||ES 771 Lab Exercise|
Aerial photographs are among the most important, widely available, and commonly utilized kinds of remotely sensed images. They are used for all manner of land resources, cartographic, and appraisal surveys in the public and private sectors. They are often employed as "base maps" upon which thematic data are portrayed. Locating appropriate aerial photographs is a fundamental first step for many land mapping and evaluation projects, and air photos often form the basis for interpretation of other kinds of remote sensing.
Many on-line sources for aerial photography exist for state and federal agencies as well as private companies. On-line availability varies from simple descriptions with agency addresses to searchable databases with metadata, locality maps, and/or browse images. Metadata refers to a summary of the basic attributes of the imagery--film type, frame number, date, location, lens, etc.
A recent trend is to convert analog aerial photographs into raster images called digital orthophoto quads (DOQ). These images have been resampled to fit accurately onto a ground coordinate grid with very high pixel resolution--usually 1 or 2 m; they may be utilized for GIS in combination with other kinds of cartographic data. DOQs are now being tested and produced for many regions of the United States.
- See DOQ description.
U.S. Sources of Aerial Photography
- U.S. Geological Survey, Global Visualization VieweróGlovis.
- EarthExplorer from the U.S. Geological Survey.
Search through available web sites to find answers to the following questions on the National Aerial Photography Program (NAPP), National High Altitude Photography (NHAP), and digital orthophoto quads (DOQ).
Now attempt to locate aerial photography for your home region--city or county. Search through web sites listed above and other sources you are able to find. You should identify an air photo to represent your city/county in both categories below. Note: distance-learning students outside the United States should attempt to locate aerial photography for their home country. If this is not feasible, you may pick a major U.S. city.
- What are the nominal scale, flight altitude (above terrain), and lens focal length for NAPP photographs?
- What are the nominal scale, flight altitude (above terrain), and lens focal length for NHAP photographs?
- What kinds of film may be utilized for NAPP and NHAP photographs?
- What does the term contract-acceptable flight specifications mean for aerial photography?
- What are some of the standard NAPP and NHAP photographic products available to the public?
- What is the typical resolution of NAPP and NHAP photographs?
- What is the primary source of air photos for input to DOQs? What other sources may be used as inputs?
- What is the typical resolution for DOQ images? How does resolution on an air photo differ from resolution in a DOQ?
- What kinds of information are contained in the header for a DOQ dataset?
- What kinds of digital formats (media) may be utilized to supply DOQ datasets to the public?
For each air photo, download the available information--metadata file, locality map, and/or browse image. Make sure to include the web address (URL) for each selected file. Briefly describe the characteristics and some possible applications for the air photos you selected. Students should submit electronic text (txt or rtf) and image (bmp, gif, or jpg) files via e-mail.
- Analog (conventional) aerial photograph.
- Digital orthophoto quad--DOQ (or DOQQ).
Note: students should not order actual photographic prints or digital datasets.
- Written answers (1-10).
- Description of applications for selected photos.
- Digital files of metadata and/or images.
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ES 771 © J.S. Aber (2016).