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GEOG 2420 (3)
Chapter 5

Geog 2420 Chapter 5

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University of Guelph
GEOG 2420
John Lindsay

Geog 2420 Chapter 5: Element of Visual Image Interpretation Jenson - photo or image interpretation is defined as the examination of images for the purpose of identifying objects and their significance The Aerial or Regional Perspective - a vertical or oblique aerial photograph or other type of visible/near infrared image records a detailed but much reduced version of reality - examination of the earth from an aerial perspective allows scientists and the general public to identify objects, patterns, and human land interrelationships that may never be completely understood if we were constrained to a earth bound vantage point - humans are accustomed to looking at the facade or side of objects and do not normally have an appreciation for what objects look like when they are recorded from a vertical view Three Dimensional Depth Perception - possible to obtain a 3d view of terrain as if were were actually airborne - one way is to abstain two images from two slightly different vantage points Obtaining Knowledge Beyond Our Human Visual Perception - our eyes are sensitive to primarily blue, green and red light - therefore a very limited portion of the electromagnetic energy that is moving about in the environment and interacting with it is sampled - sensors have been invented that can measure the activity of x rays, ultraviolet, near infrared, thermal and so on - carefully calibrated remote sensor data provides new information about an object that humans might never be able to appreciate in any other manner - healthy vegetation absorbs much of the green and red light from the sun - therefore agricultural fields show up in dark shades of grey in green and red multispectral imagery - the greater amount of biomass in an agricultural field, the greater amount of near infrared energy reflected causing heavily vegetated fields to appear bright in near infrared imagery Historical Image Record and Change Detection Documentation - we can compare new imagery with old imagery to see differences over time - this can help to develop predictable models about what has happened and what may happen in the future - remote sensing image interpretation is playing an increasingly important role in predictive modelling and simulation - especially useful in monitoring human activity through time Elements of image Interpretation - elements of image interpretation include: - location - tone and colour - size - shape - texture - pattern - shadow - height and depth - volume - slope - aspect - site - situation - association - each image is composed of individual silver halide crystals or pixels that have a unique colour or tone at a certain geographic location - this is the fundamental building block upon which all other elements are based Location - two primary methods of obtaining precise coordinate information about an object - first is surveying it in the field using traditional survey techniques or GPS instruments - the second is collect remote sensor data of the object, register the image to a baseman and then extract the x,y coordinate info directly from the rectified image itself Tone and Color - real world surface materials such a vegetation, water and bare soil often reflect different proportions of energy in the blue, green, red and near infrared portions of the electromagnetic spectrum - we can plot the amount of energy reflected from each of these materials as specific wave lengths and create a spectral reflectance curve, sometimes called a spectral signature Tone - a band of electromagnetic energy recorded by a remote sensing system may be displayed in shades of grey from black to white - these shades of grey are referred to as tone - the degree of darkness or brightness is a function of the amount of light reflected from the scene within specific wavelength interval - in black and white images (record infrared only) vegetation is displayed in bright tones - healthy vegetation reflects much of the incident near infrared - the brighter the tone from vegetation the healthier it is - water absorbs most of the near infrared energy causing it to appear dark - humans can differentiate 40-50 shades of black and white Colour - we may use additive colour combining techniques to create colour composite images from the individual bands of remote sensor data - hue, saturation and intensity Size - Length, Width, Perimeter and Area - the size of an object is one
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