Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2001-03-22
2003-04-15
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C367S088000
Reexamination Certificate
active
06549853
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides a method for determining the sea floor roughness using multibeam echosounder. The present invention also provides a method to precisely determine the beam incident angle at the sea-bottom and in consequence, acoustic backscatter data to be unambiguously related to the nature of the sea-bottom.
BACKGROUND AND PRIOR ART REFERENCES TO THE INVENTION
Multibeam sounding systems are widely used for bathyretric mapping and also have potential to provide quantitative backscatter information which can be used to classify the seabottom roughness. Because of narrow multibeam geometry, the angular dependence of the acoustic backscatter can be derived, and accurate quantitative estimate of backscatter is possible along with bathymetry. The changes in the backscatter strength for different survey areas can be compared for the same incidence angles using the shape parameters of the backscatter curves. Before initiating any model study using multibeam angular backscatter information, corrections in terms of system gain, is an important step to be carried out. Using multibeam bathymetry, accurate measurement of the bottom slopes is also possible, which can be used to compute backscatter strength for the determination of correct angle of incidence. Also, bottom insonification area normalization is an important factor to be employed before carrying out any seabottom characterization.
The multibeam systems have larger seafloor coverage when compared to the single beam system. Hence, in coming future many fold increases in the use of multibeam system is expected in comparison with the single beam system. In the multibeam processing system, the received electrical envelopes at the bottom echo processor are sampled and converted to rms voltages. Techniques for seafloor classification are still maturing and multibeam backscatter data and bathymetry data will play a significant role in the development of these techniques.
A reference may be made to Anonymous, (1993), “Atlas Hydrosweep DS—Interface specifications: Magnetic Tape Recording and data for Backscattering Analysis”, STN Atlas Elektronik BmgH, Bremen.
A reference may be made to De moustler, C. and Alexaondrou, D., (1991). Angular dependence of 12 KHz. Seafloor acoustic backscatter . Jour. Acoust. Soc. America., 90: 531-533.
A reference may be made to Jackson, D. R, D. P. Winebreuner, and A. Ishimaru, (1986). Application of the Composite roughness model to high frequency Bottom backscattering, Jour. Acoust. Soc. America., 79: 1410-1422.
A reference may be made to Anonymous, (1999), “Cruise Report of OVR Sagarkanys-Cruise Number SK-140 -B”, National Institute of Oceanography, Dona Paula, Goa, India.
A reference may be made to Talukdar, K. K. and R. C. Toyce, (1 991), “Digital Processing of sidescan images from bottom backscatter data collected by Sea Beam”, Mar. Geodesy, 14, 81-100.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a method for determining seafloor roughness using multibeam echosounder.
SUMMARY OF THE INVENTION
The present invention provides a method for determining sea floor roughness using multibeam echosounder, said method comprising providing backscatter, bathymetry and multibeam operational parameters; removing system gain from the backscatter data to obtain real seafloor backscatter data; calculating across track seafloor slope; incorporating correction factor in actual beam arrival angles; calculating seafloor area; measuring backscatter strength; obtaining backscatter strength data at 1° angle; obtaining power law parameters; using the above-obtained parameters in a seafloor roughness power law model; splicing the multibeam backscatter data; including sediment volume roughness model; and verifying the validity of the composite roughness model.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention provides a method for determining sea floor roughness using multibeam echosounder, said method comprising:
(i) providing backscatter, bathymetry and multibeam operational parameters;
(ii) removing system gain from the backscatter data to obtain real seafloor backscatter data;
(iii) calculating across track seafloor slope;
(iv) incorporating correction factor in actual beam arrival angles;
(v) calculating seafloor area;
(vi) measuring backscatter strength;
(vii) obtaining backscatter strength data at 1° angle;
(viii) obtaining power law parameters;
(ix) using the above-obtained parameters in a seafloor roughness power law model;
(x) splicing the multibeam backscatter data;
(xi) including sediment volume roughness model; and
(xii) verifying the validity of the composite roughness model.
In an embodiment of the present invention, the primary backscatter parameters recorded by the system are echo rms voltage and signal duration for each beam.
In yet another embodiment of the present invention, the overall signal processing gain (V
Tot
) consists of matching circuits gain (V
Match
), range related gain or Time varied correction gain (V
TVC
), beamformers gain (V
BF
) and filter gain (V
Filt
).
V
Tot
=V
Match
+V
TVC
+V
BF
+V
Filt
(I)
In still another embodiment of the present invention, the matching circuit gain is the gain provided by each transducer group.
In one another embodiment of the present invention, the range related gain or Time Varied Correction Gain is calculated using equations given in Anon, 1993.
In one more embodiment of the present invention, the range related gain consists of gain compensation due to signal travel through the water media and attenuation corrections and starting gain.
In an embodiment of the present invention, the starting gain V
TVC
comprises of preamplifier gain (V
v
), user selected TVC (V
corr
) and system related offset gain (V
off
).
In another embodiment of the present invention, the across track seafloor slope is calculated using bathymetry data.
In yet another embodiment of the present invention, the across track seafloor slope is calculated to incorporate correction factor in actual beam arrival angles.
In still another embodiment of the present invention, the bottom slope values with respect to each beam are computed using tangent inverse of the ratio between depth and lateral distance difference.
In one another embodiment of the present invention, the seafloor area is calculated based upon angle of incidence and bathymetry.
In one more embodiment of the present invention, the bottom sea surface area is calculated using the formula
A=A
b
exp[−(&phgr;/&phgr;
x
)
2
]+A
p
{1−exp[−(&phgr;/&phgr;
x
)
2
]} II
In an embodiment of the present invention, the actual echo root mean square level is calculated using DeMoustier and Alexandrou Formula (1991).
<20 log
10
RL
(&phgr;)>=
SL
+<10 log
10
S
B
(&phgr;)>−40*log
10
(
R
)−2&agr;
b
R
+10 log
10
A
III
In another embodiment of the present invention, the backscatter strength data at 1° angle is obtained by bining each beam at 1° angular bins and averaging the number of samples in each bin for steady areas.
In yet another embodiment of the present invention, the power law parameters are obtained by reading the measured backscatter data and subjecting it to curve fitting.
In still another embodiment of the present invention, Helmholtz-Kirchhoff approximation is used to determine interface roughness of the seabed.
In one another embodiment of the present invention, the splicing is done using Helmholtz-Kirchoff and Rayleigh-Rice theories.
In one more embodiment of the present invention, the incidence angle of 20° is used for splicing.
In an embodiment of the present invention, the sediment volume roughness inodel is created by curve fitting the entire measured angular backscatter data.
In another embodiment of the present invention, matching the theoretical curve with the measured backscatter data does the verification.
Seafloor roughness studies using bathymetry provides geometrical shapes of
Chakraborty Bishwajit
Kodagali Vijay N.
Council of Scientific & Industrial Research
McElheny Jr. Donald E.
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