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Acquisition of Aerial Photographs

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Acquisition of Aerial Photographs Lecture 8 prepared by R. Lathrop 9/99 Updated 9/07 with reference to material in Avery & Berlin 5th edition Where in the World? – 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
Where in the World?
Takla Makan desert, China
3
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

4
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/

5
National High Altitude program (NHAP)
  • Flying Height, H 12,200 m
  • color IR camera
  • f 210 mm
    scale 158,000 area per frame 13.3
    x 13.3 km
  • panchromatic camera f 152 mm
    scale 180,000 area per
    frame 18.4 x 18.4 km

6
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

7
1930s BW aerial photography mosaics of New
Jersey(source NJDEP)
8
(No Transcript)
9
1-meter resolution natural color aerial
photography of New Jersey, leaf-on July-August
2006 (source USDA-FSA APFO)
10
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

11
Army Corps NJ shore aerial photos of
1920s-30s-40s-60
http//chl.wes.army.mil/shore/newjersey/
12
NASA Astronaut Photography
  • http//eol.jsc.nasa.gov/sseop/clickmap/

13
Satellite imagery sources
  • Will be covered later in the semester

14
Contract Imagery
  • Existing aerial photographs/imagery may be
    unsuitable for certain projects
  • Special-purpose photography/imagery - may be
    contracted through commercial aerial survey firms

15
Contracting Imagery Considerations
  • Image scale ?ground coverage and resolution
    desired
  • Camera focal length
  • Camera format size
  • Film/filter
  • Overlap/sidelap
  • Photo Alignment/tilt
  • Seasonal considerations
  • Time-of-Day considerations/ cloud cover

16
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

17
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

18
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

19
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

20
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • Color film gives better water depth penetration

21
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • Major bugaboo is sunglint which obscures
    underwater features
  • Sunglint occurs when the camera view angle and
    the sun are oriented such that the suns rays are
    reflected back directly into the camera field of
    view

22
Example Flight planning for aerial photography
of submerged aquatic vegetationReducing sunglint
  • Time of day sun angles 15-30o for camera systems
  • Satellites use westward looking off-nadir view
  • Early morning to reduce wind/surface waves, as
    waves can cause sunglint even in off-nadir views

23
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 early morning to reduce wind/surface
    waves ? less turbidity
  • Tides - 2 hours of lowest tide

24
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

25
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

26
Example Flight planning for aerial photography
of submerged aquatic vegetation
  • What will be the image width(m)?

FOV 28.1o
H 1290m
27
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
28
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

From Avery Berlin, 5th ed. pp 101-102
29
Map with Study Area Footprint
20km wide
35 km long
30
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
31
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

32
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

33
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)

34
Map with Study Area Footprint and Flight Lines
20km wide
35 km long
35
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)

36
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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