Remote Sensing and Image Processing Structure • Definitions of Remote Sensing • Origins of remote sensing • Types of aerial photograph • Photogrammetry • Parallax • Human vision Aerial Photography and Photogrammetry • Conclusions Definitions of Remote Sensing Definitions of Remote Sensing Can be very general, e.g. Or more specific, e.g. “The acquisition of physical data of an “The use of electromagnetic radiation object without touch or contact ” (Lintz sensors to record images of the and Simonett, 1976) environment , which can be interpreted to “The observation of a target by a device yield useful information ” (Curran, 1985) some distance away ” (Barrett and Curtis, 1982)
Definitions of Remote Sensing Definitions of Remote Sensing Main characteristics Or more specific, e.g. • Physical separation between sensor and “The use of sensors, normally operating at target wavelengths from the visible to the • Medium = electromagnetic radiation (sonar microwave , to collect information about is an exception) the Earth’s atmosphere, oceans, land and • Device to sample and measure radiation ice surfaces ” (Harris, 1987) (sensor) • Target is the terrestrial environment (atmosphere, oceans, land surface) Physical separation between sensor and target Medium = electromagnetic radiation (sonar is an exception)
Target is the terrestrial environment (atmosphere, oceans, land surface) Device to sample and measure radiation (sensor) Structure Origins of Remote Sensing Remote sensing began with aerial photography • Definitions of Remote Sensing • Origins of remote sensing • Types of aerial photograph • Photogrammetry • Parallax • Human vision • Conclusions
Origins of Remote Sensing Origins of Remote Sensing 1858 Gasper Felix Tournachon "Nadar" First photographs taken in takes photograph of village of Petit Bicetre 1839 in France from a balloon Boston by Black and King (1860) Paris by Nadar, circa 1859
World War One was a major impetus After the war the technology was in to development of aerial photography place to begin large scale aerial surveys Structure Types of aerial photograph • Vertical • Definitions of Remote Sensing • Low oblique • Origins of remote sensing • High oblique • Types of aerial photograph • Photogrammetry • Parallax • Human vision • Conclusions
Types of aerial photograph Types of aerial photograph • Vertical • Vertical • Low oblique (no horizon) • Low oblique • High oblique • High oblique Types of aerial photograph Types of aerial photograph Vertical is most important as it has minimum distortion and can be used for taking measurements Fiducial marks
Types of aerial photograph Types of aerial photograph Fiducial Principal axes point Marginal information Types of aerial photograph Types of aerial photograph An aerial photograph mission • Endlap (or forelap) is the will be flown in strips, shutter important bit timing set for 60% endlap • It ensures every point on the (needed for parallax) and strips ground appears in at least two spaced for 30% sidelap (to avoid photographs missing bits) • Distance between principal point of adjacent photographs is known as the “air base”
Structure Photogrammetry • Definitions of Remote Sensing If you know focal length of camera and height of • Origins of remote sensing aircraft above the ground • Types of aerial photograph you can calculate the scale • Photogrammetry of the photograph • Parallax • Human vision • Conclusions Photogrammetry Photogrammetry Scale = f/H-h Scale = f/H-h f = focal length (distance H = flying height of aircraft from centre of lens to film above sea level surface) h = height of ground above sea level
Photogrammetry Photogrammetry When you know the scale you But to take “true” can take 2-D measurements measurements on an uneven from a photograph (e.g. surface you need horizontal distance, to work in 3-D horizontal area, etc.) Photogrammetry Structure But to take “true” • Definitions of Remote Sensing measurements on an uneven • Origins of remote sensing surface you need • Types of aerial photograph to work in 3-D • Photogrammetry • Parallax You can do • Human vision this thanks to • Conclusions parallax
Parallax Parallax Parallax is used to find distance to stars, using two viewing Pencil is very displaced because it is close to observer points on either side of Earth’s orbit Church is less displaced because it is further away Parallax Parallax H = height of aircraft above ground P = absolute parallax at base of object being measured* dP = differential parallax * For convenience the photo base length of a stereo pair is commonly substituted for absolute stereoscopic parallax ( P ) The same principle can be used to find height of objects in stereopairs of vertical aerial photograph s
Eye base (6-7cm) Structure Human vision Human vision is binocular in most • Definitions of Remote Sensing cases, and human eyes can resolve • Origins of remote sensing parallax as angle of convergence • Types of aerial photograph This provides perception of • Photogrammetry “depth” and enables us to judge • Parallax distances (up to 400m) • Human vision • Conclusions Human vision Human vision 3-D stereoptic viewing of Two types of the Earth’s surface is light-sensitive possible using cells are overlapping pairs of present in the vertical stereo aerial retina: photographs • Cones are sensitive to radiation of specific wavelengths (either red, green or blue) • Rods are sensitive to all visible wavelengths
Human vision Human vision Two types of light-sensitive cells are present in the Fovea Optical retina: centralis plane • Cones are clustered around the fovea centralis • Rods are widely distributed elsewhere Structure Conclusions • Remote sensing involves collecting information • Definitions of Remote Sensing about the Earth from a distance using • Origins of remote sensing electromagnetic sensors • Types of aerial photograph • It evolved from aerial photography • Photogrammetry • Vertical stereopairs of aerial photographs are used to take 3-D measurements by measuring parallax • Parallax • Human vision is binocular, enabling us to resolve • Human vision parallax for depth perception • Human vision includes perception of colour • Conclusions
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