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Acquisition of Aerial Photographs

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What is the ground coverage desired for an individual photo or image frame? ... If each photo cost approximately $25/frame, what is the total cost of the mission? ... – PowerPoint PPT presentation

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Title: Acquisition of Aerial Photographs


1
Acquisition of Aerial Photographs
  • Lecture 8
  • prepared by R. Lathrop 9/99
  • Updated 9/07
  • with reference to material in Avery Berlin 5th
    edition

2
Learning Objectives
  • Remote sensing concepts
  • Range of existing imagery sources
  • Important parameters to consider in
    planning/contracting imagery acquisition
  • Math concepts
  • Calculating number of photos required as part of
    flight planning
  • Skills
  • Lay out a flight plan and calculate number of
    photos required to cost out a flight mission

3
Aerial Photographic Sources
  • National High Altitude Photography (NHAP)
    (1980-1987) 158,000 CIR or 180,000 Pan
  • National Aerial Photography Program (NAPP)
    (since 1987) 140,000 CIR
  • NASA high altitude photography (since 1964)
    160,000-1120,000 PAN, COLOR, CIR
  • These images are archived by the Eros Data Center
    as part of the USGS Global Land Information
    System. To search archive
  • http//edcsns17.cr.usgs.gov/EarthExplorer/

4
Aerial Photographic Sources
  • USDA (since 1955) mainly PAN of
    120,000-140,000. These photos are archived by
    the Aerial Photography Field Office
    http//www.fsa.usda.gov/dam/APFO/airfto.htm
  • National Archives and Records Administration
    archives older (pre- 1950s) aerial photography
    http//www.nara.gov/research/ordering/mapordr.html

5
1930s BW aerial photography mosaics of New
Jersey(source NJDEP)
6
(No Transcript)
7
1-meter resolution natural color aerial
photography of New Jersey, leaf-on July-August
2006 (source USDA-FSA APFO)
8
Aerial Photographic Sources
  • National Ocean Survey (NOS) coastal photography
    (since 1945), color, scales of 110,000 -
    150,000
  • The photos are used for a variety of
    geo-positioning applications, which include
    delineating the shoreline for Nautical Chart
    creation, measuring water depths, mapping seabed
    characteristics, and locating obstructions to
    marine and air navigation.
  • http//mapfinder.nos.noaa.gov

9
Army Corps NJ shore aerial photos of
1920s-30s-40s-60
http//chl.wes.army.mil/shore/newjersey/
10
NASA Astronaut Photography
  • http//eol.jsc.nasa.gov/sseop/clickmap/

11
Satellite imagery sources
  • Will be covered later in the semester

12
Contract Imagery
  • Existing aerial photographs/imagery may be
    unsuitable for certain projects
  • Special-purpose photography/imagery - may be
    contracted through commercial aerial survey firms

13
Contracting Imagery Considerations
  • Camera focal length
  • Camera format size
  • Image scale ?ground coverage and resolution
    desired
  • Film/filter
  • Overlap/sidelap
  • Photo Alignment/tilt
  • Seasonal considerations
  • Time-of-Day considerations/ cloud cover

14
Seasonal considerations
  • Cloud free conditions, ideally lt 10
  • Leaf-off spring/fall when deciduous tree leaves
    are off and ground free of snow used for
    topographic/soils mapping, terrain/landform
    interpretation
  • Leaf-on summer when deciduous trees are leafed
    out or late fall when various tree species may be
    identified by foliage color used for vegetation
    analyses

15
Scale Considerations
  • What is the minimum mapping unit or size of
    smallest object that you want resolved and
    mapped?
  • What is the ground coverage desired for an
    individual photo or image frame?
  • How large of a study area to be covered?
  • 3 considerations involve trade-offs

16
Time-of-day considerations
  • Quantity of light determined by solar elevation
    angle no shadows - 2 hrs around solar
    noon shadows desired early or late day
  • Spectral quality possibility of sun/hot
    spots causing image saturation

17
Flight Alignment
  • Flight lines are planned to be parallel
  • Usually in a N-S or E-W direction. For maximum
    aircraft efficiency, they should be parallel to
    the long axis of the study area (minimize
    aircraft turns).
  • Crab or drift should be minimized
  • Tilt , 2-3o for any single photo, average lt 1o
    for entire project

18
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • Color film gives better water depth penetration

19
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • Other considerations
  • Scales of 112,000 to 124,000 needed
  • Time of year late spring-early summer
  • Time of day sun angles 15-30o, generally early
    morning to reduce wind/surface waves
  • Tides - 2 hours of lowest tide

20
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • GeoVantage Digital Camera
  • 4 bands Blue, Green, Red, NIR
  • Pixel Array Size 0.00465mm
  • Focal Length 12mm
  • Field of View 28.1o crossrange, 21.1o along
    range
  • Easily mounted on wheel strut
  • Coordinated acquisition with Inertial Measurement
    Unit to determine precise geodetic positioning to
    provide for georegistration and
    orthorectification

21
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • What Flying Height (m) needed to resolve
    individual SAV beds of 1m wide x 10 m long (0.001
    ha in size)?
  • General Rule of Thumb GSD at a minimum of ½ the
    size of smallest feature. In this case need, GSD
    of 0.5m.
  • GSD array element size H
    .
  • focal
    length
  • Example array element size 0.00465mm
  • f 12 mm GSD 0.5m H ?
  • H 0.5m 12 mm / 0.00465mm 1290 m

22
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • What will be the image width(m)?

FOV 28.1o
H 1290m
23
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • What will be the image width(m)?
  • Remember your basic trigonometry? Tan opposite
    / adjacent
  • Tan FOV/2 (1/2 image width)/H
  • Image width 2 tan14.05 1290m
  • 2 0.250 1290m
  • 645 m

FOV 28.1o
H 1290m
adj
opp
24
Example Flight Planning Mission parameters
  • Study area 20 km E-W 35 km N-S
  • Elevation of study area 500 m above sea level
  • Desired Photo scale 125,000
  • Film format 23 x 23 cm or 0.23 x 0.23 m
  • Focal length 152 mm or 0.152 m
  • Overlap 60
  • Sidelap 30

From Avery Berlin, 5th ed. pp 101-102
25
Map with Study Area Footprint
20km wide
35 km long
26
Example Flight planningFlight altitude
  • RF f / H or H RFd f
  • H (25,000) (0.152 m) 3,800 m above
    terrain
  • Flight altitude 3,800 m 500 4,300 m
    above sea level

27
Example Flight planningGround distance
  • Ground distance coverage of a single photo RF
    PD / GD or GD RFd PD
  • GD 25,000 0.23 m 5,750 m

28
Example Flight planning Number of flight lines
  • NL W / (GD)(Sg) 2 where W width of
    study area GD ground distance of single
    photo Sg sidelap gain (100 - sidelap)
    expressed as a decimal fraction 2 extra
    flight lines (1 per side)
  • NL 20 km / (5.75 km)(0.7) 2 4.97 2
    6.97 7 (always round up)

29
Map with Study Area Footprint and Flight Lines
20km wide
35 km long
30
Example Flight planning Number of photos per
flight line
  • NP L / (GD)(Og) 4 where L length of
    flight line GD ground distance of single
    photo Og overlap gain (100 -
    overlap) expressed as a decimal fraction 4
    extra photos (2 per end of flight line)
  • NP 35 km / (5.75 km)(0.4) 4 15.2 4
    19.2 20 (always round up)

31
Example Flight planning Total number of photos
  • Number of flight lines x number of photos per
    flight line or TN NP x NL
  • TN NP x NL 7 x 20 140 photos
  • If each photo cost approximately 25/frame, what
    is the total cost of the mission?
  • 140 photos 25/photo 3,500
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