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

GRASS GRASS user
1

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/m2srµm 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/m2srµm 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

2

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) 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) and Diffuse Horizontal Irradiance (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@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/m2srµm 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/m2srµm 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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