The Louisiana oil spill Geographic Information System
Color Infrared Digital OrthoPhotography Quarter Ouadrandes
As a detailed basemap to an existing Landsat Thematic Mapper satellite image mosaic, the
contractor is producing statewide USGS color infrared (CIR) Digital Orthophotography Quarter
Quadrangles (DOQQS). Unprecedented methods and cutting edge technology are being used to
accomplish this task while at the same time saving LOSCO time and money.
The DOQQS are being created through an innovative partnering agreement with the U.S.
Geological Survey (USGS). The first step upon establishing the agreement was to fly the entire
state according to National Aerial Photography Program (NAPP) standards for CIR DOQQS.
This is the first time DOQQS have been produced statewide by a single year's flight. To
accomplish this flight during the short Louisiana flying season, the USGS -NAPP contractor
Northwest Group was hired to provide the statewide photography. Three pressurized twin-engine
aircrafl equipped with Wild RC-30 cameras, onboard flight management, and airborne GPS were
used. All photography was captured from January through February 1998, in spite of the record
El Nino weather pattern.
For airborne GPS control, five GPS Continuous Operation Reference Stations (CORS) were used
around the state. Using airborne GPS during the flight greatly reduced the need for field survey
control, which is typically established with ground-based GPS. A total of 15,000 line miles of
aerial photography, including cross-strips to augment aerotriangulation, were used. These NAPP
photos were flown 20,000 feet above ground level at a scale of 1:40,000. As the next step, the
USGS office in Reston, Virginia reviewed the processed film.
Two additional time and money saving aspects of the DOQQ initiative also are being used. The
first is the use of automated aerotriangulation to extend photogrammetric control. This technique
greatly reduces the technician time required for bridging over standard Fully Analytical
Aerotriangulation (FAAT) methods. The second is a Zeiss SCAI single-pass, roll-feed scanner.
This scanner requires only a single pass for all three colors, cutting scan time by two-thirds. In
addition, the scanner has the capability for roll-feed scanning, eliminating the need to feed the
photographs in individual frames. Through an agreement with EROS Data Center, dodged
duplicate film rolls are being scanned instead of the original. This provides a high quality image
without the need for film diapositives.
Standard USGS Level II Digital Elevation Models (DEMs) are being used in the
orthorectification process. While some Level II DEMs exist, others are being created using
raster-to-vector data conversion from Mylar contour separates of the standard USGS 1:24,000
quadrangle maps.
To ensure the highest level of applicability for LOSCO and other interests, CIR photography was
chosen for the DOQQS. CIR photography, as opposed to black-and-white or standard color
photography, greatly improves one's ability to identify the land-water interface. It also has
enhanced capabilities for soil type and wetness delineation, vegetation delineation, assessment of
vegetation health and quality, and identification of cultural versus natural features. Other Gulf
States with needs similar to Louisiana are developing projects using CIR orthophotography as
well. Specifically, Texas and Florida are creating CIR digital orthophotographs for oil spill
contingency planning, land use and land cover studies, environmental assessment, and GIS
support. They are wise. DOQQS provide a proven method for creating high-resolution imagery
with well-defined costs.
Feature Location
Surface features must be located in each LOGIS category for natural resources and oil-related
facilities throughout the study area. LOSCO identified four possibilities for data sources, ranging
from existing data that is directly usable to non-existing data that must be provided through new
mapping and GIS analysis. Because many GIS and mapping projects have similar data
requirements, one of the main challenges is to prevent duplication of effort when locating data
and assessing its usability.
To collect existing information, data sets were first located and incorporated. Primary criteria for
all existing data include: spatial and content accuracy, age of the data set, update cycle,
distribution format, and general availability.
New mapping is performed for the required LOGIS layers when data do not meet this criteria.
But there is so much new data to be acquired that mapping by traditional field techniques would
be cost-prohibitive. Therefore, the mapping plan calls for using the CIR DOQQS the contractor
is producing. Through photo interpretation, natural resources and oil-related facilities are
identified on the imagery.
Traditionally, field crews mapping oil-related facilities are guided by standard topographic maps
and permits. However, mapping features through photo interpretation using the CIR DOQQS in
an all-digital environment bypasses these traditional methods of location. Using photo
interpretation methods, CIR DOQQS are displayed on a computer screen in-house. Because of
their one-meter resolution, the images reveal many oil facilities to in-house interpreters. If there
is a question about the site, field crews are then sent to a known, pinpointed location to verify the
map accuracy. This innovative method not only saves LOSCO time and money, but it is also
highly effective and thorough. Moreover, the creation of CIR DOQQS and their use for mapping
features answer, with a single solution, LOSCO'S need for high resolution imagery and surface
feature location.
