Distribution Of Water Constituents Research Articles

Development of ocean color algorithms for estimating chlorophyll-a concentrations and inherent optical properties using gene expression programming (GEP).

This paper proposes new inversion algorithms for the estimation of Chlorophyll-a concentration (Chla) and the ocean's inherent optical properties (IOPs) from the measurement of remote sensing reflectance (Rrs). With in situ data from the NASA bio-optical marine algorithm data set (NOMAD), inversion algorithms were developed by the novel gene expression programming (GEP) approach, which creates, manipulates and selects the most appropriate tree-structured functions based on evolutionary computing. The limitations and validity of the proposed algorithms are evaluated by simulated Rrs spectra with respect to NOMAD, and a closure test for IOPs obtained at a single reference wavelength. The application of GEP-derived algorithms is validated against in situ, synthetic and satellite match-up data sets compiled by NASA and the International Ocean Color Coordinate Group (IOCCG). The new algorithms are able to provide Chla and IOPs retrievals to those derived by other state-of-the-art regression approaches and obtained with the semi- and quasi-analytical algorithms, respectively. In practice, there are no significant differences between GEP, support vector regression, and multilayer perceptron model in terms of the overall performance. The GEP-derived algorithms are successfully applied in processing the images taken by the Sea Wide Field-of-view Sensor (SeaWiFS), generate Chla and IOPs maps which show better details of developing algal blooms, and give more information on the distribution of water constituents between different water bodies.

Siak River System — East-Sumatra: Characterisation of sources, estuarine processes, and discharge into the Malacca Strait

Interdisciplinary pollution studies were performed in the Siak River system in the Riau Province of East-Sumatra (Indonesia). Remote sensing investigations combined with in situ measurements in different seasons of the years 2004–2006 were focused on the identification of different sources of water masses in the tributaries and on the discharge into the estuary and Malacca Strait. Ship-borne measurements comprised the determination of the concentration and composition of optically active water constituents and water colour. Satellite data of different spectral and spatial resolution were implemented. Sources of different water masses such as humic substance dominated rivers, erosion areas of high suspended matter concentration and areas of limited bio-productivity are identified. Sources of humic substances are the rivers Tapung Kanan, Mandau, Siak Kecil, and Bukit Batu which are draining peatlands. The absorption coefficients of dissolved organic substances are partly (Siak Kecil, 51.8 m − 1 ) more than double of the currently admitted coefficients. The highest suspended matter concentrations near a channel between Siak and Siak Kecil leading to lowest transparency are caused by the estuarine turbidity maximum developing at the tidal front. The lowest Chlorophyll concentrations were measured between Pekanbaru and the channel, in and downstream of an industrial area. The concentration and distribution of water constituents are characterised by distinct regional patterns independent from the monsoon phases. The high absorption of dissolved organic humic substances originated from draining peatlands shifts the maximum of spectral reflectances to 700 nm leading to the extreme brownish to red-brownish water colour. High scattering of suspended particles increases the reflectance in the entire spectral range. The strong changes in the water colour enables satellite data of the visible spectral range to follow the distribution patterns of the Siak River discharge in the estuary which are strongly related to tidal phases. During low tide, the transport of Siak River water is directed into the Malacca Strait north-westwards and during high tide into Selat Panjang. Time series of daily available MODIS images have shown that the main transport direction in all seasons is the outflow into the Malacca Strait and further north-westwards following the large scale circulation.

Optical remote sensing of coastal plumes and run-off in the Mediterranean region

Sea surface colour data, derived from the Coastal Zone Colour Scanner (CZCS) archive, have been used to assess the space/time variability of coastal plumes and run-off in the Mediterranean Sea. A time series of 2645 scenes, collected by the CZCS from 1979 to 1985, was processed to apply sensor calibration algorithms, correct for atmospheric contamination, and derive chlorophyll-like pigment concentration. Individual images, remapped on a 1-km2 pixel grid, were generated for each available day, and then mean values calculated pixel by pixel to form monthly, seasonal and annual composites. The results obtained must be taken with caution, due to the CZCS limitations in the quantitative assessment of bio-optical pigments when high concentrations of dissolved organics or suspended sediments are present, e.g. along littorals or within plumes. Marked differences appear in the distribution of water constituents between coastal zones and open sea, northern and southern near-coastal areas, western and eastern sub-basins. The oligotrophic character of the basin contrasts with areas of high concentration related to river plumes—Ebro (Ebre), Po, Rhone, Nile—, coastal run-off patterns, and persistent mesoscale features (e.g. coastal filaments and eddies). Seasonal variability appears to be high, with higher concentrations occurring over most of the basin in the cold season, when climatic conditions are favourable to coastal run-off and vertical mixing. Atmospheric forcing (wind and rainfall over continental margins) could play an important role in establishing the observed space/time distribution of water constituents. The impact of continental interactions (fluvial and coastal run-off), or that of exchanges between coastal zone and open sea, could have paramount influence on the biogeochemical fluxes in the entire basin.