scholarly journals Studies of Internal Waves in the Strait of Georgia Based on Remote Sensing Images

2019 ◽  
Vol 11 (1) ◽  
pp. 96 ◽  
Author(s):  
Caixia Wang ◽  
Xin Wang ◽  
Jose C. B. Da Silva
Keyword(s):  
Remote Sensing ◽  
Internal Waves ◽  
River Mouth ◽  
Temporal Distribution ◽  
Tidal Currents ◽  
River Plume ◽  
Remote Sensing Images ◽  
Strait Of Georgia ◽  
Narrow Channels ◽  
Propagating Waves

This paper analyzes over 500 sets of internal waves in the Strait of Georgia (British Columbia, Canada) based on a large number of satellite remote sensing images. The spatial and temporal distribution of internal waves in the central region of the strait are discussed via statistical analysis. Possible generation origins of the observed internal waves are divided into three categories based on their different propagation directions and geographical locations: (1) the interaction between the narrow channels to the south of the Strait and the tidal currents, leading to the formation of mainly eastward and northward propagating waves; (2) the interaction between the tidal currents and the topography near Point Roberts, resulting in mainly westward propagating waves; (3) excitation by river plume, mainly near Fraser River mouth, leading to the formation of mainly westward waves along the direction of the river plume. The relation between the occurrence of internal waves in remote sensing images and wind or tide level is also discussed. It is found that most of the observed internal waves occur at low tides. However, due to the influence of the river, the eastward propagating internal waves near the river mouth seldom occur at the lowest tide. Also, internal waves are captured more easily by remote sensing images in summer due to the lower wind speed than winter and therefore the seasonal distribution of internal waves in remote sensing images may not be able to completely represent the real situation in the study area. Finally, combining the in situ measured data and model output data, the Benjamin-Ono equation is found to satisfyingly simulate the characteristic parameters of the studied internal waves.

From inflow to interflow, through plunging and lofting: uncovering the dominant flow processes of a sediment-rich negatively buoyant river inflow into a stratified lake

2021 ◽  
Author(s):  
Stan Thorez ◽  
Koen Blanckaert ◽  
Ulrich Lemmin ◽  
David Andrew Barry
Keyword(s):  
Remote Sensing ◽  
River Mouth ◽  
Ambient Water ◽  
Remote Sensing Images ◽  
Reservoir Water ◽  
Neutral Buoyancy ◽  
Wide Range ◽  
Adcp Measurements ◽  
Vorticity Production ◽  
Negatively Buoyant

<p>Lake and reservoir water quality is impacted greatly by the input of momentum, heat, oxygen, sediment, nutrients and contaminants delivered to them by riverine inflows. When such an inflow is negatively buoyant, it will plunge upon contact with the receiving ambient water and form a gravity-driven current near the bed (density current). If such a current is sediment-laden, its bulk density can be higher than that of the surrounding ambient water, even if its carrying fluid has a density lower than that of the surrounding ambient water. After sufficient sediment particles have settled however, the buoyancy of the current can reverse and lead to the plume rising up from the bed, a process referred to as lofting. In a stratified environment, the river plume may then find its way into a layer of neutral buoyancy to form an intermediate current (interflow). A deeper understanding of the wide range of hydrodynamic processes related to the transitions from open-channel inflow to underflow (plunging) and from underflow to interflow (lofting) is crucial in predicting the fate of all components introduced into the lake or reservoir by the inflow.</p><p>Field measurements of the plunging inflow of the negatively buoyant Rhône River into Lake Geneva (Switzerland/France) are presented. A combination of a vessel-mounted ADCP and remote sensing cameras was used to capture the three-dimensional flow field of the plunging and lofting transition zones over a wide range of spatial and temporal scales.</p><p>In the plunge zone, the ADCP measurements show that the inflowing river water undergoes a lateral (perpendicular to its downstream direction) slumping movement, caused by its density surplus compared to the ambient lake water and the resulting baroclinic vorticity production. This effect is also visible in the remote sensing images in the form of a distinct plume of sediment-rich water with a triangular shape leading away from the river mouth in the downstream direction towards a sharp tip. A wide range of vortical structures, which most likely impact the amount of mixing taking place, is also visible at the surface in the plunging zone.</p><p>In the lofting zone, the ADCP measurements show that the underflow undergoes a lofting movement at its edges. This is most likely caused by a higher sedimentation rate due to the lower velocities at the underflow edges and leads to a part of the underflow peeling off and forming an interflow, while the higher velocity core of the underflow continues following the bed. Here, the baroclinic vorticity production works in the opposite direction as that in the plunge zone. Further downstream, as more particles have settled and the surrounding ambient water has become denser, the remaining underflow also undergoes a lofting motion. The remnants of these lofting processes show in the remote sensing images as intermittent ‘boils’ of sediment rich water reaching the surface and traces of surface layer leakage.</p>

scholarly journals A Study on Brightness Reversal of Internal Waves in the Celebes Sea Using Himawari-8 Images

2021 ◽  
Vol 13 (19) ◽  
pp. 3831
Author(s):  
Beilei Hu ◽  
Junmin Meng ◽  
Lina Sun ◽  
Hao Zhang
Keyword(s):  
Remote Sensing ◽  
Internal Waves ◽  
Zenith Angle ◽  
Optical Remote Sensing ◽  
Remote Sensing Images ◽  
Angle Sensor ◽  
Reversal Phenomenon ◽  
Geostationary Meteorological Satellite ◽  
First Time ◽  
Meteorological Satellite

A geostationary meteorological satellite is located at a fixed point above the equator, which can continuously observe internal waves and provides great advantages in research on changes in the generation and propagation of internal waves. The scale of internal waves in the Celebes Sea is large, which is still very obvious in geostationary meteorological satellite images with a lower spatial resolution. This study considers continuous remote sensing images of geostationary meteorological satellite Himawari-8 to analyze the bright and dark features of internal waves in the Celebes Sea in optical remote sensing images. The solar zenith angle, sensor zenith angle and relative azimuth angle of internal waves in six images are calculated, and the changes are 12.45°, 0.20° and 3.44°, respectively, within 50 min. Moreover, based on the normalized sunglint radiance theory, the critical solar viewing angle is proposed and verified. The results indicate that the bright and dark features of internal waves when passing through sunglint and non-sunglint areas are greatly reversed, and the critical solar viewing angles are 18.73° and 27.41°, respectively. In this study, geostationary meteorological satellite Himawari-8 images are analyzed to study on the brightness reversal phenomenon of internal waves for the first time, and a unique brightness change in internal waves during the propagation process is revealed, which has not been reported in existing research.

scholarly journals Spatio-temporal distribution and classification of utilization of urban bare lots in low-slope hilly regions

PLoS ONE ◽  
2021 ◽  
Vol 16 (2) ◽  
pp. e0246746
Author(s):  
Qi Cao ◽  
Manjiang Shi
Keyword(s):  
Remote Sensing ◽  
Temporal Distribution ◽  
Urban Landscapes ◽  
Distribution Characteristics ◽  
Remote Sensing Images ◽  
Landscape Index ◽  
Activity Intensity ◽  
Transportation Service ◽  
Spatio Temporal

Urban bare lots are persistent phenomena in urban landscapes in the course of urbanization. In the present study, we examined the spatio-temporal distribution of urban bare lots in low-slope hilly areas, and to assess the major pathways by which they are generated and later re-transformed for exploitation. We extracted land use and land cover (LULC) change information and analyzed spatio-temporal distribution characteristics of urban bare lots using Landsat TM/OLI series remote sensing images. Subsequently, we proposed an index system for their evaluation and classification, and identified five types of urban bare lots. Urban bare lot quantity and distribution are closely correlated with human activity intensity. Stakeholders should consider the multiple effects of location, topography, landscape index, transportation, service facilities, and urban planning in urban bare lot classification activities for renovation and re-transformation.

scholarly journals Ballooning of River-Plume Bulge and Its Stabilization by Tidal Currents

2005 ◽  
Vol 35 (12) ◽  
pp. 2337-2351 ◽  
Author(s):  
Atsuhiko Isobe
Keyword(s):  
River Mouth ◽  
Tidal Currents ◽  
River Plume ◽  
Boundary Current ◽  
Inertial Instability ◽  
Long Time ◽  
Coastal Boundary ◽  
Ambient Currents ◽  
The Right ◽  
Coastal Boundary Current

Abstract When freshwater debouches into an adjacent ocean, an anticyclonic eddy (bulge) is formed in front of the river mouth. It is well known that a bulge growing offshore (ballooning) hardly reaches a steady state in the absence of either ambient currents or wind forcing. This study provides a physical interpretation for the ballooning of river-plume bulges by conducting numerical experiments in which a river plume is induced by a coastal freshwater source. Part of the freshwater released to the model ocean undergoes inertial instability. Near-inertial oscillations are predominant when disturbances are not forced in ambient waters of the river plume. These isotropic disturbances are amplified by inertial instability, so that unstabilized freshwater can move in arbitrary directions. Thus, unstabilized freshwater does not need to move toward the coastal boundary current on the right-hand side of the river mouth. Freshwater unstabilized for a long time can stay in the bulge for a long time. Unstabilized freshwater accumulates gradually in the bulge, and so ballooning occurs. When the direction of disturbances is prescribed in ambient waters, unstabilized freshwater is forced to move in the same direction. Thereby, the motion of unstabilized freshwater is restricted in the alongshore direction when background disturbances are induced by alongshore tidal currents. It is therefore concluded that tidal currents play a role in stabilizing the offshore growth of river-plume bulges in coastal and shelf waters.

scholarly journals Land Feature Extraction-Identification and Descrimincation using Geospatial Technique

10.29007/ckgd ◽  
2018 ◽  
Author(s):  
Dharmesh Modi ◽  
Subhash Bhandari ◽  
Laxmansinh B. Zala
Keyword(s):  
Remote Sensing ◽  
Time Scale ◽  
Regional Scale ◽  
High Tide ◽  
River Mouth ◽  
Tidal Currents ◽  
Tidal Range ◽  
Large Contribution ◽  
Geological Time Scale ◽  
Geomorphological Features

The Gulf of Cambay/Khambhat, (GoC), the study area is highly influenced by the tidal currents other than geological and structural set up of the region. In Gulf of Cambay, a large tidal range during high and low tides give rise to strong tidal currents and develops a mechanism of sediment transportation. Interestingly the inverted funnel shape of GoC has large contribution for the sediment deposition in this region. During high tide the tide currents move into the Gulf and encroaches the river mouth whereas during low tide, they move out. This regular phenomena since long period on geological time scale has modified the geomorphological features in this region.Along the major estuaries of Sabarmati, Mahi, Narmada and Tapi, the sediment budget is controlled by seasonal variation and also by tide and ebb phenomena.Using remote sensing images of different time scale and topographical map one can study the changes in geomorphological features. Satellite remote sensing technique has proven to be the paramount tool for studying surficial land features, especially for the inaccessible area or where time variable studies and regional scale studies are carried out. The well-developed natural or artificial features near to coastline viz salt pan, marshy land, mudflats, rocky cliffs, alluvial cliffs, wet land, mangroves, erosional and depositional features are well studied with the help of remote sensing techniques.

scholarly journals Internal Waves as a Source of Concentric Rings within Small River Plumes

2021 ◽  
Vol 13 (21) ◽  
pp. 4275
Author(s):  
Alexander Osadchiev ◽  
Roman Sedakov ◽  
Alexandra Gordey ◽  
Alexandra Barymova
Keyword(s):  
Remote Sensing ◽  
Internal Waves ◽  
High Frequency ◽  
River Mouth ◽  
Small River ◽  
Shear Instability ◽  
Joint Analysis ◽  
The Black Sea ◽  
River Plumes

This study is focused on concentric rings, which are regularly observed by remote sensing of small river plumes located in different regions worldwide. We report new aerial observations of these features obtained by quadcopters and supported by synchronous in situ measurements, which were collected during the recent field survey at the Bzyb river plume in the eastern part of the Black Sea. Joint analysis of remote sensing imagery and in situ data suggest that the observed concentric rings are surface manifestations of high-frequency internal waves generated in the vicinity of the river mouth. The obtained results demonstrate that the propagation of these waves does not induce offshore material transport within the plume induced by shear instability, which was hypothesized in a recent numerical modeling study of this process. We provide an explanation for the appearance of misleading material features in the numerical simulations discussed above. Finally, we discuss directions for future research of high-frequency internal waves generated in small river plumes.

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