Using the Iowa 2002 Color-infrared Digital Orthophoto Collection

James D. Giglierano

Iowa Geological Survey/IDNR

Presentation for 2003 Iowa Geographic Information Conference, Ames, Iowa

July 1, 2003 (July 8 Update)

 

The purpose of this presentation is to acquaint new users of color-infrared digital orthophotography with the extended spectral capabilities of this media.  Many users may be more familiar with standard black and white orthophotography available through the USGS Digital Orthophotography program (DOQQ) or with high resolution black and white orthophotos acquired by many Iowa counties and cities.  The main advantage of color-infrared aerial photography is that it enhances the ability of the airphoto interpreter to distinguish vegetation from non-vegetated areas, distinguish types of vegetation and get an idea of the vegetation condition or vigor.

 

Overview of Iowa CIR program:  The acquisition of color-infrared aerial photography in the spring of 2002 and subsequent production of one meter digital orthophoto quarter quadrangles (DOQQs) was funded by a partnership of more than 45 federal, state and local agencies, private companies and non-profit organizations.  The project was coordinated through the Iowa Geographic Information Council’s Remote Sensing Committee and managed by the Iowa Department of Natural Resources.  Color-infrared aerial photography with airborne GPS and ground control was acquired by Northwest Group of Edmonton, Alberta, Canada, to US Geological Survey National Aerial Photography Program (NAPP) standards using Kodak SO743 aerial negative film.  The original negative film will be stored at the US Department of Agriculture’s Aerial Photography Field Office (APFO) for reproduction of film or paper products from the primary media.  Production of the one meter, digital orthophoto quarter quadrangles to USGS DOQQ standards was performed by Triathlon, Inc. of Vancouver, British Columbia, using horizontal control from airborne GPS, control surveys, and USGS digital raster graphics and existing USGS DOQQs from the 1990s.  Vertical control was derived from USGS Digital Elevation Models (DEMs), both 30 and 10 meter grid spacings, which in turn were derived from topographic elevations on USGS 7.5’ Topographic Quadrangle Maps (1:24,000 scale).

 

Overview of Primary Products:

• 9683 frames of 9” x 9”, 1:40,000 scale, color-infrared negative film, with archival storage at the USDA APFO in Salt Lake City. Reproductions of negatives, film and paper positives and enlargements available at cost.  (http://www.apfo.usda.gov)
• 9683 frames if 9” x 9”, 1:40,000 scale color-infrared positive copies of original film.  Stored at Iowa Geological Survey, Iowa City, Iowa (319-335-1575).  On site viewing only, no reproduction capability.
• 4202 digital orthophoto quarter quadrangles, USGS one meter DOQQ standard products in uncompressed TIFF format, UTM projection, NAD83 datum.  Available from USGS National Mapping Program.  Also available in compressed MrSID file format from Iowa Geological Survey ftp site at:  ftp://ftp.igsb.uiowa.edu/GIS_Library/quads. Online image viewer with downloads hosted by Iowa State University GIS Facility, http://ortho.iastate.edu, has the CIR collection as well as historic BW.
• 99 one-meter, color-balanced county mosaics in compressed MrSid format, in UTM and State Plane projections, currently in production.  Will be available on the IGS ftp server later in summer of 2003.

 

Overview of Ancillary Products:

• Polygon shape file of 9683 airphoto frame outlines – includes all photos taken during 2002 flights in Iowa by contractor.
• Point shape file of 9683 airphoto frame center points. Includes acquisition date and time.
• Polygons shape file of 4292 outlines of digital orthophoto tiles produced by contractor.
• Point shape file of 4292 center points of orthophoto tiles, including date of photography used to create each orthophoto.
• Point shape file of 6600 GPS-located ground truth points collected during spring, summer and fall of 2002.  Land cover type recorded at each site.  May include reference and link to digital still photography recorded at the site.
• A collection of electronic climate files collected during the spring and summer of 2002 from various sites on the Internet.  Daily records include GOES weather satellite images, precipitation and air temperature recorded at weather stations across Iowa, radar images, and soil temperature recorded by Iowa State University.

 

These ancillary products will be available in August 2003 from IGS ftp site at ftp://ftp.igsb.uiowa.edu/pub/download/CIR2002.

 

 

Using the collection:  Because the color-infrared aerials photos were taken over a period of two months (see attached map), the infrared response of the vegetation will vary considerably, thus producing a wide range of pinks and reds on the film and digital products.  Quarter quadrangles products are made from a single image so vegetation response is consistent across the DOQQ, but county mosaics will display varying vegetation response due to the combination of images acquired on several dates.  By displaying an overlay of the polygon shape file of frame outlines with the photo dates on top of the digital mosaics, one can see which image dates contributed to the overall product.  This usually reveals why pinks and reds may appear stronger in one area of the image while more subdued elsewhere.

 

The ancillary point and polygon shape files for the airphoto frames and othophoto tiles also have information on the time of day the photography was acquired.  This will help a person viewing the images to interpret shadow lengths and directions, or decipher other instances where time of day may be a clue to what was happening at the time the film was exposed (such as a full parking lot of cars).

 

The ground truth point file and associated digital still photography can be used to look up what various types of vegetation may look like, both on the ground or from the aerial images.  The main focus of the ground truth collection was vegetation, about half the sites being permanent vegetation (prairie grasses, forest, pasture/hayland) and the rest being cropland.

 

The climate files include records of precipitation from weather stations and radar, snowfall, air and soil temperature, and clouds from various weather satellite images.  The main use of this information is to give the person using the airphoto collection an idea of the weather conditions on the day of the flight or the week or so leading up the flight.  For example, many years from now a person looking at the photos might not realize that that a major snow storm took place on “April Fool’s Day” that dropped several inches of snow on the north-eastern half of Iowa.  This snow quickly melted but did enhance moisture patterns on photos taken after the event over large areas.  By looking at records over time, total rainfall patterns and gradual temperature rising will help persons to interpret the stage or vigor of vegetation seen on the images.  More daily historical climate records for 2002 are available from the Iowa Environmental Mesonet at http://mesonet.agron.iastate.edu/archive/data/2002/.

 

 

Secondary Data Products:  As time goes by and more and more projects use the Iowa 2002 CIR Digital Orthophoto Collection, GIS data files derived from the collection will become available to users.  Currently, the collection is being used to develop a road centerline file by Iowa DOT, an inventory of animal confinement operations by Iowa DNR, common land unit boundaries by USDA Farm Service Agency, and a statewide land use inventory by IDNR.