Remote Sensing and GIS Flashcards
Define GIS
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
Components of GIS
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
Functions of GIS
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
What is entity-object correspondence
Each entity is represented by spatial features in the GIS
What is Raster and Vector data
Vector-representation of discrete objects using points lines and polygons
Raster- representation of continuously varying objects using grid cells
Raster vs Vector
In terms of:
-Data Structure
-Storage
-Spatial precision
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
Benefits of using GIS in water resource management
-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
DEM
Digital Elevation Model- a digital representation of an elevation surface
Consist of an array representing elevation at regularly spaced intervals (cells)
LULC
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
Spatial datasets for WRM
-DEM
-Land Cover
-Soil Datasets
Soil Datasets
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
Contour Elevation vs Digital Elevation
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)
How are DEMs created
-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
What is a viewshed
Viewshed for a point is the collection of areas visible from that point
Views from any non-flat locations are blocked by terrain
Define Slope and its significance in WRM
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
Define aspect
Defines the cardinal direction (0-360 degrees) a surface is facing
Useful for soil moisture and evapotranspiration calcs
Define Flood direction
-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
Define Catchment Area
Primary attribute representing the drainage area of any given cell
Indicates overland flow paths
Define Watershed
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
Advantages of Satellite observations
- 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
Define remote sensing
obtaining information about the earth, without physical contact, but by measurement of electromagnetic radiation (visible light, infrared, UV, microwaves, or thermal energy)
Passive vs Active Remote sensing
Passive measures radiation coming from a natural source
Active measures radiation coming from an artificial source
3 types of resolution for remote sensing
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
How does remote sensing monitor water quality
-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)
