[GRASS-user] From Landsat radiance (W/m2*sr*µm) to Global horizontal irradiance (W/m2) for mere mortals...

[Yann Chemin]

hey Andres

I did not know the definition of GHI:
http://www.3tier.com/en/support/solar-prospecting-tools/what-global-horizontal-irradiance-solar-prospecting/
The radiation reaching the earth's surface can be represented in a number
of different ways. Global Horizontal Irradiance (GHI)
<http://www.3tier.com/en/support/glossary/#ghi> is the total amount of
shortwave radiation received from above by a surface horizontal to the
ground. This value is of particular interest to photovoltaic installations
and includes both Direct Normal Irradiance (DNI)
<http://www.3tier.com/en/support/glossary/#dni> and Diffuse Horizontal
Irradiance (DIF) <http://www.3tier.com/en/support/glossary/#dif>.

irradiance=incoming solar radiation
Landsat radiance=reflected solar radiation
It looks from the definition of GHI that solar farming needs r.sun

to answer to your question,
- steradian (sr) is a "solid angle" of conic form, to which a circle
applies for a plan projected footprint.
- micro-meter (µm) is a spectrum value for the middle of the Landsat band
used.

Cheers,
Yann

On Wed, Jun 17, 2015 at 10:18 PM Andrés Oswaldo Calderón Romero <
aocalderon at udenar.edu.co> wrote:

>  Hello list,
>
> We are working in a solar energy project to locate potential sites for
> solar panel farms. We are using the Landsat 7 panchromatic band to derive
> radiance with i.landsat.toar (W/m2*sr*µm units). Now, we have access to
> some ground data from sensors measuring global horizontal irradiance (GHI)
> which output is in W/m2 units.  I would like to compare these datasets for
> validation, so, my question is rather simple: ¿Is there a way to convert
> radiance in W/m2*sr*µm to irradiance in W/m2?
>
> I have read in [1] that radiance = irradiance / π, but I don't completely
> understand, also, this doesn't take the spectral part (µm) into account.  I
> will very appreciate any further explanation about this... thank you very
> much in advance!!!
>
> [1] http://earth.esa.int/landtraining07/D1LB3-Su.pdf
>
> --
> Atentamente,
>
>
> *ANDRES OSWALDO CALDERON ROMERO*
> M.Sc. Geoinformation Sciences & Earth Observation
> Grupo de Investigación Aplicada en Sistemas - GRiAS
> Universidad de Nariño
> Pasto - Colombia
> T: (+57) 301 382 9659
>
> ------------------------------
> Correo Electrónico - Universidad de *Nariño*
> Pasto - Nariño - Colombia
> www.udenar.edu.co
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