PGS whitepaper
The following is a whitepaper about Prototype Global Shoreline (PGS), from the NGA website
Prototype Global Shoreline Data
(Satellite Derived High Water Line Data)
The NGA Office of Global Navigation, Maritime Division is in the process of developing a new version of World Vector Shoreline (WVS®) and in support of this effort has acquired a prototype Global Shoreline Data set. This new shoreline is an approximation of the High Water Line; it is NOT a Mean High Water Line since the source data have not been tide coordinated. As segments of the prototype version are accepted from the contractor, these segments are being made available in the interest of supporting outside users who may have immediate application for these higher resolution data. These prototype data are not currently intended for safety of navigation products and do not necessarily reflect recognition of the political status of an area by the coastal nations affected or by the United States Government.
In processing these data, NGA has encountered significant changes in the position of certain features and these have yet to be investigated by comparison to other data sources. As the prototype effort progresses, NGA will begin compilation of the new version of WVS® and make application of the revised HWL, in the WGS-84 horizontal datum, to the smaller scale, i.e., Coastal and General scale (1:75,000 and smaller), NGA navigation products.
Background
NGA developed the current version of World Vector Shoreline® through digitization of a variety of hard copy map and chart products. The limited accuracy of these products resulted in a WVS® product at an accuracy of about 250-meters, which in this era of accurate satellite positioning is of limited utility.
The prototype Global Shoreline Data set (satellite derived High Water Line) in work at NGA has been acquired from orthorectified NASA, 2000 era, LANDSAT GeoCover (multi-spectral imagery). The research and development component of NGA, InnoVision Directorate, studied the best approach for acquiring shoreline data using LANDSAT 7 multi-spectral imagery and developed a technique using the Short-Wave Infra-Red (SWIR) bands to define the land water interface. The result of testing of the SWIR band approach showed that the resulting accuracy of shoreline derived in this manner is about 50-meter (RMS). This basic technique was implemented by the contractor that collected these shoreline data.
In producing the Global Shoreline Data, the raster image data were converted to vector data, compared to existing NGA Digital Chart of the World/WVS® holdings followed by review of imagery to consider the location of identifiable debris lines.
Prototype development
NGA contracted to have the new Global Shoreline Data captured in segments matching 28 of the 29 NGA Digital Nautical Chart (DNC®) Compact Disk (CD) regions. Because there is no LANDSAT coverage of the polar-regions (coverage extends from about 60-degrees South latitude to 80-degrees North latitude) no shoreline was captured for the 29th DNC CD region of Antarctica. It is anticipated that the entire shoreline data set will eventually be made available to the public on CDs or DVD through the NOAA, National Geophysical Data Center.
Because the initial capture used LANDSAT 2000 imagery, there are gaps throughout the data set due to cloud cover and in northern areas due to ice and snow cover, which impact about 10% of the overall data set. Shoreline is captured as one set of shape files. Cloud (cloud/cloud shadow/no data) covered areas were captured as a second set of shape files. The shape files for these gap areas are not included with the on-line data since they increase file size and are of little use to users.
NGA plans to place the new World Vector Shoreline in continual maintenance with updates being made available from this NGA website. NGA has begun comparing the Global Shoreline Data set with its DNC Coastal and General scale charts and in some cases with Approach scale charts. Work is currently in progress to evaluate the radar imagery acquired from the Shuttle Radar Topography Mission (SRTM) as a possible means for filling some of the cloud covered gaps. In addition, other imagery will be evaluated for filling of the gaps as this work continues into the future.
Because the 2000 era LANDSAT imagery was acquired prior to the 2004 Indian Ocean Tsunami, which caused several major changes to shoreline, NGA has contracted for follow-on capture of shoreline to update this important region.
Low-water elevations
NOAA, which has an interest in a consistently derived global shoreline and also low water hazards identification for coral reef research, endorsed the shoreline project of NGA. At the request of NOAA, NGA initiated capture in the Caribbean region of visible sub-surface/low water hazard areas, which are potential coral growth regions (NOAA interest) and hazard areas for navigation (NGA interest). The capture of the visible shallow water hazards differed from the shoreline collection in that submerged features were identified from the reflectance of the short-wavelength electromagnetic radiation penetration into the ocean. The initial effort concentrated on the Caribbean Sea and follow-on work, post 26 December 2004, has been contracted for the Tsunami impacted regions of the Indian Ocean. The low water coral growth areas are being evaluated at NOAA. In doing so, NOAA must contend with the problem of cloud cover gaps in the data. Once processed, NOAA plans to make these data available to the public through the NOAA web site http://www.noaa.gov and U.S. Coral Reef Task Force website http://coralreef.gov. NGA will conduct a review of these data for potential application to NGA navigation products.