contributed by Jeffrey Gillan

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Various

Aerial photography has many applications for rangeland science and natural resource management. Aerial photographs can serve as great base layers in a GIS and be used for land planning, assessment and monitoring, and creating soil maps. GIS users often use aerial photographs to digitize features on the land such as buildings, roads, utilities, fences, etc. Aerial photos can also provide a historical record for studying changes in land use, management, vegetation, or habitat.

One common type of aerial photograph is an orthophoto. A digital orthophoto is a computer-generated image of an aerial photograph in which the image displacement caused by terrain relief and camera tilt has been removed. The orthophoto combines the image characteristics of the original photograph with the georeferenced qualities of a map, allowing the orthophoto to be used in conjunction with other images or spatial data layers.

Historically, most aerial photography was captured on film, and scanned into a computer. Increasingly, however, aerial photographs are being acquired using digital sensors. Aerial photographs are typically either panchromatic (B &W), natural color, or color infrared. Each format has advantages and disadvantages for specific applications.

Panchromatic film measures all visible light into one image. This fact often gives panchromatic film an ability to have higher resolution images compared with color. If your interest is in ground features or patterns that do not require color, panchromatic film may be preferred. For example, most USGS topography maps were produced from panchromatic film because their interest did not require color images.

Using film for spectral remote sensing has many disadvantages compared with digital sensors. To be useful in a quantitative way, film prints will have to be scanned into a digital format. This process generally reduces the quality of the image and requires special equipment such as densitometers. Once digitized, the images can be brought into a GIS or a remote sensing software package. The suitability of using these images for spectral quantitative analysis is fairly limited because we cannot easily derive physical properties of the surface including reflectance. Unlike digital sensors which are highly calibrated, one cannot easily relate the digital number of a digitized image to measured quantities of radiation. If your remote sensing study is only looking at a single image, this may not be a problem. For example, you can run classification schemes based on the digital numbers. However, if your study requires comparing multiple images from multiple locations or dates, making the images comparable is very difficult. Variables like sun angle and shadowing are much harder to account for.

Before you use aerial photography, make sure you find out if it was originally acquired on film or digital sensors.

Unmanned aircraft systems are a type of aerial photography.

A number of satellite sensors now provide imagery at resolutions that rival aerial photography and with other features (e.g., data depth, clarity) that exceed most aerial photography. The availability of these high-resolution satellite products, is still limited though, due to high costs and licensing restrictions. Some of these satellite sensors are:

• Ikonos
• Quickbird
• Worldview-2
• Worldview-1

There are many sources for aerial photography, and in some instances, there is almost a hundred year record of aerial photographs. This wiki page currently deals only with U.S. federal government aerial photography sources and programs. Many states also have active aerial photography programs and archives. Additionally, there are many private companies that provide custom aerial photograph acquisition.

Listed below are aerial photography programs from the U.S. federal government. Imagery has been systematically acquired through several programs since the 1940’s. Most of the imagery has a spatial resolution of 1 or 2 meters.

http://eros.usgs.gov/#/Guides/nhap
NHAP was an interagency federal effort coordinated by the USGS which operated between 1980 and 1989. The goal of the program was to provide cloud free aerial images of the entire lower 48 states. The images were acquired at 40,000 ft. elevation.

• Images captured on B & W and color infrared film
• B & W photos cover an area of 11×11 miles.
• Color infrared images cover an area of 8 x 8 miles.
• The images have a spatial resolution of 2 meters.
• The entire catalogue of images has been digitized and is free to the public through the USGS. The images can be downloaded from USGS Earth Explorer http://earthexplorer.usgs.gov/ or USGS Glovis http://glovis.usgs.gov/.
• Images can also be ordered from the USDA Farm Service Agency Aerial Photography Field Office http://www.fsa.usda.gov/FSA/apfoapp?area=apfohome&subject=landing&topic=landing
• Images come in a Tiff format, with no georeferencing or orthorectification

_{Image source: USGS}
NHAP image taken on August 8, 1981 using color infrared film, Washington County, Idaho.

http://eros.usgs.gov/#/Guides/napp
NAPP is the successor of NHAP and operated between 1987 and 2004. The mission of the program was to cover the entire U.S. except Alaska every 5 years. The aerial photography was captured at an elevation of 20,000 ft.

• Images captured on B & W and color infrared film
• Images are at a scale of 1:40,000
• 1 meter spatial resolution
• The entire catalogue of images has been digitized and is free to the public through the USGS. The images can be downloaded from USGS Earth Explorer http://earthexplorer.usgs.gov/ or USGS Glovis http://glovis.usgs.gov/.
• Images can also be ordered from the USDA Farm Service Agency Aerial Photography Field Office http://www.fsa.usda.gov/FSA/apfoapp?area=apfohome&subject=landing&topic=landing
• Images come in a Tiff format, with no georeferencing or orthorectification

_{Image source: USGS}
NAPP image taken on panchromatic (black and white) film, Owyhee County, Idaho, June 27, 1998.

http://www.fsa.usda.gov/FSA/apfoapp?area=home&subject=prog&topic=nai
The NAIP program started in 2003 and is still ongoing. The goal of the program is to photograph primarily agriculture areas during the growing season or “leaf on” period and provide orthophotos to government agencies. Their coverage includes the entire continental U.S.

• Most images are captured with natural color and some more recently have an infrared component. Though some of the images are captured on flim, the program is moving toward using mostly digital sensors.
• Imagery has spatial resolution of 1 or 2 meters
• Products are available as either digital ortho quarter quads(DOQQ) or compressed county mosaics (CCM) which are multiple DOQQs stitched together
• DOQQs come in GeoTIFF format with geographic coordinates attached
• CCMs general come in a mr. sid format or .jp2 format
• NAIP data is freely accessible to the public at no cost and can be downloaded at: http://datagateway.nrcs.usda.gov/
• To check for specific coverage and data availability: http://www.fsa.usda.gov/Internet/FSA_File/naip03_09covermaps.pdf
• Much of the NAIP imagery is available through spatial data clearinghouse sites at the state level (e.g., INSIDE Idaho http://inside.uidaho.edu or New Mexico's RGIS http://rgis.unm.edu)

_{Image from publicly available data}
Natural color NAIR image from Washington County, Idaho, 2004.

http://www.fsa.usda.gov/FSA/apfoapp?area=apfohome&subject=landing&topic=landing
The APFO houses a huge archive of aerial photography dating back to mid 1950’s. The images were originally used to support agriculture but today have many applications. The archive has images from many programs including the National High Altitude Program (NHAP), National Aerial Photography Program (NAPP), and Forest Service programs. The collection has images in many different resolutions and formats.

• 63% of the collection is B & W, 22% is natural color, and 15% is color infrared
• Most of the collection was acquired on film though some of the newer imagery is digital
• Products can be paper prints, negatives, positives, or digital media
• Most digital products will not have georeferencing information
• Ordering products does carry a cost. Specifics on prices and products can be found on the APFO price list: http://www.fsa.usda.gov/Internet/FSA_File/fsa0441a_10302007.pdf

http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/High_Resolution_Orthoimagery

• This source has digital B & W and natural color orthophotos from 2001 to present
• Much of the data has resolution finer than 1 meter
• The coverage is very sporadic throughout the continental U.S. and most of the available images are of urban areas
• Digital orthophoto quads (DOQ) are the available products (3.75 or 7.5 minute quadrangles)
• Images are distributed on CD in either GeoTIFF or native format.
• There is a base charge of $45.00 per order, plus $5.00 shipping, plus $7.50 for each black and white (grayscale) 3.75 x 3.75 DOQ purchased or $15.00 for each color DOQ. Any combination of files can be ordered.
• For ordering orthophotos contact any Earth Science information Center http://ask.usgs.gov/sils_index.html

http://www.blm.gov/noc/st/en/business/aerial.html This is a very large archive dating back 25 years. They have black & white, as well as natural color and false color infrared image of BLM or adjacent land in the western U.S. All of the images were acquired on film. Contact them for ordering and prices.

• http://www.ndop.gov/data.html
• http://www.terraserver.com/

Cost, acquisition procedures, and licensing of aerial photographs will vary depending on the source. For the most part, archived images collected as part of a U.S. government program are inexpensive or free and can be redistributed freely. Imagery from commercial providers can be more expensive and have licensing restrictions limiting its use and distribution.

Image format will also vary with the image source and provider.

• Everitt et al. (1984) used color infrared film along with field measurements of spectral signals to detect false broomweed in southern Texas.
• Goslee et al. (2003) used high-resolution aerial photography to document the encroachment of honey mesquite into semi-arid grasslands in New Mexico since the 1930's.
• Rango et al. (2005) used a time series of panchromatic aerial photographs to document the removal of and subsequent recovery of creosote and tarbush on the Jornada Experimental Range, New Mexico over a 70 year time period.
• Booth and Cox (2006) discuss the importance of very large scale aerial (VLSA) photography for monitoring rangelands at a very fine scale. It is very cost effective and provides imagery at 2.1 mm resolution.
• Seefeldt and Booth (2006) demonstrated that percent cover measures from very-large-scale aerial photography (acquired from an ultralight airplane) were comparable to (and in some cases more accurate than) field-based cover measures in Idaho sagebrush-steppe habitats.
• Strand et al. (2006) used 1-meter resolution panchromatic aerial photography over a 60 year span to document juniper encroachment in a sagebrush (Artemisia spp.) region in Idaho using a novel wavelet analysis technique.

• Booth, D. T. and S. E. Cox (2006), Very large scale aerial photography for rangeland monitoring, Geocarto International, Vol. 21, No. 3.
• Everitt, J. H. S. J. Ingle, H. W. Gausman, and H. S. Mayeux JR. (1984), Detection of false broomweed (Ericameria austrotexana) by aerial photography, Weed Science, Vol. 32, No. 5, pp. 621-624.
• Goslee, S. C., K. M. Havstad, D. P. C. Peters, A. Rango, and W. H. Schlesinger. 2003. High-resolution images reveal rate and pattern of shrub encroachment over six decades in New Mexico, U.S.A. Journal of Arid Environments 54:755-767.
• Rango, A., L. F. Huenneke, M. Buonopane, J. E. Herrick, and K. M. Havstad. 2005. Using historic data to assess effectiveness of shrub removal in southern New Mexico. Journal of Arid Environments 62:75-91.
• Seefeldt, S. S., and T. D. Booth. 2006. Measuring plant cover in sagebrush steppe rangelands: a comparison of methods. Environmental Management 37:703-711.
• Strand, E. K., A. M. S. Smith, S. C. Bunting, L. A. Vierling, D. B. Hann, and P. E. Gessler (2006), Wavelet estimation of plant spatial patterns in a multitemporal aerial photography, International Journal of Remote Sensing, vol. 27, no. 9-10, pp. 2049-2054.

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