MAPP project (2020-2023)
The overall aim of this project co-ordinated by PMOD (Physicalisch-Meteorologische Observatorium Davos, Switzerland) is to enable the SI-traceable measurement of column-integrated aerosol optical properties retrieved from the passive remote sensing of the atmosphere using solar and lunar radiation measurements. Radiometers of the three largest aerosol monitoring networks will be calibrated at NMI laboratories. Also, portable devices for the in-field calibration of network radiometers will be developed in order to validate and improve the current aerosol optical property retrievals using state-of-the-art inversion models. The goal is to standardize aerosol optical properties retrieval by shortening the calibration chain, reduce calibration downtime of network radiometers, and to establish their consistent dissemination including their uncertainty.
In the project, Metrology Research Institute will develop and utilize measurement setups for linearity and angular properties of radiometers. These are essential parameters for accurate measurements of aerosols. Also, nonuniformities of calibration sources will be studied. In the earlier environmental projects with the same consortium, we have developed novel simulation techniques to consider unknown correlations in uncertainty estimations. This work will be continued in the project and Aalto will use its gained experience in uncertainty evaluations with other partners.
During 2020 – 2021, we have built setups for measuring spatial uniformities of integrating spheres (Fig. 2), and for measuring angular responsivities of radiometers . The spatial uniformity measurement setup was tested on our own integrating sphere . Two different methodologies were tested and compared, direct measurement by scanning a small detector in front of the sphere, and a reversed method utilizing lasers. The work will continue with measurements of an integrating sphere of a project partner.
The setup for measuring angular responsivities of radiometers was used to measure angular responsivities of two radiometers of PMOD (Fig. 3). The results were compared with good agreement with the measurements of PMOD . The maximum resolution of the measurements is 9 arcsec (0.0025 deg) constrained by the gimbal system.
Contact person: Petri Kärhä
1. Iiro Harju, Measurement setup for characterising angular responsivities of optical radiometers, Candidate work, Aalto University School of Electrical Engineering, Espoo, 2020, 20 p. (in Finnish).
2. Kinza Maham, Petri Kärhä, and Erkki Ikonen, “Methodologies to measure spatial uniformities of integrating spheres,” Abstracts of CIE 2021 Conference, September 27 – 29, 2021, pp. 104 – 105. https://malaysia2021.cie.co.at/sites/default/files/cie_2021_abstract_booklet_0.pdf
3. I. Harju, P. Kärhä, E. Ikonen, J. Gröbner, N. Kouremeti, G. Hülsen, and S. Kasadzis, “Angular responsivity measurements of optical radiometers for estimating uncertainties of atmospheric aerosol measurements related to FOV effects,” 20th International Metrology Congress CIM2021, Lyon, September 7 – 9, 2021. https://www.cim2021.com/files/programmes/CIM2021-PapersAbstract-V1.pdf