244
Chapter 25
these problems became especially acute when the station was incorporated
into the Baseline Surface Radiation Network, demanding measurements of
all radiation fluxes with high quality as reference data for different tasks.
Some conclusions and ideas from this experience are presented below.
2.
RADIOMETRIC SCALE, REFERENCE
INSTRUMENTS AND CALIBRATION METHODS
The radiometric scale in the Soviet Union was based on the national
reference instrument—the Ångström pyrheliometer No. 212, which was
periodically compared with the World Radiometric Reference (WRR). In
Tõravere’s Actinometric Station, an Ångström type pyrheliometer M-59-8
No. 1981 designed by Y. Yanishevsky is in use as the reference instrument.
The pyrheliometer was periodically compared with the Soviet Union
national reference. Direct comparison with the WRR in Davos in 1995
demonstrated good agreement with an error < 0.1%. Since 1997 a new
reference is in use, namely the absolute cavity radiometer PMO-6 No.
R850405. As a secondary reference instrument for the routine calibration of
the working instruments the Yanishevsky actinometer AT-50 No. 596 is
used. The results of the calibration of the secondary reference are presented
in Fig. 1. In 1997, a new secondary reference, the normal incidence
pyrheliometer (NIP) No. 16418, was also repeatedly calibrated using AT-50
No 596 and PMO-6 No R850405 as references (Fig. 2). The figures confirm
that there are no essential differences between the M-59-S and PMO-6 and
the radiometric scale is correctly presented at the station. Fig. 3 exhibits an
example of the simultaneous record of the direct solar radiation in an almost
cloudless day using NIP No. 16418 and AT-50 No. 331. In spite of the
different angles of view of the instruments (NIP –5.7°, AT-50 –10°) the
agreement is good.
Chapter 25
these problems became especially acute when the station was incorporated
into the Baseline Surface Radiation Network, demanding measurements of
all radiation fluxes with high quality as reference data for different tasks.
Some conclusions and ideas from this experience are presented below.
2.
RADIOMETRIC SCALE, REFERENCE
INSTRUMENTS AND CALIBRATION METHODS
The radiometric scale in the Soviet Union was based on the national
reference instrument—the Ångström pyrheliometer No. 212, which was
periodically compared with the World Radiometric Reference (WRR). In
Tõravere’s Actinometric Station, an Ångström type pyrheliometer M-59-8
No. 1981 designed by Y. Yanishevsky is in use as the reference instrument.
The pyrheliometer was periodically compared with the Soviet Union
national reference. Direct comparison with the WRR in Davos in 1995
demonstrated good agreement with an error < 0.1%. Since 1997 a new
reference is in use, namely the absolute cavity radiometer PMO-6 No.
R850405. As a secondary reference instrument for the routine calibration of
the working instruments the Yanishevsky actinometer AT-50 No. 596 is
used. The results of the calibration of the secondary reference are presented
in Fig. 1. In 1997, a new secondary reference, the normal incidence
pyrheliometer (NIP) No. 16418, was also repeatedly calibrated using AT-50
No 596 and PMO-6 No R850405 as references (Fig. 2). The figures confirm
that there are no essential differences between the M-59-S and PMO-6 and
the radiometric scale is correctly presented at the station. Fig. 3 exhibits an
example of the simultaneous record of the direct solar radiation in an almost
cloudless day using NIP No. 16418 and AT-50 No. 331. In spite of the
different angles of view of the instruments (NIP –5.7°, AT-50 –10°) the
agreement is good.