A CO₂-free cloud mask from IASI radiances for climate applications

Simon Whitburn (1) , Lieven Clarisse (1) , Marc Crapeau (2) , Thomas August (2) , Tim Hultberg (2) , Pierre-François Coheur (1) , Cathy Clerbaux (1, 3)

1 SQUARES - Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing
2 EUMETSAT - European Organisation for the Exploitation of Meteorological Satellites
3 TROPO - LATMOS

With more than 15 years of continuous and consistent measurements, the Infrared Atmospheric Sounding Interferometer (IASI) radiance dataset is becoming a reference climate data record. To be exploited to its full potential, it requires a cloud filter that is both accurate, unbiased over the full IASI lifespan, and strict enough to be used in satellite data retrieval schemes. Here, we present a new cloud detection algorithm which combines (1) a high sensitivity, (2) a good consistency over the whole IASI time series and between the different copies of the instrument flying on board the suite of Metop satellites and (3) simplicity in its parametrization. The method is based on a supervised neural network (NN) and relies, as input parameters, on the IASI radiance measurements only. The robustness of the cloud mask over time is ensured in particular by avoiding the IASI channels that are influenced by CO2, N2O, CH4, CFC-11 and CFC-12 absorption lines and those corresponding to the ν2 H2O absorption band. As a reference dataset for the training, the latest version of the operational IASI Level 2 (L2) cloud product is used. We provide different illustrations of the NN cloud product, including comparisons with other existing products. We find a very good agreement overall with the last version of the operational IASI L2 with an identical mean annual cloud amount and a pixel-by-pixel correspondence of about 87 %. The comparison with the other cloud products shows a good correspondence in the main cloud regimes but with sometimes large differences in the mean cloud amount (up to 10 %) due to the specificities of each of the different products. We also show the good capability of the NN product to differentiate clouds from dust plumes.

Mots clés: IASI Instrument; Measurement Instrument; Climatology; Radiance

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]

Simon Whitburn, Lieven Clarisse, Marc Crapeau, Thomas August, Tim Hultberg, et al.. A CO₂-free cloud mask from IASI radiances for climate applications. Atmospheric Measurement Techniques Discussions, 2022, pp.(Discussions). ⟨10.5194/amt-2022-127⟩. ⟨insu-03663135v1⟩