|
Imagery
to Support USDA Agricultural Programs:
The National Agricultural Imagery
Kent Williams
Background
The USDA Farm Service Agency (FSA) has been
involved in the acquisition, use, and distribution of
aerial photography for more than 65 years. When farm price
and income support programs were established, shortly
after the Great Depression, it was necessary to accurately
record and verify planted crop acreage for farmers. FSA,
then the Agricultural Adjustment Administration, used
aerial photography to track farm records by drafting farm
tract and field boundaries onto aerial photographic
enlargements. It was one of the earliest applications of
aerial photography, on a large scale, in the world.
The farm tract and field delineated aerial
photography provided a visual representation of farm
fields, allowing a common, intuitive way for USDA staff
and individual farmers to interact and record planted
acreage. The photographs were rectified to allow accurate
measurements. Counties were furnished new photo
enlargements, on average, every five years. Beginning in
the 1970s, the need for more current information about the
land led to the use of 35mm aerial photography. Known as
the Aerial Compliance program, it has been managed and
flown by local contractors at the county level. The
photography has been acquired at least once during a
growing season, at a time best reflecting peak growing
conditions. The photography has been used to verify crop
acreage, as reported and entered in USDA farm programs,
with actual ground conditions.
In 1999, FSA began implementing GIS to better
manage farm records and geospatial data and to enhance
program delivery. A major task in the implementation
process has been digitizing farm field boundaries, known
as Common Land Units (CLU). CLU boundaries are digitized
on digital orthophotography using the tract and field
delineated photo enlargements as a reference.
The implementation of GIS required a re-evaluation
of aerial imagery programs to support FSA farm program
activity. FSA needed imagery suitable to replace or update
the ortho base imagery on a regular basis. FSA needed to
minimize the need to re-digitize or adjust existing CLU
boundaries to the new ortho image base.
FSA needed to show current agricultural conditions
such as changes to field boundaries and new conservation
practices, and provide a current view of the landscape in
general. Acquisition needed to occur at a time that best
allows visual identification or verification of crop type
and the images had to be available quickly enough to
support the Aerial Compliance program. New federal
mandates, including the coordination of geospatial
collection, data sharing, and heightened security
awareness for aerial photography collection, are also part
of the new environment.
The National Agriculture
Imagery Program
The National Agriculture Imagery Program (NAIP) was
established in 2003 to meet FSA’s evolving requirements
for imagery. NAIP
supports the acquisition of imagery under two sets of
specifications. The first set addresses the need for
replacement ortho imagery acquired on a five-year cycle,
or 20% of the country each year. The imagery is produced
at a 1-meter Ground Sample Distance (GSD). Horizontal
accuracy is specified to match the ortho base imagery used
to digitize CLU boundaries (Figure 1). The second set
addresses the need for the Aerial Compliance program, with
lower resolution and horizontal accuracy requirements, but
with a need for collection during each growing season.
Imagery in this set of specifications is produced to a
2-meter GSD, within 10 meters of reference imagery. Both
sets must be acquired annually during peak growing
conditions in color or color infrared. Together, both 1-
and 2-meter products will provide full coverage of
agricultural areas in the continental U.S. on an annual
basis.
With the narrow acquisition window and the size of
the area being covered, NAIP has presented challenges in
terms of collecting and managing the imagery. To meet
these challenges, several measures have been initiated
that mark a departure from earlier aerial photography and
digital orthophotography programs:
-
“Best Value” contracting
methods are used. This method has led to an average
price of $151 per quarter quadrangle or $11.10 per
square mile. This price point has enabled the
viability of the NAIP program.
-
An “interim” release of
ortho imagery supports annual farm programs.
Compressed county mosaics are delivered from
contractors and are available for distribution after
an initial inspection process. Full resolution quarter
quad tiles are available after a full inspection
process, up to one year after acquisition.
-
Cloud cover is acceptable.
While the vast majority of images have been cloud
free, the contract specification allows up to 10%
cloud cover per image tile.
-
By defining a product, but not
specifying how the imagery is acquired and produced,
aerial survey companies are encouraged to utilize new
technology. For example, the Leica ADS40 large format
digital sensor was used in Nebraska in 2003, and Idaho
and Texas in 2004. Customers have been very pleased
with the image quality from a direct digital image.
Aerial Survey firms involved with the NAIP program
in 2004 include Aero-Metric, Aerial Services, Horizons,
Northwest Geomatics, Land Air, Photo Science, Surdex,
Triathlon and Vargis. These contractors have been very
responsive and appear committed to making the NAIP program
a success.
Partnerships
The NAIP program has had considerable success in
attracting cost share partnerships. Cost share
partnerships with other federal agencies include the USDA
Natural Resources and Conservation Service (NRCS), USDA
Forest Service, the Bureau of Land Management, with the
U.S. Geological Survey planning to cost share in 2005.
NRCS offices are co-located with FSA in county Service
Centers. NRCS and FSA also share the same GIS platform,
geospatial data sets, and serve the same customers. NRCS
has been the largest cost share partner in NAIP to date.
State governments who have cost shared in NAIP
include Idaho, Illinois, Utah, Kentucky, Minnesota,
Missouri, Pennsylvania, and Texas. Partnership
opportunities include: new coverage beyond scheduled FSA
counties, new coverage beyond agricultural areas of a
county, and an upgrade from 2- to 1- meter GSD.
Success Factors
The 2003 NAIP projects succeeded in providing 713
counties with current ortho imagery that replaced existing
digital orthophotography that was as much as 10 years old
(Figure 2). The NAIP imagery was delivered within 30 days
from when it was flown. The 2004 projects will update
another 670 counties (Figure 3). The benefits of new
digital ortho imagery to the FSA and NRCS service centers
are clear. Current imagery means less ambiguity for
farmers and USDA staff when interacting over farm programs
and farm conservation plans. CLU boundaries that match
features visible on current digital ortho imagery mean
more accurate acreage determinations, and more efficient
administration of farm programs.
Other cost share partners report similar benefits.
The BLM has used NAIP to assist with monitoring the spread
of roads and trails due to off-road vehicle use in Idaho.
Organizations within the state of Minnesota detail
benefits ranging from enhancing coordination for emergency
response, to land use planning.
Success in using NAIP for the FSA Aerial Compliance
program has been mixed. Due to weather conditions and
other factors in 2003 and 2004, the target acquisition
window for capturing peak crop growing conditions was
missed in a significant number of counties. For counties
where the imagery was collected in the target window, the
compliance process was completed in a days rather than the
several weeks normally required.
Availability
Both 1- and 2-meter NAIP products are currently
available in two formats: MrSID compressed county mosaics,
and 3.75’ x 3.75’ quarter quadrangles in GeoTIFF
format. NAIP products are available to the general public
at a nominal cost. Early in calendar year 2005, NAIP
products will be available on the USDA Geospatial Data
Gateway http://datagateway.nrcs.usda.gov/, or directly
from The FSA Aerial Photography Field Office (APFO)
www.apfo.usda.gov. Photo products and scans from the
original NAIP film, as well as from aerial photo projects
going back to the mid 1950s, are also available from APFO.
Future Challenges
The horizontal accuracy for the 1- meter NAIP
imagery is currently tied to older digital
orthophotography that was used to digitize CLU boundaries.
By using more accurate digital elevation models, airborne
GPS, and other methods, it is likely that vendors can
produce more horizontal accuracy in digital ortho imagery
in terms of absolute ground position. Before specifying
for higher horizontal accuracy, the impact of possible mis-registration
of CLU boundaries, and other data sets developed from
older imagery, needs to be assessed.
About the Author
Kent Williams is a Management Analyst with USDA
Farm Service Agency at the Aerial Photography Field Office
in Salt Lake City, Utah. He has more than 12 years of
experience working with digital orthophotography and GIS
with the USDA Service Center Agencies. He can be reached
at [email protected].
Back
|
