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Remote Sensing of the Sea Surface and the Upper Ocean

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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Ocean Remote Sensing".

Deadline for manuscript submissions: closed (31 January 2023) | Viewed by 20109

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Special Issue Editor

Dr. Stanislav Alexandrovich Ermakov

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Guest Editor

Geophysical Research Division, Institute of Applied Physics of the Russian Academy of Sciences, Ulyanova, 46, 603950 Nizhny Novgorod, Russia
Interests: geophysical hydrodynamics; wind waves; internal waves; marine slicks; microwave radar probing of the ocean
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

It is well known that the sea surface and the near surface ocean layers contain a lot of information about oceanic/atmospheric processes, such as internal waves, turbulence, oceanic and atmospheric fronts, nonuniform currents, surface films, etc. Manifestations of these processes are due to variations of optical characteristics in the upper water layers and modulation of short wind waves on the sea surface, which are responsible for imaging the phenomena in signals of remote sensing instruments, e.g., radar, microwave, and IR radiometers, and optical scanners. Despite significant progress made toward the solution to the problem of ocean remote sensing, many aspects of electromagnetic wave scattering from the ocean surface/subsurface layers, as well as the mechanisms of imaging of the oceanic/atmospheric phenomena are still poorly understood, such as microwave polarized backscattering.

This Special Issue is focused on the latest developments in remote sensing of the ocean using active/passive microwave, optical, and IR instruments, on physical mechanisms of “imprinting” of various oceanic/atmospheric phenomena in the imagery of the sea surface and of the near-surface layers in different bands of electromagnetic waves. We would like to encourage submissions in the areas of theory and models of electromagnetic scattering, as well as in field and laboratory experiments, including but not limited to the following topics:

Radar remote sensing of the sea surface (scattering mechanisms, polarized and multiband radar probing, scatterometry, altimetry);
Optical remote sensing of the ocean and inland waters;
Detection and characterizations of oceanic/atmospheric phenomena using their manifestations on the sea surface and in the upper water layers;
Marine slicks: their dynamics and remote sensing.

Dr. Stanislav Alexandrovich Ermakov
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Sea surface
Microwave radars and scattering mechanisms
Optical/IR ocean remote sensing
Oceanic and atmospheric phenomena signatures
Wind waves, surfactant films, internal waves, fronts

Related Special Issue

Remote Sensing of the Sea Surface and the Upper Ocean II in Remote Sensing (3 articles)

Published Papers (10 papers)

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Research

20 pages, 36987 KiB

Open AccessArticle

Investigating the Effects of Super Typhoon HAGIBIS in the Northwest Pacific Ocean Using Multiple Observational Data

by Jonghyeok Jeon and Takashi Tomita

Remote Sens. 2022, 14(22), 5667; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14225667 - 09 Nov 2022

Cited by 3 | Viewed by 1743

Abstract

Various multi-source observational platforms have enabled the exploration of ocean dynamics in the Northwest Pacific Ocean (NPO). This study investigated daily oceanic variables in response to the combined effect of the 2019 super typhoon HAGIBIS and the Kuroshio current meander (KCM), which has caused economic, ecological, and climatic changes in the NPO since August 2017. During HAGIBIS, the six-hourly wind speed data estimated a wind stress power (

P_{w}

) which strengthened around the right and left semicircles of the typhoon, and an Ekman pumping velocity (EPV) which intensified at the center of the typhoon track. As a result, firstly, the sea temperature (ST) decreased along a boundary with a high EPV and a strong cyclonic eddy area, and the mixed layer depth (MLD) was shallow. Secondly, a low sea salinity (SS) concentration showed another area where heavy rain fell on the left side of the typhoon track. Phytoplankton bloom (PB) occurred with a large concentration of chlorophyll a (0.641

mg / m^{3}

) over a wide extent (56,615

{km}^{2}

; above 0.5

mg / m^{3}

) after one day of HAGIBIS. An analysis of a favorable environment of the PB’s growth determined the cause of the PB, and a shift of the subsurface chlorophyll maximum layer (SCML; above 0.7

mg / m^{3}

) was estimated by comprehensive impact analysis. This study may contribute to understanding different individually-estimated physical and biological mechanisms and predicting the recurrence of ocean anomalies. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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Figure 1

16 pages, 935 KiB

Open AccessArticle

Analysis of Data-Derived SeaWinds Normalized Radar Cross-Section Noise

by Giuseppe Grieco, Ad Stoffelen, Anton Verhoef, Jur Vogelzang and Marcos Portabella

Remote Sens. 2022, 14(21), 5444; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14215444 - 29 Oct 2022

Cited by 2 | Viewed by 1270

Abstract

The normalized standard deviation (

K_{p}

) of the noise that affects scatterometer Normalized Radar Cross-Sections (

σ_{0}

s) plays a key role in the ocean and more in particular coastal wind retrieval procedures and the a posteriori quality control. This [...] Read more.

The normalized standard deviation (

K_{p}

) of the noise that affects scatterometer Normalized Radar Cross-Sections (

σ_{0}

s) plays a key role in the ocean and more in particular coastal wind retrieval procedures and the a posteriori quality control. This paper presents a method based on SeaWinds measurements to estimate

K_{p}

s. The method computes the standard deviation of the differences between the full-resolution (slice)

σ_{0}

s and the footprint (egg)

σ_{0}

. The results are compared to the median of

K_{p}

s provided with SeaWinds

σ_{0}

s, showing some non-negligible differences.

K_{p}

s estimated on non-homogeneous surfaces are larger than those estimated on sea, whereas no differences are appreciated in the provided

K_{p}

s, which is likely due to the ability of this methodology to account for the effect of the scene variability in the estimates. The presence of inter-slice biases is demonstrated with a trend with the antenna azimuth angle. A multi-collocation slice cross-calibration procedure is suggested for the retrieval stage. Finally, a theoretical model of the distribution of

σ_{0}

s is proposed and used to validate

K_{p}

s. The results prove the efficacy of this model and that the provided

K_{p}

s seem to be largely underestimated at low-wind regimes. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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Figure 1

18 pages, 7085 KiB

Open AccessArticle

Study of Sea Surface Geophysical Parameter Changes Due to Internal Solitary Waves Using a Sentinel-3 Synthetic Aperture Radar Altimeter

by Changtian Yu, Junmin Meng, Lina Sun, Hao Zhang and Haiqi Wang

Remote Sens. 2022, 14(21), 5375; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14215375 - 27 Oct 2022

Cited by 2 | Viewed by 1128

Abstract

In this paper, a high-resolution Sentinel-3 synthetic aperture radar altimeter is used to observe ISWs in the Sulu Sea. Based on the advantages of the simultaneous observation of Sentinel-3 OLCI and SRAL, the changes in

σ_{0}

, SWH, and SSHA caused by [...] Read more.

σ_{0}

, SWH, and SSHA caused by the ISWs are quantitatively analyzed. The results show that

σ_{0}

decreases and then increases after being modulated by the ISWs in the altimeter operation direction; SWH shows a large change; and the change trend of SSHA is the same as that of

σ_{0}

. Because of the angle between the propagation direction of the ISWs and the SRAL trajectory, the actual position corresponding to the peak power in the waveform detects the ISWs before the nadir, at which time

σ_{0}

is already modulated by ISWs, resulting in the deviation of

σ_{0}

. In addition, the sea surface roughness within the SRAL footprint in this case is no longer uniform, which violates the assumption of retracking and leads to the incorrect estimation of geophysical parameters such as SWH and SSHA. With a view to correcting these errors, the effect of ISWs on the retracker must therefore be considered and the model for waveform modified accordingly. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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Figure 1

17 pages, 6721 KiB

Open AccessArticle

A Shipborne Photon-Counting Lidar for Depth-Resolved Ocean Observation

by Xue Shen, Wei Kong, Peng Chen, Tao Chen, Genghua Huang and Rong Shu

Remote Sens. 2022, 14(14), 3351; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14143351 - 12 Jul 2022

Cited by 14 | Viewed by 1998

Abstract

Depth-resolved information is essential for ocean research. For this study, we developed a shipborne photon-counting lidar for depth-resolved oceanic plankton observation. A pulsed fiber laser with frequency doubling to 532 nm acts as a light source, generating a single pulse at the micro-joule level with a pulse width of less than 1 ns. The receiver is capable of simultaneously detecting the elastic signal at two orthogonal polarization states, the Raman scattering from seawater, and the fluorescence signal from chlorophyll A. The data acquisition system utilizes the photon-counting technique to record each photon event, after which the backscattering signal intensity can be recovered by counting photons from multiple pulses. Benefitting from the immunity of this statistical detection method to the ringing effect of the detector and amplifier circuit, high-sensitivity and high-linearity backscatter signal measurements are realized. In this paper, we analyze and correct the after-pulse phenomenon of high-linearity signals through experiments and theoretical simulations. Through the after-pulse correction, the lidar attenuation coefficient retrieved from the corrected signal are in good agreement with the diffuse attenuation coefficients calculated from the in situ instrument, indicating the potential of this shipborne photon-counting lidar for ocean observation applications. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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17 pages, 5689 KiB

Open AccessArticle

Air–Sea Interface Parameters and Heat Flux from Neural Network and Advanced Microwave Scanning Radiometer Observations

by Biao Zhang, Xiaotong Yu, William Perrie and Fenghua Zhou

Remote Sens. 2022, 14(10), 2364; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14102364 - 13 May 2022

Cited by 2 | Viewed by 1581

Abstract

We present a new approach, based on a multi-parameter back-propagation neural network (BPNN) model, to simultaneously retrieve sea surface wind speed, sea surface temperature, near-surface air temperature, and dewpoint temperature over the global oceans from the Advanced Microwave Scanning Radiometer 2 (AMSR2) onboard the Global Change Observation Mission 1st-Water (GCOM-W1). The model is trained and validated with the collocations of AMSR2 multi-channel (6.9–36.5 GHz) brightness temperatures, under both clear and cloudy conditions, and National Data Buoy Center (NDBC) and Tropical Atmosphere Ocean Project (TAO) buoy measurements along with ECMWF ERA5 reanalysis data. The root-mean-square (rms) errors of BPNN-retrieved sea surface wind speed, sea surface temperature, near-surface air temperature, and dewpoint temperature are 1.13 m/s, 1.02 °C, 1.20 °C, and 1.57 °C, respectively. The first three retrieved geophysical parameters and the estimated relative humidity from near-surface air temperature and dewpoint temperature are used to compute the sensible heat flux (SHF) and latent heat flux (LHF), using an improved bulk flux parametrization. The rms errors of the estimated SHF and LHF from BPNN-derived air–sea interface variables, and those from buoy and reanalysis data, are 18.13 W/m² and 39.56 W/m². We also compare SHF and LHF estimates with the Yongxing air–sea flux tower measurements in the northern South China Sea. The estimated SHF and LHF in summer and autumn periods are closer to observations than in winter and spring. The proposed method has potential to derive instantaneous air–sea interface atmospheric and oceanic parameters as well as surface sensible and latent heat fluxes from AMSR2 along-track wide swath observations. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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Graphical abstract

16 pages, 5013 KiB

Open AccessArticle

Manifestation of Spiral Structures under the Action of Upper Ocean Currents

by Olga Shomina, Olga Danilicheva, Tatiana Tarasova and Ivan Kapustin

Remote Sens. 2022, 14(8), 1871; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14081871 - 13 Apr 2022

Cited by 5 | Viewed by 1807

Abstract

The traditional approach to the interpretation of spirals observed in radar, optical and radiometric panoramas of a sea surface is based on equating the outer spiral scale with the scale of a manifesting eddy, but the validity of this approach has been poorly studied. Using the maximum cross-correlation (MCC) method for multispectral satellite images containing a spiral structure, we found a significant discrepancy between the structures of horizontal velocity fields and the geometrical characteristics of spiral structures in each band. Each velocity field demonstrated a pair of points of zero velocity with a km-scale difference between their positions in different bands. In order to describe the observed features, an analytical description of the upper-ocean current composed of a spiral eddy and of a homogeneous drift (related, in particular, to wind forcing) is proposed. This simple model states that the spiral characteristics and the position of the spiral center depend on a drift current even when the genuine characteristics of the marine eddy are fixed. The studied example shows that the diameter of an eddy core may significantly (2–3 times) differ from the outer scale of the spiral, which demonstrates the incorrectness of the traditional approach of spiral structures interpretation. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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Graphical abstract

26 pages, 5458 KiB

Open AccessArticle

Effects of Surface Wave Breaking Caused by Internal Solitary Waves in SAR Altimeter: Sentinel-3 Copernicus Products and Advanced New Products

by Adriana M. Santos-Ferreira, José C. B. da Silva, Jorge M. Magalhaes, Samira Amraoui, Thomas Moreau, Claire Maraldi, François Boy, Nicolas Picot and Franck Borde

Remote Sens. 2022, 14(3), 587; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14030587 - 26 Jan 2022

Cited by 7 | Viewed by 3142

Abstract

We address surface wave breaking caused by oceanic Internal Solitary Waves (ISWs) and how ISWs are manifested in the SAR altimeter onboard Sentinel-3A and -3B satellites by means of their effects in Significant Wave Height (SWH). Two different regions of the ocean are selected, namely the tropical Atlantic Ocean off the Amazon shelf and the Banda Sea in the Indian Ocean, where there are scenes of Sentinel-3 OLCI acquired simultaneously with an along-track SAR mode altimeter, which include signatures of large amplitude ISWs. New data of unfocused SAR (UF-SAR 20 Hz) and fully focused SAR (FF-SAR 160 Hz) modes are analyzed, which are retracked in full range and over a reduced range of bins (truncation carried out dynamically ten gates away from the estimated epoch position). At first order, in scales of 1–3 km, a strong decrease in the normalized radar cross section (NRCS) over the rough part of the ISWs is observed followed by a small increase in the smooth part relative to the unperturbed ocean background. A second order ISW signature, in scales of 20 km, is noted: the SWH is attenuated after the passage of an ISW, considering length scales of about 10 km before and after the ISW crest. The SWH signatures are unique in showing that the surface wave energy does not return to its unperturbed level after the passage of an ISW, admittedly because intense meter-scale wave breaking results in surface wave energy dissipation. Furthermore, Sentinel-2 MSI images are analyzed and provide insights into this same phenomenon: white-capping resulting in a radiance increase at all (visible) wavelengths. Modulation of breaking waves owing to ISWs is demonstrated by estimates of the fraction of breaking waves in the presence of internal waves. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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Graphical abstract

17 pages, 5665 KiB

Open AccessArticle

Practical Dynamical-Statistical Reconstruction of Ocean’s Interior from Satellite Observations

by Hengqian Yan, Ren Zhang, Huizan Wang, Senliang Bao and Chengzu Bai

Remote Sens. 2021, 13(24), 5085; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13245085 - 14 Dec 2021

Cited by 2 | Viewed by 1790

Abstract

The algorithms based on Surface Quasi-Geostrophic (SQG) dynamics have been developed and validated by many researchers through model products, however it is still doubtful whether these SQG-based algorithms are worth using in terms of observed data. This paper analyzes the factors impeding the practical application of SQG and makes amends by a simple “first-guess (FG) framework”. The proposed framework includes the correction of satellite salinity and the estimation of the FG background, making the SQG-based algorithms applicable in realistic circumstances. The dynamical-statistical method SQG-mEOF-R is thereafter applied to satellite data for the first time. The results are compared with two dynamical algorithms, SQG and isQG, and three empirical algorithms, multivariate linear regression (MLR), random forest (RF), and mEOF-R. The validation against Argo profiles showed that the SQG-mEOF-R presents a robust performance in mesoscale reconstruction and outperforms the other five algorithms in the upper layers. It is promising that the SQG-mEOF-R and the FG framework are applicable to operational reconstruction. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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Graphical abstract

19 pages, 3653 KiB

Open AccessArticle

Detecting the Surface Signature of Riverine and Effluent Plumes along the Bulgarian Black Sea Coast Using Satellite Data

by Irina Gancheva, Elisaveta Peneva and Violeta Slabakova

Remote Sens. 2021, 13(20), 4094; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13204094 - 13 Oct 2021

Cited by 3 | Viewed by 1807

Abstract

The clear and reliable detection of effluent plumes using satellite data is especially challenging. The surface signature of such events is of a small scale; it shows a complex interaction with the local environment and depends greatly on the effluent and marine water constitution. In the context of remote sensing techniques for detecting treated wastewater discharges, we study the surface signature of small river plumes, as they share specific characteristics, such as higher turbidity levels and increased nutrient concentration, and are fresh compared to the salty marine water. The Bulgarian Black Sea zone proves to be a challenging study area, with its optically complex waters and positive freshwater balance. Additionally, the Bulgarian Black Sea coast is a known tourist destination with an increased seasonal load; thus, the problem of the identification of wastewater discharges is a topical issue. In this study, we analyze the absorption components of the Inherent Optical Properties (IOPs) for 84 study points that are located at outfall discharging areas, river estuaries and at different distances from the shoreline, reaching the open sea area at a bottom depth of more than 2000 m. The calculations of IOPs take into account all available Sentinel 2 cloudless acquisitions for three years from 2017 until 2019 and are performed using the Case-2 Regional CoastColour (C2RCC) processor, implemented in the Sentinel Application Platform (SNAP). The predominant absorber for each study area and its temporal variation is determined, deriving the specific characteristics of the different areas and tracking their seasonal and annual course. Optical data from the Galata AERONET-OC site are used for validating the absorption coefficient of phytoplankton pigment. A conclusion regarding the possibility of distinguishing riverine, marine and coastal water is derived. The study provides a sound basis for estimating the advantages and drawbacks of optical satellite data for tracking the extent of effluent and fluvial plumes with unknown concentrations of optically significant seawater constituents. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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Graphical abstract

21 pages, 4085 KiB

Open AccessArticle

Strong Modulation of Short Wind Waves and Ka-Band Radar Return Due to Internal Waves in the Presence of Surface Films. Theory and Experiment

by Stanislav A. Ermakov, Irina A. Sergievskaya and Ivan A. Kapustin

Remote Sens. 2021, 13(13), 2462; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13132462 - 24 Jun 2021

Cited by 4 | Viewed by 1728

Abstract

Strong variability of Ka-band radar backscattering from short wind waves on the surface of water covered with surfactant films in the presence of internal waves (IW) was studied in wave tank experiments. It has been demonstrated that modulation of Ka-band radar return due to IW strongly depends on the relationship between the phase velocity of IW and the velocity of drifting surfactant films. An effect of the strong increase in surfactant concentration was revealed in convergent zones, associated with IW orbital velocities in the presence of a “resonance” surface steady current, the velocity of which was close to the IW phase velocity. A phenomenological model of suppression and modulations in the spectrum of small-scale wind waves due to films and IW was elaborated. It has been shown that backscatter modulation could not be explained by the modulation of free (linear) millimeter-scale Bragg waves, but was associated with the modulation of bound (parasitic) capillary ripples generated by longer, cm–dm-scale waves—a “cascade” modulation mechanism. Theoretical analysis based on the developed model was found to be consistent with experiments. Field observations which qualitatively illustrated the effect of strong modulation of Ka-band radar backscatter due to IW in the presence of resonance drift of surfactant films are presented. Full article

(This article belongs to the Special Issue Remote Sensing of the Sea Surface and the Upper Ocean)

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