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Introduction to Aerial Photography Interpretation

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  1. Introduction to Aerial Photography Interpretation

  2. History of Aerial Photography • 1858 - Gasparchard Tournachon photographs Bievre (outside Paris) from a balloon • 1860 - James Black photographs Boston Harbor from a tethered balloon (earliest existing - perhaps first in US) Boston Harbor 1860

  3. History of Aerial Photography • US Civil War - Union General George McClellen photographs confederate troop positions in VA. • 1882 - E.D. Archibald, British Meterologist takes first kite photograph • 1906 - George Lawrence photographs San Francisco after great earthquake and fire

  4. History of Aerial Photography • 1909 - Wilbur Wright and a motion picture photographer are first to use an aircraft as a platform - over Centocelli, Italy • WW2 - Kodak develops camouflage-detection film • used with yellow filter • sensitive to green, red, NIR (0.7 - 0.9 m) • camouflage netting, tanks painted green show up as blue instead of red like surrounding vegetation

  5. Types of Air Photos • High (horizon) & Low (no horizon) Oblique • Vertical • Stereo/3D

  6. Aerial Cameras Keystone’s Wild RC-10 mapping camera A large format oblique camera

  7. Film Types • Panchromatic (B& W) • most often used in photogrammetry • cheap • Color • easy to interpret • fuzzy due to atmospheric scattering

  8. More Film Types • Black & White Infrared • popular for flood mapping (water appears very dark) • vegetation mapping • soils - dry vs. moist • False Color Infrared (CIR, Standard False Color) • vegetation studies • water turbidity

  9. Products • Contact Prints - 9”x 9”s • Film Positives - Diapositives • Enlargements • Mosaics • Indices • Rectified Photos • Orthorectified Photos • Digital Orthophotos

  10. Printed Information/Annotation • Along the top edge, you’ll find: • Date of Flight - always top left • Time - (optional - beginning/end of flight line) • Camera focal length in mm (frequently 152.598 mm = 6”) • Nominal scale (RF) • Vendor/Job # • Roll #, Flight line & Exposure # (always top right)

  11. Determining Photo Scale • Sometimes (at beginning and end of a flight line) Nominal Scaleis printed at the top of a photo, usually as RF

  12. Determining Photo Scale • More likely you will have to compute scale using ruler, map, calculator and this formula 1 (MD)(MS)/(PD) where: MD = distance measured on map with ruler (cm or in) MS = map scale denominator (e.g., 24,000 for USGS Quads) PD = photo distance measured in same units as map distance RF =

  13. Variation in Scale Tilt causes variation within a single photograph. Scales are different on either side of the tilt. FOR 220 Aerial Photo Interpretation and Forest Measurements

  14. Determining Photo Scale • You can also roughly estimate scale from cultural features, e.g., tracks, athletic fields, etc.

  15. Determining Photo Orientation • Labels and annotation are almost always along northern edge of photo • Sometimes eastern edge is used • Airport runway number x 10 gives you magnetic azimuth (to closest 10) • Only way to be certain is to use a map

  16. Calculating Object Heights • Object heights can be determined as follows: • calculate flight altitude (H) by multiplying the RF denominator by the focal length of the camera • h = d/r(H) where: h = Object height d = length of object from base to top r = distance from nadir to top of object

  17. Calculating Object Heights • Stereoscopic Parallax • Parallax bar • Parallax wedge • Shadow length • object must be vertical • on level ground • height of another object is known or sun angle and time of day are known Calculating the height of the Washington Monument via stereo parallax

  18. Photointerpretation: Recognition Elements • Pattern • Site • Association • Shadow • Shape • Size • Color/Tone • Texture

  19. Photointerpretation: Recognition Elements • Shape • cultural features - geometric, distinct boundaries • natural features - irregular shapes and boundaries • Shape helps us distinguish old vs. new subdivisions, some tree species, athletic fields, etc.

  20. Photointerpretation: Recognition Elements • Size • relative size is an important clue • apartments vs. houses • single lane road vs. multilane • horse tracks vs. runner’s tracks

  21. Photointerpretation: Recognition Elements • Color/Tone • irrigated vs. dry fields, coniferous vs. deciduous trees An algae bloom in color An algae bloom in CIR

  22. Photointerpretation: Recognition Elements • Texture • coarseness/smoothness caused by variability or uniformity of image tone or color • smoothness - crops, bare fields, water, etc. • coarseness - forest, lava flows, etc. • even-aged vs. old growth Helyer Woods and points south

  23. Photointerpretation: Recognition Elements • Pattern • overall spatial form of related features • repeating patterns tend to indicate cultural features - random = natural • drainage patterns can help geologists determine bedrock type A dendritic pattern is characteristic of flat-lying sedimentary bedrock

  24. Photointerpretation: Recognition Elements • Site • site - relationship of a feature to its environment • citrus on hillside, Atlantic. white cedar in stream corridor • Association • identifying one feature can help i.d. another - correlation • cooling towers, HT lines => reactor vessels

  25. Photointerpretation: Recognition Elements • Shadows • shadows cast by some features can aid in their i.d. • some tree types, storage tanks, bridges can be identified in this way • shadows can also accentuate terrain Powerline transmission towers

  26. Applications: Archaeology • Archaeologists and historical geographers can sometimes identify features hidden for centuries • Soil marks • Crop marks • positive • negative • Shadow marks • Snow marks Above: Positive crop mark Below: Negative crop mark

  27. Applications: Archaeology Soil marks in an English field

  28. Applications: Soils • Once bedrock geology and surface geology are known, a soil scientist can classify soil types based on soil tone, slope, etc. Soil survey

  29. Applications: Agriculture • Census and inventory • monitor production • predict yields • plan for shortfall • search for arable lands

  30. Applications: Geology • Geologic mapping • Different drainage patterns can reveal what type of geology is present • Folds and faults are sometimes more recognizable from the air San Andreas fault, Carrizo Plain, CA

  31. Applications: Geology • Mineral, hydrocarbon, and groundwater exploration • Hazards - landslide and earthquake fault assessment Berkeley CA’s Hayward fault running diagonally from lower left to upper right

  32. Applications: Forestry • Forest type maps - sometimes down to species level • Appraisal of damage due to fire, insects, and disease • Timber volume estimates • Wildlife habitat management

  33. Air Photo Acquisition • Optimal to fly late morning • low wind • clear sky • minimal shadows • What time of year? • March/April for photogrammetry • Summer for vegetation studies

  34. Problems with Aerial Photography • Clouds, haze, shadows/sun angle, snow • Distortion • tip & tilt • relief distortion • radial distortion • Limited to 0.3 - 0.9 m (UV-NIR) • Storage and handling can be a problem

  35. Getting your very own • USGS National Aerial Photography Program (NAPP) successor to National High Altitude Photography Program (NHAP) has coverage of lower 48 • NHAP CIR - 1:58K, Panchro - 1:80K • NAPP CIR - 1:40K, some panchro • approximately 334,000 photos • updated every 5 years (in theory)

  36. Getting your very own USGS EROS Data Center Customer Services Sioux Falls, SD 57198 (605) 594-6151 email: custserv@edcserver.cr.usgs.gov web: http://edcwww.cr.usgs.gov/nappmap.html • B&W paper contact prints - $6.00 CIR - $16.00 • Helpful to know lat./long. of your area of interest