Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2003-01-21
2004-08-10
McElheny, Donald (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C702S005000
Reexamination Certificate
active
06775617
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for determining hydrographic parameters describing a sea swell field in situ, particularly the sea swell, the current and the water depth, by means of a radar device which provides analog signal sequences from which a sequence of digitized signals in the form of spatial coordinates is provided. From the sequence of digitized signals in spatial coordinates, a three dimensional complex value wave number frequency spectrum is determined by means of a Fourier transformation, the wave number frequency spectrum is then filtered in accordance with the principle of dispersion relationship and the wave number and frequencies of the sea swell are inter-linked for a localization of the sea swell-specific parameters by separating the signals from the noise contained in the signal sequence supplied by the radar device. Then the height of the waves is determined from the signal to noise ratio obtained and the parameters describing the current of the sea swell close to the surface and the depth of the water are determined for the three-dimensional spectral range by localization of the signal coordinates in the surface area defined by the dispersion relationship.
A radar device linked to equipment, which provides from the analog signal sequences delivered by the radar device in polar coordinates a sequence of digitized signals corresponding to the sea swell, is known from DE -OS 43 02 122.
The determination of hydrographic parameters describing in situ a sea swell field over a certain area is a theme with which the oceanographic sciences have been concerned for decades. Information concerning the behavior of an in situ sea swell field on the open sea, in coastal waters, in tide-dependent river beds and river mouth areas as well as for coastal protection measures and port construction would place the technical world including navigation, exploration and production techniques of sea-based plants in a position to develop measures for the prevention of damage from short term sea swells and the long-term behavior of sea swells. All larger nations which, as a result of their geographical location, have access to the sea or which include coastal areas exposed to sea swells, have active research programs in this field in order to receive not only short term information concerning the behavior of sea swell fields but also to obtain from the behavior information concerning long-term changes as a basis for developing measures for the protection and maintenance of the coastal land areas. It can generally be said that the sea swell and tide flows, particularly in areas close to the coast, is inhomogeneous since the water depths are different. Reference is made in this connection to current-and-depth refraction. These processes result in long term changes of the morphology. In the area of water fortifications and harbor inlets additionally a diffraction of the sea swell field occurs to which these areas are exposed and by which additional inhomogeneities of the sea swell are induced.
Mechanical and optical in situ current sensors determine a value of a current, which is representative for a small measuring volume with typical dimensions of 10 cm×10 cm (point measurement). Vertical current profiles can be established by ADCPs (Acoustic Doppler Circuit Profiler). Horizontal current profiles, that is, current maps can be calculated so far from measurements obtained by HF radar devices. However, the application field of these remote exploration sensors is limited to salt water. Areas of up to 20 km×20 km can be measured in this manner, however, with a spatial resolution of the current map of only 500 m×500 m.
From the image sequences of nautical radar using local analysis procedures current maps can be provided with a spatial resolution which is improved by an order of magnitude and the procedure can also be used in sweet waters. Because of the high spatial resolution also small-scale inhomogeneities of the current field such as whirls can be measured. The area that can be maintained is generally 2 km×2 km.
Depth maps can be established in coastal waters by echo sounding. This procedure however is time-consuming and expensive (vessel times). Echo sounding can therefore be performed only sporadically. From the image sequences of nautical radar, however, depth maps can be prepared continuously at relatively low financial and logistic expenses by a local analysis procedure. On an experimental basis, algorithms have already been developed which permit the preparation of a map of the water depth based on certain hydrographic conditions with the knowledge of the surface currents by the analysis of the radar image sequences of inhomogeneous water surfaces. A method developed by Bell [1998] requires however that the wave field consists locally of a single wave wherein the wavelength and direction of movement is spatially variable as a result of the variable water depth. Hessner et al. [1999] was the first to divide the wave field on the basis of wave frequency before determining from the individual frequency components pixel by pixel the water depth on the basis of the dispersion relationship. This method can be used if the directional dispersion of the sea swell state to be analyzed is low, since, otherwise, partial waves arriving from different directions result in interferences.
Another procedure which is utilized for the determination of parameters which describe an in situ sea swell field resides in the measurement of a one-dimensional frequency spectrum and possibly also of the moments of directional distribution of the sea swell at individual locations by means of the so-called sea buoys. Sea buoys however are not suitable for use in low depth waters, particularly in the surf or breaker range and they permit essentially only a point determination of the sea swell field. A very important disadvantage of the known method for determining the hydrographic parameters of a sea swell field by way of sea buoys is the insufficient directional characterization of the sea swell field.
Another method is the so-called global radar image sequence analysis. With the global analysis procedure values of hydrographic parameters are determined, which represent the whole analysis area. The method is used for homogenous sea swell fields, that is, sea swell fields in which the hydrographic parameters are spatially constant over the whole area of analysis.
The signal sequences (radar image sequences), interpolated onto a Cartesian grid, are converted by a three-dimensional fast Fourier transformation (3D FFT) to a three-dimensional complex-value frequency-wave number spectrum. By the global sequence analysis, the variance spectrum calculated by the formation of the square of the absolute value is evaluated.
Subsequently, the water depth d and the components of the horizontal current vector u
x
and u
y
are determined by an adaptation of the sea swell signal coordinates of the image spectrum as selected with a threshold value of the variance to the theoretical dispersion relation of the sea swell waves [Senet, 1996, Outzen, 1998]. The method used for calculating the water depth and current is preferably the so-called “Least-Squares-procedure”. The current and depth values obtained by this procedure, which are representative for the whole analysis area, are the base values for the global procedure.
The dispersion relation defines an area in the spectral space, called “dispersion envelope”, whose shape depends on the value of the current and the water depth. The localization of the sea swell signal on the dispersion envelope makes it possible to utilize the dispersion envelope after the calculation of the current and the water depth as a spectral filter for the separation of the signal and the noise components of the image spectrum.
The sea swell spectrum, that is, the variance spectrum of the surface deviation, is linked linearly, by way of an image transmission function, to the signal to noise ratio of the image spectr
Seemann Jörg
Senet Christian M.
Ziemer Friedwart
Bach Klaus J.
GKSS-Forschungszentrum Geesthacht GmbH
McElheny Donald
LandOfFree
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