the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Mar 2025
Joint observations of oxygen atmospheric band emissions using OSIRIS and the MATS satellite
Abstract. The MATS (Mesosphere, Airglow/Aerosol, Tomography & Spectroscopy) satellite was launched in November 2022 and began collecting scientific measurements of the Mesosphere and Lower Thermosphere (MLT) in early 2023. The satellite utilises a multichannel limb-viewing instrument designed to gather images across six distinct spectral bands, each selected to capture atmospheric airglow from O2 atmospheric band emissions as well as light scattered by noctilucent clouds (NLC). This article presents a comparison between the MATS limb measurements and the observations made by the OSIRIS spectrograph on the Odin satellite. Specifically, airglow signals from excited O2, as recorded by MATS infrared (IR) channels and OSIRIS, are analysed over the polar regions under temporally and spatially aligned conditions. From December 2022 to February 2023, 36 close encounters of the two satellites were identified and analysed. The results show that the two instruments agree well on the overall structure but that the MATS signals generally exceed OSIRIS by ~20 % in magnitude. OSIRIS measurements are also compared to the radiative transfer model SASKTRAN, to investigate straylight impact on the measurements.
Competing interests: JG is a member of the editorial board of Atmospheric Measurement Techniques
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2025-493', Jaroslav Chum, 02 Apr 2025
General comment
The manuscript compares the intensities of atmospheric band of O2 air glow emission measured simultaneously by OSIRIS and MATS satellite. I believe that independent simultaneous measurements of air glow intensities are useful and interesting for community analyzing and interpreting the airglow data and I consider the topic suitable for Atmospheric Measurement Techniques. There are, however, several points that should be addressed more carefully before the publication. See the specific comments.
Specific comments
-Introduction, line 24, “As the scanning height of the instrument reaches high altitudes…” Specify the heights.
-Section 2.1, line 57, “MATS operates in a dawn-dusk Sun-synchronous orbit…” The dawn-dusk sector is rather atypical for airglow measurements. It would be useful to discuss/explain the reason for selecting such an orbit.
- Section 2.1, It would be good to specify the spectral ranges of all IR filters/channels here in this Section. A short note about the remaining channels (5, 6) would also be useful.
-Section 3.3. line 158. “…40 to 60 km (Figures 4a and 4c).”. I would say that Figure 4 displays the selected parameters from 45 km (not from 40 km.)
-Figure 4. The correspondence between Figure 4b and 4a is clear. The difference between OSIRIS measurement and SASKTRAN model is negligible for altitudes up to nearly 70 km in both Figures. However, the correspondence between Figures 4d and 4c is not so clear. The curves in Figure 4c merge at lower altitudes, whereas the differences in Figure 4d increases at lower altitudes, namely the difference for albedo=0. Is it just because of the logarithmic scale on the horizontal axis, or is it something wrong here? Some explaining comments and/or another way of displaying would be useful.
-Section 4, line 176, “433 MATS dayglow images”. There is 1333 in Table 1. What is correct?
-Section 5, line 220, “Figures 7a and 7b were made on 11 January 2023”. There is 15 January above Figure 7b.
-Figure 7 caption. “The right column is from a conjunction on 9 January 2023 while the right column is from 25 January 2023”. There is two times right column in this sentence and there are other dates above the plots. It should be corrected!
-Section 5.1, line 236, “relative difference for both channels” Should not be ratio? Specify!
Minor comments
-line 127, of 750 to 775 nm -> from 750 to 775 nm
Citation: https://doi.org/10.5194/egusphere-2025-493-RC1 -
RC2: 'Comment on egusphere-2025-493', Anonymous Referee #1, 04 Apr 2025
General comments:
The manuscript describes an evaluation of limb radiance measurements of the O2 atmospheric band near 760 nm taken with the multi-channel imager of the MATS satellite launched in November 2022. The data are compared with spectra of the limb profiler OSIRIS on the Odin satellite (launched in February 2001) in the same wavelength range. Only a small sample of 20 dayglow and 16 nightglow coincidences with sufficient agreement in time and location could be selected. On average, the O2 limb radiance is about 20% higher than in the case of OSIRIS. It is assumed that differences in the absolute calibration are the most likely explanation for the discrepancies. However, the impact of stray light remains uncertain for both instruments, even with radiative transfer calculations with SASKTRAN.
For research in the Earth's mesosphere and lower thermosphere, MATS is a promising mission. Therefore, I appreciate the submission of the manuscript by Linder et al. to AMT as it allows insights in the performance of MATS. Nevertheless, I would like to see some improvements before the start of the publication process. In particular, the design of the investigation could be better motivated. Some clarifications might be provided by another MATS-related manuscript submitted by Megner et al.. However, the present manuscript should be sufficiently self-explanatory.
Specific comments:
- Sect.1: The introduction only describes MATS and OSIRIS in a rather technical way. For a better understanding of the goals of these airglow-observing instruments and the importance of tackling the calibration issues, it would be helpful to discuss them in a broader context. There is no information on other satellite missions (or maybe ground-based observations, although the A-band cannot directly be accessed) that could contribute to solve the calibration issues. As MATS and OSIRIS data appear to have calibration and stray light issues, it would be important to understand why the study was designed in the described way.
- Fig.1: The rough extent of the images in horizontal direction could also be provided in the caption and not only in the text where it is more difficult to find.
- L.147: "MATS background channels, ..., which do not include airglow emissions": This statement is not fully correct as there are faint emissions of other O2 bands, bands of OH, and airglow (pseudo-)continua. Nevertheless, the related measurement errors for the A-band should be very small.
- Fig.5: The red, orange, and green lines are hard to distinguish. A remark in the caption could be helpful here. Moreover, the orange lines are difficult to see on a orange/pink background ("red shaded area" in the text), which is not explained in the caption. Would it be possible to use a different line colour or to change the colour of the shaded areas?
- Fig.7: Similar to Fig. 5, it is difficult to recognise the individual lines. Again, the orange lines are most challenging.
- Sect.6: As the manuscript appears to describe the first study that actually evaluates real MATS data, it would be interesting know more about the performance of the satellite/instrument compared to the expectations before the launch. At least for the calibration of the airglow radiance and stray light issues (i.e. the topic of the study), more information would be helpful. In this context: where does the statement "is reported as 3-4%" come from?
Technical corrections:
- Inconsistent spelling: "stray light" and "straylight" are used.
- Fig.8: In "(SZA > 100°), panel a)", the parentheses are not consistent with "(SZA < 90°, panel b)".
Citation: https://doi.org/10.5194/egusphere-2025-493-RC2
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