Viewshed analysis and solar radiation

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Viewshed analysis and solar radiation

• Geospatial Analysis and Modeling
• Lecture notes
• Helena Mitasova, NCSU MEAS

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Outline

• line of sight, viewshed and cumulative viewshed
• components of solar radiation in complex terrain
• cast shadow and solar inclination angle
• cumulative solar radiation, solar energy
  potential

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Line of sight

• Line of sight analysis is used to identify points
  on the terrain surface along a given line that
  are visible or invisible from a given point on
  this line.
• It is used for visibility analysis but also for
  emitor-receptor systems design - for example,
  optimization of locations of cell towers
• Computational principle
• Given a viewing point A and a target B, we define
• tan ? ( zB-zA )/ dBA
• if for any point C between AB ?C gt ? then B is
  not visible from A
• or if C is above the line that connects AB, B is
  not visible from A

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Line of sight

• tan ? ( zB-zA )/ dBA
• if for any point C between AB ?C gt ? then B is
  not visible from A
• or if C is above the line that connects AB, B is
  not visible from A

A
C
B
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Line of sight

• tan ? ( zB-zA )/ dBA
• if for any point C between AB ?C lt ? then B is
  visible from A
• or if C is below the line that connects AB, B is
  visible from A

A
B
C
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Viewshed

• viewshed is region defined by a set of grid cells
  (or triangles) visible from a given viewing
  point it is computed by applying LOS analysis
  from the viewing point to each cell within a
  given distance
• Outputs
• binary visibility map (yes/no)
• angle above/below horizontal plane
• relative elevation above/under horizontal plane

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Viewshed

• can be implemented from TIN or raster DEMs
• for long distances - impact of earth curvature
  needs to be included (distance to true horizon
  can be approximated as dkm sqrt(13hm) )

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Viewshed

• visibility analysis for finding a location for a
  webcam to support real-time monitoring of a
  watershed
• height of webcanm location above the surface 1.75
  and 6m

90 deg - horizontal 0 deg - under viewers
feet 180 deg - above viewers head
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Viewshed analysis
From Royal Bank of Canada headquarters
From RedHat headquarters
webcam
- computed from bare ground lidar based elevation
model, 30m resolution - can be compared with the
results from SRTM, higher resolution DEM and
DSM - can be overlayed with Points of Interest
map
GRASS GIS
Open Source Geospatial
Foundation
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Cumulative Viewshed

• Cumulative viewshed set of grid cells visible
  from a set of points (e.g. along a road)
• applications ?

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Cumulative Viewshed

• Cumulative viewshed set of grid cells visible
  from a set of points (e.g. along a road)
• applications
• find a path that has minimum or maximum
  visibility
• optimize distribution of signal sources to
  achieve the maximum coverage
• limit development to areas that are not visible -
  e.g. from the Blue Ridge Parkway

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Solar radiation

• Solar radiation controls the surface energy and
  water balance and thus affects the atmospheric,
  biophysical and hydrologic processes. It also
  provides a source of renewable energy.
• Surface net radiation is spatially and temporally
  variable and depends on ?

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Solar radiation

• Solar radiation controls the surface energy and
  water balance and thus affects the atmospheric,
  biophysical and hydrologic processes. It also
  provides a source of renewable energy.
• Surface net radiation is spatially and temporally
  variable and depends on
• orientation of Earth relative to Sun (or position
  of sun relative to given point on earth)
• topography slope, aspect and shadowing
• clouds and other atmospheric properties
• surrounding surface properties

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Solar radiation components
terrain direct illumination self shadow cast
shadow

• DIR direct radiation from Sun,
• DIF diffuse radiation from sky
• REF reflected radiation

Figure after Bohner Antonic, Ch. 8
Geomorphometry
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Sun position

• First calculate the sun position for a given
  date, time, and a location on Earth (usually map
  center)
• 2001.12.22, day number 356, time 142500
• long -78.678856, lat 35.736160, timezone
  -5.000
• Solar position
• azimuth (measured from North or East)
  212.7934...
• solar altitude (sun angle above horizon,
  inclination) 23.1924
• sunrise time (without refraction cor.) 072630
• sunset time (without refraction cor.) 170028
• sun declination at this day?

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Sun position

• First calculate the sun position for a given
  date, time, and a location on Earth (usually map
  center)
• 2001.12.22, day number 356, time 142500
• long -78.678856, lat 35.736160, timezone
  -5.000
• Solar position
• azimuth (measured from North or East)
  212.7934...
• solar altitude (sun angle above horizon,
  inclination) 23.1924
• sunrise time (without refraction cor.) 072630
• sunset time (without refraction cor.) 170028
• sun declination (angle between solar beam and
  earth equator) winter solstices -23.4405 (sun
  above the Tropic of Capricorn)
• atm. refraction correction inclination gt 0
  before sunrise

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Solar incidence angle

• Calculate solar incidence angle for a given grid
  cell, it is angle between the
• terrain normal (vector orthogonal to the plane
  tangent to terrain surface at a given point its
  horizontal projection is gradient vector so it is
  defined by ? and if we have a solar panel? )

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Solar incidence angle

• Calculate solar incidence angle for a given grid
  cell, it is angle between the
• terrain normal (vector orthogonal to the plane
  tangent to terrain surface at the given point
  its horizontal projection is gradient vector so
  it is defined by slope and aspect)
• solar beam (defined by solar inclination and
  azimuth)
• equation see 8.1.8 in Hengl, 2008,
  Geomorphometry
• or A.62 in Neteler 2008 Appendix

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Solar incidence angle

• Solar incidence angle for winter solstice around
  2pm, including building with cast shadow

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Solar incidence angle dynamics

• solar incidence angle dynamics during summer
  and winter solstice for a small valley at 45 deg
  lat.

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Solar incidence angle dynamics

• solar incidence angle dynamics during summer
  and winter solstice for a small valley at 45 deg
  lat.

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Solar radiation

• Solar beam (direct) radiation for inclined plane
  (terrain or solar panel) in W/m2 is function
  of
• solar incidence angle,
• solar constant W/m2,
• atmospheric factors
• Linke turbidity factor (measure of atm. turbidity
  due to aerosols - reduces direct radiation)
• relative optical air mass
• Rayleigh optical thickness (thickness of clear
  atm., function of surface pressure)
• computed as cumulative solar radiation daily,
  monthly, seasonal, annual

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Cumulative solar radiation

• beam solar radiation W/m2, diffuse and reflected
  radiation

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Cumulative solar radiation direct

• Spatial pattern of direct total beam solar
  radiation W/m2 for different days 180 an 356

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Solar radiationduration

• Spatial pattern of solar radiation duration hr
• for different days 180 an 356

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Solar radiation modeling

Application of r.sun in urban areas with 3-D city
models (cost/revenue analysis for solar panels,
building design, thermal conditions,...)
kWh/m2
Jaro Hofierka University of Presov
GRASS GIS
Open Source Geospatial
Foundation
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Photovoltaic potential

Seasonal changes in photovoltaic potential in
urban area
Monthly values of electricity potentially
produced by each building using solar panels
impact of roof area, slope, aspect,material was
included Jaro Hofierka University of Presov
GRASS GIS
Open Source Geospatial
Foundation
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Cumulative irradiation

• modeled versus measured insolation

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Photovoltaic WebGIS

• http//sunbird.jrc.it/pvgis/

see maps for horizontal, optimum and 2 axis
pannel angle
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Solar and Wind energy see www

• http//www.nrel.gov/gis/solar.html
• see PVWATS2 calculator, turn on PVWATS and click
  on location of interest
• maps are based on measured data collected by
  fixed flat plate collector

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Summary and references

• Hengl and Reuter, 2008, Geomorphometry Concepts,
  Software, Applications, Ch. 8 Bohner and Antonic
  land surface parameters specific to
  topoclimatology
• Neteler 2008, Appendix Insolation

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Project simulated landuse

• r.mapcalc "cfac1if(elevationlt90
  slopelt3,0.20,0.0005)"
• r.mapcalc "cfac2if(elevationlt90
  slopelt3,0.20,0)if(elevationgt90 elevationlt120
  slopelt6,0.01,0.0005)"
• r.mapcalc "cfac4if(elevationlt90
  isnull(streams_buff),0.20,0)if(elevationgt90
  elevationlt120 slopelt6,0.01,0.0005)"