Bruce Burger, Positive Systems Inc.

Jim Friedley, BIA-Southern Ute Agency-Branch of Forestry

The BIA-Southern Ute Agency's Branch of Forestry, in conjunction with the Southern Ute Indian Tribe, worked together with the BIA-Geographic Data Service Center (GDSC) and Positive Systems to evaluate commercially available digital aerial photo imaging technology for updating the Tribe's ten year-old resource aerial photography. The goal was to cost-effectively meet a broad set of information needs that require current aerial photographs both as traditional hard copy prints for field use, and as digital imagery for use in a changing and evolving GIS environment.

The entire Southern Ute Indian Reservation was flown with the ADAR™ System 3000 Digital Aerial Photography System to capture true color aerial photo images, with stereo overlap, at 2 meter per pixel ground sample distance. Each digital scene was printed at 1:24,000 scale for use with stereoscopes in the field in analyzing terrain and vegetative cover. The 615 digital scenes captured over the Reservation's approximately 1,150 square miles were also mosaicked through an automated, software driven process that registered them to a georeferenced Landsat TM satellite coverage.

This presentation will highlight the ways in which a commercial digitally-based aerial photography system was used to address the application, the challenges encountered in completing the project, and the planned uses of the image data within ArcView to meet resource management needs on the Southern Ute Indian Reservation.

Encompassing over 1,100 square miles, the Southern Ute Indian Reservation in southwestern Colorado includes a wide variety of land cover, terrain, natural resources, and land use. In managing timber resources for sustained growth and yield, Tribal natural resource managers work closely with professional foresters from the Bureau of Indian Affairs' (BIA) Southern Ute Agency.

In late 1995, Southern Ute Agency's Branch of Forestry began planning activities for updating the Tribe's ten year-old natural resource aerial photography. The previous aerial photo mission, completed during 1986, delivered 9"x 9" color aerial photo prints with stereo overlap. The Reservation was flown at approximately 1:16,000 scale, utilizing standard film aerial photography camera equipment.

Having recently implemented a GIS, BIA-Southern Ute Forestry's goal for the 1996 update included obtaining a digital version of the aerial photos for analytical resource mapping within their ArcView v.2.1 environment. Digital imagery could only be considered, however, if it could be cost-effectively obtained in conjunction with the high quality photographic prints required for on-the-ground activities. These activities include use with stereoscopic viewers by foresters in the field for terrain analysis.

Working closely with the BIA-GDSC in Lakewood, Colorado, Southern Ute evaluated their options. The objective from the digital perspective was to obtain a mosaic of the individual aerial photos that could provide a contiguous image data layer for use with the Reservation's vector GIS information. These existing vector data layers have, in general, been compiled at accuracies consistent with standards for 1:24,000 scale USGS 7.5 minute quad sheets.

In considering standard film-based aerial photography options, budget limitations precluded the traditional digital orthophoto process. Producing an uncontrolled mosaic in-house through digitally scanning 9"x 9" prints was also considered. However, given the costs associated with acquiring additional staff and computer equipment resources to digitize and manage this effort, when viewed in the context of the results that could be expected, this proved unrealistic.

Having determined that a color aerial photo mission made the most fiscal sense in satisfying the Tribe's field application needs, Southern Ute Forestry looked to the ADAR System 3000 true color digital aerial photography system as a potential solution. However, because digital camera systems fix pixel ground sample distance (GSD) at the time of image capture, careful consideration needed to be given to desired pixel resolution versus desired scale of the prints that would be generated from each digital scene. The ADAR System 3000's large format 3000x2000 pixel array digital camera sensor, in conjunction with newly developed ADAR automated mosaic processes turned out to offer a cost-effective alternative meeting both the digital and hard copy needs of the project.

With invaluable assistance from BIA-GDSC, Southern Ute Forestry evaluated previously captured ADAR imagery used in other forestry applications to determine the appropriate pixel GSD that would serve the Tribe's analytical needs. A number of factors influenced this evaluation. These included the average terrain elevation across the Reservation, which dictated maximum altitude for camera system operation; the number of overlapping individual digital scenes that would be generated, which directly impacted the cost of generating stereo prints and a digital mosaic; and the expected information content of the imagery at the various resolutions, which would impact its usefulness in supporting vector information within Southern Ute Forestry's ArcView GIS environment.

As a general rule, the coarsest acceptable pixel resolution will offer the lowest cost of data acquisition by requiring fewer flight lines, the lowest cost of post flight processing due the lowest possible number of frames generated, and the greatest ease of use in a digital environment due to reduced data volumes and file sizes. With all of these factors in mind, the team comprised of BIA-Southern Ute Forestry, BIA-GDSC, and Positive Systems determined that digital aerial photo imagery captured at 2 meter per pixel GSD provided the most cost effective solution.

The subsequently defined project's deliverables included individual true color digital aerial photo images, a digital aerial photo image mosaic for eventual use in ArcView, and high quality stereo prints for use by foresters in the field.

Positive Systems' flight operations team developed the mission plan for a digital aerial photo acquisition flight targeted for mid to late summer. A total of 32 parallel flight lines were generated, oriented N-S, to cover the entire Southern Ute Indian Reservation. Flight lines were spaced for 30% sidelap with the ADAR System 3000's large format 3000x2000 pixel digital camera sensor. Required operating altitude for capture of 2 meter per pixel digital photographs is 14,600 feet above terrain level. Considering the widely varying terrain relief across the Reservation, an optimal average operating flight altitude was calculated at 22,000 feet MSL (Mean Sea Level).

In completing acquisition over the entire Reservation at 60% endlap (frame to frame) and 30% sidelap (over adjacent flight lines), 615 true color digital scenes were captured over a three-day photo mission during mid-August. Each scene covered approximately 9.2 square miles at the desired 2 meter per pixel GSD resolution.

After the individual digital photos were captured, they were processed by Positive Systems for vignette correction and color interpolation. Both processes are applied to the image data set in a batch mode. The vignette correction algorithms adjust each image for internal radiometric effects of the digital CCD sensor and lens optics. The color interpolation process generates the final RGB true color digital image from the camera's native compressed image format. Delivery of the final image data set, including all 615 frames totalled approximately 12 GB, with each image slightly over 18 MB is size.

To create the hard copy prints, each digital scene was printed by Positive Systems on a Kodak XLS 8650 dye-sublimation printer. Annotated information including the flight line and scene number, as well a GPS position identifying the camera's position at exposure was included as part of each print. Similar in concept to standard 9"x 9"contact prints typical of a film mission, the digital images were printed at a 1:1 ratio (without enlargement) of the digital file to the printed photo sheet. As calculated in the planning phase, this resulted in prints at a scale of 1:24,000. Stereoscopic viewing quality has proven to be excellent.

The ability to obtain a photo mosaic at a reasonable cost was a major consideration in selection of the ADAR digital aerial photography alternative. Newly developed processes including ADAR AutoMosaic and ADAR ImageMosaic offer automated alternatives to other arduous and time intensive manual mosaic processes currently available. Mosaics created through these innovative processes can include varying levels of control to provide appropriate horizontal spatial accuracy at costs well below that of traditional photogrammetric processes.

The original contract deliverable was to be an uncontrolled, non-georeferenced mosaic created with the ADAR AutoMosaic process. This automated, software driven process rapidly mosaicked the individual ADAR digital scenes to each other to create a site-wide mosaic of all images captured across the 32 adjacent flight lines. Turnaround from the input of the digital frames to the completion of the mosaic, including a level of manual adjustment to tighten individual areas with especially difficult terrain relief took approximately 3-4 weeks.

Completion of the mosaic for the entire Southern Ute Reservation was accomplished in five separate "swaths", or sections, for ease of image file manipulation within GIS and image processing software environments. Upon completion, GDSC would complete the task of rectifying each swath to GPS ground control to create the georeferenced image layer to be used in ArcView in conjunction with existing vector data layers. ERDAS Imagine was selected as the tool to complete this 2D "best fit" rectification.

As with any aerial photo project, the challenges brought on by Mother Nature can significantly impact operations and results. The July/August timeframe was selected to allow a complete melt of all snow cover on north facing slopes at higher elevations. At this time of year however, southwestern Colorado often experiences "monsoonal flow" cloud patterns as moisture is drawn up from Mexico by stagnant high pressure systems.

Capture of cloud-free imagery was finally completed in mid-August as weather patterns began to turn more autumnal in nature. In addition to battling cloud cover, a lightning-induced forest fire in early July affected a significant area on the southeast corner of the Reservation. Eventually dubbed the Dipping Vat Fire Complex, this area experienced an extensive burn. Due to its location, most of the smoke drifted south and east of the Reservation, however smoke particulate was a constant atmospheric element throughout the project. It is believed that this is responsible for a pinkish hue that is evident in some of the imagery.

Outside of the natural elements, the major technical challenge encountered was the management of very large data volumes while producing and controlling the mosaic. As technology marches rapidly forward, these problems should resolve themselves to a large degree.

A major unexpected opportunity arose with the release of the ADAR ImageMosaic process in conjunction with the production of the Reservation-wide mosaic. ImageMosaic expands the functionality of the AutoMosaic process. In creation of the mosaic, the individual ADAR digital scenes are registered to a reference image. Assuming the reference image has been controlled and georeferenced, this control will be utilized in creation of the new mosaic, with the georeferencing applied as well. The result is a mosaic that includes a geocoding structure, as well as tighter control, especially over areas of terrain relief.

As a complete image map had been previously created by GDSC for the Southern Ute Indian Reservation using 30 meter resolution Landsat TM data, this georeferenced base image became the reference image for use in the ImageMosaic process. All 615 scenes were reprocessed with ImageMosaic to create a new mosaic with the underlying Landsat image's coordinate structure. This new mosaic was designated as the Southern Ute Indian Tribe's deliverable, which will greatly reduce the effort required by GDSC in integrating the mosaic with the existing vector GIS data layers.

The BIA Geographic Data Services Center (GDSC) has assumed an instrumental role by providing technical assistance that maximizes Southern Ute's efficient utilization of the digital aerial photo imagery. Information products produced by GDSC for use in Southern Ute Forestry's GIS environment include:

GDSC will continue to support Southern Ute's efforts, providing assistance and training on image processing software and techniques for users as needs arise.

The hard copy prints are being utilized as the resource photography for the Southern Ute Agency and the Southern Ute Indian Tribe. More specifically, the prints have been utilized by the Branch of Forestry in all phases of field work such as timber sale layout, reforestation area layout, and timber stand improvement area layout. The Tribal Energy Department has utilized the prints in geographic analysis of mineral resource areas.

In the future the prints will continue to be used for natural resource management, as well as by the Tribal Planning Department and others.

As part of the Forest Management Planning process, the digital images and mosaic will be used in the classification of Reservation lands, including woodland and timberland resources. This will include heads-up digitizing of stand boundaries in the ArcView 3.0 and Data Automation Kit software environments. Other vegetative resources, such as rangeland will also be able to be classified when desired.

Digital imagery from the ADAR System 3000 mission will be integrated with the Reservation's existing GIS data, and with GPS data collected for all types of natural resource management activities. Utilizing ArcInfo, ArcView, and other software packages, raster and vector data will be combined to create maps for resource management work, planning, and land use documentation.

While satisfying the need for stereo quality aerial photo prints to be used in traditional applications, the Southern Ute Indian Tribe has now also expanded their overall planning and resource management capability as well. Through their innovative approach to updating the Reservation's resource photography, they now have a flexible digital mapping analysis tool suitable for widespread use by any tribal management group. In addition to Forestry, the Tribal Energy Department has already initiated activities that will eventually use both digital and hard copy data from the ADAR System 3000 photo mission.

Positive Systems wishes to again thank the Southern Ute Tribal Council, BIA-Southern Ute Forestry, the GIS and image processing specialists at BIA-GDSC, and the staff from Logicon Geodynamics Services formerly under contract to BIA-GDSC during the planning and evaluation phases for their collective insight, dedication, and cooperative efforts in successfully completing this project.