Photographs Aerial and Remote Sensing
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Additional Notes:
Aerial Photographs
Air Photos are the simplest, cheapest and mostwidely available method of REMOTE SENSING Remote Sensing is based upon the collection of data based on the transmission, absorbtion, reflection and measurement of ELECTROMAGNETIC RADIATION. Remember your basic physics,
E=
hc
Where is the wavelength, c is speed of light and h is Plancks Constant.
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Additional Notes:
Electromagnetic Spectrum & Remote Sensing
Suns Energy (6000K)
0.3 m 1 m 10 m 100 m
Earths Energy (300K)
1 mm 10 mm 1m
absorbed Photography Thermal Scanners Multi-Spectral Scanners
0.3 m 1 m 10 m 100 m
transmitted
Radar & Passive Microwave
1 mm
10 mm
1m
Human Eye
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This is a very important diagram. Remote sensing is all about Electomagnetic Radiation, and as a result, depends on 3 different things: 1. The energy spectrum that is radiated by the sun and by the earth (I.e. the wavelengths available). This is a function of the temperature of the body. 2. The absorbance of that energy by the atmosphere in selective energy (wavelengths) and the resulting windows for atmospheric transmittance of EM radiation (i.e. the wavelengths that actually reach a receptor located at any reasonable distance). and; 3. The spectral sensitivity of available scanners. Additional Notes:
Visible and Near-Infrared
Aerial Photographs (visual) Monochrome or Colour
0.4
0.5
0.6
0.7
m
green
blue
red
0.3 m
1 m
10 m
100 m
Human Eye
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Visible Light mid IR Thermal IR
0.4 - 0.7 m 1.3 - 3 m 3 - 14 m.
Near-Infrared 0.7 1.3 m
Additional Notes:
Visible light: Colours may be mixed by additive or subtractive processes
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The upper photo shows colour-additive processes which occur when lights of different wavelength (colour) are superimposed. Note the central area is white. The lower photo shows colour-subtractive processes which occur when dyes (which absorb specific-wavelength radiation) are superimposed. Additional Notes:
Thermal Imaging
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The temperature variation in the great lakes is shown very dramatically in this picture. Additional Notes:
Interaction with the Atmosphere
Scattering: Why is the sky blue? Short (blue) wavelengths are scattered most by the atmosphere. Absorbtion Water vapour, carbon dioxide and ozone all act to absorb electromagnetic energy in specific wavelength bands. As a result, there are wavelength windows in which the atmosphere is particularly transmissive of EM energy.
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Scatter.
Why is the sky blue but sunsets red?
As the atmospheric path becomes longer, the scatter and absorbtion of short wavelengths is so complete that we see only the less scattered longer-wavelengths of orange and red. Dust and water vapour in the atmosphere also affect the nature and degree of scattering with a consequent effect on the observed colour of the sky. Non-selective scatter is problematic for remote sensing and occurs when the diameter of the particles causing scatter are much longer than the wavelength of the energy being sensed. Water droplets in clouds and fog have a range from 5 to 100 m and scatter all visible light (as well as near and mid-IR) about equally. As a consequence of this non-selective scatter, fogs and clouds appear white. Absorbtion and Transmission Because of the nature of atmospheric absorbance, there are particular wavelengths which represent high transmission windows. Not all of these coincide with wavelengths of use to us, or for which reliable sensors are available.
Interaction with the Surface
Incident Energy is: REFLECTED ABSORBED TRANSMITTED REFLECTION is the most important in Remote Sensing
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Reflection of surfaces may be Specular or diffuse. A perfect specular reflector is a flat mirror-like surface for which the angle of reflection equals the angle of incidence. Diffuse Reflectors are rough surfaces that reflect equally in all directions. Governed by the scale of surface roughness relative to the wavelength of incident energy. Diffuse reflections provide information about the colour of the reflecting surface and are most often what we are interested in. A spectral reflectance curve may be determined for different earth materials. For deciduous and conifereous trees, for example, the spectral reflectance in the visible spectrum is highest for green; we know that trees do appear green. If we wanted to distinguish aspen from black spruce, we might try near-infrared. The spectral-reflectance curve for vegetation reflects particular wavelengths where the energy is absorbed by the material, for example the chlorophyll absorbtion bands at 0.45 and 0.67 m. For soil, the reflectance is governed by moisture content, texture (sand / silt / clay content) surface roughness, presence of iron oxide, organic content. Presence of moisture in soil decreases The reflectance. water absorbtion bands (which apply for vegetation as well) are at 1.4, 1.9 and 2.7 m. Clay soils also have absorbtion bands at 1.4 and 2.2 m. Since sandy soils are usually well drained, with low moisture content and consequently high reflectance. In the absence of water, however, coarse grained soils may appear darker than fine grained soils. Clear water absorbs little energy of wavelength < 6 m (blue-green), but as turbidity increases, this may change dramatically.
Colour
near-Infrared False colour
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The upper photo is normal colour; note the football field and surrounding vegetation are roughly the same tone. The lower photo is colour-IR; note that the football field is built with artificial turf whivh has a low reflectance for near-IT radiation. Additional Notes:
Elements of Visual image Interpretation:
Visual Image Interpretation is applied to Aerial Photographs (usually in stereopairs) The techniques may also be applied to Satellite Images. Types of Images: Monochrome Aerial Photographs Colour Airphotos Infrared Images (colour-IR and thermal-IR) Radar Images
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Additional Notes:
Elements of Visual image Interpretation:
Fundamental Principles: Aerial & Space Images form a detailed record of features on the ground at the time of acquisition. Temporal variation in vegetation, soil moisture, water levels etc. (Also ground & water temperatures etc for thermal imaging). The image is a snapshot in time
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Additional Notes:
Aerial Photograph Interpretation for Engineering Geology
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Additional Notes:
Elements of Visual image Interpretation:
Shape Height Size Pattern Tone (hue) Texture Shadows Site Association (or context) Resolution
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These principles are general and apply to the use of any remote sensing tools for geological, soils, land use, vegetation, forestry, urban planning or other such applications. At its simplest, aerial photograph interpretation involves making observations from this list and synthesizing them with geological knowledge and understanding and (hopefully) local data and experience. Additional Notes:
Airphotos in Engineering Geology
Lineaments Drainage (morphology of drainage channels) Colour Texture Slopes (shape and grade) Cross-section of drainage channels or gullies Erosion Vegetation Association (or context)
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Additional Notes:
Airphotos in Engineering Geology
Elements of Terrain Analysis
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Additional Notes:
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Additional Notes:
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Additional Notes:
Stages in the Geomorphological Cycle
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