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GEOG 480 > Lesson 1 Flashcards > Flashcards

Lesson 1 Flashcards

1
Q

Sensor and Platform

A
  • Sensor: the instrument use to record data
    • every sensor is designed with a unique field of view defining the size of are instantaneously imaged on the ground.
  • Platform: the vehicle use to deploy the sensor
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2
Q

Sensor Footprint

A

The sensor field of view combined with the height of the sensor platform above the ground determines the sensor footprint. A sensor with a very wide field of view on a high-altitude platform may have an instantaneous footprint of hundreds of square kilometers; a sensor with a narrow field of view at a lower altitude may have an instantaneous footprint of ten of square kilometers.

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3
Q

Resolution

A
  • refers to the degree of fineness with which an image can be produced and the degree of detail that can be discerned.
  • 4 kinds of resolution: Spatial, Temporal, Spectral, and Radiometric
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4
Q

Spatial resolution

A
  • A measure of the finest detail distinguishable in an image.
  • Depends on the sensor design and is often inversely related to the size of the image footprint.
  • Sensors with very large footprints = low spatial resolution
  • Sensors with very small footprints = high spatial resolution
  • Varies from tens of kilometers per pixel to sub-meter. Spatial resolution is closely tied to Ground Sample Distance (GSD) which is the nominal dimension of a single side of a square pixel in ground units.
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5
Q

Temporal resolution

A
  • Refers to the frequency at which data are captured for a specific place on the earth.
  • The more frequently data they are captured by a particular sensor, the better or finer is the temporal resolution of that sensor.
  • Often quoted as a “revisit time” or “repeat cycle.” Temporal resolution is relevant when using imagery or elevations datasets captured successively over time to detect changes to the landscape.
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6
Q

Spectral resolution

A
  • Describes the way an optical sensor responds to various wavelengths of light.
  • High spectral resolution =
    • Records multiple, very narrow bands of wavelengths.
    • “hyperspectral” sensor can discern and distinguish between many shades of a color, recording many gradations of color across the infrared, visible, and ultraviolet wavelengths.
  • Low spectral resolution =
    • the sensor records the energy in a wide band of wavelengths as a single measurement
    • most common “multispectral” sensors divide the electromagnetic spectrum from infrared to visible wavelengths into four generalized bands: infrared, red, green, and blue.
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7
Q

Spectral signature

A
  • The way a particular object or surface reflects incoming light can be characterized as and can be used to classify objects or surfaces within a remotely sensed scene.
  • example, an asphalt parking lot, a corn field, and a stand of pine trees will have all have different spectral signatures.
  • Automated techniques can be used to separate various types of objects within a scene.
  • Can be misleading because it implies that distinctiveness and consistency that seldom can be observed in nature.
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8
Q

Radiometric resolution

A
  • Refers to the ability of a sensor to detect differences in energy magnitude.
  • Low radiometric resolution sensors - can detect only relatively large differences in the amount of energy received.
  • High radiometric resolution sensor - can detect relatively small differences.
  • The range of possible values of brightness that can be assigned to a pixel an image file or band is determined by the file format and is also related to radiometric resolution. In an 8-bit image, values can range from 0 - 255; in a 12-bit image, values can range from 0 - 4096; in a 16-bit image, values can range from 0 - 65536; and so on.
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9
Q

Difference between remote sensing images and everyday experience

A
  • Image presentation
  • Unfamiliar scales and resolutions
  • Overhead views from aircraft or satellites
  • Use of several regions of the electromagnetic spectrum
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10
Q

Remote Sensing Definition

A

The practice of deriving information about the earth’s land and water surfaces using images acquired from a n overhead perspective, using electromagnetic radiation in one or more regions of the electromagnetic spectrum, reflected or emitted from the earth’s surface.

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11
Q

Overview of Remote Sensing Process

A

Physical Objects - TO - Sensor Data - TO - Extracted Information - TO - Applications

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12
Q

Spectral Response Patterns

A
  • Same idea as spectral signature, but less rigid of a concept.
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13
Q

Spectral Differentiation

A
  • Depends on the difference in the energy reflected or emitted from feature of interested.
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14
Q

Multispectral Remote Sensing

A
  • The science of observing features at varied wavelengths in an effort to derive information about these features and their distributions.
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15
Q

Radiometric Differentiation

A
  • The differentiation of objects based on the brightness of the object and the feature. The scene should have contrasting brightness and the remote sensing instrument must be capable of recording this contrast.
  • Backgrounds can cause a problem if the background and object don’t have high contrasting brightness.
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16
Q

Spatial Differentiation

A
  • The ability to record spatial detail is influenced primarily by the choice of sensor and the altitude at which it is used to record images of the Earth.
  • Landscapes vary greatly in their spatial complexity. Some may be represented clearly at coarse levels of detail and some are so complex that the finest level of detail is required to record their essential characteristics.
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17
Q

Pixels

A

The smallest areal units identifiable on the imaged.

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18
Q

Temporal Dimension

A
  • The use of many images of the same region acquired over time.
  • There has been a long history of using temporal dimension using sequential aerial photography, but its full value was discovered when satellite systems could systematically observe the same regions on a repetitive basis. This provided aerial images on the same platform at regular intervals which lead to temporal dimensions full potential.
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19
Q

Geometric Transformation

A
  • Ideal remote sensing instrument would be able to create an image with accurate and consistent geometric relationships between points on the ground and their corresponding representations on the image. Such image could form the basis for accurate measurements of areas and distances.

Positional errors often occur caused by:

  • The perspective of the sensor optics
  • Motion of scanning optics
  • Terrain relief
  • Earth Curvature
  • Some instances the locational error can be removed, but the integrity of the image can be jeopardized if it is use for measuring areas and distances and must be considered.
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20
Q

Role of the Atmosphere

A
  • The sensors from the satellite must pass through a large depth of the Earth’s atmosphere to be received. This can alter the intensity and wavelength by particles and gases in the atmosphere. These changes appear on the image in ways that degrade image quality and the accuracy of interpretations.
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21
Q

Employers report that they seek employees who:

A
  • Have a good background in at least one traditional discipline
  • Are reliable and able to follow instructions without detailed supervision
  • Can write and speak effectively
  • Work effectively in teams with other in other disciplines
  • Are familiar with common business practices
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22
Q

The American Society for photogrammetry and Remote Sensing – ASPRS

A
  • Founded in 1934 by a small group of like-minded pioneers in a unique and emerging field.
  • Today, over 7000 individuals worldwide are members.
  • There are many other ways that ASPRS membership can support professional development and career advancement.
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23
Q

International Society for Photogrammetry and Remote Sensing - (ISPRS)

A
  • founded in 1910
  • devoted to the development of international cooperation for the advancement of photogrammetry and remote sensing and their applications.
  • National organizations, such as ASPRS, are the voting members; individuals can take part in activities, conferences, technical Working Groups, and Commissions through affiliation with one of the Member organizations.
  • The ISPRS Congress, an international conference dedicated to photogrammetry and remote sensing, takes place every four years and is hosted by the home country of the elected President.
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24
Q

What forms the basis for photographs?

A
  • The sun provides a source of radiation that passes through the atmosphere before reaching the earth’s surface. Some radiation is reflected upward from earth’s surface which forms the basis for photographs and similar images. Other radiation is absorbed at the surface and is then reradiated as thermal energy.
  • Man-mad radiation generated by imaging radars is also used for remote sensing
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25
Q

Wavelength of ER

A
  • The distance from one wave crest to the next.
  • Can be measured in everyday units of length, although very short wavelengths have such small wave crest that extremely short measurement units are required.
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26
Q

Frequency of ER

A
  • Measured as the number of crests passing a fixed point in a given period of time.
  • Often measured in hertz, units each equivalent to one cycle per second.
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27
Q

Amplitude of ER

A
  • The height of each peak.

- Often measured as energy levels (spectral irradiance), expressed as watts per square meter per micrometer.

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28
Q

Phase of a waveform

A
  • The extent to which the peaks of one waveform align with those of another.
  • If two waves are aligned, they oscillate together and are said to be “in phase” (phase shift of 0 degrees).
  • If a pair of waves are aligned such that the crests match with the troughs, they are said to be “out of phase” (phase shift of 180 degrees)
  • Measured in angular units (degrees or radians)
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29
Q

Ultraviolet Spectrum

A
  • A zone of short-wavelength radiation that lies between the X-ray and the limit of human vision regions.
  • Sometimes is subdivided into near ultraviolet, far ultraviolet, and extreme ultraviolet.
  • Region discovered in 1801 by German scientist Johann Wilhelm Ritter.
  • Ultraviolet means “beyond the violet” designating it as the region just outside of violet region, the shortest wavelengths visible to human eye.
  • Near ultraviolet is known to induce fluorescence, emission of visible radiation, in some materials.
  • Ultraviolet radiation is easily scattered by the Earth’s atmosphere, so it is not generally used for remote sensing of earth’s materials.
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30
Q

Visible Spectrum

A
  • Consists of a very small portion of the spectrum but is obviously very significant in remote sensing.
  • Isaac Newton during 1665 and 1666 investigated visible radiation by conducting experiments that revealed three segments of visible light using prisms. Today we know these segments as the additive primaries.
31
Q

Additive Primaries

A
  • Blue: 0.4 to 0.5 µm
  • Green: 0.5 to 0.6 µm
  • Red: 0.6 to 0.7 µm
32
Q

Primary colors

A
  • Defined such that no single primary can be formed from a mixture of the other two and that all other colors can be formed by mixing the three primaries in appropriate proportions.
  • Equal proportion of the three additive primaries combine to form white light.
33
Q

Subtractive Primaries

A
  • Defined as the colors of pigments and dyes. Each of these colors absorbs a third of the visible spectrum and an equal mixture of these pigments yields black (complete absorption of the visible spectrum).
  • Used in reproduction colors on films, photographic prints, and other images.
    • Yellow: absorbs blue light and reflects red and green
    • Cyan: absorbs red light and reflects blue and green
    • Magenta: absorbs green light and reflects red and blue
34
Q

Infrared Spectrum

A
  • Designated as the section with longer wavelengths that the red portion of the visible spectrum.
  • Discovered in 1800 by British astronomer William Herschel
  • This segment extends from 0.72 to 15 µm making it more than 40 times as wide as the visible light spectrum.
  • Broken into two categories: Near infrared and Mid infrared, and Far infrared
35
Q

Near infrared and Mid infrared

A
  • Regions closest to the visible spectrum.
  • Remote sensing in the near infrared region can use films, filters, and cameras with designs like those intended for use with visible light since the radiation in the near infrared region behaves similarly to the visible spectrum.
36
Q

Far infrared

A
  • Consists of wavelengths well beyond visible and border on the microwave region.
  • Far infrared radiation is emitted by the earth and consists of “heat” or “thermal energy”.
  • At times this portion of the spectrum is referred to as the ‘emitted infrared’.
37
Q

Microwave Energy

A
  • Longest wavelengths 1 mm to 1 µm are commonly used in remote sensing. Shortest wavelengths in this range have much in common with the thermal energy of the far infrared.
  • Longer wavelengths merge into the radio wavelengths used for commercial broadcasts.
  • Knowledge of this region stems from the work of Scottish physicist James Clerk Maxwell and German physicist Heinrich Hertz.
38
Q

Radiant Flux (Φe)

A
  • The rate at which photons (quanta) strike a surface, measured in watts (W)
  • Measure specifies energy delivered to a surface in a unit of time.
39
Q

Irradiance (E e)

A
  • Defined as radiant flux per unit area, usually measured as watts per square meter.
  • Measure’s radiation that strikes a surface.
40
Q

Radiant Exitance (M e)

A
  • Defines the rate at which radiation is emitted from a unit area, also measured in watts per square meter.
41
Q

Temp of an object

A
  • All objects with temps above zero have temp and emit energy. The amount of energy and the wavelengths it emits depends on the temp of the object.
  • Increase temp = total amount of energy emitted also increases and the wavelength of maximum peak emission becomes shorter.
42
Q

Blackbody

A
  • The relationship between temp and wavelength. A hypothetical source of energy that behaves in an idealized manner, it absorbs all incident radiation and none is reflected.
  • It is hypothetical because all objects in nature reflect at least a small proportion of radiation that strikes them. A blackbody emits energy with perfect efficiency; it’s effectiveness as a radiator of energy varies only as temp varies.
43
Q

Emissivity (E)

A
  • The ratio between the emittance of a given object (M) and that of a blackbody at the same temp (Mb)
  • Emissivity is a useful measure of the effectiveness as radiators of electromagnetic energy.
  • High emissivity = objects that end to absorb high proportions of radiation.
  • Low emissivity = objects that are less effective ad absorbing radiation.
44
Q

Wien’s displacement law

A
  • Specifies the relationship between the wavelength of radiation emitted and the temp of a blackbody.
  • As blackbodies become hotter, the wavelength of maximum emittance shifts to shorter wavelengths.
  • The earth, being much cooler than the sun, must emit radiation at much longer wavelengths than the sun.
  • The sun at 6,000 K has a mx intensity at 0.5 µm in the green portions of the visible spectrum
  • The earth at 300 K emits with max intensity near 10 µm in the far infrared spectrum.
45
Q

Scattering

A
  • The redirection of electromagnetic energy by particles suspended in the atmosphere or by large molecules of atmospheric gases.
  • The amount of scattering that occurs depends on the sizes of these particles, their abundance, the wavelength of the radiation, and the depth of the atmosphere through which the energy is traveling.
  • In the late 1890s, British scientist Lord J.W.S. Rayleigh discovered the common form of scattering. He demonstrated that a perfectly clean atmosphere, consisting only of atmospheric gases, causes scattering of light in a manner such that the amount of scattering increases greatly as wavelength becomes shorter.
46
Q

Rayleigh scattering

A
  • Occurs when atmospheric particles have diameters that are very small relative to the wavelength of the radiation.
  • Particles could be very small specks of dust or larger molecules of atmospheric gases (nitrogen (N2) and oxygen (O2)).
  • This scattering is wavelength-dependent, meaning that the amount of scattering changes greatly as one examines different regions of the spectrum.
  • Rayleigh scattering is the cause of both the blue color of the sky and the brilliant red and orange colors often seen at sunset.
  • Blue light is scattered about 4 times as much as red light.
  • Ultraviolet light is scattered almost 16 times as much as red light.
  • An observer at Earth’s surface sees the blue light redirected by Rayleigh scattering at midday with the sun is high in the sky and the atmospheric path of the solar beam is relatively short and direct.
  • At sunset, observers on Earth’s surface can see only those wavelengths that pass through the long atmospheric path caused by the low solar elevation. Only long wavelengths can penetrate this distance without being disrupted by scattering.
47
Q

Clear atmosphere scattering

A
  • When Rayleigh scattering occurs in the absence of atmospheric impurities. It is the dominate scattering process high in the atmosphere, up to altitude of 9-10 km, the upper limit for atmospheric scattering.
48
Q

Mie scattering

A
  • Caused by large atmospheric particles including dust, pollen, smoke, and water droplets.
  • These particles are many times larger than those responsible for Rayleigh scattering.
  • These particles have diameters that are roughly equivalent to the wavelength of the scattered radiation.
  • Mie scattering can influence a broad range of wavelengths in and near the visible spectrum.
  • Mie scattering is wavelength-dependent and tends to be greatest in the lower atmosphere (0 to 5 km) where large particles are abundant.
49
Q

Nonselective scattering

A
  • Cause by particles that are much larger than the wavelength of the scattered radiation.
  • Might be large water droplets or large particles of airborne dust.
  • The scattering is not wavelength-dependent, so we observe it as a whitish or grayish haze.
50
Q

Effects of Scattering

A
  • Scattering causes the atmosphere to have a brightness of its own allowing us to see objects in shadows because of light being redirected by particles. It can make dark objects appear brighter that they would otherwise and vis versa (bright objects appear darker).
  • Because of the wavelength dependency of Rayleigh scattering, radiation in the blue and ultraviolet regions of the spectrum is usually not considered useful for remote sensing.
  • Because images recording these spectrums tend to record the brightness of the atmosphere and not the brightness of the scene itself causing remote sensing instruments to often exclude short-wave radiation (blue and ultraviolet wavelengths) by use of filters or decreased sensitivities of films to these wavelengths.
  • Scattering can direct energy from outside the sensor’s field of view and decreases the spatial detail recorded by the sensor.
51
Q

Refraction

A
  • The bending of light rays at the contact area between two media that transmit light.
  • Examples of refracting: lenses of cameras or magnifying glasses which bend light rays to project or enlarge images.
  • Also occurs in the atmosphere as light passes through the atmospheric layers
  • Influenced by variations of clarity, humidity, and temp affecting the density of the atmospheric layers.
52
Q

Surface Normal

A
  • A line perpendicular to the surface at the point at which the light ray enters the denser medium.
  • As the light passes into a denser medium, it is deflected toward the surface normal.
53
Q

Absorption

A
  • Occurs when the atmosphere prevents transmission of radiation or its energy through the atmosphere.
  • 3 gasses responsible for most absorption:
  • Ozone (O3) - formed by the interactions of high- energy ultraviolet radiation with oxygen molecules
    high in the atmosphere.
    • Mainly less that 0.24 µm is absorbed and reaches the lower atmosphere.
  • Carbon Dioxide (CO2) - occurs in low concentration, mainly in the lower atmosphere.
    • Effective in absorbing radiation in the mid and far infrared regions of the spectrum
    • Strongest absorption occurs in the regions from about 13 to 17.5 µm in the mid infrared.
  • Water Vapor (H2O) - commonly present in the lower atmosphere
    • Amounts vary from 0 to 3% by volume
    • Amount varies greatly based on time and place.
    • Several times more effective in absorbing radiation than the other gases.
    • Highest absorption between 5.5 and 7 µm and above 27 µm.
54
Q

Atmospheric Windows

A
  • Areas where wavelengths are relatively easily transmitted through the atmosphere.
  • Positions, extents, and effectiveness of atmospheric windows are determined by the absorption spectra of atmospheric gases.
55
Q

Interactions with the Atmosphere

A
  • Scattering
  • Refraction
  • Absorption
  • Atmospheric Windows
56
Q

Path of the wavelength:

A
  • First, absorbed by ozone
  • Second, reflected from clouds
  • Third, absorbed by dust and gases
  • Fourth, absorbed by ground
  • Fifth, anything not absorbed is reflected from ground
57
Q

Of the 100 units of shortwave radiation that reach the outer edge of the earth’s atmosphere:

A
  • About 3 units are absorbed in the ozone
  • About 25 are reflected from counts
  • About 19 are absorbed by dust and gases in the lower atmosphere.
  • About 8 units are reflected from the ground surface
  • About 45 units are ultimately absorbed and then reradiated by the earth’s surface.
58
Q

Of the 143 units of long-wave radiation from the ground surface to the atmosphere:

A
  • About 8 units are transferred from the ground surface to the atmosphere by ‘turbulent transfer’.
  • About 22 units are lost to the atmosphere by evaporation of moisture in the soil, water bodies, and vegetation.
  • About 113 units are radiated directly to the atmosphere.
59
Q

Turbulent Transfer

A
  • Heating of the lower atmosphere by the ground surface, which causes upward movement of air, then movement of cooler air to replace the original air.
60
Q

Interactions with Surface:

A
  • Reflection
  • Bidirectional Reflectance Distribution Function (BRDF)
  • Transmission
  • Fluorescence
  • Polarization
  • Reflectance
61
Q

Reflection

A
  • Occurs when a ray of light is redirected as it strikes a nontransparent surface
  • Depends on the sizes of surface irregularities (roughness or smoothness)
62
Q

Specular Reflection

A
  • Occurs if the surface is smooth relative to wavelength

- Redirects all or almost all of the incident radiation in a single direction.

63
Q

Diffuse or Isotropic reflection

A
  • Occurs when the surface is rough relative to wavelength
  • Energy is scattered more or less equally in all directions
  • Occurs on many natural surfaces
64
Q

Bidirectional Reflectance Distribution Function (BRDF)

A
  • Reflection characteristics of a surface.

- A mathematical description of the optical behavior of a surface with respect to angle of illumination and observation.

65
Q

Transmission

A
  • Occurs when radiation passes through a substance without significant reduction.
  • From a given thickness or depth of a substance, the ability of a medium to transmit energy is measured as the transmittance.
  • Example: plant leaves are generally opaque to visible radiation but transmit significant amounts of radiation in the infrared.
66
Q

Fluorescence

A
  • Occurs when an object illuminated with radiation of one wavelength emits radiation at a different wavelength.
  • Familiar examples: sulfide minerals emit visible radiation when illuminated with ultraviolet radiation.
  • Contrasting surfaces illustrate the effectiveness of fluorescence in revealing differences between healthy and stressed leaves.
67
Q

Polarization

A
  • Defined as the asymmetry of vibration direction relative to spreading direction. It denotes the orientation of the oscillations within the electric field of electromagnetic energy.
  • Example: polarizing sunglasses specifically designed to reduce glare. They are manufactured with molecules that can absorb the horizontally polarized bright radiation and reduce the glare.
68
Q

Reflectance

A
  • Expressed as the relative brightness of a surface as measure for a specific wavelength interval.
  • Expressed as a percentage
69
Q

Active Remote Sensing

A
  • Sensors have their own source of energy. They can emit a controlled beam of energy to the surface and measure the amount of energy reflected back to the sensor.
  • Examples:
    • Camera with a flash - flash is light source
    • Radar - sends out microwave ER and times the delay
    • LIDAR (Light detecting and ranging) - Measures distances with laser light and measures the reflection with a sensor. Data is used to make 3D representations of the target.
70
Q

Passive Remote Sensing

A
  • Sensors do not have their own source of energy. They measure reflected sunlight emitted from the sun that can only take place during the daytime.
  • Examples:
    • Camera without flash - sun is the light source
    • Infra Red - every object emits thermal radiation in the form of heat. Used for heat mapping and night vision devices
71
Q

Kirchhoff’s Law

A
  • States that the ratio of emitted radiation to absorbed radiation flux is the same for all blackbodies at the same temperature.
  • This law forms the basis for the definition of emissivity (E).
72
Q

Stefan-Boltzmann Law

A
  • Defines the relationship between the total emitted radiation (W) and temperature (T). This law states that hot blackbodies emit more energy per unit area than do cool blackbodies.
73
Q

Snell’s Law

A
  • The angel that defines the path of the refracted ray
74
Q

Lambert’s laws of illumination

A
  • States that the perceived brightness of a perfectly diffuse surface does not change with the angle of view.

GEOG 480 (3 decks)

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