AVHRR GAC Sea Surface Temperature Reanalysis Version 2

Round 1

Reviewer 1 Report

 

Overview: This manuscript presented a summary on a 40-year SST dataset retrieved from the Advanced Very High-Resolution Radiometers (AVHRR) products onboard ten NOAA satellites. SST products are critical important to both climate and weather modeling and to explore many remaining coupling questions. I am glad to see the advent of a new product. This topic fits the scope of Remote Sensing quite well. The manuscript is overall well-organized and I would consider it as a high-quality work in terms of science. I myself have learned a lot from reviewing this manuscript. However, I do think the manuscript failed in several aspects, including the frequent wordy and complicated sentences, the inconsistent formatting (e.g., indent), lack of labels for figures, and too many acronyms. See my comments below for more details. I would suggest a major revision before this manuscript could be accepted for publication.

 

Line 50: change “dead” to “inactive”

Line 71: What is “this overarching goal”

Table 1: What is “EXT”?

Line 123: change “corrupt” to “corrupted”

Line 134: change “regression SST retrieval algorithms” to something like “regression-based algorithms for SST retrievals”

Line 136: change “Customarily” to “Traditionally”

Figure 2: The authors should contact the journals or publishers to get the permission to use this figure and include the copyright. The figure quality needs to be improved.

Check the incidents of each paragraph.

Figure 3: Label each panel and cite the corresponding panel in the text.

Figure 3 (top): Why does the bias go up since 2017 in N18 & N15?

The discussion of Figure 3 in the text is a bit wordy. You might want to think about the main information you want to impress readers and make the description more concise. 

Lines 223-226: Please rewrite these sentences because they are super confusing. 

Line 243: remove “)”.

Line 244: “collating” or “collocating”?

Line 248: “Compared datasets” sounds weird.

Too many abbreviations are used in the manuscript. I would suggest that spelling full names if they are only used a couple of times in the text.

Line 297: I would use “conservative” here

Figure 5: Again, label all the panels and refer to the individual panel when citing one.

Line 308: “masking” to “are masked”, “observation” to “observations”

Figures 5 and 6: Please add the coastline.

Figure 7: Add unit for this (i.e., %).

Line 334: collating -> collocating 

Figure 7: Hovmoller diagrams often have time as the y-axis. Please replete. 

Change the caption “Latitudinal Hovmöller diagrams” to “Hovmöller diagrams (Latitude x time)”

Line 378: Rewrite this sentence. 

Figures 10–11: The figure quality should be improved.

Lines 407–408: This sentence should be rewritten. 

Line 444: You might want to discuss what caused the sudden drops of the # of obs.

Lines 463-464: Rewrite this sentence. 

Line 506: Remove () for the sentence “Note that …”

Lines 588-599: Rewrite this sentence.

Section 7: This section has a lot of individual sentences as paragraphs, which is weird to me. The organization of this summary is quite confused. As a new product, this section should highlight the advantages of the new dataset and include a concise summary of limitations for readers and future potential users.  The example order might be: A brief summary of research goal -> major findings -> highlight benefits -> limitations -> future plan. 

References: some of the dot links don’t work. Please go back to check your references. 

Author Response

Overview: This manuscript presented a summary on a 40-year SST dataset retrieved from the Advanced Very High-Resolution Radiometers (AVHRR) products onboard ten NOAA satellites. SST products are critical important to both climate and weather modeling and to explore many remaining coupling questions. I am glad to see the advent of a new product. This topic fits the scope of Remote Sensing quite well. The manuscript is overall well-organized and I would consider it as a high-quality work in terms of science. I myself have learned a lot from reviewing this manuscript. However, I do think the manuscript failed in several aspects, including the frequent wordy and complicated sentences, the inconsistent formatting (e.g., indent), lack of labels for figures, and too many acronyms. See my comments below for more details. I would suggest a major revision before this manuscript could be accepted for publication.

 

We appreciate positive feedback and thorough comments of the Reviewer. Our responses to each item are given below in italic. The line numbers given in parentheses correspond to the updated version (with changes tracked).

 

Line 50: change “dead” to “inactive”.

• Dead satellite, sensor, detector etc. is an established terminology in the satellite and remote sensing communities – see for instance https://www.space.com/15608-huge-satellite-envisat-dead-space.html and https://www.space.com/ingenuity-mars-helicopter-troubleshooting-dead-navigation-sensor. You can google many similar examples. The word ‘inactive’ does not fully reflect the reality, as it implies that the sensor can be activated, but in reality, it cannot. (Line 52)

 

Line 71: What is “this overarching goal”?

• We have changed text and it now reads “In this context, ..” The context is described in the previous two lines 69-70 “process the entire data records and create long term, consistent SST time series from both LEO and GEO sensors” (Line 73).

 

Table 1: What is “EXT”?

• We have changed it to LEXT (local equator crossing time; already defined earlier). We have provided an Appendix with a Table of all acronyms used in the paper. We hope that adding this Table makes the paper easier to follow.

 

Line 123: change “corrupt” to “corrupted”.

• Changed (line 123).

 

Line 134: change “regression SST retrieval algorithms” to something like “regression-based algorithms for SST retrievals”.

• Changed to “regression-based SST retrieval algorithms” (line 138).

 

Line 136: change “Customarily” to “Traditionally”.

• Changed (line 136).

 

Figure 2: The authors should contact the journals or publishers to get the permission to use this figure and include the copyright. The figure quality needs to be improved.

• No permission is needed for using Fig. 2, which is taken directly from iQuam, which is an open-access system in a public domain. Our co-author, A. Ignatov, is also the co-author of iQuam. IQuam developers recommend citing the iQuam sources and 2014 JTECH paper. This is done in the manuscript. The quality of the Fig. 2 is improved.

 

Check the incidents of each paragraph.

• Checked and fixed.

 

Figure 3: Label each panel and cite the corresponding panel in the text.

• The panels are labeled with letters in Figs. 3 & 9-20 and with names of datasets in Figs. 5-6.

 

Figure 3 (top): Why does the bias go up since 2017 in N18 & N15?

• The long-term drifts in T_is-T₀ biases are caused mainly by orbital evolution. In particular, the N15 and N18 biases warm up near 2017 because their orbits evolved from ‘afternoon’ to ‘early morning’ overpass times (cf. Fig. 1). This is explained in Section 2.3 (lines 207-214). This part of the text is now separated into a stand-alone paragraph, to make the point more prominent.

 

The discussion of Figure 3 in the text is a bit wordy. You might want to think about the main information you want to impress readers and make the description more concise. 

• This discussion of Figure3 was shortened (lines 188-221). We hope that addresses Reviewer’s concern.

 

Lines 223-226: Please rewrite these sentences because they are super confusing. 

• The following two sentences “Ideally, ACSPO retrieval domain, retrieved SSTs, and monitoring of sensor BTs, should all be insensitive to first guess SST. In reality, however, the quality of first guess SST is often important, and may degrade ACSPO product” were dropped (end of line 276). There is a message to convey there, and we tried, but the way we did it probably causes more confusion than helps.

 

Line 243: remove “)”.

• Removed (line 298).

 

Line 244: “collating” or “collocating?”

• Collating is the right word here (line 299).

 

Line 248: “Compared datasets” sounds weird.

• We changed it to “Other datasets used in this study”.

 

Too many abbreviations are used in the manuscript. I would suggest that spelling full names if they are only used a couple of times in the text.

• We have provided Appendix with a Table of acronyms (Lines 963-965).

 

Line 297: I would use “conservative” here

• Exactly this word is currently used (line 357). We hope this addresses Reviewer’s request.

 

Figure 5: Again, label all the panels and refer to the individual panel when citing one.

• In Figs. 5-6 the panels are labeled with the names of the data sets. We believe that adding more labels would be redundant, in this particular case. In all other Figs, panels are labeled.

 

Line 308: “masking” to “are masked”, “observation” to “observations”

• The sentence “The previous observation that masking in RAN2 is less conservative than in CCI and PF, is confirmed by the regional imagery” was dropped. It is not critical for what we are trying to convey, and if causes confusion, it is better excluded. (Lines 364-365).

 

Figures 5 and 6: Please add the coastline.

• We believe that adding the coastline to these Figures is redundant. The land is already marked with a unique color. We have added text to Fig. 5 caption “Land is rendered in light grey and ocean data with missing SST in darker grey.” We hope that this facilitates reading Figs. 5-6.(Lines 383-384)

 

Figure 7: Add unit for this (i.e., %).

•  

 

Line 334: collating -> collocating.

• Collating is the right word here (line 399).

 

Figure 7: Hovmoller diagrams often have time as the y-axis. Please replete.

• We agree with the “often” connotation. However, not always. We see many examples in the literature using time on x-axis – e.g. https://www.climate.gov/news-features/understanding-climate/hovm%C3%B6ller-diagram-climate-scientist%E2%80%99s-best-friend. Reviewer can find more examples. Overall, it appears to be a matter of taste, rather than an established and generally accepted practice. We believe that in this particular case, x-axis is more appropriate, because time series are very long and easier to view this way, and prefer to keep it this way. 

 

Change the caption “Latitudinal Hovmöller diagrams” to “Hovmöller diagrams (Latitude x time)”.

• Changed to “Hovmöller diagrams (latitude vs. time)” (line 442).

 

Line 378: Rewrite this sentence. 

• The sentence has been rewritten (lines 446-448).

 

Figures 10–11: The figure quality should be improved.

• All Figures in this paper have been regenerated with the goal to improve quality.

 

Lines 407–408: This sentence should be rewritten. 

• The sentence has been rewritten (lines 474-480).

 

Line 444: You might want to discuss what caused the sudden drops of the # of obs.

• The explanation has been added (lines 508-510).

 

Lines 463-464: Rewrite this sentence. 

• Rewritten (lines 539-541).

 

Line 506: Remove () for the sentence “Note that …”

• Removed (line 553).

 

Lines 588-599: Rewrite this sentence.

• Rewritten (lines 685-690).

 

Section 7: This section has a lot of individual sentences as paragraphs, which is weird to me. The organization of this summary is quite confused. As a new product, this section should highlight the advantages of the new dataset and include a concise summary of limitations for readers and future potential users.  The example order might be: A brief summary of research goal -> major findings -> highlight benefits -> limitations -> future plan. 

• We have made edits and additionally structured the text, to improve its readability. However, we would like to keep section 7 organized as it is now, with bullet points along three major lines: relative merits of the three available datasets; RAN2 limitations; and future work to mitigate those. We hope that the Reviewer would find the current organization agreeable.

 

References: some of the dot links don’t work. Please go back to check your references. 

• All references were revisited, corrected where necessary and all links have been double-checked.

Reviewer 2 Report

Petrenko et al introduced AVHRR GAC Sea Surface Temperature Reanalysis Version 2 in this manuscript, all figures in this work are poorly presented which needs to be improved:

Major comments:

1. The resolution of Figure 2 is too low, please make it clear.

2. Please check the resolution of all figures, make sure all figures are well presented.

3. No labels are shown in each subplot, such as Figure.12(a), (b)……

Generally, please replot all figures.

Author Response

Petrenko et al introduced AVHRR GAC Sea Surface Temperature Reanalysis Version 2 in this manuscript. All figures in this work are poorly presented which needs to be improved:

We appreciate feedback from this reviewer. Below are our responses to individual comments in blue italic.

 

Major comments:

1. The resolution of Figure 2 is too low, please make it clear
   • Figure 2 is replotted.

 

2. Please check the resolution of all figures, make sure all figures are well presented.
   • All Figures in the paper were regenerated with the goal to improve quality.

 

3. No labels are shown in each subplot, such as Figure.12(a), (b)……
   • All Figures in the paper are now labeled. Multiple panels have been consolidated into single images to avoid the panel overlaps.

 

Generally, please replot all figures.

- Done

 

Reviewer 3 Report

good paper, no further comment

Author Response

Good paper. No further comments.

We appreciate feedback from this Reviewer.

Reviewer 4 Report

  This paper describes the process and details of creating a modified AVHRR SST product based on the NOAA’s Advanced Clear Sky Processor. The authors produced a 40-year modified database of RAN2 SST. They validated the new product using the previous NOAA SST databases. Furthermore, RAN2 data were trained against  and in situ data. The result showed that the resulted SST database has a higher quality and spatial coverage that the previous ones. The topic is relevant to the oceanography community, specially when it comes to verifying baroclinic circulation models. I would like to recommend this paper for  publishing in /remote Sensing after applying the following minor corrections:

 

 

-        Ln 38-40:  is any Near-infrared channel used in combination to infrareds for estimation of SST by AVHRR?

-        Does the new SST product only improves AVHRR data for cloudiness? What about gaps between swaths?

-        Microwave SST data as Optimally Interpolated (OI, https://images.remss.com/sst/sst_data_daily.html) provides  cloud-free daily SST maps mostly for open ocean. The 9 km product from this database combined microwave and near infrared SST data to also include the coastal areas. This could be a good product to compare with RAN2 outputs. I suggest that the authors include some qualitative comparison between two databases, This OI product has successfully used in several recent studies to study upper ocean mixing and response to storms. 

 

-        Page 6: Output link on this page 6  not work:

https://coastwatch.noaa.gov/pub/socd2/coast-

watch/sst/ran/avhrr_gac/

 

Please double check this link and replace it with the most recent correct link. This is important since the data base is of great uses for other researchers.

Author Response

This paper describes the process and details of creating a modified AVHRR SST product based on the NOAA’s Advanced Clear Sky Processor. The authors produced a 40-year modified database of RAN2 SST. They validated the new product using the previous NOAA SST databases. Furthermore, RAN2 data were trained against in situ data. The result showed that the resulted SST database has a higher quality and spatial coverage that the previous ones. The topic is relevant to the oceanography community, specially when it comes to verifying baroclinic circulation models. I would like to recommend this paper for publishing in /remote Sensing after applying the following minor corrections:

We appreciate positive feedback from this Reviewer. Below are our responses to individual comments in italic. The line numbers given in parentheses correspond to the updated version (with track changes accepted)

1. Ln 38-40: is any Near-infrared channel used in combination to infrareds for estimation of SST by AVHRR?
   • As stated in lines 99-101, SST is estimated from the IR bands only. The visible band 1 (0.63 µm) and near-infrared band 2 (0.83 µm) are used for the daytime cloud masking.
2. Does the new SST product only improves AVHRR data for cloudiness? What about gaps between swaths?
   • (See lines 101 and 359) RAN2 SST does not cut off by VZA and reports SST within full range of AVHRR view zenith angles, |VZA|<68°, resulting in no gaps between swaths. This is in contrast with CCI (|VZA|<60°) and Pathfinder (|VZA|<55°) SSTs, leading to gaps between neighboring swaths (see Figs. 5-6 where imagery from 3 products is compared).
3. Microwave SST data as Optimally Interpolated (OI, https://images.remss.com/sst/sst_data_daily.html) provides cloud-free daily SST maps mostly for open ocean. The 9 km product from this database combined microwave and near infrared SST data to also include the coastal areas. This could be a good product to compare with RAN2 outputs. I suggest that the authors include some qualitative comparison between two databases, This OI product has successfully used in several recent studies to study upper ocean mixing and response to storms.
   • As stated in Section 2.4 (lines 285-289), the RAN2 SST is presented in three formats: L2P (swath), L3U (gridded, uncollated) and L3C (gridded, collated), separately for each of 10 satellites. This paper is focused on the comparison of SST products available in the same formats or processing levels, L3C or L2P, which allows to reveal the efficiencies of the processing algorithms used in each product. In contrast, the REMSS OI SST is a higher-level L4 product, which combines data from multiple MW and IR satellites and sensors. We agree, however, that such comparison would be very valuable and can be a subject of the future work.
4. Page 6: Output link on this page 6 not work: https://coastwatch.noaa.gov/pub/socd2/coast-watch/sst/ran/avhrr_gac/. Please double check this link and replace it with the most recent correct link. This is important since the
   • The link has been corrected and replaced (see lines 286-287).

Round 2

Reviewer 2 Report

I suggest accept the paper.