Kippzonen BSRN Scientific Solar Monitoring System Instrukcja Użytkownika Pobierz pdf (Strona 25)

Philipona, R., E.G. Dutton, T. Stoffel, J. Michalsky, I.Reda, A. Stifter, P. W endling, N. W ood, S.A. Clough,

E. J. Mlawer, G. Anderson, H.E. Revercomb and T.R. Shippert, 2001: Atmospheric longwave irradiance

uncertainty: Pyrgeometers compared to an absoulte sky-scanning radiometer, atmospheric emitted

radiance interferometer, and radiative transfer model calculations. J. Geophys. Res., 106 (D22) 28129 -

28141.

A recent comparison indicates that the uncertainty associated with infrared measurements

approximate the BSRN target values when the instrument responsivities used are those of the

independent calibration laboratories. When using field calibrations, one-hour mean irradiances

are found to compare to approximately 1 W m for night conditions and 2 W m during daylight

-2 -2

hours. These differences are attributable to different methods used in the determination of the flux

from the instrument outputs. The most significant finding of the comparison is the need to develop

an absolute calibration method that will eliminate the large uncertainties associated with

laboratory calibrations.

Parameters to be acquired are: outputs of pyrgeometer thermopile; instrument body temperatures

and dome temperatures of the pyrgeometer for instruments requiring such measurements. Only

the values associated with the calculated irradiance (mean, maximum, minimum and standard

deviation) are required by BSRN archive. All other raw data should be archived at the centre

responsible for the measurements.

2.2.1.6 Upwelling Infrared Radiation

This measurement, required at BSRN stations undertaking the expanded programme, will be

done with the same type of ventilated pyrgeometer used for observing the downward infrared

irradiance. It is suggested that a horizontal shadow band be installed to protect the instrument

dome from heating due to direct solar radiation when the sun is at low solar elevation. The angle

sustained will be less than 5° (i.e., covering nadir angles 85° to 90°). The instrument should be

mounted on a tower with a minimum height of 30 m to provide a representative measurem ent of

the surrounding area. The actual height of the downfacing sensor should be reported to the

archive.

Parameters to be acquired are: outputs of pyrgeometer thermopile, and instrument body and

dome temperatures for pyrgeometers requiring such measurements. Only the values associated

with the calculated irradiance (mean, maximum , minim um and standard deviation) are required by

BSRN archive. All other raw data should be archived at the centre responsible for the

measurements.

2.2.2 Accuracy of Meteorological Measurements

The requirement of meteorological observations at or near BSRN sites infers that certain levels of

confidence must be placed in the measurements. Most of these observations are made at

stations that are part of national observing networks where changing instruments to meet BSRN

needs are difficult or even impossible. In such cases, the site scientist should determine the

uncertainty of each of these observations either directly, or by consulting the appropriate experts,

and provide it to the BSRN Archive.

Where instrumentation is obtained specifically for the measurement of meteorological variables at

a BSRN site, research quality instrumentation should be obtained. Table 2.2 presents a guideline

on the uncertainty and resolution for some typical measurement fields. Experts in the appropriate

measurement fields familiar with the climatology of the BSRN station should be consulted on

specific instruments.

2.3 Accuracy of Data Acquisition Equipment

2.3.1 Tim e

Tim e is critical with respect to the frequency of the measurem ent sequence and the absolute tim e

of the observation. This requires that the clocks for all observations be maintained to within ±1%

of the averaging period used for the most frequent measurem ents. For a one m inute average this

equates to a time accuracy of 0.6 seconds. Because of the difficulty in manually setting a clock to

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