Received: 17 Jun 2022 – Discussion started: 29 Jul 2022
Abstract. Wind transport alters the snow topography and microstructure on sea ice through snow redistribution controlled by deposition and erosion. The impact of these processes on radar signatures is poorly understood. Here, we examine the effects of snow redistribution on Arctic sea ice from Ka- and Ku-band radar signatures. Measurements were obtained during two wind events in November 2019 during the MOSAiC expedition. During both events, changes in Ka- and Ku-band radar waveforms and backscatter coincident with surface height changes measured from a terrestrial laser scanner are observed. At both frequencies, snow redistribution events increased the dominance of the air/snow interface at nadir as the dominant radar scattering surface, due to wind densifying the snow surface and uppermost layers. The radar waveform data also detect the presence of previous air/snow interfaces, buried beneath newly deposited snow. The additional scattering from previous air/snow interfaces could therefore affect the range retrieved from Ka- and Ku-band satellite radar altimeters. The relative scattering contribution of the air/snow interface decreases, and the snow/sea ice interface increases with increasing incidence angles. Relative to pre-wind conditions, azimuthally averaged backscatter at nadir during the wind events increases by up to 8 dB (Ka-band) and 5 dB (Ku-band). Binned backscatter within 5° azimuth bins reveals substantial backscatter variability in the radar footprint at all incidence angles and polarizations. The sensitivity of the co-polarized phase difference is linked to changes in snow settling and temperature-gradient induced grain metamorphism, demonstrating the potential of the radar to discriminate between newly deposited and older snow on sea ice. Our results reveal the importance of wind, through its geophysical impact on Ka- and Ku-band radar signatures of snow on sea ice and has implications for reliable interpretation of airborne and satellite radar measurements of snow-covered sea ice.
(1) Title. I find the title to be quite confusing and uninformative; of course wind transport of snow affects radar (and indeed all) signals (sic) over sea ice as it alters the surface height if nothing else ! I recommend formulating a title that informs the reader as to what has been found, and not something generic like this.
(2). Novelty. It seem from that the data that the authors have observed that increases in snow density (asscoiated with wind transport) lead to reduced volume scattering. This in of itself is not an especially novel conclusion, and so I am wondering whether it is reasonable to claim that this topic is poorly undestood as the authors state in the abstract.
(3) Terminology. I am confused by the use of the term "signatures"; what does this mean? It is implicit, not explicit. Do you mean the radar echoes, or some property of them (e.g. backscattered power., range, etc), or something else?
(4) Qualitative. As presently written the abstract is almost entirely qualitative, despite there being quite signfiicatn numerical analysis within the paper itself. I recommend using the abstract to summarise the main quantitative conlcusions, which should also support the qualitative conclusions drawn.
(5) Rigour. Despite collecting a robust and valubale dataset, the authors have stopped short and only report the signal they record rather than complete the analysis to assess the significance of their findings. This leaves the reader to specualte as to whether the findings are in any way important. How much wind is needed to impact on radar data? How are the radar data affected? Is the effect more or less important at Ka or Ku? How does this impact on the scattering horizon, range measurement? How might the effect scale to airborne and satellite measumrents? How typical are the required conditions across the Arctic? There is useful data here, but more work is required to make this a useful contribution to the literature. I recommend that the authors explore the extent to which the changes impact on derived range measurements, for example.
Supplemental Video 2: Ranging Analysis of KuKa Radar on snow-covered Arctic sea ice during MOSAiC ExpeditionWillatt, Rosemary; Clemens-Sewall, David https://doi.org/10.5446/57132
Supplemental Video 1: CCTV Footage of the remote sensing footprint between 9 and 16 November 2019 from the MOSAiC ExpeditionSpreen, Gunnar; Huntemann, Marcus https://doi.org/10.5446/56641
Vishnu Nandan et al.
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We show that, wind blows and redistributes snow on sea ice, and Ka- and Ku-band radar signatures detect both newly deposited and buried snow layers that can critically affect snow depth measurements on ice. Radar measurements, meteorological and snow physical data were collected during the MOSAiC Expedition. With frequent occurrence of storms in the Arctic, our results provide baseline information that are vitally important for accurately calculating snow depth on sea ice from satellite radars.
We show that, wind blows and redistributes snow on sea ice, and Ka- and Ku-band radar signatures...
