Remote Sensing Survey of Altiplano-Puna Volcanic Complex Rocks and Minerals for Planetary Analog Use

Round 1

Reviewer 1 Report

The manuscript “Remote sensing survey of Altiplano-Puna Volcanic Complex 2 rocks and minerals for planetary analog use” authored by Gen Ito and colleagues evaluates the benefits and limitations of three remote sensing methods for mapping key minerals and capturing rock diversity in three regions of the Altiplano-Puna Volcanic Complex in Chile, which has been using as analogue for planetary studies.

The manuscript is well organised and presented, very well written and illustrated. I believe it is an important contribution and will attract the interest of a broad range of researchers. There are only minor issues that need to be addressed prior to publication:

• Line 14: replace “expansive” by “extensive” and the preposition “on” by “of”.
• Line 71: the number of the reference does not match with the reference listed, e.g., the reference 13 is “Ruff, S. W.; Farmer, J. D. Silica deposits on Mars with features resembling hot spring biosignatures at El Tatio in Chile. Nature 770 Comm. 2016”, not “Aert et al. [13]” as written in the body of the text.
• In the same line, fix the numbers for Flahaut et al. [17], Ruff et al. [20] (same issue as above).
• Line 442: replace “petrological analysis” by “geochemical analysis”, as you are refereeing to chemical compositions, not mineralogy.
• Line 494-Table 2: as above.
• Line 646: Fix the format of the references: “Christensen et al., 2004; Murchie et al., 2007.” You should use an index, not the year, to be consistent with the rest of the text.
• Line 683: replace “measurements” by “geochemical analysis”.

I congratulate the authors for the high-quality work and recommend its acceptance for publication once the issues above were addressed.

Carlos

Comments for author File: Comments.pdf

Author Response

Dear Carlos (Reviewer 1),

We greatly appreciate your constructive comments and a careful inspection of our manuscript. We are humbled by your positive remarks. Below, we provide responses in red to each bullet point comment that you have provided.

We are grateful for your time and effort in reviewing our manuscript. We thank you again.

Sincerely,

On behalf of all authors,

Gen Ito

The manuscript “Remote sensing survey of Altiplano-Puna Volcanic Complex 2 rocks and minerals for planetary analog use” authored by Gen Ito and colleagues evaluates the benefits and limitations of three remote sensing methods for mapping key minerals and capturing rock diversity in three regions of the Altiplano-Puna Volcanic Complex in Chile, which has been using as analogue for planetary studies.

The manuscript is well organised and presented, very well written and illustrated. I believe it is an important contribution and will attract the interest of a broad range of researchers. There are only minor issues that need to be addressed prior to publication:

• Line 14: replace “expansive” by “extensive” and the preposition “on” by “of”.

Both changes have been implemented.

• Line 71: the number of the reference does not match with the reference listed, e.g., the reference 13 is “Ruff, S. W.; Farmer, J. D. Silica deposits on Mars with features resembling hot spring biosignatures at El Tatio in Chile. Nature 770 Comm. 2016”, not “Aert et al. [13]” as written in the body of the text.
• In the same line, fix the numbers for Flahaut et al. [17], Ruff et al. [20] (same issue as above).

There was a mix up of reference orders and one missing on line 71. The correct numbering is “Ruff et al. [13], Aerts et al. [17], Flahaut et al. [20,21].” This has been corrected and reference ordering has been shifted from 21 to 32 as former reference number 32 was supposed to be number 21 (Lines 72, 96, 99–100, 102, 112, 121–122, 257, 442, 447, 461, 620–621, 626, 637, 703–704, 709).

• Line 442: replace “petrological analysis” by “geochemical analysis”, as you are refereeing to chemical compositions, not mineralogy.

This change has been implemented.

• Line 494-Table 2: as above.

This change has been implemented.

• Line 646: Fix the format of the references: “Christensen et al., 2004; Murchie et al., 2007.” You should use an index, not the year, to be consistent with the rest of the text.

These two references were missing. We added the two references in the reference list and updated reference numbers accordingly (lines 656–662, 673, 679, 917–923).

• Line 683: replace “measurements” by “geochemical analysis”.

This change has been implemented.

I congratulate the authors for the high-quality work and recommend its acceptance for publication once the issues above were addressed.

Reviewer 2 Report

I reviewed, “Remote sensing survey of Altiplano-Puna Volcanic Complex rocks and minerals for planetary analog use,” by Ito, Flahaut, González-Maurel, Godoy, Payet, and Barthez.  The article details remote sensing (RS) mineral/chemical identification and quantification using a combination of RS data sets to broadly simulate planetary orbiter instruments.

Overall, I found the article to be very well written.  As I read and had questions, I found them answered later or a quick reread of the methods answered them.  The manuscript details a considerable amount of work done on a relatively geologically unexplored location on Earth, and that alone I think gives the article value. I do have questions about how applicable what was done in the article is to Mars given our current lack of ground truth there.  The quantifications done on the “simulated probe” would likely not hold on Lunar or Martian instruments (or would have much less certainty).  The article (in many ways) sets up a situation of “what would a field site on Earth look like using a planetary orbiter” rather than the reverse.  That said, in a qualitative sense (e.g. mineral ID), it does have application and it opens the door for further study and is a step in the direction planetary work is trying to go.  The emphasis on band maths is a good reminder for some of us that tend to only look at features in spectra.  I would love to see a Martian case study as a future follow-up.  I have a few questions and comments:

Why wasn’t ASTER SWIR or VIS used?  I think these have higher spatial resolution.  The article should comment as to why they were not chosen.

Line 54: Consider “…lava fields in the western United States (e.g. Craters of the Moon National Monument, Idaho)[8–12].”  If the current refs do not cover it, there are several that are easy to find to add.  That site is seeing much recent attention.

Line 107: Reads, “The green vegetation band ratio is subtracted again to remove effects of vegetation.”  Since the effects of vegetation can never be fully removed (at least in the present approach), the authors might consider  ”…to further mitigate effects of vegetation.”  Or similar.

Where calculated quantifications are used that are not based directly on ground truth, I think care should be taken to point out they are estimates or approximate.  For example, in Figure 2, “(f) ASTER silica percentage,” the authors might consider something like “(f) estimated silica from ASTER imagery”

The article has a few typos and minor grammar issues, many having to do with singular vs. plural.  For example, Lines 511-513: Reads as,

“The result did not yield a significant trend in ASTER vs. sample differences as a function of silica content, however, the overall agreement was lower than equation 3 that excluded ultramafics (Table A3). For this reason, estimations based on equation 3 is preferred.”

I believe in the first sentence, the second clause supports the first.  Therefore (if that is the case), the “however” should just be an “and”.  In the second sentence, it should be, “…estimations based on equation 3 are preferred.” 

Another example are the subheading numbers in section 3 are incorrect.  Section 3.1.2 shows up 4 times!

Figure 2.  More obvious outlining/noting of the field areas would be very welcome.  It is hard to see.

In Figures 5 & 6, outlines/footprints of the sweeps in the SAM panel would be helpful.  In the other panels and figures it is more obvious, but not here.

Author Response

Dear Reviewer 2,

Thank you very much for your insightful comments and a careful inspection of our manuscript. Your remarks, particularly on follow-up future study, are inspirational for us. Below, we provide responses in red text to comments that you have provided.

We are grateful for your time and effort in reviewing our manuscript. We thank you again.

Sincerely,

On behalf of all authors,

Gen Ito

I reviewed, “Remote sensing survey of Altiplano-Puna Volcanic Complex rocks and minerals for planetary analog use,” by Ito, Flahaut, González-Maurel, Godoy, Payet, and Barthez. The article details remote sensing (RS) mineral/chemical identification and quantification using a combination of RS data sets to broadly simulate planetary orbiter instruments.

Overall, I found the article to be very well written.  As I read and had questions, I found them answered later or a quick reread of the methods answered them.  The manuscript details a considerable amount of work done on a relatively geologically unexplored location on Earth, and that alone I think gives the article value. I do have questions about how applicable what was done in the article is to Mars given our current lack of ground truth there.  The quantifications done on the “simulated probe” would likely not hold on Lunar or Martian instruments (or would have much less certainty).  The article (in many ways) sets up a situation of “what would a field site on Earth look like using a planetary orbiter” rather than the reverse.  That said, in a qualitative sense (e.g. mineral ID), it does have application and it opens the door for further study and is a step in the direction planetary work is trying to go.  The emphasis on band maths is a good reminder for some of us that tend to only look at features in spectra.  I would love to see a Martian case study as a future follow-up.  I have a few questions and comments:

Why wasn’t ASTER SWIR or VIS used?  I think these have higher spatial resolution.  The article should comment as to why they were not chosen.

We inserted a sentence at the end of the first paragraph of section 2.2 to address this question as, “The VNIR-SWIR bands of ASTER are not used in this work because the mineralogical information that can be derived from them are redundant to or less informative than the OLI+Hyperion combination considering spectral resolution, wavelength coverage, spatial resolution, and spatial coverage (one minor benefit is 15 m/pixel resolution but only in bands 1–3; other bands have 30 m/pixel resolution)” (Lines 184–189).

Line 54: Consider “…lava fields in the western United States (e.g. Craters of the Moon National Monument, Idaho)[8–12].”  If the current refs do not cover it, there are several that are easy to find to add.  That site is seeing much recent attention.

This suggestion has been applied.

Line 107: Reads, “The green vegetation band ratio is subtracted again to remove effects of vegetation.”  Since the effects of vegetation can never be fully removed (at least in the present approach), the authors might consider  ”…to further mitigate effects of vegetation.”  Or similar.

This suggestion has been applied (I believe it was line 170 instead of 107).

Where calculated quantifications are used that are not based directly on ground truth, I think care should be taken to point out they are estimates or approximate.  For example, in Figure 2, “(f) ASTER silica percentage,” the authors might consider something like “(f) estimated silica from ASTER imagery”

This suggestion has been applied in the Figure 2 caption. It has been applied to other similar occurrences (lines 327, 338, 366–367, 436). 

The article has a few typos and minor grammar issues, many having to do with singular vs. plural. For example, Lines 511-513: Reads as,

“The result did not yield a significant trend in ASTER vs. sample differences as a function of silica content, however, the overall agreement was lower than equation 3 that excluded ultramafics (Table A3). For this reason, estimations based on equation 3 is preferred.”

I believe in the first sentence, the second clause supports the first. Therefore (if that is the case), the “however” should just be an “and”. In the second sentence, it should be, “…estimations based on equation 3 are preferred.”

These corrections have been applied on lines 511–513. Other similar occurrences have been corrected as well (lines 283, 375).

Another example are the subheading numbers in section 3 are incorrect.  Section 3.1.2 shows up 4 times!

This mistake has been corrected.

Figure 2.  More obvious outlining/noting of the field areas would be very welcome.  It is hard to see.

Outlines of the three regions of interest have been enhanced. The same enhancement has also been applied to Figure A1.

In Figures 5 & 6, outlines/footprints of the sweeps in the SAM panel would be helpful.  In the other panels and figures it is more obvious, but not here.

This suggestion has been implemented.

Reviewer 3 Report

Interesting and relevant study on geological remote sensing of a potential Martian analog field site. Worthy of publishing but some English expression, equation descriptions and references need improving. Also an improvement of the provided published geological mapping is needed, at least with the major units labelled and referred to within the text (Fig A1b).

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 3,

Thank you very much for a thorough review of our manuscript. Below, we indicate improvements made in the manuscript considering your suggestions provided in the pdf file.

We are grateful for your time and effort in reviewing our manuscript. We thank you again.

Sincerely,

On behalf of all authors,

Gen Ito

Line 28: “synthetic” was changed to “integrated” (new line 29).

Line 44: Website addresses were inserted for references 1–4 in the reference list (new lines 780–788).

Lines 56–59: The sentence was restructured to, “Other analog studies focused on geochemical aspects of volcanic fields, mainly alterations of minerals and rocks. For example, at the Atacama Desert of northern Chile, Ruff et al. [13] investigated silica deposits of El Tatio hydrothermal field that closely resembled observations made by the Mars Exploration Rover. Flahaut et al. [14] and Yant et al. [15] compared the Solfatara volcanic crater in central Italy and Kilauea’s December 1974 Flow in Hawai’i, respectively, to fumarolic alterations on Mars” (new lines 58–63).

Lines 79–86: The sentence was restructured to, “We use Landsat 8 Operational Land Imager (OLI) visible near-infrared (VNIR; 0.5–0.9 µm) and shortwave infrared (SWIR; 1.2–2.5 µm) bands, Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) thermal infrared (TIR; 8–15 µm) bands, and Earth Observing-1 (EO-1) Hyperion VNIR-SWIR bands to simulate a set of instruments available on lunar and Martian orbiters. This set of instruments covers wide ranges of wavelength, spectral resolution, spatial coverage, and spatial resolution, and the instruments complement each other’s strengths and weaknesses” (new lines 80–87).

Line 87: Labels were added to Figure A1b and the caption was updated to “(b) Geological map of Chile from Servicio Nacional de Geología y Minería [63]. Some geological units and features mentioned in the main text are indicated. Red triangles indicate volcanoes: 1 Azufre and Chanka, 2 San Pedro-San Pablo and La Poruña, 3 Lascar, 4 El Negrillar. Full descriptions of the geological units are extensive, and the reader is referred to reference [69]” (new lines 771–774).

Line 122: Flahaut et al. (2022) was removed from the list of references. All references after [33] were renumbered accordingly.

Line 139: Website address of L3Harris ENVI software was added (new lines 140–141).

Line 164: The sentence was clarified as, “As done for index 4, the green vegetation band ratio is subtracted from the 2/1 band ratio to further mitigate effects of vegetation” (new lines 166–167).

Line 179: “Tradem” was changed to “Trade” (new line 181).

Line 223: Website address for the reference Payet et al. (2020) was added (new lines 890–891).

Line 232: References for FLAASH have been updated to [53–55] (new lines 235, 895–900).

Line 264: The term R_b in equation 4 was supposed to be R_c, and it was corrected.

Line 423: Labels were added to Figure A1b and the caption was updated to “(b) Geological map of Chile from Servicio Nacional de Geología y Minería [63]. Some geological units and features mentioned in the main text are indicated. Red triangles indicate volcanoes: 1 Azufre and Chanka, 2 San Pedro-San Pablo and La Poruña, 3 Lascar, 4 El Negrillar. Full descriptions of the geological units are extensive, and the reader is referred to reference [69]” (new lines 771–774).

Line 512: The term A₁ in equation 7 refers to the same A₁ in equation 2, and the following was added: “where A₁ is from equation 2” (new line 521).

Line 522: The confidence in feldspar detections using our spectral index in the VNIR-SWIR domain was demonstrated by ground-truthing (new lines 537–543; Figure 9). We added a sentence to clarify this: “These observations give confidence to feldspar detections based on the 1.3 µm spectral feature” (new lines 544–545). Additionally, we added the following sentences in the first paragraph of section 4.3 to acknowledge that feldspar and other silicate mineral identification can be done in the TIR domain, but current lack of hyperspectral TIR instruments leads to our chosen approach: “Often, the preferred approach for identifying feldspar or other silicate minerals is to detect the diagnostic reststrahlen bands in high spectral resolution TIR spectra (e.g., Lyon [42]), however, for both the Earth and Mars, orbital TIR hyperspectral imagery with high enough spatial resolution (10’s of m/pixel) does not currently exist. The combination of feldspar detections with the 1.3 µm spectral feature in hyperspectral VNIR-SWIR imagery and silica percentages derived from multispectral TIR imagery is a robust approach at the current moment (e.g., Rogers and Nekvasil [64]). The outcome of the preferred interpretations of feldspar detections on Mars has a major impact on our understanding of Martian geological history, and thus, follow-up investigations of the feldspar detections demonstrated in this work are crucial. We are planning to send a geological field expedition to the Dacite Dome D area to gather further ground-truth data” (new lines 635–645). We also emphasized that feldspar detections on Mars are based on VNIR-SWIR spectral analysis in section 2.3: “Additionally, we specifically searched for feldspar minerals as the geological interpretation of remote sensing detection of feldspar minerals in the VNIR-SWIR on Mars is a currently debated topic [31,32,62–65], and thus, a comparable detection of feldspars at the APVC is eminently beneficial” (new lines 259–262).

Line 610: “Map” was changed to “Mapping” (new line 616).

Line 614: “Reemphasis” was changed to “Re-emphasis” (new line 620).

Line 733: ID labels along with instrument and data type are enough information for acquisition identification. We updated Table A1 and verified that image ID’s in this table can correctly retrieve images from the shown four types of data on USGS EarthExplorer. Dates and times of images are not included in the table because they are not available on all images and redundant (dates are already in the ID for some and explanations are provided in EarthExplorer).