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cvc109 water > Remote Sensing and GIS > Flashcards

Remote Sensing and GIS Flashcards

1
Q

Define GIS

A

Geographic- relating to a specific location, georeferenced data based on a coordinate system

Information- Data to which some value or attribute has been added

Systems-Computer hardware and software that allows synthesis and processing of the data

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2
Q

Components of GIS

A

Hardware- computer platform, input & output devices, storage media

Software- many different comprehensive packages, ArcGIS, QGIS

Data- collected through remote sensing, aerial photography, national mapping programmes

Humans

Set of Protocols

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3
Q

Functions of GIS

A

Input- encoding spatial and attribute data into GIS database format

Manipulate- edit errors and update. Databases matched spatially by georeferencing

Manage- kept and organised. data structures

Query and Analyse- enquire by place or attribute, relationships and modelling

Visualise/Present- present in easily understandable forms

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4
Q

What is entity-object correspondence

A

Each entity is represented by spatial features in the GIS

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5
Q

What is Raster and Vector data

A

Vector-representation of discrete objects using points lines and polygons

Raster- representation of continuously varying objects using grid cells

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6
Q

Raster vs Vector

In terms of:
-Data Structure
-Storage
-Spatial precision

A

Data Structure: Raster usually simpler

Storage: More storage tends to be required for raster data without compression

Spatial Precision: For raster data the floor is set by the cell size. Whereas for vector limited only by positional measurements

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7
Q

Benefits of using GIS in water resource management

A

-Provides a receptacle for scattered data from various sources

-Improves the visualisation, management and analysis of data

-Supports statistical and numerical modelling, contouring and impact analyses to enhance understanding of interactions between water and land processes

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8
Q

DEM

A

Digital Elevation Model- a digital representation of an elevation surface

Consist of an array representing elevation at regularly spaced intervals (cells)

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9
Q

LULC

A

Land Use and Land Cover- the surface cover of a watershed

Important to characterise hydrologic processes at the watershed scale- permeable, impervious etc.

Collected through direct observation and remote sensing

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10
Q

Spatial datasets for WRM

A

-DEM
-Land Cover
-Soil Datasets

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11
Q

Soil Datasets

A

The soil types of the watershed

How water is partitioned among various compartments
-Estimating infiltration and groundwater recharge, ground surface evaporation and transpiration and flooding characteristics

Sources:
-Soil surveys
-Remote sensing data

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12
Q

Contour Elevation vs Digital Elevation

A

Contour elevation: contour shows a line of constant elevation. Generally used as a cartographic representation

DEM: consists of an array representing elevation values at regularly spaced intervals (cells)

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13
Q

How are DEMs created

A

-Each cell usually stores the average elevation of the grid cell

-Typically they store the value at the centre of the grid cell

-Elevations are presented graphically in shades or colours

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14
Q

What is a viewshed

A

Viewshed for a point is the collection of areas visible from that point

Views from any non-flat locations are blocked by terrain

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15
Q

Define Slope and its significance in WRM

A

Describes overland and subsurface flow velocity and runoff rate

Quantifies the maximum rate of change in value from each cell to its neighbours

Used for runoff rate, precipitation, vegetation, soil water content

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16
Q

Define aspect

A

Defines the cardinal direction (0-360 degrees) a surface is facing

Useful for soil moisture and evapotranspiration calcs

17
Q

Define Flood direction

A

-Excess water at a point will flow in a given direction
-Flow may be on or below the earths surface but always in the direction of the steepest descent
-Directions stored as a compass angle in raster data layer

18
Q

Define Catchment Area

A

Primary attribute representing the drainage area of any given cell
Indicates overland flow paths

19
Q

Define Watershed

A

An area that contributes flow to a point on the landscape

Water falling anywhere in the upstream area of a watershed will pass through that point

20
Q

Advantages of Satellite observations

A
  • Available for large regions- only source of global information for some parameters
  • Long time series and data continuity- tracks progress, and establish trends for some phenomena
  • Consistency and comparability- among multiple countries
  • Diversity of measurements
  • Complements traditional statistical methods
  • Mostly free and open access
21
Q

Define remote sensing

A

obtaining information about the earth, without physical contact, but by measurement of electromagnetic radiation (visible light, infrared, UV, microwaves, or thermal energy)

22
Q

Passive vs Active Remote sensing

A

Passive measures radiation coming from a natural source

Active measures radiation coming from an artificial source

23
Q

3 types of resolution for remote sensing

A

Spatial resolution- decided by its pixel size

Temporal resolution- how frequently a satellite observes the same area of the Earth

Spectral Resolution- ability of a sensor to define fine wavelength intervals. Finer spectral channels enable remote sensing of different parts of the atmosphere

24
Q

How does remote sensing monitor water quality

A

-Measures water colour

-Dissolved and suspended matter in water change the waters optical properties which changes its colour

Ratio of scattered radiation over total radiation (scattered and absorbed)

25
Q

Factors effecting water quality

A
  • Nutrient loading- eutrophication
  • Pollution
  • Water Temperature
  • Food web changes
  • Introduced species
  • Changes in water flow- following hurricanes, droughts and floods
26
Q

Water quality indicators observed from remote sensing

(x8)

A
  • Turbidity and Sediments
  • Coloured Dissolved Organic Matter
  • Sea Surface Temperature
  • Chlorophyll
  • Salinity
  • Total suspended Solids
  • Fluorescence Line Height
  • Euphotic Depth
27
Q

How is water quality qualitatively assessed using RS

A

Simple image interpretation

28
Q

How is water quality quantitively assessed using RS

A

-Satellite sensors measure top of atmosphere (TOA) radiances

-The TOA radiances result from a combination of what is coming from the surface and the atmosphere

29
Q

What does water leaving reflectance depend on

A

-Backscattering and absorption of radiation due to water, sediments, phytoplankton and coloured dissolved organic matter (CDOM)

30
Q

Atmospheric correction for water quality monitoring

A
  • There are a range of correction techniques:
    o NASA Ocean Biology Processing Group Algorithm
    o 6S: Second Simulation of the Satellite Signal in the Solar Spectrum
    o HydroLight
  • Requires radiative transfer modelling along with atmospheric conditions, clouds and aerosol information
31
Q

What is Google Earth Engine

A
  • Remote sensing archive with petabytes (50) of data in one location
  • A cloud-based geospatial processing platform for executing large scale data analysis
  • Public data catalogue- vast amounts of publicly available data
  • Processing power- computation engine
32
Q

Benefits and limitations of google earth engine

A
  • Benefits:
    o Good for projects that requires data coverage for a large region
    o Extensive data library
    o High speed, intensive processing capacity
    o Advanced raster processing tools
  • Limitation
    o Better suited to image analyses than vector-based analyses
    o Analysis based on pixel. Spatial relations are harder to complete, because of the processing on multiple CPUs Image segmentation and hydrologic modelling options are limited or in testing phases

cvc109 water (13 decks)

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