The Use of Surveying in Mapping Features within the Physical Landscape - Term Paper Example

The Use of Surveying in Mapping Features within the Physical landscape Morphological Mapping Morphological mapping is the process of delineating different features in a landscape based on their surface form or morphology. The primary information needed for this method is topographic elevation. This may be derived from topographic maps or digital elevation models This method involves the mapping of point properties and/or specific landforms. Point properties include elevation, relief, slope, aspect, and curvature (Evans 1972). In the state of Michoacan, Mexico, relief and slope were used to classify the landscape into different landforms such as plains, piedmonts, plateaus, hills and sierras (Bocco et al. 2001). In the Oregon Coast Range, Roering et al. (2005) were able to distinguish a debris-flow terrain from a deep-seated landslide terrain by means of a topographic index determined by slope and curvature. The applicability of morphological mapping depends on the scale and resolution of the elevation data and the scale of the features to be investigated. For example, a 1:50000 or 1:100000 topographic map may not be appropriate for studying the surface morphology of glacial moraines and ablation areas, thus the need to do topographic mapping at larger scales (Sharp 1984; Watanabe 1985). Conversely, the study of the continental- to global-scale topographic relief may prove too cumbersome if 1:50000 maps are used. Computer technology has greatly improved the state of morphological mapping. The practice has been revolutionized by the digitization of elevation data, the increased processing capabilities of computers, and the development of various terrain analysis softwares. The increasing use of remotely-sensed images jointly with digital elevation data has further enhanced the discipline of morphological mapping (Florinsky 1998). Plane Tabling A plane table survey set-up consists of a drawing platform, a tripod, an alidade, and a device for measuring distances (Gillespie 1868; McCormac 2004). The platform is mounted on the tripod such that the former can be levelled and rotated. Paper for plotting is fixed on top of the platform. The alidade consists of a telescope mounted on a ruler such that a vertical plane contains both the edge of the ruler and the telescopes line of sight. A vertical arc indicates the inclination of the telescope. With the alidade, a stadia rod can be used to measure distances. Plane table surveying employs direct plotting in the field. First, the alidade is mounted on the platform and a line of sight from the observation point, A, to a target feature, B, is established using the telescope. Without moving the alidade, this line of sight is plotted on the paper using the edge of the ruler. The actual distance from A to B is measured using the stadia and the appropriately scaled distance is drawn on the plotted line of sight. Plane table surveying may be conducted using the methods of radiation, propagation and intersection (Gillespie 1868). The first two methods require distance and direction, as discussed in the previous paragraph. Intersection involves triangulation, wherein the location of a target feature is determined even without measuring its distance from either one of the two known observation points. Vertical positioning can be done through trigonometric levelling (McCormac 2004). By measuring the horizontal or slope distance, and the inclination of the telescope, the difference in elevation between the observation point and the target feature can be calculated. A major advantage of this method is that the surveyor can readily verify the drawing with the actual terrain. This minimizes the chances of making wrong measurements or missing out key terrain features (McCormac 2004). But the method is difficult to use in wet climate, as moisture may ruin the paper. The size of the instrument makes it unstable compared to theodolites. As a result levelling can be easily disturbed during the works progress (Duggal, 2006). While rendered almost obsolete by significant improvements in survey methods and instruments, plane table surveys remain practical for projects that do not need high degrees of accuracy and precision or for mapping at scales usually ranging from 1:2000 to 1:4000 (Duggal 2006). As late as the 1980s, plane-table surveys are still being used in glacial studies. In south-east Iceland, the annual movements of a glacier terminus was studied using a ~1:2000 map of moraine ridges constructed from plane tabling (Sharp 1984). Surface morphology of the Khumbu Glacier in Nepal was investigated using 1:1000 maps generated from plane table and theodolite surveys (Watanabe et al. 1986). Theodolite and GPS Surveying The theodolite is an instrument that measures horizontal and vertical angles and distances, similar to the operating principles of the plane table discussed in the previous section. The major difference is that the theodolite has mechanical or electronic features, such as verniers and optical or digital read-outs, which allow greater accuracy and precision in measuring angles (McCormac 2004). This results to a more accurate and more precise survey output. Also in contrast to plane tabling, plotting in the field is not done during the theodolite survey. Global Positioning System (GPS) surveying differs from the plane table and the theodolite in terms of the operating principle. This survey makes use of a network of space-borne satellites which sends and detects radio signals to and from a GPS receiver unit located on the ground (McCormac 2004). Satellites send out radio signals and measures the time the signals take to reach the receiver unit. Knowing the travel time and velocity of radio signals, the distances of the satellites from the receiver unit can be calculated. From these distances, the location of the receiver unit can be determined. Because of their accuracy, theodolite and GPS survey are being used for studying beach morphology and coastal erosion. Both survey methods have been used in the study of Rodas Beach in north-west Iberian Peninsula (Costas et al. 2005). The surveys involved the establishment and monitoring of several beach profile lines to determine the effects of storms on the morphology of modal low-energy beaches. The onshore segments were surveyed using the theodolite, whereas the offshore part was surveyed using an echo sounder and GPS on a boat. Remote Sensing and aerial photography Remote sensing is the process of obtaining information about the earths surface from an overhead perspective. Information, in the form of images, is usually generated by an aircraft- or satellite-mounted sensor that receives electromagnetic radiation from the earths surface (Campbell 2002). Electromagnetic waves used in remote sensing may be in the form of visible light, infrared, microwave or radio wave (Campbell 2002). Aerial photography is one type of remote sensing. Generally, the process of remote sensing begins with the target object on the ground emitting or reflecting electromagnetic radiation. The radiation is detected by the sensor, which generates the sensor data. Image interpretation transforms the sensor data or image into a specific information that can be used by specific applications to solve specific problems (Campbell 2002). Because data is obtained remotely from the air or from space, accessibility to and physical presence on a target site is not a requisite. Many sensors have the capability to gather information for a large area within a short period of time. For example, the NOAA-AVHRR can cover a 2399-km swath several times a day. Some sensors offer considerable accuracy given the amount of time needed to produce the information. SPOT-5 panchromatic data, with 5-m resolution and covering 60- to 80-km swaths, can be produced in less than 3 days (Joyce et al, 2009). Recent advances in remote sensing have increased the use of the technology in the field of natural hazards science . Joyce et al. (2009) identified different sensors which are being used or which have potential for this field. Remotely-sensed images taken before and after the occurrence of a natural hazard can show changes in the topography and ground cover. Normal difference vegetation index (NDVI) images can be used to differentiate recent volcanic debris and the adjacent vegetated areas (Castro & Carranza 2005). With these information, rapid damage assessment can easily be conducted. Multi-temporal images are also being used for monitoring hazards. Monitoring may be conducted for wildfires on a daily basis by using MODIS (Giglio & Kendall 2001). It may also be employed for slow events such as landslides with velocities in the order of several centimetres per year using ERS-SAR (Rott & Nagler, 2006). Reference List Bocco, G, Mendoza M, & Velazquez A 2001, Remote sensing and GIS-based regional geomorphological mapping—a tool for land use planning in developing countries, Geomorphology, vol. 39, pp. 211–219. Campbell, J 2002, Introduction to remote sensing, 3rd edn. The Guilford Press, New York. Castro, OT & Carranza, EJM 2005, Remote sensing of temporal variations in spatial distributions of lahar and pyroclastic-flow deposits, West Mount Pinatubo, Philippines in Remote sensing and GIS for environmental studies, volume 113, eds S Erasmi, B Cyffka & M Kappas, Gottinger Geographische Abhandlungen, Gottingen, pp. 223–229. Costas, S, Alejo, I & Nombela, MA 2005, Persistence of storm-induced morphology on a modal low-energy beach: A case study from NW-Iberian Peninsula, Marine Geology, vol. 224, pp. 43– 56. Duggal, SK 2004, Surveying, vol 1, 2nd edn. Tata McGraw-Hill Publishing Co. Ltd., New Delhi, India. Evans, IS 1972, General geomorphometry, derivatives of altitude, and descriptive statistics in Spatial Analysis in Geomorphology, ed RJ Chorley, Methuen, London, pp. 17-90. Florinsky, IV 1998, Combined analysis of digital terrain models and remotely sensed data in landscape investigations, Progress in Physical Geography, vol. 22, no. 1, pp. 33–60. Giglio, L & Kendall, JD 2001, Application of the Dozier retrieval to wildfire characterization: a sensitivity analysis, Remote Sensing of Environment, vol. 77, pp. 34–49. Gillespie, WM 1868, A treatise on land-surveying: Comprising the theory developed from five elementary principles; and the practice with the chain alone, the compass,the transit, the theodolite, the plane table, &c. D. Appleton and Company, New York. Joyce, KE, Belliss, SE, Samsonov, SV, McNeill, SJ & Glassey, PJ 2009, A review of the status of satellite remote sensing and image processing techniques for mapping natural hazards and disasters, Progress in Physical Geography, vol. 33 no. 2, pp. 183–207. Roering, J, Kirchner, J & Dietrich, W 2005, Characterizing structural and lithologic controls on deep-seated landsliding: Implications for topographic relief and landscape evolution in the Oregon Coast Range, USA, GSA Bulletin, vol. 117, no. 5-6, pp. 654-668 Rott, H & Nagler, T 2006, The contribution of radar interferometry to the assessment of landslide hazards, Advances in Space Research, vol. 37, pp. 710–719. Sharp, M 1984, Annual moraine ridges at Skálafellsjökull, south-east Iceland, Journal of Glaciology, vol. 30, no. 104, pp. 707-714. Watanabe, O, Iwata, S, & Fushimi, H 1986, Topographic Characteristics in the Ablation Area of the Khumbu Glacier, Nepal Himalaya, Annals of Glaciology, vol. 8, pp. 177-180. Read More