Kippzonen BSRN Scientific Solar Monitoring System Uživatelský manuál stáhnout pdf (Strana 134)

122

Figure C 2.5. Dependence of the HUNI/HUNIII on direct radiation.

C 2.4 Reduction of measurements to standard geometry

The empirical formulae in section C 2.4.2 are valid for HunIII. Since

Hu nIII

RATIO = HunI/HunIII ~ Standard/HunIII,

therefore the reduction of measurements of HunIII to standard geometry can be made by using any

of the two formulae. The correction of other diffusometers are connected to that of HunIII in Table C

2.3 by the normalized deficit.

The normalized deficit of other diffusometers can be estimated by the following equation:

NORM

DEFICIT = a*SLOPE + b*LIMIT + c

where a = 0.425

b = 0.496

c = - 2.270

These empirical constants derived from the data of the 10 instruments found in Tables C 2.1 and C

2.3. The correlation is 0.991. This way any diffusometer can be “placed “ into the last column of Table

C 2.3 if its slope and limit angles have been calculated for “vertical position”. Since

1 + DEFICIT = Standard/Diffuse

where “Diffuse” = the output of the diffusometer so that the “Standard” value can be derived.

C 2.5 Results

(1) The following equipments have almost identical geometry: the two Australian diffusometers, the

German BSRN station diffusometer and the SciTec-Kipp diffusometer, this way they could be regarded

as a geometrically standard group of diffusometers.

(2) The relation of the HunIII diffusometer to the standard (in practice to the SciTec-Kipp) is described

by two empirical equations derived from 18 months measurements made in Budapest.

(3) The relation of any diffusometer to HunIII is described by an other empirical equation (based on

calculated circumsolar irradiances) that requires the radius of the shader, the radius of the sensor

and the distance between them.

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Kippzonen BSRN Scientific Solar Monitoring System Uživatelský manuál Strana 134