Michael Baker Jr. Inc. recently completed a 10-Year Strategic Geographic Information System (GIS) Plan for the Virginia Department of Transportation (VDOT). As part of the development of this plan, the increased used of various forms of remote sensing was assessed. The development and maintenance of transportation-related spatial information was the focus for remote sensing use. SPOT imagery, standard aerial mapping photography, terrestrial photography, video imagery and commercial satellite imagery are the primary remote sensing sources which will benefit the VDOT operational applications over the coming years. This article discusses these remote sensing opportunities in context with VDOT's GIS requirements, introduces the implementation considerations and actions recommended to realize the potential benefits from using complementing remote sensing.

VDOT'S REMOTE SENSING ROAD MAP

SPOT Imagery
SPOT imagery has recently been acquired covering the commonwealth of Virginia. This was ortho-corrected to U.S. Geological Survey (USGS) 7.5 Minute Quadrangle projections by using digital elevation data from the USGS. This imagery is planned to be used for road centerline location certification, other transportation-related information (e.g., airfield information) and supporting right-of-way analysis over the next one to three years. It can be used in digital raster form and overlaid with digital vector formatted, enhanced TIGER data on workstations to perform "heads-up" digitizing to delineate and identify transportation feature locations. Figure 3 depicts an area near Suffolk airport in Southeastern Virginia. This shows the SPOT imagery enlarged to 1/12,000 scale with enhanced 1990 TIGER road vectors overlaid. The 1990 TIGER data is used to guide the interpreter in delineating features from the SPOT image scenes. Since the TIGER data is already five to 10 years old, it will not contain all the roads, but it will help in the depiction of most of the roads-as well as natural features.
      Later, after the road information has been extracted, the TIGER files can be adjusted and this information, along with the address data elements may be helpful to Enhanced-911 users around the State of Virginia. The SPOT imagery can also, be useful as background to snow map overlays and other VDOT products generated by the operational divisions working at 1/24,000 and smaller scales. The investment in the SPOT coverage and Enhanced TIGER data will be a little over $200,000. This will be useful, as is, for at least 2-5 years and can be augmented with new image scenes and year-2000 TIGER data, when available.

Standard Aerial Mapping Photography
Aerial mapping photography has been used for many years for all types of location and design applications within the VDOT. It will continue to be used in a similar manner, however, it will also be used as the source for digital orthophotography and digital imagery from scanned film for detailed engineering and construction support. The digital orthophotos may be used to extract transportation features for 1/12,000 scale mapping and related analysis. Figure 1 is a digital orthophoto of an area in Caroline County, Va., enlarged to 1/6,000 and the roads which have been extracted from it are shown as vector-overlaid lines. A qualified image interpreter can use image enhancement software to make use of this imagery when it is enlarged to over 1/1,000 scale in many rural areas. This type of digital raster imagery is used similarly with SPOT imagery, but the level of detail and location accuracy of feature information may increase if proper procedures are used, since the ground sample distance for each image pixel is 1 meter for the orthophotos versus 10-12 meters for the SPOT imagery. Driveways and other smaller roads are resolvable from this orthophotography from aerial mapping cameras.
      It will take a little over 3,000 digital orthophoto quarter-quadrangles (DOQQs) to cover Virginia and if a production estimate of $1,000 per DOQQ is used, it means over $3,000,000 will be required to provide this base of material. Of course, an important consideration, is that these DOQQs can benefit many other Commonwealth of Virginia users beyond the VDOT; therefore, the cost can reasonably be amortized across multiple organizations.
      Figure 5 shows an aerial photo over the Danville, Va. area similar to what is used to support standard analytical photogrammetric operations and photo interpretation/display board preparation for road design, engineering and construction monitoring. This type of imagery is a source for 1/500 to 1/6,000 scale map products and GIS analysis of small geographic areas. This imagery will be scan-digitized for use with digital photogrammetric workstations on a more frequent basis over the next decade at VDOT and by its contractors.
      Global Positioning System (GPS) receiver information will continue to be used for ground control densification with aerial mapping photography. The GPS will also be increasingly used in conjunction with the aerial photography collection to produce GPS-derived geographic coordinates for the nadir of each image exposure station. This will significantly improve and cut the costs for aerotriangulation and ground control survey operations.

Terrestrial Photography
Terrestrial photography will be used to collect both non-calibrated camera image scenes and monoscopic or stereoscopic images from calibrated cameras. The former will be used more frequently. All of these types of images will be accessed by using a GIS interfaced to document image system files or as separate image files. Figure 2 shows an example of one of many terrestrial photos which may be in a database for each bridge in Virginia. These images will be useful when using GIS to support bridge inspection preparation and reporting as part of the VDOT Bridge Management System in response to the Federal Intermodal Surface Transportation Efficiency Act (ISTEA).

Video Imagery
Video imagery has increasing potential as augmenting input to update GIS database information. It is currently being used to collect road-related feature information at the same time road centerline locations are being collected by moving, van-mounted GPS receiving stations. This video imagery, as shown in Figure 4, is stored for reference and coordination viewing by planning, maintenance and others in the VDOT. It is being used in conjunction with van-mounted GPS receivers to collect data for VDOT's Pavement Management System within the Fredericksburg District. In the future, airborne video may be very useful to update right-of-way and or roadway information. Digital image processing and digital photogrammetric techniques are available to convert and use video, either monoscopically or stereoscopically. Video imagery is also being used in near real-time and in real-time to assist in traffic congestion management. This will increase as the VDOT implements Intelligent Transportation Systems.

Commercial Satellite Imagery
Another type of remote sensing imagery will soon be available to VDOT. This is the commercial satellite, high resolution imagery now being prepared for acquisition by at least three teams of private companies within the United States. This source of 1 meter ground resolution imagery is being seriously considered by VDOT as an alternative to digital orthophotography. Figure 6 is a simulated example of this type of image showing the expected resolvable spatial detail.
      There are unknowns with this imagery, such as the calibration and math models to support digital and film-based photogrammetric operations. Also, the distribution, pricing and reference data aspects for customer-support for these types of systems are yet to be announced.
      Mapping and feature interpretation experience in the past with this type of imagery under classified conditions, does suggest it will be very applicable and cost advantageous for VDOT to use in support of many applications, such as base mapping up-dates, road system planning and certain types of pre- and post-emergency analysis/reporting.

Implementation Considerations
Since the VDOT is transitioning from only using film-based aerial mapping photography to many other types and formats, a number of institutional and technological considerations need to be considered. The need to assure airborne GPS and aerial mapping camera calibration when collecting GPS-augmented aerial photography for mapping is important. The use of "softcopy" or digital photogrammetric tools, digital image processing tools, digital document library systems, modern high resolution scanners and color plotters need to become commonplace before efficient use can be made of some of these emerging remote sensing images.
      There is also a need to understand modern relational database management systems interfaces to GIS software. Fiscal records from construction projects, ownership data, and historical site information during right-of-way analyses are examples of these relational data requirements at VDOT. Many times these involve remote sensing imagery and its respective metadata.
      As with any infusion of new technologies or changing methods for doing certain functions in a large organization such as VDOT, which employs over 10,000 persons and manages over 55,000 miles of roads, certain actions can and should be considered. To facilitate the introductions, transition, and maturing of these new techniques and procedures, VDOT can assist the process with: early technology and procedural workshops; strategic consensus-building work sessions; industry and educational partnership agreements; consistent, frequent, useful products early-on; long-term training and familiarization programs; the use of support data- base transition and administration; and a long-term strategic implementation plan.
      A successful transition by VDOT into increased uses for its GIS and various remote sensing techniques will foster an enhanced exchange of information with associate agencies within and outside the commonwealth of Virginia. The benefits from which will be realized in providing local and area development planning, disaster response, federal agency coordination and cost-sharing spatial data, natural resource management, plus numerous other services. When carried out, this will create a model for data exchange with government and private organizations that other states will want to replicate.

About the Author:
Stanford T. Hovey has over 35 years in the development and use of remote sensing applied to military and civilian applications. He serves as a system consultant for Michael Baker Jr. Inc. for remote sensing applied to geographic information system installations, and can be reached at 804-282-1821. (Edit-review by Larry W. Minor and Daniel P. Gayk.)

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