Certain characteristics of radio signals scattered by a sea surface in directions close to the direction of specular reflection

1973 ◽  
Vol 16 (10) ◽  
pp. 1153-1157
Author(s):  
A. I. Kalmykov ◽  
A. S. Kurekin ◽  
V. Yu. Levantovskii ◽  
I. E. Ostrovskii ◽  
V. V. Pustovoitenko
Keyword(s):  
Specular Reflection ◽  
Sea Surface ◽  
Radio Signals

scholarly journals Monte Carlo Radiative Transfer Simulation to Analyze the Spectral Index for Remote Detection of Oil Dispersed in the Southern Baltic Sea Seawater Column: The Role of Water Surface State

2022 ◽  
Vol 14 (2) ◽  
pp. 247
Author(s):  
Zbigniew Otremba ◽  
Jacek Piskozub
Keyword(s):  
Baltic Sea ◽  
Spectral Index ◽  
Zenith Angle ◽  
Specular Reflection ◽  
Sea Surface ◽  
Optical Parameters ◽  
Angle Of Incidence ◽  
Water Emulsion ◽  
Southern Baltic Sea ◽  
Southern Baltic

The article presents the results of simulations that take into account the optical parameters of the selected sea region (from literature data on the southern Baltic Sea) and two optically extreme types of crude oil (from historical data) which exist in the form of a highly watered-down oil-in-water emulsion (10 ppm). The spectral index was analyzed based on the results of modeling the radiance reflectance distribution for almost an entire hemisphere of the sky (zenith angle from 0 to 80°). The spectral index was selected and is universal for all optically different types of oil (wavelengths of 650 and 412 nm). The possibility of detecting pollution in the conditions of the wavy sea surface (as a result of wind of up to 10 m/s) was studied. It was also shown that if the viewing direction is close to a direction perpendicular to the sea surface, observations aimed at determining the spectral index are less effective than observations under the zenith angle of incidence of sunlight for all azimuths excluding the direction of sunlight’s specular reflection.

scholarly journals Improving the GNSS-R Specular Reflection Point Positioning Accuracy Using the Gravity Field Normal Projection Reflection Reference Surface Combination Correction Method

2018 ◽  
Vol 11 (1) ◽  
pp. 33 ◽  
Author(s):  
Fan Wu ◽  
Wei Zheng ◽  
Zhaowei Li ◽  
Zongqiang Liu
Keyword(s):  
Gravity Field ◽  
Specular Reflection ◽  
Correction Method ◽  
Sea Surface ◽  
Reference Surface ◽  
Reflection Point ◽  
Positioning Accuracy ◽  
Normal Projection ◽  
Point Positioning ◽  
Surface Correction

Global Navigation Satellite System Reflectometry (GNSS-R) is of great significance for the extraction and research of precise information of sea surface topography. Improving measurement accuracy is necessary for realizing spaceborne GNSS-R sea surface altimetry application. The main error source of GNSS-R distance measurement is the error of the specular reflection point positioning, which directly affects the sea surface altimetry accuracy on the reference datum. There is an elevation error of several tens of meters between the reflection reference surface used by the existing specular reflection point geometric positioning methods and the sea surface elevation, which is importantly influenced by the earth’s gravity field. Therefore, the gravity field reflection reference surface correction is the key to improving the specular reflection point positioning accuracy. In this study, based on the correction of the GNSS-R reflection reference surface, research on improving the positioning accuracy of the specular reflection point is carried out. Firstly, in order to reduce the positioning error caused by the elevation difference between the reflection reference surface and the sea surface, the gravity field reflection reference surface correction method (GFRRSCM) which corrects the reflection reference surface from the WGS-84 ellipsoid to geoid is proposed, and the positioning accuracy is improved by 25.15 m. Secondly, the normal projection reflection reference surface correction method (NPRRSCM) is proposed to correct the specular reflection point determined by the GFRRSCM from the reflection reference plane of the radial to that of the normal. Additionally, in the process of solving the spatial geometric relationship of the reflection path, the approximate substitution error is reduced by directly solving the normal projection on the plane, and the positioning accuracy is further improved by 13.05 m towards the normal. Thirdly, based on the gravity field normal projection reflection reference surface combination correction method (GF-NPRRSCCM), the specular reflection point positioning accuracy is synthetically improved by 28.66 m.

scholarly journals Improving the Positioning Accuracy of Satellite-Borne GNSS-R Specular Reflection Point on Sea Surface Based on the Ocean Tidal Correction Positioning Method

2019 ◽  
Vol 11 (13) ◽  
pp. 1626 ◽  
Author(s):  
Fan Wu ◽  
Wei Zheng ◽  
Zhaowei Li ◽  
Zongqiang Liu
Keyword(s):  
Specular Reflection ◽  
Tidal Height ◽  
Sea Surface ◽  
Time Varying ◽  
Reference Surface ◽  
Positioning Error ◽  
Reflection Point ◽  
Positioning Accuracy ◽  
Static State ◽  
Elevation Difference

The positioning error of the specular reflection point is the main error source of Global Navigation Satellite System Reflectometry (GNSS-R) satellite sea surface altimetry. The existing specular reflection point geometric positioning methods do not consider the static-state elevation difference of tens of meters and the decimeter-level time-varying elevation difference between the reflection reference surface and the instantaneous sea surface. The resulting positioning error restricts the GNSS-R satellite sea surface altimetry from reaching cm-level high accuracy on the reference datum. Under the premise of the basic static-state elevation positioning error correction, reducing the time-varying elevation positioning error is the key to improving positioning accuracy. In this study, based on the principle of elevation correction of GNSS-R reflection reference surface, the main parameter that determines the real-time variation of sea surface height, ocean tide, is used to correct the specular reflection point from geoid to ocean tidal surface. The positioning error caused by the time-varying elevation error of the reflection reference surface is reduced, the positioning accuracy is improved, and the improvement is quantified. According to the research results, the ocean tidal correction positioning (OTCP) method improves the positioning accuracy by 0.31 m. The positioning accuracy improvement has a good correlation with the corresponding tidal height modulo, and the improvement is 1.07 times of the tidal height modulo. In the offshore, the tidal height gradient modulo is greater than the deep sea, the gradient of the tidal positioning correction has a good response to the tidal height gradient modulo, while the sensitivity of this response decreases in the deep sea.

The Effect of Sea State on the Polarization of Reflected Beidou B1 Signals

2020 ◽  
Vol 13 (5) ◽  
pp. 736-742
Author(s):  
Tingting Lyu ◽  
Shuang Sha ◽  
Min Zhang ◽  
Hao Zhang ◽  
Thomas A. Gulliver
Keyword(s):  
Reflection Loss ◽  
Specular Reflection ◽  
Signal To Noise Ratio ◽  
Incident Angle ◽  
Surface States ◽  
Sea Surface ◽  
Polarization Diversity ◽  
Angle Of Incidence ◽  
Circularly Polarized ◽  
Surface Conditions

Background: Oceanographic buoys generally employ satellites for positioning and data transmission. However, sea surface conditions can affect these signals. The Signal to Noise Ratio (SNR) of small observation buoys can be improved by exploiting polarization diversity. Methods: This paper discusses the effect of sea surface conditions on the polarization and reflection loss of Beidou B1 reflected signals for the purposes of exploiting polarization diversity. The Rayleigh roughness criterion is used to assess the roughness of the sea surface. The Fresnel reflection coefficients are derived to analyze the polarization and reflection loss of the Beidou B1 reflected signals with different sea surface states. Results: The results obtained show that for the Beidou B1 signals, the sea surface is considered rough for most sea surface states and incident angles. For smooth sea surfaces, the Beidou B1 reflected signals are mainly Left Hand Circularly Polarized (LHCP) waves, but Right Hand Circularly Polarized (RHCP) waves dominate when the incident angles are larger than the Brewster angle. The reflected loss is between -2 dB to -3.4 dB. In rough sea surfaces and the signals propagation is dominated by diffuse reflection. The reflection loss decreases with the incident angle and there is a fluctuation when the incident angle is around 49 degrees. The specular reflection signal has a significant amplitude when the angle of incidence is large. RHCP waves are the main component of the reflected signals, and the reflection loss is relatively small which can be employed for polarization diversity or marine remote sensing. Conclusion: polarization diversity is only useful with good sea conditions, and the corresponding gain decreases with the deterioration of the sea surface conditions.

Fluctuation Statistics of Short-Wave Millimeter Waveband Radio Signals Propagating Above Sea Surface

2003 ◽  
Vol 59 (5-6) ◽  
pp. 9
Author(s):  
V. G. Gutnik ◽  
N. V. Gorbach ◽  
V. N. Gorobets ◽  
L. I. Sharapov
Keyword(s):  
Short Wave ◽  
Sea Surface ◽  
Millimeter Waveband ◽  
Radio Signals

scholarly journals Fusion applied to phase altimetry in a GNSS buoy system

2020 ◽  
Author(s):  
Williams Kouassi ◽  
Georges Stienne ◽  
Serge Reboul
Keyword(s):  
Specular Reflection ◽  
Real Data ◽  
Satellite System ◽  
Two Dimensions ◽  
Sea Surface ◽  
High Rate ◽  
Important Indicator ◽  
Linear Evolution ◽  
The Earth ◽  
In Situ Experiments

<p>It has been shown that the earth surface can be observed using Global Navigation Satellite System (GNSS) signals as signals of opportunity. An important advantage of GNSS in this regard is that it provides a global coverage of the earth thanks to dozens of satellites, projected to be 120 by 2030, distributed in various constellations.</p><p>GNSS signals parameters such as the carrier phase and the amplitude can be used for example for soil moisture estimation, sea ice detection or sea surface altimetry, which is an important indicator for studying climate evolution. As the sea level varies in centimeters, sea surface altimeters have to be very precise. This accuracy can be achieved using satellite altimeters, provided the availability of precise validation and calibration techniques and in-situ experiments. The objective of this study is the definition of an original GNSS buoy system for satellite altimeters calibration.</p><p>GNSS buoy systems are a cheap and light alternative solution to mareographs and can provide high rate measurements. In our approach using this system, we consider, as observable, the phase difference between incoming GPS-L1 signals at a reference, fixed antenna at ~10m height on the ground and at a buoy antenna on the sea. In an analogy with a GNSS reflectometry system, the buoy can be compared to a specular reflection point, but presents the advantage of collecting the data from all visible satellites at the same location. The signals sensed by both antennas are digitized before processing.</p><p>Assuming that the horizontal two-dimensions position of the buoy is accurately known by GNSS positioning (which is more efficient in these dimensions than for estimating the height of the buoy), a new phase observable evolving linearly in the [-π , π] interval as a function of the sine of the satellite elevation can be defined. The slope of this linear evolution is proportional to the height between the two antennas, which is the parameter to estimate. For accuracy and robustness purpose, the estimation of this slope is realized using a circular-linear regression technique that includes the fusion of the data from all visible satellites signals. Indeed, we can show that, using the full span of the sines of visible satellites elevations, centimeter accuracy can be reached for integration times as short as a few milliseconds. The GNSS buoy technique described in this work is evaluated on synthetic and real data.</p>

scholarly journals OIL SPILL AISA+ HYPERSPECTRAL DATA DETECTION BASED ON DIFFERENT SEA SURFACE GLINT SUPPRESSION METHODS

2018 ◽  
Vol XLII-3 ◽  
pp. 2083-2087
Author(s):  
J. Yang ◽  
G. Ren ◽  
Y. Ma ◽  
L. Dong ◽  
J. Wan
Keyword(s):  
Oil Spill ◽  
Specular Reflection ◽  
Remote Sensing Data ◽  
Hyperspectral Data ◽  
Sea Surface ◽  
Filter Method ◽  
Data Detection ◽  
Detection Accuracy ◽  
Oil Spill Detection ◽  
Mean Filter

The marine oil spill is a sudden event, and the airborne hyperspectral means to detect the oil spill is an important part of the rapid response. Sun glint, the specular reflection of sun light from water surface to sensor, is inevitable due to the limitation of observation geometry, which makes so much bright glint in image that it is difficult to extract oil spill feature information from the remote sensing data. This paper takes AISA+ airborne hyperspectral oil spill image as data source, using multi-scale wavelet transform, enhanced Lee filter, enhanced Frost filter and mean filter method for sea surface glint suppression of images. And then the classical SVM method is used for the oil spill information detection, and oil spill information distribution map obtained by human-computer interactive interpretation is used to verify the accuracy of oil spill detection. The results show that the above methods can effectively suppress the sea surface glints and improve the accuracy of oil spill detection. The enhanced Lee filter method has the highest detection accuracy of 88.28 %, which is 12.2 % higher than that of the original image.

scholarly journals Monte Carlo Radiative Transfer Simulation to Analyze the Spectral Index for Remote Detection of Oil Dispersed in the Southern Baltic Sea Seawater Column: The Role of Water Surface State

2021 ◽  
Author(s):  
Zbigniew Otremba ◽  
Jacek Piskozub
Keyword(s):  
Baltic Sea ◽  
Spectral Index ◽  
Zenith Angle ◽  
Specular Reflection ◽  
Sea Surface ◽  
Optical Parameters ◽  
Angle Of Incidence ◽  
Water Emulsion ◽  
Southern Baltic Sea ◽  
Southern Baltic

The presented results of simulations take into account the optical parameters of the selected sea region (from literature data on the southern Baltic Sea) and two optically extreme types of crude oil (from historical data) which exist in the form of a highly diluted oil-in-water emulsion (10 ppm). The spectral index was analyzed based on the results of modelling the radiance reflectance distribution for almost an entire hemisphere of the sky (zenith angle from 0 to 80o). The spectral index was selected and is universal for all optically different types of oil (wavelengths 650 and 412 nm). The possibility of detecting pollution in the conditions of the wavy sea surface (as a result of wind of up to 10 m/s) was studied. It has been also shown that if the viewing direction is close to a direction perpendicular to the sea surface, observations aimed at determining the spectral index are less effective than observation under the zenith angle of incidence of sunlight for all azimuths excluding the direction of sunlight specular reflection.

scholarly journals The Spatial Correlation of a Multiple-Input Multiple-Output and Channel Model using Huygens-Fresnel Principle for Underwater Acoustic

2019 ◽  
Vol 15 (4) ◽  
pp. 343-350
Author(s):  
Shahideh Kiehbadroudinezhad ◽  
Adib Shahabi ◽  
Mohammad Ali Kiehbadroudinezhad
Keyword(s):  
Spatial Correlation ◽  
Channel Model ◽  
Specular Reflection ◽  
Multiple Input Multiple Output ◽  
Acoustic Propagation ◽  
Sea Surface ◽  
Analytical Models ◽  
Underwater Acoustic ◽  
Multiple Input ◽  
Input Multiple Output

In this work, the spatial correlation of a multiple-input multiple-output (MIMO) for underwater acoustic (UWA) channel is modelled. To obtain the spatial correlation for such a channel, a mathematical method to model the effect of the surface on the acoustic propagation is studied. The sea surface has a significant impact on the underwater acoustic propagation (UWA) channel since the sound field is scattered, particularly in rough sea conditions. In a situation where the sea surface is calm, the reflection is specular. In contrast, a sea surface subject to high sea states generates scattered waves. In these conditions, more complex mathematical equations are required to model the propagation. Current analytical models have limitations in terms of complexity and are not practical. Therefore, this study aims to consider a specular reflection to model the time-varying sea surface on the UWA channel. It is a simple model with low computationally complexity and can be used to assess the performance of UWA communications. Specifically, the specular reflection and transmission of an acoustic wave at a calm sea surface is studied, using the Huygens-Fresnel principle and the superposition theorem. The analytical model is developed using physical oceanic parameters representing the sea conditions. The results show a good agreement with the experimental analysis.

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