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Remote Sensing

Topic 2: Photographic PrinciplesChapter 2: Avery and Berlin

Chapter 2: Lillesand and Keifer

Six Advantages of Aerial Photography Over Ground Observation

Basic B/W Film Photography

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A Simple Camera

1/f = 1/o + 1/i

f = focal length of the camera o = object distancei = image distance note: when o is v.big i = f

ExposureExposure (E) at any point in a photograph is dependent on:

E = sd2t / 4f2

where: s = scene brightness d = diametert= time/shutter speed f = focal length

So how do we control the range of exposure?Diameter of the lens opening (d) is adjusted by setting the aperture or f-stop = f / d

E = st / 4F2

Shorter exposure times prevent blurring/image motion, but require high speed films (grainier)Longer exposure times allow more light, so slower (crisper) films can be used, but may result in blurring

Extraneous EffectsExposure falloff is the result of :

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Effect of Exposure Falloff

Film Density Measurements Film density is a measure of ?

Determined using a _________________?

What are measure of film density used for?

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Characteristic Curves - Contrast

Characteristic Curves - Resolution

Low ContrastLow Slope ()Poorer Radiometric Resolution

High ContrastHigh Slope ()Better Radiometric Resolution

Characteristic Curves – Exp. Lat.

Low Exposure Latitude

High Exposure Latitude

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Characteristic Curves – Film Speed

Slow FilmMore ExposureBetter Spatial Resolution

Fast FilmLess ExposurePoorer Spatial Resolution

B/W Panchromatic Films

B/W Infrared Films

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Panchromatic vs. Infrared Photo

Colour Aerial Films

What are the advantages of colour photography?

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Colour TheoryR, G, B are additive primaries

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Colour TheoryYellow, magenta, and cyan are subtractive primaries

Colour TheoryComplimentary colours are those that produce white light when combined

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How Colour Film WorksColour film is based on the principles of subtractive primary coloursYellow, magenta, and cyan dyes are used to filter differing proportions of blue, green, and red lightThe dyes are introduced into different layers of colour film each containing silver halide crystals modified by organic molecules known as spectral sensitizers The subtractive primaries are used to control the relative proportions of additive primaries reflected back to our eye

How Colour Film WorksWhen developed, yellow, magenta, and cyan dyes are introduced inversely proportional to the amount of blue, green, and red light reflected

Spectral Sensitivity

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How Colour IR Film WorksAssignment of dyes to an emulsion layer is arbitrary

Colour infrared films have same dyes assigned to different portion of EMS

Also called false colour film

Spectral Sensitivity

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How Colour IR Film WorksBlue wavelengths are filtered out of incoming light using a filter placed in front of the camera lensNear infrared cyan dye - controls red reflectance to our eyeRed magenta dye - controls green reflectance to our eyeGreen yellow dye - controls blue reflectance to our eye

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FiltersMade of glass or gelatin

Wavelength selectors

Example yellow filter absorbs blue wavelengths allows green and red to pass through commonly used to reduce haze

High vs. low pass

Reduces exposure, so adjustments necessary

Aerial CamerasWide variety can be used

Hand-held 35 mm SLR camerasHand-held digital camerasSingle lens frame camerasMulti-lens frame cameraStrip CameraPanoramic CameraAnalog and digital video recorders

Single Lens Frame Camera

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Single Lens Frame Camera

Standard 9 in. Vertical Photo

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Altimeter

Number of CameraNumber of PhotoFocal Length

A18658 - 138

Multi-Lens Frame Camera

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Strip Camera

Panoramic Camera

Digital ImagingUtilize an rectangular array of solid-state detectors; either CCDs or CMOSSize of array (# photosites or pixels) determines image resolution

Advantages:Increased spectral and radiometric resolutionAbility to digitally process/analyze imageryLinear response to incident energyCan record GPS positionGreater storage capacity

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Digital ImagingPhotosites are actually colour blindFilter are used to control λdetected at each photositeCalled a Bayer mask

in each 4x4 pixel area 2 green, one red, one blue

Interpolation algorithim is used to fill in the resulting checker board pattern with missing colours

Bayer Mask

Large Format Digital Aerial CamerasGyro- stabilized, computer controlled IMCEight-camera system, 12 bit radiometric res.Four panchromatic bands mosaicked into 14,000 x 8000 (112 Mega pixel) imageOther 4 bands are B, G, R, and NIR at 3000 x 2000 (6 M pixel)