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A COMPARISON OF SCAPP RADIATION DATA WITH GLOBAL, DIFFUSE AND DIRECT RADIATION

A COMPARISON OF SCAPP RADIATION DATA WITH GLOBAL, DIFFUSE AND DIRECT RADIATION AS WELL SUNSHINE DURATION. Klaus Behrens and Rolf-Dieter Grewe German Weather Service Meteorological Observatory Lindenberg. klaus.behrens@dwd.de rolf-dieter.grewe@dwd.de. TECO, Bucharest, 04.-07.05.2005.

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A COMPARISON OF SCAPP RADIATION DATA WITH GLOBAL, DIFFUSE AND DIRECT RADIATION

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  1. A COMPARISON OF SCAPP RADIATION DATA WITH GLOBAL, DIFFUSE AND DIRECT RADIATION AS WELL SUNSHINE DURATION Klaus Behrens and Rolf-Dieter Grewe German Weather Service Meteorological Observatory Lindenberg klaus.behrens@dwd.de rolf-dieter.grewe@dwd.de TECO, Bucharest, 04.-07.05.2005 Scapp 01

  2. Outline • Introduction • The Scanning Pyrheliometer/Pyranometer • Technical Description • Calibration • Comparisons of SCAPP with pyrheliometer and pyranometer data • hourly means • daily totals • Conclusions TECO, Bucharest, 04.-07.05.2005 Scapp 02

  3. about 30 manned stations • 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 lGlobal radiation ¤ Global and diffuse solar radiation uAtmospheric downward radiation Radiation Network of the German Weather Service TECO, Bucharest, 04.-07.05.2005 Scapp 03

  4. 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 TECO, Bucharest, 04.-07.05.2005 Scapp 04

  5. 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 The SCAPP as it is used for measuring direct, diffuse and global solar radiation as well as sunshine duration. TECO, Bucharest, 04.-07.05.2005 Scapp 05

  6. 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 Schematic courses of the SCAPP signal during one rotation of the head describing different conditions (a) and (b). TECO, Bucharest, 04.-07.05.2005 Scapp 06

  7. 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 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. TECO, Bucharest, 04.-07.05.2005 Scapp 07

  8. 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. TECO, Bucharest, 04.-07.05.2005 Scapp 08

  9. 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. TECO, Bucharest, 04.-07.05.2005 Scapp 09

  10. 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. TECO, Bucharest, 04.-07.05.2005 Scapp 10

  11. TECO, Bucharest, 04.-07.05.2005 Scapp 11

  12. Hourly ratios Gsca/Gref in dependence on Gref for July and December. TECO, Bucharest, 04.-07.05.2005 Scapp 12

  13. Annual courses for the daily ratios Gsca/Gref and Dsca/Dref. TECO, Bucharest, 04.-07.05.2005 Scapp 13

  14. 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! TECO, Bucharest, 04.-07.05.2005 Scapp 14

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