Meteorologisches Observatorium Lindenberg A COMPARISON OF SCAPP RADIATION DATA WITH GLOBAL, DIFFUSE AND DIRECT RADIATION AS WELL SUNSHINE DURATION Klaus

Meteorologisches Observatorium Lindenberg

A COMPARISON OF SCAPP RADIATION DATAWITH GLOBAL, DIFFUSE AND DIRECT RADIATION

AS WELL SUNSHINE DURATION

Klaus Behrens and Rolf-Dieter Grewe

German Weather ServiceMeteorological Observatory Lindenberg

TECO, Bucharest, 04.-07.05.2005 Scapp 01

[email protected]@dwd.de



Outline

• Introduction• The Scanning Pyrheliometer/Pyranometer

• Technical Description• Calibration

• Comparisons of SCAPP with pyrheliometer and pyranometer data• hourly means• daily totals

• Conclusions



• about 30 manned stations

Radiation Network of theGerman Weather Service

Global radiation Global and diffuse solar radiationAtmospheric downward radiation

• two ventilated and heated CM11 measuring global and diffuse solar radiation• sunshine duration is measured by a SONIe• rising requests from several users for a higher spatial resolution• to extend the radiation network at a stable number of manned is only possible with an instrument allowing an automatic (unmanned) operation



• Bergholter and Dehne (1992) showed the possibility to measure global, diffuse and direct solar radiation with one instrument the so called SCAnning Pyrheliometer/Pyranaometer (SCAPP)

• in future the radiation network of the German Weather Service will consist of about 30 manned stations using pyranometers (basic network) and an extending one of about 130 automatic (unmanned) stations applying the SCAPP



The SCAPP as it is used for measuring direct, diffuse and global solar radiation as well as sunshine duration.

Head and sensor module of the SCAPP consist of a spherical sector diaphragm (1), a diffuser (2), a beam-guide (3), two filter slides KG4 (4a), BG34 (4b) glass and a photodetector (5).

weight: 5 kg

height: 260 mm

diameter: 185 mm

data transmission via RS232 or RS422/485



Time

Sig

nal

Signal (a)

Signal (b)

Signal of the direct beam

Signal of the sky Signal of the sky

Schematic courses of the SCAPP signal during one rotation of the head describing different conditions (a) and (b).

• SCAPP needs more than one factor for the correct calculation of the different radiation quantities• a basic sensitivity of diffuse radiation• diffuse radiation inside the SCAPP depends on direct radiation• a correction factor for the diffuse radiation is necessary• a sensitivity of the direct radiation has to be determined

• SCAPP calibration has to be made outside using the Sun as source• direct and diffuse solar radiation have to be measured in parallel with the registration of the voltage of the SCAPP



Radiation platform at the Meteorological Observatory Lindenberg with the reference instruments from the BSRN station for the comparison with the SCAPP.

The SCAPP at the radiation platform during the comparison.

Reference instruments:• CH1 960129• CM22 020073• CM22 020074

• voltages were recorded by a COMBILOG data logger and then converted into irradiances• SCAPP data were converted by its own microprocessor• all data stored as 1 minute means



Global Radiation, March

y = 0.9516x - 1.4715

R2 = 0.9991

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700Gref (W/m²)

Gsc

a (

W/m

²)

GscaLinear (Gsca)

a) Diffuse Solar Radiation, March

y = 0.9398x - 0.8387

R2 = 0.9983

050

100

150200250300

350400

0 100 200 300 400

Dref (W/m²)

Dsc

a (

W/m

²)

DscaLinear (Dsca)

b)

Direct Solar Radiation, March

y = 0.9611x - 2.0443

R2 = 0.9908

0

200

400

600

800

1000

0 200 400 600 800 1000

Iref (W/m²)

Isca

(W

/m²)

IscaLinear (Isca)

c) Fig. a-c: Scatter diagrams of hourly means of global (G), diffuse (D) and direct solar radiation (I) measured by the SCAPP (sca) and pyranometers as well as a pyrheliometer as reference instruments (ref) and the corresponding regression lines in March, respectively. Furthermore, in the text boxes the regression coefficients and the coefficient of determination (R²) are given.



Global Radiation, July

y = 1.0288x - 4.0348

R2 = 0.9989

0

200

400

600

800

1000

0 200 400 600 800 1000Gref (W/m²)

Gsc

a (

W/m

²)

GSLinear (GS)

Diffuse Solar Radiation, July

y = 1.0091x - 0.3897

R2 = 0.9989

0

50

100

150

200

250

300

350

400

450

500

0 100 200 300 400 500Dref (W/m²)

Dsca

(W

/m²)

DSLinear (DS)

Direct Solar Radiation, July

y = 1.0272x - 2.4586

R2 = 0.9951

0

200

400

600

800

1000

0 200 400 600 800 1000Iref (W/m²)

Isca

(W

/m²)

ISLinear (IS)

Fig. a-c: Scatter diagrams of hourly means of global (G), diffuse (D) and direct solar radiation (I) measured by the SCAPP (sca) and pyranometers as well as a pyrheliometer as reference instruments (ref) and the corresponding regression lines in July, respectively. Furthermore, in the text boxes the regression coefficients and the coefficient of determination (R²) are given.



Global Radiation, December

y = 0.9706x - 1.0241

R2 = 0.9956

0

50

100

150

200

250

0 50 100 150 200 250Gref (W/m²)

Gsc

a (

W/m

²)

GscaLinear (Gsca)

a) Diffuse Solar Radiation, December

y = 0.9414x - 0.5673

R2 = 0.9967

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140Dref (W/m²)

Dsc

a (

W/m

²)

DscaLinear (Dsca)

b)

Direct Solar Radiation, December

y = 0.9664x - 1.7518

R2 = 0.9644

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700Iref (W/m²)

Isca

(W

/m²)

IscaLinear (Isca)

c) Fig. a-c: Scatter diagrams of hourly means of global (G), diffuse (D) and direct solar radiation (I) measured by the SCAPP (sca) and pyranometers as well as a pyrheliometer as reference instruments (ref) and the corresponding regression lines in December, respectively. Furthermore, in the text boxes the regression coefficients and the coefficient of determination (R²) are given.



Regression constants (m: slope coefficient; c: point of intersection with the y-axis) and thecoefficients of determination (R²) of the hourly means of the SCAPP and the correspondingreference instruments for global, diffuse and direct solar radiation

Month global diffus directm c R² m c R² m c R²

Jan 0.931 -0.812 0.997 0.920 -0.584 0.998 0.932 -2.189 0.960Feb 0.945 -1.043 0.999 0.933 -0.679 0.999 0.956 -1.629 0.983Mar 0.952 -1.472 0.999 0.940 -0.839 0.998 0.961 -2.044 0.991Apr 0.974 -2.658 0.998 0.951 -0.700 0.998 0.989 -4.542 0.992May 0.995 -2.388 0.998 0.984 -1.347 0.999 1.028 -0.382 0.977Jun 1.011 -2.364 0.999 1.012 -1.807 0.999 1.032 -2.108 0.994Jul 1.029 -4.035 0.999 1.009 -0.390 0.999 1.027 -2.459 0.995Aug 1.021 -3.344 0.999 1.002 -0.548 0.999 1.026 -3.923 0.996Sep 1.013 -2.450 0.999 0.995 -0.331 0.998 1.006 -5.241 0.992Oct 0.989 -1.355 0.999 0.979 -0.615 0.999 0.986 -2.929 0.982Nov 0.976 -1.002 0.998 0.979 -0.735 0.998 0.985 -1.051 0.970Dec 0.971 -1.024 0.996 0.941 -0.567 0.997 0.966 -1.752 0.964



0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800 1000Gref (W/m²)

Gsc

a/G

ref

Gsca/Gref (Jul)Gsca/Gref (Dec)

Hourly ratios Gsca/Gref in dependence on Gref for July and December.



0.6

0.7

0.8

0.9

1.0

1.1

Gsc

a/G

ref;

Dsc

a/D

ref

Gsca/GrefDsc/Dref

new calibration constants

J F M A M J J A S O N D

Annual courses for the daily ratios Gsca/Gref and Dsca/Dref.



Conclusions:

• The comparison showed that the measurements of the SCAPP in most cases are in good agreement with the results of the reference instruments.

• At lower global radiation (about <75 W/m²) the SCAPP results are frequently to low in comparison with the reference. In future this will be improved.

• The SCAPP is a multisensor of „Moderate quality“, which is suitable for radiation measurements where highest quality is not demanded.

Thank you for your attention!

Documents

Meteorologisches Observatorium Lindenberg A COMPARISON OF SCAPP RADIATION DATA WITH GLOBAL, DIFFUSE AND DIRECT RADIATION AS WELL SUNSHINE DURATION Klaus