Cloud mask algorithm from the EarthCARE multi-spectral imager: the M-CM products
Abstract. The EarthCARE satellite mission will provide new insights into aerosol-cloud and radiation interactions by means of synergistic observations of the Earth's atmosphere from a collection of active and passive remote sensing instruments, flying on a single satellite platform. The Multi-Spectral Imager (MSI) will provide visible and infrared images in the cross-track direction with a 150 km swath and a pixel sampling at 500 m. The suite of MSI cloud algorithms will deliver cloud macro- and micro-physical properties complementary to the vertical profiles measured from the ATmospheric LIDar (ATLID) and the Cloud Profiling Radar (CPR) instruments. The MSI cloud mask algorithm (M-CM) provides a cloud flag, cloud phase and cloud type product which are essential parameters for the cloud optical and physical properties (M-COP) as well as for the aerosol optical properties (M-AOT). Synthetic test scenes from the EarthCARE end-to-end simulator provide a first overview of the expected performance of the M-CM products before launch. Validation of the MSI cloud mask algorithm against satellite products from MSG SEVIRI and MODIS demonstrates a good performance of the algorithm. The MSI cloud detection performance is not completely aligned with that from MODIS, which is however not surprising when considering the rather limited number of spectral channels of MSI in comparison to MODIS. The direct comparison to MODIS shows that some threshold tuning should be done especially over desert or sun glint regions once real observations are available. However the MSI bands are less affected by sun glint because of the asymmetric view of the imager.
Anja Hünerbein et al.
Status: final response (author comments only)
RC1: 'Comment on egusphere-2022-1240', Anonymous Referee #1, 11 Jan 2023
- AC1: 'Reply on RC1', Anja Hünerbein, 20 Mar 2023
RC2: 'Comment on egusphere-2022-1240', Anonymous Referee #2, 31 Jan 2023
- AC2: 'Reply on RC2', Anja Hünerbein, 20 Mar 2023
Anja Hünerbein et al.
Anja Hünerbein et al.
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In the study “Cloud mask algorithm from the EarthCARE multi-spectral imager:
the M-CM products” by Hünerbein et al. the MSI cloud mask algorithm is described and its performance compared to selected test scenes of the EarthCARE simulator. A first validation shows a good agreement of the M-CM algorithm with 45 MODIS scenes as well as 12 MSG SEVIRI cloud mask algorithms of one selected scene.
A description and first tests of the M-CM algorithm is very valuable for the cloud community and on time before the launch of EarthCARE that will provide simultaneous measurements of clouds and aerosol properties as well as radiation fluxes.
The paper is written in a clear and concise way. Some minor deficits are noted in the abstract and conveyed messages of the paper. It is recommended for publication after minor revisions.
The abstract needs modification as the study’s purpose is not clearly stated. What is the study’s motivation, goal, result and outlook?
From my perspective a description of the M-CM algorithm is provided together with a first validation.
The terms “validation” and “verification” should not be used interchangeably as they describe different things. Verification determines if the algorithm developed is suited to the specified requirements. This can be done by testing selected scenes. However, a profound validation should contain a quantitative analysis of a larger and well suited test data set that will follow after the launch as explained in the conclusion. Please check and correct the appropriate usage of these terms throughout the manuscript.
l.14 Comma is missing after “However”. Please check this throughout the manuscript.
l.34 “a a decision tree”. Delete "a"
l.122 "makes no sense" Please be more specific. Why does it make no sense? Is a probability more useful for the user's applications as it provides a confidence measure or is there another reason? Please rephrase l.121-124 for clarity.
l.130 How are these surface dependent thresholds derived?
l.180 Please rephrase the sentence for clarity. Is the following correct?
The same applies for the tri-spectral brightness temperature difference test. Further investigation is needed to define the base threshold, which is strongly dependent on surface and water vapor.
l.190 “probabilities that the pixel is clear” --> probabilities of a pixel being clear
l.237 "the the" --> that the
l. 269 “synthetic atmospheric test scenes created with” atmospheric test scenes created synthetically with …
Fig. 6 Figure subtitle >0.1 disagrees with caption and text (≥ 0.1)
l. 303 “difference” is not true.The term “confusion matrix” would be more appropriate.
l. 307 "while the true cloud flag". This may be misleading as the 3D simulations are not ground truth and are highly dependent on the assumptions (l. 276). Might be better to use the word test or simulated cloud flag instead.
l. 315 “data form the Copernicus” –> data from the Copernicus
l. 351 "Twelve groups" what is meant by this? Where do the 12 algorithms originate from?