rsaga.solar.radiation {RSAGA}R Documentation

Potential incoming solar radiation

Description

This function calculates the potential incoming solar radiation in an area either using a lumped atmospheric transmittance model or estimating it based on water and dust content.

Usage

rsaga.solar.radiation(in.dem, out.grid, out.duration, latitude, 
    unit = c("kWh/m2", "J/m2"), solconst = 1367, 
    method = c("lumped", "components"), transmittance = 70, 
    pressure = 1013, water.content = 1.68, dust = 100, 
    time.range = c(0, 24), time.step = 1, days = list(day = 21, month = 3), 
    day.step = 5, ...)

Arguments

in.dem name of input digital elevation model (DEM) grid in SAGA grid format (default extension: .sgrd)
out.grid output grid file for potential incoming solar radiation sums
out.duration Optional output grid file for duration of insolation
latitude Geographical latitude in degree North (negative values indicate southern hemisphere)
unit unit of the out.grid output: "kWh/m2" (default) or "J/m2"
solconst solar constant, defaults to 1367 W/m2
method specifies how the atmospheric components should be accounted for: either based on a lumped atmospheric transmittance as specified by argument transmittance ("lumped", or numeric code 0; default); or by calculating the components corresponding to water and dust ("components", code 1)
transmittance transmittance of the atmosphere in percent; usually between 60 (humid areas) and 80 percent (deserts)
pressure atmospheric pressure in mbar
water.content water content of a vertical slice of the atmosphere in cm: between 1.5 and 1.7cm, average 1.68cm (default)
dust dust factor in ppm; defaults to 100ppm
time.range numeric vector of length 2: time span (hours of the day) for numerical integration
time.step time step in hours for numerical integration
days a list with components day and month specifying a single day of the year for radiation modeling
day.step if days indicates a range of days, this specifies the time step (number of days) for calculating the incoming solar radiation
... optional arguments to be passed to rsaga.geoprocessor, including the env RSAGA geoprocessing environment

Note

SAGA uses zero-based days and months, but this R function uses the standard one-based days and months (e.g. day 1 is the first day of the month, month 1 is January) and translates to the SAGA system.

In SAGA 2.0.2, solar radiation sums calculated for a range of days, say days=c(a,b) actually calculate radiation only for days a,...,b-1 (in steps of day.step - I used day.step=1 in this example). The setting a=b however gives the same result as b=a+1, and indeed b=a+2 gives twice the radiation sums and potential sunshine duration that a=b and b=a+1 both give.

The solar radiation module of SAGA 2.0.1 had a bug that made it impossible to pass a range of days of the year or a range of hours of the day (time.range) to SAGA. These options work in SAGA 2.0.1.

This function uses module 2 from SAGA library ta_lighting.

Author(s)

Alexander Brenning (R interface), Olaf Conrad (SAGA module)

References

Wilson, J.P., Gallant, J.C. (eds.), 2000: Terrain analysis - principles and applications. New York, John Wiley & Sons.

See Also

rsaga.hillshade, rsaga.insolation

Examples

## Not run: 
# potential solar radiation on Nov 7 in Southern Ontario...
rsaga.solar.radiation("dem","solrad","soldur",latitude=43,
    days=list(day=7,month=11),time.step=0.5)
# ...in fact a cold, cloudy, windy day...
## End(Not run)

[Package RSAGA version 0.9-1 Index]