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Peer review report 1 On “Tracing the Flow of Carbon Dioxide and Water Vapor between the Biosphere and Atmosphere: A Review of Optical Isotope Techniques and their Application”
Agricultural and Forest Meteorology 201S (2015) 531–532
Contents lists available at ScienceDirect
Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet
Peer Review Report
Peer review report 1 On “Tracing the Flow of Carbon Dioxide and Water Vapor between the Biosphere and Atmosphere: A Review of Optical Isotope Techniques and their Application”
Original Submission Recommendation Major Revision Comments to Author The ms presents a summary of outcomes from mostly the first generation of optical instruments (line 171, TDLAS, Campbell Sci.) for use in stable isotope field studies of water vapour and carbon dioxide, and application of stable isotopes in micrometeorology, to both of which the author and colleagues made significant research contributions in the past decade. The author is an authority on the topic of the ms, with published work on use of optical systems for co2 and h2o isotope research, and relevant micrometeorological methods. The ms leaves me with a split opinion. The discussion and summary of relevant optical implementations and their outcomes are really useful, but the discussion on optical measurement technology is poorly structured and imprecise; the recommendations for future research made here bring little additional insights following recent papers/reviews, nor brings much direction and recommendations for development of new micro-meteorological approaches. Last, I strongly urge the author to critically review if relevant other works were missed in his review study. The ms would require fundamental change, for which I argument with following comments: 1. The reference to technology throughout the text seems imprecise, perhaps incomplete, and appears more structured according to availability on the commercial market for environmental research instruments. Section 3 and further; TDLAS, QCL, CWL, OA-ICOS, are introduced as if they are fundamentally different systems. They are not. TDLAS and QCL are different lasers, which could be the light source for ICOS cells or FTIR measurement if the engineers
DOIs of published articles: http://dx.doi.org/10.1016/j.agrformet.2013.02.008, http://dx.doi.org/10.1016/j.agrformet.2013.02.009 0168-1923/$ – see front matter http://dx.doi.org/10.1016/j.agrformet.2015.07.201
had decided so. For instance line 249 “CRDS is a TDLAS approach” is a flawed definition. And, not only TD lasers and detectors for water vapor need cryogenic cooling (line 194-197). Laser temperature stability is not the only or primary engineering improvement (line 481). TDLAS, QCL, CWL are acronyms for lasers, with more acronyms bound to join in the rapid field of laser engineering. FTIR and Cavity ring-down are different approaches for signal integration. Presenting strict distinction between technologies and their acronyms, while comparing different engineering components will confuse the reader and may make the work obsolete by the time it reaches its audience. Same is true for the reference to specific models marketed for use in environmental studies of stable isotopes. As the author notes, the TDLAS instrument models as used in the majority of the cited works are no longer manufactured. I strongly suggest to revise the ms and give an accurate account on the current technology and their components. In addition, I think that mentioning technologies per study in section 4 and 5 is not at all that relevant - only their outcomes are. 2. I think the ms does not sufficiently address how to properly implement the optical “new tools” for isotopic measurement in the field or micrometeorology (thus, failing objective 1, line 53). It would have been a useful addition to discuss methods of characterization of a systems performance, and how to interpret them. Because the performance of a TDLAS in one study is no indication for another or another instrument using TD lasers. No TD laser is ever produced with the same specifications, nor any LAS system in the used literature was implemented in exactly the same way in the field. This really limits the usefulness of defining precisions for TDLAS, QCL, CWL based lasers, or other used technology (like ICOS, FTIR), or refering to studies by their laser technology (section 4,5). I think the ms does too little to inform the reader on value of the numbers mentioned in literature on measurement precision, particularly when awareness on how to report measurement quality (e.g. Werle et al., 2004, 2010) came later. A specific mentioning goes to integration times behind precision numbers. For IRMS this works from sample statistics, but for LAS a precision number is not usable for atmospheric applications without indication on how it was derived (integration time, source). Table 2 summarized such numbers, but from where? And why not down to the 1H/10 Hz range? Also, precision is one aspect, memory effects (instrument, setup) another. This received little
532
Peer Review Report / Agricultural and Forest Meteorology 201S (2015) 531–532
attention, unfortuneately, and a recommendation would be simple: without guaranteed turbulent flow up to the end of the measurement cell one should stay away from EC applications, even if the instrument is capable of outputting >1 Hz. Adding words on memory effects and use of long known and standardised ways to characterise systems performance may actually lead to a more critical review of key works getting much attention here. Only the instrument output is found to be the limitation (line 375385) for EC? This is not the conclusion of other recentliterature. I suggest to aggregate and generalize the accuracy and precision numbers, and add text to inform the “non-specialist” of the need to know how an instrument actually preforms in the field or the lab. 4. Tables & Figures: I see little added value for the figures. These are either reproduced, or not discussed in enough detail. I suggest to remove them. The tables would need references. A tool can hardly be called new (title) if already used for nearly a decade, nor are the discussed micro-meteorological approaches very new. Also, in other interpretations of new: the combination of co2 and water vapor isotopes was the topic of other recent reviews, and this ms, I think the ms brings limited new insights to call a combination use ‘new’. More than half of the text is a discussion of isotope applications in micrometeorolog (objective 2, line 51), which is poorly expressed in the title. I suggest to remove the word “optical” and the part after the colon from the title. We should expect a review to be an objective and representative discussion of relevant works, and inclusive from a broad range of sources - especially from an established authority in a field of research. Much of the discussed papers stay ‘close to home’ between the author, his collaborators and the people acknowledged (line 1077). From about 180 citations I would estimate a quarter to be citations to work of this group. Not surprising, considering the huge contribution of these researchers to this field of science in the last decade. But it would be a pity if the reader is left with the wrong impression of bias which I am sure the author had not intended. I think there are much more recent works on carbon dioxide and water vapor isotope fluxes (or micromet measurement using novel optical systems) worth discussing than a quick review of the reference list would suggest. For example, did Hogberg, Lai, Gamnizer, Bahn, Kayler, Seibt, McDowell, Pumpanen, Moyes, Bond, Epron, Dawson, and colleagues not add some insights to micromet approaches too? These may not all have been optical instrument approaches, but the ms reviews a mix of IRMS and LAS based studies already in section 5. Also, the reader is made aware of technical advances on the forefront of LAS systems for continuous isotope measurements, such as using QCL. I am surprised to see no works of Nelson/Zahniser (or Tuscon/Mohn) mentioned for application of QCL-based instruments, other feasibility studies of QCL technology are (e.g. involving the author, line 1070). The final highlight is discussed in 7 lines (1059-1065) and a figure that receives minimal attention. This seems short on a 1000+ line ms. Please remove the highlight on virtual studies. 8. Section 5 may benefit from adding subsection structure.
Minor comments Title: “New tools”. the abstract informs on data-sets extending the 5-year mark. Are these still ‘new tools’ when the first generation instruments are being retired? Line 48-49. A special issue was dedicated to this recently, but only one work is cited here. http://www.biogeosciences.net/special issue87.html Line 85. Were these the first to use this? Line 93. remote “and is multiplied. the result”. More accurate would be to define “per mil” with a value of 10-3. Only on a pocket calculator we multiply by a number to get % or permil. Line 96. I suggest to add Tyler Coplon’s recent “Protocol” work in RCM. This includes a long discussion of stable isotope expression. doi: 10.1002/rcm.5129 Line 128. “using” to “to use” Line 132. Is this method still used? For co2 the current alternative is mentioned, why not for water? Line 138. Issues with water vapour happen to LAS too, e.g. interference. I did not find it discussed, beyond calibration systems for water vapour. Line 146-153. The numbers are not well specified, nor compared to a similar LAS setup. Forinstance: A LAS setup is still not for sale for $5000, so what is “relatively” low cost? An IRMSand top line LAS could both be found for 200k. Also, does 2.6 M include a new IRMS lab or only operational cost and labour? I suggest to remove or shorten the line section. Line 314. Mohn et al showed this in 2007 or 2008, with better precision. Line 316. are the wavelengths at all relevant? Line 436. It would benefit from a textbook reference. Line 651. Interesting point! Line 658. Citation order reversed. Line 235: “delta stretching” seems to be jargon. Reference? Table 1, where are these numbers coming from? Did the author derive these (here or in his 2004a work)? I don’t think the author is a authority on the VSMOW or VPDB standards (table 1), I suggest using another reference. Table 2 presents manufacturer numbers, not representative for field application or a specificsetup. It would not be wise to let the reader believe this is the number to report in publication. What is the source of these numbers? Figure 3 The figure is only very briefly discussed. I suggest to remove it. Also, consider adding.the time as annotation, simplifying the caption. Figure 4 There are no errorbars on the Fn and Fr scales. Line 634 states variability in the.delta R is of importance, then please add information on confidence intervals of the derived F R. Figure 5 6, 7: Reproduced. I do not see why the figures needs to be added to support the text. Figure 9, provided with little detail in the text. suggest to remove Anonymous Available online 6 August 2015
Contents lists available at ScienceDirect
Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet
Peer Review Report
Peer review report 1 On “Tracing the Flow of Carbon Dioxide and Water Vapor between the Biosphere and Atmosphere: A Review of Optical Isotope Techniques and their Application”
Original Submission Recommendation Major Revision Comments to Author The ms presents a summary of outcomes from mostly the first generation of optical instruments (line 171, TDLAS, Campbell Sci.) for use in stable isotope field studies of water vapour and carbon dioxide, and application of stable isotopes in micrometeorology, to both of which the author and colleagues made significant research contributions in the past decade. The author is an authority on the topic of the ms, with published work on use of optical systems for co2 and h2o isotope research, and relevant micrometeorological methods. The ms leaves me with a split opinion. The discussion and summary of relevant optical implementations and their outcomes are really useful, but the discussion on optical measurement technology is poorly structured and imprecise; the recommendations for future research made here bring little additional insights following recent papers/reviews, nor brings much direction and recommendations for development of new micro-meteorological approaches. Last, I strongly urge the author to critically review if relevant other works were missed in his review study. The ms would require fundamental change, for which I argument with following comments: 1. The reference to technology throughout the text seems imprecise, perhaps incomplete, and appears more structured according to availability on the commercial market for environmental research instruments. Section 3 and further; TDLAS, QCL, CWL, OA-ICOS, are introduced as if they are fundamentally different systems. They are not. TDLAS and QCL are different lasers, which could be the light source for ICOS cells or FTIR measurement if the engineers
DOIs of published articles: http://dx.doi.org/10.1016/j.agrformet.2013.02.008, http://dx.doi.org/10.1016/j.agrformet.2013.02.009 0168-1923/$ – see front matter http://dx.doi.org/10.1016/j.agrformet.2015.07.201
had decided so. For instance line 249 “CRDS is a TDLAS approach” is a flawed definition. And, not only TD lasers and detectors for water vapor need cryogenic cooling (line 194-197). Laser temperature stability is not the only or primary engineering improvement (line 481). TDLAS, QCL, CWL are acronyms for lasers, with more acronyms bound to join in the rapid field of laser engineering. FTIR and Cavity ring-down are different approaches for signal integration. Presenting strict distinction between technologies and their acronyms, while comparing different engineering components will confuse the reader and may make the work obsolete by the time it reaches its audience. Same is true for the reference to specific models marketed for use in environmental studies of stable isotopes. As the author notes, the TDLAS instrument models as used in the majority of the cited works are no longer manufactured. I strongly suggest to revise the ms and give an accurate account on the current technology and their components. In addition, I think that mentioning technologies per study in section 4 and 5 is not at all that relevant - only their outcomes are. 2. I think the ms does not sufficiently address how to properly implement the optical “new tools” for isotopic measurement in the field or micrometeorology (thus, failing objective 1, line 53). It would have been a useful addition to discuss methods of characterization of a systems performance, and how to interpret them. Because the performance of a TDLAS in one study is no indication for another or another instrument using TD lasers. No TD laser is ever produced with the same specifications, nor any LAS system in the used literature was implemented in exactly the same way in the field. This really limits the usefulness of defining precisions for TDLAS, QCL, CWL based lasers, or other used technology (like ICOS, FTIR), or refering to studies by their laser technology (section 4,5). I think the ms does too little to inform the reader on value of the numbers mentioned in literature on measurement precision, particularly when awareness on how to report measurement quality (e.g. Werle et al., 2004, 2010) came later. A specific mentioning goes to integration times behind precision numbers. For IRMS this works from sample statistics, but for LAS a precision number is not usable for atmospheric applications without indication on how it was derived (integration time, source). Table 2 summarized such numbers, but from where? And why not down to the 1H/10 Hz range? Also, precision is one aspect, memory effects (instrument, setup) another. This received little
532
Peer Review Report / Agricultural and Forest Meteorology 201S (2015) 531–532
attention, unfortuneately, and a recommendation would be simple: without guaranteed turbulent flow up to the end of the measurement cell one should stay away from EC applications, even if the instrument is capable of outputting >1 Hz. Adding words on memory effects and use of long known and standardised ways to characterise systems performance may actually lead to a more critical review of key works getting much attention here. Only the instrument output is found to be the limitation (line 375385) for EC? This is not the conclusion of other recentliterature. I suggest to aggregate and generalize the accuracy and precision numbers, and add text to inform the “non-specialist” of the need to know how an instrument actually preforms in the field or the lab. 4. Tables & Figures: I see little added value for the figures. These are either reproduced, or not discussed in enough detail. I suggest to remove them. The tables would need references. A tool can hardly be called new (title) if already used for nearly a decade, nor are the discussed micro-meteorological approaches very new. Also, in other interpretations of new: the combination of co2 and water vapor isotopes was the topic of other recent reviews, and this ms, I think the ms brings limited new insights to call a combination use ‘new’. More than half of the text is a discussion of isotope applications in micrometeorolog (objective 2, line 51), which is poorly expressed in the title. I suggest to remove the word “optical” and the part after the colon from the title. We should expect a review to be an objective and representative discussion of relevant works, and inclusive from a broad range of sources - especially from an established authority in a field of research. Much of the discussed papers stay ‘close to home’ between the author, his collaborators and the people acknowledged (line 1077). From about 180 citations I would estimate a quarter to be citations to work of this group. Not surprising, considering the huge contribution of these researchers to this field of science in the last decade. But it would be a pity if the reader is left with the wrong impression of bias which I am sure the author had not intended. I think there are much more recent works on carbon dioxide and water vapor isotope fluxes (or micromet measurement using novel optical systems) worth discussing than a quick review of the reference list would suggest. For example, did Hogberg, Lai, Gamnizer, Bahn, Kayler, Seibt, McDowell, Pumpanen, Moyes, Bond, Epron, Dawson, and colleagues not add some insights to micromet approaches too? These may not all have been optical instrument approaches, but the ms reviews a mix of IRMS and LAS based studies already in section 5. Also, the reader is made aware of technical advances on the forefront of LAS systems for continuous isotope measurements, such as using QCL. I am surprised to see no works of Nelson/Zahniser (or Tuscon/Mohn) mentioned for application of QCL-based instruments, other feasibility studies of QCL technology are (e.g. involving the author, line 1070). The final highlight is discussed in 7 lines (1059-1065) and a figure that receives minimal attention. This seems short on a 1000+ line ms. Please remove the highlight on virtual studies. 8. Section 5 may benefit from adding subsection structure.
Minor comments Title: “New tools”. the abstract informs on data-sets extending the 5-year mark. Are these still ‘new tools’ when the first generation instruments are being retired? Line 48-49. A special issue was dedicated to this recently, but only one work is cited here. http://www.biogeosciences.net/special issue87.html Line 85. Were these the first to use this? Line 93. remote “and is multiplied. the result”. More accurate would be to define “per mil” with a value of 10-3. Only on a pocket calculator we multiply by a number to get % or permil. Line 96. I suggest to add Tyler Coplon’s recent “Protocol” work in RCM. This includes a long discussion of stable isotope expression. doi: 10.1002/rcm.5129 Line 128. “using” to “to use” Line 132. Is this method still used? For co2 the current alternative is mentioned, why not for water? Line 138. Issues with water vapour happen to LAS too, e.g. interference. I did not find it discussed, beyond calibration systems for water vapour. Line 146-153. The numbers are not well specified, nor compared to a similar LAS setup. Forinstance: A LAS setup is still not for sale for $5000, so what is “relatively” low cost? An IRMSand top line LAS could both be found for 200k. Also, does 2.6 M include a new IRMS lab or only operational cost and labour? I suggest to remove or shorten the line section. Line 314. Mohn et al showed this in 2007 or 2008, with better precision. Line 316. are the wavelengths at all relevant? Line 436. It would benefit from a textbook reference. Line 651. Interesting point! Line 658. Citation order reversed. Line 235: “delta stretching” seems to be jargon. Reference? Table 1, where are these numbers coming from? Did the author derive these (here or in his 2004a work)? I don’t think the author is a authority on the VSMOW or VPDB standards (table 1), I suggest using another reference. Table 2 presents manufacturer numbers, not representative for field application or a specificsetup. It would not be wise to let the reader believe this is the number to report in publication. What is the source of these numbers? Figure 3 The figure is only very briefly discussed. I suggest to remove it. Also, consider adding.the time as annotation, simplifying the caption. Figure 4 There are no errorbars on the Fn and Fr scales. Line 634 states variability in the.delta R is of importance, then please add information on confidence intervals of the derived F R. Figure 5 6, 7: Reproduced. I do not see why the figures needs to be added to support the text. Figure 9, provided with little detail in the text. suggest to remove Anonymous Available online 6 August 2015