Applications of GIS in assessing Coastal Change Rachel Hehre November 30, 2004 NRS 509 OVERVIEW

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1 Applications of GIS in assessing Coastal Change Rachel Hehre November 30, 2004 NRS 509 OVERVIEW ITRODUCTION Due to the dynamic nature of coastal systems, representing coastal change with precision and accuracy presents a challenge to coastal scientists. Traditional methods used to quantify coastal change, include time-consuming ground surveys, coupled with topographic mapping, or at best standard aerial photography. As newer technologies, such as digital photogrammetry, and light detection and ranging (LIDAR) are becoming more readily available, traditional methods are being supplemented and in some cases replaced. The application of Geographic Information Systems allow for the integration of traditional and modern data such that they may both be represented in geographically correct space, and interpretations of change through time may be assessed. GROUND SURVEYS Traditional surveying of coastal features employed profiling dune normal transects, or establishing grids to survey points. Dune normal transects monitor profile changes over time. The relative ease with which a transect can be collected, allows for a characterization of changes in the beach system, due to storm activity or events on a small time scale. However, there is no topology within transects, as the two dimensional representation cannot account for features or changes that exist in the alongshore direction. By establishing a grid over the area of interest, points may be surveyed and interpreted as a three-dimensional surface. This method is more time consuming than the transect method, requiring careful measure of grid points and orientation. However, once a grid is established, placing markers may allow for repeated measurement at known locations. Modern methods of field surveying have developed survey instruments that can determine geographic positioning in x, y, and z coordinates. These total stations no longer require a fixed or manually gridded set up, allowing for the inclusion of all topographic features of interest. (Andrews et al. 2002) The limitations of ground survey methods for coastal change include, tide constraints, inability to collect near shore data, and the human interpretation of features for survey (not all points of potential interest may be selected). Because of the selective nature of ground survey, there exists a need for extensive coverage of coastal areas that enable careful interpretation of coastal features. AERIAL PHOTOGRAPHY The use of aerial photographs to describe and interpret coastal data provides the best complete record of historical coastal change. In the 1920 s aerial photographs were available from a wide variety of sources including Federal agencies, state and local governments. Although they provide a long record of coastal change, the photographs themselves have inherent distortions and displacements. (Hapke, C.J.) In addition, because many aerial photographs were taken, not for use by coastal scientists, but for agencies with alternative needs, the captured image of the shoreline is not the focus of the photograph, and inherent distortions, sun reflection, and lack of tide information are

2 expected. To correct for some of the distortions, a process known as orthorectification has been developed. ORTHOPHOTOGRAPHY Aerial images that have been oriented and registered to contain plannometrically correct points are called orthophotographs. Although full rectification of aerial photos is time consuming and expensive, once established, coastal features can be delineated, and measured with the use of a GIS software, to make accurate interpretations of coastal features. Because historical images can be corrected and aligned to correspond to modern images, coastal change through time can not only be interpreted but also accurately assessed and measured. Data, such as high water lines, can be interpreted from orthophotos as a wet/dry line that runs along the coast. Such interpretations can aid coastal geologists in determining the change in high water, and the occurrence of erosion through time. DIGITAL PHOTOGRAMMETRY Photogrammetry can be defined as the process of deriving information about an object through photo measurements. The goal of photogrammetry is to establish the geometric relationship between an object and an image and derive information about the object strictly from the image. After finding corresponding points by image matching, a Digital elevation model (DEM) can be generated. In digital photogrammetry, aerial films are converted into digital image data with high resolution. A DEM is automatically generated with stereo matching using digital photogrammetric workstation. It is still very expensive but only a method for automated mapping. There is a need for further research if the patterns of terrain features are to be identified automatically. LIDAR DATA LIDAR stands for light detection and ranging. Interpreting the travel time of laser pulses, a distance from a receiver can be calculated. Coupled with a GPS system to monitor the flight path, and height of the source, an exact location of ground elevation and coordinates can be determined for any given point. Improved technologies have supported the development of laser scanning systems, and have improved accuracy of geometric results, in terms of position, distance, altitude and coordinates. LIDAR data must undergo processing steps to distill the extremely dense elevation data sets into a form that is readily usable for interpretation in GIS. With all the processing, and cost to generate usable data, LIDAR is expensive to produce and thus to use. A software package called Laser Map supports the creation of point elevation data, enables the gridding of entire surveys into compact files, an allows the assembly of large elevation image maps over selected regions. LaserMap would limit the processing steps by the user, by creating LIDAR products that can be directly inserted into a Geographic Information System (Brock et al.) Of particular interest in coastal change, LIDAR data provides optimal reception of air-water detection. Laser surveying has proven to be an excellent method for regional mapping of geomorphic change, the prediction and assessment of cliffed coasts, loss of land due to coastal erosion, and even predicting storm impact, and inundation mapping. CONCLUSIONS: Geographic Information Systems are an integral part of modern coastal change assessment. The acquisition of modern high quality data and the integration of historic

3 data within GIS allow for complex understanding of coastal change through time. Once data is incorporated into GIS any number of spatial and temporal analysis can be generated. Standard GIS tools, and simple data capture methods can be used to produce relatively high quality terrain representations. Data sets, once collected can be used over and to perform any number of calculations including erosion rates, dune migration, sediment transport, as well as smaller scale features of a beach such as, berm crests, beach cusps, and near shore bars. The use of LIDAR to interpret underwater environments allows for a non-invasive approach to monitoring habitat or the migration of dredged material in a system. As coastal environments are dynamic, and event driven, there is a need for current, and consistent monitoring through time. In the future, as more data are amassed for the study of coastal areas, the capacity to interpret and predict future coastal changes will increase considerably. References: (1) Tao, V.C.; Digital Photogrammetry The Future of Spatial Data Collection (2) Digital Mapping by Aerial Photogrammetry APPLICATIONS OF GIS IN ASSESING COASTAL CHANGE ANNOTATED BIBLIOGRAPHY Hapke, C.J. ;The Measurement and Interpretation of Coastal Cliff and Bluff Retreat; U.S. Geological Survey Professional Paper 1693, p This paper illustrates the variety of techniques for measuring coastal erosion along rocky or bluffed coasts, providing a general overview of traditional, as well as detailed explanations of modern technologies and techniques to determine coastal erosion. As newer technologies, such as digital photogrammetry, and light detection and ranging (LIDAR) are becoming more readily available, traditional methods, such as field surveying, profiling, and standard aerial photographic techniques are being supplemented and in some cases replaced. This paper addresses the compatibility of newer technologies with the need for accurate spatial data in a dynamic, storm driven coastal environment. Ackermann, F.; Airborne laser scanning present status and future expectations; ISPRS Journal of Photogrammetry & Remote Sensing; vol.54 p ; This paper introduces airborne laser scanning systems from their developed in the 1970s and 1980s, with early systems by NASA. Improved technologies have supported the development of laser scanning systems, and have improved accuracy of geometric results, in terms of position, distance, altitude and coordinates. The principle application of laser scanning concerns the generation of high quality topographic Digital Terrain

4 Models. (DTMs) Compared to traditional methods of DTM generation, the appeal of airborne laser is in its versatility, and virtually automatic methods for obtaining terrain information. Limitations include failure to capture detail, through a pre-fixed rigid pattern. The prospects for development and potential integration with imaging sensors are expected to accelerate airborne data acquisition to a new level of performance. For applications in coastal geomorphology, the need for accurate elevation models is integral to the understanding of dune, beach, and cliff retreat. Andrews, B.D., Gares, P.A., Colby, J.D.; Techniques for GIS modeling of coastal dunes; Geomorphology; vol. 48 p ; The prediction of coastal dune change by repeated measurement of topography over time is supported by the advent of GIS technology. This paper introduces the variety of data sources, high-resolution satellites, aerial photographs, Light Detection and Ranging (LIDAR) and ground surveys by hand, that may be used and manipulated in GIS in order to analyze spatial characteristics in geographically correct space. While the alternative techniques are mentioned, this paper focuses on the use of GIS to manage ground survey data sets in the form of dune normal transects, a gridded dune area, and the total station applications. This paper devotes much time to the determination of effective point densities and sampling routines for ground survey. Once these are established, data is acquired, processed, and analyzed to elevation change maps. The development of GIS software, and the generation of DEMs enable coastal researchers to visualize coastal features in a more intuitive (3D) way, as opposed to the traditional two-dimensional profiles. Livingstone, D., Raper, J., McCarthy, T.; Integrating aerial videography and digital photography with terrain modeling: an application for coastal geomorphology; Geomorphology; vol. 29 p ; The use of GIS technologies to integrate airborne and digital camera imagery with terrain data from ground survey is key to low-budget small-scale geomorphological investigations. This paper explores the benefits and consequences of utilizing cheap, available data, while at the same time preserving accuracy and resolution. Alternative forms of geomorphologic investigation are explained, including satellite sensors, aerial photography and archived photography. Digital resources have a distinct advantage in all forms, as they require fewer processing steps, and therefore a reduced production cost. The emphasis for this paper suggests that standard GIS tools, and simple data capture methods can be used to produce relatively high quality terrain representations. When studying and modeling dynamic coastal environments, there is a need for consistent monitoring and modeling. The high quality data, that is available, and inexpensive presents an opportunity for coastal geomorphologists to amass a wealth of geospatial data. Brock, J.C., Wright, C.W., Sallenger, A.H., Krabill, W.B., Swift, R.N.; Basis and Methods of NASA Airborne Topographic Mapper LIDAR surveys for Coastal Studies; Journal of Coastal Research; vol. 18 No.1, 2002.

5 Airborne laser surveying has a wide range of applications for coastal scientific investigations. This paper describes the methods use in the acquisition and processing of Airborne Topographic Mapper (ATM) data. In general, airborne laser surveying, or ALS, has proved to be an excellent method for mapping of the geomorphic change along coastlines to monitor coastal change and depict coastal hazards. There is some technical complexity to the article, including equations for laser data acquisition, and processing steps, which are difficult for the average reader to process. While the article explains this complexity, it also introduces a software package called LaserMap that would limit the processing steps by the user, by creating LIDAR products that can be directly inserted into a Geographic Information System. These products may be used by coastal scientists for a multitude of coastal studies. White, S.A., Wang, Y.; Utilizing DEMs derived from LIDAR data to analyze morphologic change in the North Carolina coastline; Remote Sensing of Environment; vol. 85 p ; This article provides an overview of the applications of digital elevation models to investigate morphologic change of five North Carolina barrier islands. The support for this technology in the form of annual surveys has enabled researchers to visually quantify barrier islands response to storm activity, and other coastal processes that occur on small time scale. This research found that beaches differed statistically if different management practices were applied to them, which is the basis behind managing beaches, and beach replenishment programs. What is interesting is that the differences were minimized, or disappeared if sequential hurricanes or storms affected the beaches. This has tremendous applications in coastal management, as beach replenishment projects can be costly, and have adverse environmental effects. Irish, J.L., Lillycrop, W.J.; Scanning laser mapping of the coastal zone: SHOALS system; ISPRS Journal of Photogrammetry & Remote Sensing; vol. 54 p ; The SHOALS system stands for Scanning Hydrographic Operational Airborne Lidar Survey. Developed for the US Army Corp of Engineers, the SHOALS system uses Lidar data to collect accurate, high-density measurements of bathymetry and topography in coastal regions. Airborne lidar bathymetry is capable of measuring water depths in very shallow, or environmentally sensitive waters that are unreachable by conventional survey method. This article explains the technical complexity of the SHOALS laser transmitter and set up, for optimal reception of air-water detection. In addition to its speed and accuracy, the SHOALS has a down-look video camera that is georeferenced to provide a visual record of the survey area. This is extremely useful when mapping coastal features, and reduces the need for field checks, or anomalous data found during post flight processing. Because coastal geomorphology includes areas of the coast that are submerged, the SHOALS system is extremely beneficial for studying the migration of offshore material, and features. Moore, L.J., Griggs, G.B.; Long-term cliff retreat and erosion hotspots along the central shores of the Monterey Bay National Marine Sanctuary; Marine Geology; vol.181 p ; 2002.

6 This paper provides background information regarding the need for increased monitoring and understanding of shoreline behavior. Coastlines experience dynamic conditions occurring at all time scales, and the need for quantification of landward movement in a system that is dominated by episodic and storm driven events is necessary. This paper presents a methodology to characterize cliff behavior, using mean erosion rates combined with an understanding of regional marine and terrestrial processes.