the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Oct 2023
Retrieval of sea ice drift in the Fram Strait based on data from Chinese satellite HaiYang (HY1-D)
Dunwang Lu
Jianqiang Liu
Lijian Shi
Tao Zeng
Bin Cheng
Suhui Wu
Manman Wang
Abstract. Melting of sea ice in the Arctic ocean has accelerated due to global warming. The Fram Strait (FS) serves as a crucial pathway for sea ice export from the Arctic to the North Atlantic Ocean. Monitoring sea ice drift (SID) in FS provides insights into how Arctic sea ice responds to the climate change. The SID has been retrieving from Sentinel-1 SAR, AVHRR, MODIS and AMSR-E, and using optical data to retrieve SID still needs further exploration. In this paper, we retrieve SID in the FS using China's HaiYang1-D (HY1-D) satellite equipped with the Coastal Zone Imager (CZI). Multi-template matching technique is employed to calculate cross-correlation, and subpixel estimation is used to locate displacement vectors from the cross-correlation matrix. The dataset covering March to May 2021 is divided into hourly and daily intervals for analysis, and validation is performed using Copernicus Marine Environment Monitoring Service (CMEMS) SAR-based product and IABP buoy measurements. Comparison with CMEMS SID product reveals a high correlation at the daily level; however, due to spatial and temporal variability in sea ice motion, differences are observed at an hourly resolution. Additionally, validation against IABP buoy data shows a velocity bias of 0.004 m/s and RMSE of 0.027 m/s at the day-level, along with a flow direction bias of 0.057 rad and RMSE of 0.313 rad respectively; while at the hour-level, velocity bias is negligible (0 m/s), with an RMSE value of 0.022 m/s; similarly for flow direction bias which remains negligible. During the validation against buoys, we find that the accuracy of retrieving the SID flow direction is highly interrelated with the sea ice displacement.
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Dunwang Lu et al.
Status: open (extended)
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RC1: 'Comment on egusphere-2023-1927', Anonymous Referee #1, 21 Oct 2023
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Review on “Retrieval of sea ice drift in the Fram Strait based on data from Chinese satellite HaiYang (HY1-D)”
Using the observation data of optical sensors onboard the China's HaiYang1-D (HY1-D) satellite, the author proposed an optimized algorithm to calculate the sea ice motion velocity in the Fram Strait region of the Arctic, and validated and evaluated it using CMEMS SAR products and IABP sea ice drifter data. This is of great significance for describing the kinematic characteristics of Arctic sea ice movement and changes in Arctic sea ice outflow, and is a method worth promoting. However, the advantages of data products relative to other products and the quantification results of validation are not yet very clear. Therefore, I recommend that the manuscript needs to undergo major revisions before considering publication.
General comments:
The biggest problem with optical remote sensing is the impact of clouds. Although the paper has discussed the impact of clouds on sea ice motion products, the extent of the impact and its impact on the effective data are not very clear. Further clarification is needed. In addition, it is also necessary to consider whether the topographic features of summer sea ice surfaces, such as snow hummocks and ice ridges, have an impact on the inversion results. The impact of sea ice motion speed itself on the errors of data product needs to be further quantified, and the spatial and seasonal differences in retrieval errors also need to be quantitatively explained. At present, the paper mainly uses examples to illustrate the above issues, rather than providing statistical results, which is not conducive to objective evaluation of the data product.
Special comments:
- Line 34 “leading to accelerated sea ice break-up”-- ice break-up generally describes the situation of synoptic scale processes.
- Line 40 “the TPD transports large quantities of multiyear ice outward from the central Arctic toward the FS”-- not just the Fram Strait, but also the Barents Sea and Baffin Bay.
- Line 46 “which gradually melts during outward transport”--If the sea ice outflow occurs during winter, sea ice growth may also occur.
- Line 50 “between the polar regions and the outside world”--what is the meaning of “outside of world”
- Line 59 “low temporal resolution SID product may fail to provide accurate sea ice drift patterns”-- The main limitation of low-temporal-resolution sea ice motion products is that they cannot depict the subdaily-scale signals of the sea ice kinematics.
- Line 81 “However, it has been observed that the accuracy of the SID product with AVHRR is not good in s regions like East Greenland”-- What are the reasons for poor observation results?
- Line 132 “the product includes the North Pole and South Pole”--1) change to the product is available from both Arctic Ocean and South Ocean; 2) The language of the entire text must be more strictly controlled.
- Figure 2: “The drifting trajectories of 69 IABP buoys from March to May 2021”: How independent are these data, that is, they are not deployed in a very close area, especially the buoys deployed during the MOSAiC; In addition, whether to conduct quality control on the data and eliminate the data with noise and buoy data that are already at sea (not over the ice).
- Line 156 “we design a quality control session to remove the lowquality data from the results”-- How much data will be lost during the study period due to the impact of clouds?
- The error in the direction of sea ice movement: We know that the sea ice movement in the Fram Strait is relatively stable, so it is possible that the angle error may be small. Can you further evaluate the angle error of sea ice motion under different meandering coefficients?
- Hourly data: Does the data have the ability to identify the subdaily-scale characteristics of sea ice motion and compare them with buoy data on a frequency basis?
- BIAS: Relative deviation is also very important.
- Figure 12: What is the confidence level of the correlation coefficient?
- Figure 15: In the caption of the illustration, a lot of information is missing, which is only appear in the main text.
- Figure 16: This is an obvious result, and this illustration is not necessary. It is necessary to add an explanation of the classification evaluation under different conditions with various meandering coefficients and sea ice motion speed. And provide clustering statistical results for different sub regions.
Citation: https://doi.org/10.5194/egusphere-2023-1927-RC1
Dunwang Lu et al.
Dunwang Lu et al.
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