Hy
I´m using GRASS GIS for the first time and I´m going to use the r.sun model
for a project.
When I was reading the explanation of the model, some questions appeared.
One is left.
I don´t understand the input parameter/raster coefbh/coefdh.
Both of them can be values between 0-1 and they are described by atmospheric
factors such as cloudiness. This is what is written in the explanation. But
how do I determine coefbh/coefdh? What other factors are influencing them?
How are the parameters combined, so that a value between 0-1 is given? Is it
possible to determine them in a not too complicated way?
I already read one post on coefbh/coefdh. Unfortunately, I didn´t understand
it.
I´m looking forward to get some answers.
Thanks
--
View this message in context: http://osgeo-org.1803224.n2.nabble.com/r-sun-ambiguities-about-coefbh-coefdh-tp6090593p6090593.html
Sent from the Grass - Users mailing list archive at Nabble.com.
Thanks Jaro,
I have added your citation in the manual including a text reference:
http://trac.osgeo.org/grass/changeset/45620
(while I was at it, I have also turned the table into a real HTML table).
best
Markus
On Thu, Mar 10, 2011 at 1:54 PM, Jaro Hofierka <jhofierka@gmail.com> wrote:
Hi Markus,
The r.sun model is described in this paper:
Šúri, M., Hofierka, J. (2004): A New GIS-based Solar Radiation Model and Its
Application to Photovoltaic Assessments. Transactions in GIS 8, pp. 175-190.
...
The coefficients coefbh, coefdh are defined in the section 3.2 Computing
radiation under overcast conditions - eqs. (41), (42).
These are beam and diffuse components of the clear sky index.
That means the r.sun module can compute a clear-sky radiation right away,
however if you want a real-sky radiation (with the effects of cloudiness)
then you need some kind of coefficient saying how much the clear-sky
radiation is attenuated by the cloudiness.
Therefore you have to use raster maps with spatial distribution of these
coefficients separatelly for beam and diffuse radiation.
I hope this helps.
Best wishes,
Jaro
Markus Neteler wrote:
Hi Jaro,
on the GRASS list the email below appeared which I cannot really
answer. Do you have any hints for us? If ok, I would relay your answer
to the list then.
From the manual:
coefbh=string
Name of real-sky beam radiation coefficient input raster map [-]
coefdh=string
Name of real-sky diffuse radiation coefficient input raster map [-]
"Besides clear-sky radiations, the user can compute a real-sky radiation
(beam, diffuse) using coefbh and coefdh input raster maps defining the
fraction of the respective clear-sky radiations reduced by atmospheric
factors (e.g. cloudiness). The value is between 0-1. Usually these
coefficients can be obtained from a long-terms meteorological
measurements."
Thanks
Markus
On Sat, Mar 5, 2011 at 1:30 AM, TimNorwey<timmy_weyrer@live.at> wrote:
Hy
I´m using GRASS GIS for the first time and I´m going to use the r.sun
model
for a project.
When I was reading the explanation of the model, some questions appeared.
One is left.
I don´t understand the input parameter/raster coefbh/coefdh.
Both of them can be values between 0-1 and they are described by
atmospheric
factors such as cloudiness. This is what is written in the explanation.
But
how do I determine coefbh/coefdh? What other factors are influencing
them?
How are the parameters combined, so that a value between 0-1 is given? Is
it
possible to determine them in a not too complicated way?
I already read one post on coefbh/coefdh. Unfortunately, I didn´t
understand
it.
I´m looking forward to get some answers.
Thanks
--
View this message in context:
http://osgeo-org.1803224.n2.nabble.com/r-sun-ambiguities-about-coefbh-coefdh-tp6090593p6090593.html
Sent from the Grass - Users mailing list archive at Nabble.com.
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user