The primary goal of the FORUM mission is to measure the Earth's top-of-atmosphere emission spectrum in the 100 to 1600 cm-¹ spectral region covering the observational gap of the Far IR (100-667 cm-¹), which has never been observed from space in its entirety. This measurement will provide an improved understanding of the climate system by supplying, for the first time, most of the spectral features of the Far IR contribution to the Earth radiation budget, particularly focusing on the water vapour contribution related to the continuum absorption in the rotational band, cirrus cloud and ice/snow surface emissivity. This goal is achieved by measuring the spectrum with a nominal resolution of 0.3 cm-¹, and with an absolute calibration accuracy of 0.1 K, benchmarked against international standards. A precision of 0.4 mW/m² sr cm-¹ on the radiance will also allow the retrieval of the atmospheric state and cloud parameters with improved accuracy. A demonstration of the FORUM capabilities in improving the characterisation of the atmospheric radiative properties using the Far IR is shown by means of ground-based observations performed at high-altitude sites where the air is sufficiently transparent to sound the Far IR spectral features of the atmospheric emission. To this aim, two instruments are used: the REFIR-PAD (Radiation Explorer in the Far InfraRed - Prototype for Applications and Development) instrument, which has been deployed on the Antarctic Plateau, where it has been acquiring downwelling longwave radiation spectra continuously since 2012, and the FORUM prototype, which will be deployed at the Zugspitze summit at the end of 2018 - early 2019. Both instruments are Fourier transform spectrometers with an optical configuration of the interferometer similar to FORUM. They cover the Far IR spectral region down to 100cm-¹ and can be operated under all sky non-precipitating conditions. In this presentation, a review of the measurement requirements of the FORUM mission will be provided with a description of the measurement results obtained during the high-altitude Antarctic and Zugspitze campaigns.
Measurement Requirements of the FORUM Mission and Ground-Based Field Campaigns
Luca Palchetti;Marco Ridolfi;Samuele Del Bianco;Bianca Maria Dinelli;Marco Barucci;Giovanni Bianchini;Elisa Castelli;Ugo Cortesi;Francesco D'Amato;Piera Raspollini;Silvia Viciani;
2019
Abstract
The primary goal of the FORUM mission is to measure the Earth's top-of-atmosphere emission spectrum in the 100 to 1600 cm-¹ spectral region covering the observational gap of the Far IR (100-667 cm-¹), which has never been observed from space in its entirety. This measurement will provide an improved understanding of the climate system by supplying, for the first time, most of the spectral features of the Far IR contribution to the Earth radiation budget, particularly focusing on the water vapour contribution related to the continuum absorption in the rotational band, cirrus cloud and ice/snow surface emissivity. This goal is achieved by measuring the spectrum with a nominal resolution of 0.3 cm-¹, and with an absolute calibration accuracy of 0.1 K, benchmarked against international standards. A precision of 0.4 mW/m² sr cm-¹ on the radiance will also allow the retrieval of the atmospheric state and cloud parameters with improved accuracy. A demonstration of the FORUM capabilities in improving the characterisation of the atmospheric radiative properties using the Far IR is shown by means of ground-based observations performed at high-altitude sites where the air is sufficiently transparent to sound the Far IR spectral features of the atmospheric emission. To this aim, two instruments are used: the REFIR-PAD (Radiation Explorer in the Far InfraRed - Prototype for Applications and Development) instrument, which has been deployed on the Antarctic Plateau, where it has been acquiring downwelling longwave radiation spectra continuously since 2012, and the FORUM prototype, which will be deployed at the Zugspitze summit at the end of 2018 - early 2019. Both instruments are Fourier transform spectrometers with an optical configuration of the interferometer similar to FORUM. They cover the Far IR spectral region down to 100cm-¹ and can be operated under all sky non-precipitating conditions. In this presentation, a review of the measurement requirements of the FORUM mission will be provided with a description of the measurement results obtained during the high-altitude Antarctic and Zugspitze campaigns.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
