JP2010175377A - Radar apparatus, ocean-radar observation apparatus, and doppler frequency data calculation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radar apparatus and an ocean-radar observation apparatus which detect rapidly changing surface flow rates. <P>SOLUTION: A processing unit 25 calculates first amplitude data by azimuth resolution processing of a received data Dr; groups these first amplitude data, while overlapping each of n-cycle portions of the sweep cycles with an optional sweep cycle of less than n; calculates for each group, second amplitude data in a sweep cycle unit, which show the amplitude for each predetermined distance in the predetermined direction, by performing Fourier transformation on the first amplitude data in a sweep cycle unit; groups for every group of the second amplitude data, by rearranging each of the second amplitude data included in each of the groups for each of the predetermined distances, in the order of the sweep cycles; prepares the new second amplitude data by adding, for every group, predetermined number of zero-data showing zero-amplitude to the second amplitude data which is grouped by the rearrangement; and calculates Doppler spectra Ddp1, Ddp2 for each predetermined distance by performing Fourier transformation of the second amplitude data to which the zero-data is added. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a radar apparatus that observes the surface velocity of the sea at a predetermined distance along a predetermined direction using a reflected signal of a transmission signal whose frequency is swept at a predetermined period, and includes a plurality of such radar apparatuses. The present invention relates to a marine radar observation apparatus for observing the surface velocity of the sea, and a Doppler frequency data calculation method used in these apparatuses.

  As a basic configuration of this type of radar apparatus, a configuration of a radar apparatus (radar station) disclosed as a conventional technique in Patent Document 1 below is known. In this radar apparatus, first, in the first FFT processing, FFT analysis is performed in units of one sweep, and spectra corresponding to the number of sweeps are calculated. In this case, this spectrum represents the energy distribution of echoes in the range (distance) direction. Next, a rearrangement process for rearranging the calculated number of sweep-numbered spectra for each distance is executed. In this process, energy values of echoes of the same distance are collected from the spectrum calculated in the first FFT process to create a time series. Next, a second FFT process is performed on the time series for each distance to calculate a Doppler spectrum. Finally, in order to earn the S / N of the Doppler spectrum, the Doppler spectrum calculated from several time series is averaged. In this case, the finally calculated Doppler spectrum shows the flow velocity in the line-of-sight direction of the antenna.

JP 2000-314773 A (page 3, FIG. 6)

  However, the radar apparatus having the above basic configuration has the following problems to be solved. That is, in this radar apparatus, in order to earn the S / N of the Doppler spectrum as described above, a process for averaging the Doppler spectra calculated from several time series is performed. Therefore, in this radar apparatus, the final Doppler spectrum calculation cycle is limited by the cycle for calculating several time series (necessary number), so that the final Doppler spectrum calculation cycle can be further shortened easily. However, there is a problem to be solved that it is difficult to detect a phenomenon such as a tsunami that causes a rapid change in the surface layer flow velocity.

  The present invention has been made to solve such a problem, and a radar apparatus and a marine radar observation apparatus that can detect a phenomenon in which a surface layer flow velocity changes rapidly, and a primary scattering spectrum that appears in Doppler frequency data while shortening the calculation period. The main object of the present invention is to provide a Doppler frequency data calculation method capable of detecting a phenomenon in which a change in the surface layer flow velocity is fast when used in these apparatuses so that the peak frequency can be accurately calculated.

  In order to achieve the above object, the radar apparatus according to claim 1, wherein the first amplitude indicating the amplitude of the reflected signal by sampling the reflected signal from the predetermined direction for the transmission signal whose frequency is swept at a predetermined sweep period. A radar apparatus that converts data into data and calculates Doppler frequency data for each predetermined distance in the predetermined direction based on the first amplitude data, and includes a processing unit, and the processing unit A grouping process in which n cycles (n is an arbitrary integer equal to or greater than 2) of the sweep cycles are grouped while being overlapped by an arbitrary sweep cycle less than n; By performing Fourier transform on the amplitude data in units of the sweep cycle, the second amplitude data indicating the amplitude for each predetermined distance in the predetermined direction is converted into the sweep cycle. For each group of the second amplitude data and the first Fourier transform processing calculated in the order, the second amplitude data included in each group is rearranged for each predetermined distance in the sweep cycle order. A new second amplitude data obtained by adding a predetermined number of zero data indicating an amplitude of zero for each group to the rearrangement process for grouping and the second amplitude data grouped by the rearrangement process. The zero data adding process and the second amplitude data included in each group subjected to the zero data adding process are subjected to Fourier transform to calculate the Doppler frequency data for each predetermined distance 2 Next Fourier transform processing is executed.

  The radar device according to claim 2 is the radar device according to claim 1, wherein the processing unit is configured to perform the first Fourier transform processing before the Fourier transform in units of the sweep cycle, for each sweep cycle. Zero data whose amplitude is zero is filled by a predetermined number to obtain new first amplitude data.

  According to a third aspect of the present invention, the radar apparatus according to the first or second aspect of the present invention is the radar apparatus according to the first or second aspect, wherein the reception is output from each of the plurality of reception antennas that receive the reflected wave of the radar signal transmitted from the transmission antenna toward the ocean. An A / D conversion unit that samples a signal and converts the received signal into reception data indicating the amplitude of the reception signal, and the processing unit applies a predetermined beam forming method to the reception data. An azimuth decomposition process for converting into amplitude data is executed.

  According to a fourth aspect of the present invention, there is provided the radar apparatus according to the third aspect, wherein the radar apparatus includes the plurality of reception antennas, and at least one of the plurality of reception antennas includes a signal generation unit that outputs a transmission signal. It is configured to be connectable to the A / D conversion unit alternately, and functions as the transmission antenna that transmits the transmission signal as the radar signal when connected to the signal generation unit.

  According to a fifth aspect of the present invention, there is provided the radar apparatus according to the first or second aspect, wherein a single reception antenna having a directivity for receiving a reflected wave of a radar signal transmitted from the transmission antenna toward the ocean is provided. And an A / D converter that samples the received signal output from the receiving antenna and converts the received signal into received data indicating the amplitude of the received signal, and outputs the received data as the first amplitude data. Yes.

  A marine radar observation apparatus according to claim 6 is a desired sea area in the ocean based on the plurality of radar apparatuses according to any one of claims 1 to 5 and the Doppler frequency data respectively calculated by the radar apparatuses. And a processing device for calculating the flow velocity and direction of the surface current.

  The Doppler frequency data calculation method according to claim 7, wherein a reflected signal from a predetermined direction for a transmission signal whose frequency is swept in a predetermined sweep cycle is sampled and converted into first amplitude data indicating an amplitude of the reflected signal. A Doppler frequency data calculation method for calculating Doppler frequency data for each predetermined distance in the predetermined direction based on the first amplitude data, wherein the first amplitude data includes n cycles (n Is an arbitrary integer greater than or equal to 2) and is grouped while overlapping each other with an arbitrary sweep cycle of less than n, and for each group, the first amplitude data in units of the sweep cycle By performing a Fourier transform, second amplitude data indicating the amplitude for each predetermined distance in the predetermined direction is calculated in units of the sweep cycle. For each group of the first-order Fourier transform process and the second amplitude data, the second amplitude data included in each group is rearranged and grouped by the predetermined distance in the sweep cycle order. Zero data that is a new second amplitude data by adding a predetermined number of zero data indicating an amplitude of zero for each group to the rearrangement process and the second amplitude data grouped by the rearrangement process An addition process and a second-order Fourier transform process for calculating the Doppler frequency data for each predetermined distance by performing a Fourier transform on the second amplitude data included in each group subjected to the zero data addition process And execute.

  In the radar apparatus according to claim 1 and the marine radar observation apparatus according to claim 6, the processing unit calculates n cycles of the sweep period for the first amplitude data indicating the amplitude of the reflected signal from the predetermined direction. , Continuously performing the grouping process while overlapping at an arbitrary sweep period less than n, and performing the first-order Fourier transform process on the first amplitude data grouped in this way ( The second amplitude data is calculated by performing a distance decomposition (by performing a so-called short-time Fourier transform process), and the second amplitude data is rearranged for each processing distance in the order of the sweep cycle and grouped. A second-order Fourier transform process is performed on the second amplitude data to calculate Doppler frequency data. Therefore, since the averaging process for averaging Doppler frequency data calculated from several time series is not performed, the final calculation period of Doppler frequency data can be sufficiently shortened. As a result, the detection accuracy of a phenomenon (for example, tsunami) in which the flow velocity of the surface ocean current changes in a short time can be dramatically increased.

  Further, according to the radar apparatus and the marine radar observation apparatus, the processing unit performs Doppler frequency data by performing Fourier transform on the second amplitude data including the added zero data in the second order Fourier transform process. Therefore, the frequency resolution in calculation can be improved, and thereby the frequency of the primary scattering spectrum peak appearing in the Doppler frequency data (Doppler spectrum) can be accurately calculated. As a result, it is possible to accurately calculate the shift amount from the frequency at which the primary scattering spectrum peak appears in the state where the surface current does not occur. As a result, the flow velocity of the surface current can be accurately calculated based on this shift amount. Can do.

  According to the radar device according to claim 2 and the ocean radar observation device according to claim 6, the processing unit adds zero data to the first amplitude data to be subjected to the first-order Fourier transform process, thereby reducing the number of data. By increasing the number, the number of second amplitude data calculated by the first-order Fourier transform can be increased (distance resolution is improved).

  According to the radar device according to claim 3 and the ocean radar observation device according to claim 6, the reception signals respectively output from the plurality of reception antennas that have received the reflected waves of the radar signal transmitted from the transmission antenna toward the ocean. For the received data indicating the amplitude of the received signal obtained by sampling the received signal, the processing unit executes the beam forming method such as the DBF method and performs the azimuth decomposition process. Since the actual rotation processing can be made unnecessary, the final Doppler frequency data calculation cycle can be greatly shortened.

  According to the radar device according to claim 4 and the marine radar observation device according to claim 6, since at least one of the plurality of reception antennas functions as a transmission antenna, the number of antennas can be reduced.

  According to the radar device according to claim 5 and the ocean radar observation device according to claim 6, the reflected wave of the radar signal transmitted from the transmitting antenna toward the ocean is received using one receiving antenna having directivity. Since it is received, the azimuth decomposition process can be omitted.

  The Doppler frequency data calculation method according to claim 7, wherein a reflected signal from a predetermined direction for a transmission signal whose frequency is swept at a predetermined sweep period is sampled and converted into first amplitude data indicating the amplitude of the reflected signal. When calculating Doppler frequency data for each predetermined distance in a predetermined direction based on the first amplitude data, the first amplitude data is overlapped by n cycles of the sweep cycle with an arbitrary sweep cycle less than n. Grouping processing for grouping, and by performing Fourier transform on the first amplitude data in units of sweep periods for each group, second amplitude data indicating the amplitude for each predetermined distance in a predetermined direction is obtained in units of sweep periods For each group of the first-order Fourier transform processing calculated in step 2 and the second amplitude data, the second amplitude data included in each group. For the second amplitude data grouped by the rearrangement process and the second amplitude data grouped by the rearrangement process, a predetermined number of zero data whose amplitude is zero for each group Zero data addition processing to add new second amplitude data, and Doppler frequency data for each predetermined distance by performing Fourier transform on the second amplitude data included in each group subjected to the zero data addition processing And a secondary Fourier transform process for calculating.

  Therefore, according to this Doppler frequency data calculation method, since the averaging process of averaging Doppler frequency data calculated from several time series is not performed, the final calculation period of Doppler frequency data can be sufficiently shortened. . Further, in the second order Fourier transform process, the Doppler frequency data is calculated by performing the Fourier transform on the second amplitude data including the added zero data, so that the frequency resolution in calculation can be improved. The frequency of the primary scattering spectrum peak appearing in the Doppler frequency data (Doppler spectrum) can be accurately calculated.

1 is a configuration diagram of an ocean radar observation apparatus 1 and an ocean radar station 2. FIG. It is explanatory drawing which showed typically the 1st amplitude data D1 of the state by which direction decomposition was carried out. It is explanatory drawing which showed typically the content which groups the 1st amplitude data D1 for 1 direction of FIG. 2 by a grouping process. It is explanatory drawing which showed typically the content which carries out the distance decomposition | disassembly of the grouped 1st amplitude data D1 of FIG. 3, and makes it 1st amplitude data D2. It is explanatory drawing which showed typically the content which rearranges the 2nd amplitude data D2 by which the distance decomposition | disassembly of FIG. 4 was rearranged. It is explanatory drawing which showed typically the content which adds the zero data v (0) by the zero data addition process to the rearranged 2nd amplitude data D2 of FIG. It is a characteristic view which shows the Doppler spectrum Ddp obtained by a secondary Fourier transform process. In a 1st simulation, it is a characteristic view which shows the time change about the flow velocity Vr of the surface sea current used as a reference | standard. In a 1st simulation, it is a characteristic figure which shows the time change about the flow velocity Vr of the surface sea current obtained by the simulation which added the zero data v (0). In a 1st simulation, it is a characteristic figure which shows the time change about the flow velocity Vr of the surface sea current obtained by the simulation which does not add the zero data v (0). In a 2nd simulation, it is a characteristic view which shows the time change about the flow velocity Vr of the surface layer sea current used as a reference | standard. In a 2nd simulation, it is a characteristic figure which shows the time change about the flow velocity Vr of the surface layer current obtained by the simulation which added the zero data v (0). In a 2nd simulation, it is a characteristic figure which shows the time change about the flow velocity Vr of the surface layer ocean current obtained by the simulation which does not add zero data v (0). In a 3rd simulation, it is a characteristic view which shows the time change about the flow velocity Vr of the surface layer sea current used as a reference | standard. In a 3rd simulation, it is a characteristic figure which shows the time change about the flow velocity Vr of the surface sea current obtained by the simulation which added the zero data v (0). In a 3rd simulation, it is a characteristic figure which shows the time change about the flow velocity Vr of the surface layer current obtained by the simulation which does not add zero data v (0). It is explanatory drawing which showed typically the content which adds zero data u (0) to the 1st amplitude data D1 by zero data addition process.

  Hereinafter, embodiments of a radar apparatus and an ocean radar observation apparatus according to the present invention will be described with reference to the accompanying drawings, and embodiments of a Doppler frequency data calculation method used in the radar apparatus will be described.

  A marine radar observation apparatus 1 shown in FIG. 1 includes a plurality of (as an example, two) marine radar stations 2A and 2B (hereinafter also referred to as “marine radar station 2” unless otherwise distinguished), and a base station (processing in the present invention). An example of the apparatus) 3 is provided so that the ocean current vector V (velocity and direction) of the surface ocean current in an arbitrary sea area A on the ocean can be observed.

  Each marine radar station 2 is composed of a radar apparatus according to the present invention, and has a predetermined sweep cycle such as an FMCW (Frequency Modulated Continuous Wave) method or an FMICW (Frequency Modulated Interleaved Wave) method. Radar signal) is applied to the sea surface, and a reflected signal (echo) that is returned after Bragg backscattering on the sea surface is received, and the azimuth decomposition process, the distance resolution process, and the Doppler frequency decomposition process are executed, which will be described later. A Doppler spectrum (Doppler frequency data in the present invention) Ddp is calculated for the surface current in all unit sea areas in the observation sea area.

  Specifically, as shown in FIG. 1, each marine radar station 2 includes one transmission antenna 21, a signal generation unit 22, a plurality of (in this example, eight as an example) reception antennas 23, reception antennas 23, and the like. The same number of signal receiving units 24 and one processing unit 25 are provided. In this case, the signal generator 22 generates a short-wave band transmission signal Stx whose frequency is swept (frequency-modulated) at a predetermined sweep period by the FMCW method or the FMICW method, and outputs the transmission signal Stx to the transmission antenna 21. As an example, the signal generating unit 22 generates a transmission signal Stx by frequency-modulating a signal having a radar frequency of frequency f0 (for example, 24.5 MHz) with a frequency sweep width of ± f1 (for example, ± 150 KHz). . The transmission antenna 21 is a Yagi antenna as an example, and transmits the input transmission signal Stx as a radar signal on the sea in a broad beam state. For example, when the sea area included in the scanning angle range of −45 ° to 45 ° when the front direction of the marine radar station 2 is the reference angle (0 °) is the observation sea area, the transmitting antenna 21 is at least the scanning angle. Radar signals are transmitted in a range including the range (for example, a range of ± 90 ° centered on a reference angle of 0 ° (scanning angle of −90 ° to 90 °)).

  Each receiving antenna 23 is composed of, for example, an omnidirectional antenna. In addition, each receiving antenna 23 has a 0.5λ (λ is the wavelength of the transmission signal Stx) interval so that, for example, a beam pattern of the receiving antenna that can ensure the angular resolution required in the azimuth resolution process described later can be formed. Are arranged on a virtual straight line perpendicular to the reference angle 0 °. In addition, each receiving antenna 23 receives a radar signal (reflected wave) reflected from the sea surface and outputs it to the corresponding signal receiving unit 24. Each signal receiver 24 demodulates the signal output from the corresponding receiving antenna 23 with an intermediate frequency to a baseband signal and outputs it as a received signal Srx.

  As illustrated in FIG. 1, the processing unit 25 includes the same number of A / D converters (indicated as “A / D” in the figure) 25 a and the number of signal receiving units 24 (also the same number as the receiving antennas 23). A processing processor (denoted as “DSP” in the figure) 25b and a memory 25c are provided. In this case, each A / D converter 25a generates reception data Dr indicating the amplitude of the reception signal Srx by sampling the reception signal Srx output from the corresponding signal reception unit 24 at a predetermined sampling period. The signal processor 25b receives the reception data Dr output from each A / D converter 25a and stores it in the memory 25c. Further, the signal processor 25b performs azimuth decomposition processing on the reception data Dr of each reception signal Srx stored in the memory 25c, and relates to amplitude data calculated by this processing according to the present invention. By executing the Doppler frequency data calculation method, that is, grouping processing, first-order Fourier transform processing (distance decomposition processing), rearrangement processing, zero data addition processing, and second-order Fourier transform processing (Doppler frequency decomposition processing). By executing, the Doppler spectrum Ddp for the surface current in the minimum sea area (unit sea area) obtained by dividing the observation sea area by the azimuth resolution in the azimuth resolution process and the distance resolution in the distance resolution process is calculated over the entire observation sea area. And stored in the memory 25c. In the ocean radar station 2A, the signal processor 25b outputs the Doppler spectrum Ddp stored in the memory 25c to the base station 3 as the Doppler spectrum Ddp1, and in the ocean radar station 2B, the signal processor 25b This Doppler spectrum Ddp stored in 25c is output to the base station 3 as a Doppler spectrum Ddp2.

  The base station 3 is connected to each of the ocean radar stations 2A and 2B via a communication line, and a Doppler spectrum Ddp1 for the surface current of all unit ocean areas in the observation ocean area output from each of the ocean radar stations 2A and 2B. Ddp2 is received. Further, the base station 3 calculates the flow velocity and current direction (sea current vector V) of the surface current in the desired sea area (unit sea area) A based on these Doppler spectra Ddp1 and Ddp2.

  Next, operations of the marine radar stations 2A and 2B and the marine radar observation apparatus 1 will be described with reference to the drawings.

  In the operation state of the ocean radar observation apparatus 1, each of the ocean radar stations 2A and 2B irradiates the sea surface with a radar beam from each transmission antenna 21, and each reception antenna 23 receives the reflected wave. 24 outputs the received signal Srx, and the processing unit 25 repeatedly generates and outputs the Doppler spectra Ddp1 and Ddp2 to the base station 3 based on the received signal Srx.

Specifically, the detailed operation of the processing unit 25 in each of the marine radar stations 2A and 2B will be described with reference to the drawings. Since the operations of the ocean radar stations 2A and 2B are the same, the operation will be described taking the ocean radar station 2A as an example. In the ocean radar station 2 </ b> A, the signal generator 22 generates a transmission signal Stx and outputs it to the transmission antenna 21. As a result, the transmission signal Stx is emitted from the transmission antenna 21 to the sea as a radar signal in a broad beam state. Next, the irradiated radar signal becomes a scattered wave on the sea surface, and a part thereof returns to the ocean radar station 2A as a reflected wave. The reflected wave observed by the ocean radar station 2A is a component along the line-of-sight direction (radar line-of-sight direction) of the ocean radar station 2A in the scattered wave. As shown in FIG. Due to the Bragg scattering phenomenon, two primary scattering spectrum peaks P1 and P2 appear in the plus frequency region and the minus frequency region when the frequency f0 of the transmission signal Stx is used as a reference (zero). Specifically, the two primary scattering spectrum peaks P1 and P2 appear at the position of the frequency (± fd0) even when the surface current does not exist. However, when the surface current exists, the two primary scattering spectrum peaks P1 and P2 correspond to the current direction of the surface current. Appearing at a frequency (± fd) position. In detail, when the surface current flows close to the ocean radar station 2, as shown in FIG. 7, it appears shifted to a positive frequency, and when it moves away, it becomes a negative frequency contrary to FIG. Appears shifted. Further, the flow velocity (line-of-sight flow velocity) Vr of the surface ocean current at this time is calculated based on a frequency shift amount (fd−fd0) caused by the presence of the surface ocean current, as shown in the following equation.
Flow velocity Vr = speed of light × (fd−fd0) / (2 × f0)

  Each receiving antenna 23 receives reflected waves from all sea areas (reflected waves from all distances coming from all angles) and outputs the received signals to the corresponding signal receiving unit 24. Each signal receiving unit 24 demodulates the signal input from the corresponding receiving antenna 23 into a baseband signal, and outputs it as a received signal Srx. In this case, since each receiving antenna 23 is installed with a predetermined interval (0.5λ) as described above, even if the reflected waves are from the same sea area, the receiving antennas 23 are positioned according to the difference in their installation positions. The reflected wave is received in a state where a phase difference has occurred. As a result, a similar phase difference occurs between the reception signals Srx.

  In the processing unit 25, each A / D converter 25a receives the reception signal Srx output from the corresponding signal reception unit 24 and performs A / D conversion, thereby receiving the amplitude (level) of the reception signal Srx. Data Dr is generated and output to the signal processor 25b. The signal processor 25b stores each received data Dr in the memory 25c. Next, the signal processor 25b performs data processing on each received data Dr stored in the memory 25c.

  In this data processing, the signal processor 25b first performs azimuth decomposition processing on each received data Dr stored in the memory 25c. In this azimuth decomposition processing, the signal processor 25b, as an example, performs beam forming processing on the received data Dr (this example) each time the received data Dr for the transmission signal Stx for one sweep period is stored in the memory 25c. Then, as an example, a DBF method as a beam forming method) is applied to form a beam pattern in which the main beam is directed in a predetermined line-of-sight direction, and a reception obtained when a reflected wave from the sea area is received by an antenna of this beam pattern First amplitude data D1 (u (1), u (2),..., U (j) as data, where j is the sampling number of the A / D converter 25a during one sweep cycle) It is calculated based on the data Dr and stored in the memory 25c in correspondence with a predetermined line-of-sight direction (scanning angle). The signal processor 25b performs the beam forming process and the calculation / storage process of the first amplitude data D1 over a predetermined scanning angle range (for example, −45 ° to 45 °). This is executed while increasing the line-of-sight direction (scanning angle) by a predetermined scanning angle (arbitrary unit scanning angle, for example, 5 °). As a result, as shown in FIG. 2, the memory 25c stores the first amplitude data D1 for one sweep period, which is azimuthally resolved for each unit scanning angle (each line-of-sight direction), sequentially stored in order of the number of sweeps. Go.

  Next, the signal processor 25b performs a grouping process for each azimuth on the first amplitude data D1 that is azimuth-decomposed for each unit scanning angle (each sight line direction). In this grouping process, the signal processor 25b continuously performs a process of grouping n sweep periods (n is an arbitrary integer equal to or greater than 2) by overlapping each sweep period less than n. And execute. In the example shown in FIG. 3, n (= 256) periods are grouped while being overlapped by 128 (= 256/2) sweep periods as an example. In this example, as an example, the first amplitude data D1 for 256 periods corresponds to data for 2 minutes, and thus is grouped while being overlapped by 1 minute. In FIG. 3, in order to facilitate understanding of the invention, the grouping process for the first amplitude data D1 in one direction is shown, but the grouping process is performed for the first amplitude data D1 in all directions. Executed.

  Subsequently, the signal processor 25b executes a first-order Fourier transform process (distance resolution process) for each group on the first amplitude data D1 in each direction grouped in the grouping process. In this first-order Fourier transform process, the signal processor 25b performs Fourier transform (one example of the window function) with respect to the first amplitude data D1 for each group of the first amplitude data D1, as shown in FIG. As the second amplitude data D2 (v (1), v (2),...) Indicating the amplitude of the received signal Srx for each predetermined distance in a predetermined direction (predetermined line-of-sight direction). v (k), where k is an integer of 2 or more determined by the distance resolution, is calculated in units of sweep periods and stored in the memory 25c. In the figure, in order to facilitate understanding of the invention, a first-order Fourier transform process is performed on the first amplitude data D1 in one azimuth, but the first-order Fourier transform process is performed with the first amplitude in all azimuths. It is executed for data D1.

  Next, the signal processor 25b executes rearrangement processing for rearranging the grouped second amplitude data D2 in each direction within each group. In this rearrangement process, as shown in FIG. 5, the signal processor 25 b sets the second amplitude data D <b> 2 of the same distance as a pair in each group as surrounded by a broken line frame, and sets each group as a distance. The second amplitude data D2 is rearranged by arranging in this order. In this case, the second amplitude data D2 (for example, v (1),..., V (1)) included in one distance set are arranged in order of the number of sweeps. Note that, in order to facilitate understanding of the invention, the rearrangement process for the second amplitude data D2 in one azimuth is shown in the figure, but the rearrangement process is executed for the second amplitude data D2 in all azimuths. Is done.

  Subsequently, as shown in FIG. 6, the signal processor 25 b receives zero data v (0) indicating that the amplitude is zero, as shown in FIG. 6, for each group of the second amplitude data D <b> 2 in each direction subjected to the rearrangement processing. A zero data addition process is performed by adding a predetermined number to make new second amplitude data D2. Specifically, in this zero data addition processing, the signal processor 25b sets each pair (v (1),..., V (1)) of the second amplitude data D2 included in each group shown in FIG. 6), zero data v (0) is added by a predetermined number (as an example, the same number as the second amplitude data D2 of each set) as shown in FIG. The number of data D2 is increased to a number that can ensure the accuracy required in the second-order Fourier transform process described later. In the figure, for easy understanding of the invention, the zero data addition process for the second amplitude data D2 in one direction is shown, but the zero data addition process is the second amplitude data D2 in all directions. Executed about. Further, in the figure, zero data v (0) is added to the upper side in the figure for the second amplitude data D2 of each set, but zero data v (0) is given to the lower side in the figure. It is also possible to adopt a configuration in which

  Next, the signal processor 25b executes a second order Fourier transform process. In this second-order Fourier transform process, the signal processor 25b performs a Fourier transform on the second amplitude data D2 (including the added zero data v (0)) included in each set of each group in each direction. Thus, a Doppler spectrum Ddp (see FIG. 7) for each predetermined distance in each direction is calculated. Regarding the calculation of the calculated Doppler spectrum Ddp, as described above, the number of second amplitude data D2 included in each set subjected to the second-order Fourier transform processing is increased by the number of zero data v (0). Therefore, the frequency resolution in calculation is enhanced as compared with the Doppler spectrum obtained by performing the second order Fourier transform process in a state where the zero data v (0) is not given. For this reason, the frequency (± fd) of the primary scattering spectrum peaks P1 and P2 appearing in the Doppler spectrum can be calculated more accurately. Further, the signal processor 25b stores the calculated Doppler spectrum Ddp for each predetermined distance in each direction in the memory 25c in association with the direction (gaze direction) and the predetermined distance.

  The signal processor 25b calculates the Doppler spectrum Ddp and stores it in the memory 25c for all unit sea areas of the observation sea area, that is, unit sea areas located at all distances in all directions defined by the scan angle range. Run about. Further, after completing the calculation of the Doppler spectrum Ddp for all the unit sea areas in the observation sea area and the storage in the memory 25c, the signal processor 25b reads the Doppler spectrum Ddp for all the unit sea areas from the memory 25c, and The spectrum Ddp1 is output to the base station 3. The marine radar station 2B calculates the Doppler spectrum Ddp in the same manner as the marine radar station 2A, and outputs the calculated Doppler spectrum Ddp to the base station 3 as the Doppler spectrum Ddp2.

  Based on the Doppler spectra Ddp1 and Ddp2 received from each ocean radar station 2, the base station 3 calculates the surface current velocity and direction (current vector V) in the desired unit sea area. For example, when the desired unit sea area (sea area A) is located at the intersection of the line-of-sight direction of the scanning angle θ1 in the ocean radar station 2A and the line-of-sight direction of the scan angle θ2 in the ocean radar station 2B, the base station 3 First, the distance L1 from the marine radar station 2A to the sea area A and the scanning angle θ1 are calculated, and the distance L2 from the marine radar station 2B to the sea area A and the scanning angle θ2 are calculated. Next, from the Doppler spectrum Ddp1 received from the marine radar station 2A, the Doppler spectrum Ddp for the unit sea area where the line-of-sight direction coincides with the scanning angle θ1 and located at the distance L1 is specified, and is along the scanning angle θ1. Calculate the velocity Vr and direction of the surface current. Further, from the Doppler spectrum Ddp2 received from the marine radar station 2B, the Doppler spectrum Ddp for the unit sea area whose line-of-sight direction coincides with the scanning angle θ2 and located at the distance L2 is identified, and is along the scanning angle θ2. Calculate the velocity Vr and direction of the surface current. Finally, the two calculated flow velocities Vr are combined in consideration of the flow directions of each other. Thereby, the velocity and direction of the surface current in the sea area A are observed (measured).

  As described above, in the marine radar station 2 and the marine radar observation apparatus 1, the signal processor 25b that executes the above-described Doppler frequency data calculation method uses the first amplitude that is azimuthally resolved for each unit scanning angle (for each line-of-sight direction). Over the data D1, every n cycles of the sweep cycle (n is an arbitrary integer greater than or equal to 2) is exceeded by an arbitrary sweep cycle less than n (more specifically, an arbitrary integer greater than or equal to 1 and less than n). While continuously performing the process of grouping while wrapping, the Doppler spectrum Ddp in the unit sea area is calculated by so-called short-time Fourier transform based on the first amplitude data D1 grouped in this way. Therefore, according to the marine radar station 2, unlike the conventional radar apparatus, since the averaging process for averaging the Doppler spectra calculated from several time series is not performed, the final calculation period of the Doppler spectrum Ddp is set to the conventional one. This can be sufficiently shortened as compared with the radar apparatus. As a result, the detection accuracy of a phenomenon (for example, tsunami) in which the flow velocity of the surface ocean current changes in a short time can be dramatically increased.

  Further, according to the marine radar station 2 and the marine radar observation apparatus 1, the signal processor 25b performs a Fourier transform on the second amplitude data D2 including the added zero data v (0) in the secondary Fourier transform process. Since the conversion is performed to calculate the Doppler spectrum Ddp, the frequency resolution in calculation can be improved, and thereby the frequency (± fd) of the primary scattering spectrum peaks P1 and P2 appearing in the Doppler spectrum Ddp can be accurately calculated. Can do. As a result, the shift amount (fd−fd0) from the frequency (± fd0) at which the primary scattering spectrum peaks P1 and P2 appear in a state where no surface current is generated can be calculated accurately. Based on (fd−fd0), the velocity Vr of the surface current can be accurately calculated.

  A simulation was performed on how the calculation accuracy of the surface current velocity Vr is improved by adding zero data v (0) to the second amplitude data D2. The results are shown in FIGS.

  In the first simulation, in one ocean radar station 2, the flow velocity Vr of the surface sea current in a unit sea area located at a predetermined distance (short distance: 1.5 km) in a predetermined line-of-sight direction is temporal as shown in FIG. Assuming that the flow velocity Vr of the surface sea current in this unit sea area is calculated by adding zero data v (0), and the result calculated without adding zero data v (0) It is calculated by simulation. According to the result of this simulation, as shown in FIG. 9, the temporal change in the flow velocity Vr of the surface sea current in the unit sea area when the zero data v (0) is added is shown in FIG. 8. It becomes very close to the temporal change of the flow velocity Vr of the surface sea current as a reference, and it is confirmed that the peak of the flow velocity Vr can be accurately detected. On the other hand, as shown in FIG. 10, the temporal change in the flow velocity Vr of the surface ocean current in the unit sea area when the calculation is performed without adding the zero data v (0) is a waveform in which the peak of the flow velocity Vr is crushed. It is confirmed that the peak of the flow velocity Vr cannot be accurately detected.

  In the second simulation, in one ocean radar station 2, the flow velocity Vr of the surface sea current in a unit sea area located at a predetermined distance (medium distance: 40.5 km) in a predetermined line-of-sight direction is temporal as shown in FIG. Assuming that the flow velocity Vr of the surface sea current in this unit sea area is calculated by adding zero data v (0), and the result calculated without adding zero data v (0) It is calculated by simulation. According to the result of this simulation, as shown in FIG. 12, the temporal change in the flow velocity Vr of the surface sea current in the unit sea area when the zero data v (0) is added is shown in FIG. It becomes very close to the temporal change of the flow velocity Vr of the surface sea current as a reference, and it is confirmed that the peak of the flow velocity Vr can be accurately detected. On the other hand, the temporal change in the flow velocity Vr of the surface ocean current in the unit sea area when the zero data v (0) is not added is completely reproduced as shown in FIG. Thus, it is confirmed that the peak of the flow velocity Vr cannot be accurately detected.

  In the third simulation, in one marine radar station 2, the flow velocity Vr of the surface sea current in a unit sea area located at a predetermined distance (far distance: 60 km) in a predetermined line-of-sight direction changes with time as shown in FIG. Assuming that the flow velocity Vr of the surface sea current in this unit sea area is calculated by adding zero data v (0), and the result calculated without adding zero data v (0) are simulated. Is to be calculated. According to the result of this simulation, the temporal change in the flow velocity Vr of the surface current in the unit sea area when the zero data v (0) is added is calculated as shown in FIG. However, it is confirmed that the peak of the flow velocity Vr can be detected to some extent accurately because the waveform reproduces the temporal change of the flow velocity Vr of the surface ocean current as a reference shown in FIG. 14 to some extent. On the other hand, as shown in FIG. 16, the temporal change in the velocity Vr of the surface sea current in the unit sea area when the zero data v (0) is added is not reproduced at all. Thus, it is confirmed that the peak of the flow velocity Vr cannot be accurately detected.

  From the above simulation results, by adding zero data v (0) to the second amplitude data D2, the calculation accuracy of the flow velocity Vr of the surface ocean current is improved over a wide distance range from a short distance to a long distance. That is confirmed.

  Further, according to the marine radar station 2 and the marine radar observation apparatus 1, the signal processor 25b executes the beam forming process such as the DBF method and performs the azimuth decomposition process. Therefore, the final calculation period of the Doppler spectrum Ddp can be greatly shortened.

  In addition, this invention is not limited to said structure. For example, by adding zero data v (0) to the second amplitude data D2 to be subjected to the second order Fourier transform process to increase the number of data, the Doppler spectrum Ddp calculated by the Fourier transform is calculated. As described above with respect to the example in which the configuration for improving the frequency resolution is adopted, as shown in FIG. 17, a predetermined number of first amplitude data D1 to be subjected to the first-order Fourier transform processing (for example, the first set of each set). By increasing the number of data by adding zero data u (0) by the same number as the amplitude data D1, the number of second amplitude data D2 calculated by the first order Fourier transform is increased (distance resolution is improved). You can also.

  Moreover, although the example provided with the two marine radar stations 2A and 2B has been described above, a configuration including three or more marine radar stations 2 may be employed. Further, although a configuration in which the transmission antenna 21 is provided independently of the reception antenna 23 is adopted, at least one of the plurality of reception antennas 23 is switched to and connected to the signal generation unit 22 at the time of transmission (reception) A configuration in which at least one of the antennas 23 is alternately connected to the signal generation unit 22 and the signal reception unit 24 to serve as the transmission antenna 21 can also be used. Thus, for example, when a configuration is adopted in which one of the plurality of receiving antennas 23 is switched to and connected to the signal generating unit 22 at the time of transmission, the one receiving antenna 23 is connected to the A / D converter 25a (specifically Specifically, when switched from the signal receiving unit 24) connected to the A / D converter 25a to the signal generating unit 22, it functions as a transmission antenna that transmits the input transmission signal Stx as a radar signal. For this reason, the number of antennas can be reduced by omitting the transmission antenna 21.

  In addition, a plurality of receiving antennas 23 are provided, and the processing unit 25 performs azimuth decomposition processing on the reception data Dr of each reception signal Srx based on the signal from each reception antenna 23 and is included in a predetermined scanning angle range. Although the configuration for calculating the Doppler spectrum Ddp for the sea area (observation sea area) has been described above, when the observation direction is limited to one direction, a single receiving antenna having directivity is used to A configuration for receiving the reflected wave can also be adopted. According to this configuration, the received signal Srx output from one receiving antenna (specifically, the received signal Srx output from one signal receiving unit 24 connected to the receiving antenna) is A / D converted. Since the unit 25a samples and converts the received data Dr into the received data Dr, the Doppler spectrum Ddp for the one direction can be calculated based on the received data Dr without performing the orientation decomposition process.

DESCRIPTION OF SYMBOLS 1 Ocean radar observation apparatus 2 Ocean radar station 25 Processing part D1 1st amplitude data D2 2nd amplitude data Ddp Doppler spectrum Srx reception signal Stx transmission signal

Claims (7)

A reflected signal from a predetermined direction for a transmission signal whose frequency is swept at a predetermined sweep cycle is sampled and converted into first amplitude data indicating the amplitude of the reflected signal, and the predetermined amplitude is determined based on the first amplitude data. A radar device that calculates Doppler frequency data for each predetermined distance in a direction,
With a processing unit,
The processing unit
A grouping process for grouping the first amplitude data by overlapping each n cycles of the sweep cycle (n is an arbitrary integer of 2 or more) with an arbitrary sweep cycle less than n;
For each group, the second amplitude data indicating the amplitude for each predetermined distance in the predetermined direction is calculated for each sweep cycle by performing Fourier transform on the first amplitude data for each sweep cycle. First-order Fourier transform processing;
For each group of the second amplitude data, a rearrangement process for rearranging and grouping the second amplitude data included in each group for each predetermined distance in the sweep cycle order;
A zero data addition process for adding a predetermined number of zero data indicating an amplitude of zero for each group to obtain new second amplitude data for the second amplitude data grouped by the rearrangement process;
A second-order Fourier transform process is performed in which the second amplitude data included in each group subjected to the zero data addition process is subjected to a Fourier transform to calculate the Doppler frequency data for each predetermined distance. Radar device.   In the first-order Fourier transform process, the processing unit fills a predetermined number of zero data indicating that the amplitude is zero at each sweep cycle before the Fourier transform in units of the sweep cycle, thereby generating new first amplitude data. The radar apparatus according to claim 1. A / D that samples reception signals output from a plurality of reception antennas that have received reflected waves of radar signals transmitted from the transmission antenna toward the ocean, and converts them into reception data indicating the amplitude of the reception signals. With a conversion unit,
The radar apparatus according to claim 1, wherein the processing unit executes azimuth decomposition processing for converting the received data into the first amplitude data by applying a predetermined beam forming method. Comprising the plurality of receiving antennas;
When at least one of the plurality of receiving antennas is configured to be connectable by switching alternately between a signal generation unit that outputs a transmission signal and the A / D conversion unit, and when connected to the signal generation unit The radar apparatus according to claim 3, wherein the radar apparatus functions as the transmission antenna that transmits the transmission signal as the radar signal. A receiving antenna having one directivity for receiving a reflected wave of a radar signal transmitted from the transmitting antenna toward the ocean;
A reception signal output from the reception antenna is sampled and converted into reception data indicating the amplitude of the reception signal, and an A / D converter that outputs the reception data as the first amplitude data is provided. Item 3. The radar device according to item 1 or 2. A plurality of radar devices according to any one of claims 1 to 5;
A marine radar observation apparatus comprising: a processing device that calculates a flow velocity and a flow direction of a surface current in a desired sea area in the ocean based on the Doppler frequency data calculated by each radar device. A reflected signal from a predetermined direction for a transmission signal whose frequency is swept at a predetermined sweep cycle is sampled and converted into first amplitude data indicating the amplitude of the reflected signal, and the predetermined amplitude is determined based on the first amplitude data. A Doppler frequency data calculation method for calculating Doppler frequency data for each predetermined distance in a direction,
A grouping process for grouping the first amplitude data by overlapping each n cycles of the sweep cycle (n is an arbitrary integer of 2 or more) with an arbitrary sweep cycle less than n;
For each group, the second amplitude data indicating the amplitude for each predetermined distance in the predetermined direction is calculated for each sweep cycle by performing Fourier transform on the first amplitude data for each sweep cycle. First-order Fourier transform processing;
For each group of the second amplitude data, a rearrangement process for rearranging and grouping the second amplitude data included in each group for each predetermined distance in the sweep cycle order;
A zero data addition process for adding a predetermined number of zero data indicating an amplitude of zero for each group to obtain new second amplitude data for the second amplitude data grouped by the rearrangement process;
A second-order Fourier transform process is performed in which the second amplitude data included in each group subjected to the zero data addition process is subjected to a Fourier transform to calculate the Doppler frequency data for each predetermined distance. Doppler frequency data calculation method.

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