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SURVEYING > SURVEYING METHODS > Flashcards

SURVEYING METHODS Flashcards

- EDM - GNSS - Remote sensing - GIS

1
Q

What are the benefits of EDM

A
  • easy
  • quick
  • accurate
  • economy
  • reliable
  • independent of terrain conditions
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2
Q

What changes has EDM brought forward?

A
  1. Traversing on a grandiose scale
  2. Inclusion of more distances into triangulation - scale error control
  3. setting out and photogrammetric control
    offshore position fixing
    deformation monitoring to sub-millimeter accuracies
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3
Q

What are the methods of EDM measurement?

A
  1. Pulse method
  2. Phase difference method
  3. Interferometry
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4
Q

Explain the Pulse method

A

A short, intensive pulse of radiation is transmitted to a
reflector target, which immediately transmits it back, along
a parallel path, to the receiver.

The measured distance is computed from the velocity of the signal multiplied by the time it took to complete its journey.

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5
Q

Explain the Phase difference method

A

It is a method of measuring phase differences of
continuous waves for distance measurement.

The instrument measures the amount (wavelength) by which the reflected signal is out of phase with the emitted signal.

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6
Q

Explain the Interferometry method

A

Used for high precision distance measurements over short distances.

They are based of the principle of optical interference. Interferometers have a range of about 80m and are mainly used indoors.

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7
Q

Carrier waves

A

To overcome these unsuitable waves for transmission through the atmosphere, they are superimposed electronically on other waves known as carrier waves.

Carrier waves are of a much higher frequency and act as a medium for carrying distance information. This process of electronic superimposition is known as modulation.

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8
Q

What are the types of modulation?

A
  1. Amplitude modulation (light waves)
  2. Frequency modulation (microwaves)
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9
Q

Sources of errors in EDM measurement

A
  1. Errors in the determination of light velocity
  2. Modulation frequency errors
  3. Refractive index errors
  4. Errors in phase difference determination
  5. Zero errors (calibration errors)
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10
Q

What does GNSS stand for?

A

(Global Navigation Satellite Systems)

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11
Q

What are the 3 major components/segments of GNSS

A
  1. Space segment
    GNSS satellites orbiting above earth
  2. Control segment
    Ground-based network of master control stations, data uploading stations, and monitor
    stations.
    Master station - adjust satellites’ orbit parameters/ on-board high-precision clocks
    Monitor station - monitor status and signal of satellites
    Uploading station - upload change in status
  3. User segment
    Contains antennas and receivers to determine info like position, velocity, time
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12
Q

GNSS steps to determine time and position

A
  1. satellites
  2. propagation
  3. reception
  4. computation
  5. application
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13
Q

Satellite constellation geometry

A

Dilution of Precision (DOP) depends on the distribution of the satellites in space.

Clear visibility, many satellites, low DOP, good geometry (and vice versa)

Dilution of Precision (PDOP) used to measure geometric strength as an expression of the quality of the satellites geometry, which is essential for ambiguity resolution.

Desirable PDOP value: 1<x>6</x>

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14
Q

What are the GNSS Error sources

A
  1. Satellite clocks
  2. Orbit errors
  3. Ionospheric delays
  4. Receiver noise
    5, Multipath
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15
Q

GNSS applications

A
  1. Transportation
  2. Timing
  3. Machine Control
  4. Marine
  5. Surveying
  6. Defence
  7. Port Automation
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16
Q

Types of Remote Sensing/Earth observation

A
  1. Visible & Reflective IR remote sensing
    Radiation source: The sun
    Object: Reflectance
  2. Thermal remote sensing
    Radiation source: Object
    Object: Thermal radiation (emissivity, temperature)
  3. Microwave remote sensing
    Radiation source: Object/ Radar
    Object: Microwave radiation/ Backscatter coefficient
17
Q

Remote sensing process

A
  1. source of energy
  2. propagation through the atmosphere
  3. interaction with targets
  4. re-transmission through the atmosphere
  5. imaging platform
  6. image data
  7. interpretation and analysis
  8. information products
  9. users
18
Q

Why mapping? (importance)

A
  1. creates a model of the world.
  2. required to describe resources and
    environment.
  3. an indispensable instrument for planning
    sustainable development.
19
Q

What is an image?

A

Data that is organized in a grid of columns and rows that usually represents a geographical area

20
Q

How are images made?

A
  1. Passive remote sensing
    result of light from the sun reflecting off
    objects on the earth’s surface
  2. Active remote sensing
    result of backscattering of energy from objects on the earth’s surface
21
Q

Pixels (concept)

A

Each pixel stores a digital number
(DN) measured by the sensor.

Represents individual areas
scanned by the sensor.

The smaller the pixel or the
higher the spatial resolution of
the sensor, the easier it is to see
detail.

22
Q

Swath

A

It is a strip of the earth’s surface

Sensors collect 2D images of the surface in a swath below the sensor

23
Q

Light classification

A
  1. Gamma
  2. x-rays
  3. uv
  4. visible
  5. infrared
  6. microwave
  7. tv/radio

(wavelength increases downwards)

24
Q

Types of images

A
  1. Remotely sensed images
    Continuous data - quantitative, remote sensing
    Types:
    a. Panchromatic - 1 band/layer
    b. Multispectral - 2+ bands
  2. Thematic images
    Discrete data - qualitative, GIS
25
Q

Characteristics of Remote sensing Data

A
  1. Spatial resolution
    determines the smallest object or level of detail that can be perceived in an image
  2. Spectral resolution
    Defines the number and size of the bands a sensor is able to record
  3. Radiometric resolution
    sensitivity of a sensor to incoming radiance/ how much change in radiance there must be on the sensor before a change in recorded brightness value takes place
  4. Temporal resolution
    duration it takes a sensor to return to a previously imaged location
26
Q

What is GIS

A

Geographic Information System (GIS) is defined as a special type of information system that is used to input, store, retrieve, process, analyze and visualize geospatial data and information in
order to support decision making.

basically a computer-based information system
for handling spatially referenced data and information.

27
Q

Name the 2 types of geographic data that GIS handles

A
  1. Spatial data
    describe the location and shape of
    geographic features and their spatial relationships
  2. Attribute Data
    describe the characteristics of spatial data.
28
Q

Geometric data models in GIS

A
  1. Vector model
    uses discrete points, lines and/or areas corresponding to discrete objects with name or code number of attributes.
  2. Raster model
    employs regularly spaced grid cells set out in a specific sequence.
29
Q

Basic GIS functions

A
  1. Data input and processing
    Map digitizing, map/photo scanning, editing,
    topology building, format conversion etc.
  2. Database management
    Data archiving, data retrieval, data updating
    etc.
  3. Spatial analysis
    Query, measurements, reclassification,
    coverage rebuilding, overlay operations,
    connectivity analysis etc.
  4. Graphic output and visualization
    Map projection, graphic representation, map
    production, DEM generation, bird’s eye
    views etc.
30
Q

GIS data capture and editing

A
  1. data identification
  2. data collection and capture (spatial/non-spatial data)
  3. data processing and verification
  4. data ( correct?)
  5. GIS database
31
Q

What is spatial analysis

A

It is the means of adding value to geographic data that allows the conversion of data into useful information and knowledge.

It gives more insight into a place and helps in
focusing and prioritizing actions or decisions.

SURVEYING (4 decks)

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