Turbidity Patterns Research Articles

Study of the dynamics of estuarine and coastal waters using remote sensing: the Tinto-Odiel estuary, SW Spain

This paper deals with the application of satellite images to characterize some aspects of the circulation dynamics of the Tinto-Odiel estuary using turbidity patterns as ‘natural tracers’. 15 images (Landsat TM and Spot HRV) were processed to provide synoptic, instantaneous views of the circulation patterns under different environmental conditions. In addition, a comparison was made between results of oceanographic field work, using biplanes and fluorescent tracers, and satellite image turbidity patterns used as ‘ground truth’ data for specific hydroclimatic situations. This approach allowed (1) the identification and mapping of dynamic processes of interest during a theoretical tidal cycle, (2) the elaboration of additional information on the ‘flow schemes’ at the mouth of the estuary with improved spatial and temporal resolution, and (3) the supply of basic data to improve the knowledge of exchange processes between estuarine and coastal waters. The results of this study are considered to be useful for the management of the estuarine system.

Potential Usage of Remote Sensing Data in Studying the Behaviour of Shore Drift Along Kerala Coast, India

Landsat images were analysed to examine direction, amount and behaviour of long-shore drift and its contribution towards deciding areas vulnerable to coastal erosion and accretion along the coast of Kerala. Two approaches are adopted while utilizing the remote sensing data. Net shore-drift direction is determined firstly by studying various coastal landform indicators and secondly by studying offshore turbidity distribution patterns. Landform indicators study suggest that during the south-west monsoon period, strong southerly currents are eroding protruded sectors and depositing eroded material, though partially, along varying sectors. Whereas during the rest of the year, under the influence of a northerly current, accretion is taking place along retreating sectors which has been reflected in the development of beach ridges. Turbidity pattern distribution exhibited by satellite image suggests that for January and February, long-shore drift is from south to north. The results of the two studies were found to be comparable. It may be concluded that shore-drift direction, which can be determined effectively by remote sensing, is season-dependent and plays a significant role in deciding the areas of coastal erosion and accretion.

TURBIDITY GRADIENTS IN TWO INDO-PACIFIC ESTUARIES AND THEIR INFLUENCE ON FISH DISTRIBUTION

Summary Research undertaken in two widely separated estuaries in the Indo-Pacific, showed that both have distinct turbidity gradients. In the turbid St Lucia System, on the South East Coast of Africa (range 2 to 568 Nephelometric Turbidity Units (NTU)), different turbidity patterns were observed during summer and winter. The Embley Estuary, on the eastern side of the Gulf of Carpentaria, Queensland, Australia, although also turbid, had a much more restricted range (0.6 to 55.0 NTU), and showed three distinct seasonal patterns, referred to as the Wet, Early Dry and Late Dry. Studies undertaken at St Lucia illustrated that turbidity had a direct influence on fish distribution in the system. The Embley Estuary was found to have species groups which were associated with specific turbidity levels. As only a limited range of turbidity occurred, these groups were somewhat restricted in composition. Comparisons made of the turbidities occupied by 13 fish taxa common to the different systems showed that nine had s...

Determination of turbidity patterns of the Zhujiang estuarine region, South China, using satellite images and a GIS approach

Abstract Landsat MSS images and SPOT HRV data were employed to map the changes in turbidity levels in the Zhujiang estuarine region, South China, during the dry season in the period 1973–1987 at low and high tides. Analysis of turbidity trends and changes in the spatial pattern of high turbidity class was carried out with a GIS software—IDRISI. It was concluded that with the use of OVERLAY and RECLASS functions in the GIS approach a large number of turbidity maps could be easily compared and the turbidity trend determined. The GIS approach further permitted evaluation of the importance of such factors as water depths, mean tidal differences, and water salinity to sedimentation in the study region.

TURBIDITY AND OTHER PHYSICAL FACTORS IN NATAL ESTUARINE SYSTEMS PART 2: ESTUARINE LAKES

SUMMARY Data on turbidity, temperature and salinity and the factors which affect them, such as wind and substratum, were collected from Natal's two estuarine Lakes. The effects of wind and substratum, were collected from Natal's two estuarine Lakes. The effects of wind and substratum type on turbidity within these lakes and their effects on the turbidity regime of each was investigated. The results showed that the St Lucia System was by far the diverse in terms of the occurrence and variability of the physical factors and particularly turbidity. The Kosi system on the other hand is remarkably uniform with very low turbidities. Turbidity patterns in South Lake, St Lucia were investigated in detail under varying wind conditions and this led to the compilation of maps showing the turbidity patterns which predominate in the Lake. These have assisted with the interpretation of the influence which turbidity exerts on the system.

Phytoplankton periodicity of the Waitaki lakes, New Zealand

The Waitaki River system in the South Island of New Zealand includes three large glacially-formed headwater lakes, Tekapo, Pukaki and Ohau, which drain into the manmade Lake Benmore. Phytoplankton periodicity was followed from December 1975 to January 1980 as part of a study investigating possible changes in these lakes as a consequence of hydroelectric development. The phytoplankton was highly dominated by diatoms, e.g., Diatoma elongatum, Cyclotella stelligera, Asterionella formosa, and Synedra acus, but in lakes Ohau and Benmore populations of green algae occasionally developed. In all four lakes seasonal phytoplankton periodicity was observed with maximum biomass in spring and summer. In Lake Tekapo, the first lake in the chain, maximum biomass did not exceed 300 mg m-3, but in the very turbid Lake Pukaki the maximum summer biomass ranged between 300 and 800 mg m-3. In Lake Ohau, the least turbid lake, maximum biomass was around 1 000 mg m-3. In the newly created Lake Benmore periodicity was less evident and summer maxima reached over 1 500 mg m-3. The phytoplankton periodicity in these lakes is greatly influenced by seasonal patterns of turbidity from inflowing glacial silt.

Sobre la presencia de algunos metales pesados en la atmósfera de la Ciudad de México

Las concentraciones de Cd y Pb en Ciudad Universitaria han aumentado 1.4 y 3.6 veces respectivamente en los últimos dos años. El Cu, Zn y Cd presentan una variación estacional y siguen el patrón de turbiedad atmosférica de la Ciudad de México (Lat. 19°20' N, 2, 268 m. s.n.m.). El Fe y el Pb se comportan aleatoriamente durante todo el año. Las concentraciones de Fe, Cd y Pb presentan una distribución log-normal; el Cu y Zn se aproximan muy débilmente a este tipo de distribución. Estos resultados fueron obtenidos recolectando muestras de aerosoles atmosféricos durante 14 meses (julio 79 - agosto 80) en el Observatorio de Radiación Atmosférica de Ciudad Universitaria, ubicado al sur de la Ciudad de México. Por el método de absorción atómica se analizaron 59 muestras, escogidas al azar y se determinaron las concentraciones de los cinco metales pesados ya mencionados.

Phytoplankton Pigments from the Nimbus-7 Coastal Zone Color Scanner: Comparisons with Surface Measurements

The removal of atmospheric effects from Nimbus-7 Coastal Zone Color Scanner (CZCS) images reveals eddy-like ocean turbidity patterns not apparent in the original calibrated images. Comparisons of the phytoplankton pigment concentrations derived from the corrected CZCS radiances with surface measurements agree to within less than 0.5 log C, where C is the sum of the concentrations of chlorophyll a plus phaeopigments a (in milligrams per cubic meter).

Nearshore current pattern off south texas: an interpretation from aerial photographs

Current patterns in a 4-km-wide zone along the south Texas coast were interpreted from patterns of water turbidity visible in aerial photographs taken during a winter day of moderate northerly winds. Features of the turbidity pattern remained recognizable on photographs taken 25 min apart. Currents measured from the movements of these features were southward and nearly parallel to shore, increasing from about 17 cm/sec in an offshore zone to about 40 cm/sec at the line of breaking waves. The shoreward increase in velocity was probably a manifestation of wave-driven longshore currents. Rip-current plumes were drifting with this longshore current and during their drift were deformed by the horizontal shear of the current. As a result of the shear, the plume axes trended seaward in an obliquely updrift direction. Much of the turbidity visible in the photographs was caused by suspended sediment apparently supplied to the Gulf of Mexico through Aransas Pass, a tidal inlet from which a large ebb-tidal plume of turbid water was issuing at the time of the photography. Another discrete mass of turbid water along the coast to the south was probably the preceding ebb-tidal plume, which had become separated from the inlet and was drifting with the shore-parallel shelf current. Still farther south, a linear pattern of turbid and less turbid bands in the offshore zone suggested the development of Langmoir circulation having cell axes parallel to the shelf current. The turbid bands probably marked the zones of surface divergence and upwelling of the Langmuir circulation. The spacing between the turbid bands averaged about ten times the water depth, and thus the cells were much flatter than Langmuir cells that have been observed in deeper water.

Regional Surface Turbidity and Hydrographic Variability on the South Texas Continental Shelf

ABSTRACT Regional surface-water turbidity patterns and associated hydrography were monitored on the South Texas Continental Shelf during an 18-month period (November 1975-May 1977) as part of an environmental study. On six monitoring cruises, quasi-synoptic surface measurements were made of water transmissivity, suspended-sediment concentrations, temperature, salinity, and drifter trajectories. Time-sequence patterns of these parameters illustrate substantial spatial and temporal variability; temporal variations take place at both the seasonal and annual time scales. Turbidity and hydrographic patterns suggest a surface-sediment dispersal system regulated by a lateral shelf-water exchange process, driven by both wind and thermohaline forcing agents. Relatively turbid inner-shelf waters reflect the offshore and alongshore transport of sediment derived from coastal sources. Turbidity patterns along the tuner shelf are characterized by a regional gradient of shoreward-increasing turbidity with superimposed local gradients established at major tidal inlets that serve as prominent sediment point sources and dispersal centers. Turbidity variability along the inner shelf is jointly attributed to variations in coastal runoff, wind-driven currents, and relative flux from individual tidal inlets. Relatively nonturbid outer-shelf waters suggest the shelfward incursion of an open-ocean water mass regulated by deep-Gulf circulation; the extent of incursion appears to vary spatially and temporally, resulting in outer-shelf turbidity variations. The overall shelf turbidity patterns reflect the degree of lateral interchange between the gulfward movement of turbid inner-shelf waters and the shelfward incursion of clear open-ocean waters.

Surface Turbidity and Hydrographic Variability on South Texas Continental Shelf, Gulf of Mexico--Time-Sequence Study: ABSTRACT

Regional surface-water turbidity patterns and associated hydrography were monitored on the south Texas continental shelf over an 18-month period (fall 1975 to spring 1977). During six monitoring cruises, quasi-synoptic surface measurements were made of water transmissivity, suspended-sediment concentrations, temperature, salinity, and drifter trajectories. Time-sequence patterns of these parameters illustrate substantial temporal and spatial variability; temporal variations occur at both the seasonal and annual time scales. Turbidity and hydrographic patterns indicate a surface-sediment dispersal system regulated by a shelf-water exchange process consisting of opposing lateral movements of inner-shelf and outer-shelf water masses. Relatively turbid inner-shelf waters reflect the offshore and alongshore transport of coastal-derived sediment. The inner shelf has a regional gradient of shoreward-increasing turbidity; superimposed local gradients are established at major tidal inlets that serve as prominent End_Page 527------------------------------ sediment point sources and dispersal centers. Turbidity variability along the inner shelf is jointly attributed to variations in coastal runoff, relative tidal sediment flux from individual inlets, and ambient wind-induced hydrographic conditions. The outer-shelf patterns suggest the shelfward incursion of open-ocean waters, the extent of which varies spatially and temporally. Regional turbidity patterns appear to reflect the degree of interchange between the gulfward movement of turbid inner-shelf waters and the shelfward incursion of clear open-ocean waters. The observed variability is compatible with a conceptual model of the regional dispersal system based on seafloor sediment distribution, which suggests both net offshore and net southward alongshore transport on a wind-dominated shelf. End_of_Article - Last_Page 528------------

Objective sensor placement for sampling regional turbidity

Objective sensor-placement techniques are applied to the process of selecting locations for a network of ten pyranometers, which will be used to investigate regional patterns of high turbidity across the northeastern United States. The techniques involve adjusting via nonlinear programming methods the values of coefficients in a continuous function that describes correlations between turbidity values separated by temporal and spatial intervals, in order to best describe the structure of turbidity. With the correlation structure function that is found, sensor locations are evaluated by calculating the normalized residual variance obtained from objective analyses performed at gridpoints across the region of interest. Sensor positions are shifted by nonlinear programming methods until residual variance is minimized. A comparison is made between simultaneous and sequential methods of sensorplacement optimization, in which the incremental value of adding sensors is determined objectively.