Feasibility study of a satellite-borne terahertz heterodyne spectrometer for the retrieval of atomic oxygen and temperature in the Earth's atmosphere
Bibliographic record
Abstract
Atomic oxygen is one of the main species in the mesosphere and lower thermosphere (MLT) of the Earth’s atmosphere. Thus, atomic oxygen and the local temperature plays an important role for the energy balance in the MLT region. By remote sensing of the emission from the atomic oxygen fine-structure transitions at 2.06 THz and the 4.74 THz, atomic oxygen concentration profiles and neutral temperature profiles of the atmosphere can be derived. By resolving the line profile, heterodyne spectroscopy enables access to layers of the atmosphere for which the oxygen line is saturated. The first spectrally resolved measurements of the 4.74-THz line of atomic oxygen in the atmosphere were performed with the heterodyne spectrometer GREAT on board of the airborne astronomic observatory SOFIA [1]. Based on the experiences from GREAT, the heterodyne spectrometer OSAS-B was developed as a balloon-borne instrument dedicated to the measurement of atomic oxygen in Earth’s atmosphere [2].In this study, we investigate the feasibility of a satellite-borne heterodyne spectrometer for the retrieval of atomic oxygen concentration and temperature in the MLT. Compared to airborne observations, a satellite instrument has the advantage of a limb observation geometry which facilitates the retrieval. A satellite instrument also has the advantage of a fast and almost global coverage.For investigating the feasibility of such an instrument, we use the vertical density and temperature profiles provided by the NRLMSIS 2.0 atmosphere model to simulate 2.06 THz and 4.74 THz emission spectra as measured by a satellite. We then apply retrieval algorithms for the atomic oxygen concentration and temperature and compare the retrieved profiles to the reference, i.e. the original NRLMSIS 2.0 profiles. We consider the scenario of a satellite in a circular orbit at an altitude of 500 km and an inclination of 8°. The emission spectra are simulated using radiative transfer under the assumption of local thermodynamic equilibrium.By considering two separate heterodyne receivers with sensitivity of 11,000 K and 25,000 K noise temperature for the 2.06 THz and 4.74 THz lines, respectively, and data accumulated over 100 seconds of measurement time, corresponding to a ground track of 700 km, we can retrieve a vertical temperature profile from 100 km altitude to 300 km altitude with 5 % relative uncertainties and an atomic oxygen concentration profile from 120 km to 300 km with 5 % relative uncertainties. From 100 km to 120 km the uncertainty in the atomic oxygen concentration is higher and within 25 %.[1] Richter, H. et al. Commun Earth Environ 2,19 (2021), doi: 10.1038/s43247-020-00084-5[2] Wienold, M. et al. 48th IRMMW-THz, Montreal, Canada (2023), doi: 10.1109/IRMMW-THz57677.2023.10299165
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".