Kippzonen BSRN Scientific Solar Monitoring System Bedienungsanleitung PDF herunterladen (Seite 82)

For example: International Pyrheliometer Comparisons IPC VII, 24 September to 12 October 1990,

Results and Symposium. Working Report No. 162, Swiss Meteorological Institute, Davos and Zurich,

March 1991, 91 pages.

9.0 Radiation Data Reduction and Quality Assurance Procedures

9.1 Introduction

To be certain that the quality of the data obtained is of a high standard, care must be taken from the

initial site set-up through the selection of the instrumentation and DAS to the daily maintenance of

the radiom eters. Once a voltage or resistance measurement is taken, nothing can be done to improve

the quality of that measurement. Nevertheless, if quality assessment is done in near-real-time, any

inaccuracies found in the process can be corrected so that future data are of a higher quality. This

section will suggest a num ber of operations that can be perform ed on the data to aid in the rapid

assessment of the measurements.

Although the BSRN Archive has carefully laid out the format required for the measurements to be included

in the archive, it is recommended that all measurements be kept in their original form (e.g., voltage,

resistance, counts etc.), either at the network observatory or the parent institution. Maintaining these

data eliminates the need for any back processing of engineering data when new, improved or corrected

algorithms need to be applied. Furthermore, unless the instrument can be shown to be malfunctioning

or disconnected, data should not be removed from the data stream, but only flagged because of unlikely

values. The use of the daily log report of activities associated with the station is crucial when considering

the removal of data.

9.2 Standard Data Reduction Procedures

Local quality assurance procedures provide a means of assuring that the data are internally consistent

(to some level of uncertainty) within the site. However, to ensure consistency throughout the network,

more is required than simply providing calibration traceability; the actual means of reducing the transducer

signals to engineering units must have common outcomes. Within the BSRN instruments made by

a variety of companies are being used in an attempt to measure the same radiative and meteorological

variables. The results of these measurements can only be compared if the differences are known not

to come from the algorithms chosen by individual station managers in the conversion of transducer

signals to engineering units. In an attempt to overcome this increased uncertainty, the following section

sets out protocols to be followed in the data reduction process.

9.2.1 Cavity Radiometer and Pyrheliometer

The reduction of all data from cavity radiometers should be fully compatible with the WRC procedures

used in the calculation of the WRR and the conversion of electrical signals to irradiance values used

during International Radiation Comparisons and published by the WRC .

For pyrheliometer signals, the conversion should be based upon the assigned responsivity determined

through comparison with a cavity radiom eter following the subtraction of any zero signal. The responsivity

of the instrument should be normalized to the tem perature at which the calibration was obtained if

the change in responsivity over the temperature range of the instrument changes by greater than a

0.5%. The irradiance would then be calculated as:

T Z

F = R C T(K) C (V - V )

where F = the irradiance in W m

-2

R the instrument’s responsivity at temperature T in µV W m

-1 2

T(K) = the ratio of the responsivity of the instrument at temperature

K to that at the calibration temperature T

V = the signal in mv under irradiance

V = the zero offset voltage.

9.2.2 Pyranometers

Pyranometer signals should be corrected for zero offset before the responsivity factor is applied to

the transducer signal. In the same manner as the pyrheliometer, if the responsivity of the instrument

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