Abstract
Abstract. Information content analyses on cloud top altitude (CTOP) and geometrical thickness (CGT) from multi-angular A-band measurements in the case of monolayer homogeneous clouds are conducted. In the framework of future multi-angular radiometer development, we compared the potential performances of the 3MI (Multi-viewing, Multi-channel and Multi-polarization Imaging) instrument developed by EUMETSAT, which is an extension of POLDER/PARASOL instrument and MSPI (Multiangle SpectroPolarimetric Imager) developed by NASA's Jet Propulsion Laboratory. Quantitative information content estimates were realized for thin, moderately opaque and opaque clouds for different surface albedo and viewing geometry configurations. Analyses show that retrieval of CTOP is possible with a high accuracy in most of the cases investigated. Retrieval of CGT is also possible for optically thick clouds above a black surface, at least when CGT > 1–2 km and for thin clouds for CGT > 2–3 km. However, for intermediate optical thicknesses (COT ≃ 4), we show that the retrieval of CGT is not simultaneously possible with CTOP. A comparison between 3MI and MSPI shows a higher information content for MSPI's measurements, traceable to a thinner filter inside the oxygen A-band, yielding higher signal-to-noise ratio for absorption estimation. Cases of cloud scenes above bright surfaces are more complex but it is shown that the retrieval of CTOP remains possible in almost all situations while the information content on CGT appears to be insufficient in many cases, particularly for COT < 4 and CGT < 2–3 km.
Highlights
Clouds play an important role in the Earth radiation budget by modulating both the incoming and outgoing solar and thermal radiation that in turn directly act on the heating and cooling rates within the atmosphere
We evaluated whether information could be obtained for cloud geometrical thickness (CGT) if a priori knowledge is used for cloud top altitude (CTOP)
We anticipate that multi-angle measurements will be more robust to noise but it remains to be investigated how the various errors on measurements and non-retrieved parameters impact the a posteriori errors on CGT for single-view or multiangular observations. This issue is clearly outside the scope of our present study since we focus on multi-angle measurements to simultaneously retrieve CTOP and CGT with no further a priori information on either
Summary
Clouds play an important role in the Earth radiation budget by modulating both the incoming and outgoing solar and thermal radiation that in turn directly act on the heating and cooling rates within the atmosphere. Turning to narrowband bispectral multiangular measurements in the A-band, Ferlay et al (2010) suggested using the correlation between the angular standard deviation of the cloud oxygen pressure and the cloud geometrical thickness The feasibility of this technique was later on confirmed by Desmons et al (2013), who compared POLDER3/PARASOL retrievals of cloud geometrical thickness to information derived from collocated active sensors (CALIOP/CLOUDSAT). Several studies have demonstrated the great interest of combining multi-spectral, multi-angular and polarized measurements in the visible, near and shortwave infrared to better constrain retrievals of cloud microphysical (Bréon and Doutriaux-Boucher, 2005; Zhang et al, 2009; Riedi et al, 2010) and macrophysical (Ferlay et al, 2010; Desmons et al, 2013) properties In this context, several missions that will fly a new generation of polarimetric multi-angular sensors that are currently being formulated.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
