National Ocean Service Shoreline Mapping Program
Captain Richard P. Floyd, NOAA
Chief, Photogrammetry Division
Silver Spring, MD 20910
The Photogrammetry Division of the National Ocean Service (NOS) is responsible for delineating the official shoreline of the U.S. domestic waters and territories, including the outer coast, the estuaries, and the Great Lakes. Though the primary objective of the program is to serve nautical charting requirements, the data collected and information produced is of great value to others, too. The policy of the Division is to pursue cooperative arrangements with others in conjunction with the execution of its own mission. Technological advancements over the past few years have made this a workable endeavor, and shared capabilities can result in greater exploitation of the vast amount of information contained in aerial photographs. The Photogrammetry Division currently has agreements with agencies in Florida, California, and Massachusetts, and is pursuing agreements with Washington, Oregon, and Louisiana. Planning for these collaborative efforts begins with clearly identifying all interested parties' basic objectives and requirements.
Missions of NOS and the Photogrammetry Division
The missions of NOS are manyfold. It establishes and maintains accurate networks of geodetic control, which constitute a framework for geopositioning spatial data. It provides charts and related information for the safe navigation of marine and air commerce. It promotes "sustainable development" of coastal ecosystems, so that economic benefit can be realized while conserving the biodiversity and long-term productivity of these areas. It compiles and provides data and information collected for these purposes to scientists, engineers, and managers who have various needs for it.
The Photogrammetry Division is part of the National Geodetic Survey, a component of NOS. A primary mission of the Division is to accurately map the official U.S. shoreline for the production of nautical charts, and adjunct scientific and engineering purposes. Mapped features normally include the mean high water line and the mean lower low water line, along with other coastal features--both natural and cultural. The geographic area of responsibility of the Photogrammetry Division encompasses the coast of the United States, including the Great Lakes, and its possessions. The Division's mapping responsibility is limited in extent to a rather narrow strip along the coast and connecting waterways. In the past, the main product was a graphic map, called a "shoreline map" or "T sheet," or "TP sheet." Today, digital data is produced, which can be used in a GIS or to make a map using a plot program of the user's choice.
Recent Policy and Management Developments
Traditionally, the coastal mapping mission of the Photogrammetry Division was funded by direct appropriation. Funding has remained relatively level over recent years, resulting in reduced spending power. This, in conjunction with a change in management philosophy, resulted in outreach activities, where the Division sought cooperative ventures with other organizations, Federal, state, and local. The thrust of the outreach activities was to coordinate with others so that photogrammetric data would be acquired in such a manner as to serve needs in addition to those of nautical charting. Priorities are still based on nautical charting requirements, but projects are designed with the needs of collaborating agencies in mind. These cooperative ventures have proven very worthwhile.
Coincidentally, NOS has been making a strong effort to bring cohesion to its many missions.
NOS was formed from a conglomeration of Federal agencies engaged in related activities. These
included mapping and charting, establishing geodetic frameworks, producing tide and current
predictions, coastal zone management, and assessment and prediction of coastal conditions.
Although these activities were all loosely affiliated, they never became intimately linked, with a
common, overall, well-defined goal. Attempts to bring the activities together by decree were
Our approach to building cohesion has been changing over the recent past. The change started with an earnest attempt to induce partnerships among NOS components and organizations outside NOS, by providing much-needed funding to those units that formulated meritorious partnership proposals. This was a good attempt at unification, but it still fell short of developing sincere and close association among the NOS activities. The most recent effort at motivating close coordination between NOS line organizations is destined for success. The cornerstone of the strategy is geographic focus. Many NOS activities are directed toward matters in the coastal zone. By concentrating in specific areas of concern in the coastal zone, NOS can bring many of its resources to bear in solving regional problems. This geographic focus provides a common interest about which to marshal NOS forces.
Photogrammetry is a branch of remote sensing in which precise spatial relationships between objects are extracted from photographs. In this paper, the discussion is limited to the use of aerial photographs for determining geographic positions of objects and features on the ground or sea floor. Geometric relationships equating photo coordinates to ground coordinates are determined, then used to map features of interest that can be identified in the photographs. First, in a process called "aerotriangulation," the position and orientation of the camera at the precise instant of exposure are determined. This is achieved, in part, by relating the positions of a few strategically-placed ground control points to measurements of their images in the photographs. Sets of stereo pairs are needed for this process to determine distances between the camera exposure station and the ground control points, just as we need two eyes to judge distance in our everyday activities. Once the positions and orientations of the photos at the times of exposure are determined, positions of other points and features on the ground can be resolved using a process called "compilation." Again, stereo pairs are needed. Film deformations and distortions caused by individual camera characteristics are taken into account in these procedures. The Photogrammetry Division uses sophisticated analytical stereoplotters for making the photo measurements and doing the computations. Digital files are the output.
Using proper procedures and precise instrumentation, surprisingly accurate results can be obtained. The traditional rule of thumb for predicting the accuracy for a planned project was that the obtainable horizontal and vertical accuracies at the 90% confidence level for aerotriangulated, discrete image points would be 1/10,000 and 1/5,000 of the flying altitude, respectively. The Photogrammetry Division generally acquires photography at an altitude of 24,000 feet, resulting in horizontal and vertical accuracies for aerotriangulated points of 2.4 feet (0.7 meters) and 4.8 feet (1.5 meters), respectively, from 1:48,000 scale photographs. Aerotriangulation, a process that concludes with a rigorous mathematical adjustment of newly determined positions of discrete points, lays the foundation for the compilation phase, where the accuracy of discrete points is about half as good (1.4 meters horizontal, and 2.8 meters vertical). Kinematic GPS positioning of the camera exposure station and airborne calibration techniques have improved the obtainable accuracy in both aerotriangulation and compilation by a factor of at least two. The Photogrammetry Division exploits these techniques. Accuracies at which indistinct features can be mapped are lower, due primarily to softness of their boundaries and uncertainty in interpretation.
Recent technological developments have significantly improved the ability of the Photogrammetry Division to acquire aerial photographs efficiently. However, while data acquisition has become much more efficient, aerotriangulation and the compilation of shoreline data from the imagery has not seen a concomitant increase in efficiency (though they have become more accurate). A bottle neck in throughput results. The effect is that the Photogrammetry Division is in a position to provide imagery to collaborating agencies in a timely manner, but compiled data may take longer than desired.
Technological improvements that have already been implemented and are having an impact on efficiency or improving the accuracy of Photogrammetry Division products are listed below. Also listed are technological advancements now being developed, which will ultimately streamline the Division's throughput.
Global Positioning System - The use of GPS in the aircraft for determining the positions of camera exposure stations decreases the amount of ground control needed for photogrammetric aerotriangulation. On the ground GPS allows geodetic control to be established at more convenient sites, thus reducing the field effort. GPS also facilitates navigation of the aircraft during the photographic mission, which virtually eliminates re-flights caused by mis-navigated flight lines.
Aerial Cameras - Image motion compensation is a process in which photographic film is transported within the film magazine while an image is being exposed, to account for movement of the camera over the ground during exposure. This results in better quality imagery, which in turn allows the imagery to be collected at altitudes more appropriate for efficient, or effective, operations.
Stereo Plotters - The first stereo plotters were analog devices that relied on intricate arrangements of optics and mechanisms to recreate the camera orientation for each photograph taken, in order to properly map features. They produced only a graphic product. Many of the mechanical elements found in analog stereo plotters were replaced with servo systems under the control of mathematical models found in the next generation of stereo plotters. These analytical stereo plotters generated digital data rather than graphic plots. The Photogrammetry Division uses analytical stereo plotters for its coastal mapping program. The latest generation of stereoplotters is referred to as "softcopy." Here, the optics of the system are replaced by electronics, and the operator sees stereo on a computer monitor, using special eye glasses. The big advantages of softcopy over analytical stereo plotters include lower cost equipment needing less maintenance, potential for automated aerotriangulation and semi-automated compilation, and automated production of ortho photos. The Photogrammetry Division has acquired a softcopy workstation and software, and is currently in the process of getting familiar with it, so the technology can be integrated into the production system.
The Photogrammetry Division has been making a dedicated effort to collaborate with other Federal agencies, and state and local organizations during the planning and execution of projects. In Florida, for example, the Division is working with the NOS Office of Ocean Resources Conservation and Assessment, the NOS Office of Ocean and Coastal Resource Management, the NOAA National Marine Fisheries Service, the NOAA Coastal Ocean Program, and the Florida Department of Environmental Protection (DEP). The primary objectives of the venture are to produce contemporary shoreline mapping data and to map benthic communities in Florida Bay and along the Keys. The DEP's contribution to the project is to delineate and classify the benthic communities, which the Photogrammetry Division will then compile, along with the other features it maps. Though resource limitations and technical difficulties have hampered work, a demonstration prototype was very successful, and progress is being made on the remainder of the project.
In California, where the entire outer coast is being mapped by the Division, personnel from NOS are working with State and local authorities to realize increased benefit from the undertaking. Another California project being planned covers San Francisco Bay. Collaborating organizations involved in these two ventures include the California Coastal Commission, the California Coastal Conservancy, and the San Francisco Bay Conservation and Development Commission, among many others. Aerial photographs along flight lines in addition to those strictly needed by NOS were acquired while the aircraft was conducting its mission over the outer coast. The Photogrammetry Division expects to be compensated for this work through increased sales of aerial photographs, and through in-kind contributions such as field verification and conversion of imagery to digital form.
In San Francisco Bay a novel arrangement involves the State's endeavor to produce digitized data
in topologically-structured vector format from historic NOS shoreline maps to meet their GIS
needs. In preparation, the Photogrammetry Division is scanning the maps in raster format. The
Division will get the vector files from the State in return. This will contribute to the Division's
effort to digitize its historic shoreline map series, as well as aid in the compilation of revised
shoreline when that mapping project is undertaken. Both South Florida and San Francisco Bay
are examples of where the NOS thrust for a regional focus is redoubling efforts in which the
Photogrammetry Division has already been involved.
Massachusetts is another state where the Photogrammetry Division is working closely with others on a coastal mapping project. Here, the Division extended some flight lines short distances in order to provide aerial photography in some areas needed by the State. In this project, the State has a great interest in acquiring digital imagery, which will be used for rough as well as rigorous mapping applications. The State's Coastal Zone Management Program is scanning the Photogrammetry Division's color transparencies, and will provide copies of the digital images to the Division in return for use of the transparencies. The Federal Emergency Management Agency is also involved in the project. FEMA has contributed funding for the Division to georeference flood insurance rate maps and to map erosion reference features. These are such features as debris lines, crests of dunes, edges of bluffs, berms, and the like. They are used to establish set-back limits for new construction.
The States of Washington and Oregon were approached last fall with a solicitation to collaborate on an upcoming project. Both states responded with much interest, in some cases requesting work that substantially differs from that required to meet NOS' nautical charting needs. Local requirements are currently being considered in the planning of the project, but without a commitment of funding, the Division will be unable to satisfy those needs that differ too much from its own. Others can be met with minor shifting or extension of some flight lines. Close coordination will be maintained with the local agencies, so that features of interest to them can be paneled just before the flight mission. State agencies have offered to reciprocate by establishing ground control for the project.
Louisiana is being brought into the fold for a project to be conducted along its coast next winter. The first step was to contact someone in the State who would likely have interest in the project, and who could suggest an appropriate forum in which the Division could make an overture to other potentially interested state and local agencies. In this case, the Louisiana Department of Transportation and Development suggested the Photogrammetry Division Chief attend a GIS/remote sensing workshop to establish contacts through one-on-one interactions. The aim was to identify a partner who would be willing to serve as a focal point for the State's interests. This was accomplished. The Department of Environmental Quality will serve that role. The next step will be for the DEQ to arrange a more formal meeting, where the Division will explain its plans for the project, and solicit input from all interested parties. This will be followed by an evaluation of the state and local wishes, and final planning of the project.
Direct funding for the Photogrammetry Division comes from the Mapping and Charting budget line item. Congressional conference language obligates the Division to spend those funds, in the most cost-effective way possible, for nautical charting purposes. The actual purchasing power of direct funding has decreased substantially over the years, causing the Division to seek additional, reimbursable funds in exchange for products and services. This occurs at a time when most other government agencies are also operating on reduced budgets. The situation stimulates creative agreements based on close cooperation and earnest compromise.
When agreements are struck, the Photogrammetry Division must ensure that the public trust is honored by expending its direct funding exclusively in support of the nautical charting mission. Photogrammetric requirements for nautical charting are fairly straightforward. First and foremost, particular water level or tidal datum lines must be mapped. In tidal waters, the mean high and mean lower low water lines are the datums of interest. Often these lines are mapped using black and white infrared film flown at the appropriate stage of tide. Black and white, or "panchromatic," IR photography renders water as black. This provides a very distinct and accurate delineation of the water-land interface. The location of the mean high water line is sometimes interpreted from natural color photographs using closely correlated physical evidence, such as debris lines or the wet-dry sand abutment. The mean lower low water line is always mapped using panchromatic IR photography acquired at time of mean lower low tide. The mean lower low water line is the baseline from which marine boundaries are drawn. The shoreline is peppered with many manmade features such as piers, jetties, groins, and bulkheads, which are mapped as a matter of course. Aids to navigation, landmarks, and cultural features such as roads are also mapped for nautical charting purposes. The scale of the nautical charts in the survey area dictate the required accuracy, which generally can be obtained with 1:48,000 scale photography. Additional mapping may only be accomplished if funded by the requesting agency or through quid pro quo arrangements.
When available funding is limited, reimbursement in kind offers numerous opportunities to accomplish objectives of multiple organizations. Some examples were cited above. For completeness, they are repeated here, along with others, as follow: Local authorities are usually in a much better position than the Photogrammetry Division to make logistical arrangements. They can arrange for or provide transportation to remote locations, and gain access to or through private properties. They can provide advice on seasonal factors and monitor environmental conditions, such as water clarity, when the flight mission is underway. State and local authorities can sometimes provide people to assist in the field. As mentioned earlier, such people might establish ground control. Or, they might lend or operate GPS reference receivers necessary for the photographic mission. Or, they could place, monitor, and retrieve photo panels. Once the photography is acquired, state and local agencies can provide expertise for interpreting and delineating special features they want mapped. These services would be furnished in exchange for the extra mapping effort required of the Photogrammetry Division.
It is to everyone's benefit to cooperate in the design and execution of a photogrammetric mapping project. Shared capabilities can result in greater exploitation of the vast amount of information contained in aerial photographs. Limited means makes it absolutely essential that the Photogrammetry Division deals with one and only one agency per state, willing to serve as a focal point in coordinating state and local needs. These needs should be expressed in basic terms, such as features to be mapped and accuracy desired in the final products, rather than specifications such as resolution, or scale, or film type. With sufficient forethought, the potential for synergism in coastal mapping projects conducted by the Photogrammetry Division is exceptionally promising.