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Activities > 2004 Aerial Imagery Program |
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CCMPO / CCRPC 2004 Aerial Imagery ProgramIntroductionThe Chittenden County Metropolitan Planning Organization (CCMPO) and the Chittenden County Regional Planning Commission (CCRPC) worked with several Chittenden County municipalities and the Vermont Mapping Program in 2004-2005 to provide high resolution orthoimagery and digital terrain models for several communities in Chittenden County. Project funding was provided through CCMPO's federal transportation planning funds (PL funds) along with a 20% match from each participating municipality in the county. EarthData International was selected to perform the data collection efforts and Green Mountain Geographics performed the Quality Assurance / Quality Checking (QA/QC) review. The total project budget was approximately $270,000.
A map of the area of coverage for the CCMPO/CCRPC imagery project is below. The tiles highlighted in light green are the tiles included in the area of coverage for the project. Several communities in the county elected not to participate.
A PDF version of this map is available for download here:
A GIS shapefile of the ortho tile boundaries in Vermont State Plane, NAD 83, meters is available for download here: 20040421_ccmpo_earthdata_grid_final.zip (14 kB)
Project Specifications
ImageryThe imagery was obtained with a Leica Geosystems ADS40 digital push broom sensor in lieu of a more conventional approach using film. The digital sensor allowed for the collection of panchromatic, natural color, and false color infrared all at the same time. More information on the ADS 40 sensor is available on the Leica Geosystems website at this location: http://www.gis.leica-geosystems.com/products/ads40/ The imagery products include the following:
The imagery products will be available in georeferenced GeoTIFF files and MrSID compressed files (10 times compression). The projection is Vermont State Plane, NAD 83, with meters as units.
Terrain ModelThe digital terrain model (DTM) elevation data was captured using the Leica Geosystems ALS40 LIDAR sensor. LIDAR stands for Light Detection And Ranging, and the data collection works using the same principles as RADAR. The DTM was used in the orthorectification process to remove distortions introduced due to topography, but there are many additional uses for this data. Here are several links to more information on LIDAR: NOAA Coastal Services Center: http://www.csc.noaa.gov/crs/rs_apps/sensors/lidar.htm Airborne Laser Mapping: http://www.airbornelasermapping.com/ALMBackground.html Leica ALS50 Sensor (next generation device): http://www.gis.leica-geosystems.com/products/als50/default.asp
The DTM products include the following:
The DTM products are available as DXF point files. The projection is Vermont State Plane, NAD 83, with meters as units. The North American Vertical Datum of 1988 (NAVD 88) is used for the elevation data.
Project StatusEarthData completed the first series of flights in late April 2004. After reviewing the data collected EarthData discovered serious problems with the color and near infrared imagery data obtained on these flights. In response to this, EarthData completed a second series of flights in early May 2004. The project data collection specifications called for leaf-off imagery and after reviewing the data available from the second series of flights, it was deemed to have too much leaf-out conditions to meet the specifications. EarthData committed to providing data in conformance with our specifications and in so doing provided the black and white panchromatic imagery from the first set of flights in leaf-off conditions along with the natural color and false color infrared from the second series of flights in more leaf-out conditions. Dealing with this issue created significant delays in the project schedule. Final delivery of the imagery and lidar products occurred in May 2005.
Quality Assurance / Quality Checking (QA/QC) ReviewGreen Mountain Geographics (GMGG) completed a QA/QC review of the imagery and LIDAR data. The QA/QC process will included an examination of the spatial accuracy of the data using targets provided by the Vermont Agency of Transportation Geodetic Survey along with other sources of high-accuracy position data which were identifiable in the imagery.
Green Mountain Geographics has prepared the following summary of the QA/QC process as it related to USGS National Map Accuracy Standards: 1. National Map Accuracy Standards - Horizontal Accuracy. “For maps on publication scales larger than 1:20,000, not more than 10 percent of the points tested shall be in error by more than 1/30 inch, measured on the publication scale;…”
The Chittenden County orthophotos have a defined publication scale of 1:1,1250. Thus, no more than 10 % of the tested points can be off by more than 3.47 feet. Prior to the flight, 34 survey points were marked with white plastic on the ground. During the review, the coordinates on the image were compared with the known survey point location coordinates. Not one survey point was found to be off by more than 1 foot.
Supplementing this surveyed data were spot comparisons with older orthophotos, Global Positioning System (GPS) coordinate location of power poles from a utility (most power poles are clearly visible on the imagery) and alignment with the E911 road network Geographic Information System (GIS) layer. All showed a very high correlation with the new imagery. This imagery, as tested, meets or exceeds National Map Accuracy Standards.
2. National Map Accuracy Standards - Vertical Accuracy. “Vertical accuracy, as applied to contour maps on all publication scales shall be such that not more than 10 percent of the elevations tested shall be in error more than one-half the contour interval.”
The contract for this flight specified that the data be capable of producing a two (2) foot interval contour map. Thus, to comply with the vertical National Map Accuracy Standards for this data acquisition, not more than 10% for the tested points could be off by more than 1 foot. A total of 114 surveyed points, with known elevation values were tested for compliance with the spatial accuracy requirements of the contract. Initial testing found that 103 of 114 (90.4%) points fell within this range. Review of the points that not meeting the standard found that all fell on bridge abutments (not on the bare earth) or were covered with soil to hide their location from vandalism. Correcting for these conditions, only one point was found to be just slightly over the 1-foot limit (1.4ft.). The overall average elevation difference between the known elevation and the LIDAR data was calculated to be less than ½ foot (.493 ft). As with the image data, the LIDAR was accepted as meeting or exceeding National Map Accuracy Standards.
Review of the data went beyond the quantitative measures specified in the National Map Accuracy Standards. The review also looked at edge matching the 260 tiles of imagery to make sure the data appeared seamless and free of visual defects. Relief displacement of buildings and other tall features is still present and is a normal part of orthophotography. Users are cautioned not to attempt to use this data in applications where a licensed surveyor or engineer may be required.
Data AvailabilityAll data is now available through the Vermont Mapping Program 4. Near Infrared orthoimagery - Now available through the Vermont Mapping Program
For More InformationMore background on orthoimagery in general and other orthoimagery available for Chittenden County is available at these links:
For more information on other geographic data available in Vermont, please visit the Vermont Center for Geographic information (VCGI) at: http://www.vcgi.org/
For more information on the imagery project, contact David Roberts on the CCMPO staff at (802) 660-4071 x 16, or Pamela Brangan on the CCRPC staff at (802) 846-4490 x22. Orthoimagery RFP / RFQ InformationThe original RFP for the imagery development and the RFQ for QA/QC are available for reference purposes below.
last updated 11/29/2005
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20040421_ccmpo_imagery_area.pdf (88 kB)|
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