Meteorologisches Observatorium Lindenberg 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 TECO, Bucharest, Scapp 01

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 02 Outline Introduction The Scanning Pyrheliometer/Pyranometer Technical Description Calibration Comparisons of SCAPP with pyrheliometer and pyranometer data hourly means daily totals Conclusions

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 03 about 30 manned stations Radiation Network of the German Weather Service Global radiation  Global and diffuse solar radiation  Atmospheric 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

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 04 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

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 05 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

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 06 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

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 07 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: CH CM CM 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

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 08 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.

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 09 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.

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 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.

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 11

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 12 Hourly ratios Gsca/Gref in dependence on Gref for July and December.

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 13 Annual courses for the daily ratios Gsca/Gref and Dsca/Dref.

Meteorologisches Observatorium Lindenberg TECO, Bucharest, Scapp 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!