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  • Author or Editor: Masataka Shiobara x
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Shoji Asano
,
Masataka Shiobara
,
Yuji Nakanishi
, and
Yukiharu Miyake

Abstract

The design and performance of a spectral radiometer system are described for airborne measurements of solar flux reflectance by clouds. The system consists of a pair of identical multichannel pyranometers: one installed on the top and the other on the bottom of an aircraft fuselage to measure the downward and upward solar irradiances, respectively. This measurement scheme has an advantage in that reflectances derived from ratios between the upward and downward irradiances can avoid the need for absolute radiometric calibrations. The multichannel cloud pyranometer (MCP) system measures near-monochromatic solar irradiances at nine discrete wavelengths between 420 and 1650 nm by using interference filters with very narrow bandwidths. Included among these wavelengths are 760 and 938 nm in the oxygen and water vapor absorption bands, respectively. Solar radiation passing through the filters is instantly detected by a silicon photodiode for wavelength λ<1 µm and by a germanium photodiode for λ>1 µm. Good performance of the MCP system was confirmed through laboratory calibrations and airborne tests. The MCP system is suitable for remote sensing application to retrieve cloud physical parameters of water clouds from airborne spectral reflectance measurements.

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Rolf Philipona
,
Claus Fröhlich
,
Klaus Dehne
,
John DeLuisi
,
John Augustine
,
Ellsworth Dutton
,
Don Nelson
,
Bruce Forgan
,
Peter Novotny
,
John Hickey
,
Steven P. Love
,
Steven Bender
,
Bruce McArthur
,
Atsumu Ohmura
,
John H. Seymour
,
John S. Foot
,
Masataka Shiobara
,
Francisco P. J. Valero
, and
Anthony W. Strawa

Abstract

With the aim of improving the consistency of terrestrial and atmospheric longwave radiation measurements within the Baseline Surface Radiation Network, five Eppley Precision Infrared Radiometer (PIR) pyrgeometers and one modified Meteorological Research Flight (MRF) pyrgeometer were individually calibrated by 11 specialist laboratories. The round-robin experiment was conducted in a “blind” sense in that the participants had no knowledge of the results of others until the whole series of calibrations had ended. The responsivities C(μV/W m−2) determined by 6 of the 11 institutes were within about 2% of the median for all five PIR pyrgeometers. Among the six laboratories, the absolute deviation around the median of the deviations of the five instruments is less than 1%. This small scatter suggests that PIR pyrgeometers were stable at least during the two years of the experiment and that the six different calibration devices reproduce the responsivity C of PIR pyrgeometers consistently and within the precision required for climate applications. The results also suggest that the responsivity C can be determined without simultaneous determination of the dome correction factor k, if the temperature difference between pyrgeometer body and dome is negligible during calibration. For field measurements, however, k has to be precisely known. The calibration of the MRF pyrgeometer, although not performed by all institutes, also showed satisfactory results.

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