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Geospatial Communications > Midterm 2 > Flashcards

Midterm 2 Flashcards

(41 cards)

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1
Q

Qualities of effective georeferencing systems.

A
  1. unique- should only refer to one location on the Earth
  2. meaning of the location should be shared by those who use the system properly
  3. locations should be persistent through time
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2
Q

Define the sexagesmal scale. When is it used?

A

A circle is divided into 360 degrees.
A degree is divided into 60 minutes.
A minute is divided into 60 seconds.

*These measurements are used in GIS for Lat/Long

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3
Q

Characteristics of latitude (parallels).

A
  • reference = equator
  • range = 0-90 degrees North and South
    *the equator = a great circle
    other parallels= small circles
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4
Q

Characteristics of longitude (meridians)

A
  • reference= prime meridian
  • no natural fixed reference point
  • range = 0-180 degrees East and West
  • *ALL Meridians = Great Circles
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5
Q

Define a loxodrome.

A

Lines on the globe that follow a constant compass bearing.

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6
Q

Define geoid. Why can’t it be used for georeferencing?

A

the true shape of the Earth

- Earth has bulges, depressions bc of unequal distribution of the earth's crust (centrifugal force)  - the surface where the force of gravity is perpendicular (equipotential surface)  * NOT the actual surface of the earth's crust 
- (geoid would be equal to sea level if undisturbed by tides/weather)

Too complex to be used for georef.

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7
Q

Describe a reference ellipsoid/spheroid. (oblate spheroid)

A

Simplified version/ mathematical figure of a geoid used in georeferencing, projections and cartography.
- minor differences, minor errors

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8
Q

Why are there different ellipsoids?

A
  1. over time, we improve our ability to measure the Earth
    (most recent usually the most accurate)
  2. Different ellipsoids “fit” the local geoid better in various parts of the world
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9
Q

What 3 things are specified by a datum? What are the 2 types of datum?

A
  1. The reference ellipsoid
  2. The position of the reference ellipsoid in relation to the geoid
  3. The orientation of the reference ellipsoid in relation to the geoid

2 types can be either local or global:
1. horizontal datum- describes horizontal position (latitude/longitude)

  1. vertical datum - describes vertical position (elevation)
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10
Q

Local vs. Global Datums

A

Local - reference ellipsoid “fits” a specific area more accurately
Global= Earth-centred, fits the entire planet more accurately but may not be the best fit for a specific area

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11
Q

Describe a Conformal distortion.

A

When only shape is preserved - unable to preserve area.
Best used for small areas and navigation (loxodromes).
Scale changes between areas, areas are inconsistent.

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12
Q

Describe an equal area distortion.

A

When only area is preserved- unable to preserve shape.
Shapes in small areas are disorted.
Best for portraying property maps.

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13
Q

Describe an equi-distant distortion.

A

When only distance is preserved, equal area must be distorted.
Occurs when true distances are measured from the centre of the projection.

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14
Q

What are the three developable surfaces (what you can unfold onto a flat map).

A
  1. Cylinder
  2. Cone
  3. Plane (Azimuth)
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15
Q

Tangent vs. Secant Projections

A 
Tangent= one point of intersection-no distortion
Secant = two points of intersection- no distortion
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16
Q

What are the 3 families of projection?

A
  1. Azimuthal (distance) = planar
  2. Conic
  3. Cylindrical
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17
Q

Describe azimuthal projections.

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A

Displays radial symmetry.

Distance/Direction from a central point are preserved.

18
Q

Describe cylindrical projections.

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A
  • Preserves distances or areas
    -In equatorial aspect, all parallels are straight
    horizontal and all meridians are straight vertical and
    uniformly spaced
    -Usually display linear symmetry in scale/distortion
    patterns
    -Gross distortions away from the standard line
    -The further away you get, the worse the distortion
    -Commonly used for regional maps of tropical zones
19
Q

Describe conic maps.

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A

-PRESERVES ANGLES
- In the normal (polar) aspect, meridians are straight,
equidistant lines, converging towards a point
-Conic pattern of distortion
- Distortion is constant along each parallel (in normal aspect)
- Commonly used for regional maps of temperate
zones

20
Q

3 questions to ask to choose the most proper projection.

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A
  1. What quantitative measures are required?
  2. How are the results best presented?
  3. Is there a commonly used projection?
21
Q

Describe UTM georeferencing system. (Universal Transverse Mercator)

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A

Mercator = cylindrical projection wrapped around the equator
Easting = fancy term for X
Northing = fancy term for Y
UTM units are in meters - preferred
- Determines how far north or east you are from the equator
- Meters are universal measurements- easier to understand
- Each strip called a “zone” and the world is split into 6 strips

22
Q

Describe the Dominion Land Survey georeferencing system.

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A

Divided most of Western Canada into 1-square mile sections for settlement purposes.
anchored by 2 controlling survey lines:
1. Principal Meridian - runs N-S
2. Baseline - runs E-W

23
Q

What is the difference between a datum and a coordinate system?

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A

Datum - a mathematical model that describes Earth as an ellipsoid (can be local or global)
Coordinate system - Uses a specific datum to describe where 0’N and 0’E meet and builds from there

24
Q

Define the projection process.

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A

The transformation of Earth’s coordinates to Cartesian coordinates (x,y). The process of projecting the Earth (3D) onto a map (2D).

25
The role of remote sensing in geospatial analysis. Define and give examples.
It is the art of gathering info on something without coming into contact with it. (ex. aerial photography)
26
Describe the two types of aerial photographs. (Oblique vs. Vertical) Which has the least scale distortion?
Oblique air photos: optical axis greater than 3% of vertical High oblique: horizon is visible Low oblique: horizon is not visible Vertical air photo: camera’s optical axis is within 3% of vertical Least scale distortion - Most useful for mapping
27
What are the elements of visual image interpretation?
-Shape General form, configuration, or outline -Size In context of the image scale; relative or absolute -Pattern Spatial arrangement or repetition of objects -Tone/Hue Relative brightness or colour of objects -Texture Characteristic repetition of tone or colour -Site Geographic or topographic location -Association Occurrence of features in relation to others -Shadows
28
What are the 2 issues for image interpretation?
1. Classification system: the criteria to be used for separating various categories 2. Selection of a minimum mapping unit (MMU): the smallest-sized areal entity to be mapped as a discrete area
29
Describe image interpretation keys.
Helps visual image interpretation by providing guidance regarding the identification of classes or features in an image. Two parts: (i) captioned images, and (ii) graphic or word descriptions, normally with explicit reference to the elements of image interpretation
30
Define black bodies.
A theoretical object that completely absorbs all incident radiation, converting it to internal energy. Therefore it does not permit any transmittance or reflectance but emits the absorbed energy at the maximum possible rate. (Stefan-Boltzmann Law)
31
Within what range (um) does the sun peak at wavelength emittance (range in which visible light is seen)
0.30-0.70 um
32
What is the importance of EMR with remote sensing?
Electromagnetic radiation is the engine that drives remote sensing. Remote sensing instruments collect data across specific wavelengths, depending on the instrument’s purpose, platform, and technology.
33
In-Situ vs. Remote Sensing
In-situ sensing is done in direct contact with the object of interest while remote is not.
34
Describe transmission/refraction (transmittance).
The bending of light that occurs when EMR travels through matter - wavelength dependent
35
Describe scattering. What are the different types?
Unpredictable form of reflection. 1. Raleigh - when particles are smaller than the wavelength (molecular) - caused by gases in the upper atmos. (what makes the sky blue) 2. Mie - when particles are same size as the wavelength caused by dust/smoke in lower atmos. 3. Non-Selective w respect to visible wavelengths - when particles are much larger than the wavelength - caused by water droplets/ice crystals in lower atmos.
36
Describe absorption.
Occurs when EMR is absorbed by material and converted into other forms of energy Water vapour, CO2, oxygen, ozone, chlorophyll, minerals Wavelength dependent: those not greatly affected called ‘atmospheric windows’
37
Define atmospheric windows
The "windows" in the atmosphere where EMR can be transmitted through depending on wavelength.
38
Describe reflectance. Give an example.
Re-radiation of photons in unison, in a layer approximately ½ wavelength deep ‘Bouncing off’ a surface ex. clouds reflecting most of the incident radiation from the sun
39
Specular vs. Diffuse Reflection
Specular = Incoming radiation is reflected in a single direction - Mirror-like reflectance from a ‘smooth’ surface Diffuse = Incoming radiation is reflected across many angles ‘Rough’ surface consisting of many specular planes
40
Spatial vs. Spectral resolution
spatial resolution = -Ground size of the smallest recording unit - Smallest area on the ground that can be seen or resolved by a sensor spectral resolution = -The number and dimension of electromagnetic wavelength intervals to which a remote sensing instrument is sensitive
41
Temporal vs. radiometric resolution
Temporal resolution = -The revisit frequency for a particular area on the earth’s surface Radiometric resolution = -The sensitivity of a remote sensing instrument to differences in electromagnetic flux

Geospatial Communications (3 decks)

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