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<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Hi Dylan,<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'>Probably you have cleared your doubt but I'll try to
expound how I see the question. The most important thing is you firstly have to
think if you are dealing with flux or energy.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'>The flux is something (let say, particles or light photons)
coming through a normal surface to the beam (for example, persons through a
door). Therefore the unit of flux has to be something like particles per
squared meter and per second (how many particles have reached the normal
surface in a second). In case of light (photons) we talk in terms of energy to count
the particles, so we have J/m2*s = W/m2 (because W = J/s). Then, when you
measure the solar radiation with a sensor, the measurement is usually in units
of flux [W/m2]. What does it mean? Let suppose in a given moment the sensor
reads 500 W/m2. That equals to 500 J/s/m2 = 500 J/m2/s, i.e. in a second you have
received 500 Joules per squared meter so, in 2 seconds, you will have 1000
joules in a squared meter. In 3 seconds you will have 1500 joules in a squared
meter and so on. Now we have sum (or integrated) the flux throw the time and
the magnitude can be seen as energy per unit of surface in a certain period of
time, let say hour, day, month,…<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><st1:place w:st="on"><font size=2 face="Courier New"><span
lang=EN-GB style='font-size:10.0pt'>Watts</span></font></st1:place><span
lang=EN-GB> per hour is a measurement of energy used in engineering not in
science. The only reason I think is because the magnitude of its value is more appropriate
than J or MJ. The equivalence is 1 Wh = (1 J/s)*3600 s = 3600 J = 0.0036 MJ<o:p></o:p></span></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'>I work with radiometric sensors and sometimes I have
used r.sun. The approach I follow is to express both in J/m2/dia. With r.sun
the output is in Wh/m2/dia so directly multiply by 0.0036 and you will have
MJ/m2/dia and will know how much energy you have in a squared meter when the
day finish. Now let suppose you are getting a measurement every 10 minutes,
i.e. every 600 seconds. In that lapse of time you will have S[W/m2]*600seconds,
where S is the measurement. In a day you will have Sday[J/m2/dia] = S1*600s +
S2*600s + S3*600s + … and so on for all measurements in the day.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'>________________________________<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'> <o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'>José A. Ruiz Arias<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'>Departamento de Física<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span lang=EN-GB
style='font-size:10.0pt'>Escu</span>ela Politécnica Superior<o:p></o:p></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Edificio A-3, Campus Lagunillas<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Universidad de Jaén<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>23071 Jaén Spain<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Tlf. +34 953212474<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Email: jararias@ujaen.es<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>_____________________________________<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> -----Mensaje original-----</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> De: grassuser-bounces@grass.itc.it
[mailto:grassuser-bounces@grass.itc.it]</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> En nombre de Dylan Beaudette</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> Enviado el: jueves, 30 de noviembre de 2006 22:55</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> Para: Glynn Clements</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> CC: grassuser@grass.itc.it; GRASS devel</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> Asunto: Re: [GRASS-user] Clarification on units used in r.sun</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> </span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> On Wednesday 29 November 2006 12:31, Glynn Clements wrote:</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > Dylan Beaudette wrote:</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > Quick question on the units used for the ouput of r.sun
in mode 2</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> (daily</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > sums):</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > ></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > In the manual pages for r.sun, the following 'unit' is
included in the</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > description:</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > ----------------------------</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > The solar radiation maps for given day are computed
integrating the</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > relevant irradiance between sunrise and sunset times for
given day.</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> The</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > user can set finer or coarser time step step used for
all-day</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> radiation</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > calculations. A default value of step is 0.5 hour.
Larger steps (e.g.</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > 1.0-2.0) can speed-up calculations but produce less
reliable results.</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> The</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > output units are in Wh per squared meter per given day
[Wh/(m*m)/day].</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > -------------------------</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > ></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > Is one to interpret this as "watt-hour per square
meter per day" ?</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > This would seem a little odd, as the the unit
'watt-hour' is not an SI</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > > unit.</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> ></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > More odd (to me) is having (different) units of time in both
the</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > numerator and denominator. I would have thought it more
logical to</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> > divide the result by 24 to give Watts per square metre
[W/(m^2)].</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> </span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> I need to check with some local experts, but judging from some
recent</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> tests -</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> the output from r.sun is comparible to that from a weather
station, with</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> *hourly* averaged data in W/(m^2) which i think is analogous to
the</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> Wh/(m^2)</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> units that r.sun uses.</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> </span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> --</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> Dylan Beaudette</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> Soils and Biogeochemistry Graduate Group</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> University of California at Davis</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> 530.754.7341</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> </span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> _______________________________________________</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> grassuser mailing list</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> grassuser@grass.itc.it</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> http://grass.itc.it/mailman/listinfo/grassuser</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> </span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> __________ Información de NOD32 1894 (20061130) __________</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> </span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> Este mensaje ha sido analizado con NOD32 antivirus system</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> http://www.nod32.com</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
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