The overall objective of the SIGMA project is to enable the determination of the characteristics (i.e. fine scale structure and sediment properties) of the sea bed using remote sensing technologies based on the reflection of acoustic signals.
The objective will be achieved by means of a multidisciplinary approach: acoustic modelling, development of inverse procedures, calibration, generation of optimal test signals, system identification, validation by tank experiments, development of specific instruments, sea trials, sea data processing and archiving.
The acoustic parameters of the sediments will be estimated from wide frequency band measurements, which yield from the use of a steerable parametric array combined to a towed array of receivers. Such a source will allow to generate narrow spot measurements on the sediments and to estimate with high accuracy their acoustic properties.
The marine environment will be treated as a complex system to be identified. A MIMO (Multiple Input Multiple Output) SI (System Identification) scheme will be proposed to determine the sea bed characteristics.
To stimulate the marine system active acoustic sources will be used. Acoustic signals (Multiple Inputs) will be generated using a steerable parametric array and a vertical down looking parametric array, mounted in a tow fish. This will enable to transmit relatively high power acoustic signals into a spot on the sea bed, under a predefined angle. Complementary, an high resolution shear wave seismic chirp source will be used as well.
To observe the response of the marine system the scattered and reflected acoustic signals from the sea bed and from sub-bottom layers will be detected by means of a towed hydrophone array (Multiple Outputs). To compensate for the motion of the tow fish (acoustic transmitter) a real time electronically stabilised system will be developed, while for the compensation of the movement of the towed array a special purpose acoustic device will be developed as well. Theoretical and numerical accurate acoustic wave propagation models as well as inverse procedures will be investigated. The models and procedures will be generalised to include realistic cases like rough and oblique interfaces, hybrid velocity profiles (continuously layered and stepped variations), inhomogeneities and inclusions. Direct inversion computational methods and parameter estimators, such as an MLE (Maximum Likelihood Estimator), will be developed and analysed taking into account instrumental factors, such as noise and the transmitter and receiver characteristics, which will be obtained by extensive calibration measurement procedures.
The theoretical models and inverse procedures will be validated based on the design of measurement procedures adapted to the wave propagation models. The validation will first be performed based on tank experiments (laboratory scale), before being applied to data from sea experiments (real-life). Ground truth will be obtained using conventional equipment and improved geophysical and geotechnical instruments like high resolution seismics and a geotechnical module.
Data analysis will be performed in order to investigate, in detail, the functional relations between the estimated acoustic parameters and sedimentological properties obtained by ground truth in the sea trials or from tank experiments, where the simulated sea bed can be made composed of calibrated sediments.
The data obtained, during the sea trials, will be compiled in a GIS (Geographical Information System). The surveys, conducted in selected representative test areas, will, therefore, lead to the constitution of a well controlled data base on bottom characteristics. This data base will be available on a CD-ROM and the small test areas may be used as benchmark for future instrument calibration.
Funding SchemeCSC - Cost-sharing contracts
LE11 3TU Loughborough