Kippzonen BSRN Scientific Solar Monitoring System Manual do Utilizador descarregar pdf (Página 143)

131

Figure C 4.3a. Relationship between the shadow disc

and the sensor of a pyranometer.

Figure C 4.3b. Detail of the sensor projection

on to the normal plane parallel to the

shadow disc.

C 4.4 Sun at an arbitrary zenith angle

The relationship between a pyranometer sensor and the shading disc is illustrated in Figure C 4.3a.

The details on the geometrical situation on and near the sensor is presented in Figure C 4.3b. In this

case the irradiance F at r' on the projected surface must be integrated for the surface of the ellipse

which is projected on the plane normal to the direction of the sun. The solar zenith angle is designated

to be q, then the distance from the centre of the ellipse to its edge l will be expressed as:

Then the absolute amount of radiative flux for the entire surface will be,

The irradiance for the unit sensor surface on a horizontal surface will become

The resuts of the computation of irradiance for the standard pyrheliometer and various diffusometers

are presented in Table C 4.1. From this result it can be concluded that most diffusometers used in

the BSRN show less than 3 W m influence. The best proposal is presented in the second right hand

-2

column in the table.

1 2 ... 138 139 140 141 142 143 144 145 146 147 148 ... 187 188

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Kippzonen BSRN Scientific Solar Monitoring System Manual do Utilizador Página 143