Preprints
https://doi.org/10.5194/amt-2022-94
https://doi.org/10.5194/amt-2022-94
 
12 May 2022
12 May 2022
Status: this preprint is currently under review for the journal AMT.

TROPOMI/S5P Total Column Water Vapor Validation against AERONET ground-based measurements

Katerina Garane1, Ka Lok Chan2,3, Maria-Elissavet Koukouli1, Diego Loyola2, and Dimitris Balis1 Katerina Garane et al.
  • 1Laboratory of Atmospheric Physics (LAP), Aristotle University of Thessaloniki (AUTH), 54124 Thessaloniki, Greece
  • 2Deutsches Zentrum für Luft und Raumfahrt (DLR), Institut für Methodik der Fernerkundung (IMF), 82234 Oberpfaffenhofen, Germany
  • 3Rutherford Appleton Laboratory Space (RAL), OX11 0QX Harwell Oxford, United Kingdom

Abstract. Water vapor plays a very important role on the greenhouse effect, rendering it an atmospheric constituent that requires continuous and global monitoring by different types of remote sensing instruments. The TROPOMI/S5P Total Column Water Vapor (TCWV) is a new product retrieved from the blue wavelength band (435 –455 nm), using an algorithm that was originally developed for the GOME-2/Metop sensors. For the purposes of this work, 2.5 years of continuous satellite observations at high spatial resolution are validated against co-located (in space and in time) precipitable water Level 2.0 (quality-assured) ground-based measurements from the NASA AERONET (AErosol RObotic NETwork). The network uses CIMEL sunphotometers located at approximately 1300 stations globally to monitor precipitable water among other products. The two datasets, satellite and ground-based, were co-located and the percentage differences of the comparisons were calculated and statistically analyzed. The correlation coefficient of the two products is found to be 0.9 and the mean bias of the relative percentage differences is of the order of only -3 % for the mid-latitudes and the tropics (±60°). The effect of various influence quantities, such as air mass factor, solar zenith angle, clouds and albedo are also presented and discussed. It was found that the cloud properties affect the validation results, leading the TCWV to a dry bias of -19 % for low cloudiness (CTP > 800 hPa). The cloud albedo introduces a wet bias of 10 % when the cloud albedo is below 0.3 and a dry bias up to -20 % when the clouds are more reflective. Overall, the TROPOMI/S5P TCWV product, on a global scale and for moderate albedo and cloudiness, agrees well at -4.0 ± 4.3 % with the ground-truth.

Katerina Garane et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-94', Anonymous Referee #1, 13 Jun 2022
    • AC1: 'Reply on RC1', Katerina Garane, 21 Sep 2022
  • RC2: 'Review of Garane et al. amt-2022-94', Anonymous Referee #2, 11 Jul 2022
    • AC2: 'Reply on RC2', Katerina Garane, 21 Sep 2022

Katerina Garane et al.

Katerina Garane et al.

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Short summary
2.5 years of TROPOMI/S5P Total Column Water Vapor (TCWV) observations are validated against co-located precipitable water measurements from the NASA AERONET, that uses CIMEL sunphotometers globally. The correlation coefficient is 0.9 and the mean bias of the relative percentage differences is only -3 % for the mid-latitudes and the tropics (±60°). Overall, the TROPOMI/S5P TCWV product, on a global scale and for moderate albedo and cloudiness, agrees well at -4.0 ± 4.3 % with the ground-truth.