rs 3 optical imaging

8/9/2019 RS 3 Optical Imaging

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www.geocities.com/bssafaee/index.html


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Optical Imaging Optical Imaging Optical Imaging

Chapter 3Chapter 3Chapter 3

Reflective & Thermal ImageryReflective & Thermal Imagery


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• Optical Remote Sensing Systems

– Cameras and aerial photography

– Multi Spectral Scanning Systems

– Thermal Imaging Systems

• Geometric Distortions in Optical Imagery


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Satellite Imaging Systems Any data acquisition system for remote sensing includes two parts,

• the platform and

• the sensor

Types of platforms

• Conventional tripod• Any other types of vehicles, boats, balloons, aircrafts, spacecrafts & satellites, etc.

Types of Scanners

• Cameras & Aerial Photography • Multi Spectral Imaging

• Thermal Imaging • Microwave Imaging


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Cameras and Aerial Photography

Cameras are framing systems which acquire a near-instantaneous "snapshot" of an area (A), of thesurface. Camera systems are passive optical sensorsthat use a lens (B) (or system of lenses collectivelyreferred to as the optics) to form an image at the focal

plane (C), the plane at which an image is sharplydefined.

Cameras and their use for aerial photography are the simplest and oldest ofsensors used for remote sensing of the Earth's surface.


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Components of a camera system


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Layers in black and white films and colour films

The most important part of the film is the emulsion layer. An emulsion layercontains light sensitive chemicals. When it is exposed in the light, chemical

reaction occurs and a image is formed. After developing the film, the emulsionlayer will show the image.


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Types of Films:• Negative

• Positive

Types of Films with respect to spectral Sensivity:• Black and white (B/W)• B/W Infrared

• Color• Color Infrared

B/W negative films are those films that have the brightest part of the scene

appearing the darkest while the darker part of the scene appearing brighteron a developed film.


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Cameras and Aerial PhotographySpectral Sensivity of Films:

• Photographic films: sensitive to light from 0.3 mm to 0.9 mm in wavelength

covering the ultraviolet (UV), visible, and near-infrared (NIR).• Panchromatic films: sensitive to the UV and the visible portions of the spectrum.

Panchromatic film produces black and white images and is themost common type of film used for aerial photography.


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Cameras and Aerial Photography•The ground coverage of a photo depends on the focal length of the lens, theplatform altitude, and the format and size of the film.

Vertical and Oblique photographs, Stereoscope, Photogrammetry

Vertical and slant aerial photography


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Cameras and Aerial Photography1. Single lens cameras

Properties of Single lens cameras

• Metric cameras• Stereoscopic Imaging

• IMC device


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Cameras and Aerial Photography2. Multi lens cameras

Properties of Multi lens cameras

• Contains multi lenses• Capability of taking Multi spectral images• also called Multi band cameras• May be the number of cameras more than one• none metric cameras

• no capability of taking stereoscopic images• images mostly used for interpretation


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Cameras and Aerial Photography3. Convergent Cameras

Properties of Convergent cameras

• 100% Overlap of successive images• increase of height accuracy

• stereoscopic imaging


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Cameras and Aerial Photography4. Strip Cameras

Properties of Strip cameras

• Don’t have shutter• move of film with plane’s motion• scanning the ground line by line• use of pushbroom technology

• Dynamic geometry• number of unknown parameters for each image is nmultiplied by 6 positon ang orientation of each line which nis number of lines imaged by an image• No need for image motion compensation

• capability of acquiring stereo images by using 2 cameras• high value of B/H ratio in this cameras• Good height accuracy


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University MSc Entrace Konkoor- 1382


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Cameras and Aerial Photography5. Panaromic Cameras

Properties of Panaromic cameras

• imaging lines are parallel to the flight line• Panaromic effect: images are not exactly rectangular


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Instead of using film, digital cameras use a gridded array

of silicon coated CCDs (charge-coupled devices) thatindividually respond to electromagnetic radiation


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Multispectral ScanningMultispectral Scanners (across-track scanning, along-track scanning)

• across-track scanners (whiskbroom scanners)

• Optical-Mechanical Scanners

• Scanning (Rotating mirror (A), detectors (B))

• Spatial resolution depends on IFOV and platform Height.

• Linear array CCDs

dwell time: the length of time the IFOV "sees" a ground resolution cell as therotating mirror scans which is generally quite short and influences the design ofthe spatial, spectral, and radiometric resolution of the sensor.


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Multispectral ScanningMultispectral Scanners (across-track scanning, along-track scanning)

• along-track scanners (Pushbroom Scanners)

Scanning (array of detectors (A), focal plane (B), lens systems (c))

A separate linear array is required to measure each spectral band or channel.


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Multispectral Scanning

Advantages of Along-Track scanners over Across-Track scanners:

• increased Dwell time increased detected energy

• Solid state, smaller, lighter, less needed power

because they have no moving part

Disadvantage: cross-calibrating thousands of detectors to achieveuniform sensitivity across the array is necessary and complicated.


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Stripping error of linear array CCDs


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Advantages of Scanning systems over photographic systems:

• increased spectral range

• increased Spatial Resolution

• no need to separate lens system for detecting different bands

• increased dynamic range by electronically recording energy

• more easy to transmit data and processing


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Thermal ImagingThermal spectral Band (3-15µm)

The detectors are cooled to temperatures close to absolute zero in order to limittheir own thermal emissions.

Thermal sensors essentially measure the surface temperature and thermalproperties of targets.

The data are generally recorded on film and/or magnetic tape and thetemperature resolution of current sensors can reach 0.1 °C

Because of the relatively long wavelengthof thermal radiation (compared to visibleradiation), atmospheric scattering is

minimal.However, absorption by atmospheric gasesnormally restricts thermal sensing to twospecific regions - 3 to 5 µm and 8 to 14µm.


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Thermal ImagingImagery which portrays relative temperature differences in their relative spatiallocations are sufficient for most applications. Absolute temperature measurementsmay be calculated but require accurate calibration and measurement of thetemperature references and detailed knowledge of the thermal properties of the

target, geometric distortions, and radiometric effects.

The Spatial resolution of Thermal images are lower because the emitted energydecreases by increasing wavelength.

Thermal images can be acquired

Day/night


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How would thermal imagery be useful in an urban environment?

Detecting and monitoring heat loss from buildings in urban areas is an excellentapplication of thermal remote sensing

Thermal imaging in both residential and commercial areas allows us to identifyspecific buildings, or parts of buildings, where heat is escaping

Quiz


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Geometric Distortion in Imagery Any remote sensing image (acquired by multispectral scanner on satellite/ aphotographic system/ other platform/sensor combination) will have various geometricdistortions due to:

• The perspective of the sensor optics,• The motion of the scanning system,• The motion and instability of the platform,• The platform altitude, attitude, and velocity,• The terrain relief, and• The curvature and rotation of the Earth.


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Geometric Distortion in Imagery And the errors are:

• Relief displacement (photographic, along-track & across-track Sensors)

The geometry of along-track scanner imagery is similar to that of an aerialphotograph for each scan line

• Errors caused by changes in their speed, altitude, and attitude

This is more important in aircraft platforms because of satellite’s stable orbits

• Skew Distortion (caused by Earth rotation)


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Geometric Distortion in ImageryThe effect of Earth Rotation

L: the size of image re : radius of Earth wS : angular velocity of SatellitetS : Time of taking an image

So, The Time of acquiring a scene of Landsat image (185 km) by the above formulawill be 28.6 seconds.

Ve: Linear Velocity of Earth we : angular Velocity of Earth Φ : Latitude Δ xe : amount of Earth rotation for a point on Φ Latitude at the ts period of time

At the time of taking a Landsat image: Δxe=11.02 km


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University MSc Entrace Konkoor- 1382



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If you wanted to map a mountainous region, limiting geometricdistortions as much as possible, would you choose a satellite-basedor aircraft-based scanning system?

Although an aircraft scanning system may provide adequategeometric accuracy in most instances, a satellite scanner wouldprobably be preferable in a mountainous region. Because of thelarge variations in relief, geometric distortions as a result of reliefdisplacement would be amplified at aircraft altitudes much morethan from satellite altitudes. Also, given the same lightingconditions, shadowing would be a greater problem using aircraftimagery because of the shallower viewing angles and wouldeliminate the possibility for practical mapping in these areas.

Quiz


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