This project consists of two components, aerial imagery acquisition and digital orthophoto production, covering a project site within portions of the states of Louisiana, Mississippi, and Alabama. The project area is comprised of approximately 38,000 square miles. Wetlands restoration efforts conducted by the Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA) in Louisiana use monitoring techniques to determine the effectiveness of these efforts. The Coastwide Reference Monitoring System (CRMS) is being developed to assist in a multiple reference approach that uses aspects of hydrogeomorphic functional assessments and probabilistic sampling for monitoring. As part of CRMS, digital orthophoto quarter quadrangles (DOQQs) for the coastal region of Louisiana were created. A DOQQ is a raster image in which displacement in the image caused by sensor orientation and terrain relief has been removed and combines the image characteristics of a photo with geometric qualities of a map. The DOQQs generated for this project were created using digital mapping camera (DMC) technology. This technology allows for the creation of four components: digital imagery (non-georeferenced pan 1 meter and non-georeferenced Red, Green, Blue, and IR 4Band 1 meter), aerotriangulation solution for stereo creation, stereo pair generation (4.75 meter stereo images), and 4Band digital orthophotography (1 meter 4Band DOQQs).
Data from this project are being developed primarily to support multi-use applications, including environmental impact management, coastal wetlands monitoring, homeland security and the business of government. The CWPPRA Task Force will use the data as part of Coastwide Reference Monitoring System (CRMS). These data depict geographic features on the surface of the earth. DOQQs serve a variety of purposes, from interim base maps to field references for earth science investigations and analysis. For the CRMS project, the DOQQs will be used to map coastal wetlands for the CWPPRA monitoring program activities.
This dataset was produced in accordance with USGS Standards for Digital Orthophotos, 1996 12. Review was provided by the USGS National Geospatial Technical Operations Center (NGTOC).
Acknowledgement of the USGS National Wetlands Research Center and CWPPRA Task Force as a data source would be appreciated in products developed from these data, and such acknowledgment as is standard for citation and legal practices for data source is expected by users of this data. Sharing new data layers developed directly from these data would also be appreciated by NWRC staff. Users should be aware that comparison with other data sets for the same area from other time periods may be inaccurate due to inconsistencies resulting from changes in photo-interpretation and mapping conventions over time. Users should be aware that temporal changes may have occurred since this data set was collected and that some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations. These data are not legal documents and are not to be used as such.
Produced by Photo Science, Inc for the U.S. Geological Survey, National Wetlands Research Center. The following partners provided funding or services for the collection and production of these data: The Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA) Task Force; the Coastwide Reference Monitoring System (CRMS); the U.S. Geological Survey
Imagery was captured using a Z/I DMC Sensor. Attribute data consists of four bands of eight bit data. Valid values for each color band range from 0 to 255. Image brightness values may deviate from the brightness values of the original images because of image value interpolation during the scanning and rectification processes as well as histogram modifications made to produce tonal-balanced imagery. Radiometric differences may exist between adjacent orthoimage files; these are due primarily to differences in source image capture dates and sun angles along flight lines. These differences can be observed in an image's general lightness or darkness when it is compared to adjacent orthoimage file coverages.
All DOQQ header data and image file sizes are validated using USGS software before being archived. This validation process ensures correct physical format and field values for header elements. Logical relationships between header elements are tested. Overlap regions between individual DOQQs are visually inspected for excessive horizontal displacement.
The area of coverage for a standard USGS digital quarter quadrangle is 3.75 minutes of latitude by 3.75 minutes of longitude plus 300 meters overedge. DOQQ images are visually inspected for completeness to ensure that no gaps or image misplacements exist in the 3.75' image area or in overedge coverage. DOQQ images can be derived by mosaicking multiple images to ensure complete coverage. DOQQ's are cloud free within the 3.75' image area. National Aerial Photography Program (NAPP) source photography is leaf-off in deciduous vegetation regions.
The DOQQ horizontal positional accuracy and the assurance of that accuracy depend, in part, on the accuracy of the data inputs to the rectification process. These inputs consist of the digital elevation model (DEM), aerotriangulation control and methods, sensor calibration, and aerial imagery that meet National Aerial Photography Program (NAPP) standards. The vertical accuracy of the verified USGS format DEM is equivalent to or better than a USGS level 1 or 2 DEM, with a root mean square error (RMSE) of no greater than 7.0 meters. Field control is acquired by third-order class 1 or better survey methods sufficiently spaced to meet National Map Accuracy Standards (NMAS) for 1:12,000-scale products. Photo-identifiable ground test points are identified in the orthorectified image and measured. The image coordinates are compared to the known positions of these points and the radial differences for each point computed. A radial RMSE value is then calculated for the DOQQ. Note: Adjacent DOQQ's, when displayed together in a common planimetric coordinate system, may exhibit positional discrepancies across common DOQQ boundaries. Linear features, such as streets, may be offset between images. However, these edge mismatches still conform to NMAS positional horizontal accuracy requirements.
Federal Geographic Data Committee, 1998, Geospatial Positioning Accuracy Standard, Part 3, National Standard for Spatial Data Accuracy, FGDC-STD-007.3-1998
DMC Imagery Flown at 25,000 feet above average ground elevation. Provides the imagery for the digital orthoimage.
USGS format elevation data covering a 7.5- x 7.5-minute quadrangle in extent. Used to provide ground elevations for orthorectification process.
Airborne GPS positions were computed by Photo Science, Inc. and used as control in the aerotriangulation process. Ground checkpoints were provided by USGS and used to verify the accuracy of the airborne GPS.
The DMC images, ABGPS data, ground check point data, and camera calibration data were used as external orientation parameters to provide the geospatial control for each photograph during orthorectification. Vertical control for the orthorectification process was obtained from existing USGS Digitial Elevation Models (DEM). During the orthorectification process, elevation data were extracted and resampled to meet user-specified intervals and bounds. The orthorectified imagery is resampled to a 1-meter ground resolution with a ground extent of 3.75 minutes in latitude and in longitude. An overedge of 300 meters beyond the extreme primary and secondary corner ticks was included in the DOQQ. Quarterquad corner ticks, representing both NAD83 and NAD27 horizontal datums are burned into the DOQQ image. An easily viewable ASCII text header is added to the DOQQ. This header is padded to the same length as a line of image data. The header contains information on structure, display, georefencing, and production information. Images were written out using a 8-bit 4Band GeoTIFF format. Orthoproduction was performed using the Intergraph Ortho Pro. Seamlines were auto generated and tone balanced between frames prior to cutting out into the DOQQ's. All orthoimages are individually inspected for content, misalignments along mosaic seamlines, and void areas. Source information was collected and verified manually during the production process.
4Band orthoimagery is organized in four color bands or channels which represent the near-infrared, red, green, and blue portions of the spectrum. Each image pixel is assigned a quadruplet of numeric values, one for each color band. Numeric values range from 0 to 255.
U.S. Department of the Interior, U.S. Geological Survey, 1996, Standards for Digital Orthophotos: Reston, VA.
700 Cajundome Blvd
Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that these data are directly acquired from a U.S. Geological Survey server, and not indirectly through other sources which may have changed the data in some way. It is also strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein.
700 Cajundome Blvd.