Chapter 4 - Aerial Photography

Question 1

Vertical Photograph

Answer 1

camera’s optical axis is within 3° of being perpendicular to earth’s surface

Question 2

Additive Color Theory - primary colors & secondary

Answer 2

What happens when light is mixed
blue, green, red = primaries
blue + red = magenta
blue + green = cyan
red + green = yellow

Question 3

How Filters Work

Answer 3

Filters subtract (block) some spectrum of light. A yellow filter appears yellow because it absorbs blue light (yellow filters are often used to correct for Rayleigh scattering). A red filter absorbs green & blue light.

Question 4

Haze filters

Answer 4

absorb light shorter than 400 nm. Used to keep photos from being “contaminated” by UV light.

Question 5

Structure of film

Answer 5

1. Emulsion layer(s) - contain light-sensitive silver-halide crystals (AgX) embedded in a gelatin
2. A base or support material that may be transparent or opaque
3. An anti-halation layer - absorbs light that passes through emulsion & base to prevent reflection

Question 6

Types of Black & White Photographic emulsions

Answer 6

Orthochromatic - sensitive to blue & green light to approx .6µm
*Panchromatic - sensitive to UV, blue, green & red to approx 0.7µm
Near Infra-red - BGR & near infra-red to approx 0.9µm
- care must be taken b/c bands to represent what we expect

Question 7

Development of Image (what happens)

Answer 7

Emulsion contains latent “invisible image” -> must be developed. In development areas that saw lots of light turn to free silver & become black (the inverse of how they’re presented in the world - negative)

Question 8

Enlarger

Answer 8

Produces a positive print by shining light through the negative

Question 9

Transmittance

Answer 9

Ability of a portion of developed film to pass light - black = 0%, clear = 100%
Ti,j = (light passing through film)/(total incident light)

Question 10

Opacity

Answer 10

Inverse of Transmittance (Ti,j)

Oi,j = 1/Ti,j

Question 11

Density

Answer 11

Human visual system doesn’t respond linearly to light stimulation, but logarithmically
Di,j = log10(O,i,j) = Log10(Ti,j)

Question 12

Characteristic Curve & what it’s used for

Answer 12

DlogE curves, provide important information about film emulsion

Used for determining exposure time

Question 13

Elements of a characteristic curve

Answer 13

toe, linear section (gamma = ∆D/∆logE), shoulder, gross fog, speed point

Question 14

Gamma γ

Answer 14

provides info about the contrast of film

Question 15

Speed point

Answer 15

a way to compare films with different exposure speeds

Question 16

Planning Aerial Photography Missions

Answer 16

Time of day - within 2 hours of solar noon (sun btwn 30° & 52°) unless shadows are desired for topology/ terrain representation
Weather - a few days after passage of a frontal system so water vapor & particulates (smog) are removed from the air, no clouds in sky