Remote Sensing

Research

20 pages, 7994 KiB

Open AccessArticle

The Wave Period Parameterization of Ocean Waves and Its Application to Ocean Wave Simulations

by Jialei Lv, Wenjing Zhang, Jian Shi, Jie Wu, Hanshi Wang, Xuhui Cao, Qianhui Wang and Zeqi Zhao

Remote Sens. 2023, 15(22), 5279; https://doi.org/10.3390/rs15225279 - 7 Nov 2023

Cited by 1 | Viewed by 2045

Abstract

The wave period is a wave parameter that is significantly influenced by factors such as wind speed and bottom topography. Previous research on wave period parameterization has primarily focused on wind-dominated sea areas and may not be applicable to certain regions, such as [...] Read more.

The wave period is a wave parameter that is significantly influenced by factors such as wind speed and bottom topography. Previous research on wave period parameterization has primarily focused on wind-dominated sea areas and may not be applicable to certain regions, such as the equatorial calm or coastal areas dominated by swell waves. To address this limitation, this paper utilizes the third-generation wave numerical model SWAN to perform wave numerical simulations for a portion of the Northwest Pacific Ocean. The simulation incorporates observational data from nearshore stations, buoys, and satellite altimeters for error analysis. To develop a new wave parameterization scheme (WS-23), we employ extensive NDBC buoy data and incorporate the exponential rate and wave age characteristics that were previously established by predecessors. Our scheme introduces a judgement mechanism to distinguish between wind waves, swell waves, and mixed waves. The resulting ocean wave factor enhances the mean wave period values calculated using the model and other parameterization schemes. The experimental results demonstrate that our new parameterization scheme effectively improves the abnormal peak of the fitting data. Comparing the output values of the mean wave period element output of the SWAN model with our new parameterization scheme, we observe a reduction in the mean values of

E_{a}

,

E_{c}

, and

R M S E

by 0.231, 1.94%, and 0.162, respectively, while increasing the average

r

by 0.05. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

20 pages, 12662 KiB

Open AccessArticle

Enhanced Impact of Land Reclamation on the Tide in the Guangxi Beibu Gulf

by Jingfang Lu, Yibo Zhang, Ruichen Cao, Xianqing Lv, Minjie Xu, Guandong Gao and Qiang Liu

Remote Sens. 2023, 15(21), 5210; https://doi.org/10.3390/rs15215210 - 2 Nov 2023

Cited by 1 | Viewed by 1269

Abstract

Based on the method for identifying the boundary of movable water bodies (MWBB), the spatial distribution of reclamation projects in the Guangxi Beibu Gulf were identified over the past 40 years and the impact of these engineering facilities on hydrodynamics was also evaluated. [...] Read more.

Based on the method for identifying the boundary of movable water bodies (MWBB), the spatial distribution of reclamation projects in the Guangxi Beibu Gulf were identified over the past 40 years and the impact of these engineering facilities on hydrodynamics was also evaluated. The results showed that 163.8 km² of natural sea areas in the Guangxi Beibu Gulf were occupied through reclamation in the last 40 years. The effects of land reclamation on tidal amplitude were more pronounced in the second period (2001–2018) than in the first period (1987–2001), particularly in the tidal channels of Qinzhou Bay and Fangcheng Bay, where the amplitude difference ranged from 8 to 15 cm, representing a 40–55% increase. The reduction in the sea area because of land reclamation has changed the hydrodynamics in the Guangxi Beibu Gulf, including reducing the tidal volume, altering the amplitude variations, and increasing the seaward residual currents, all of which could cause significant problems for the coastal environment. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

18 pages, 30482 KiB

Open AccessArticle

Investigating the Storm Surge and Flooding in Shenzhen City, China

by Peng Bai, Liangchao Wu, Zhoujie Chen, Jianjun Xu, Bo Li and Peiliang Li

Remote Sens. 2023, 15(20), 5002; https://doi.org/10.3390/rs15205002 - 18 Oct 2023

Cited by 1 | Viewed by 2205

Abstract

Tropical cyclones affecting Shenzhen city have shown a remarkable tendency to increase in both intensity and quantity, highlighting the urgency of accurate forecasts of storm surges and flooding for effective planning and mitigation. Utilizing satellite and field observations together with the advanced high-resolution [...] Read more.

Tropical cyclones affecting Shenzhen city have shown a remarkable tendency to increase in both intensity and quantity, highlighting the urgency of accurate forecasts of storm surges and flooding for effective planning and mitigation. Utilizing satellite and field observations together with the advanced high-resolution baroclinic wave–current model (SCHISM), a comprehensive investigation aimed at storm surge and flooding in Shenzhen was conducted. Statistical work of historical tropical cyclones revealed that Shenzhen was most vulnerable to cyclones propagating from the southeast toward the northwest and passing Shenzhen down the Pearl River Estuary. Thus, a representative, i.e., super typhoon Hato (2017), was selected for further study. Validations of numerical results suggested satisfactory model performance in mapping the wave, tide, and surge processes. Remarkable differences in spatiotemporal distribution and intensity of storm surge and flooding were found along the Shenzhen coast, which was dominated by the propagation of far-field surge and tidal waves, cooperation between wind direction and coastline orientation, estuary morphology, and the land terrain. Intervention of wave–current interaction improved the simulation of the surge and flooding and triggered an earlier occurrence time of the maximum surge in specific areas. The Pearl River discharge significantly elevated the sea level height inside the estuary and contributed to a more severe surge. Given the extremely complicated river networks and huge freshwater flux of Pearl River and the increasing trend of concurrent heavy precipitation of tropical cyclones, future investigations on compound flooding were suggested. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

19 pages, 18560 KiB

Open AccessArticle

Characterizing the Effect of Ocean Surface Currents on Advanced Scatterometer (ASCAT) Winds Using Open Ocean Moored Buoy Data

by Tianyi Cheng, Zhaohui Chen, Jingkai Li, Qing Xu and Haiyuan Yang

Remote Sens. 2023, 15(18), 4630; https://doi.org/10.3390/rs15184630 - 21 Sep 2023

Viewed by 1823

Abstract

The ocean surface current influences the roughness of the sea surface, subsequently affecting the scatterometer’s measurement of wind speed. In this study, the effect of surface currents on ASCAT-retrieved winds is investigated based on in-situ observations of both surface winds and currents from [...] Read more.

The ocean surface current influences the roughness of the sea surface, subsequently affecting the scatterometer’s measurement of wind speed. In this study, the effect of surface currents on ASCAT-retrieved winds is investigated based on in-situ observations of both surface winds and currents from 40 open ocean moored buoys in the tropical and mid-latitude oceans. A total of 28,803 data triplets, consisting of buoy-observed wind vectors, current vectors, and ASCAT Level 2 wind vectors, were collected from the dataset spanning over 10 years. It is found that the bias between scatterometer-retrieved wind speed and buoy-observed wind speed is negatively correlated with the ocean surface current speed. The wind speed bias is approximately 0.96 times the magnitude of the downwind surface current. The root-mean-square error between the ASCAT wind speeds and buoy observations is reduced by about 15% if rectification with ocean surface currents is involved. Therefore, it is essential to incorporate surface current information into wind speed calibration, particularly in regions with strong surface currents. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

15 pages, 15248 KiB

Open AccessArticle

Study on the Polarization Pattern Induced by Wavy Water Surfaces

by Haoyuan Cheng, Qianli Zhang, Zhenhua Wan, Zhongyuan Zhang and Jin Qin

Remote Sens. 2023, 15(18), 4565; https://doi.org/10.3390/rs15184565 - 16 Sep 2023

Cited by 5 | Viewed by 1720

Abstract

In nature, the wavy ocean surface is a common polarizer, which can change the polarization state of incident light by refraction and reflection and form a new polarization pattern different from the atmosphere. In this paper, we establish the polarized optical transmission model [...] Read more.

In nature, the wavy ocean surface is a common polarizer, which can change the polarization state of incident light by refraction and reflection and form a new polarization pattern different from the atmosphere. In this paper, we establish the polarized optical transmission model of wavy ocean surface reflection and refraction and simulate polarization patterns induced by wavy ocean surfaces. We study the polarization patterns reflected by wavy water surfaces and polarization patterns inside and outside Snell’s window under wavy ocean surfaces. The correctness of the simulation results is verified by qualitative and quantitative analysis. The environmental factors affecting the corresponding polarization patterns are discussed. Through contrastive analysis, we find that polarization patterns induced by wavy water surfaces are predictable and regular, which has great potential for human application. This kind of polarization pattern is influenced by the sun’s position and water surface condition. The study will promote the development of remote sensing, target detection, and polarization navigation. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Graphical abstract

21 pages, 7642 KiB

Open AccessArticle

A New Approach for Ocean Surface Wind Speed Retrieval Using Sentinel-1 Dual-Polarized Imagery

by Yuan Gao, Yunhua Wang and Weili Wang

Remote Sens. 2023, 15(17), 4267; https://doi.org/10.3390/rs15174267 - 30 Aug 2023

Cited by 2 | Viewed by 1263

Abstract

A synthetic aperture radar (SAR) has the capability to observe ocean surface winds with a high spatial resolution, even under extreme conditions. The purpose of this work was to develop a new method for wind speed retrieval with the combination of SAR dual-polarized [...] Read more.

A synthetic aperture radar (SAR) has the capability to observe ocean surface winds with a high spatial resolution, even under extreme conditions. The purpose of this work was to develop a new method for wind speed retrieval with the combination of SAR dual-polarized signals. In this study, we collected 28 tropical cyclone imageries observed using the Sentinel-1 dual-polarization mode. These imageries were collocated with radiometer wind speed measurements and reanalysis of wind vector products. In the new method, the wind speed was set as the output. VV-polarized (vertical transmitting–vertical receiving polarized) normalized radar cross section (NRCS), incident angle, VH-polarized (vertical transmitting–horizontal receiving polarized) NRCS, and wind direction were set as the inputs. Based on different output combinations, wind retrieval models were developed with multiple linear regression (MLR). According to the validation and comparison, the proposed models performed better than the traditional piecewise VH-polarization geophysical model functions (GMFs). The impact of thermal noise on the retrieval of low wind speeds (<10 m/s) could be partially reduced. The input of wind direction is unnecessary if the combination of VV- and VH-polarized imageries has been utilized. These results suggest that the use of MLR and the dual-polarization combination can improve SAR wind retrieval accuracy. Compared with SMAP measurements, our SAR retrievals can provide fine structures of TC wind fields. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

21 pages, 6498 KiB

Open AccessArticle

Toward a High-Resolution Wave Forecasting System for the Changjiang River Estuary

by Yan Jiang, Zengrui Rong, Yiguo Li, Cheng Li and Xin Meng

Remote Sens. 2023, 15(14), 3581; https://doi.org/10.3390/rs15143581 - 17 Jul 2023

Cited by 1 | Viewed by 1242

Abstract

Based on a high-resolution unstructured SWAN model and GFS forecast wind, an operational wave forecasting system is conducted for the Changjiang River Estuary (CRE). The performance of the wave forecasting system is evaluated by comparing it with the altimeter observations and in situ [...] Read more.

Based on a high-resolution unstructured SWAN model and GFS forecast wind, an operational wave forecasting system is conducted for the Changjiang River Estuary (CRE). The performance of the wave forecasting system is evaluated by comparing it with the altimeter observations and in situ wave buoys. The present operational system shows good accuracy in reproducing the seasonal and the synoptic-scale wave characteristics over the CRE. The forecasting capability in three different horizons, including 24 h, 48 h, and 72 h forecasts, is evaluated. Waves over the CRE exhibit distinct seasonal variability. Larger waves occur in both the summer and winter when typhoons and cold weather events affect the CRE. In contrast, waves with longer wave periods take place mainly in the wind transition seasons, i.e., the spring and fall, and the wave directions are more dispersed in these seasons. A seasonal varied forecasting capability is also revealed: better in the winter and spring than in the summer and fall and better during cold weather events than during typhoons. A cross comparison with the model analysis suggests that there is a systematic difference between wave measurements by Jason-3 and Sentinel-3A/3B. The significant wave height from Jason-3 compares best with the model analysis and forecasts and is systematically lower than Sentinel-3A/3B in lower wave conditions (<4 m) in the East China Sea. Substantial discrepancies exist among the three altimeters when the significant wave height exceeds 4 m, and further efforts are needed to discern their merits. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

17 pages, 9979 KiB

Open AccessArticle

A New Upwelling Index for the Moroccan Atlantic Coast for the Period between 1982–2021

by Hanae Belmajdoub, Khalid Minaoui, Anass El Aouni, Karim Hilmi, Rachid Saadane and Abdellah Chehri

Remote Sens. 2023, 15(14), 3459; https://doi.org/10.3390/rs15143459 - 8 Jul 2023

Cited by 6 | Viewed by 1728

Abstract

Being a component of the Eastern Boundary Upwelling (EBU) ecosystem, Morocco’s Atlantic coast presents high biological production throughout the year, with seasonal variations in upwelling dynamics. This characterization reflects the inherent nature of EBU’s ecosystems. In this work, we develop a novel methodology [...] Read more.

Being a component of the Eastern Boundary Upwelling (EBU) ecosystem, Morocco’s Atlantic coast presents high biological production throughout the year, with seasonal variations in upwelling dynamics. This characterization reflects the inherent nature of EBU’s ecosystems. In this work, we develop a novel methodology to compute a new upwelling index based on the analysis of sea surface temperature (SST) images. Our new upwelling index is not only simple to calculate but also efficient. Indeed, it is limited only to the upwelling region, which has allowed the improvement of the quantification and analysis of the seasonal and interannual variability of the upwelling dynamics. The new proposed upwelling index is based on the application of a recent segmentation method that allows for the monitoring of upwelling dynamics using satellite observations. The proposed upwelling index is applied to a 40-year database of weekly SST images covering the period from 1982 to 2021, and the results are used to analyze seasonal and interannual variations of the upwelling in the region. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

20 pages, 21240 KiB

Open AccessArticle

Analysis of the 20-Year Variability of Ocean Wave Hazards in the Northwest Pacific

by Rui Li, Kejian Wu, Wenqing Zhang, Xianghui Dong, Lingyun Lv, Shuo Li, Jin Liu and Alexander V. Babanin

Remote Sens. 2023, 15(11), 2768; https://doi.org/10.3390/rs15112768 - 26 May 2023

Cited by 6 | Viewed by 1856

Abstract

In the Northwest Pacific (NWP), where a unique monsoon climate exists and where both typhoons and extratropical storms occur frequently, hazardous waves pose a significant risk to maritime safety. To analyze the 20-year variability of hazardous waves in this region, this study utilized [...] Read more.

In the Northwest Pacific (NWP), where a unique monsoon climate exists and where both typhoons and extratropical storms occur frequently, hazardous waves pose a significant risk to maritime safety. To analyze the 20-year variability of hazardous waves in this region, this study utilized hourly reanalysis data from the ECMWF ERA5 dataset covering the period from 2001–2020, alongside the wave risk assessment method. The ERA5 data exhibits better consistency, in both the temporal and spatial dimensions, than satellite data. Although hazardous wind seas occur more frequently than hazardous swells, swells make hazardous waves travel further. Notably, the extreme wave height (EWH) shows an increasing trend in high- and low-latitude areas of the NWP. The change in meridional wind speeds is the primary reason for the change in the total wind speed in the NWP. Notably, the maximum annual increase rate of 0.013 m/year for EWH exists in the region of the Japanese Archipelago. This study elucidated the distributions of wave height intensity and wave risk levels, noting that the EWHs of the 50-year and 100-year return periods can reach 20.92 m and 23.07 m, respectively. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

21 pages, 8192 KiB

Open AccessArticle

Influence of Wave-Induced Radiation Stress on Upper-Layer Ocean Temperature during Typhoons

by Qianhui Wang, Jian Shi, Jingmin Xia, Kaifeng Han, Wenbin Xiao, Wenjing Zhang, Haodi Wang and Jialei Lv

Remote Sens. 2023, 15(9), 2442; https://doi.org/10.3390/rs15092442 - 6 May 2023

Viewed by 1585

Abstract

Radiation stress is defined as the excess momentum caused by ocean waves, which exerts an indispensable impact on the upper-layer ocean conditions as waves pass by. Previous research concentrated on sea surface cooling caused by typhoons. In this paper, we investigated the effect [...] Read more.

Radiation stress is defined as the excess momentum caused by ocean waves, which exerts an indispensable impact on the upper-layer ocean conditions as waves pass by. Previous research concentrated on sea surface cooling caused by typhoons. In this paper, we investigated the effect of wave-induced radiation stress on upper-layer ocean temperature (including sea surface temperature (SST) and mixed-layer temperature) under typhoon conditions, as well as the effect of radiation stress on the surface current field. The FVCOM-SWAVE model, which is based on the SWAN model, is used to simulate the response of upper-layer ocean temperature to radiation stress. The simulated results, when validated with Jason-3 satellite and ARGO data, could reproduce the observed phenomenon well in general. Compared to simulations without radiation stress, the bias in the SST results is reduced by about 1 °C if the radiation stress term is taken into account. The mixed-layer depth temperature is expected to be simulated more accurately, with a root mean square error (RMSE) of less than 1.63 °C and a correlation coefficient (COR) of about 0.94. Results show that wave-induced radiation stress enhances the surface current and causes certain deviations to the right so that the upper water diverges and upwelling increases, resulting in a decrease in SST. When the influence of double typhoons is considered, the airflow of LEKIMA(L) rotates from the northwest toward KROSA (R), limiting the development of significant wave height (SWH) and reducing the cooling range. As a result, the present study is of tremendous importance in precisely forecasting the ocean state of the western North Pacific (WNP). Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

20 pages, 7177 KiB

Open AccessArticle

Assessment of Antarctic Sea Ice Cover in CMIP6 Prediction with Comparison to AMSR2 during 2015–2021

by Siqi Li, Yu Zhang, Changsheng Chen, Yiran Zhang, Danya Xu and Song Hu

Remote Sens. 2023, 15(8), 2048; https://doi.org/10.3390/rs15082048 - 12 Apr 2023

Viewed by 1949

Abstract

A comprehensive assessment of Antarctic sea ice cover prediction is conducted for twelve CMIP6 models under the scenario of SSP2-4.5, with a comparison to the observed data from the Advanced Microwave Scanning Radiometer 2 (AMSR2) during 2015–2021. In the quantitative evaluation of sea [...] Read more.

A comprehensive assessment of Antarctic sea ice cover prediction is conducted for twelve CMIP6 models under the scenario of SSP2-4.5, with a comparison to the observed data from the Advanced Microwave Scanning Radiometer 2 (AMSR2) during 2015–2021. In the quantitative evaluation of sea ice extent (SIE) and sea ice area (SIA), most CMIP6 models show reasonable variation and relatively small differences compared to AMSR2. CMCC-CM4-SR5 shows the highest correlation coefficient (0.98 and 0.98) and the lowest RMSD (0.98 × 10⁶ km² and 1.07 × 10⁶ km²) for SIE and SIA, respectively. In the subregions, the models with the highest correlation coefficient and the lowest RMSD for SIE and SIA are inconsistent. Most models tend to predict smaller SIE and SIA compared to the observational data. GFDL-CM4 and FGOALS-g3 show the smallest mean bias (−4.50 and −1.21 × 10⁵ km²) and the most reasonable interannual agreement of SIE and SIA with AMSR2, respectively. In the assessment of sea ice concentration (SIC), while most models can accurately predict the distribution of large SIC surrounding the Antarctic coastal regions, they tend to underestimate SIC and are unable to replicate the major patterns in the sea ice edge region. GFDL-CM4 and FIO-ESM-2-0 exhibit superior performance, with less bias (less than −5%) and RMSD (less than 23%) for SIC in the Antarctic. GFDL-CM4, FIO-ESM-2-0, and CESM2 exhibit relatively high positive correlation coefficients exceeding 0.60 with the observational data, while few models achieve satisfactory linear trend prediction of SIC. Through the comparison with RMSD, Taylor score (TS) consistently evaluates the Antarctic sea ice cover and proves to be a representative statistical indicator and applicable for its assessment. Based on comprehensive assessments of sea ice cover, CESM2, CMCC-CM4-SR5, FGOALS-g3, FIO-ESM-2-0, and GFDL-CM4 demonstrate more reasonable prediction performance. The assessment findings enhance the understanding of the uncertainties associated with sea ice in the CMIP6 models and highlighting the need for a meticulous selection of the multimodel ensemble. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

24 pages, 35825 KiB

Open AccessArticle

The Respondence of Wave on Sea Surface Temperature in the Context of Global Change

by Ru Yao, Weizeng Shao, Mengyu Hao, Juncheng Zuo and Song Hu

Remote Sens. 2023, 15(7), 1948; https://doi.org/10.3390/rs15071948 - 6 Apr 2023

Cited by 10 | Viewed by 2111

Abstract

Several aspects of global climate change, e.g., the rise of sea level and water temperature anomalies, suggest the advantages of studying wave distributions. In this study, WAVEWATCH-III (WW3) (version 6.07), which is a well-known numerical wave model, was employed for simulating waves over [...] Read more.

Several aspects of global climate change, e.g., the rise of sea level and water temperature anomalies, suggest the advantages of studying wave distributions. In this study, WAVEWATCH-III (WW3) (version 6.07), which is a well-known numerical wave model, was employed for simulating waves over global seas from 1993–2020. The European Centre for Medium-Range Weather Forecasts (ECMWF), Copernicus Marine Environment Monitoring Service (CMEMS), current and sea level were used as the forcing fields in the WW3 model. The validation of modelling simulations against the measurements from the National Data Buoy Center (NDBC) buoys and Haiyang-2B (HY-2B) altimeter yielded a root mean square error (RMSE) of 0.49 m and 0.63 m, with a correlation (COR) of 0.89 and 0.90, respectively. The terms calculated by WW3-simulated waves, i.e., breaking waves, nonbreaking waves, radiation stress, and Stokes drift, were included in the water temperature simulation by a numerical circulation model named the Stony Brook Parallel Ocean Model (sbPOM). The water temperature was simulated in 2005–2015 using the high-quality Simple Ocean Data Assimilation (SODA) data. The validation of sbPOM-simulated results against the measurements obtained from the Array for Real-time Geostrophic Oceanography (Argo) buoys yielded a RMSE of 1.12 °C and a COR of 0.99. By the seasonal variation, the interrelation of the currents, sea level anomaly, and significant wave heights (SWHs) were strong in the Indian Ocean. In the strong current areas, the distribution of the sea level was consistent with the SWHs. The monthly variation of SWHs, currents, sea surface elevation, and sea level anomalies revealed that the upward trends of SWHs and sea level anomalies were consistent from 1993–2015 over the global ocean. In the Indian Ocean, the SWHs were obviously influenced by the SST and sea surface wind stress. The rise of wind stress intensity and sea level enlarges the growth of waves, and the wave-induced terms strengthen the heat exchange at the air–sea layer. It was assumed that the SST oscillation had a negative response to the SWHs in the global ocean from 2005–2015. This feedback indicates that the growth of waves could slow down the amplitude of water warming. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

19 pages, 6737 KiB

Open AccessArticle

An Investigation of Impacts of Surface Waves-Induced Mixing on the Upper Ocean under Typhoon Megi (2010)

by Wenqing Zhang, Rui Li, Donglin Zhu, Dongliang Zhao and Changlong Guan

Remote Sens. 2023, 15(7), 1862; https://doi.org/10.3390/rs15071862 - 30 Mar 2023

Cited by 3 | Viewed by 1932

Abstract

Surface waves play an essential role in regulating the mixing processes in the upper ocean boundary, and then directly affect the air–sea exchange of mass and energy, which is important for the intensity prediction of tropical cyclones (TCs). The relative and integrated impacts [...] Read more.

Surface waves play an essential role in regulating the mixing processes in the upper ocean boundary, and then directly affect the air–sea exchange of mass and energy, which is important for the intensity prediction of tropical cyclones (TCs). The relative and integrated impacts of the wave breaking (WB) and the wave orbital motion (WOM) on the mixing and ocean response to TC forcing are investigated under typhoon Megi (2010), using the modeled data from a fully coupled air–sea–wave model. It is shown that the WOM can effectively increase the turbulence mixing in the upper ocean, thus significantly deepening the mixing layer depth and cooling the sea surface temperature. The WB can modulate the mixing layer depth and sea surface temperature to some extent in the cold tail zone with a shallow mixing layer (owing to typhoon forcing), whereas the WOM plays a predominant role. On the aspect of ocean currents driven by typhoon winds, the WOM-induced mixing significantly weakens the current velocity and shear strength in the upper ocean mixing layer, while the relative contribution for turbulence production between the WOM and the current shear differs at different vertical regions. Moreover, the effect of the WOM on the upper ocean turbulent mixing are dependent on the location with respect to the typhoon center, the local vertical thermal structure, and surface wave states. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

26 pages, 8824 KiB

Open AccessArticle

Effects of Surface Wave-Induced Mixing and Wave-Affected Exchange Coefficients on Tropical Cyclones

by Wenqing Zhang, Jialin Zhang, Qingxiang Liu, Jian Sun, Rui Li and Changlong Guan

Remote Sens. 2023, 15(6), 1594; https://doi.org/10.3390/rs15061594 - 15 Mar 2023

Cited by 1 | Viewed by 2344

Abstract

Surface waves perform a crucial role in modulating tropical cyclone (TC) systems and have proved to be key for numerical TC predictions. In this study, we investigate the effects of wave-induced mixing and wave-affected surface exchange coefficients using a coupled ocean–atmosphere–wave model for [...] Read more.

Surface waves perform a crucial role in modulating tropical cyclone (TC) systems and have proved to be key for numerical TC predictions. In this study, we investigate the effects of wave-induced mixing and wave-affected surface exchange coefficients using a coupled ocean–atmosphere–wave model for two real TC cases: Shanshan (2018) and Megi (2010). The results demonstrate that wave-affected surface exchange coefficients enhance air–sea heat fluxes and have a significantly positive effect on simulated TC intensity, size, and strengthening process. In contrast, the wave-induced mixing has a negative impact on TC intensity and size and is not conducive to TC intensification and maintenance. The net effect of these two factors is a balance between the wave-affected positive contribution and the negative contribution from wave-induced sea surface temperature cooling. We find that the effect of wave-induced mixing on a TC system depends on the local thermal structure of the ocean. When the thermocline is weak and there is warm water at the wave-induced mixing penetration depth, the negative effect of the wave-induced mixing is weak. However, when there is cold subsurface water and a strong thermocline, wave-induced mixing has a significant impact, which exceeds the wave-driven positive feedback. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Graphical abstract

24 pages, 8626 KiB

Open AccessArticle

Approach for Preservation and Reconstruction of Two-Dimensional Wave Spectra and Its Application to Boundary Conditions in Nested Wave Modeling

by Xingjie Jiang, Daolong Wang, Yongzeng Yang, Meng Sun and Qianqian He

Remote Sens. 2023, 15(5), 1360; https://doi.org/10.3390/rs15051360 - 28 Feb 2023

Viewed by 1561

Abstract

Typically, storing a two-dimensional wave spectrum could occupy more than one thousand storage units, making saving and reading boundary spectra computationally burdensome in nested wave simulations. This paper proposes a new approach for preservation of a wave spectrum that can reduce the required [...] Read more.

Typically, storing a two-dimensional wave spectrum could occupy more than one thousand storage units, making saving and reading boundary spectra computationally burdensome in nested wave simulations. This paper proposes a new approach for preservation of a wave spectrum that can reduce the required number of storage units to dozens. Using a corresponding reconstruction approach, the spectrum can then be rebuilt with intact spectral characteristics. Experimental application confirmed that the reconstructed spectra could be adopted as boundary conditions in nested wave modeling. The newly proposed approach for preservation and reconstruction of spectra allows long-term spectral information covering the entire simulated domain to be saved with more acceptable storage consumption, and such information can then be adopted as nesting conditions for nested-child simulations without the limitations of predefined boundaries. The above-mentioned properties of the new method could help support engineering projects concerning wave environments, research focused on wave climatology, and studies associated with wave energy assessment. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

18 pages, 9570 KiB

Open AccessArticle

Evaluation of CFOSAT Wave Height Data with In Situ Observations in the South China Sea

by Bo Li, Junmin Li, Shilin Tang, Ping Shi, Wuyang Chen and Junliang Liu

Remote Sens. 2023, 15(4), 898; https://doi.org/10.3390/rs15040898 - 6 Feb 2023

Cited by 3 | Viewed by 1982

Abstract

The wave spectrometer operated by the China–France Oceanography Satellite (CFOSAT) can provide global ocean wave observation data. Although a lot of work on calibration and verification has been carried out in the open oceans dominated by swells, the quality of the data in [...] Read more.

The wave spectrometer operated by the China–France Oceanography Satellite (CFOSAT) can provide global ocean wave observation data. Although a lot of work on calibration and verification has been carried out in the open oceans dominated by swells, the quality of the data in the relatively enclosed sea area with complex terrain still lacks sufficient examination. The objective of this study is to assess the performance of the significant wave height data of the CFOSAT in the South China Sea (SCS), a unique sea area characterized by semi-enclosed basin and multi-reef terrain, and to recognize the environmental factors affecting the data quality. Compared against the long-term observations from five mooring or buoy sites, we find that the data is well performed in the relatively open and deep areas of the SCS, with an average correlation coefficient as high as 0.87, and a low average root-mean-square error of 0.47 m. However, the combined effects of complex topography, monsoons, and swell proportion variation will affect the performance of data. In the southern deep areas, the waves may be affected by a large number of dotted reefs, leading to wave deformations and energy dissipation in different seasons. In the northern nearshore areas, waves tend to be sheltered by the land or distorted by the shallow topography effects. These processes make it difficult for the swell to fully develop as in the open oceans. The low proportion of swell is a disadvantage for the CFOSAT to correctly observe the wave data and may lead to possible errors. Our results emphasize the importance of more verification when applying the CFOSAT data in certain local seas, and the necessity to adjust the algorithm of inverting wave spectra according to specific environmental factors. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

25 pages, 8549 KiB

Open AccessArticle

Sudden Track Turning of Typhoon Prapiroon (2012) Enhanced the Upper Ocean Response

by Yihan Zhang, Yuhao Liu, Shoude Guan, Qian Wang, Wei Zhao and Jiwei Tian

Remote Sens. 2023, 15(2), 302; https://doi.org/10.3390/rs15020302 - 4 Jan 2023

Cited by 8 | Viewed by 2214

Abstract

Due to the change in environmental steering flow influenced by the surrounding synoptic systems, typhoon tracks often manifest sudden turnings, potentially prolonging the residence time of typhoon wind forcing and, thus, exerting a remarkable upper ocean response. Typhoon Prapiroon (2012) in the western [...] Read more.

Due to the change in environmental steering flow influenced by the surrounding synoptic systems, typhoon tracks often manifest sudden turnings, potentially prolonging the residence time of typhoon wind forcing and, thus, exerting a remarkable upper ocean response. Typhoon Prapiroon (2012) in the western North Pacific, had a very complex track and underwent two sudden-turning stages over its lifespan. On the basis of satellite and Argo float observations, this paper studies the surface and subsurface ocean environmental responses to Prapiroon. The observations show that the oceanic responses during the two sudden-turning stages of Prapiroon were much more remarkable than those in the straight-moving stage, including significant sea surface temperature (SST) cooling (~7 °C), sea surface chlorophyll-a (Chl-a) concentration increase (>0.30 mg m⁻³), and sea surface height anomaly (SSHA) reduction (<−50 cm), compared with those in the straight-moving stage, with SST cooling weaker than 3 °C, Chl-a concentration increase less than 0.05 mg m⁻³, and SSHA reduction less than −10 cm. By employing the three-dimensional Price–Weller–Pinkel (3DPWP) model to conduct a series of sensitivity experiments, we separate the contribution of the typhoon track’s sudden turnings to the upper ocean response and find that the relative contributions of the two sudden turnings to SST cooling (sea surface salinity salinification) reached 38.4% (23.5%) and 46.8% (28.0%), respectively. In addition, the model experiments further show that the sudden turning could also induce stronger upwelling in the subsurface ocean. Our results demonstrate that typhoon track sudden turning could result in more kinetic energy input into the upper ocean, enhancing the physical and biological responses in the upper ocean. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

27 pages, 13092 KiB

Open AccessArticle

Significant Wave Height Retrieval Using XGBoost from Polarimetric Gaofen-3 SAR and Feature Importance Analysis

by Tianran Song, Qiushuang Yan, Chenqing Fan, Junmin Meng, Yuqi Wu and Jie Zhang

Remote Sens. 2023, 15(1), 149; https://doi.org/10.3390/rs15010149 - 27 Dec 2022

Cited by 10 | Viewed by 1888

Abstract

Empirical algorithms have become the mainstream of significant wave height (SWH) retrieval from synthetic aperture radar (SAR). But the plentiful features from multi-polarizations make the selection of input for the empirical model a problem. Therefore, the XGBoost models are developed and evaluated for [...] Read more.

Empirical algorithms have become the mainstream of significant wave height (SWH) retrieval from synthetic aperture radar (SAR). But the plentiful features from multi-polarizations make the selection of input for the empirical model a problem. Therefore, the XGBoost models are developed and evaluated for SWH retrieval from polarimetric Gaofen-3 wave mode imagettes using the SAR features of different polarization combinations, and then the importance of each feature on the models is further discussed. The results show that the reliability of SWH retrieval models is independently confirmed based on the collocations of the SAR-buoy and SAR-altimeter. Moreover, the combined-polarization models achieve better performance than single-polarizations. In addition, the importance of different features to the different polarization models for SWH inversion is not the same. For example, the normalized radar cross section (NRCS), cutoff wavelength (λ_c), and incident angle (θ) have more decisive contributions to the models than other features, while peak wavelength (λ_p) and the peak direction (φ) have almost no contribution. Besides, NRCS of cross-polarization has a more substantial effect, and the λ_c of hybrid polarization has a stronger one than other polarization models. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

21 pages, 10702 KiB

Open AccessArticle

Study on Retrievals of Ocean Wave Spectrum by Spaceborne SAR in Ice-Covered Areas

by Bingqing Huang and Xiaoming Li

Remote Sens. 2022, 14(23), 6086; https://doi.org/10.3390/rs14236086 - 30 Nov 2022

Cited by 2 | Viewed by 1866

Abstract

The sea ice in the Arctic is retreating rapidly and ocean waves may accelerate the process by interacting with sea ice. Though Synthetic Aperture Radar (SAR) has shown great capability of imaging waves in ice, there are few attempts to retrieve the ocean [...] Read more.

The sea ice in the Arctic is retreating rapidly and ocean waves may accelerate the process by interacting with sea ice. Though Synthetic Aperture Radar (SAR) has shown great capability of imaging waves in ice, there are few attempts to retrieve the ocean wave spectrum (OWS) by SAR in ice-covered areas. In this study, based on the previously developed nonlinear inversion scheme, i.e., the Max Planck Institute (MPI) scheme, and the Sentinel-1 SAR data acquired in the Barents Sea, ocean wave spectra were retrieved by using the different combinations of modulation transfer functions (MTFs) in the MPI scheme: (1) using the same MTFs as those used in open water; (2) by neglecting both the hydrodynamic and tilt modulations; (3) by neglecting the hydrodynamic modulation but involving a newly fitted tilt modulation over ice for HH-polarized SAR data. We compared the simulated SAR image spectra based on the retrievals with the observational SAR image spectra to quantify their respective performances. The comparisons suggest that neglecting hydrodynamic modulation can significantly improve the retrievals. The remaining tilt modulation can further improve the retrievals, particularly for range-travelling waves. This study enhances the understanding of the principles of SAR imaging waves in ice and provides basics for retrievals of ocean wave spectra by SAR data in ice-covered areas. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

19 pages, 3533 KiB

Open AccessArticle

Evaluation of Multi-Incidence Angle Polarimetric Gaofen-3 SAR Wave Mode Data for Significant Wave Height Retrieval

by Chenqing Fan, Tianran Song, Qiushuang Yan, Junmin Meng, Yuqi Wu and Jie Zhang

Remote Sens. 2022, 14(21), 5480; https://doi.org/10.3390/rs14215480 - 31 Oct 2022

Cited by 11 | Viewed by 1428

Abstract

Significant wave height (SWH) is one of the most important descriptors for ocean wave fields. The polynomial regression (PolR) and Gaussian process regression (GPR) models are implemented to explore the effects of polarization and incidence angles on the SWH estimation from multi-incidence angle [...] Read more.

Significant wave height (SWH) is one of the most important descriptors for ocean wave fields. The polynomial regression (PolR) and Gaussian process regression (GPR) models are implemented to explore the effects of polarization and incidence angles on the SWH estimation from multi-incidence angle quad-polarization Gaofen-3 SAR wave mode data, based on the collocated data set of approximately 12,000 Gaofen-3 wave mode imagettes, matched with SWH from the fifth generation reanalysis (ERA5) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The results show that the model performance improves, as long as polarimetry information increases. The hybrid polarizations perform stronger than the co-polarizations or cross-polarizations alone, and they show better performance over the low to high seas. The lower incidence angles are more favorable for SAR SWH inversion. It is superior to introduce incidence angle in piecewise way, rather than to include it as an independent variable in the models. Then, the final PolR and GPR models, with the superior input scheme that includes the quad-polarized features and introduces the incidence angle in piecewise way, are assessed independently through a comparison with observations from altimeter and buoys. The accuracies of our SWH estimates are comparable or even higher than other published results. The GPR model outperforms the PolR model, due to the superiority of the added nonlinearity of GPR. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

16 pages, 7672 KiB

Open AccessArticle

Wind Field Retrieval with Rain Correction from Dual-Polarized Sentinel-1 SAR Imagery Collected during Tropical Cyclones

by Weizeng Shao, Zhengzhong Lai, Ferdinando Nunziata, Andrea Buono, Xingwei Jiang and Juncheng Zuo

Remote Sens. 2022, 14(19), 5006; https://doi.org/10.3390/rs14195006 - 8 Oct 2022

Cited by 19 | Viewed by 2190

Abstract

The purpose of this study is to include rain effects in wind field retrieval from C-band synthetic aperture radar (SAR) imagery collected under tropical cyclone conditions. An effective and operationally attractive approach to detect rain cells in SAR imagery is proposed and verified [...] Read more.

The purpose of this study is to include rain effects in wind field retrieval from C-band synthetic aperture radar (SAR) imagery collected under tropical cyclone conditions. An effective and operationally attractive approach to detect rain cells in SAR imagery is proposed and verified using four Sentinel-1 (S-1) SAR images collected in dual-polarized (vertical-vertical (VV) and vertical-horizontal (VH)) interferometric-wide swath imaging mode during the Satellite Hurricane Observation Campaign. SAR images were collocated with ancillary observations that include sea surface wind and rain rate from the Stepped-Frequency Microwave Radiometer (SFMR) on board of the National Oceanic and Atmospheric Administration aircraft. The winds are inverted from VV- and VH-polarized S-1 image using the CMOD5.N and S1IW.NR geophysical model functions (GMFs), respectively. Location and radius of cyclone’s eye, together with the TC central pressure, are calculated from the VV-polarized SAR-derived wind and a parametric model. A cost function is proposed that consists of the difference between the measured VV-polarized SAR normalized radar cross section (NRCS) and the NRCS predicted using CMOD5.N forced with the wind speed retrieved by the VH-polarized SAR images using S1IW.NR GMF and the wind direction retrieved from the patterns visible in the SAR image. This cost function is related to the SFMR rain rate. Experimental results show that the difference between measured and predicted NRCS values range from 0.5 dB to 5 dB within a distance of 100 km from the cyclone’s eye, while the difference increases spanning from 3 dB to 6 dB for distances larger than 100 km. Following this rationale, first the rain bands are extracted from SAR imagery and, then, the composite wind fields are reconstructed by replacing: (1) dual-polarized SAR-derived winds over the rain-free regions; (2) winds simulated using the radial-vortex model over the rain-affected regions. The validation of the composite wind speed against SFMR winds yields a <2 m s⁻¹ and >0.7 correlation (COR) at all flow directions up to retrieval speeds of 70 m s⁻¹. This result outperforms the winds estimated using the VH-polarized S1IW.NR GMF, which call for high error accuracy, such as about 4 m s⁻¹ with a 0.45 COR ranged from 330° to 360°. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Figure 1

22 pages, 15584 KiB

Open AccessArticle

Improving the Modeling of Sea Surface Currents in the Persian Gulf and the Oman Sea Using Data Assimilation of Satellite Altimetry and Hydrographic Observations

by Mahmoud Pirooznia, Mehdi Raoofian Naeeni, Alireza Atabati and Mohammad J. Tourian

Remote Sens. 2022, 14(19), 4901; https://doi.org/10.3390/rs14194901 - 30 Sep 2022

Cited by 4 | Viewed by 2004

Abstract

Sea surface currents are often modeled using numerical models without adequately addressing the issue of model calibration at the regional scale. The aim of this study is to calibrate the MIKE 21 numerical ocean model for the Persian Gulf and the Oman Sea [...] Read more.

Sea surface currents are often modeled using numerical models without adequately addressing the issue of model calibration at the regional scale. The aim of this study is to calibrate the MIKE 21 numerical ocean model for the Persian Gulf and the Oman Sea to improve the sea surface currents obtained from the model. The calibration was performed through data assimilation of the model with altimetry and hydrographic observations using variational data assimilation, where the weights of the objective functions were defined based on the type of observations and optimized using metaheuristic optimization methods. According to the results, the calibration of the model generally led the model results closer to the observations. This was reflected in an improvement of about 0.09 m/s in the obtained sea surface currents. It also allowed for more accurate evaluations of model parameters, such as Smagorinsky and Manning coefficients. Moreover, the root mean square error values between the satellite altimetry observations at control stations and the assimilated model varied between 0.058 and 0.085 m. We further showed that the kinetic energy produced by sea surface currents could be used for generating electricity in the Oman Sea and near Jask harbor. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures

Graphical abstract

19 pages, 6967 KiB

Open AccessArticle

Ocean Wave Inversion Based on a Ku/Ka Dual-Band Airborne Interferometric Imaging Radar Altimeter

by Chunyong Ma, Lichao Pan, Zhiwei Qiu, Da Liang, Ge Chen, Fangjie Yu, Hanwei Sun, Daozhong Sun and Weifeng Wu

Remote Sens. 2022, 14(15), 3578; https://doi.org/10.3390/rs14153578 - 26 Jul 2022

Cited by 4 | Viewed by 2226

Abstract

Ocean wave parameters (OWPs), including wave propagation direction (WPD), significant wave height (SWH), and main wave wavelength (MWW) can be typically retrieved using an interferometric imaging radar altimeter (InIRA). However, the inversion accuracy of ocean waves in Ku (15.8 GHz) and Ka (35.8 [...] Read more.

Ocean wave parameters (OWPs), including wave propagation direction (WPD), significant wave height (SWH), and main wave wavelength (MWW) can be typically retrieved using an interferometric imaging radar altimeter (InIRA). However, the inversion accuracy of ocean waves in Ku (15.8 GHz) and Ka (35.8 GHz) bands has not yet been evaluated due to the lack of field observation data. In this paper, to assess the inversion accuracy of OWPs in Ku and Ka bands, an airborne observation experiment using simultaneous Ku and Ka bands was carried out for the first time in Rizhao, Shandong Province, China. A dual-band InIRA (DInIRA) was configured with small incidence angles (4°–18°) and a Global Navigation Satellite System (GNSS) buoy; a mobile weather station was placed at the intersection of the plane routes for validation. Afterward, the WPD, SWH, and MWW were retrieved based on the imaging of sea surface height. As compared with the field in situ data, the WPD inversion results of main wind wave were found to be consistent with the measurement environmental wind direction. The SWH inversion biases, retrieved by the Ku and Ka bands, were 0.38 m and 0.27 m; the MWW inversion biases for the swells were equal to 16.75 m and 3.67 m; and the MWW inversion biases about the wind waves were 2.32 m and 0.57 m. Ultimately, it was established that the OWPs could be effectively retrieved by the DInIRA, and the inversion accuracy of the SWH and the MWW in the Ka band outperformed that in the Ku band. Full article

(This article belongs to the Special Issue Advances in the Ocean Surface Dynamics: Ocean Waves, Wind, and Air-Sea Interaction - in Memory of Professor Shengchang Wen)

► Show Figures