Review for egusphere-2023-145

Detection of aerosol and cloud features for the EarthCARE lidar ATLID: the A-FM product

by

Gerd-Jan van Zadelhoff, David P. Donovan and Ping Wang

General comments

This manuscript introduces a feature mask product for the lidar instrument ATLID that will be on board the EarthCARE satellite due to be launched very soon. This feature mask is an important processing unit within the full processing chain delivering geophysical products from the satellite. There are a few minor items to consider in order for this manuscript to suitable for publication. 

More discussion is needed on how the FeatureMask works in situations where there is significant variation in profile-to-profile attenuation, e.g. when identifying lower-level features below an upper-level cloud that has gaps in it. Are the kernels in the median-filter approach adjusted, or does the the method rely on pixel value adjustment only? Is this information propagated to subsequent smoothing algorithms somehow?

The verification section would be better served by calculating the contingency tables based on the signal fields (or attenuated backscatter coefficient) rather than the extinction field, since this provides a more direct comparison of the cumulative effect of atmospheric attenuation on feature detection. Verification before and after combination of the strong and weak feature masks would clearly show the additional benefit of the full FeatureMask algorithm.

Lines 25-29: Here, it is stated that measurements from 4 sensors are combined, in order to be compared to measurements from 1 of them. Abstract states that measurements from 3 sensors are combined..

Lines 70: What do you mean by 'effects' here? I assume that you mean that is is not just the mask that is propagated, but also decisions made on smoothing. Using 'decisions made' would be clearer.

Lines 95-96: Correlation of what data?

Lines 115-117: It would be clearer to mention the ideal case here and then discuss the cross-talk, its correction and implications after line 141.

Lines 348-351: Need to be more specific here. Is this procedure performed for each feature value separately? What is the order of precedence if the process finds overlapping features with different values? Features from which mask receive a penalty, and why do some receive a 2 point penalty? 

Technical comments

Line 4: Replace 'state is estimated, which then are used' with 'state is estimated and then used'.

Line 18 and elsewhere: Choose one format for displaying extinction and backscatter values throughout the manuscript.

Line 30: Replace 'have being developed' with either 'are being developed' or 'have been developed'.

Line 35: Replace 'rations' with 'ratios'.

Line 38: Explain what Aeolus is here (a satellite wind lidar mission) as this is the first time it is mentioned in the main text.

Line 66: Replace 'aerosols regimes' with 'aerosol regimes'.

Line 67: Replace 'liquid clouds signals are not mixed with aerosol of' with 'liquid clouds are not mixed with aerosol or'.

Line 79: Replace 'FeaturMask' with 'FeatureMask'. Suggest using 'regions' rather than 'areas' - 'areas' imply a 2-dimensional (horizontal) spatial extent, whereas the FeatureMask is of time-height dimensions.  

Line 89: Replace 'to to' with 'to'.

Line 91: Replace 'the the' with 'the'.

Line 118: Replace 'correction' with 'corrections'.

Line 125: Replace 'depend both' with 'both depend'.

Line 172: Replace 'area's' with 'areas'.

Line 176: Do you mean 'quantitative' here?

Lines 206-207: Is the vertical cross-talk pixel-to-pixel only? Or does it extend beyond neighbouring pixels?

Line 240: Should mention here how the standard deviation of the signal is calculated.

Lines 244-246: Do you mean single pixel elements in both the vertical and spatial sense? Not sure that you need to specify 'Cumulus' here as such 'single pixel elements' could also arise from liquid clouds or other features which may be narrow in one dimension (along track) but extensive in the other spatial dimension (perpendicular to the track).

Line 265: For 'Those pixels' do you mean 'Co-polar Mie pixels'?

Lines 268-269: Paragraph needs fixing.

Line 278: What is 'features in 1' referring to?

Lines 290-291: Replace 'detects' with 'detect'. What do you mean by 'cutting corners'? It might be safer to write 'artificially rounding the corners of 2-dimensional features'.

Line 414: Replace 'ot' with 'it'.

Figures: Some figures will require their colour scales to be modified in order to meet the journal publication requirements.

Figure 5: Replace 'cut of' with 'cut off'.

Figure 7: Replace 'verticals scale' with 'vertical scale'.