JPH0228115B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a measuring device for determining the propagation velocity and wavelength of waves by Fourier transform of signals reflected from waves in radar image processing.

Conventional devices of this kind perform A-D conversion and recording of video signals over a wide range where reflected waves from waves can be seen on the radar screen, and convert the radar image from polar coordinates to rectangular coordinates. , two-dimensional Fourier transform, two-dimensional signal correlation coefficient calculation, etc.
In addition to the long time required for measurement, it is difficult to determine the propagation speed and wavelength of waves by signal analysis for each image of each rotation of the antenna, despite using a high-speed computer equipped with a large number of memory elements. It was hot.

In view of the above-mentioned circumstances, the present invention has been developed to detect signals reflected from the regular wave crests of waves under rough weather, by limiting the orientation to the propagation direction of the waves on the screen of a general radar. Focusing on the fact that Fourier transform is possible, the purpose is to instantaneously measure the propagation speed and wavelength of waves relative to the radar by signal analysis at each rotation of the antenna. A means for processing the received signal for each antenna rotation extracted from the range of and the distance where sea surface reflection exists into a spatial spectrum signal through fast Fourier transform, and extracting the spatial spectrum with the largest amplitude from this signal to determine the wavelength of the waves. This is a wave speed and wavelength measuring device using radar, comprising means for calculating the wave speed and wavelength, and means for calculating the wave propagation speed by detecting the phase difference of the spatial spectrum for each rotation of the antenna.

An embodiment of the device of the present invention will be described below with reference to the drawings. In the figure, 1 is a radar antenna, 2 is a log-linear characteristic receiving circuit, 3 is a radar indicator, and 4 is a radar antenna that can be used automatically or manually. This gate setting device 4 takes out signals from the wave propagation direction and the distance (hereinafter simply referred to as distance) range where sea surface reflection exists, and this gate setting device 4 sets the gate circuit for the wave propagation direction and distance range. The received signal that has passed through the gate circuit set by the gate setter 4 is passed through the gain characteristic correction circuit 5 in the next stage so that the amplitude is approximately constant with respect to the distance, and
(Analog-digital) converter 6 converts it into a digital signal. Next, when this signal is Fourier transformed by the fast Fourier transformer 7, a spectral component which is a component of a repetitive signal with respect to time is outputted, as in the case of Fourier transforming a signal whose amplitude changes over time.

In radar, a signal whose amplitude changes over time is a reflected signal that represents the magnitude of reflection at a point in space corresponding to each instant of time.
Therefore, the output spectral component becomes a repetitive signal with respect to distance, that is, a spatial spectrum signal.

The spatial spectrum calculated by fast Fourier transform performed in the system of the present invention is also calculated by calculations similar to general Fourier transform.

For example, when a musical tone is Fourier transformed for one second, it is separated into various frequency components, but a frequency is a signal that represents the number of repetitions in one second, and a spatial spectrum is a signal that is Instead of seconds, it refers to the wave number, which is the number of wave crests that repeat over a certain distance.

In an actual circuit example, if the sample interval is 100 nanoseconds, this corresponds to a radar distance interval of 15 meters, but the time interval when the number of sample points is 128 is 100 nanoseconds x (128-1) = 12.7 millisecond, and the distance interval is 15 meters x (128-1) = 1905 meters, so if you Fourier transform the signal in this time and distance interval, you will get the frequency and wave number, which are the numbers that repeat in this time and space interval. A spectrum covering the following is calculated.

As a result of Fourier calculation analysis of the signal when the antenna is oriented in the direction of wave arrival, several frequencies and wave numbers N are calculated that are less than half of the number of samples of 128. The two function components of the trigonometric function, the amplitude A _SN sine wave AS _N and the amplitude A _CN cosine wave AC _N, of the trigonometric function that expresses the angle in radians for one of the N frequencies and wave numbers are: AS _N = A _SN sin2πN AC _N = A _CN cos2πN If the amplitudes of A _SN and A _CN are calculated vectorially, the composite amplitude A N of the spectrum of wave number N is A _{N =} (A _SN ² + A _CN ² ) from the amplitudes of the sine wave and cosine wave above. The ^1/2 phase is calculated as θ=tan ^-1 (A _SN /A _CN ), and the functional formula when expressed only with a sine wave is _SN = A _N sin (2πN + θ).

In this way, each component spectrum is calculated. 8 is a dominant wavelength spectrum extracting circuit for extracting a spatial spectrum having the largest amplitude component from this spatial spectrum signal. The output spectrum signal from this circuit 8 is guided to a wave wavelength calculation circuit 10, where the time length of the signal when input to the fast Fourier transformer 7, that is, the corresponding distance section, is divided by the frequency of the output spectrum, that is, the wave number. The wavelength corresponding to each wave number of waves that existed within this observation distance can be found.

These calculations are performed by storing, reading, calculating, etc. in a dedicated calculation circuit assembled on the board in exactly the same way as each digitized signal is processed in a normal small computer, but functionally circuit 8
The output spectrum signal is also guided to the dominant wavelength spectrum storage circuit 9, where it is digitally stored.

Surrounding waves observed by radar The waves propagate on the sea surface at a speed that depends on the wavelength of their components, so the moment when the radar antenna points toward the arrival direction of the waves and the moment when it rotates and then faces in that direction. The waves are out of place.

Among the spectra of two sets of signals when the antenna rotates and faces the same angle for the signal expressed only by the sine wave shown in the above equation, the signal with the same wave number N is extracted from each spectrum and the mutual phase value is calculated. Calculating the difference is phase comparison, and this operation is performed by the dominant wavelength spectrum phase detection circuit 11. The wave propagation velocity per one rotation of the antenna is determined in the wave velocity calculation circuit 12 from the value of the phase difference comparatively detected by this circuit 11, and from that value, the velocity per second and the velocity per hour are calculated. . That is,
Since the total phase value of one wavelength is 2π radians, the phase value corresponds to the fraction of the wavelength, so it corresponds to the actual distance, and the wave velocity can be determined from the phase change within a predetermined time. In the case of a ship radar, since it is a vector sum with the ship's speed, the wave speed can be obtained by subtracting the ship's speed from the moving speed. These speed values and the wavelength value from the wave wavelength calculation circuit 10 are displayed on the wavelength/wave speed display 13.

As described in detail above, the present invention processes the received signal for each rotation of the antenna using one-dimensional fast Fourier transform in the wave propagation direction by the radar and the distance range where sea surface reflection exists, and based on this processed signal, Since it is designed to instantaneously measure the propagation speed and wavelength of waves relative to the radar,
This device has a simpler structure than the conventional device, and has the outstanding effect of being able to easily and quickly capture highly reliable wave information based on signal analysis of images for each rotation of the antenna.

[Brief explanation of drawings]

The figure is a block diagram showing one embodiment of the device of the present invention. DESCRIPTION OF SYMBOLS 1... Radar antenna, 2... Log-linear characteristic receiving circuit, 3... Radar indicator, 4... Gate setting device, 5... Gain characteristic correction circuit, 6... A-D converter, 7... Fast Fourier transformer, 8... Dominant wavelength spectrum extraction circuit, 9... Dominant wavelength spectrum storage circuit, 10... Wave wavelength calculation circuit, 11...
Main wavelength spectrum phase difference detection circuit, 12...Wave speed calculation circuit, 13...Wavelength/wave speed indicator.

Claims (1)

[Claims] 1 Set the wave propagation direction by radar and the distance range where sea surface reflection exists, and calculate the spatial spectrum of the received signal for each antenna rotation extracted from the set range through fast Fourier transform, and calculate the amplitude and phase values. means for processing the wave number signal into a sinusoidal wave number signal, means for extracting the wave number signal with the largest amplitude from this signal and calculating the wave wavelength from the wave number within the set range, and processing the wave number signal for each rotation of the antenna. A wave speed and wavelength measuring device using radar, comprising means for extracting a phase difference between signals having the same wave number and calculating wave propagation speed from the phase difference and antenna rotation time.