JP2013205046A - Radio altimeter and method of measuring altitude - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio altimeter reduced in measurement error due to the dullness of a reception pulse.SOLUTION: A radio altimeter transmitting a pulse and receiving a reflection pulse by a ground surface to calculate altitude from a time difference between the pulse and the reflection pulse, includes: a change point detector for detecting a change point with a first threshold adjacent to the ground level of a reception signal; a monitoring device for determining whether the change point detector detects the reflection pulse a plurality of times during a predetermined monitoring time when it detects a change in the reception signal, and outputting a reception pulse when it continuously detects the reflection pulse during the monitoring time; and an altitude calculator for subtracting the transmission time of the pulse from the output time of the reception pulse and further subtracting the monitoring time to output altitude information on the basis of the result.

Description

  The present invention relates to a radio altimeter and an altitude measuring method, and more particularly to a radio altimeter and an altitude measuring method excellent in measurement accuracy at a low altitude.

  The radio altimeter measures the time difference from the transmission of a pulse to the reception of a reflected pulse from the ground surface, and indicates the altitude. In the radio altimeter, the dullness of the received pulse waveform is an error during altitude measurement. At high altitudes, this error accounts for a small percentage of the measured altitude and has a low impact on the measured altitude. However, at a low altitude, the ratio of this error to the measured altitude is high, which adversely affects altitude measurement.

  With reference to FIG. 1, the occurrence of a high degree of error due to the dullness of the waveform of the received pulse will be described. Here, FIG. 1A is a diagram illustrating time measurement using an ideal waveform. FIG. 1B is a diagram for explaining time measurement using an actual waveform. In FIG. 1, the horizontal axis represents time, and the vertical axis represents radio wave intensity (arbitrary unit).

  In FIG. 1A, the radio altimeter transmits a rectangular wave toward the ground surface. The reflected wave from the ground surface is ideally a rectangular wave. The radio altimeter calculates the altitude of the aircraft using the time difference between the rise of the transmission wave and the rise of the reception wave.

  However, the reflected wave from the ground surface is actually dull from the rectangular wave shown in FIG. In addition, the threshold for determining reception pulse detection needs to be set higher than the noise level. Therefore, the detection of the rising edge of the received wave used by the radio altimeter includes an error.

  Patent Document 1 discloses a radio altimeter that accurately measures altitude when the altitude distance to be measured is short. This radio altimeter delays the reception pulse for a predetermined time by a delay line provided between the reception circuit and the intermediate frequency amplifier, and eliminates the overlap with noise generated in the transmission circuit. This radio altimeter can be separated from noise when the altitude distance is short. However, this radio altimeter cannot solve the measurement error due to the dullness of the received pulse.

JP 2006-266788 A

  An object of the present invention is to reduce a measurement error due to blunting of a received pulse in a radio altimeter.

  The above-described problem is that in a radio altimeter that transmits a pulse, receives a reflected pulse from the ground surface, and calculates an altitude from the time difference between the pulse and the reflected pulse, the first threshold value close to the ground level of the received signal is used. When the change point detector that detects the change point and the change point detector detects a change in the received signal, it is determined whether to detect the reflected pulse a plurality of times during the predetermined monitoring time. Altitude calculation that outputs the altitude information based on the result of subtracting the transmission time of the pulse from the output time of the received pulse and the monitoring time that subtracts the monitoring time from the output time of the received pulse when the detection continues Can be achieved by a radio altimeter including

  In the altitude measurement method for transmitting a pulse, receiving a reflected pulse from the ground surface, and calculating an altitude from a time difference between the pulse and the reflected pulse, the received signal is received at a first threshold value close to the ground level of the received signal. A step of detecting a change point, a step of determining whether to detect a reflected pulse a plurality of times during a predetermined monitoring time, a step of determining, and a step of outputting a received pulse when a reflected pulse is detected. This can be achieved by an altitude measuring method including the steps of subtracting the pulse transmission time from the output time of the received pulse and further subtracting the monitoring time and outputting the altitude information based on the calculation result.

  According to the present invention, it is possible to reduce the measurement error due to the dullness of the received pulse.

It is a time chart explaining the altitude measurement error by blunting of a received waveform. It is a hardware block diagram of a radio altimeter. It is a time chart explaining altitude measurement error reduction by change point detection. It is a time chart explaining malfunction prevention by noise. It is a flowchart of the altitude measurement of the radio altimeter.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings using examples. The same reference numerals are assigned to substantially the same parts, and the description will not be repeated.

  The hardware block of the radio altimeter will be described with reference to FIG. In FIG. 2, a radio altimeter 100 includes a transmitter 101, a transmission antenna 102, a reception antenna 103, a receiver 104, an IF amplifier 105, a detector 106, a change point detector 107, and a change time monitor. 108, an altitude calculator 109, an altitude indicator 110, a pulse oscillator 111, a CW oscillator 112, a local oscillator 113, and a sampling signal oscillator 114.

  The transmitter 101 performs pulse modulation on the rectangular wave output from the pulse oscillator 111 with a signal from a CW (Continuous Wave) oscillator 112 and outputs a transmission pulse. The transmission antenna 102 converts the transmission pulse into a radio wave and transmits it to the ground surface. The receiving antenna 103 receives radio waves reflected from the ground surface.

  The receiver 104 mixes the received pulse from the receiving antenna 103 and the signal from the local oscillator 113 provided to extract the intermediate frequency from the received pulse, and converts the mixed signal into an intermediate frequency signal. The IF amplifier 105 amplifies the intermediate frequency signal. The detector 106 detects the intermediate frequency signal amplified by the IF amplifier 105.

  The change point detector 107 is composed of a comparator or the like, detects a change in signal at a point closest to the GND level of the intermediate frequency signal, and shapes the signal into a rectangular wave. The change time monitor 108 uses the signal from the change point detector 107 and the sampling signal, and recognizes the received pulse as a received pulse when the pulse continues for a predetermined monitoring time. Output as a received pulse. The change time monitor 108 does not output the received pulse when the duration of the pulse is finished in less than the monitoring time.

  The altitude calculator 109 subtracts the monitoring time of the change time monitor 108 from the time difference between the received pulse from the change time monitor 108 and the reference pulse from the pulse oscillator 111 to calculate the time difference from transmission to reception. , Convert to advanced information. The altitude indicator 110 indicates the altitude based on the altitude information from the altitude calculator 109.

  The pulse oscillator 111 outputs a 4.9 kHz rectangular wave. The CW oscillator 112 outputs a rectangular wave of 4.3 GHz. The local oscillator 113 outputs a rectangular wave of 4.36 GHz. The sampling oscillator outputs a sampling signal. The intermediate frequency is 60 MHz which is the difference between the frequency of the CW oscillator 112 and the frequency of the local oscillator 113.

  With reference to FIG. 3, altitude measurement error reduction due to change point detection will be described. FIG. 3A is a diagram for comparison, and is the same diagram as FIG. In FIG. 3B, the horizontal axis represents time, and the vertical axis represents signal intensity. In FIG. 3B, the received signal from the receiver 104, the output signal from the change point detector 107, the sampling signal, and the output signal from the change time monitor 108 are shown in order from the top. Note that the output signal of the change point detector 107, the sampling signal, and the output signal of the change time monitor 108 are binary signals.

  In FIG. 3B, when the reception unit 104 receives a reception signal, the change point detector 107 detects an increase in the reception signal with a very low threshold and sets the output to High. The change time monitor 108 repeatedly monitors whether the signal is continuously received at the rising edge of the sampling signal during the monitoring time after the output of the change point detector 107 becomes High. When the reception signal continues during the monitoring time, the change time monitor 108 recognizes it as a reception pulse and sets its output to High. Note that the threshold for determining the continuation of the received signal is low at the first sampling, and is set to the threshold (threshold above the noise level) in FIG.

  An altitude calculator 109 (not shown) subtracts the monitoring time of the change time monitor 108 from the time difference between the received pulse from the change time monitor 108 and the reference pulse from the pulse oscillator 111 to obtain the time difference from transmission to reception. calculate. As a result, the error is improved as compared with FIG.

  With reference to FIG. 4, prevention of malfunction due to noise will be described. In FIG. 4, the horizontal axis represents time, and the vertical axis represents signal intensity. In FIG. 4, the reception signal from the receiver 104, the output signal from the change point detector 107, the sampling signal, and the output signal from the change time monitor 108 are shown in order from the top.

  In FIG. 4, when the reception unit 104 receives a reception signal, the change point detector 107 detects an increase in the reception signal with a very low threshold, and sets the output to High. The change time monitor 108 repeatedly monitors whether the signal is continuously received at the rising edge of the sampling signal during the monitoring time after the output of the change point detector 107 becomes High. However, since the received signal is not detected at the second rising edge of the sampling signal, the change time monitor 108 ends the monitoring. That is, for the noise, the change point detector 107 sets the output to High. However, the change time monitor 108 ends without setting the output to High.

  The altitude measurement process of the radio altimeter will be described with reference to FIG. In FIG. 5, the radio altimeter 100 transmits a pulse to the ground surface (S11). The radio altimeter 100 starts signal reception (S12). The radio altimeter 100 determines whether a change point has been detected (S13). When the determination is NO, the radio altimeter 100 returns to step 13. When YES in step 13, the radio altimeter 100 starts monitoring (S14). The radio altimeter 100 determines whether there is a received pulse by sampling (S16). When the determination is NO, the radio altimeter 100 transitions to step 13. When YES in step 16, the radio altimeter 100 determines the end of monitoring (S17). When the determination is NO, the radio altimeter 100 transitions to step 16. When YES in step 17, the radio altimeter 100 recognizes the received pulse (S18). The radio altimeter 100 measures the time difference between the reference pulse and the recognized received pulse (S19). The radio altimeter 100 subtracts the monitoring time from the measured time difference (S21). The radio altimeter 100 calculates the altitude based on the subtraction result (S22). The radio altimeter 100 displays the altitude (S23), and proceeds to step 11 again.

  According to the embodiment described above, it is possible to reduce the measurement error due to the dullness of the received pulse.

  DESCRIPTION OF SYMBOLS 100 ... Radio altimeter 101 ... Transmitter 102 ... Transmit antenna 103 ... Receive antenna 104 ... Receiver 105 ... IF amplifier 106 ... Detector 107 ... Change point detector 108 ... Change time monitor 109 ... altitude calculator, 110 ... altitude indicator, 111 ... pulse oscillator, 112 ... CW oscillator, 113 ... local oscillator, 114 ... sampling signal oscillator.

Claims (4)

In a radio altimeter that sends a pulse, receives a reflected pulse from the ground surface, and calculates the altitude from the time difference between the pulse and the reflected pulse,
A change point detector for detecting a change point of the received signal with a first threshold value close to a ground level of the received signal;
When the change point detector detects a change in the received signal, it is determined whether to detect the reflected pulse a plurality of times during a predetermined monitoring time, and received when the detection of the reflected pulse is continued during the monitoring time. A monitoring device that outputs a pulse;
An altitude calculator that subtracts the transmission time of the pulse from the output time of the received pulse, further subtracts the monitoring time, and outputs altitude information based on the result. . The radio altimeter according to claim 1,
The radio wave altimeter, wherein the monitoring device aborts the detection of the reflected pulse when the reflected pulse is not detected during the monitoring time. The radio altimeter according to claim 1 or 2,
The monitoring device uses the first threshold value for a first detection threshold value in the monitoring time, and uses a second threshold value larger than the first threshold value for a second detection threshold value. Radio altimeter. In an altitude measurement method for transmitting a pulse, receiving a reflected pulse from the ground surface, and calculating an altitude from a time difference between the pulse and the reflected pulse,
Detecting a change point of the received signal with a first threshold value close to a ground level of the received signal;
Determining whether to detect the reflected pulse a plurality of times during a predetermined monitoring time;
A step of outputting a received pulse when the reflected pulse is detected in the determining step;
Subtracting the transmission time of the pulse from the output time of the reception pulse, and further subtracting the monitoring time;
Outputting altitude information based on the calculation result.

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