Spatial dynamics of estuarine water surface temperature from airborne remote sensing

This paper examines the applicability of airborne remote sensing to the characterization and quantification of the spatial dynamics of water surface temperature (WST) within estuaries. For this, a series of successive airborne Thematic Mapper thermal images was acquired of Kirkcudbright Bay, an estuary in the United Kingdom, on two dates. Spatial dynamics were determined by two techniques: (1) qualitatively, which involved interpreting features ‘by eye’; and (2) by the velocimetric technique of maximum cross correlation (MCC). Qualitatively, complex spatial dynamics were identified over a wide range of spatial and temporal scales, associated with the creation and dissipation of eddies, and the convergence and divergence of fronts, all of which were superimposed on the synoptic tidal flow. MCC was effective for producing synoptic velocity fields, but the minimum cell size was constrained by image noise, limiting the ability to analyze small-scale spatial dynamics. The effectiveness of MCC was related to the ratio of spatially correlated variance to spatially independent variance, as estimated from the variogram. Suggestions for optimizing the application of airborne remote sensing to estuarine spatial dynamics are presented.     

Classification of mesoscale features in the Brazil-Falkland Current confluence zone

The south-western Atlantic region, 30–46°S, 35–55°W is noted for the confluence of the warm Brazil Current and the cold Falkland Current, as well as the eddies created from the two systems. Previous studies of the Brazil-Falkland Current confluence have concentrated on the formation of eddies south of 35°S. However, in situ measurements and TOPEX/POSEIDON imagery of the region reveal eddies developing as far north as 32°S. These features are not evident in the coincident AVHRR (Advanced Very High Resolution Radiometer) imagery. In this study, the origin of the eddies identified are discussed with reference to the contemporary in situ measurements of temperature and salinity. Using the combination of satellite imagery and in situ data, it can be determined that the surface waters of the eddies north of 36°S are influenced by water from an estuarine source. TOPEX imagery enables the movements and variability of the regions water masses: estuarine outflow, Falkland and Brazil currents, to be monitored synoptically. The combination of satellite imagery and the higher resolution of in situ AMT measurements enables these water masses to be better identified.     

Quantitative estimation of intertidal sediment characteristics using remote sensing and GIS

High spatial resolution satellite data (IKONOS) combined with in situ data was used to quantitatively estimate the spatial distribution of tidal flat characteristics for the Hwangdo tidal flat, Cheonsu Bay, Korea. The classification result was accurate in terms of a comparison with the in situ data, and the overall accuracy was 90.7%, which confirmed the validity of the classification. GIS analysis based on a probabilistic model was applied to a quantitative estimation of the relationship between each surface sediment facies and the spectral reflectance. Mud flat facies showed a high positive correlation (R² = 0.91), and sand flat facies showed a high negative correlation (R² = 1.00), which was a good reflection of the sedimentary characteristics of Hwangdo tidal flat. Relationships between each sediment facies and DEM also showed good agreement with the topographic characteristics in the study area. The study revealed that intertidal surface sediment classification using high resolution remote sensing imagery and in situ data successfully shows spectral and topographic characteristics of the study area. It was noted that spectral reflectance was affected by a combination of environmental factors, including grain size, topography, and remnant surface water. It is possible to determine the type of tidal flat through quantitative estimates of the spatial distribution of surface sediments according to their spectral reflectance.     

黄海潮生陆架锋的数值模拟研究

采用海洋三维热结构及环流模式,模拟了黄海在Ｍ２潮流混合作用下,夏季温度的分布和变化特征。从数值研究的角度,对黄海陆架水域的海洋锋现象,诸如苏北浅滩外、山东半岛东端、大连、木浦水域的锋面以及锋面沿岸一侧的表层冷水区的成因及分布进行了探讨,模拟结果再现了黄海陆架锋的潮生性质。     

Potentially mobile pools of phosphorus and silicon in sediment from the Bay of Brest: Interactions and implications for phosphorus dynamics

Competitive interactions between silicate and phosphate at ligand exchange sites in the sediment surface layer may increase the release of phosphorus (P) from the sediment into the water column. In this study, the role of silicon (Si) in the release of P from the sediment surface layer was studied in a marine estuarine environment, the Bay of Brest, with the aid of a sequential sediment fractionation procedure developed for P, and the addition of inorganic or diatom-bound Si to surface sediment samples in vitro. The potentially mobile pools of P in the surface sediment (loosely bound P + Fe/Al-bound-P) amounted to 5.0 μmol g⁻¹ dry sed., 42% of the total extractable and 33% of the total amount of P in the sediment, while the similarly extracted pools of Si were bigger (ca. 20 μmol g⁻¹ dry sed., 50% of the total extractable Si). Additions of inorganic Si increased the concentration of dissolved P in the sediment interstitial water in a bottle experiment, and the addition of both inorganic Si and cultivated diatoms to intact sediment cores increased the outward flux of dissolved P. Model calculations based on the regression equation from the bottle experiment and Si and P water column data showed that the sedimentation of spring diatoms could cause Si pulses to the sediment which would produce a P flux to the water column of ca. 44 μmol m⁻² d⁻¹. Field data from the bay show that in spring, decreases in P and Si and an increase in chl a due to diatom production are often followed by a small separate P peak which may be caused by Si-induced P fluxes from the sediment surface.     

Modeling uncertainty in estuarine system by means of combined approach of optical and radar remote sensing

Coastal environments are complex systems undergoing continuous evolution at a range of spatial and temporal scales. In this context, geomorphological and ecological features can be strongly related. We propose a synoptic remote sensing approach to monitor the temporal dynamics of both biotic and abiotic factors in estuarine and coastal ecosystems. Through the combination of spaceborne optical and SAR imagery, we derived both ecological and morphological parameters, to be integrated for a multi-temporal analysis of the dominant processes and trends in coastal landscapes. These dynamics were studied at three locations: Bevano (IT), the Scheldt (B-NL) and Erme (UK). The objectives were to detect and analyze interannual variations of processes and environmental dynamics.The results highlight that over time, the morphology of different subsystems represents a balance between inputs (forcing agents like tidal range) and natural responses (related responses of the vegetation evolution). As a final remark the calculation of the uncertainties (subsidence rates) using new monitoring techniques such as satellite remote sensing has a specific added value that could be used for simulations over varying time scales and it should be considered as a potential ‘add in’ for an integrated management approach to coastal monitoring and control.     

Asymmetric tidal straining across an inlet: Lateral inversion and variability over a tidal cycle

Tidal straining is a phenomenon of temporal variations in stratification and mixing resulting from the interaction of a longitudinal salinity gradient with the vertical shear of the horizontal tidal velocity. As a result, the theory predicts stronger and weaker stratification during ebb/low tide and flood/high tide, respectively. In contrast to this well-known temporal asymmetry, in this study, we document in situ measurements demonstrating a lateral asymmetry and lateral inversion of tidal straining at Barataria Pass, a narrow (∼600 m wide) tidal inlet of Barataria Bay in southeastern Louisiana. During flood, the eastern side of the channel had strong stratification of 4 PSU salinity change over a 1.5 m thin layer while the western side had a 2 PSU change over a 12 m water column. This strong lateral difference decreased as flood continued until near the end of the flood when it reached vertically well-mixed condition across the channel. During ebb it was just the opposite such that the western side became stratified while the eastern end was well-mixed. This resulted to a small correlation coefficient of −0.05 for stratification between the west and east sides, although the central channel and east side have a high correlation coefficient of 0.88. The tidally averaged salinity was higher on the western end than the eastern end except in a narrow boundary layer close to the eastern shore. This is an apparent contradiction to what the Coriolis effect would produce in classical estuarine dynamics. Our hypothesis for the observed difference arises from the influence of the river water coming out of the Mississippi River through the Southwest Pass of the Birdfoot Delta. This water mass may have played a role in the observed, complicated lateral inversion of the tidal straining. This study underlines the complexity of estuarine dynamics proximal to large deltaic systems and we anticipate that these results will underscore the need for a modeling study to further investigate this dynamic process.     

Inputs of iron,manganese and aluminium to surface waters of the Northeast Atlantic Ocean and the European continental shelf

Dissolved Fe, Mn and Al concentrations (dFe, dMn and dAl hereafter) in surface waters and the water column of the Northeast Atlantic and the European continental shelf are reported. Following an episode of enhanced Saharan dust inputs over the Northeast Atlantic Ocean prior and during the cruise in March 1998, surface concentrations were enhanced up to 4 nmol L^− 1 dFe, 3 nmol L^− 1 dMn and 40 nmol L^− 1 dAl and returned to 0.6 nmol L^− 1 dFe, 0.5 nmol L^− 1 dMn and 10 nmol L^− 1 dAl towards the end of the cruise three weeks later. A simple steady state model (MADCOW, [Measures, C.I., Brown, E.T., 1996. Estimating dust input to the Atlantic Ocean using surface water aluminium concentrations. In: Guerzoni. S. and Chester. R. (Eds.), The impact of desert dust across the Mediterranean, Kluwer Academic Publishers, The Netherlands, pp. 301–311.]) was used which relies on surface ocean dAl as a proxy for atmospheric deposition of mineral dust. We estimated dust input at 1.8 g m^− 2 yr^− 1 (range 1.0–2.9 g m^− 2 yr^− 1) and fluxes of dFe, dMn and dAl were inferred. Mixed layer steady state residence times for dissolved metals were estimated at 1.3 yr for dFe (range 0.3–2.9 yr) and 1.9 yr for dMn (range 1.0–3.8 yr). The dFe residence time may have been overestimated and it is shown that 0.2–0.4 yr is probably more realistic. Using vertical dFe versus Apparent Oxygen Utilization (AOU) relationships as well as a biogeochemical two end member mixing model, regenerative Fe:C ratios were estimated respectively to be 20 ± 6 and 22 ± 5 μmol Fe:mol C. Combining the atmospheric flux of dFe to the upper water column with the latter Fe:C ratio, a ‘new iron’ supported primary productivity of only 15% (range 7%–56%) was deduced. This would imply that 85% (range 44–93%) of primary productivity could be supported by regenerated dFe. The open ocean surface data suggest that the continental shelf is probably not a major source of dissolved metals to the surface of the adjacent open ocean. Continental shelf concentrations of dMn, dFe, and to a lesser extent dAl, were well correlated with salinity and express mixing of a fresher continental end member with Atlantic Ocean water flowing onto the shelf. This means probably that diffusive benthic fluxes did not play a major role at the time of the cruise.     

Turbidity limits gas exchange in a large macrotidal estuary

In estuaries, the gas transfer velocity (k) is driven by a combination of two major physical drivers, wind and water current. The k values for CO₂ in the macrotidal Gironde Estuary were obtained from 159 simultaneous pCO₂ and floating chamber flux measurements. Values of k increased with wind speed and were significantly greater when water currents and wind were in opposing directions. At low wind speeds (<1 m s⁻¹), k increased with water current velocities (0–1.5 m s⁻¹) following an exponential trend. The latter was a good proxy for the Y-intercept in a generic equation for k versus wind speed in estuaries. We also found that, in this turbid estuary, k was significantly lower at high turbidity. The presence of suspended material in great concentrations (TSS > 0.2 g L⁻¹) had a significant role in attenuating turbulence and therefore gas exchange. This result has important consequences for modeling water oxygenation in estuarine turbidity maxima. For seven low turbidity estuaries previously described in the literature, the slope of the linear regression between k and wind speed correlates very well with the estuary surface area due to a fetch effect. In the Gironde Estuary, this slope follows the same trend at low turbidity (TSS < 0.2 g L⁻¹), but is on average significantly lower than in other large estuaries and decreases linearly with the TSS concentration. A new generic equation for estuaries is proposed that gives k as a function of water current velocity, wind speed, estuarine surface area and TSS concentration.     

卫星海洋水色遥感的辐射模式研究

海洋水体向上的辐射由水中多种成分的浓度所决定，同时辐射的强度十分微弱并随着时间和空间在变化。因此，海洋水色遥感需要从水体和大气辐射传递机理出发，研究到达卫星遥感器的辐射模式，以达到模拟仿真卫星水色遥感图像和卫星图像质量预测的目的。本研究通过叶绿素、悬浮泥沙和黄色物质等海洋水色的主要因子，分别从可见光波段和荧光波段对辐射的贡献出发，发展了海洋水体离水辐射率模式。在卫星水色遥感机理的基础上，同时运用Iqbal，Gordon和Sturm等的大气程辐射模式和太阳耀光模式，使卫星海洋水色遥感的辐射模式系统化，模拟仿真了我国1990年9月3日发射的FYIB卫星两个海洋水色通道的全轨道辐射图像，同时利用从德国柏林大学气象中心接收到的1990年9月23－25日卫星图像进行验证。结果认为，本文所发展的模式可应用于卫星图像质量的预测和水色信息的提取。     

Airborne imagery of a disintegrating Sargassum drift line

Airborne hyperspectral and thermal infrared imagery collected over the Florida Current provide a view of the disintegration of a Sargassum drift line in 5 m s⁻¹ winds. The drift line consists mostly of rafts 20-80 m² in size, though aggregations larger than 1000 m² also occur. Rafts tend to be elongated, curved in the upwind direction, and 0.1-0.5 °C warmer than the surrounding ocean surface. Long weed ‘trails’ extending upwind from the rafts are evidence of plants dropping out and being left behind more rapidly drifting rafts. The raft line may be a remnant of an earlier Sargassum frontal band, which is detectible as an upwind thermal front and areas of submerged weed. Issues are identified that require future field measurements.     

Retrieval of Substrate Bearing Strength from Hyperspectral Imagery during the Virginia Coast Reserve (VCR’07) Multi-Sensor Campaign

Hyperspectral imagery (HSI) derived from remote sensing can delineate surface properties of substrates such as type, moisture, and grain size. These are critical parameters that determine the substrate bearing strength. Although HSI only sees the surface layer, statistics can be derived that relate surface properties to the likely bearing strength of soils in particular regions. This information can be used to provide an initial map estimate on large scales of potential bearing strength. We describe an initial validation study at the Virginia Coast Reserve relating airborne HSI to in situ spectral and geotechnical measurements through a spectral-geotechnical lookup table (LUT).     

Processes governing the carbon chemistry during the SAGE experiment

Measurements of pCO₂, pH and alkalinity in the surface waters of an iron fertilised patch of sub-Antarctic water were made during SAGE (SOLAS SAGE: Surface-Ocean Lower Atmosphere Studies Air-Sea Gas Experiment). The iron addition induced a minor phytoplankton bloom, however the patch dynamics were dominated by physical processes which suppressed and masked the biological effects. The Lagrangian nature of the experiment allowed the carbonate chemistry in the patch to be followed for 15.5 days, and the relative importance of the biological and physical factors influencing the surface water pCO₂ was estimated. The pCO₂ of the surface waters of the patch increased from 327 ??atm prior to iron addition to 338 ??atm on Day 14, effects of vertical and horizontal mixing offset the 15 ??atm drawdown that would have occurred had the induced biological uptake been the sole factor to influence the pCO₂. The air-sea carbon flux calculated using the measured skin temperature and a piston velocity parameterisation determined during SAGE (Ho et al., 2006) was 98.5% of the flux determined using conventional bulk temperature measurement and the Wanninkhof (1992) piston velocity parameterisation. The skin temperature alone contributed to an 8% increase in the flux compared with that determined using bulk temperature.     

Understanding spatial and temporal dynamics of key environmental characteristics in a mesotidal Atlantic estuary (Douro,NW Portugal)

Ecosystem management and decision making process are dependent of a good knowledge of ecosystem functioning. Conceptual models allow knowledge organization through representation of relationships between variables and processes, facilitating management decisions. In this study, spatial and temporal characterization of key environmental variables, as well as relationships between them, was studied aiming the design of a conceptual model of the Douro estuary. This temperate mesotidal estuary is limited upstream by a hydroelectric power dam that controls freshwater inflow and prevents the propagation of the tide upstream, which, in turn, influences water circulation and biogeochemical dynamics of the system. During one year, from December 2002 to December 2003, water column data were collected monthly at 10 stations along the estuary, during ebb and flood tides. Spatial and temporal variability of water column salinity, temperature, nutrients, phytoplankton biomass, total particulate matter (TPM), phytoplankton primary production (PP), faecal coliform bacteria (FC) and community respiration (CR) were analysed. Salinity stratification was assessed by means of the Estuary Number (Ne) and variation of this index as well as other key characteristics with river flow was analysed. Freshwater discharge controlled salinity stratification and freshwater residence time. Ne indicated that the Douro was stratified for river flows <300 m³ s⁻¹, and freshwater residence time was >1 day for the same conditions. A decaying exponential relationship between PP and river flow was found, whereas nitrate and TPM increased logarithmically and linearly, respectively, with river flow. Regarding spatial distribution, nitrate and PP decreased downstream, showing that the river was a source of nutrients and phytoplankton, while the opposite trend was found for TPM, FC, ammonium and CR. The latter increase was probably due to untreated sewage discharge in the urbanized middle and lower estuarine stretches. Reduction of nitrate coming from the watershed and of bacterial contamination in the urban stretches of this highly modified water body, according to the European Water Framework Directive, emerges as the main water quality issues for this estuarine ecosystem.     

Remote sensing of turbidity in seawater intrusion reaches of Pearl River Estuary – A case study in Modaomen water way,China

Based on field experiments and analysis, the study examined the spectral characteristic and spatial variability of turbidity in the Pearl River Estuary by using the EO-1 ALI satellite imagery collected on December 18, 2005. A negative regression model (turbidity = −439.52 × R (570) + 22.913, R² = 0.9042, n = 11) between the in-situ turbidity and the reflectance at 570 nm (maximum correlation spectral band between 350 and 2500 nm), resulting from increasing of organic matters in suspended solids, was built and applied to ALI band 4 (0.525–0.605 nm). Simple in-water spectral pairs calibration method of bright and dark targets provided the good atmospheric correction of ALI with a root mean square error of 0.00061, and mean absolute percentage error of 2.04%. The study also found the seawater turbidity is a more accurate indicator of Chl_a concentration (R² = 0.7442) than TSS (R² = 0.7061). Also, there is a large correlation between TSS and the turbidity (R² = 0.86, N = 22) for Modaomen watercourse. The model-deduced turbidity distribution from ALI band 4 exhibited distinctive spatial variability of turbidity in the dry season, accordant with seasonal in-situ investigation. The ALI data provides accurate estimates of the mean water clarity conditions in the PRE (RMSE = 1.878 and MAPE = 11.7%) and has potential importance for water quality monitoring of optical remote sensing in the similar estuaries and its future operation.     

The influence of prolonged mouth closure on selected components of the hyperbenthos in the littoral zone of the temporarily open/closed Kasouga Estuary,South Africa

The influence of prolonged mouth closure on the population dynamics of the caridian shrimp, Palaemon peringueyi and the estuarine isopod, Exosphaeroma hylocoetes, in the littoral zone of temporarily open/closed Kasouga Estuary located on the south-eastern coastline of southern Africa was assessed monthly over the period October 2007 to September 2008. Prolonged mouth closure of the estuary contributed to hypersaline conditions (psu > 35) prevailing throughout the estuary for the last four months of the study. The high salinities coincided with a decrease in the areal extent (up to 80%) of the submerged macrophytes, mainly Ruppia maritima, within the littoral zone of the estuary. Total abundance and biomass values of the shrimp and isopod over the period of investigation ranged from 0 to 14.6 ind m⁻², from 0 to 13.3 mg dwt m⁻², from 12 to 1540 ind m⁻² and from 0.1 to 2.16 mg dwt m⁻², respectively. Maximum values of both the shrimp and isopod were recorded in the upper reaches of the estuary in close association with R. maritima. Over the course of the investigation, both the abundance and biomass values of the shrimp decreased significantly (P < 0.05 in both cases) which could be related to reduced habitat availability, R. maritima, that acts as a refuge against fish predation. Additionally, the decrease in abundance and biomass values could be attributed to reduced recruitment opportunities for the shrimp and the cessation of reproduction in the estuarine isopod. The establishment of a link to the marine environment following an overtopping event in September 2008 contributed to a decrease in salinity within the system although no recruitment of either the isopod or shrimp was recorded.     

Natural organics as fluorescent tracers of river-sea mixing

The use of dissolved organic matter fluorescence as a tracer of river-sea mixing was examined in two South Carolina estuaries. Fluorescence declined linearly with seawater dilution in laboratory mixing studies, and also behaved conservatively in an estuary where a single river emptied into a bay. Fluorescence-salinity relationships were also studied in another estuary where a piedmont river (high suspended sediment, low fluorescence) and a coastal plains river (low sediment, high fluorescence) mixed with ocean water. The factor of 2 or greater difference in fluorescence between the two rivers allowed their relative contribution to the estuarine water mass to be distinguished. Petroleum hydrocarbons, measured in estuarine water at 0·7-1·8 μg l⁻¹ concentrations, contributed negligibly to water fluorescence.     

The cycling and oxidation pathways of organic carbon in a shallow estuary along the Texas Gulf Coast

The cycling and oxidation pathways of organic carbon were investigated at a single shallow water estuarine site in Trinity Bay, Texas, the uppermost lobe of Galveston Bay, during November 2000. Radio-isotopes were used to estimate sediment mixing and accumulation rates, and benthic chamber and pore water measurements were used to determine sediment-water exchange fluxes of oxygen, nutrients and metals, and infer carbon oxidation rates. Using ⁷Be and ²³⁴Th_XS, the sediment-mixing coefficient (D_b) was 4.3 ± 1.8 cm² y⁻¹, a value that lies at the lower limit for marine environments, indicating that mixing was not important in these sediments at this time. Sediment accumulation rates (S_a), estimated using ¹³⁷Cs and ²¹⁰Pb_XS, were 0.16 ± 0.02 g cm⁻² y⁻¹. The supply rate of organic carbon to the sediment-water interface was 30 ± 3.9 mmol C m⁻² d⁻¹, of which ∼10% or 2.9 ± 0.44 mmol C m⁻² d⁻¹was lost from the system through burial below the 1-cm thick surface mixed layer. Measured fluxes of O₂ were 26 ± 3.8 mmol m⁻² d⁻¹ and equated to a carbon oxidation rate of 20 ± 3.3 mmol C m⁻² d⁻¹, which is an upper limit due to the potential for oxidation of additional reduced species. Using organic carbon gradients in the surface mixed layer, carbon oxidation was estimated at 2.6 ± 1.1 mmol C m⁻² d⁻¹. Independent estimates made using pore water concentration gradients of ammonium and C:N stoichiometry, equaled 2.8 ± 0.46 mmol C m⁻² d⁻¹. The flux of DOC out of the sediments (DOC_efflux) was 5.6 ± 1.3 mmol C m⁻² d⁻¹. In general, while mass balance was achieved indicating the sediments were at steady state during this time, changes in environmental conditions within the bay and the surrounding area, mean this conclusion might not always hold. These results show that the majority of carbon oxidation occurred at the sediment-water interface, via O₂ reduction. This likely results from the high frequency of sediment resuspension events combined with the shallow sediment mixing zone, leaving anaerobic oxidants responsible for only ∼10–15% of the carbon oxidized in these sediments.     

Introduction to the airborne marine surveillance platform and its application to water quality monitoring in China

China Marine Surveillance Force was equipped with modern aerial equipments for marine lawexecute with the advantage of functioning agilely at a large scale of surveillance coverage, providing powerful all-round safeguard, which is of benefit to the harmonious and sustainable development of coastal economy. Onboard the planes, three kinds of remote sensing sensors have been installed, including a marine airborne multi-spectrum scanner (MAMS), an optical-electronic platform, and an airborne hyper-spectral system AISA+. The specifications of remote sensing platforms were introduced briefly first, then examples of water quality monitoring by airborne remote sensing were presented, including the monitoring in coastal suspended material, oil-spill and abnormal warm water, etc.     

Pattern Recognition of Forest Vegetation from Hyperspectral Airborne and Multichannel Satellite Data of High Spatial Resolution: Comparison of Results and Estimation of Their Accuracy

Izvestiya, Atmospheric and Oceanic Physics - The pattern recognition of a forest surface from remote sensing data (both airborne hyperspectral data and WorldView-2 multichannel satellite data of...