JP4893883B2 - Radio altitude speed measuring apparatus and altitude speed measuring method using radio wave - Google Patents

Description

  The present invention relates to a pulse type radio altitude speed measuring apparatus and an altitude speed measuring method using a pulse type radio wave.

  In general, spacecraft that land on the moon and planets are equipped with radio altitude velocity measuring devices suitable for navigation guidance. This can measure the horizontal speed and altitude of the ground surface (target surface) to which radio waves are transmitted with high accuracy using pulse radio waves.

  A so-called Doppler radar is widely known as an aircraft speed measurement method using pulse-modulated radio waves (microwaves). An aircraft guidance Doppler radar uses a relatively high frequency (Ku band or the like) to narrow the beam width (beam divergence angle) of a radio wave transmitted from an antenna to about several degrees. Moreover, in the aircraft guidance Doppler radar, most of the target surface on which radio waves are reflected is a wide and smooth surface on the ocean.

  On the other hand, in the spacecraft, the weight resource is severe, so it is difficult to mount the altimeter and the speedometer separately in the lunar planetary mission, and for the convenience of testing, the bandwidth is allocated for the altimeter. In many cases, a configuration is employed in which both altitude and speed are measured using radio waves in a band (4 GHz to 8 GHz). When C-band radio waves are used, if the beam divergence angle is reduced to a few degrees, similar to the Doppler radar for aircraft guidance, the weight of the antenna required for this will increase, and the load on the entire spacecraft will increase. growing. As a result, the weight of the antenna must be minimized, and as a result, the beam divergence angle must be expanded to about a dozen degrees. In the case of a spacecraft, the lunar surface and planetary surface, which are the target surfaces from which radio waves are reflected, are complex terrain, and are different from the Doppler radar for aircraft guidance.

  In future lunar and planetary exploration, a pinpoint landing at a target point is planned, and as described above, a radio wave sensor capable of detecting not only the altitude from the ground surface but also the horizontal velocity with respect to the target surface is required. As described above, it is not realistic to install an altimeter and a speedometer as in an aircraft guidance system in lunar / planetary missions where the weight resources are severe. In addition, the characteristics of the reflected signal to be handled are greatly different from the aircraft guidance Doppler radar. Therefore, high-precision measurement of the horizontal velocity is required using an altimeter-integrated radio wave velocity meter suitable for mounting on a spacecraft.

  The present invention has been made in view of the above points, and its object is to be compatible with a spacecraft for lunar planetary missions with severe weight resources and to have a high degree of altitude and velocity measurement. An altitude speed measuring apparatus and an altitude speed measuring method using radio waves are provided.

A radio altitude velocity measuring device for measuring the altitude of a flying object according to the present invention and the horizontal velocity with respect to the target surface,
An altitude measuring unit that measures the altitude of the flying object using radio waves;
A radio wave sending unit for sending a radio wave having a predetermined beam divergence angle from the flying object to the target surface and sending it as a pulse at a predetermined time interval;
A radio wave receiver that receives a reflected wave from the target surface of the radio wave;
An orthogonal demodulation unit that orthogonally demodulates the reflected wave received by the radio wave reception unit and outputs an I signal and a Q signal;
An A / D converter for digitizing the I signal and the Q signal;
A Doppler frequency estimation processing unit for estimating a Doppler frequency for a plurality of points on the range time axis based on the digitized I signal and Q signal;
Fitting a theoretical formula of Doppler frequency obtained by substituting a plurality of sets of range time and Doppler frequency obtained in the Doppler frequency estimation processing unit and an altitude value obtained in the altitude measuring unit into a theoretical formula A fitting processing unit that performs processing to calculate a horizontal speed of the flying object;
It is characterized by comprising.

に基づいて水平方向速度を算出するとともに、このｈに含まれ得る誤差の範囲（±Δｈ）を適当なステップで刻み、ｋ個の高度値について同様の処理を実行してｋ個の水平方向速度ｖを算出し、これに基づいて、フィッティングの回帰残差を評価関数

とすることにより、ｋ個の高度値の中で最適な値を決定する処理も行う。 The fitting processing unit further calculates a gaze direction angle corresponding to each point on the range time axis when a set of a plurality of range times and Doppler frequencies is input,

The horizontal speed is calculated based on the above, and the error range (± Δh) that can be included in h is cut in an appropriate step, and the same processing is executed for the k altitude values to obtain k horizontal speeds. v is calculated, and based on this, the regression residual of the fitting is evaluated

By doing so, the process of determining the optimum value among the k altitude values is also performed.

The radio wave altitude velocity measuring method for measuring the altitude of the flying object according to the present invention and the horizontal velocity with respect to the target surface,
An altitude measuring step of measuring the altitude of the flying object using radio waves;
A radio wave sending step for sending radio waves having a predetermined beam divergence angle from the flying object toward the target surface and sending them as pulses at predetermined time intervals;
A radio wave receiving step of receiving a reflected wave from the target surface of the radio wave;
An orthogonal demodulation step of orthogonally demodulating the reflected wave received by the radio wave reception step and outputting an I signal and a Q signal;
An A / D conversion step for digitizing the I signal and the Q signal;
A Doppler frequency estimation processing step of estimating a Doppler frequency for a plurality of points on the range time axis based on the digitized I signal and Q signal;
Fitting a theoretical formula of Doppler frequency obtained by substituting a plurality of sets of range time and Doppler frequency obtained in the Doppler frequency estimation processing unit and an altitude value obtained in the altitude measuring unit into a theoretical formula A fitting processing step of performing processing to calculate a horizontal speed of the flying object;
It is characterized by comprising.

  According to the present invention, the horizontal velocity of the flying object can be measured with high accuracy by performing the Doppler frequency estimation processing and the fitting processing. Also, the accuracy of the altitude measurement value can be increased by the value that gives the regression residual in the fitting process.

  In addition, altitude measurement and horizontal velocity measurement can be realized as a single integrated device, so navigation navigation sensors for spacecraft that land on the moon and planets, which are particularly limited in weight and space. However, when applied to various fields where downsizing and integration of devices such as unmanned helicopters and unmanned airplanes are required, great effects can be expected.

  In the radio altitude velocity apparatus described above, the pulse used for measuring the horizontal velocity is, as shown in FIG. 1, a constant beam divergence angle and duration in a direction inclined by an appropriate angle from the vertical direction (line-of-sight direction). With time, each pulse is sent out at a constant time interval T. In such a situation, the received reflected pulse spreads in the time direction, and the Doppler frequency is distributed according to the difference in the incident direction on the target surface according to the time position (range bin) in the pulse. Here, if the incident direction of radio waves is simply calculated from the range bin that estimates the Doppler frequency and altitude information that is measured separately, and the horizontal speed is derived using that value, it is limited by the transmission pulse width. Due to the uncertainty of the Doppler frequency associated with the range direction resolution to be performed, an error occurs in the speed measurement. Furthermore, in the above case, since the altitude measurement value is directly used for estimation of the incident direction of the radio wave, the measurement error directly affects the accuracy of the speed measurement.

  In the present invention, as will be described in detail below, in the radio altitude speed measurement device in which an altimeter and a speedometer are integrated, the Doppler frequency uncertainty due to the range direction resolution and the altitude measurement error are respectively the horizontal speed. It is possible to reduce the influence on the measurement accuracy, obtain the horizontal speed with high accuracy, and further reduce the high measurement error.

  By fitting multiple measurement points and theoretical curves on the range-Doppler frequency plane, the influence of Doppler frequency uncertainty due to range direction resolution on the measurement accuracy of horizontal speed is reduced, as will be described later. Is done.

FIG. 1 schematically shows a positional relationship among a flying object (antenna) 10, a radio wave beam transmitted from the flying object, and a target surface. In the case shown in FIG. 1, the theoretical curve of the Doppler frequency f _{d in} the line-of-sight direction is expressed as the following equation (1). In equation (1), v represents the horizontal velocity with respect to the surface, λ represents the wavelength of the carrier radio wave, h represents the altitude to the ground, c represents the speed of light, and t represents the range direction time (pulse reciprocation time).

A method such as Fast Fourier Transform (FFT) or Discrete Fourier Transform (DFT) is used for each of a plurality of sample points having a relatively good signal-to-noise ratio in the pulse (that is, not where the waveform is cut). The Doppler frequency at each point is estimated, and a set of the time t corresponding to the number of samples and the Doppler frequency f _d is obtained. Then, the horizontal speed v is obtained from the shape comparison between these distributions and the theoretical curve. Specifically, in the shape comparison with the theoretical curve, the curvature a = 2v / λ is analytically derived from the regression curve by the least square method, and v is obtained by the following equation (2).

Further, the expression (2) includes an altitude h when the object surface is viewed from the flying object. As this h, an immediate value of h obtained from a simple altitude measurement function based on the pulse propagation time can be used, but here, h is used as a reference value, and h is swept for a possible altitude error range. By using the sequence, it is possible to absorb the influence of the altitude error on the horizontal speed to a certain extent and provide a more accurate altitude estimation value. That is, using the fitting regression residual given by the following equation (3) as an evaluation function, h that minimizes this and the horizontal velocity v at that time are output.

  In the system where the Doppler frequency at each sample point has uncertainty due to the transmission pulse width by performing the fitting process between a plurality of measurement samples and the theoretical curve in the range-Doppler frequency plane, The horizontal speed can be measured with high accuracy. Further, as will be described in detail later, by measuring the altitude value of the flying object used for the theoretical curve for the error range, the measurement of the horizontal velocity with reduced influence due to the altitude error is realized. Furthermore, it is possible to increase the accuracy of the altitude measurement value by the value that gives the minimum regression residual in the fitting process.

  Next, examples of the present invention will be described. As shown in FIG. 1, it is assumed that a radio wave transmission unit (not shown) provided in the lower part of the flying body 10 transmits radio wave transmission pulses having a predetermined pulse width toward the ground surface. This transmission pulse is repeatedly transmitted with a period T. The period T is the reciprocal of the pulse repetition frequency (PRF) and is a time interval such as 100 milliseconds (ms). As shown in FIG. 1, each transmission pulse is transmitted with a spread of a predetermined angle, and when it reaches the ground surface, a part of it is reflected (backscattered) and returned to the flying object 10, and a radio wave receiving unit (not shown) ).

FIG. 2 is a graph schematically showing how the reflection intensity of one pulse changes with time. Since the transmission pulse has a divergence angle as shown in FIG. 1, the time required for the radio wave (radio wave with a small line-of-sight direction angle θ) to reach a close point when viewed from the flying object 10 is short, It takes a long time for a radio wave that has reached a far point (a radio wave with a large viewing direction angle θ) to return. Let θ _j be the line-of-sight direction angle of the radio wave reflected back at the point j. In FIG. 2, there is a reflected wave having the intensity of the vertical axis in FIG. 2 at time t _j in the range direction time, and the Doppler frequency of this reflected wave is f _j .

  FIG. 3 is a block diagram of a part for calculating the horizontal velocity of the flying object 10 by processing the received pulse received by the radio wave receiving unit. FIG. 3 shows processing after the received signal is down-converted to the intermediate frequency (I / F).

  In FIG. 3, the quadrature demodulator 20 extracts an I (Inphase) signal and a Q (Quadrature) signal from the I / F signal. The I signal and Q signal are digitized by the A / D converter 22. These processes are performed for each pulse received at period T. Then, data of n-point range bins (time positions within one pulse) are stored in the memory unit 24 for each pulse.

  When the required number of pulses is received (for example, 512 pulses), the Doppler frequency estimation processing unit 26 estimates the Doppler frequency for each of the n-point range bins of each pulse. For the Doppler frequency estimation process, a method such as FFT or DFT is used. FIG. 4 shows the graph shown in FIG. 2 for four consecutive pulses, and the values indicated by white circles of the pulses indicate the values of the received signal amplitudes in the n-point range bins.

The n-point Doppler frequency takes different values depending on the range bin (range direction time) depending on the difference in the viewing direction angle. N sets of the range time t and the Doppler frequency f _d for each point are input to the fitting processing unit 28. On the other hand, the theoretical Doppler frequency can be calculated by substituting altitude measurement value h, carrier frequency λ, and speed of light c into equation (1). The solid line in FIG. 5 shows the theoretical curve calculated based on this theoretical formula (1). The fitting processing unit 28 performs a fitting process between the theoretical curve and the Doppler frequencies of n range bins estimated by the Doppler frequency estimation processing unit 26. FIG. 5 shows a conceptual state of this fitting process.

FIG. 6 is a flowchart showing a processing procedure in the fitting processing unit 28. As described above, when n sets of the range time t and the Doppler frequency fd are input from the Doppler frequency estimation processing unit 26 to the fitting processing unit 28, first, the radio wave to the target surface at each of n points. The incident angle is calculated. This is nothing but computing the argument of the sin function in equation (1), that is, cos ⁻¹ part. Thus, the horizontal speed v is obtained by the calculation of the least square method of the equation (2).

  The altitude h used for this initial processing is given as a reference value from a simple altitude measuring function based on the pulse propagation time. Then, an error range (± Δh) that can be included in h is engraved in an appropriate step, and the above processing is looped for k altitude values. As a result, k horizontal velocities v are obtained, and an optimal value is determined among the k altitude values by using the regression regression of fitting as an evaluation function. The evaluation function is shown in equation (3). The altitude at which the optimal horizontal velocity v that minimizes the evaluation function is output is output as a refined value of a simple altitude reference value based on the pulse propagation time.

  As described above, both the horizontal speed v and the altitude value h are obtained, and each is obtained through the above-described processing, so that it can be obtained as a more accurate value.

It is the figure which showed roughly the positional relationship of a flying body, the beam sent from a flying body, and a target surface. It is the graph which showed roughly how the reflection intensity of one pulse changes with time. It is a block diagram of the part which processes the received pulse received by the radio wave receiver and calculates the horizontal velocity of the flying object. It is the graph which showed the graph corresponding to FIG. 2 about four continuous pulses. It is the figure which showed the conceptual mode of the fitting process. It is the flowchart which showed the process sequence in a fitting process part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Flying object 20 Orthogonal demodulation part 22 A / D conversion part 24 Memory part 26 Doppler frequency estimation process part 28 Fitting process part

Claims (2)

In the radio altitude velocity measuring device that measures the altitude of the flying object and the horizontal velocity relative to the target surface,
An altitude measuring unit that measures the altitude reference value h of the flying object using a round-trip time of radio waves;
A radio wave sending unit for sending a radio wave having a predetermined beam divergence angle from the flying object to the target surface and sending it as a pulse at a predetermined time interval;
A radio wave receiver that receives a reflected wave from the target surface of the radio wave;
An orthogonal demodulation unit that orthogonally demodulates the reflected wave received by the radio wave reception unit and outputs an I signal and a Q signal;
An A / D converter for digitizing the I signal and the Q signal;
A Doppler frequency estimation processing unit for estimating a Doppler frequency for a plurality of points on the range time axis based on the digitized I signal and Q signal;
The altitude reference value h obtained by the altitude measuring unit is expressed by a theoretical formula.

(T: range time, f _d : Doppler frequency, λ: wavelength, v: horizontal speed, c: speed of light)
The horizontal time velocity of the flying object is calculated by fitting a plurality of sets of the range time and the Doppler frequency obtained in the Doppler frequency estimation processing unit to the range time-Doppler frequency curve obtained by substituting A fitting processing unit;
Comprising
The fitting processing unit further calculates a gaze direction angle (h / (ct / 2)) corresponding to each point on the range time axis when a set of a plurality of range times and Doppler frequencies is input.

The horizontal speed is calculated based on the above, and a similar process is performed on k altitude value candidates obtained by engraving an error range (± Δh) that can be included in the altitude reference value h in a predetermined step. k horizontal velocity candidates are calculated, and based on this, the regression residual of the fitting is evaluated

Thus , the radio altitude speed measuring apparatus is characterized in that an optimum value is determined from among the k altitude value candidates and the altitude value and the horizontal speed are estimated with higher accuracy . A radio altitude speed measurement method for measuring the altitude of a flying object and the horizontal direction relative to the target surface,
An altitude measuring step of measuring the altitude reference value h of the flying object using a round-trip time of radio waves;
A radio wave sending step for sending radio waves having a predetermined beam divergence angle from the flying object toward the target surface and sending them as pulses at predetermined time intervals;
A radio wave receiving step of receiving a reflected wave from the target surface of the radio wave;
An orthogonal demodulation step of orthogonally demodulating the reflected wave received by the radio wave reception step and outputting an I signal and a Q signal;
An A / D conversion step for digitizing the I signal and the Q signal;
A Doppler frequency estimation processing step of estimating a Doppler frequency for a plurality of points on the range time axis based on the digitized I signal and Q signal;
The altitude reference value h obtained by the altitude measuring unit is expressed by a theoretical formula.

(T: range time, f _d : Doppler frequency, λ: wavelength, v: horizontal speed, c: speed of light)
The horizontal velocity of the flying object is calculated by fitting a plurality of sets of the range time and the Doppler frequency obtained in the Doppler frequency estimation processing step to the range time-Doppler frequency curve obtained by substituting Fitting process,
Comprising
In the fitting processing step, when a set of a plurality of range times and Doppler frequencies is input, a corresponding gaze direction angle (h / (ct / 2)) is calculated for each point on the range time axis,

To calculates the horizontal rate based executes the same processing for the candidate altitude reference value range of errors that may be included in h (± Δh) k number of altitude values obtained Nde time a predetermined step k horizontal velocity candidates are calculated, and based on this, the regression residual of the fitting is evaluated

The radio altitude speed measuring method is characterized in that an optimal value is determined from among the k altitude value candidates, and the altitude value and the horizontal speed are estimated with higher accuracy .

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