Retrieval of Cloud, Atmospheric, and Surface Properties from Far-Infrared Spectral Radiances Measured by FIRMOS-B During the 2022 HEMERA Stratospheric Balloon Campaign

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript by Natale et al. presents a retrieval of cloud properties, atmospheric state, and surface temperature from far-infrared (FIR) spectral radiances measured by the FIRMOS-B instrument during a stratospheric balloon campaign in August 2022 over Timmins, Canada. This study represents a valuable contribution to atmospheric remote sensing and satellite mission preparation, particularly in support of the upcoming FORUM mission. The methodology is well-founded, the results are robust, and the scientific conclusions are clearly presented. I recommend minor revisions to further enhance clarity and address the following analytical points before acceptance:

1. While SACR and FARM are well described, the differences in retrieved cloud top height and surface temperature warrant deeper discussion, particularly regarding the underlying model assumptions and limitations. A more thorough analysis of potential error sources would strengthen the interpretation of these discrepancies.
2. The relatively poor precision in ice particle size and thermodynamic phase (ice fraction) retrievals merits further quantitative investigation. A sensitivity analysis demonstrating the impact of measurement noise or retrieval assumptions would help clarify these limitations.
3. Given the study’s preparatory nature for FORUM, the authors should expand on concrete recommendations for the satellite mission. For instance, specific accuracy requirements, optimal observation conditions, or lessons learned for instrument performance would be highly valuable additions.

These refinements would further solidify the manuscript’s scientific rigor and its relevance to future FIR remote sensing missions.

 

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The authors make original contributions to the study of the radiative properties of clouds, the atmosphere, and the Earth's surface by analysing far-infrared (FIR) spectral measurements taken by the FIRMOS-B instrument. This instrument was launched on a stratospheric balloon as part of the HEMERA campaign in 2022.

The FIRMOS-B instrument measures spectral radiance in the range of 100–1000 cm⁻¹. This covers an area of the electromagnetic spectrum that is ideal for studying the thermal flux emitted by the Earth, but which is rarely explored by other instruments.

The measurements were taken in the stratosphere, at an altitude of around 36 km, with a similar observation geometry to that of the future ESA FORUM mission. This enables faithful simulation of observations at the upper limit of the atmosphere. The article presents original experimental data from the FIR and sets out an integrated methodology for extracting atmospheric parameters and clouds. It also addresses significant gaps in the literature and paves the way for the scientific exploitation of the future ESA FORUM mission.

The study proposes a retrieval procedure based on a Bayesian approach. Using three different direct models for comparison increases the robustness of the results. Even in the presence of relatively high measurement noise, parameters such as the optical depth of the clouds, the effective particle size and the altitude of the cloud tip were extracted with good accuracy.

Revisions:

- the Bayesian approach is only mentioned in the abstract. Elsewhere in the article, the authors neither explain the method in detail nor present the implementation or parameters used. Nor do they discuss the advantages or limitations of this approach in the context of their study.

Author Response

Please see the attachment

Author Response File: Author Response.docx