongly concluded that the users of Google Earth have to test the accuracy of elevation data by comparing with reference data before using it.

Geological evolution and inundation hazard: an analysis through geotechnologies

ABSTRACT Rosa, M.L.C.C; Barboza, E.G.; Menegon, B.S.; Frota, P.C.; and Anoni, R.A.O., 2016. Geological evolution and inundation hazard: an analysis through geotechnologies. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1227 - 1231. Coconut Creek (Florida), ISSN 0749-0208. In the southern coastal plain of Rio Grande do Sul, southern Brazil, part of the city of Santa Vitoria do Palmar was studied to analyze inundation hazard and its relation to geological evolution. Remote sensing, GNSS, total station surveys, laser scanning and photogrammetric reconstructions with a low cost UAV were combined and compared aiming at defining four main units with different levels of inundation susceptibility, which correspond to geological units of different ages. The allogenic factor related to the development of these units is sea level, which controls lagoon lev...

A DEM of the 2010 surface topography of Storglaciären, Sweden

ABSTRACTDuring the summer of 2010 the surface elevation of Storglaciären in northern Sweden was measured using high-precision GNSS and reflectorless Total Station surveys. The DEM created from these data contain less noise than those created from orthophotographic methods over snow covered glaciers and is therefore smoother, with fewer erroneous features in the data. The principal, though not sole, intended use for the DEM is in the calculation of surface mass balance, which has influenced decisions on what constitutes a functional part of a glacier, leading to the exclusion of features such as snow aprons and perennial ice above the bergschrund. Other peripheral features have changed since the previous, aerial survey from 1999 leading to a reduction in size of approximately 0.17 km2.

Development of Water Resources for Micro Watershed at Chinamushidiwada Village in Visakhapatnam, Andhra Pradesh, India

An attempt made to develop water resource for micro watershed of Visakhapatnam Urban Area. The study area extends from 17° 47’ 02’’ N to 17° 48’ 38’’ N latitudes and 83° 11’ 51’’ E to 83° 14’ 45’’ E longitudes, covering an aerial extent of 9.18 km2. A detailed examination of the existing three tanks in the study area is carried out using both spatial technology and ground based observations. The alteration of the terrain topography is studied from the survey of India toposheets and Total Station survey conducted in the study area. The 3-Dimensional terrain model is generated and the drainage network is simulated to study its interaction with the results of the change detection analysis. For the quantification of surface water bodies, Total Station survey is carried out for the tanks. Geophysical explorations are carried out, which identifies the thicknesses of top soil, weathered rock, fractured rock, hard fractured rock and hard rock formations, to assess the volume of the groundwater that can be stored in the aquifer system.

基于Hegyi改进模型的毛竹林空间结构竞争动态分析

PDF HTML阅读 XML下载 导出引用 引用提醒 基于Hegyi改进模型的毛竹林空间结构和竞争分析 DOI: 10.5846/stxb201406131227 作者: 作者单位: 浙江农林大学环境与资源学院,浙江省森林生态系统碳循环与固碳减排重点实验室,浙江农林大学环境与资源学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(31170595);国家十二五科技支撑计划(2012BAD22B0503);浙江省重点科技创新团队(2010R50030);教育部留学回国人员科研启动金项目(20101561);国家林业局造林司委托项目(SFA2130218-2) Analysis of the spatial structure and competition with a Phyllostachys edulis standbased on an improved Hegyi model Author: Affiliation: School of Environment and Resource, Zhejiang A & F University,Zhejiang Provincial Key Laboratory of Carbon Cycling in Forest Ecosystems and Carbon Sequestration,Lin’an,Zhejiang Provincial Key Laboratory of Carbon Cycling in Forest Ecosystems and Carbon Sequestration,Lin’an;Management Office,National Nature Reserve of Tianmu Mountain,Lin’an;The forestry specialty bureau of Tiantai country,Tian’tai Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以浙江省天目山国家级自然保护区内少受干扰的毛竹林为研究对象,设置100m×100m的固定标准地,进行连续5a的每竹调查,用全站仪精确测定每竹坐标(X,Y,Z)。提出新的竞争指数--竞争势(CP)。利用CP对2009-2013年毛竹林分竞争动态进行定量分析,并分别研究各年份毛竹林竞争强度与对象竹胸径、年龄之间的动态关系。结果表明:毛竹大小年现象明显,毛竹大年(2010、2012)的林分竞争强度明显大于小年(2009、2011、2013),且大小年之间竞争强度存在显著性差异(P < 0.01),毛竹大年之间林分竞争强度无显著性差异(P > 0.05),毛竹小年(2011、2013)之间林分竞争强度无显著性差异(P > 0.05),2009年毛竹林受雪灾和新竹株数影响,与其它年份林分竞争强度存在显著性差异(P < 0.01);毛竹林竞争强度随对象竹径阶的增大而减小,且服从幂函数关系;毛竹林竞争强度随对象竹龄级的增大而增大,且服从线性函数关系。CP在Hegyi模型的基础上,增加考虑毛竹生理特性,使对毛竹竞争关系的分析有了进一步拓展,从而更加全面有效地描述毛竹林分的竞争关系,应用CP分析毛竹林竞争动态规律,可为毛竹林经营提供参考依据。 Abstract:At present, many individual tree competition indices are used to measure the competitive ability of trees, and they are generally divided into distance-independent indices and distance-dependent indices depending on whether one is considering the space between trees. Distance-dependent indices are commonly used, especially the Hegyi competition index (CH). The CH was used to analyze the spatial structure of a Phyllostachys edulis stand studied by Tang et al., but we found that this CH needs to be improved. P. edulis is a Bambusoideae (Gramineae) species and does not have secondary cambium tissue, resulting in the termination of diameter at breast height (DBH) growth after completion of the stem growth. Unfortunately, there are different competitive intensities associated with the spatial structure of P. edulis stands, even in situations where the same distance exists between object and competition bamboo plants. This means they might have the same DBH, but would be considered to be of a different age. Such distinctions cannot be provided by the existing CH. In fact, competition within a P. edulis stand is affected significantly by intensity of physiological activity, which changes with variation of the metabolic turnover and aging process of an individual, or with its material growth period. Material growth periods are divided into enhancement stages, stationary stages, and declining stages, depending on different intensity of physiological activities. In the light of characteristic of P. edulis, considering its metabolic turnover and aging process, and adding a material growth period factor, a new competition index-competition potential (CP), which is based on CH (the Hegyi model), was proposed to analyze the spatial structure of P. edulis stands. A permanent plot measuring 100 m × 100 m, including a relatively lightly disturbed P. edulis stand, was established in the Tianmu Mountain National Nature Reserve, Zhejiang province. There have been five annual surveys of the plot. Each bamboo tree was tallied and its coordinates (X, Y, Z) were measured using a total station survey device. From 2009 to 2013, we used the new competition index, CP, to quantitatively analyze the dynamic competition within the bamboo stand, as well as to study the dynamic relationship between intensity competition and DBH, and the dynamic relationship between intensity competition and age class. The results showed that the P. edulis stand has clear on-year/off-year cycles and that the competitive intensity of on-years (2010, 2012) is obviously higher than that of off-years (2009, 2011, 2013). The difference in competitive intensity within the P. edulis stand between on-years and off-years was significant (P < 0.01). The difference in competitive intensity within the P. edulis stand between on-years was not significant (P > 0.05), as was the difference in competitive intensity between off-years (2011and 2013; P > 0.05). Because of a snow disaster and the emergence of a number of new shoots, the competitive intensity within the P. edulis stand in 2009 showed significance difference (P < 0.01) from other years. The competitive intensity within the P. edulis stand decreased with increasing objective diameter class, and the results showed that the competition had a powerful relationship with DBH. The competitive intensity within the P. edulis stand increased with increasing age class and also had a significantly linear correlation with DBH.A combination of the growth characteristics and adopted physiological characteristics of P. edulis was used to develop an expanded analysis of competition between individuals of P. edulis. This allowed us to develop a more comprehensive and effective model (CP) to describe competition within a P. edulis stand. The new CP is therefore a feasible and reliable way to analyze competition within P. edulis stands and their dynamic characteristics. For these reasons, it could provide a theoretical basis for management of artificial P. edulis stands. 参考文献 相似文献 引证文献

Understanding the kinematic behavior of the active Gascons rockslide from in-situ and satellite monitoring data

The monitoring of the 410000m3 coastal Gascons rockslide, began in 2009. This paper presents and analyzes combined in-situ and satellite-based monitoring data to interpret the kinematic behavior of the slide and the evolution of the rockslide and the possible mechanisms that can lead to an accelerating phase of movement. The available data are (1) relative displacements, measured by thirteen crackmeters and manually with an extensometer tape; (2) absolute displacements, obtained from inclinometers and vertical shape accelerometer arrays in boreholes, total station surveys, and satellite-based point-target-analysis-InSAR (PTA); (3) the settlement of the railway ballast monitored by two horizontal shape accelerometer arrays; (4) groundwater pressures from nine vibrating wire piezometers; and (5) weather conditions. The study indicates that the role of water on displacements varies spatially within the rockslide. The rockslide's kinematic behavior enables us to develop evolution scenarios of the rockslide, which could be useful to conduct a risk analysis. This leads to the identification of critical zones for railroad safety. The unique set of monitoring data helps to elucidate the complexity of the rockslide's behavior.

Evaluation of Lidar-derived DEMs through Terrain Analysis and Field Comparison

AbstractTopographic analysis of watershed-scale soil and hydrological processes using digital elevation models (DEMs) is commonplace, but most studies have used DEMs of 10m resolution or coarser. Availability of higher-resolution DEMs created from light detection and ranging (lidar) data is increasing but their suitability for such applications has received little critical evaluation. Two different 1m DEMs were re-sampled to 3, 5, and 10m resolutions and used with and without a low-pass smoothing filter to delineate catchment boundaries and calculate topographic metrics. Accuracy was assessed through comparison with field slope measurements and total station surveys. DEMs provided a good estimate of slope values when grid resolution reflected the field measurement scale. Intermediate scale DEMs were mostconsistent with land survey techniques in delineating catchment boundaries. Upslope accumulated area was most sensitive togrid resolution, with intermediate resolutions producing a range of UAA values useful in soil and groundwater analysis.

ADVANCES IN MULTI-SENSOR SCANNING AND VISUALIZATION OF COMPLEX PLANTS: THE UTMOST CASE OF A REACTOR BUILDING

Abstract. In a context of increased maintenance operations and workers generational renewal, a nuclear owner and operator like Electricité de France (EDF) is interested in the scaling up of tools and methods of “as-built virtual reality” for larger buildings and wider audiences. However, acquisition and sharing of as-built data on a large scale (large and complex multi-floored buildings) challenge current scientific and technical capacities. In this paper, we first present a state of the art of scanning tools and methods for industrial plants with very complex architecture. Then, we introduce the inner characteristics of the multi-sensor scanning and visualization of the interior of the most complex building of a power plant: a nuclear reactor building. We introduce several developments that made possible a first complete survey of such a large building, from acquisition, processing and fusion of multiple data sources (3D laser scans, total-station survey, RGB panoramic, 2D floor plans, 3D CAD as-built models). In addition, we present the concepts of a smart application developed for the painless exploration of the whole dataset. The goal of this application is to help professionals, unfamiliar with the manipulation of such datasets, to take into account spatial constraints induced by the building complexity while preparing maintenance operations. Finally, we discuss the main feedbacks of this large experiment, the remaining issues for the generalization of such large scale surveys and the future technical and scientific challenges in the field of industrial “virtual reality”.

Assessment of Outer and Inner Slope Profiles of Volcanic Craters on Biu Plateau, Borno State, Nigeria

This research examined the outer and inner slope profiles of volcanic craters on the Biu Plateau. The objectives of the study are to identify the types of slopes; examine the types of geomorphic processes in the craters; and determine the socio-economic relevance of the craters. Data used for this study were generated from field observations, topographic map, total station survey and group interview. Three sampled craters namely Kumba, Tilla and Jali Tagurmi were purposively selected for the study. Profiles of each craters were plotted using autoCARD where geomorphic processes, and human activities were observed between the stations in relations to slope gradient. Three group interviews and participatory rural appraisal were conducted in the vicinity of each of the craters on the socio-economic importance. Results showed that there are fourteen craters on the Biu plateau; four large (> 300m) in diameter, five medium (200-300m) and five small (< 200m). The morphology of the Kumba crater is conical with an elevation range of 700m to 765m, Tilla crater is circular with elevation range of 736m to 742m while the Jali crater has an oval shape with spot height of 690m to 740m asl. Denudational processes observed on the rims of the craters include weathering, sheet, rill, gully erosions and mass wasting (rock fall, soil creep, debris creep and slides). Socio-economic activities associated with the craters according to group interview and participatory rural appraisal include livestock watering, market gardening, quarrying, tourism, medication and domestic water supply. Other related negative human activities observed include bush burning, deforestation, accelerated erosion, poaching, hunting, and extraction of fuelwood. From the findings of the research it is recommended that public enlightenment campaign on environmental management be conducted, sustainable environmental management of land based resources be ensured. Access roads, afforestation, beneficial cultural practices and tourism be encouraged.

Assessments of land subsidence in the Gippsland Basin of Australia using ALOS PALSAR data

In this paper, the land deformation in the Gippsland Basin, Victoria, Australia has been mapped using the interferometric synthetic aperture radar (InSAR) time-series analysis with the ALOS L-band SAR data. Land subsidence in the basin resulting from mining activities has already been known over the past few decades. There has been ongoing concern that irrigation and off-shore oil and natural gas extraction has significantly lowered groundwater levels on-shore, and that this may lead to further subsidence. Therefore it is important to map the land surface change in the basin in order to understand the actual impact of these activities. The total area of Gippsland Basin is approximately 46,000km2, where approximately one-third of the basin is located onshore. Because of the large area of the basin, ALOS PALSAR data from 4 different paths were used to map the land displacement over the basin. The InSAR result suggests that the land displacement at 98% of the measurement points in the basin was between −10mm/year and 10mm/year. The InSAR result has been compared to the ground survey data in several areas, collected with GPS and total station surveys. The comparison of results suggested that the InSAR measurement and the ground survey measurement agree with each other in general.The standard deviation of difference between the InSAR results and the ground survey data is approximately 4mm/year near the coastal area and 15mm/year near the mining sites. Several rapidly deforming areas have been identified at the mining sites and the surrounding areas. Deformation rate at up to −82.9mm/year is observed in these areas. The deformation at the mining sites and the surrounding areas are expected to be resulted from mining activities and associated mine dewatering. Moreover, several minor displacement zones have been observed and investigated in the area between the Loy Yang Mines and the Gippsland coast as well as the area between Yanakie and Wilsons Promontory.

Remote Sensing of Sonoran Desert Vegetation Structure and Phenology with Ground-Based LiDAR

Long-term vegetation monitoring efforts have become increasingly important for understanding ecosystem response to global change. Many traditional methods for monitoring can be infrequent and limited in scope. Ground-based LiDAR is one remote sensing method that offers a clear advancement to monitor vegetation dynamics at high spatial and temporal resolution. We determined the effectiveness of LiDAR to detect intra-annual variability in vegetation structure at a long-term Sonoran Desert monitoring plot dominated by cacti, deciduous and evergreen shrubs. Monthly repeat LiDAR scans of perennial plant canopies over the course of one year had high precision. LiDAR measurements of canopy height and area were accurate with respect to total station survey measurements of individual plants. We found an increase in the number of LiDAR vegetation returns following the wet North American Monsoon season. This intra-annual variability in vegetation structure detected by LiDAR was attributable to a drought deciduous shrub Ambrosia deltoidea, whereas the evergreen shrub Larrea tridentata and cactus Opuntia engelmannii had low variability. Benefits of using LiDAR over traditional methods to census desert plants are more rapid, consistent, and cost-effective data acquisition in a high-resolution, 3-dimensional context. We conclude that repeat LiDAR measurements can be an effective method for documenting ecosystem response to desert climatology and drought over short time intervals and at detailed-local spatial scale.

The Orientations of the Giza Pyramids and Associated Structures

This paper presents the results of a week-long Total Station survey undertaken by the authors during December 2006 whose principal aim was to clarify the basic data concerning the orientation of each side of the three large Giza pyramids and to determine, as accurately as possible, the orientations of as many as possible of the associated structures. The survey focused upon measurements of sequences of points along multiple straight and relatively well-preserved structural segments, with best-fit techniques being used to provide the best estimate of their orientation, as opposed to simple triangulation between directly identified or extrapolated corners.

The potential of small unmanned aircraft systems and structure-from-motion for topographic surveys: A test of emerging integrated approaches at Cwm Idwal, North Wales

Novel topographic survey methods that integrate both structure-from-motion (SfM) photogrammetry and small unmanned aircraft systems (sUAS) are a rapidly evolving investigative technique. Due to the diverse range of survey configurations available and the infancy of these new methods, further research is required. Here, the accuracy, precision and potential applications of this approach are investigated. A total of 543 images of the Cwm Idwal moraine–mound complex were captured from a light (<5kg) semi-autonomous multi-rotor unmanned aircraft system using a consumer-grade 18 MP compact digital camera. The images were used to produce a DSM (digital surface model) of the moraines. The DSM is in good agreement with 7761 total station survey points providing a total vertical RMSE value of 0.517m and vertical RMSE values as low as 0.200m for less densely vegetated areas of the DSM. High-precision topographic data can be acquired rapidly using this technique with the resulting DSMs and orthorectified aerial imagery at sub-decimetre resolutions. Positional errors on the total station dataset, vegetation and steep terrain are identified as the causes of vertical disagreement. Whilst this aerial survey approach is advocated for use in a range of geomorphological settings, care must be taken to ensure that adequate ground control is applied to give a high degree of accuracy.

Crew variability in topographic surveys for monitoring wadeable streams: a case study from the Columbia River Basin

ABSTRACTDigital elevation models (DEMs) derived from ground‐based topographic surveys have become ubiquitous in the field of fluvial geomorphology. Their wide application in spatially explicit analysis includes hydraulic modeling, habitat modeling, and morphological sediment budgeting. However, there is a lack of understanding regarding the repeatability and precision of DEMs derived from ground‐based surveys conducted by different, and inherently subjective, observers. This is of particular concern when we consider the proportion of studies and monitoring programs that are implemented across multiple sites and over time by different observers. We used a case study from the Columbia Habitat Monitoring Program (CHaMP), where seven field crews sampled the same six sites, to quantify the magnitude and effect of observer variability on DEMs interpolated from total station surveys. We quantified the degree to which DEM‐derived metrics and measured geomorphic change were repeatable. Across all six sites, we found an average elevation standard deviation of 0.05 m among surveys, and a mean total range of 0.16 m. A variance partition between site, crew, and unexplained errors for several topographically derived metrics showed that crew variability never accounted for &gt; 1.5% of the total variability. We calculated minor geomorphic changes at one site following a relatively dry flow year between 2012 and 2011. Calculated changes were minimal (unthresholded net changes ±1–3 cm) with six crews detecting an indeterminate sediment budget and one crew detecting a minor net erosional sediment budget. While crew variability does influence the quality of topographic surveys, this study highlights that when consistent surveying methods are employed, the data sets are still sufficient to support derivation of topographic metrics and conduct basic geomorphic change detection. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Building response to adjacent deep basement construction

Field observations of the response of a building adjacent to a 23-m-deep basement excavation for a development adjacent to Harrods department store in London, are presented and discussed. This paper focuses on No. 3 Hans Crescent located within the most critical zone, on a re-entrant corner, of the excavation. Top-down construction and underpinning techniques were implemented to minimise ground movements and building damage. Vertical and horizontal displacements were monitored using precise levelling and total station surveys, allowing building responses to be synthesised and related to construction activities. Primary observed and deduced trends are that the effects of underpinning and diaphragm walling were local, whereas piling and excavation had a global impact, and that settlement was primarily caused by diaphragm walling and piling, whereas piling and excavation caused the most horizontal displacement. The zone of influence of horizontal displacements extended farther than that for vertical displacements, which became negligible at a distance of about twice the excavation depth. The No. 3 Hans Crescent property experienced hogging for most construction stages, and sagging developed towards the end of excavation, with in-plane distortions of the building walls and out-of-plane tilting. Observations from monitoring results and post-construction condition surveys indicate that the damage category was negligible, corroborating pre-construction predictions.

EVALUATION OF ADVANCED SURVEYING TECHNOLOGY FOR ACCIDENT INVESTIGATION

The objective was to evaluate the use of advanced technology for the investigation of traffic accidents. Substantial time and manpower are sometimes required to properly investigate serious vehicular crashes and document on-scene data. An alternative to the traditional coordinate method for on-scene data collection is the use of electronic total stations. This is a form of digital surveying equipment that can be used to obtain detailed measurements, with the option of plotting the stored data by computer. The study compared the use of advanced surveying technology with the traditional coordinate method. Detailed estimates of data collection activity were documented for a selected accident sample, and accident clearance times were documented for a much larger sample. The analysis indicated that the investigation of traffic accidents by using total-station surveys provides a substantial improvement over the traditional coordinate procedure. The number of measurements obtained at an accident scene increased by a factor of approximately 2 when the total-station equipment was used. The time to collect the data decreased by about 33%, and the man-hours decreased by about one-half. Computer plotting by the total-station procedure also resulted in a significant time savings. Decreased data collection time resulted in significant time and fuel savings to the driving public. Recommendations were made for continued use of the equipment and the purchase of more equipment when funds become available. In addition, policies for using the total-station equipment at all fatal and serious injury traffic accidents are recommended.

A comparison between LiDAR and photogrammetry digital terrain models in a forest area on Tenerife Island

This paper compares two types of digital terrain models (DTMs) with ground elevation measures collected through field work in a dense forest area on the island of Tenerife (Canary Islands, Spain). The first was an existing DTM derived from altimetric features obtained by manual photogrammetric restitution. The second DTM was computed from aerial LiDAR data with a nadir density of 0.8 points·m−2. Both DTMs have a pixel size of 5 m. The field work consisted of measuring three elevation profiles by land surveying techniques using a total station survey and taking into account different vegetation covers. The analysis of the profiles by means of nonparametric techniques showed an accuracy at the 95th percentile between 0.54 m and 24.26 m for the photogrammetry-derived DTM and between 0.22 m and 3.20 m for the LiDAR-derived DTM. Plotting the elevation profiles allowed for the visual detection of locations where the models failed. The LiDAR data were able to reflect more accurately the true ground surface in areas of dense vegetation, especially in places where the ground was invisible to photogrammetric operators as in the case of Canarian pine forest with understory.

Gully Morphology and Gully Erosion Control in Calabar, Cross River State, Nigeria

Gully erosion is a highly visible form of soil erosion that results in large volume of soil and sediment transport. Gully processes have a three dimensional nature that are affected by a wide array of factors and processes which include topography, soils, land use and climatic events. In this study the four major Gully erosion sites in Calabar including Ikot Efangha Mkpa, Bebobsco, Inyang Ansa (Atimbo) and Winners, present case studies scenarios. Morphological parameters of the gullies including length, width, depth, slope, area e.t.c were determined from GPS and Total Station Surveys. Meteorological data were obtained from meteorological station in Calabar while soil characteristics for the study areas were obtained from soil samples collected from the site and analysed in the laboratory. The effects of these on the rate of soil loss and gullying were determined.Using hydrological, hydraulics and structural analysis along with the acquired data, control measures were proposed for the gully sites. These included the design of drop structures to control the runoff from the gully heads and prevent further under cutting of the heads. The use of Vertiver grass for bank stabilization and catchment areas protection was proposed. The results of the studies and control measures proposed can be adopted for planning for gully remediation and control in other similar situations.