San Diego County Aerial Imagery (May - June 2012)

The imagery for this project was flown at a nominal acquisition altitude (AGL) of 9,500 and 14,500 feet. Differential baseline lengths were kept to a minimum by the use of the nearest available CORS stations to the project area. Maximum baselines were less than 60 km with the mean distance less than 30 km. GPS coordinates were referenced to the National Spatial Reference System (NSRS) through connections to active CORS and/or passive monumented control stations. The film camera(s) were calibrated by USGS within 3 years prior to the date of photography. Digital camera(s) were calibrated by the manufacture and the camera parameters refined through in-situ proprietary procedures.

0.3m data captured between May 20 - May 22, 2012 

0.5m data captured between May 27 - June 6, 2012

Radiometry is verified by visual inspection of the digital orthophoto. Slight systematic 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. Tonal balancing may be performed over a group of images during the mosaicking process which may serve to lighten or darken adjacent images for better color tone matching.

GeoTIFFs conform to the specifications set forth by the USGS for production of orthophotos in the Task Order Number G12PD00530. Orthoimages are visually inspected for completeness to ensure that no gaps or image misplacements exist within and between adjacent images. These images are derived by mosaicking multiple images to ensure complete coverage. Source imagery is cloud free.

The 0.30 meter ortho image horizontal accuracy does not exceed 1.52-meters NSSDA 95% confidence (0.88-meters Root Mean Squared (RMSE) Error XY (0.62 meter RMSE X or Y).

The 0.5 meter ortho image horizontal accuracy does not exceed 2.52-meters NSSDA 95% confidence (1.4681-meters Root Mean Squared (RMSE) Error XY (1.0363 meter RMSE X or Y).

The horizontal accuracy of the orthorectified images is mainly determined by the quality of the DEM. The elevation data consists of auto-correlated data generated and edited by AeroMetric. Airborne GPS/IMU data was used. All photo identifiable checkpoints were measured and compared to the surveyed checkpoints to determine the RMSE. All rectified chip overlap was checked for mismatch. All final tiles were checked visually for edge matching.

The digital images were aero-triangulated to support digital ortho image production for the San Diego, CA project area. Ground check point data was provided by AeroMetric, Inc. The project was referenced to the North American Datum of 1983 (NAD83), UTM Zone 11 horizontally and to the North American Vertical Datum of 1988 (NAVD88) vertically. Units were in meters.

The images, ABGPS/IMU data, and ground check point data were used as inputs to the Zeiss/Intergraph ImageStation Automatic Triangulation (ISAT) softcopy program. ISAT correlated image points and aerotriangulated the block of images to create exposure station exterior orientations. All ground points were manually measured on the imagery. These points were included in the aerotriangulation adjustments for absolute ground location verification. The scale of the aerial photos was 1"=2011'. The photography was exposed between 5/20/12 and 5/22/12.

Rectification was done using the aerotriangulation data, raw images, and DEM data. These rectified images were used to generate seamlines which were then reviewed and edited. The rectified images were mosaicked, balanced, and cut into final image sheets. The final sheets were viewed and artifacts were removed as well as other edits performed. A QC step was performed along with any needed corrections and the final tiles were formatted and checked before delivery.The imagery for the city of San Diego, Poway, and Chula Vista was resampled to 0.3 meter resolution from native 0.15 meter orthoimagery. 

The digital images were aero-triangulated to support digital ortho image production for the San Diego, CA project area. Ground check point data was provided by AeroMetric, Inc. The project was referenced to the North American Datum of 1983 (NAD83), UTM Zone 11 horizontally and to the North American Vertical Datum of 1988 (NAVD88) vertically. Units were in meters.

The images, ABGPS/IMU data, and ground check point data were used as inputs to the Zeiss/Intergraph ImageStation Automatic Triangulation (ISAT) softcopy program. ISAT correlated image points and aerotriangulated the block of images to create exposure station exterior orientations. All ground points were manually measured on the imagery. These points were included in the aerotriangulation adjustments for absolute ground location verification. The scale of the aerial photos was 1"=3069'. The photography was exposed between 5/27/12 and 6/6/12. Rectification was done using the aerotriangulation data, raw images, and DEM data. These rectified images were used to generate seamlines which were then reviewed and edited. The rectified images were mosaicked, balanced, and cut into final image sheets. The final sheets were viewed and artifacts were removed as well as other edits performed. A QC step was performed along with any needed corrections and the final tiles were formatted and checked before delivery.

Four band orthoimagery is organized in four color bands or channels which represent the red, green, blue, and near-infrared portions of the spectrum. Each image pixel is assigned a quadruple numeric value, one for each color band. Numeric values range from 0 to 255. Areas where data is incomplete due to lack of full image coverage are represented with the numeric value of 0.