the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Feb 2023
Proposal of an instrument design to observe annual changes in Spectral Outgoing Radiation
Abstract. From the wide range of possibilities, we propose an instrument capable of measuring annual changes in global Spectral Outgoing Radiation (SORa) from the entire Earth's surface between 200 nm and 1100 nm with a stability of 0.1 Wm-2 over a period of one solar cycle or beyond. Photomultiplier tubes (PMTs) as detectors provide data with a cadence of one second and high dynamic range. Based on Total Solar Radiation TSI(t) data with a stability of 0.01 Wm-2 per year, Spectral Solar Irradiance SSI(t) can be derived and normalized to ΣSSI(t)=TSI(t) for using the Sun as a referenced radiation source supported by solar modeling. Calibrated by SSI(t), a set of 12 spectrometers with 60 PMTs in total and 16 photometers simultaneously detect SOR(t). This database can also be provided to calibrate other space instruments to allow improved comparison of results. In previous missions in space, it has already been shown that the spectrometer design can detect both solar and terrestrial radiation with high dynamic range. The established measurement technique compensates for degradation through repeated calibration. The instrument also enables the determination of the global green Earth coverage and its annual changes by measuring chlorophyll absorption from 350 nm to 490 nm and 620 nm to 690 nm and green backscatter from 500 nm to 600 nm. Mapping the Earth will also make it possible to track annual local changes in green coverage and to assess the impact of different climate policies and climate engineering actions. Another aspect is the derivation of a correction parameter for the Earth Energy Imbalance derived from changes in green areas. Data evaluation can also include determining further parameters such as the Normalized Difference Vegetation Index, the Enhanced Vegetation Index, and the Global Leaf Area Index.
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RC1: 'Comment on egusphere-2023-139', Anonymous Referee #1, 12 Apr 2023
This paper purportedly addresses Earth’s outgoing scattered radiation in the spectral range from 200-1100 nm using many instruments on a single payload to measure spectral (at some unknown resolution) and broad-band outgoing and incoming radiation. Unfortunately, the paper appears to be written rather hurriedly, making it nearly impossible to understand the full concept. In places where some aspects of the concept can be interpreted, it appears to be flawed. In order for readers to fully comprehended their instrument design, the paper needs to be rewritten in a more orderly way, and many additional details must be provided. (A few examples are in the listed comments below.)
Another major weakness, in addition to missing fundamental information like spectral resolution, is the complete lack of measurement and mission requirements that are justified to meet science requirements. Stability is the lone variable requirement listed but the origin of that requirement is not given. Nothing is said about accuracy or precision, as if they are irrelevant.
Another issue that need mentioning is that the measurement/instrument concept does not measure over the full shortwave spectrum nor does it measure Earth’s emitted radiation. As such, it is inadequate to address the Earth’s radiation imbalance. This is more of a minor comment – the authors mention energy imbalance only briefly – but considering the attention this topic is receiving in the peer-review literature, this should be recognized.
One final major point: it appears that a growing trend in the community is to submit measurement and mission concepts to the peer review literature before submitting those concepts to agencies that fund mission and instrument proposals. That is certainly fine, and in fact, welcome and encouraged, but the instrument concepts published in the peer-reviewed literature require much more detail than what is provided here. The rather ambiguous diagrams in this paper provide no insights into how a single instrument actually works, let alone several tens of instruments the authors propose. The authors even call this a "proposal" in the title. A journal paper is distinct from a proposal. (On the other hand, this does not really look like a proposal either.) I repeat what I state at the top, I think this was a hurried submission. The authors are a quite capable group of scientists. I encourage them to do a complete rewrite of this paper.
Below is a only small, partial list of specific items that either need addressing or reveal fundamental flaws. Upon fully and better articulating the proposed concept, a more thorough list may be compiled.
Line 8: “From the wide range of possibilities” Awkward start to abstract. Possibilities of what?
Line 29: I don’t understand the term in parentheses in “SOR (SORa)”.
Line 32: “The proposed instrument is equipped with simultaneously measuring 12 spectrometers and 16 photometers.” Perhaps: “The proposed instrument is equipped with 12 spectrometers and 16 photometers that make simultaneous measurements.”
Line 33: I have no idea what “20 radiation attenuators enable the adjustment of the Solar Spectral Irradiance SSI(t) to natural SOR values” means. (Edit: I think I understand after reading the entire paper that these are actually variable apertures. Those should not be called attenuators, a very misleading term.)
Line 34: Have not identified the subscript in SORa
Line 36: No analysis is provided to justify the adequacy the listed stability. This is, apparently a capability. What is required to meet the science goals?
Line 54: “Besides using a different measurement method”. Different from what?
Lines 79-87: This entire paragraph only superficially covers how the spectrometers will be calibrated using solar irradiance. The jump from TSI to SSI is insufficient to account for spectrally varying changes in either the instruments or the Sun.
Line 85: “Normalizing TSI(t) to ΣSSI(t) adjusts the stability of both quantities so that in-space spectrometers and photometers can be calibrated with high stability to compensate for the instrument degradation.” No, this is very misleading. This can only be applied uniformly across the spectrum but instrument degradation will have a wavelength dependance, as will solar variability and both of those are indistinguishable.
Lines 88-95: This paragraph is essentially incomprehensible. It appears to use a combination of solar irradiance models and a fixed TSI measurement, neither of which is accurate enough to account for solar variability required to meet the specified stability. I trust that the authors have something else in mind but I was unable to decipher that from what was written.
Line 96: How does one account for the bandpass filter shapes and the fact that they will change over time?
Line 113: Absorption by water vapor is curiously missing from this sentence.
Page 5: Much of what is on this page reads as though it is from someone’s notes rather than text for a peer-reviewed manuscript.
Line 172: “The spectral resolution should be adjusted to the requirements of the spectral regions of the observables.” What are those requirements and what drives them?
Line 173-176: This works only if the sole source of instability is gaussian-distributed noise. There will be many other sources of instability.
Line 188: “Changes in TSI(t) cause corresponding changes in SSI(t) and SOR(t).” But the spectral compositions of those changes is unknown. Seen comment on L. 79.
Line 288: One of the co-authors (Jacobi) is listed in acknowledgements. It should be one or the other, not both.
Citation: https://doi.org/10.5194/egusphere-2023-139-RC1 -
AC1: 'Reply on RC1', Gerhard Schmidtke, 17 Apr 2023
Dear Referee #1,
I would like to thank you for your thorough work, because you gave good tips to better explain the content of the manuscript to outsiders. The procedure is simple: With the SOLACER instrument we get SSI(t) very precisely and can use it to calibrate SORACES and compensate for the degradation. And the adjustment of the radiation levels SSI versus SOR succeeds with the metallic attenuators.
With best regards,
Gerhard Schmidtke. -
AC4: 'Reply on RC1', Gerhard Schmidtke, 24 Apr 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-139/egusphere-2023-139-AC4-supplement.pdf
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AC1: 'Reply on RC1', Gerhard Schmidtke, 17 Apr 2023
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AC2: 'Comment on egusphere-2023-139', Gerhard Schmidtke, 27 Apr 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-139/egusphere-2023-139-AC2-supplement.pdf
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AC3: 'Comment on egusphere-2023-139', Gerhard Schmidtke, 28 May 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-139/egusphere-2023-139-AC3-supplement.pdf
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RC2: 'Comment on egusphere-2023-139', Sebastian Schmidt, 19 Feb 2024
Publisher’s note: a supplement was added to this comment on 26 February 2024.
See attachment.
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AC5: 'Reply on RC2', Gerhard Schmidtke, 24 Apr 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-139/egusphere-2023-139-AC5-supplement.pdf
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AC5: 'Reply on RC2', Gerhard Schmidtke, 24 Apr 2024
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