Pan-Arctic ocean wind and wave data by spaceborne SAR

Figures & data

Figure 1. The S1 EW sub-images in HH polarization acquired by S1A at 7:47 UTC on 1 December 2018 in the Norwegian sea presenting a mixture of sea ice (upper-left corner) and open water, in which wind streaks are visible. The wave-like patterns are visible in the zoomed sub-image (right panel). the image ID is S1A_EW_GRDM_1SDH_20181201T074714_20181201T074814_024829_02BBC2_BE2B.SAFE.

Figure 2. Amount of S1 EW images processed in the pan-Arctic ocean for producing wind and wave products in each month through January 2017 to May 2021.

Table 1. Cross-comparison of SWH data between June 2018 and June 2020 from the four RA missions over the pan-Arctic ocean.

	Jason-2		Jason-3		SARAL
	Bias (m)	RMSE (m)	Bias (m)	RMSE (m)	Bias (m)	RMSE (m)
CryoSat-2	−0.02	0.02	−0.03	0.02	−0.11	0.02
Jason-2	/	/	0.03	0.01	−0.01	0.03
Jason-3	/	/	/	/	−0.01	0.03

Table 2. Cross-comparison of SSWS data between June 2018 and June 2020 from the four RA missions over the pan-Arctic ocean.

	Jason-2		Jason-3		SARAL
	Bias (m/s)	RMSE (m/s)	Bias (m/s)	RMSE (m/s)	Bias (m/s)	RMSE (m/s)
CryoSat-2	−0.20	0.02	−0.11	0.03	−0.39	0.02
Jason-2	/	/	0.15	0.00	−0.13	0.03
Jason-3	/	/	/	/	−0.20	0.03

Table 3. Summary of the previous comparisons of S1 retrievals of SSWS and SWH with different reference data (Li, Qin, & Wu, 2020) and (Wu, Li, & Huang, 2021).

Retrievals	Reference data	No. Col.	Bias	RMSE	Scatter Index (SI)
SSWS	ASCAT	1,740,509	0.20 m/s	1.27 m/s	15.17%
	In situ Buoy	305	0.09 m/s	1.41 m/s	22.68%
	XueLong R/V	23	−0.23 m/s	1.16 m/s	14.59%
SWH	RA	31,532	0.02 m	0.63 m	21.07%
	CFOSAT/SWIM (nadir)	32,403	0.15 m	0.60 m	18.98%

Figure 3. Flowchart of producing S1-based SSW and SWH data in the pan Arctic ocean.

Figure 4. The topology structure of BP neural network used for retrieving SSWS or SWH by S1 data.

Table 4. List of variables and their descriptions in the S1 SSW and SWH products.

No.	Variables	Description
1	Latitude	Latitude at Wind/Wave Cell Center
2	Longitude	Longitude at Wind/Wave Cell Center
3	WindSpeed	SAR Retrieved Sea Surface Wind Speed
4	WindDirection	Interpolated Sea Surface Wind Direction of ERA5 Reanalysis Model (clockwise relative to North)
5	SWH	S1 Retrieved Significant Wave Height
6	IncidenceAngle	Incidence Angle at Wind/Wave Cell Center
7	Sigma0	Normalized Radar Cross Section
8	Mask	0 for acceptable S1 sub-images for retrieval 1 for inhomogeneous S1 sub-images 2 for ice-covered S1 sub-images 3 for land-covered S1 sub-images
9	qc_flag	0 for a good record 1 for a suspect record 2 for a bad record 3 for an unprocessed record

Table 5. Definition of quality control flags and their criteria for the SSW products.

Record	Criteria
Good record (qc_flag = 0)	a. 0 m/s < SSW < 30 m/s and b. homogeneity factor ≤ 1.05
Suspect record (qc_flag = 1)	a. SSW > 30 m/s or b. 1.05 < homogeneity factor ≤ 1.50
Bad record (qc_flag = 2)	a. SSW < 0 m/s or b. 1.50 < homogeneity factor ≤ 3.00
Unprocessed record (qc_flag = 3)	a. Mask = 2 or Mask = 3 or b. homogeneity factor > 3.00

Table 6. Definition of quality control flags and their criteria for the SWH products.

Record	Criteria
Good record (qc_flag = 0)	a. 0 m ≤ SWH ≤ 10 m and b. homogeneity factor ≤ 1.05 and c. $\overline{{\sigma }_0}$ – NESZ ≥ 3 dB and d. image variance ≤ 0.25
Suspect record (qc_flag = 1)	a. SWH > 10 m or b. 1.05 < homogeneity factor ≤ 1.50 and c. $\overline{{\sigma }_0}$ – NESZ ≥ 3 dB and d. image variance ≤ 0.25
Bad record (qc_flag = 2)	a. SWH < 0 m or b. 1.50 < homogeneity factor ≤ 3.00 or c. $\overline{{\sigma }_0}$ – NESZ < 3 dB or d. 0.25 < image variance ≤ 0.50
Unprocessed record (qc_flag = 3)	a. Mask = 2 or Mask = 3 or b. homogeneity factor > 3.00 or c. image variance > 0.50

Figure 5. Examples of (a) SSW and (b) SWH products produced by S1 EW data acquired in the Arctic. the gray represents areas covered by sea ice. the image ID is S1A_EW_GRDM_1SDH_20201202T024920_20201202T025025_035501_042682_F0C5.

Table 7. Comparisons of SSWS by S1 with ASCAT/RA data for different homogeneity factors.

Homogeneity factor	Comparing data	Counts	Bias (m/s)	RMSE (m/s)	SI (%)	Correlation
≤1.05	ASCAT_SSW	805,851	−0.02	1.45	16.83	0.94
	RA_SSW	65,780	0.61	1.61	17.54	0.94
(1.05, 1.50]	ASCAT_SSW	23,476	0.51	1.54	34.08	0.95
	RA_SSW	2,906	0.47	1.69	35.93	0.94
(1.50, 3.00]	ASCAT_SSW	1,264	0.57	2.44	96.55	0.75
	RA_SSW	238	1.49	4.42	160.68	0.55

Figure 6. Comparisons of SSWS by S1 and the collocated (a) ASCAT and (b) RA from June 2018 to June 2020. The gray dots are the detected outliers by quartiles. The color indicates the amount of collocated data pairs. The error bars in an interval of 2 m/s are overlaid.

Table 8. Comparisons of the SSWS by S1 and RA from different missions.

RA	No. Col.	Bias (m/s)	RMSE (m/s)	SI (%)
CryoSat-2	21,594	0.68	1.44	12.49
Jason-2	13,268	0.40	1.22	12.10
Jason-3	24,574	0.62	1.41	12.71
SARAL	3,942	0.58	1.69	14.80

Table 9. Comparisons of SWH by S1 with RA data with different combinations of homogeneity factor and image variance.

Homogeneity Factor Image variance	Statistical Parameters	≤1.05	(1.05, 1.50]
[0, 0.25]	No. Col.	64,719	815
	Bias (m)	0.23	0.10
	RMSE (m)	0.76	1.18
	SI (%)	26.36	48.59
	Correlation	0.89	0.67
(0.25, 0.50]	No. Col.	2092	18
	Bias (m)	0.81	0.50
	RMSE (m)	1.93	3.26
	SI (%)	95.00	122.40
	Correlation	0.38	0.03

Figure 7. Comparison of SWH by S1 and the collocated RA during the period of June 2018 to June 2020. the gray dots are the outliers detected by quartiles. the color indicates the amount of collocated data pairs.

Li, X. M., Qin, T. T., & Wu, K. (2020). Retrieval of sea surface wind speed from spaceborne SAR over the Arctic marginal ice zone with a neural network. Remote Sensing, 12, 20.

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Wu, K., Li, X.-M., & Huang, B. Q. (2021). Retrieval of ocean wave heights from spaceborne sar in the arctic ocean with a neural network. Journal of Geophysical Research: Oceans, 126(3). doi:https://doi.org/10.1029/2020JC016946

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Data availability statement

This dataset is freely available at Science Data Bank http://www.dx.doi.org/10.11922/sciencedb.00834.