CN101545974A - Stratigraphic profile acoustic detection method for sub-bottom profiler - Google Patents

Abstract

The invention provides a stratigraphic profile acoustic detection method for a sub-bottom profiler, which comprises the following steps that: 1, the sub-bottom profiler firstly generates linear frequency modulation emission signals, and the linear frequency modulation emission signals are added with a sine-squared one eighth window function to form Chirp emission signals; and 2, the Chirp emission signals are transmitted to water body through a transmitting transducer, a receiving hydrophone receives echoed signals returned by stratum and then performs related processing on the echoed signals, and result output of the related processing is displayed on a display screen to give a string of pixels with different shading for reflecting interface characteristics of the stratum, wherein when the echoed signals are subjected to the related processing, frequency response compensation is performed on the sub-bottom profiler so as to detect a frequency response curve of the sub-bottom profiler, and the detected frequency response curve is utilized to perform frequency domain compensation on the echoed signals so as to remove frequency response interference of the sub-bottom profiler and improve signal correlation.

Description

The stratigraphic section acoustic detection method that is used for sub-bottom profiler

Technical field

The present invention relates to a kind of stratigraphic section echoed signal that is used for oceanographic instrumentations such as sub-bottom profiler and handle particularly a kind of stratigraphic section acoustic detection method that is used for sub-bottom profiler

Background technology

In the matched filter processing of sub-bottom profiler, for suppressed sidelobes, carry out windowing process to transmitting, conventional sub-bottom profiler adopts Blackman-Harris window or Dolph-Chebyshev window to carry out windowing process to transmitting usually.

Said method has following shortcoming:

1, the side lobe levels of auto-correlation output is higher, and stratigraphic resolution is reduced;

2, cause the bandwidth that transmits to narrow down after the windowing;

3, forward and backward in windowing, the transmit signal energy loss is bigger, exports at amplifier under the situation of same power, and the stratum penetration depth decreases.

Summary of the invention

Fundamental purpose of the present invention is to provide a kind of stratigraphic section acoustic detection method that is used for sub-bottom profiler, and the transmit signal energy loss that exists in the solution prior art is bigger, and fuzzy relatively shortcoming and defect is differentiated on the stratum.

The present invention is achieved through the following technical solutions.A kind of stratigraphic section acoustic detection method that is used for sub-bottom profiler may further comprise the steps:

One, sub-bottom profiler at first produces linear frequency modulation and transmits

x(t)＝Re{exp[j2πt(f1+Kt/2)]} (1)

In the formula: x (t) transmits for linear frequency modulation; Re Re{exp[j2 π t (f1+Kt/2)] } for it is got real part;

f ₁Initial frequency for FM signal; Then chirp rate K is: K=Δ f/ Δ t

△ f is the frequency span of FM signal;

△ t is the time span of FM signal;

Linear Frequency Modulation transmits and adds sinusoidal square 1/8 windowed function w (t) among the x (t), forms Chirp and transmits:

s(t)＝x(t)*w(t)； (2)

Sinusoidal square 1/8 a windowed function w (t) is:

$w\left(t\right)=\left\{\begin{array}{cc}1& N/8-1<t\&le;7N/8-1\\ {\sin }^2(4\mathrm{t\&pi;}/N)& 0\&le;t\&le;N/8-1\\ {\sin }^2(\mathrm{\&pi;}/2-4(t-7N/8+1)\mathrm{\&pi;}/N& 7N/8-1<t\&le;N-1\end{array}\right.---\left(3\right)$

In the formula, N is the sampling number that linear frequency modulation transmits;

Two, Chirp s emission signal s (t) is launched to water body through transmitting transducer, receiving hydrophone receives the echoed signal that the stratum is returned, then echoed signal is done relevant treatment, result's output of relevant treatment is shown on the display screen, provides the pixel of a string deep or light reflection bed boundary feature that differs.

Wherein, when echoed signal is carried out relevant treatment, sub-bottom profiler is carried out the frequency response compensation, record the frequency response curve of sub-bottom profiler, the frequency response curve that utilization records carries out frequency domain compensation to echoed signal, remove the frequency response of sub-bottom profiler and disturb, improve the correlativity of signal.

The stratigraphic section acoustic detection method that is used for sub-bottom profiler of the present invention, adopt sinusoidal square 1/8 windowing process technology, when reducing the transmit signal energy loss, the relevant output of stratum echoed signal has less side lobe levels, it is darker to make sub-bottom profiler and section plotter in the past compare earth penetrating, and the stratigraphic section layering of measurement is more clear.

Description of drawings

Fig. 1 is the signal graph of the Blackman-Harris window of traditional sub-bottom profiler employing;

Fig. 2 is the auto-correlation output map of the Blackman-Harris window of traditional sub-bottom profiler employing;

Fig. 3 adopts the signal graph of sinusoidal square 1/8 windowed function for the present invention;

Fig. 4 adopts the auto-correlation output map of sinusoidal square 1/8 windowed function for the present invention;

The echoed signal figure that Fig. 5 returns for stratum in the specific embodiment of the invention;

Fig. 6 is that the echoed signal relevant treatment is exported figure as a result in the specific embodiment of the invention.

Embodiment

The present invention is described in detail below in conjunction with accompanying drawing.

If the frequency range that linear frequency modulation transmits is 3kHz～8kHz, the initial frequency f1=3kHz of FM signal, the frequency span △ f=5kHz of FM signal, the time span △ t=10ms of FM signal, it is as follows that signals sampling frequency f s=100kHz is rewritten into the discrete digital form with (1) formula:

x(n)＝Re{exp[j2πt(f1+Knt/2)]} (4)

In the formula: n=0～N-1.

Can produce the digitizing linear frequency modulation time series signal of 3kHz～8kHz by formula (4).

It is as follows that sinusoidal square 1/8 windowed function is rewritten into the discrete digital form:

$w\left(n\right)=\left\{\begin{array}{cc}1& N/8-1<n\&le;7N/8-1\\ {\sin }^2(4\mathrm{n\&pi;}/N)& 0\&le;n\&le;N/8-1\\ {\sin }^2(\mathrm{\&pi;}/2-4(n-7N/8+1)\mathrm{\&pi;}/N& 7N/8-1<n\&le;N-1\end{array}\right.---\left(5\right)$

In the formula, w (n) is the time series of windowed function, n=0～N-1.

The discrete digital time series of sinusoidal square 1/8 windowing linear FM signal

s(n)＝x(n)*w(n) (6)

In the formula, s (n) is the discrete digital time series of windowed function linear FM signal, n=0～N-1.

For example, when n=0～9, the linear frequency modulation s emission signal s (n) after the windowing is respectively 0.0002,0.0005,0.0008,0.0008 ,-0.0001 ,-0.0019 ,-0.0047 ,-0.0084 ,-0.0123 ,-0.0157.

Linear frequency modulation after the windowing transmits and launches to water body through transmitting transducer, after the emission, the echoed signal that the stratum is returned as shown in Figure 5, the result of echoed signal relevant treatment is as shown in Figure 6.

At last, it is also to be noted that what more than enumerate only is specific embodiments of the invention.Obviously, the invention is not restricted to above embodiment, many distortion can also be arranged.All distortion that those of ordinary skill in the art can directly derive or associate from content disclosed by the invention all should be thought protection scope of the present invention.

Claims (1)

1, a kind of stratigraphic section acoustic detection method that is used for sub-bottom profiler is characterized in that, may further comprise the steps:

One, sub-bottom profiler at first produces the linear frequency modulation x (t) that transmits:

x(t)＝Re{exp[j2πt(f1+Kt/2)]} (1)

In the formula:

X (t) transmits for linear frequency modulation; Re{exp[j2 π t (f1+Kt/2)] } for it is got real part;

F1 is the initial frequency of FM signal; Then chirp rate K is: K=Δ f/ Δ t

Δ f is the frequency span of FM signal;

Δ t is the time span of FM signal;

Linear Frequency Modulation transmits and adds sinusoidal square 1/8 windowed function w (t) among the x (t), forms linear frequency modulation s emission signal s (t):

s(t)＝x(t)*w(t)； (2)

In the formula, w (t) is the time series of windowed function, t=0～N-1;

Sinusoidal square 1/8 a windowed function w (t) is:

$w\left(t\right)=\left\{\begin{array}{cc}1& N/8-1<t\&le;7N/8-1\\ {\sin }^2(4\mathrm{t\&pi;}/N)& 0\&le;t\&le;N/8-1\\ {\sin }^2(\mathrm{\&pi;}/2-4(t-7N/8+1)\mathrm{\&pi;}/N& 7N/8-1<t\&le;N-1\end{array}\right.---\left(3\right)$

In the formula, N is the sampling number that linear frequency modulation transmits;

Two, linear frequency modulation s emission signal s (t) is launched to water body through transmitting transducer, receiving hydrophone receives the echoed signal that the stratum is returned, then echoed signal is done relevant treatment, result's output of relevant treatment is shown on the display screen, provides the pixel of a string deep or light reflection bed boundary feature that differs;

Wherein, when echoed signal is carried out relevant treatment, sub-bottom profiler is carried out the frequency response compensation, record the frequency response curve of sub-bottom profiler, the frequency response curve that utilization records carries out frequency domain compensation to echoed signal, remove the frequency response of sub-bottom profiler and disturb, improve the correlativity of signal.

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