[GRASS-user] r.sun - ambiguities about coefbh/coefdh

[Markus Neteler]

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 at 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 at 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 at lists.osgeo.org
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>>>
>>
>