[GRASS-user] Re: [GRASS-dev] Changes to r.sun made Feb 2006
[resolved]
Dylan Beaudette
dylan.beaudette at gmail.com
Wed Dec 13 15:37:11 EST 2006
On Wednesday 13 December 2006 03:04, José Antonio Ruiz Arias wrote:
> Hi Dylan,
>
> I agree with you, probably is a better choice the correlation of Erbs
> (equation [9] in Jacovides el al.).
Hi Jose, thanks for the quick reply. I have had nearly equal results with the
Erbs equation and (Jacovides et al., 2006) equation 2: (Reindl et al.,
1990).
> It seems that you are calculating the Linke turbidity for all the days. As
> you can read in the Cucumo paper, this parameter is used to estimate beam
> and diffuse solar radiation in a determinated location for clear days. What
> happens under overcast conditions (normal situation in winter) is that kt
> is smaller than in a clear day, so kd is greater and you are
> underestimating the beam component. For this reason, according to the
> expression [10] in Cucumo et al., the Linke turbidity is overestimated.
Yes. I am calculating Linke values for each day of the year. In an *attempt*
to get *only* clear days I have used the *maximum* global radiance observed
at the weather station over an 11 year period. Perhaps I need more years of
data to get the true clear sky radiance.
> That means that probably you should use some kind of filtering on your data
> to rule out the cloudy days. For example, basing on the daily clearness
> index, you could take only those days with daily kt greater then 0.6 more
> or less.
>
> Try this filtering. Probably you will improve the results
ok. i will look into this. I was hoping for daily values. But if I can get
*good* monthly or weekly values I will interpolate accordingly.
I'll post the results back later today.
Cheers,
Dylan
> Cheers,
>
> ________________________________
>
> José A. Ruiz Arias
> Departamento de Física
> Escuela Politécnica Superior
> Edificio A-3, Campus Lagunillas
> Universidad de Jaén
> 23071 Jaén Spain
> Tlf. +34 953212474
> Email: jararias at ujaen.es
> _____________________________________
>
> > -----Mensaje original-----
> > De: Dylan Beaudette [mailto:dylan.beaudette at gmail.com]
> > Enviado el: martes, 12 de diciembre de 2006 23:27
> > Para: grassuser at grass.itc.it
> > CC: José Antonio Ruiz Arias
> > Asunto: Re: [GRASS-user] Re: [GRASS-dev] Changes to r.sun made Feb 2006
> > [resolved]
> >
> > Hi Jose, some updates:
> >
> > 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.
> > >
> > > 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.
> > >
> > > 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.
> >
> > Ok. I found these papers and have read over them. I think that if I were
> > to
> > get this approach working* I will use equation 7 from Jacovides et al.
> >
> > 2006.... details below:
> > > where kt is the ratio of global to extraterrestrial 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.
> >
> > Ok. this is the expression I used (after calculating kt and kd):
> >
> > kt = global radiance at 12pm / extraterrestrial radiance
> > kd = (from eqation 2 or 9)
> >
> > unfortunately, when i compute a normal beam radiance from the kd values:
> >
> > B = G(1 - kd)
> > Bn = B/sin(alpha)
> >
> > and then compute linke turbidity values (using the equation from Cucumo
> > et al
> > 2000) : I end up with very high Linke values in the winter months:
> >
> > http://169.237.35.250/~dylan/temp/reindl_linke_bad-estimates.png
> >
> > This may be a result of not having a *single* clear day for my winter
> > months
> > (I am using the max radiance at 12pm, over the course of 11 years to get
> > as
> > close as possible to clear sky conditions).
> >
> > Note that linke turbidity values in the above figure track those that I
> > had
> > been estimating in the summer months: with the diffuse = 10-20% of beam
> > radiance assumption.
> >
> > Quite possibly I am doing something incorrectly :)
> >
> > Cheers,
> >
> > Dylan
> >
> > > 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.
> > >
> > > Cheers,
> > >
> > > Jose A.
> > >
> > > > -----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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> > > >
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> > --
> > Dylan Beaudette
> > Soils and Biogeochemistry Graduate Group
> > University of California at Davis
> > 530.754.7341
> >
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> >
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--
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341
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