JP2837484B2 - Doppler speed detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an apparatus for detecting the velocity of a tidal current or the like from the Doppler effect generated in ultrasonic waves propagating in water.

[Prior art]

Ultrasonic waves are emitted from a transducer attached to the bottom of the ship, and thereby, echo signals obtained from underwater floating substances such as plankton and fine dust or the sea floor have a Doppler shift frequency due to the Doppler effect. By measuring the Doppler shift frequency, the tidal speed or the speed of the ship can be obtained. For example, in order to determine the ship speed, as shown in FIG. 3, when an ultrasonic wave (frequency f ₀ ) is emitted obliquely downward (angle θ) from the transducer, the Doppler shift of the echo signal from the sea floor is obtained. The frequency fd is fd ≒ 2V · f ₀ · cos θ / c. Here, V is the ship speed, and c is the sound speed. Therefore,
The boat speed V can be obtained from the equation V ≒ c · fd / (2f ₀ · cos θ). For that purpose, it is necessary to detect the Doppler shift frequency fd from the echo signal, and the following three methods can be considered as the method. Frequency tracking method A method in which a variable frequency oscillator is provided in the measuring device and the difference from the frequency of the echo signal is controlled to be 0, and the frequency of the echo signal is obtained from the frequency changed at this time. In this system, the oscillator has a complicated circuit configuration employing a PLL system and the like, and the frequency tracking speed and range are limited, so that it is difficult to accurately obtain the Doppler shift frequency with one echo signal of transmission and reception. . As shown in Figure 4 pulse counting method, sets the measurement time with up to t ₁ from t _0, is a method for counting the number of pulses of the detected echo signal within this time, the frequency of one second wavenumber Since the measurement time is Δt and the number of pulses counted during this time is n, the Doppler shift frequency can be obtained from n / Δt. However, in order to perform accurate frequency detection, it is necessary to take the measurement time longer, this measuring layer thickness corresponding to t ₁ from the time t ₀ will be increased (FIG. 3 shown) As a result, the resolution in the depth direction deteriorates, so that it becomes difficult to measure the Doppler shift frequency from a desired depth. Contrary to the period detection method, an average period T (= Δt / n) per one pulse of the echo signal is calculated by obtaining a time Δt required to count a predetermined number of n pulses of the echo signal. In this method, the Doppler shift frequency is obtained from the reciprocal (1 / T). As shown in FIG. 5, this method uses a counting clock having a frequency extremely higher than the frequency of the echo signal for n pulses. Since the detection time of the echo signal is measured, it is possible to obtain the Doppler shift frequency with higher accuracy than the method of the first embodiment. However, the echo signal reflected by a body of water such as plankton is very weak, and the S / N ratio is usually not very good. Therefore, if the pulse being counted is interrupted, the measurement time Include a pulse with an abnormal frequency (period) due to the influence of noise and the like included in the echo signal. When this abnormal pulse is counted, the measurement time fluctuates greatly, and the accuracy of the Doppler shift frequency to be detected is high. Decrease. Furthermore there is a problem that can not be precisely defined echoes desired depth as mentioned in the method (time t ₁ is changed in FIG. 3).

[Problems to be solved by the invention]

As can be seen from the above description, in order to accurately detect the Doppler shift frequency and cope with the case of a plurality of measurement layers, i) detection of the Doppler shift frequency is possible with one transmission / reception, and ii) increased hardware. Perform multi-point continuous measurement without depending on the number of measurement layers without making any measurement. Iii) Improve measurement resolution in the depth direction by reducing the measurement layer thickness (measurement time). Iv) Have an abnormal period due to the influence of noise, etc. It is important to delete received echo data and satisfy the above items. An object of the present invention is to provide a device that can accurately detect a Doppler shift frequency by satisfying the above items.

[Means for Solving the Problems]

The Doppler type speed detecting device of the present invention is a Doppler type speed detecting device which detects a tidal current or a ship speed by detecting a Doppler shift frequency generated in an ultrasonic echo signal propagating in water. K-bit counter (4
A), a k-bit flip-flop (4B) for latching the count value, and the count value latched in the k-bit flip-flop (4B) each time each pulse of the ultrasonic echo signal is detected. k-bit flip-flop (6A), 1-bit counter (5) for counting the number of pulses of the ultrasonic echo signal, 1-bit flip-flop (6B) for storing the count value, and k-bit flip-flop (6A) Calculate the cycle of each pulse from the count value stored in step 2. Exclude faulty pulses outside a predetermined range from those cycles, and determine the fault from the remaining normal cycle and the count value of the 1-bit flip-flop (6B). An arithmetic unit (8) for obtaining an average period from the number of normal pulses obtained by subtracting the number of pulses and obtaining a Doppler shift frequency from the average period. And

[Action]

Consider how you can perform each of the above items. First,
In order to satisfy item (i), it is impossible with the above-described frequency tracking method, and it is necessary to apply a pulse counting method or a cycle detection method. Further, from the item (iii), the period detection method can increase the detection accuracy of the Doppler shift frequency in a short time measurement. Therefore, it suffices if the other required items (ii) and (iv) can be realized by the cycle detection method. A block configuration as shown in FIG. 6 can be considered as a period detection method for that purpose. That is, in order to count n pulses from the echo signal, as shown in FIG. 7, a pulse is generated with respect to the beginning and end of one pulse period obtained by dividing the frequency by the n divider 61. It is obtained from the number of counting clocks counted by the counter 63 between the start pulse and the end pulse output from the detector 62. However, with this circuit configuration, the abnormal period pulse described in the item (iv) may be frequency-divided by the n frequency divider 61. Therefore, the circuit configuration shown in FIG. 8 can be considered as a method for continuously and reliably detecting the period of the echo signal every pulse after satisfying the condition (ii). As the counter 81, a free-running counter that continues counting up with a counting clock is used. If the frequency of the counting clock is fc and the number of bits of the counter 81 is k bits, this counter sets the counting clock to 0 to 0. repeatedly counting up in the range of 2 ^k -1, the count output is a counting clock 2 ¹ to 2 ^k division signal. This counter value is latched by the latch circuit 82 at each rising edge of the echo signal, and the latch output is written to a memory or the like at regular intervals while sequentially changing addresses, and the measured depth is changed from the measurement start depth to the measurement end depth of the measurement layer. If data is read from the corresponding address, the Doppler shift frequency for the measurement layer to be obtained can be obtained. In this circuit configuration, as shown in FIG. 9, if the count value latched at the edge of the first pulse of a certain echo signal is x ₁ , and the latch output by the next one pulse is x ₂ , The period τ of one pulse of a signal is expressed by τ = (x ₁ −x ₂ ) × cycle of counting clock = (x ₁ −x ₂ ) / fc. By calculating 1 / τ, the Doppler shift frequency can be detected from one pulse of the echo signal, and the latch output is output for each pulse of the echo signal. Can be detected, and the Doppler shift frequency can be obtained from an arbitrary measurement depth without changing hardware. By the way, since the Doppler shift frequency to be detected can predict a certain band range, by setting the band range with respect to the period τ detected for each pulse of the echo signal, the period τ detected for each pulse can be calculated. Pass / fail judgment can be made, and the above item (iv) can be satisfied. Further, when a desired resolution cannot be obtained in frequency detection from a cycle of one pulse, the resolution of the detection frequency can be improved by obtaining an average cycle from cycle detection values of several pulses. In this case, the time required to detect several pulses of the echo signal corresponds to the measurement width from a certain measurement depth. Therefore, by adjusting the measurement time, an arbitrary measurement width can be obtained. However, in the method of dividing the pulse of the echo signal by n as described in FIG. 6, the measurement time required to detect the n pulse is unknown because the cycle of the echo signal itself is unknown. Therefore, the measurement width is also unknown, and cannot be said to have been detected in a desired measurement time (measurement width). Therefore, the present invention determines the period of each pulse of the echo signal for a desired measurement time, determines whether the determined period is a normal period, and increases the frequency detection resolution. A Doppler shift frequency is detected from a plurality of determined periods, and a specific implementation method will be described in detail in the following embodiments.

【Example】

FIG. 1 is a control block diagram showing one embodiment of the apparatus of the present invention. 1 is a transmitter / receiver for transmitting an ultrasonic wave and detecting an echo signal of the transmitted ultrasonic wave, and 2 is a transmitter / receiver 1
Is a transmitter that outputs the transmission power to be applied to the transmitter. Reference numeral 3 denotes a receiver for amplifying the reception echo from the transmitter / receiver 1;
Is a transmission / reception switch for switching between transmission and reception. Reference numeral 4 denotes a cycle detector for detecting the cycle of each pulse of the echo signal output from the receiver 3, and reference numeral 5 denotes a pulse counter for counting the number of pulses of the echo signal. Reference numeral 6 denotes a memory for storing the cycle and the number of pulses output from the cycle detector 4 and the pulse number detector 5;
Is an oscillator that supplies a counting clock and a sampling clock to the cycle detector 4 and the memory 6, respectively. Reference numeral 8 denotes a calculation unit which stores a memory for the measurement start depth (time t _{0 in} FIG. 5) and the measurement width (time t ₀ to t ₁ in FIG. 5) set for the calculation unit 8. 6
The calculation unit calculates the Doppler shift frequency based on the read data and calculates the Doppler shift frequency, and includes a determination unit 8A that determines whether the obtained cycle is normal. FIG. 2 shows a detailed circuit diagram of the cycle detector 4, the pulse counter 5, and the memory 6. The cycle detection unit 4 includes a k-bit counter 4A and a flip-flop circuit 4B, and the pulse counting unit 5 includes an l-bit counter. The memory 6 is a k-bit flip-flop circuit.
6A and an l-bit flip-flop circuit 6B. Next, the operation of the apparatus having the above configuration will be described. When an ultrasonic wave is transmitted from the transmitter / receiver 1 and its echo signal is detected by the transmitter / receiver 1 and a predetermined echo signal is output from the receiver 3, the cycle detector 4 outputs each pulse of the echo signal. Is detected based on the counting clock, and the pulse counting unit 5 counts the number of pulses of the echo signal. The detected period and number of pulses are taken into the memory 6 based on the sampling clock. The output is sent to the operation unit 8, and the operation unit 8 receives the following sampling output. In the above series of data, x _i and y _i are the data at the time corresponding to the measurement start depth (corresponding to time t ₀ ), and x _j and y _j are the data at the time corresponding to the measurement end depth (corresponding to time t ₁ ). If it is data, x _i to x _j from the cycle detection unit 4 and
Y _i or y _j from the pulse counting unit 5 is the measurement width (measurement time)
It becomes the data in. Therefore, the pulse width Δx _m and the number of counted pulses Δy _m in the sampling period are represented by the following equations. Therefore, by taking the sum of the above equations within the above measurement time, the total number of pulses Y and the time X required for the total number of pulses within the measurement time can be obtained. From this, the average frequency f within the measurement time is f = Y / X
However, if the data obtained by the expression (1) is used as it is, as described above, the data of the abnormal period will be included, so the processing described below is performed by the arithmetic unit 8. In other words, since the speed detection range is usually determined in the specification of this type of device, the frequency bandwidth due to the Doppler shift of the echo signal can be determined. Accordingly, the pulse period can be determined from the frequency bandwidth. Can also be set. Also, since the speed of a ship or the like rarely changes rapidly, a certain range can be set for the speed fluctuation, in other words, the fluctuation amount of the Doppler shift frequency and the period. Thus, the normal period range Δτ
By setting min to Δτmax, the instantaneous period Δτ for one pulse of the echo signal obtained from equation (1) (=
Δx _m / Δy _m ) satisfies the following equation (3) to determine whether or not the detected cycle is due to a normal pulse. Δτmin ≦ Δτ ≦ Δτmax (3) In this way, the above-described determination is performed for each pulse, and the total sums X ′ and Y ′ of Δx _m and Δy _m of the normal period τ are obtained. Thereafter, the average Doppler shift frequency f based on the normal cycle can be obtained from the following equation (5). f = Y '/ X' (5) In Doppler sonars and tidal current meters, three or four beam systems are mainly used to reduce the influence of hull movements. In the configuration, the period detection unit 4 and the pulse number counting unit 5 are provided for each beam.
Is not necessary for each beam and each measurement layer unit unlike the frequency tracking method, so that hardware can be simplified and the number of parts can be reduced.

【The invention's effect】

As described above, according to the present invention, the period of each pulse in the echo signal is obtained, and only normal ones are collected from the obtained period. Further, since the Doppler shift frequency is obtained from a plurality of normal cycles, the detection accuracy can be further improved.

[Brief description of the drawings]

FIG. 1 is a control block diagram showing an embodiment of the Doppler speed detector of the present invention, FIG. 2 is a block diagram showing a detailed configuration of a main part in the device of FIG. 1, and FIG. FIGS. 4 and 5 used to explain the measurement method of FIG.
FIG. 6 is a time chart showing the operation of a pulse counting method and a period detection method used for detecting a Doppler shift frequency from an echo signal. FIG. 6 is a block diagram of a period detection circuit obtained by improving the above-mentioned period detection method. FIG. 7 shows the sixth
8 is a block diagram of a cycle detection circuit obtained by further improving the cycle detection of FIG. 6, and FIG. 9 is a time chart showing the operation of the block diagram of FIG. It is. DESCRIPTION OF SYMBOLS 1 ... Transceiver, 2 ... Transmitter, 3 ... Receiver, S ... Transceiver switch, 4 ... Period detection part, 5 ... Pulse number counting part, 6 ... Memory, 7 ... Oscillator , 8 ... calculation part, 8a ... determination part.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01S 7/52-7/64 G01S 15/00-15/96

Claims (1)

(57) [Claims] 1. A Doppler type speed detector for detecting a tidal current or a ship speed by detecting a Doppler shift frequency generated in an ultrasonic echo signal propagating in water, wherein the k-bit counter counts a counting clock. (4A)
And a k-bit flip-flop (4B) for latching the count value, and a k-bit flip-flop (4B) for storing the count value latched in the k-bit flip-flop (4B) each time each pulse of the ultrasonic echo signal is detected. A flip-flop (6A), a 1-bit counter (5) for counting the number of pulses of the ultrasonic echo signal, a 1-bit flip-flop (6B) for storing the count value, and a k-bit flip-flop (6A) The cycle of each pulse is obtained from the count value obtained, and defective pulses outside a predetermined range are excluded from those cycles, and the number of defective pulses is calculated from the remaining normal cycle and the count value of the 1-bit flip-flop (6B). And an arithmetic unit (8) for obtaining an average period from the normal pulse number obtained by subtracting the above, and obtaining a Doppler shift frequency from the average period. That Doppler speed detection device.