Campaign of an Infrared Spectrometer from the Belgian Institute for Space Aeronomy (IASB) at the Izaña Atmospheric Observatory

During the last week of May, a team of the Belgian Institute for Space Aeronomy( IASB) D.Gillotay, D.Bolsée, W.Decuyper and N.Pereira, visited the facilities of the Izaña Atmospheric Observatory to deploy an Infrared Spectrometer system. The goal of the campaign is to obtain high-quality Near Infrared (NIR) direct solar irradiance measurements through atmospheric windows ranging from 600 to 2300 nm, relying on the following aspects:

•    An high performance Bentham double spectroradiometer with a peltier-cooled lead sulphide cell (PbS) as detector and an EKO Str-22 as a precise sun pointing device.

•    An absolute calibration performed at Physikalisch-Technische Bundesanstalt (PTB) in Germany against a highly stable black body radiator (BB3200pg) that is the primary standard for spectral irradiance scales. The transfer of the PTB radiometric scale between the PTB and Izaña was certified using a set of secondary standards of spectral irradiance (1000 W tungsten lamps). The stability of the Bentham absolute calibration after the delivery to Izaña was checked using these lamps at the Observatory dark room facilities.

•    The excellent observation conditions at Izaña: low optical thickness, clear sky, temporal and spatially homogenous atmospheric conditions (far from urban sites) are crucial for direct sun measurements. Also the excellent support from the Izaña team, both for maintenance and for technical assistance during the deployment and the campaign is crucial for the success of the experiment.

The measurement campaign is expected to last all summer as long as precipitation and cloudiness are negligible.

The NIR irradiance spectra obtained during this campaign will be used to retrieve the top-of-atmosphere (TOA) solar spectral irradiance through wavelength ranges free of O2, O3, CO2 and H2O absorption the Bouguer-Langley technique. 

The results will be obtained within this campaign are expected to solve some discrepancies observed in published TOA solar spectra in the infrared range. An accurate knowledge of the NIR TOA solar irradiance is important due to its role in Earth radiative budget, namely atmospheric and upper layer of the ocean absorption processes. NIR TOA is also needed to validate semi empiric models of the solar atmosphere.

Calibration at Izaña dark room                             Installation of the equipment in the platform

Sun Tracker                                                        General view of the equipment and the IASB team

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