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HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances

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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Satellite Missions for Earth and Planetary Exploration".

Deadline for manuscript submissions: closed (15 February 2023) | Viewed by 11943

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Special Issue Editors

Prof. Dr. Zhenzhan Wang

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Guest Editor

The CAS Key Laboratory of Microwave Remote Sensing, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
Interests: microwave radiometer calibration and application, especially to microwave polarimeter systems and full-polarized calibrator design, ocean surface emissivity model development and ocean parameter retrieval; microwave transfer models and atmospheric profile sounding using microwave and THz radiometers

Prof. Dr. Mingsen Lin

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Guest Editor

National Satellite Ocean Application Service, Beijing 100081, China
Interests: microwave backscatter and application; ocean wind field retrieve; microwave radiometric transfer model and salinity algorithm; ocean dynamic satellite and application

Prof. Dr. Xiaolong Dong

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Guest Editor

National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
Interests: theory and techniques of microwave remote sensing; research and development of advanced microwave remote sensing systems; applications of microwave remote sensing for earth and space science

Special Issue Information

Dear Colleagues,

China’s first marine power environment satellite, the Ocean 2 satellite (HY-2), was successfully launched at the Taiyuan Satellite Launch Center at 6:57 on August 16, 2011. The HY-2 satellite is equipped with four microwave remote sensors: a microwave scatterometer, a radar altimeter, a scanning microwave radiometer and a calibration microwave radiometer, with high-precision orbit determination and all-weather, all-day global detection capability. The objective of HY-2 is to monitor the dynamic ocean environment with microwave radar and radiometer sensors to measure sea surface wind field, sea surface height and sea surface temperature, directly providing measured data for early warning and forecasting of catastrophic sea conditions, for marine disaster prevention and mitigation, and to protect maritime rights and interests [https://www.globalsecurity.org/space/world/china/hy-2.htm].

The HY-2A satellite has been operating on orbit for 10 years (as of the end of September 2021), and has produced a huge volume of datasets and products, which need to be calibrated and validated in a long duration scale for further application. The results, successes and lessons learned from HY-2A should be summarized, which will benefit the following missions of HY-2 satellites and other remote sensing satellites.

Authors are invited to submit papers on the application of active and passive microwave sensors on the HY-2A satellite, especially on evaluating the data consistency, the accuracy or precision of the product, the trends and varied features derived from the long-term data, and other topics related to the sensors and applications of the HY-2A satellite.

We will welcome contributions where four microwave sensors are combined with each other or with other sensors in applied research and cross-calibration.

The following list provides some examples of topics of interest to ensure the consistency of the papers in this Special Issue:

Calibration and product consistency evaluation of microwave sensors;
Data product algorithm development, assessment and validations for 10 years of HY-2A operation;
Applications of active and passive microwave sensors to the ocean environment;
Fusion and assimilation of HY-2A data.

We invite all prospective authors to share their research results.

Prof. Dr. Zhenzhan Wang
Prof. Dr. Mingsen Lin
Prof. Dr. Xiaolong Dong
Guest Editors

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Keywords

HY-2 satellite
microwave remote sensors
ocean application
calibration and validation
retrieval algorithms
ocean geophysical products
data fusion/assimilation

Published Papers (8 papers)

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29 pages, 9750 KiB

Open AccessArticle

Daily Sea Ice Concentration Product over Polar Regions Based on Brightness Temperature Data from the HY-2B SMR Sensor

by Suhui Wu, Lijian Shi, Bin Zou, Tao Zeng, Zhaoqing Dong and Dunwang Lu

Remote Sens. 2023, 15(6), 1692; https://doi.org/10.3390/rs15061692 - 21 Mar 2023

Cited by 1 | Viewed by 1347

Abstract

Polar sea ice profoundly affects atmospheric and oceanic circulation and plays a significant role in climate change. Sea ice concentration (SIC) is a key geophysical parameter used to quantify these changes. In this study, we determined SIC products for the Arctic and Antarctic from 2019 to 2021 using data from the Chinese marine satellite Haiyang 2B (HY-2B) with an improved bootstrap algorithm. Then the results were compared with similar operational SIC products and ship-based data. Our findings demonstrate the effectiveness of the improved algorithm for accurately determining SIC in polar regions. Additionally, the results of the study demonstrate that the SIC product obtained through the improved bootstrap algorithm has a high correlation with other similar SIC products. The daily average SIC of the different products showed similar inter-annual trends for both the Arctic and Antarctic regions. Comparison of the different SIC products showed that the Arctic BT-SMR SIC was slightly lower than the BT-SSMIS and BT-AMSR2 SIC products, while the difference between Antarctic SIC products was more pronounced. The lowest MAE was between the BT-SSMIS SIC and BT-SMR SIC in both regions, while the largest MAE was between the NT-SMR and BT-SMR in the Arctic, and between the NT-SSMIS and BT-SMR in the Antarctic. The SIE and SIA time series showed consistent trends, with a greater difference in SIA than SIC and a slight difference in SIA between the BT-AMSR2 and BT-SMR in the Arctic. Evaluation of the different SIC products using ship-based observation data showed a high correlation between the BT-SMR SIC and the ship-based SIC of approximately 0.85 in the Arctic and 0.88 in the Antarctic. The time series of dynamic tie-points better reflected the seasonal variation in sea ice radiation characteristics. This study lays the foundation for the release of long-term SIC product series from the Chinese autonomous HY-2B satellite, which will ensure the continuity of polar sea ice records over the past 40 years despite potential interruptions. Full article

(This article belongs to the Special Issue HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances)

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17 pages, 23871 KiB

Open AccessArticle

Performance of Haiyang-2 Derived Gravity Field Products in Bathymetry Inversion

by Xiaoyun Wan, Huaibing Wang, Yongjun Jia and Wenjie Ma

Remote Sens. 2023, 15(1), 32; https://doi.org/10.3390/rs15010032 - 21 Dec 2022

Cited by 3 | Viewed by 1377

Abstract

Haiyang-2A (HY-2A), China’s first altimetry satellite mission, was launched more than ten years ago, and its follow-up satellites, HY-2B, HY-2C, and HY-2D, have also been launched. More attention has been paid to the evaluation of these satellite observations in marine gravity field inversion. However, this is not the case for bathymetry inversion. This study is aimed at evaluating the performance of HY-2 gravity field products in bathymetry recovery. Not only gravity anomaly, but also deflection of the vertical from the HY-2 series’ observations is also used. The results show that the bathymetry derived from the deflection of the vertical from HY-2A has a precision of around 128~130 m, and the north-south component performs better than the east-west component. Three versions of the gravity anomaly are used in bathymetry inversion, i.e., HY2ONLY_GRA, WHU16_GRA, and NSOASS22_GRA, and three bathymetry models are derived correspondingly, named as HY2ONLY_BAT, NSOASS22_BAT, and WHU16_BAT, respectively. The results show that HY2ONLY_BAT has a precision of 82.93 m, which is a little poorer than WHU16_BAT; NSOAS22_BAT has the best performance in bathymetry inversion among the three versions of the gravity anomaly. It indicates that HY-2 observations can also contribute to bathymetry inversion compared to current altimetry datasets, since the main difference between WHU16_GRA and NSOASS22_GRA is the use of HY-2 observations. According to spatial analysis results, considerable improvements appear in the west of the Pacific and Indian oceans, and most of the improvements are within 20 m. Meanwhile, the improvements are stronger in the regions with depths ranging between 2600~5500 m. Correlation analysis demonstrates that NSOASS22_BAT is very close to SIO V19.1 and DTU21BAT, which once again indicates the excellent performance of NSOASS22_BAT. Full article

(This article belongs to the Special Issue HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances)

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19 pages, 5754 KiB

Open AccessArticle

GNSS Data Processing and Validation of the Altimeter Zenith Wet Delay around the Wanshan Calibration Site

by Wanlin Zhai, Jianhua Zhu, Mingsen Lin, Chaofei Ma, Chuntao Chen, Xiaoqi Huang, Yufei Zhang, Wu Zhou, He Wang and Longhao Yan

Remote Sens. 2022, 14(24), 6235; https://doi.org/10.3390/rs14246235 - 09 Dec 2022

Cited by 3 | Viewed by 990

Abstract

The Wanshan calibration site (WSCS) is the first in-situ field for calibration and validation (Cal/Val) of HY-2 satellite series in China. It was built in December, 2018 and began business operation in 2020. In order to define an accurate datum for Cal/Val of altimeters, the permanent GNSS station (PGS) data of the WSCS observed on Zhiwan (ZWAN) and Wailingding (WLDD) islands were processed using GAMIT/GLOBK software in a regional solution, combined with 61 GNSS stations distributed nearby, collected from the GNSS Research Center, Wuhan University (GRC). The Hector software was used to analyze the trend of North (N), East (E), and Up (U) directions using six different noise models with criteria of maximum likelihood estimation (MLE), Akaike Information Criteria (AIC), and the Bayesian Information Criteria (BIC). We found that the favorite noise models were white noise plus generalized Gauss–Markov noise (WN + GGM), followed by generalized Gauss–Markov noise (GGM). Then, we compared the PGS velocities of each direction with the Scripps Orbit and Permanent Array Center (SOPAC) output parameters and found that there was good agreement between them. The PGSs in the WSCS had velocities in the N, E, and U directions of −10.20 ± 0.39 mm/year, 31.09 ± 0.36 mm/year, and −2.24 ± 0.66 mm/year for WLDD, and −10.85 ± 0.38 mm/year, 30.67 ± 0.30 mm/year, and −3.81 ± 0.66 mm/year for ZWAN, respectively. The accurate datum was defined for Cal/Val of altimeters for WSCS as a professional in-situ site. Moreover, the zenith wet delay (ZWD) of the coastal PGSs in the regional and sub-regional solutions was calculated and used to validate the microwave radiometers (MWRs) of Jason-3, Haiyang-2B (HY-2B), and Haiyang-2C (HY-2C). A sub-regional PGS solution was processed using 19 continuous operational reference stations (CORS) of Hong Kong Geodetic Survey Services to derive the ZWD and validate the MWRs of the altimeters. The ZWD of the PGSs were compared with the radiosonde-derived data in the regional and sub-regional solutions. The difference between them was −7.72~2.79 mm with an RMS of 14.53~18.62 mm, which showed good consistency between the two. Then, the PGSs’ ZWD was used to validate the MWRs. To reduce the land contamination of the MWR, we determined validation distances of 6~30 km, 16~28 km, and 18~30 km for Jason-3, HY-2B, and HY-2C, respectively. The ZWD differences between PGSs and the Jason-3, HY-2B, and HY-2C altimeters were −2.30 ± 16.13 mm, 9.22 ± 22.73 mm, and −3.02 ± 22.07 mm, respectively. Full article

(This article belongs to the Special Issue HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances)

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22 pages, 6937 KiB

Open AccessArticle

Coastal Waveform Retracking for HY-2B Altimeter Data by Determining the Effective Trailing Edge and the Low Noise Leading Edge

by Zhiheng Hong, Jungang Yang, Shanwei Liu, Yongjun Jia, Chenqing Fan and Wei Cui

Remote Sens. 2022, 14(19), 5026; https://doi.org/10.3390/rs14195026 - 09 Oct 2022

Viewed by 1505

Abstract

As an important remote sensing technology, satellite altimetry provides a large amount of observations of sea surface height over the global ocean. In coastal areas, the accuracy of satellite altimetry data decreases greatly due to issues arise in the vicinity of land, related to poorer geophysical corrections and artifacts in the altimeter reflected signals linked to the presence of land within the instrument footprint. To improve the application of HY-2B altimetry data in coastal areas, this study proposes a coastal waveform retracking strategy for HY-2B altimetry mission, which depends on the effective trailing edge and the leading edge, which are less affected by coastal ‘contamination’, to retrieve accurate waveform information. The HY-2B pass 323 and pass 196 data are reprocessed, and the accuracy of the reprocessing results in the range of 0–40 km offshore is validated against the tide gauge data and compared with the HY-2B standard SGDR data. According to the analysis conclusion, the accuracy of the reprocessed data is higher than that of the SGDR data and has good performance within 15 km offshore. For the pass 323, the mean value of correlation coefficient and RMS of the reprocessed data against the corresponding tide gauge data are 0.893 and 45.1 cm, respectively, in the range within 0–15 km offshore, and are 0.86 and 33.6 cm, respectively, in the range beyond 15 km offshore. For the pass 196, the mean value of correlation coefficient and RMS of the reprocessed data against the corresponding tide gauge data in the range within 0–12 km offshore are 0.84 and 33.0 cm, respectively, and in the range within 0–5 km offshore to the island are 0.90 and 29.3 cm, respectively, and in the range beyond 5 km offshore to the island are 0.92 and 36.2 cm, respectively, which are all better than the corresponding values of the SGDR data, especially in the range closed to the land. The results indicate that the proposed coastal waveform retracking strategy for HY-2B altimetry greatly improves the quality of HY-2B altimetry data in coastal areas. Full article

(This article belongs to the Special Issue HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances)

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19 pages, 17809 KiB

Open AccessArticle

Evaluation and Calibration of Remotely Sensed High Winds from the HY-2B/C/D Scatterometer in Tropical Cyclones

by Xiaohui Li, Jingsong Yang, Jiuke Wang and Guoqi Han

Remote Sens. 2022, 14(18), 4654; https://doi.org/10.3390/rs14184654 - 17 Sep 2022

Cited by 2 | Viewed by 1765

Abstract

Haiyang-2 scatterometers (HY-2A/B/C/D) have limitations in high wind speed retrieval due to the complexity of the remote sensing mechanism and the influence of rainfall on the radar cross section under the conditions of tropical cyclones. In this study, we focus on the evaluation of Chinese scatterometer operational wind products from HY-2B/C/D over the period from July 2019 to December 2021. HY-2B/C/D scatterometer wind products are collocated with SMAP (Soil Moisture Active Passive) L-band radiometer remotely sensed measurements. The results show that the underestimation of high wind speed occurs in the HY-2B/C/D wind speed products. The machine learning algorithms are explored to improve this underestimation issue, including the back propagation neural network (BP-NN), K-nearest neighbor (KNN), support vector machine (SVM), decision tree (DT), random forest (RF), and Bayesian ridge (BR) regression algorithms. Comparisons show that the BP-NN algorithm shows the best performance with a small RMSE (root-mean-square error) of 3.40 m/s, and high correlation coefficient of 0.88, demonstrating an improvement of 20.4% in RMSE (root-mean-square error) compared with the HY-2B/C/D wind speed products. In addition, the revised high winds are in good agreement with the ground truth measurements from the SFMR (Stepped Frequency Microwave Radiometer), which are useful for tropical cyclone disaster prevention and mitigation and are of vital importance in the numerical simulation of storm surges. Full article

(This article belongs to the Special Issue HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances)

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25 pages, 7085 KiB

Open AccessArticle

Performance of HaiYang-2 Altimetric Data in Marine Gravity Research and a New Global Marine Gravity Model NSOAS22

by Shengjun Zhang, Runsheng Zhou, Yongjun Jia, Taoyong Jin and Xiangxue Kong

Remote Sens. 2022, 14(17), 4322; https://doi.org/10.3390/rs14174322 - 01 Sep 2022

Cited by 13 | Viewed by 1646

Abstract

Haiyang-2 (HY-2) missions have accumulated sea surface height (SSH) observations on a global scale for more than 10 years. Four satellites, HY-2A, HY-2B, HY-2C and HY-2D, provide even but differently distributed data, which play a complementary role in marine gravity studies with other missions. Therefore, this paper evaluates the performances of HY-2 altimetric data in marine gravity modeling from the following four perspectives: SSH accuracy, geoid signal resolution ability, vertical deflections and gravity anomaly. First, the centimeter-magnitude accuracy level of HY-2 data is proved by analyzing SSH discrepancies at crossover points within a certain time limit. Second, the spectral analysis of repetitive along-track data sequences in a time domain shows a geoid resolution range from 18 to 24 km. Taking HY-2 exact repeat missions (ERM), for example, the resolution could be remarkably enhanced by stacking repetitive cycles. Third, validation with an XGM2019 model showed that vertical deflections were reliably computed for all HY-2 missions, but HY-2A performed slightly worse than the other HY-2 missions. Meanwhile, HY-2C and HY-2D with a ~66° orbital inclination obviously had an improved ability to capture east–west signals compared to HY-2A and HY-2B. Finally, we constructed global marine gravity results based on three input datasets, HY-2 dataset only, multi-satellite dataset without HY-2 and multi-satellite dataset with HY-2. Validations were performed using published models and shipborne gravimetric data. The results showed that the HY-2 dataset is capable of improving marine gravity anomaly recoveries and that the accuracy of NSOAS22 with incorporated HY-2 data is comparable to DTU21 and SS V31.1. Furthermore, HY-2 observations should not be the only input dataset to construct a 1’ × 1’ resolution marine gravity model. Full article

(This article belongs to the Special Issue HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances)

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13 pages, 3894 KiB

Open AccessTechnical Note

Blending Sea Surface Winds from the HY-2 Satellite Scatterometers Based on a 2D-Var Method

by Sirui Lv, Wenming Lin, Zhixiong Wang and Juhong Zou

Remote Sens. 2023, 15(1), 193; https://doi.org/10.3390/rs15010193 - 29 Dec 2022

Cited by 1 | Viewed by 1118

Abstract

The launch of the Haiyang-2 (HY-2) satellite constellation fosters the quick acquisition of global sea surface vector winds from the perspective of remote sensing. This study intends to develop a six-hourly mesoscale analysis of sea surface winds based on the microwave scatterometers onboard the HY-2 satellite series, with the objective of meeting the considerable demand for accurate and gap-free ocean wind forcing products. First, the accuracy of HY-2 scatterometers (HSCATs) in measuring wind is evaluated. In particular, the standard deviation (SD) errors of HSCATs data are assessed using the collocated buoy measurements with different temporal windows in order to account for the temporal representativeness errors in the blending analysis. Afterwards, a two-dimensional variational (2D-Var) method is implemented to blend the HSCATs measured winds and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis winds over the global ocean surface. This approach is different from existing methods in that it takes both wind error and background error correlation into account. The results show that the blended wind product is of a promising quality compared with independent wind references. Interestingly, the blended winds derived from 2D-Var in combination with an empirical background error correlation show smaller SD errors than those using a Gaussian error correlation function. Overall, the blended wind product should be valuable for forcing global ocean models or describing air-sea interaction processes on a scale close to the scatterometer measurements. Full article

(This article belongs to the Special Issue HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances)

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14 pages, 1810 KiB

Open AccessTechnical Note

On the Quality Control of HY-2 Scatterometer High Winds

by Shuyan Lang, Wenming Lin, Yi Zhang and Yongjun Jia

Remote Sens. 2022, 14(21), 5565; https://doi.org/10.3390/rs14215565 - 04 Nov 2022

Cited by 1 | Viewed by 1206

Abstract

The operational wind processor for the Ku-band scatterometers onboard HY-2 satellite series uses a quality control (QC) scheme based on the maximum likelihood estimator (MLE). Since it is difficult to discriminate rain contamination from “true” high winds, the MLE-based wind QC is set in a conservative way, which rejects up to ~35% of high winds (w ≥ 20 m/s) in HY-2 scatterometers (HSCATs). In this paper, the sensitivity of MLE and its spatially averaged value (i.e., MLE_m) to wind quality and rain is reconsidered by analyzing the collocated HSCAT observations and buoy data, as well as rain data from the global precipitation measurement satellite’s microwave imagers. It shows that MLE_m is more effective than MLE in terms of flagging rain data. More interestingly, the HSCAT high winds are much less strongly affected by rain, compared to the prior Ku-band pencil-beam scatterometers (e.g., RapidScat). Consequently, a MLE_m-based approach is proposed to improve the HSCAT wind QC, particularly for high winds. The new QC method results in ~8% rejections at 20 m/s and above. Compared to the collocated buoy winds, the HSCAT high winds preserved by the new QC (but rejected by the operational QC) are of fairly good quality. Full article

(This article belongs to the Special Issue HY-2 Satellite Microwave Remote Sensing of Ocean for 10 Years: Applications and Advances)

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