Remote sensing of tidal networks and their relation to vegetation

The study of the morphology of tidal networks and their relation to salt marsh vegetation is currently an active area of research, and a number of theories have been developed which require validation using extensive observations. Conventional methods of measuring networks and associated vegetation can be cumbersome and subjective. Recent advances in remote sensing techniques mean that these can now often reduce measurement effort whilst at the same time increasing measurement scale. The status of remote sensing of tidal networks and their relation to vegetation is reviewed. The measurement of network planforms and their associated variables is possible to sufficient resolution using digital aerial photography and airborne scanning laser altimetry (LiDAR), with LiDAR also being able to measure channel depths. A multi-level knowledge-based technique is described to extract networks from LiDAR in a semi-automated fashion. This allows objective and detailed geomorphological information on networks to be obtained over large areas of the inter-tidal zone. It is illustrated using LIDAR data of the River Ems, Germany, the Venice lagoon, and Carnforth Marsh, Morecambe Bay, UK. Examples of geomorphological variables of networks extracted from LiDAR data are given. Associated marsh vegetation can be classified into its component species using airborne hyperspectral and satellite multispectral data. Other potential applications of remote sensing for network studies include determining spatial relationships between networks and vegetation, measuring marsh platform vegetation roughness, in-channel velocities and sediment processes, studying salt pans, and for marsh restoration schemes

River Run Off Measurement With SAR Along Track Interferometry

The paper summarizes the need for global space borne river run-off measurements. It reports about an airborne SAR experiment aimed to measure the surface velocity of the river Isar in Bavaria / Germany. The results from two different SAR techniques, including Along Track Interferometry (ATI) show good correspondence. Finally suggestions for further studies are given

Use of an inertial navigation system for accurate track recovery and coastal oceanographic measurements

A data acquisition system using a Litton LTN-51 inertial navigation unit (INU) was tested and used for aircraft track recovery and for location and tracking from the air of targets at sea. The characteristic position drift of the INU is compensated for by sighting landmarks of accurately known position at discrete time intervals using a visual sighting system in the transparent nose of the Beechcraft 18 aircraft used. For an aircraft altitude of about 300 m, theoretical and experimental tests indicate that calculated aircraft and/or target positions obtained from the interpolated INU drift curve will be accurate to within 10 m for landmarks spaced approximately every 15 minutes in time. For applications in coastal oceanography, such as surface current mapping by tracking artificial targets, the system allows a broad area to be covered without use of high altitude photography and its attendant needs for large targets and clear weather

Sediment and associated radionuclide dynamics within the Ribble Estuary, North West England.

Intertidal environments represent a spatially complex and dynamic system, rendering point sampling geographically and temporally isolated within the context of the entire estuarine system. Airborne remote sensing has the potential to place these spatially isolated sampling points into a quantitative spatial context. Furthermore it provides a valuable data source for quantifying processes within estuarine zones and can supply calibration and validation information for hydrodynamic models. This study focuses on the Ribble Estuary, Lancashire, England which is accumulating elevated radionuclide concentrations derived from authorized industrial discharges from BNFL Sellafield and Westinghouse Springfields. An image mixture modeling approach was used on Airborne Thematic Mapper (ATM) data to derive accurate estimates of intertidal clay, in comparison to concurrent field sampling (r2=0.828) and radionuclide concentrations (r2= 0.822). Data processed for 2003 was compared with similar data from May 1997 (Rainey 1999; Rainey et aL., 2000; 2003) to investigate spatial changes in intertidal clay and 137Cs contamination. These results compared with field sampling data demonstrates considerable reduction (c.52%) in the activity concentrations, which is primarily attributed to processes of sediment dilution. Calibrated Compact Airborne Spectrographic Imager (CASI) imagery combined with concomitant ground reference data, was used to characterize the suspended sediment concentrations and the total suspended load over each flight line. Two sets of time series image data were compared to assess the spatial and temporal changes in suspended sediment and associated radionuclide transportation within the estuarine environment. In conjunction with total volumetric estimates generated from a two-dimensional vertically resolving hydrodynamic model, this data then allowed estimation of the total flux of suspended sediment and radionuclide over the flood and ebb tidal cycle to a reasonable precision (40%). To establish whether these flux estimates are realistic, the results are compared with time series field based observations collected from monthly observations over a two year cycle. The results provide a unique quantitative insight into the understanding of contaminant and sediment transport within this estuarine environment and the environmental processes controlling them. The contribution of field data with the intertidal and flood-ebb tide imagery has provided an enhanced understanding of the interactions of tides and fluvial flow on the spatial distribution of sediments within the Ribble Estuary. It could also be possible to apply the calibrated clay intertidal maps to other heavy metal pollutants that have a high affinity with fine-grained clay particles i.e. Pb, Zn, Cu, Al in estuarine sediments

Evolution and Dynamics of Tropical River Plumes in the Great Barrier Reef: An Integrated Remote Sensing and In Situ Study

[1] The short-lived but intense discharge of freshwater from tropical rivers into the Great Barrier Reef (GBR) Lagoon and the associated salinity reductions are a critical consideration in marine research and management of the ecologically sensitive GBR World Heritage Area. Salinity provides a unique tracer that gives clues to the origin of river-borne contaminants and allows the influences of storm-induced resuspension and river discharge on turbidity to be clearly distinguished. We describe a field investigation of the evolution and dynamics of the Herbert River plume in the central GBR. Its primary goals were to use an airborne salinity mapper and in situ instruments to study the three-dimensional structure and evolution of the plume and to lay a foundation for numerical modeling studies of its dynamics. The aircraft surveys provided a rapid assessment of the plumes spatial extent, while the in situ data revealed details of its subsurface structure. The Herbert River plume was produced by heavy rainfall associated with tropical storms during the La Nina-dominated 1999/2000 monsoon season. In the near field, the surface expression of the plume boundaries was indicated by sharp color and salinity fronts that were clearly visible from the air and sea surface. In the far field and middle Lagoon, the plume was more dispersed and ultimately merged with the larger-scale salinity gradients and with the remnant plume of the more distant, and larger, Burdekin River. The plume location and structure evolved in response to changing river flows, tidal and subtidal circulation, and wind. Using Garvine\u27s Kelvin number-based scheme, the plume was classified as intermediate in dynamical character and thus is subject to a variety of forcings. The plume evolved in response to changes in the relative intensity of tidal currents and low-frequency circulation due to wind and western boundary current forcing. It also displayed a characteristic hook-shaped\u27\u27 structure, which has been identified previously in numerical plume model studies. This structure appeared in the presence of accelerating along-shelf current flow and horizontal shear and it indicates that the plume circulation had a strongly three-dimensional character. The approach demonstrates the efficacy of combining airborne and in situ methods to observe rapidly evolving coastal salinity structure and dynamics and sets the stage for future satellite-borne studies of larger-scale features showing contrasting salinity distributions

Evolution and dynamics of tropical river plumes in the Great Barrier Reef: an integrated remote sensing and in situ study

The short-lived but intense discharge of freshwater from tropical rivers into the Great Barrier Reef (GBR) Lagoon and the associated salinity reductions are a critical consideration in marine research and management of the ecologically sensitive GBR World Heritage Area. Salinity provides a unique tracer that gives clues to the origin of river-borne contaminants and allows the influences of storm-induced resuspension and river discharge on turbidity to be clearly distinguished. We describe a field investigation of the evolution and dynamics of the Herbert River plume in the central GBR. Its primary goals were to use an airborne salinity mapper and in situ instruments to study the three-dimensional structure and evolution of the plume and to lay a foundation for numerical modeling studies of its dynamics. The aircraft surveys provided a rapid assessment of the plumes spatial extent, while the in situ data revealed details of its subsurface structure. The Herbert River plume was produced by heavy rainfall associated with tropical storms during the La Nina-dominated 1999/2000 monsoon season. In the near field, the surface expression of the plume boundaries was indicated by sharp color and salinity fronts that were clearly visible from the air and sea surface. In the far field and middle Lagoon, the plume was more dispersed and ultimately merged with the larger-scale salinity gradients and with the remnant plume of the more distant, and larger, Burdekin River. The plume location and structure evolved in response to changing river flows, tidal and subtidal circulation, and wind. Using Garvine’s Kelvin number-based scheme, the plume was classified as intermediate in dynamical character and thus is subject to a variety of forcings. The plume evolved in response to changes in the relative intensity of tidal currents and low-frequency circulation due to wind and western boundary current forcing. It also displayed a characteristic ‘‘hook-shaped’’ structure, which has been identified previously in numerical plume model studies. This structure appeared in the presence of accelerating along-shelf current flow and horizontal shear and it indicates that the plume circulation had a strongly three-dimensional character. The approach demonstrates the efficacy of combining airborne and in situ methods to observe rapidly evolving coastal salinity structure and dynamics and sets the stage for future satellite-borne studies of larger-scale features showing contrasting salinity distributions

Application of remote sensing for prediction and detection of thermal pollution, phase 2

The development of a predictive mathematical model for thermal pollution in connection with remote sensing measurements was continued. A rigid-lid model has been developed and its application to far-field study has been completed. The velocity and temperature fields have been computed for different atmospheric conditions and for different boundary currents produced by tidal effects. In connection with the theoretical work, six experimental studies of the two sites in question (Biscayne Bay site and Hutchinson Island site) have been carried out. The temperature fields obtained during the tests at the Biscayne Bay site have been compared with the predictions of the rigid-lid model and these results are encouraging. The rigid-lid model is also being applied to near-field study. Preliminary results for a simple case have been obtained and execution of more realistic cases has been initiated. The development of a free-surface model also been initiated. The governing equations have been formulated and the computer programs have been written

Validating the use of Airborne Remote Sensing in the Coastal Zone and its Application to Suspended Sediment Flux Estimation

Coastal and estuarine environments are dynamic yet highly sensitive which makes them particularly susceptible to any changes dictated by external forces. The interaction between environmental forces and those imposed by humans who live and work in the area is a very delicate one and needs to be considered through an holistic management approach to ensure the maintenance of a sustainable equilibrium. The use of airborne remote sensing in the coastal zone has been employed and validated for the specific aims of suspended particulate matter (SPM) concentration and flux quantification in the Humber Estuary and sea-surface temperature and salinity determination in the Tweed Estuary. Routines for the effective radiometric, atmospheric, thermal and geometric correction of Compact Airborne Spectrographic Imager (CASQ and Airborne Thematic Matter (ATM) data were tested and enhanced. Validations at all stages were executed through comparison with sea-based optical data acquired coincident with the images. The data acquired from the sea-surface also yielded important information regarding the nature and content of the waters. Water classification techniques were addressed and a new algorithm for use in case II waters based on the Austin & Petzold (1981) K^{490) routine derived. A new algorithm to determine SPM concentration in the Humber Estuary from CASI images was successfully determined and validated. SPM flux estimates were ascertained through the incorporation of image data, hydrodynamic models and depth profiles determined from hydrographic charts. In the Tweed Estuary, ATM images were used to determine sea-surface temperature and salinity using thermal image calibration and comparison with surface monitoring. The results provide an hitherto unseen insight into the dynamics of the Humber and the Tweed Estuaries. In particular, information regarding SPM concentration and fluxes in the Humber supports the so far unproved hypothesis that most of the SPM moves into and out of the mouth in elongated streaks. The use of the width of a streak (or patch) to predict the SPM concentration and / or flux and so eliminate the necessity for surface-based monitoring was addressed. Algorithms to determine SPM concentration and flux were devised using patch size and within-patch water depth alone. A model to apply these algorithms to all data was unsuccessful due to the sparse temporal coverage of the image data. The analyses exemplified in this study give an invaluable insight into the forces at play in coastal and estuarine environments and would provide key information sources for hydrodynamic modellers and coastal zone managers.Centre for Coastal and Marine Science, Plymouth Marine Laborator

Investigating radionuclide bearing suspended sediment transport mechanisms in the Ribble estuary using airborne remote sensing

BNFL Sellafield has been authorised to discharge radionuclides to the Irish Sea since 1952. In the aquatic environment the radionuclides are adsorbed by sediments and are thus redistributed by sediment transport mechanisms. This sediment is known to accumulate in the estuaries of the Irish Sea. BNFL Springfields is also licensed to discharge isotopically different radionuclides directly to the Ribble estuary. Thus there is a need to understand the sediment dynamics of the Ribble estuary in order to understand the fate of these radionuclides within the Ribble estuary. Estuaries are highly dynamic environments that are difficult to monitor using the conventional sampling techniques. However, remote sensing provides a potentially powerful tool for monitoring the hydrodynamics of the estuarine environment by providing data that are both spatially and temporally representative. This research develops a methodology for mapping suspended sediment concentration (SSC) in the Ribble estuary using airborne remote sensing. The first hypothesis, that there is a relationship between SSC and l37Cs concentration is proven in-situ (R2=O.94), thus remotely sensed SSC can act as a surrogate for \37Cs concentration. Initial in-situ characterisation of the suspended sediments was investigated to identify spatial and temporal variability in grain size distributions and reflectance characteristics for the Ribble estuary. Laboratory experiments were then perfonned to clearly define the SSC reflectance relationship, identify the optimum CASI wavelengths for quantifying SSC and to demonstrate the effects on reflectance of the environmental variables of salinity and clay content. Images were corrected for variation in solar elevation and angle to give a ground truth calibration for SSC, with an R2=O.76. The remaining scatter in this relationship was attributed to the differences in spatial and temporal representation between sampling techniques and remote sensing. The second hypothesis assumes that a series of images over a flood tide can be animated to provide infonnation on the hydrodynamic regime, erosion, and deposition. Spatial and temporal data demonstrated the complex controls on sediment transport. The data also showed the importance of microphytobenthos in the stabilisation of intertidal sediments, highlighting their importance in defining sources and sinks of radionuclides in intertidal areas. Water volume data from the VERSE model were combined with SSC from the imagery to calculate the total sediment in suspension for each flight line. This provided the figures used to detennine total erosion and deposition, which were then used to derive net suspended sediment and l37Cs influxes of 2.01xl06kg and 604MBq per flood tide

Riverine skin temperature response to subsurface processes in low wind speeds

Both surface and subsurface processes modulate the surface thermal skin and as such the skin temperature may serve as an indicator for coastal, estuarine, and alluvial processes. Infrared (IR) imagery offers the unique tool to survey such systems, allowing not only to assess temperature variability of the thermal boundary layer, but also to derive surface flow fields through digital particle image velocimetry, optical flow techniques, or spectral methods. In this study, IR time-series imagery taken from a boat moored in the Hudson River estuary is used to determine surface flow, turbulent kinetic energy dissipation rate, and characteristic temperature and velocity length scales. These are linked to subsurface measurements provided by in situ instruments. Under the low wind conditions and weak stratification, surface currents and dissipation rate are found to reflect subsurface mean flow (r^2 = 0.89) and turbulence (r^2 = 0.75). For relatively low dissipation rates, better correlations are obtained by computing dissipation rates directly from wavenumber spectra rather than when having to assume the validity of the Taylor hypothesis. Furthermore, the subsurface dissipation rate scales with the surface length scales (L) and mean flow (U) using ε ∝ U^3/L (r^2 = 0.9). The surface length scale derived from the thermal fields is found to have a strong linear relationship (r^2 = 0.88) to water depth (D) with (D/L) ∼ 13. Such a relation may prove useful for remote bathymetric surveys when no waves are present