Undulating Terrain Research Articles

An enhanced technique in construction of the discrete drainage network from low-resolution spatial database

A digital elevation model (DEM) of a watershed can be used to acquire various parameters such as basin-wide information about overland flow direction, flow accumulation and area contributing flow to any point. The resolution and quality of a DEM are important to achieve a significant level of accuracy in derived parameters. Inadequate elevation information exacerbated by applied interpolation methods, reduce DEM accuracy, resulting in pits and flat areas and makes flow tracing a difficult task. These types of problems are more prominent in cases of residual undulating terrains. In the present paper, an attempt has been made to review and suggest an improved method for the generation of a DEM from raster contour data. Further, a criteria-based region growing method (CBRGM) is presented for the extraction of discrete drainage network (cell size: 20×20 m) of the watershed. Here, the flat area removal algorithm, with a variable increment, is used to generate the DEM. This induces a gradual slope even in the case of a large contour interval (20 m) extended over larger area, as is commonly available from a topographic map at a scale of 1:50,000. Further, in order to capture topographic information in flow tracing, the CBRGM is followed. The rasterised stream network from the same topographic sheet is used as ancillary data to make the concentrated flow lines to follow the channel. The methodology has been tested over Gandheshwari subwatershed under the lower part of Chhotanagpur Plateau in Eastern India. The DEM generated using this method gives a better representation of the terrain, which shows good agreement with the terrain information delineated by using the contour and channel information available in the topographic sheet. The drainage network derived shows additional extra-concentrated flow lines, many of which match the drainage network obtained from satellite imagery (cell size: 23.5×23.5 m). The algorithm thus shows superiority over other available methods for the extraction of drainage networks.

How Long Do Pilots Look Forward? Prospective Visual Guidance in Terrain-Hugging Flight

The title of this paper reflects the notion that pilots need to predict their future flight trajectory, and hence exercise prospective control, to ensure safe passage through and over cluttered and undulating terrain. Of critical importance is how long, in time, a pilot needs to be able to see into the future to maintain an adequate safety margin for guidance. The emphasis here is on how long in time, rather than how far in space. Understanding the nature of the temporal mental ‘models’ required to support this prediction is considered key to understanding the workings of the human motion perception system, and how they might be exploited in the design of aids to flight guidance in degraded visual conditions. A related question is how the safety margin might connect to the handling qualities construct, the Usable Cue Environment, which was developed to help determine the optimum control augmentation requirements for flight in poor visibility. Answers to these questions can be used to inform the design of pilot vision aids on the one hand and to provide a more quantitative basis for the UCE construct on the other. The paper reports results from research underway in a collaborative project involving The University of Liverpool and the French Research Laboratory, ONERA, aimed at developing a more quantitative basis for the UCE, based on fundamental perception principles. In the present paper the visual requirements for vertical manoeuvring over undulating terrain are addressed, and how these lead to natural relationships between the selected speed and height. The theoretical framework is supported by results from piloted simulation trials, with a detailed examination of the temporal variables associated with vertical and horizontal flight path control in degraded visual conditions.

Conservation of tanks/lakes in the Bangalore metropolitan area

PurposeThe purpose of this paper is to build up perspectives for the conservation and restoration of the various spoilt water bodies within the Bangalore metropolitan area.Design/methodology/approachThis paper describes how Bangalore city is typical of the features of peninsular India in that it is made up of ridges, valleys and undulating terrain. Monsoon rainfall is substantial and the tanks and lakes can receive and contain substantial amounts of water from rains. Only thing is to de‐clog the natural water flow routes and to restore the bunds of tanks and repair the spillways and put in place legal and administrative measures to preserve the interiors of tanks; free them from construction activities and launch suitable afforestation programs to contain soil erosion, improve the quality of subsoil water and raise if possible medicinal and ornamental trees so that Bangalore gains in its aesthetic appeal.FindingsThe study reveals that the existence of water bodies is an important asset to the environment of Bangalore. It has a beneficial impact on the microclimate of the city and serves as outdoor recreational areas, which are very much needed as a source of change and relief for the city dwellers. It is good for developing open spaces with greenery along the valleys. There is much scope for water‐front developments to enhance urban aesthetics in the surrounding areas. It is possible to improve the ground water table, so that there will be scope for tapping ground water through bore wells all through the year, particularly during summers.Practical implicationsThis work will draw the attention of government authorities as well as local residents, NGOs and experts to keep the tanks/lakes conserved in and around the BMA and to prevent silting of tanks by offshore development and large‐scale tree planting and also removal of encroachments within the study area.Originality/valueThis study will stimulate interest in recreation, conservation, open space beautification, pollution abatement and a myriad other ways to improve the quality of urban environment.

Honeybee navigation: distance estimation in the third dimension

Honeybees determine distance flown by gauging the extent to which the image of the environment moves in the eye as they fly towards their goal. Here we investigate how this visual odometer operates when a bee flies along paths that include a vertical component. By training bees to fly to a feeder along tunnels of various three-dimensional configurations, we find that the odometric signal depends only upon the total distance travelled along the path and is independent of its three-dimensional configuration. Hence, unlike walking desert ants, which measure the distance travelled in the horizontal plane whilst traversing undulating terrain, flying bees simply integrate the image motion that is experienced on the way to the goal, irrespective of the direction in which the image moves across the eyes. These findings raise important questions about how honeybee recruits navigate reliably to find the food sources that are advertised by scouts.

Insect Navigation: Measuring Travel Distance across Ground and through Air

Walking insects probably monitor leg movements to estimate how far they travel, whereas flying insects monitor optic flow.

Malaria control using indoor residual spraying and larvivorous fish: a case study in Betul, central India

To assess the impact of intensified malaria control interventions in an ethnic minority community in Betul using existing tools. Two rounds of indoor residual spraying with synthetic pyrethroid insecticide were applied and larvivorous fish introduced, followed by intensive surveillance for early detection of Plasmodium falciparum with rapid diagnostic tests and prompt treatment with sulphadoxine pyrimethamine. Pre-intervention surveys revealed a very high fever rate in the community in all age groups with a slide positivity rate of >50% with >90%P. falciparum. The post-intervention phase showed a sharp steady decline in number of malaria cases (beta 0.972; P < 0.0001, 95% CI 0.35-0.47). Monitoring of entomological results revealed a significant decline in both Anopheles species and An. culicifacies (P < 0.0001). A combination of indoor residual spraying and early detection and prompt treatment complemented by rapid diagnostic tests and larvivorous fishes successfully brought malaria under control. These approaches could be applied in other regions of different endemicity to control malaria in India.

Comparison of grid‐based algorithms for computing upslope contributing area

Terrain attributes based on upslope contributing area, A, are used widely in distributed hydrologic models. Several grid‐based algorithms are available for estimating A. In this study, five algorithms (D8, ρ8, MFD, DEMON, and D∞) were compared quantitatively on two undulating agricultural fields (63 and 109 ha) in northeastern Colorado. Global positioning system (GPS) data (0.02‐m accuracy) were used to generate grid digital elevation models (DEMs) at 5‐, 10‐, and 30‐m cell sizes. Relative differences between A values estimated using single‐ and multiple‐direction algorithms increased with decreasing grid cell size. Relative differences were greatest along ridges and side slopes, and differences decreased where the terrain became more convergent. Multiple‐direction algorithms (MFD, DEMON, and D∞), allowing for flow divergence, are recommended on these undulating terrains for 5‐ and 10‐m grids where A is most sensitive to the algorithm selection.

Mucuna bracteate-Biomass, Litter and Nutrient Production

The rate of dry litter production of four-year-old Mucuna bracteata cover under full sun was found to be equivalent to 13.0 mt per hectare per year on undulating terrain in inland soil of West Kalimantan. The nutrients from the litter mulch are equivalent to 8.3 kg per palm per year of fertilisers (5.1 kg urea + 0.8 kg RP + 1.0 kg MOP + 1.4 kg kieserite) at a palm density of 138 per hectare. One hundred percent Mucuna bracteata cover still persisted under eight-year-old palm stand, but the total biomass was 40 per cent less than Mucuna bracteata in the open. However, the nutrient levels of green parts of Mucuna bracteata under shade were higher than in the open. When the Mucuna bracteata cover was slashed at six-monthly intervals, the rate of biomass returned to the soil was 17.7 mt per hectare per year, 36 per cent higher than the litter produced of undisturbed Mucuna bracteata. The nutrients from the slashed biomass were equivalent to 10.5 kg per palm per year (6.0 kg urea + 1 kg RP + 1.8 kg MOP + 1.7 kg kieserite). Keywords: Biomass, litter, green manure, Mucuna bracteata, legume cover crop

COMPOST AND MULCH EFFECTS ON GASEOUS FLUX FROM AN ALFISOL IN OHIO

Accelerating soil erosion, leading to loss of the surface soil, is a common occurrence in croplands on undulating terrain. Yet the impact of erosion and reclamation measure on emission of greenhouse gases (GHG) is not known. Three predominant GHG emitted from cropland are as follows: carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). The most abundant GHG is CO2, but N2O and CH4 are also important, with global warming potentials (GWP) of 297 and 23, respectively. The objectives of this study were to evaluate the effect of imitated soil erosion on gaseous emission, to determine the effects of application of wheat (Triticum aestivum) residue mulch and swine manure and soybean (Glycine max) residue compost as soil-restorative measures on fluxes of CO2, N2O, and CH4 from uncropped, undisturbed, and desurfaced plots, and to determine relations between GHG fluxes and air and soil temperature, precipitation, and soil-moisture regimes. The microplot (2 × 2 m) experiment was established in 2002 on a Crosby silt loam (fine mixed Aeric Ochraqudalf) near South Charleston, Ohio. The experimental design included two soils: undisturbed and desurfaced soil in which the top 0-cm to 20-cm layer was mechanically removed to simulate severe soil erosion. There were three cover treatments: bare soil, wheat mulch at the rate of 8 Mg dry matter ha−1 y−1, and compost made from swine manure and soybean residues at the rate of 20 Mg drymatter ha−1 y−1. All plots received mineral fertilizer at the rate of 100kgN ha−1. Desurfacing decreased soil moisture, increased temperature, decreased daily and annual CO2 fluxes (1.05 vs. 1.59 g CO2-C m−2 d−1), and increased N2O fluxes (3.58 vs. 1.81 mg N2O-N m−2 d−1). Daily CO2 and annual fluxes were higher from compost than mulch plots. The lowest daily CO2 flux was measured from bare plots. The daily N2O fluxes significantly increased after compost application but were more significantly affected by rainfall events. CH4 fluxes were characterized by a high variability; however, more uptake was observed in compost (−0.41 kg ha−1 y−1) than in mulch (0.60 kg ha−1 y−1) and bare plots (2.75kgha−1 y−1). Daily CO2 fluxes were positively correlated with soil (r = 0.82) and air temperatures (r = 0.84) and negatively correlated with soil-moisture content (r = −0.53). Daily N2O fluxes were highly correlated with precipitation (r = 0.88). Fluxes of CO2 and N2O were mutually correlated (r = 0.56), but CH4 fluxes were not correlated with temperature, moisture, precipitation, or fluxes of other GHG. Computed GWP was higher in compost-covered plots than in mulched and bare plots. Estimation of fluxes of GHG indicates that N2O accounts for 13% to28% and CH4 for −0.5% to 5% of the total emission. Therefore, acompleted assessment of flux of GHG must be based on measurement ofall three gases (i.e., CO2, N2O, and CH4).

A study on the applicability of repeat‐pass SAR interferometry for generating DEMs over several Indian test sites

Repeat‐pass synthetic aperture radar interferometry (InSAR) appears to be an excellent tool for generating digital elevation models (DEMs) of high spatial and vertical resolution. However, in recent years, it has been noticed that the atmosphere causes errors in the elevation accuracy. The objective of this paper is to try to identify climatic regions in India where InSAR can be used for generating DEMs. A detailed study was carried out to quantify atmospheric effects on the DEMs derived from repeat‐pass InSAR. Three test sites were selected for the analysis: one over Mumbai, which is a part of the western ghats region with hilly terrain, lakes and forests; another is the Kolar area with gently undulating terrain with agricultural and forested lands; and the last was Bhuj, an arid plains region which is close to the Rajasthan Thar desert, India. Six interferograms of the Bhuj area derived from two tandem pairs were analysed and it was found that there were varying atmospheric effects of the order of 0.2λ to 1λ and at specific locations more than λ. In the case of the Mumbai and Kolar study areas with two interferograms each, the atmospheric effects were almost negligible. In these cases, it is shown that it was also possible to estimate the height of buildings to an accuracy of 1–2 m. Therefore, it is concluded that one should be cautious when using InSAR techniques for generating DEMs of desert/arid regions where the climate may be very dynamic and only small amounts of water vapour can cause strong atmospheric artefacts.

USM PUSHING THE FRONTIERS OF TOWN PLANNING

The USM Campus in Penang is arguably one of the most beautiful in Malaysia set amidst undulating terrain with a rich treasure trove of exotic flora and fauna and panoramic views. But this former Military Camp has been subjected to 30 years of unrelenting development threatening its unique assets. Efforts are being made to protect those treasures in line with the aspirations of Agenda 21 but rather than following the conventional path, the USM Campus Planning Project has attempted to chart new frontiers in the use of JCT for planning and realigning the philosophy towards sustainable development. Amongst the innovations introduced are "publish as we plan", online surveys and the notion that we should "only take what we need" from nature up to a maximum threshold beyond which further development will be considered detrimental to the well-being of the campus community.

USM PUSHING THE FRONTIERS OF TOWN PLANNING

The USM Campus in Penang is arguably one of the most beautiful in Malaysia set amidst undulating terrain with a rich treasure trove of exotic flora and fauna and panoramic views. But this former Military Camp has been subjected to 30 years of unrelenting development threatening its unique assets. Efforts are being made to protect those treasures in line with the aspirations of Agenda 21 but rather than following the conventional path, the USM Campus Planning Project has attempted to chart new frontiers in the use of JCT for planning and realigning the philosophy towards sustainable development. Amongst the innovations introduced are "publish as we plan", online surveys and the notion that we should "only take what we need" from nature up to a maximum threshold beyond which further development will be considered detrimental to the well-being of the campus community.

Across-path DN gradient in Landsat TM imagery of Amazonian forests: A challenge for image interpretation and mosaicking

An analysis of tropical rain forest covering Amazonian lowlands has highlighted a systematic across-path, east–west radiometric gradient within Landsat TM imagery. Visual assessment of 45 and quantitative analysis of 20 Amazonian Landsat-4 and -5 TM scenes show that the gradient is band dependent and pronounced in visible light bands 1 to 3 but significant also in IR bands 4 to 7. The results show that the scan line location of a pixel explains a considerable amount of the DN variation of forests in the width of the entire scene (B1: 70%, B2: 52%, B3: 44%, B4: 34%, B5: 46%, B7: 39%). In digital numbers, the difference between east and west side of a scene may be small (9, 4, 3, 10, 9, 3, respectively) but these differences become significant if the images are to be mosaicked, or the data are used for mapping relatively subtle differences of natural forests. Apparently, the gradient is a result of at least three factors: 1) shadows caused by the undulating terrain, 2) anisotropic reflectance of the varying surfaces, and 3) atmospheric scattering. The phenomenon becomes more significant when the sun is high and the scanning line is close to solar azimuth direction—a condition more easily encountered in lower latitudes of the earth.

Stream use by the large-footed myotis Myotis macropus in relation to environmental variables in northern New South Wales.

The large-footed myotis (Myotis macropus) feeds by trawling aquatic invertebrates and small fish from water surfaces, but little is known about what types of streams are used. We investigated habitat use by M. macropus in northern New South Wales (NSW) by analysing data-base records, conducting field surveys and assessing environmental variables on or near waterways. A GIS comparison of 222 data-base records of M. macropus with broad environmental patterns indicated that most records were near large and permanent waterways at low elevations, in flat or undulating terrain, usually surrounded by vegetation. Three different field surveys were carried-out. First, 25 waterways on the NSW mid-north coast were stratified into five size classes and sampled (December 1996-January 1997) using harp traps and ultrasonic detectors. Just two captures and 20 passes were recorded. No M. macropus were detected on either the smallest or largest waterways, although the latter may have been under-sampled due to their broad expanse. Records of M. macropus were significantly associated with larger, more permanent waterways (when the largest size class was omitted). Non-metric multi-dimensional scaling of sites, described by their environmental attributes, failed to separate sites on the basis of presence/absence of M. macropus. The second survey (February 1998) targeted 25 sites on waterways within 10 km of a known roost in Kerewong State Forest. Twenty-eight passes were recorded, all confined to just three sites on Upsalls Creek, a large 4th order stream. The third survey (February 2000) investigated the use of adjacent riparian vegetation in the vicinity of the Kerewong roost. At each of 12 sites, one detector was placed on the stream, one 10 m from it and a third 20 m into adjacent vegetation. An average of 11 M. macropus passes per night was recorded over streams (total passes = 273), whereas no passes were recorded in adjacent vegetation. We conclude that M. macropus is sparsely dispersed across streams in forests of north-east NSW and that they are most likely to be recorded on large streams in the lower end of catchments. Management implications for timber production forests include redirecting effort from pre-logging surveys to monitoring the changing status of M. macropus over time, especially at day roosts where local populations are concentrated.

Path integration in a three-dimensional maze: ground distance estimation keeps desert ants Cataglyphis fortis on course

In this study, we investigate the ability of desert ants to gauge the ground distances of sloped sections in a three-dimensional (3D) outbound path. Ground distance estimation, as opposed to a simple measurement of walking distances, is a necessary prerequisite for precise path integration in undulating terrain. We trained ants to visit a feeder along a path that included an angular turn as well as a 'hill', resulting in an outbound path with a distinct 3D structure. We then observed the ants' return path in a test field on level ground. From the angles of the ants' return path on the test field one can infer which property of the hill segment was fed into the ants' path integration module, the actual walking distance or the ground distance. The results show clearly that it is the ground distance that Cataglyphis fortis feeds into its path integrator, and suggest that the ants are able to keep an accurate home vector also in hilly terrain.

FORAGING ANTS AREN'T CONFUSED BY A CLIMB

Without fail, desert ants make a beeline for their nests after a meandering foraging trip - and they manage this without spotting any landmarks or sniffing any scent trails. `It's amazing what these animals can do with a brain that's only a tenth of a milligram', says Bernhard Ronacher. To find out how desert ants measure distances on their long marches in search of food,Ronacher teamed up with Rüdiger Wehner of the University of Zürich and Gunnar Grah of Humboldt University in Berlin to test desert ants in hilly terrain (p. 4005).Desert ants use dead reckoning (path integration) to make their way home,which means that they must be able to measure both the direction and distance they've travelled from the nest. But what distance information do ants gather on their journeys across a hilly landscape - do they project their trajectories onto the horizontal plane as they travel over undulating terrain to measure the ground distance they've covered (`as the crow flies'), or do they measure the actual distance walked, which is much longer than the ground distance if the ants travel up and down hills?To find out, the team travelled to Wehner's field site on saltpans near Maharès, Tunisia. They trained three groups of desert ants to walk from their nest to a food site through L-shaped aluminium channels. The first group walked a straight stretch on the ground, then for the second leg of their trip they took a right-angled turn up a steep incline, walked another short straight stretch and then down a steep incline to ground level, where a bowl filled with biscuit crumbs awaited their arrival. The second group stayed at ground level, with the second leg of their L-shaped trip covering the same ground distance that the first group had travelled. Finally, the third group also walked along the ground, but the second leg of their journey was much longer, covering the same walking distance as the first group.The angle at which the ants subsequently set off for home would reveal whether the climbing ants (the first group) had gauged the ground or the walking distance during their L-shaped journey. Would climbing ants act like ants that had travelled the ground distance or like ants that had travelled the walking distance? When each ant had secured a treat from the bowl and held the crumb in its jaws for the homeward journey, the team scooped the unsuspecting insect into a box and took it to a flat field some distance away. To determine which direction an ant considered to be homeward bound, the team placed the ant on a grid painted on the ground and traced its movements on a piece of grid paper. They found that the ants that had climbed up the steep slopes set off at the same angle as the second group of ants, which had travelled the same ground distance as the first group. But the third group of ants, which had covered the first group's walking distance, took off at a completely different angle. Ants from the first two groups also travelled similar distances before they began circling to search for the nest entrance. The team concluded that ants measure the ground distance as they walk across hills, and don't measure the total distance walked. Importantly, desert ants incorporate this information into their path integration to calculate the correct angle to take a beeline back to the nest. If these ants ever find themselves crossing desert dunes, they certainly won't get lost on the way home.

Development and testing of models for predicting crown fire rate of spread in conifer forest stands

The rate of spread of crown fires advancing over level to gently undulating terrain was modeled through nonlinear regression analysis based on an experimental data set pertaining primarily to boreal forest fuel types. The data set covered a significant spectrum of fuel complex and fire behavior characteristics. Crown fire rate of spread was modeled separately for fires spreading in active and passive crown fire regimes. The active crown fire rate of spread model encompassing the effects of 10-m open wind speed, estimated fine fuel moisture content, and canopy bulk density explained 61% of the variability in the data set. Passive crown fire spread was modeled through a correction factor based on a criterion for active crowning related to canopy bulk density. The models were evaluated against independent data sets originating from experimental fires. The active crown fire rate of spread model predicted 42% of the independent experimental crown fire data with an error lower then 25% and a mean absolute percent error of 26%. While the models have some shortcomings and areas in need of improvement, they can be readily utilized in support of fire management decision making and other fire research studies.

一般座標を用いた乱れの計算におけるＩＢＭ法の適用

An Immersed Boundary Method (IBM) has been incorporated in a finite-difference code to solve the three-dimensional incompressible fluid flow using the boundary-fitted general curvilinear coordinate system. IBM has been developed for solving flows over complex boundary shapes on rectangular grids. In the present work it has been extended to be used in the boundary fitted coordinate system in order to represent complex objects on curving boundaries, such as undulating terrain with buildings and other objects. Basic verification study has been conducted by computing laminar flows over a model terrain and model rectangular objects to verify merits and efficiency of such a procedure compared with conventional methods. It is found that the IBM technique incorporated in a sigma-coordinate system in which the first coordinate follows the boundary representing the terrain and the second coordinate axis is taken in the straight vertical direction is most appropriate in both accuracy and efficiency, and is suited for calculating flow over topography with objects of various shapes.

The effect of a wildfire on stream water quality and catchment water yield in a tropical savanna excluded from fire for 10 years (Kakadu National Park, North Australia)

The wet/dry tropics of the Australian savannas are particularly prone to fire due to the highly seasonal rainfall and accumulation of grassy fuels. The effect of an early dry season wildfire (May, 1998) on the water quality of a seasonally flowing stream (December–June) was examined for a lowland savanna forest in Kakadu National Park (northern Australia) which had remained unburnt for 10 years. The water quality variables assessed were: total and volatile suspended sediment, phosphorus, nitrogen, iron and manganese. Compared to three years of pre-fire water quality data and 5 years of stream flow data, there was no detectable impact of the wildfire on the volume of stream flow, mean concentrations and the total mass transported by the stream for each water quality variable, except possibly nitrogen. The limited effect on water quality is attributed primarily to the timing of the wildfire and the low intensity relative to fires later in the dry season (September). The retention of canopy cover and the accumulation of leaf litter following the wildfire, and the catchment's gently undulating terrain all contributed to the negligible impact on water quality. Early dry season fires appear to be a viable management option for reducing accumulated fuel loads and hence reducing the risk of destructive wildfires later in the dry season.

Highway traffic noise prediction using method fully compliant with ISO 9613: comparison with measurements

In this study, we introduce outdoor sound simulation that is fully compliant with ISO 9613 yet with some complementary methods that enhance its applicability; for example, calculation of sound attenuation due to undulating terrain in octave bands, geometric divergence in the near-field of the source, and short-term wind effects. Using the method, we have carried out highway traffic noise prediction and measurement for 12 sites with representative road shapes and structures. In the prediction, the sound power level for a road segment was estimated by the method suggested in ASJ Model-1998 with experimental corrections to the overall noise level and spectrum. Comparing results between predicted and measured noise levels show good correspondence at direct, diffracted and reflected sound fields within 30m from the center of the near side lane.