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| Titel |
Reconstruction of high-resolution time series from slow-response broadband terrestrial irradiance measurements by deconvolution |
| VerfasserIn |
A. Ehrlich, M. Wendisch |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 9 ; Nr. 8, no. 9 (2015-09-11), S.3671-3684 |
| Datensatznummer |
250116572
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| Publikation (Nr.) |
 copernicus.org/amt-8-3671-2015.pdf |
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| Zusammenfassung |
Broadband solar and terrestrial irradiance measurements of
high temporal resolution are needed to study inhomogeneous
clouds or surfaces and to derive vertical profiles of
heating/cooling rates at cloud top. An efficient method to
enhance the temporal resolution of slow-response measurements
of broadband terrestrial irradiance using pyrgeometer is
introduced. It is based on the deconvolution theorem of
Fourier transform to restore amplitude and phase shift of high
frequent fluctuations. It is shown that the quality of
reconstruction depends on the instrument noise, the
pyrgeometer response time and the frequency of the
oscillations.
The method is tested in laboratory measurements for synthetic time
series including a boxcar function and periodic oscillations using
a CGR-4 pyrgeometer with response time of 3 s. The
originally slow-response pyrgeometer data were reconstructed to
higher resolution and compared to the predefined synthetic time
series. The reconstruction of the time series worked up to
oscillations of 0.5 Hz frequency and 2 W m−2
amplitude if the sampling frequency of the data acquisition is
16 kHz or higher. For oscillations faster than 2 Hz,
the instrument noise exceeded the reduced amplitude of the
oscillations in the measurements and the reconstruction failed.
The method was applied to airborne measurements of upward
terrestrial irradiance from the VERDI (Vertical Distribution
of Ice in Arctic Clouds) field campaign. Pyrgeometer data
above open leads in sea ice and a broken cloud field were
reconstructed and compared to KT19 infrared thermometer data.
The reconstruction of amplitude and phase shift of the
deconvoluted data improved the agreement with the KT19 data.
Cloud top temperatures were improved by up to 1 K
above broken clouds of 80–800 m size (1–10 s
flight time) while an underestimation of 2.5 W m−2
was found for the upward irradiance over small leads of about
600 m diameter (10 s flight time) when using
the slow-response data. The limitations of the method with
respect to instrument noise and digitalization of measurements
by the data acquisition are discussed. |
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