[GRASS-user] Re: [GRASS-dev] Changes to r.sun made Feb 2006
[resolved]
Dylan Beaudette
dylan.beaudette at gmail.com
Tue Dec 12 13:58:32 EST 2006
Hi Jose,
Thank you for the great references, replies below:
On Tuesday 12 December 2006 03:59, José Antonio Ruiz Arias wrote:
> Hi all,
>
> as I promised you (Dylan), here you have a useful reference to derive the
> direct beam component from the global radiation.
just printed the paper....
> Jacovides, C.P., Tymvios, F.S., Assimakopoulos, V.A, and Kaltsounides N.A.
> (2006): ' Comparative study of various correlations in estimating hourly
> diffuse fraction of global solar radiation' Renewable Energy, 31, 2492-2504
>
> This paper offers a comparative analysis of different correlations between
> diffuse and global radiation. The references [2], [3], [4] and [9] on it, I
> think are especially interesting. I mention only this paper because on it
> you can find a summary of the most important correlations.
I wil look into these references as well.
> Reference [3] is especially simple and easy to read although it only uses
> measurements of Toronto. Also very interesting for you, perhaps, is the
> reference [4] since it is based on five USA locations. For example, this
> author proposes the correlation
>
> kd = 1.45-1.67kt for 0.3<kt<0.78
> kd = 1.02-0.248kt for kt<=0.3
> kd = 0.147 for kt>=0.78.
This looks *similar* to the method proposed by
Cucumo, M.; Kaliakatsos, D. & Marinelli, V. A calculation method for the
estimation of the Linke turbidity factor Renewable Energy, 2000, 19, 249-258
... the various coeficients are different, suggesting the local emperical
nature of these relationships...
> where kt is the ratio of global to extraterrestri
> al hourly radiation and kd
> is the ratio of diffuse to global hourly radiation. Therefore, to calculate
> kt only need the measured global radiation and the extraterrestrial
> radiation, theoretically calculated for a given location and time (see for
> example, Iqbal, Muhammad (1983). An Introduction to Solar Radiation.
> Academic Press, New York). Then you get kd from the correlation, and
>
> Direct Beam = Global*(1-kd).
>
> So, if you dispose of global measurements, you can get the direct beam
> radiation directly applying the former expression.
... need to read up on this...
> By the way, I would like to know what you are trying to do, improving
> r.sun? or just working in a personal project? I have used r.sun a little
> bit and I would like to collaborate with r.sun. I could work with the model
> and/or even developing some snippets of code.
This thread started with my wanted a better set of estimated linke turbidity
factors for my study area- to best parameterize r.sun. Since then, it has
become apparent that others might be interested in a small document for
r.sun: i.e. establishing local linke turbidity values based on pyranometer
data for use in r.sun.
> Cheers,
>
> Jose A.
Thanks Jose.
Cheers,
Dylan
> > -----Mensaje original-----
> > De: grassuser-bounces at grass.itc.it
> > [mailto:grassuser-bounces at grass.itc.it] En nombre de jararias at ujaen.es
> > Enviado el: viernes, 08 de diciembre de 2006 13:09
> > Para: grassuser at grass.itc.it
> > Asunto: Re: [GRASS-user] Re: [GRASS-dev] Changes to r.sun made Feb 2006
> > [resolved]
> >
> > Hi all,
> >
> > firstly, I really hope not to interfere in this conversation. I assist
> > expectant to the thread cause is very interesting for me.
> >
> > It seems you want to get diffuse component from global radiation. If I
> > have understood well, you estimate it as the 10%-20% of the global one.
> > Just a little suggestion that I hope not to be very simplistic. Have you
> > think about a correlation between the clearness-index and the proportion
> > of diffuse? There exist several correlations around the world such as the
> > studies of Orgill, Reindl, Erbs, Holland or Duffie, for example. They
> > usually use hourly values. You can easily obtain a estimation for the
> > hourly diffuse component (and, therefore, for the hourly direct beam one)
> > from the hourly global irradiation measured with a pyranometer as the
> > LICOR. If you are interesting in this approach just let me know and I
> > will be delighted of sending you more references. Now I can't be more
> > explicit because I don't have access to my personal data-base cause I am
> > not at the office.
> >
> > Kind regards,
> >
> > José A.
> >
> > > On 12/7/06, Hamish <hamish_nospam at yahoo.com> wrote:
> > >> Dylan Beaudette wrote:
> > >> > > > > Get local Linke values from the SoDa Solar radiation Databases
> > >> > > > > http://www.soda-is.com/
> > >> > > >
> > >> > > > Tried this, and got unrealistic values for my site.
> > >> > >
> > >> > > how so? Have you calculated good Linke values from your light
> > >> > > meters? (formula for that, please?)
> > >>
> > >> ..
> > >>
> > >> > Attached is a plot of estimated Linke turbidity values, compared to
> > >> > the SoDa derived data. Details on this calculation soon to follow
> > >> > in a new thread.
> > >
> > > Hi Hamish,
> > >
> > > Looks like I sent an update this morning with an attachment that was
> > > too large!
> > >
> > > I'll Include it at the bottom of my replies to you last message.
> > >
> > >> I assume the physical basis for the Linke turbidity factor is the
> >
> > amount
> >
> > >> of scattering dust, ash, water vapour, turbulence etc. in either the
> > >> column of air directly above the sampling site or in the ray between
> >
> > the
> >
> > >> site and the Sun (which will pass through more atm in winter due to
> > >> the lower angle). Maybe the paper sheds some light on that. So e.g. LA
> > >> county would have very high turbidity numbers.
> > >>
> > >> I would figure in the winter the air to be crisper/clearer due to less
> > >> water vapour, less turbulence, and less upwelling of aerosol laiden
> >
> > warm
> >
> > >> air from the Earth's surface. So lower turbidity numbers in the winter
> > >> as the SoDa data shows. BUT if you live in a place which is prone to
> > >> inversion layers in winter and many locals heat their homes with wood
> >
> > or
> >
> > >> coal, winter air quality may turn out to be much more turbid.
> > >
> > > Actually have a couple good papers on the defintion for the Linke
> > > turbidity values:
> > >
> > > Louche, A.; Peri, G. & Iqbal, M. An analysis of linke turbidity factor
> > > Solar Energy, 1986, 37, 393-396
> > >
> > > Rapti, A. S. Atmospheric transparency, atmospheric turbidity and
> > > climatic parameters Solar Energy, 2000, 69, 99-111
> > >
> > > Kasten, F. The linke turbidity factor based on improved values of the
> > > integral Rayleigh optical thickness Solar Energy, 1996, 56, 239-244
> > >
> > > My site is in a mediterranean, semi-coastal / semi-arid setting where
> > > winter time moisture and summer time dryness are the usual weather
> > > patterns. Summer through fall are usually cloud free, and quite warm.
> > > Also- this site is rather remote, so urban ag-related dust influences
> > > are minimal. These are some of the reasons that I was having second
> > > thoughts about the SoDa values.
> > >
> > >> > I have calculated Linke turbidity for my site with the equation
> > >>
> > >> T_linke = ln( G / ( I_0 * sin(h) * 0.84) ) * ( sin(h) / -0.027 )
> > >>
> > >> > Unfortunately, there are some aspects to this equation which
> > >> > I do not understand: namely the two constants present.
> > >>
> > >> perhaps they are empirically derived?
> > >
> > > Ok- big change in direction. I posted an update to the use of the
> > > above equation earlier today but it was rejected due to a large
> > > attachment. Details below....
> > >
> > >> I take it I_0 is pure-clear air intentensity?; h is latitude?; and is
> > >> G measured intensity, or ..?
> > >
> > > G = global radiance measured on the ground (beam+diffuse)
> > > I_o = extraterrestrial radiance
> > > h = solar elevation (angle)
> > >
> > >> > 1. Becker, S. Caclulation of Direct Solar And Diffuse Radiation in
> > >> > Israel International Journal of Climatology, 2001, 21, 1561 - 1576
> > >>
> > >> I will have to track down a copy of that. Holy cow, for once our
> >
> > library
> >
> > >> is actually subscribed to the e-journal. Downloading the PDF now..
> > >
> > > ... i know how that can be sometimes!
> > >
> > >> What software did you use to make that plot? Looks nice.
> > >
> > > Thanks. It was made in R, a fun command-line based environment for
> > > plotting, analysis, etc. I can post the code used after a small
> > > cleanup.
> > >
> > > Ok, here is the text from the message rejected this morning:
> > >
> > >
> > > Some updates on my findings with respect to obtaining optimal Linke
> > > turbidity values via local pyranometer measurements.
> > >
> > > Chatting with a local atmospheric scientist, I learned that it is
> > > possible (with a loss of some precision of course) to dissaggregate
> > > beam radiance from global radiance (as measured by pyranometer), for
> > > use in an equation [1] for the linke turbidity factor. Compared to a
> > > previous paper I mentioned on grass-dev [2], the equation presented in
> > > [1] is a much more appropriate approach to calculating Linke turbidity
> > > values.
> > >
> > > The key points to using the equation from [1] are:
> > >
> > > - historical pyranometer data from a weather station, with coordinates!
> > > - r.sun mode 1 to calculate solar elevation at this station, for each
> > > day at some time. extraterrestrial radiance is also calculated in this
> > > step
> > > - dissagregation of the beam component from global radiance with the
> > > assumption that diffuse radiance is approx 10%-20% that of the beam
> > > radiance
> > > - conversion of dissaggregated beam radiance to beam radiance on the
> > > normal (B/sin alpha)
> > >
> > > here is a link to a bit of my thesis on this topic: (rather
> > > incomplete!) http://169.237.35.250/~dylan/temp/linke-cucumo2000.png
> > >
> > > Here is a link of linke turbidity values, as calculated by the method
> > > described above, along with a comparison to the SoDa-derived values.
> > > There is considerable difference between the two sources!
> > >
> > > http://169.237.35.250/~dylan/temp/cucumo-
> >
> > estimated_daily_linke_values.png
> >
> > > With the equation from [1] it is possible to estimate the linke
> > > turbidity value for each day (using the 12pm calculation as
> > > representative for an entire day), and use these estimates in r.sun
> > > mode 2. here is a summary of the incorporation of estimated linke
> > > values into r.sun - as compared to the weather station data:
> > >
> > > http://169.237.35.250/~dylan/temp/11-yr_variation_vs_modeled.png
> > >
> > >
> > > I'll post some updates as they come. If I have anything wrong please
> > > don't hesitate to point it out!
> > >
> > > Cheers,
> > >
> > > Dylan
> > >
> > >
> > > 1. Cucumo, M.; Kaliakatsos, D. & Marinelli, V. A calculation method
> > > for the estimation of the Linke turbidity factor Renewable Energy,
> > > 2000, 19, 249-258
> > >
> > > 2. Becker, S. Caclulation of Direct Solar And Diffuse Radiation in
> > > Israel International Journal of Climatology, 2001, 21, 1561 - 1576
> > >
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--
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341
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