Patent Publication Number: US-2021181230-A1

Title: Wind speed measuring device, wind speed measuring method, and program

Description:
TECHNICAL FIELD 
     The present disclosure relates to a wind speed measuring device, a wind speed measuring method, and a program. More specifically, the present disclosure relates to a wind speed measuring device, a wind speed measuring method, and a program for detecting a wind speed and a wind direction by using acoustic waves. 
     BACKGROUND ART 
     For example, windmill-type devices are often used as devices for detecting wind speeds and wind directions. However, there have been a problem that a windmill-type device is difficult to be downsized because of having a movable part, and a problem that a windmill-type device has difficulty to carry out precise measurement in a case where a wind speed is high or low. 
     In order to solve such problems, there has been a wind speed-and-wind direction measuring device that uses acoustic waves and ultrasonic waves. 
     For example, PTL 1 (JP Sho 57-077965A) discloses a configuration in which ultrasonic wave transmitters and ultrasonic wave receivers are arranged at fixed intervals Lx and Ly respectively in an X axis and a Y axis which are orthogonal to each other on the upper part of a vehicle body so that respective propagation times Tx and Ty are measured to measure the wind speeds in the respective axis directions, and the measured wind speeds are combined to measure a wind speed. 
     However, such a wind speed-and-wind direction measuring device that uses acoustic waves or ultrasonic waves has a problem that the measurement accuracy is deteriorated due to the effect of noise sounds based on ambient noise, vibration noise, or the like. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     JP Sho 57-077965A 
     SUMMARY 
     Technical Problem 
     The present disclosure has been made in view of the above problems, for example, and an object thereof is to provide a wind speed measuring device, a wind speed measuring method, and a program by which a wind speed and a wind direction can be precisely detected even under an environment including a noise sound based on ambient noise, vibration noise, or the like. 
     Solution to Problem 
     A first aspect of the present disclosure is a wind speed measuring device including 
     an acoustic wave transmitting section that transmits a measurement acoustic wave, 
     an acoustic wave receiving section that receives the measurement acoustic wave transmitted from the acoustic wave transmitting section, 
     a signal selecting section that determines a characteristic of the measurement acoustic wave outputted from the acoustic wave transmitting section, and 
     a wind speed calculating section that calculates a wind speed by analyzing a signal received by the acoustic wave receiving section, in which 
     the signal selecting section selects, as the measurement acoustic wave outputted from the acoustic wave transmitting section, an acoustic wave that mainly includes a low-intensity frequency bandwidth selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. 
     Furthermore, a second aspect, of the present disclosure is a wind speed measuring method which is executed by a wind speed measuring device. The method includes 
     a signal selecting step in which a signal selecting section determines a characteristic of a measurement acoustic wave outputted from an acoustic wave transmitting section, 
     a step in which the acoustic wave transmitting section transmits the measurement acoustic wave, 
     a step in which an acoustic wave receiving section receives the measurement acoustic wave transmitted from the acoustic wave transmitting section, and 
     a step in which a wind speed calculating section calculates a wind speed by analyzing a signal received by the acoustic wave receiving section, in which 
     in the signal selecting step, 
     an acoustic wave is selected as the measurement, acoustic wave outputted from the acoustic wave transmitting section, the acoustic wave mainly including a low-intensity frequency bandwidth selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. 
     Furthermore, a third aspect of the present disclosure is a program for causing a wind speed measuring device to execute a wind speed measuring process. The program causes the wind speed measuring device to execute 
     a signal selecting step of causing a signal selecting section to determine a characteristic of a measurement acoustic wave outputted from an acoustic wave transmitting section, 
     a step of causing the acoustic wave transmitting section to transmit the measurement acoustic wave; 
     a step of causing an acoustic wave receiving section to receive the measurement acoustic wave transmitted from the acoustic wave transmitting section, and 
     a step of causing a wind speed calculating section to calculate a wind speed by analyzing a signal received by the acoustic wave receiving section, in which 
     in the signal selecting step, 
     an acoustic wave is selected as the measurement acoustic wave outputted from the acoustic wave transmitting section, the acoustic wave mainly including a low-intensity frequency bandwidth selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. 
     It is to be noted that the program according to the present disclosure can be provided by a storage medium or communication medium for providing the program in a computer readable format to an information processing device or computer system that is capable of executing various program codes, for example. By providing such a program in a computer readable format, processes according to the program are executed in the information processing device or the computer system. 
     Other objects, features, and advantages of the present disclosure will become apparent from more detailed description based on embodiments and attached drawings which are described later. It is to be noted that, in the present description, a system refers to a logical set configuration including a plurality of devices, and the devices of the configuration are not necessarily included in the same casing. 
     Advantageous Effects of Invention 
     According to a configuration of one embodiment of the present disclosure, a device capable of measuring a wind speed and a wind direction with high precision while reducing the effect of ambient noise is realized. 
     Specifically, for example, the device includes an acoustic wave transmitting section that transmits a measurement acoustic wave, an acoustic wave receiving section that receives the measurement acoustic wave transmitted from the acoustic wave transmitting section, a signal selecting section that determines a characteristic of the measurement acoustic wave, and a wind speed calculating section that calculates a wind speed by analyzing a signal received by the acoustic wave receiving section. The signal selecting section selects, as the measurement acoustic wave, an acoustic wave that mainly includes a low-intensity frequency bandwidth selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. Further, the plural acoustic wave receiving sections are disposed at different relative positions with respect to the acoustic wave transmitting section, and the wind speed calculating section functions as a wind direction-and-wind speed calculating section to calculate a wind direction as well as a wind speed by analyzing signals received by the respective plural acoustic wave receiving sections. 
     With this configuration, a device capable of measuring a wind speed and a wind direction with high precision while reducing the effect of ambient noise is realized. 
     It is to be noted that the effects disclosed in the present description are merely examples and are not necessarily limitative. Any other additional effects may be further provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram of a configuration example of a wind speed measuring device according to the present disclosure. 
         FIG. 2  is an explanatory diagram of one example of a measurement acoustic wave that is outputted by the wind speed measuring device according to the present disclosure. 
         FIG. 3  is a diagram depicting a flowchart for explaining a process sequence of processes which are executed by the wind speed measuring device according to the present disclosure. 
         FIG. 4  is an explanatory diagram of an arrangement example of acoustic wave receiving sections in a wind direction-and-wind speed measuring device according to the present disclosure. 
         FIG. 5  is an explanatory diagram of a configuration example of the wind direction-and-wind speed measuring device according to the present disclosure. 
         FIG. 6  is a diagram for explaining arrangement examples of the acoustic wave receiving sections in the wind direction-and-wind speed measuring device according to the present disclosure. 
         FIG. 7  is a diagram for explaining other arrangement examples of the acoustic wave receiving sections in the wind direction-and-wind speed measuring device according to the present disclosure. 
         FIG. 8  is a diagram depicting a flowchart for explaining a process sequence of processes which are executed by the wind direction-and-wind speed measuring device according to the present disclosure. 
         FIG. 9  is an explanatory diagram of an example of a process of selecting a measurement acoustic wave outputted by a wind speed measuring device according to the present disclosure. 
         FIG. 10  is an explanatory diagram of a process in a case where a wind direction-and-wind speed measuring device is mounted on a mobile apparatus. 
         FIG. 11  is an explanatory diagram of a configuration example of the wind direction-and-wind speed measuring device according to the present disclosure. 
         FIG. 12  is an explanatory diagram of an example of a process of measuring a wind direction and a wind speed to the ground. 
         FIG. 13  is an explanatory diagram of a configuration example in which a wind direction and a wind speed can be measured in a three-dimensional (3D) space. 
         FIG. 14  is an explanatory diagram of a process of measuring a wind direction and a wind speed in a 3D space. 
         FIG. 15  is a diagram depicting a hardware configuration example of a device that can be adopted as the wind speed measuring device according to the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a wind speed measuring device, a wind speed measuring method, and a program according to the present disclosure will be explained in detail with reference to the drawings. It is to be noted that the explanation will be given according to the following items. 
     1. Configuration and Processes in First Embodiment of Wind Speed Measuring Device According to Present Disclosure 
     2. Configuration and Processes in Second Embodiment of Wind Speed Measuring Device According to Present Disclosure 
     3. Process of Selecting Measurement Acoustic Wave 
     4. Configuration and Processes of Wind Direction-And-Wind Speed. Measuring Device That Is Mounted on Mobile Body 
     5. Configuration Example of Measuring Wind Direction and Wind Speed in 3D Space 
     6. Hardware Configuration Example of Wind Speed Measuring Device 
     7. Conclusion of Configurations According to Present Disclosure 
     [1. Configuration and Processes in First Embodiment of Wind Speed Measuring Device According to Present Disclosure] 
     First, a configuration and processes in a first embodiment of a wind speed measuring device according to the present disclosure will be explained. 
       FIG. 1  is a block diagram depicting a configuration of the first embodiment of a wind speed measuring device  100  according to the present disclosure. 
     As depicted in  FIG. 1 , the wind speed measuring device  100  includes a control section  101 , an acoustic wave receiving section  102 , a signal analyzing section  103 , a propagation time measuring section  104 , a wind speed calculating section  105 , a signal selecting section  106 , an acoustic wave generating section  107 , and an acoustic wave transmitting section  108 . 
     The acoustic wave receiving section  102  and the acoustic wave transmitting section  108  are located to be spaced from each other by a predetermined distance. The spaced distance is previously measured. 
     A time that is taken until an acoustic wave (measurement acoustic wave) transmitted from the acoustic wave transmitting section  108  is received by the acoustic wave receiving section  102 , that is, a propagation time varies depending on the flow of air between the acoustic wave transmitting section  108  and the acoustic wave receiving section  102 , that is, depending on a wind speed. Further, the frequency also varies depending on the wind speed. 
     The wind speed measuring device  100  depicted in  FIG. 1  calculates a wind speed by measuring at least either the propagation time or variation of the frequency. It is to be noted that a wind speed in the direction of a straight line connecting the acoustic wave transmitting section  108  to the acoustic wave receiving section  102  is calculated. 
     However, not only a measurement acoustic wave that is transmitted from the acoustic wave transmitting section  108  in order to measure a wind speed, but also ambient noise, that is, noise is inputted to the acoustic wave receiving section  102 . Presence of the noise increases the likelihood of occurrence of an error in a result of wind speed analysis. That is, a wind speed cannot be measured with high precision. 
     In order to solve this problem, in the wind speed measuring device  100  depicted in  FIG. 1 , noise which the acoustic wave receiving section  102  receives while no measurement acoustic wave is outputted from the acoustic wave transmitting section  108  is first analyzed. That is, the signal components of the noise are analyzed, and a low-intensity (level) signal component (frequency component) is selected from among the signal components (frequency components) of the noise. Further, a measurement acoustic wave signal having the selected frequency component is generated and is outputted through the acoustic wave transmitting section  108 . 
     As a result of these processes, the acoustic wave transmitting section.  108  outputs a measurement acoustic wave signal having a frequency bandwidth that is substantially not included in noise. An acoustic wave signal having this frequency bandwidth is selected from among signals inputted from the acoustic wave receiving section  102 , and a propagation time and a frequency variation thereof are calculated. Accordingly, a wind speed can be measured with high precision while a measurement error that is caused by noise is reduced. 
     Specific processes which are executed by the wind speed measuring device  100  depicted in  FIG. 1  will be explained. The wind speed measuring device  100  depicted in  FIG. 1  executes the following two processes. 
     (Process 1) Analysis of Noise 
     (Process 2) Analysis of a Wind Speed 
     Hereinafter, these processes will be explained in order. 
     (Process 1) Analysis of Noise 
     First, analysis of noise will be explained. 
     The acoustic wave receiving section  102  of the wind speed measuring device  100  depicted in  FIG. 1  performs A/D conversion of a sound received while no acoustic wave is transmitted from the acoustic wave transmitting section  108 , that is, performs A/D conversion of noise, and transmits the converted noise to the signal analyzing section  103 . 
     The signal analyzing section  103  performs signal processing such as FFT (fast Fourier transform) to analyze the frequency spectrum and the signal level of the noise and reports the result of the analysis to the signal selecting section  106 . The signal selecting section  106  determines a measurement acoustic wave characteristic on the basis of the noise analysis result and reports the characteristic to the acoustic wave generating section  107 . 
     That is, the signal selecting section  106  determines, as the measurement acoustic wave characteristic, a low-intensity (level) signal component (frequency component) among the signal components (frequency components) of the noise, causes the acoustic wave generating section  107  to generate a measurement acoustic wave signal having the determined frequency component, and outputs the measurement acoustic wave signal through the acoustic wave transmitting section  108 . 
     A specific process example will be explained with reference to  FIG. 2 .  FIG. 2  depicts a noise analysis result (noise spectrum) obtained by the signal analyzing section  103 . The horizontal axis indicates a frequency. The vertical axis indicates a signal intensity. The frequency components of noise include various frequency components ranging from a low frequency to a high frequency. However, the level of the signal intensity varies without being uniform over the frequencies. It can be seen that, in particular, a frequency (fx) depicted in  FIG. 2  is a frequency bandwidth at which the signal intensity is significantly low. 
     The signal selecting section  106  determines, as the measurement acoustic wave characteristic, a low-intensity (level) frequency component (fx) among the signal components (frequency components) of nose, as explained above, causes the acoustic wave generating section  107  to generate a measurement acoustic wave signal mainly including the determined frequency component, and outputs the measurement acoustic wave signal through the acoustic wave transmitting section  108 . 
     It is to be noted that information regarding the measurement acoustic wave signal characteristic (e.g., the frequency fx) selected by the signal selecting section  106  is also reported to the control section  101  and is stored into a memory (storage section) which is not depicted. 
     (Process 2) Analysis of a Wind Speed 
     Next, analysis of a wind speed using a measurement acoustic wave signal having the frequency bandwidth determined on the result of the noise analysis executed in (Process 1) described above. 
     The acoustic wave generating section  107  generates an acoustic wave having the characteristic reported by the signal selecting section  106 . That is, the acoustic wave generating section  107  generates a measurement acoustic wave signal that mainly including a low-intensity (level) frequency component (fx) among the signal components (frequency components) of the noise and outputs the measurement acoustic wave signal to the acoustic wave transmitting section  108 . 
     The acoustic wave transmitting section  108  performs D/A conversion of the measurement acoustic wave generated by the acoustic wave generating section  107  and outputs the converted wave to the outside of the wind speed measuring device  100  through a loudspeaker or the like. 
     It is to be noted that an output timing of the measurement acoustic wave is controlled by the control section  101 . The control section  101  stores, into a memory (storage section) which is not depicted, output signal waveform information (signal waveform on a time axis) including information regarding a measurement acoustic wave output time. 
     The acoustic wave receiving section  102  receives an acoustic wave including noise superimposed on the measurement acoustic wave transmitted from the acoustic wave transmitting section  108 , performs A/D conversion of the received acoustic wave, and outputs the resultant acoustic wave to the propagation time measuring section  104  and the signal analyzing section  103 . It is to be noted that the data outputted from the acoustic wave receiving section  102  to the propagation time measuring section  104  and the signal analyzing section  103  includes signal waveform data on a time axis, and the reception timing (time information) of the data is analyzable. 
     The propagation time measuring section  104  receives, from the control section  101 , the signal waveform on the time axis at the transmission time of the measurement acoustic wave, measures, on the basis of the signal waveform inputted from the acoustic wave receiving section  102 , the propagation time of the measurement acoustic wave, that is, an elapsed time from the transmission timing of the measurement acoustic wave at the acoustic wave transmitting section  108  to the reception timing at the acoustic wave receiving section  102 , and reports the propagation time to the wind speed calculating section  105 . 
     The signal analyzing section  103  receives the measurement acoustic wave characteristic from the control section  101 , performs signal Processing such as FFT on a signal transmitted from the acoustic wave receiving section  102 , measures the frequency variation with respect to the measurement acoustic wave, and reports the frequency variation to the wind speed calculating section  105 . 
     It is to be noted that the propagation time measuring section  104  and the signal analyzing section  103  analyze the propagation time and the frequency variation of only an acoustic wave having a frequency component around a frequency region corresponding to the measurement acoustic wave. As a result of this process, the analysis can be carried out while the effect of noise is reduced. 
     The wind speed calculating section  105  calculates a wind speed by using the propagation time reported by the propagation time measuring section  104  and the frequency variation reported by the signal analyzing section  103 . 
     As previously explained, the propagation time and the frequency vary depending on the flow of air between the acoustic wave transmitting section  108  and the acoustic wave receiving section  102 , that is, depending on a wind speed. The wind speed calculating section  105  calculates a wind speed on the basis of such variations. It is to be noted that a wind speed in the direction of a straight line connecting the acoustic wave transmitting section  108  to the acoustic wave receiving section  102  is calculated. 
     The wind speed calculating section  105  holds, for example, a table in which data on the correspondence between a propagation time and a wind speed is recorded, and a table in which data on the correspondence between a frequency variation and a wind speed is recorded, and calculates a wind speed by referring to the table. Alternatively, a wind speed is calculated through calculation using a function for calculating a wind speed from a propagation time, or a function for calculating a wind speed from a frequency variation. 
     It is to be noted that, in the present embodiment, both data on the propagation time reported by the propagation time measuring section  104  and data on the frequency variation reported by the signal analyzing section  103  are used to calculate a wind speed, but only either the propagation time or the frequency variation may be used to calculate a wind speed. In a case where both data on the propagation time and data on the frequency variation are used to calculate a wind speed, computation of calculating the average of values calculated on the basis of the respective data, or calculating a weighted average by using a weight coefficient corresponding to a predetermined reliability degree, for example, can be conducted. 
     The wind speed measuring device  100  depicted in  FIG. 1  calculates a wind speed by measuring at least either the propagation time or the frequency variation. It is to be noted that a wind speed in the direction of a straight line connecting the acoustic wave transmitting section  108  to the acoustic wave receiving section  102  is calculated. 
     The control section  101  performs overall control of processes which are executed by the sections of the wind speed measuring device  100 . For example, the control section  101  performs control according to a program stored in a memory (storage section) which is not depicted. Specifically, for example, in order to carry out signal analysis of noise only and signal analysis for measuring a wind speed in time division, control to output process commands to the acoustic wave generating section  107 , the propagation time measuring section  104 , and the signal analyzing section  103  is performed. 
     That is, in order to perform the aforementioned. (Process 1) and (Process 2) in time division, the control section  101  controls the acoustic wave generating section  107 , the propagation time measuring section.  104 , and the signal analyzing section  103 . 
     Specifically, the following two processes are performed. 
     (Process 1) Noise signal analysis 
     (Process 2) Wind-speed analysis of determining a measurement acoustic wave characteristic on the basis of the result of the noise analysis, and transmitting/receiving a measurement acoustic wave having the determined characteristic 
     As explained previously, in the wind speed measuring device  100  depicted in  FIG. 1 , a signal having a low-level frequency component among the components of the noise is set as a measurement acoustic wave to be outputted from the acoustic wave transmitting section  108 . Further, in analysis of a signal received by the acoustic wave receiving section  102 , the propagation time and the frequency variation of only a frequency component around a frequency region corresponding to the measurement acoustic wave are analyzed. As a result of these processes, the analysis can be carried out while the effect of the noise is reduced. 
     As a result of this, highly precise wind speed measurement using a measurement acoustic wave having a frequency characteristic with few noise components can be performed. 
     Next, a sequence of a wind speed measuring process of the present first embodiment will be explained with reference to a flowchart depicted in  FIG. 3 . It is to be noted that processes following this flow can be executed according to a program stored in a storage section, not depicted in  FIG. 1 , of the wind speed measuring device  100  depicted in  FIG. 1  and under control of a control section (data processing section) equipped with a CPU or the like having a program executing function. Steps of the flow depicted in  FIG. 3  will be explained in order. 
     (Step S 101 ) 
     First, at step S 101 , while an output of a measurement acoustic wave from the acoustic wave transmitting section  108  is halted, A/D conversion of an acoustic wave, that is, noise received by the acoustic wave receiving section  102  is performed. 
     This step is executed by the acoustic wave receiving section  102 . 
     (Step S 102 ) 
     Next, at step S 102 , frequency spectrum analysis of the noise received and A/D converted at step S 101  is carried out. 
     This step is executed by the signal analyzing section  103 . 
     The signal analyzing section  103  analyzes the frequency spectrum and the signal level of the noise by performing signal processing such as FFT (fast Fourier transform). 
     (Step S 103 ) 
     Next, at step S 103 , it is determined that a measurement acoustic wave characteristic is having, as a main bandwidth, a frequency bandwidth with a relatively low intensity among the frequency components constituting the noise, and a measurement acoustic wave having the determined characteristic is generated. 
     This step is executed by the signal selecting section  106  and the acoustic wave generating section  107 . 
     The signal selecting section  106  determines the measurement acoustic wave characteristic on the basis of the result of the noise analysis at step S 102 . That is, the signal selecting section  106  determines, as the measurement acoustic wave characteristic, a low-intensity (level) signal component (frequency component) among the signal components (frequency components) of the noise, and causes the acoustic wave generating section  107  generate a measurement acoustic wave signal having the determined frequency component. 
     (Step S 104 ) 
     Next, at step S 104 , the measurement acoustic wave generated by the acoustic wave generating section  107  is outputted through the acoustic wave transmitting section  108 . 
     (Step S 105 ) 
     Next, at step S 105 , A/D conversion of the acoustic wave signal received by the acoustic wave receiving section  102  is performed. 
     This step is executed by the acoustic wave receiving section  102 . 
     It is to be noted that, in the acoustic wave signal received by the acoustic wave receiving section  102 , the measurement acoustic wave outputted from the acoustic wave transmitting section  108  and noise are mixed. 
     (Step S 106 ) 
     Next, at step S 106 , analysis of the frequency spectrum of the acoustic wave signal received by the acoustic wave receiving section  102  is carried out. 
     This step is executed by the signal analyzing section  103 . 
     The signal analyzing section  103  analyzes the frequency spectrum and the signal level of the received acoustic wave (measurement acoustic wave signal+noise) by performing signal processing such as FFT (fast Fourier transform). 
     (Step S 107 ) 
     Next, at step S 107 , the propagation time and the frequency variation of the acoustic wave is analyzed. 
     This step is executed by the propagation time measuring section  104  and the signal analyzing section  103 . 
     The propagation time measuring section  104  and the signal analyzing section  103  analyze the propagation time and the frequency variation of only an acoustic wave having a frequency component around a frequency region (the frequency fx in  FIG. 2 ) corresponding to the measurement acoustic wave. 
     That is, the propagation time and the frequency variation of only an acoustic wave signal having a frequency component close to the frequency component of the measurement acoustic wave outputted from the acoustic wave transmitting section  108  at step S 104  are analyzed. As a result of this step, analysis can be carried out while the effect of the noise is reduced. 
     (Step S 108 ) 
     Finally, at step S 108 , the wind speed is calculated on the basis of the analysis result of the propagation time and the frequency variation analyzed at step S 107 . 
     This step is executed by the wind speed calculating section  105 . 
     The wind speed calculating section  105  calculates a wind speed by using the propagation time reported by the propagation time measuring section  104  and the frequency variation reported by the signal analyzing section  103 . 
     As previously explained, the wind speed calculating section  105  holds, for example, a table in which data on the correspondence between a propagation time and a wind speed is recorded, and a table in which data on the correspondence between a frequency variation and a wind speed is recorded, and calculates a wind speed by referring to the table. Alternatively, a wind speed is calculated by calculation using a function for calculating a wind speed from a propagation time, or a function for calculating a wind speed from a frequency variation. It is to be noted that a wind speed in the direction of a straight line connecting the acoustic wave transmitting section  108  to the acoustic wave receiving section  102  is calculated. 
     It is to be noted that, in the explained flow, both data on the propagation time reported by the propagation time measuring section  104  and data on the frequency variation reported by the signal analyzing section  103  are used to calculate a wind speed, but only either the propagation time or the frequency variation may be used to calculate a wind speed, as previously explained. In a case where both data on the propagation time and data on the frequency variation are used to calculate a wind speed, computation of calculating the average of values calculated on the basis of the data, or calculating a weighted average by using a weight coefficient according to a predetermined reliability degree, for example, can be carried out. 
     The processes following the flowchart in  FIG. 3  are performed so that highly precise wind-speed measurement using a measurement acoustic wave having a frequency characteristic with few noise components can be performed. 
     [2. Configuration and Processes in Second Embodiment of Wind Speed Measuring Device According to Present Disclosure] 
     Next, a configuration and processes in a second embodiment of the wind speed measuring device according to the present disclosure will be explained. 
     While the aforementioned wind speed measuring device according to the first embodiment measures only a wind speed, the wind speed measuring device according to the second embodiment measures a wind direction as well as a wind speed. 
     Specifically, a wind direction and a wind speed are measured by a configuration including plural sets each including an acoustic wave transmitting section and acoustic wave receiving sections in different directions. 
     A specific example will be explained with reference to  FIG. 4 . 
       FIG. 4  depicts an arrangement example in a case where a wind direction and a wind speed are measured with one acoustic wave transmitting section shared by plural acoustic wave receiving sections a to h. 
     In the example depicted in  FIG. 4 , the plural acoustic wave receiving sections a to h are disposed at an equal distance from the acoustic wave transmitting section which is located at the center, and the adjacent acoustic wave receiving sections are equally spaced. 
     Acoustic waves received by the respective plural acoustic wave receiving sections a to h are analyzed so that a wind direction as well as a wind speed can be analyzed. 
       FIG. 5  is a block diagram depicting a configuration of a wind direction-and-wind speed measuring device  200  according to the second embodiment of the present disclosure having the configuration depicted in  FIG. 4 . 
     As depicted in  FIG. 5 , the wind direction-and-wind speed measuring device  200  includes a control section  201 , acoustic wave receiving sections  202   a  to  h , a signal analyzing section  203 , a propagation time measuring section  204 , a wind direction-and-wind speed calculating section  205 , a signal selecting section  206 , an acoustic wave generating section.  207 , and an acoustic wave transmitting section  208 . 
     The wind direction-and-wind speed measuring device  200  differs from the wind speed measuring device  100  which has been explained above with reference to  FIG. 1  in that the plural acoustic wave receiving sections  202   a  to  h  are provided instead of one acoustic wave receiving section  102  of the first embodiment, and that the wind direction-and-wind speed calculating section  205  is provided instead of the wind speed calculating section  105  of the first embodiment. 
     The arrangement configuration of the plural acoustic wave receiving sections  202   a  to  h  is the configuration explained above with reference to  FIG. 4 , for example. Specifically, the plural acoustic wave receiving sections  202   a  to  h  are disposed at different relative positions with respect to the one acoustic wave transmitting section  208 . That is, the plural acoustic wave receiving sections  202   a  to  h  are disposed at an equal distance from the one acoustic wave transmitting section  208  which is located at the center, and the adjacent acoustic wave receiving sections are equally spaced. 
     It is to be noted that the configuration using eight acoustic wave receiving sections has been explained in the example explained above with reference to  FIG. 4 , but the number of the acoustic wave receiving sections is not limited to eight, and can be set to any number that is two or greater. However, in a case where analysis of a wind direction is carried out, arrangement of two or more acoustic wave receiving sections needs to be designed such that the one acoustic wave transmitting section and the plural acoustic wave receiving sections are not aligned on a single straight line. Configuration examples using two or more acoustic wave receiving sections will be explained later. 
     Also in the second embodiment, the following two processes are executed, as in the first embodiment which has been explained above. 
     (Process 1) Noise signal analysis 
     (Process 2) Analysis of a wind speed 
     In the (Process 1) Noise signal analysis, acoustic signals received by one or plural acoustic wave receiving sections are analyzed, and a measurement acoustic wave characteristic is selected. 
     That is, as in the first embodiment, a low-intensity (level) frequency component (fx), among the signal component (frequency components) of noise, is determined as a measurement acoustic wave characteristic, the acoustic wave generating section  207  is caused to generate a measurement acoustic wave signal mainly including the frequency component, and the measurement acoustic wave signal is outputted through the acoustic wave transmitting section  208 . 
     Further, in the (Process 2) Analysis of a wind speed, analysis of a wind speed is carried out through transmission/reception of the measurement acoustic wave having the characteristic determined in the above (Process 1). In the second embodiment, the propagation time and the frequency variation of each of acoustic wave signals received by the respective plural acoustic wave receiving sections  202   a  to  h  disposed at plural positions are measured by the propagation time measurement  204  and the signal analyzing section  203 . 
     Furthermore, the wind direction-and-wind speed calculating section  205  calculates wind speed components in the respective directions from the acoustic wave transmitting section  208  to the acoustic wave receiving sections  202   a  to  h  by using the plural measurement results, and calculates the final wind direction and the final wind speed on the basis of the wind speed components in these plural different directions. 
     In the present second embodiment, plural acoustic wave receiving sections disposed at different relative positions with respect to the acoustic wave transmitting section  208  is used to enable measurement of a wind direction as well as a wind speed. 
     By disposing the plural acoustic wave receiving sections at different relative positions with respect to the acoustic wave transmitting section  208  is provided, not only measurement of a wind direction is enabled but also the accuracy of the measured data can be improved. 
     Specific examples will be explained with reference to  FIGS. 6 and 7 . 
       FIGS. 6 and 7  depict the following five arrangement examples of the acoustic wave receiving sections. 
     (Example 1) Example in which one acoustic wave receiving section a is disposed 
     (Example 2) Example in which two acoustic wave receiving sections a and b are disposed at opposed positions on a straight line with an acoustic wave transmitting section located at the intermediate position therebetween 
     (Example 3) Example in which two acoustic wave receiving sections a and c are disposed on respective axes that are orthogonal to each other with an acoustic wave transmitting section set as an origin 
     (Example 4) Example in which two acoustic wave receiving sections a and c are disposed on respective axes that are orthogonal to each other with an acoustic wave transmitting section set as an origin, and a third acoustic wave receiving section d is disposed at the intermediate position between the orthogonal axes 
     (Example 5) Example in which two acoustic wave receiving sections a and b are disposed at opposed positions on a straight line with an acoustic wave transmitting section located at the intermediate position therebetween, one acoustic wave receiving section c is disposed on an axis orthogonal to the straight line, and further, acoustic wave receiving sections d and e are disposed at the intermediate positions between the straight line and the respective orthogonal axes. 
     Black vectors indicated by black arrows depicted in (Example 1) to (Example 5) each have a length corresponding to a wind speed which is analyzed on the basis of an acoustic wave signal measured by the corresponding acoustic wave receiving section. 
     In addition, white vectors indicated by white arrows depicted in (Example 2) to (Example 5) include wind direction information (=direction of the vector) and wind speed information (length of the vector) calculated on the basis of a plurality of the black vectors. 
     (Example 1) Example in which One Acoustic Wave Receiving Section a is Disposed 
     This acoustic wave receiving section arrangement example corresponds to the configuration of the first embodiment which has been explained above. In this example, only a wind speed on a straight line connecting one acoustic wave transmitting section to one acoustic wave receiving section can be detected. 
     In addition, in the example, which is depicted in (Example 2), two acoustic wave receiving sections a and b are disposed at opposed positions on a straight line with an acoustic wave transmitting section located at the intermediate position therebetween, the average value of wind speeds analyzed at each of the two acoustic wave receiving sections a and b is calculated to calculate a white vector which is depicted in the drawing. The length of the white vector corresponds to the average wind speed of the wind speeds analyzed at each of the two acoustic wave receiving sections a and b. Detection of a wind speed can be carried out with higher precision than that in a case where an analysis result obtained by one acoustic wave receiving section is used. 
     In each of acoustic wave receiving section arrangements depicted in (Example 3) to (Example 5), one acoustic wave transmitting section and plural acoustic wave receiving sections are designed so as not to be aligned on a single straight line. With such a configuration, a wind direction as well as a wind speed can be analyzed. 
     (Example 3) Example in which Two Acoustic Wave Receiving Sections a and c are Disposed on Respective Axes that are Orthogonal to Each Other with the Acoustic Wave Transmitting Section Set as an Origin 
     In this example, the acoustic wave receiving sections a and c can detect wind speeds in different directions. Two black vectors depicted in (Example 3) of  FIG. 6  have lengths corresponding to the wind speeds in the corresponding directions analyzed on the basis of signals detected by the respective acoustic wave receiving sections a and c. 
     One white vector depicted in the drawing is generated by combining the two vectors. 
     In the white vector, the actual wind direction (=direction of the vector) and the actual wind speed (=length of the vector) are correctly reflected. 
     Since the one acoustic wave transmitting section and the plural acoustic wave receiving sections are designed so as not to be aligned on a single straight line, as described above, a wind speed and a wind direction can be analyzed. 
     (Example 4) which is Depicted in FIG.  7  and in which Two Acoustic Wave Receiving Sections a and c are Disposed on Respective Orthogonal Axes with an Acoustic Wave Transmitting Section Set as an Origin, and a Third Acoustic Wave Receiving Section d is Disposed at the Intermediate Position (at an Angle of 45 Degrees Toward an Obliquely Upward Direction from the Acoustic Wave Transmitting Section) Between the Orthogonal Axes 
     This example is obtained by adding, to the two acoustic wave receiving sections a and c depicted in (Example 3), another acoustic wave receiving section d at a position at which the angle with respect to the acoustic wave transmitting section is substantially equal to a half of the angle between the acoustic wave receiving sections a and c. 
     The three acoustic wave receiving sections a, c, and d detect wind speeds in different directions. Three black vectors depicted in (Example 4) of  FIG. 7  have lengths corresponding to wind speeds in respective directions analyzed on the basis of signals detected by the respective acoustic wave receiving sections a, c, and d. 
     One white vector depicted in FIG. is generated by combining the three vectors. 
     In the white vector, the actual wind direction (=direction of the vector) and the actual wind speed length of the vector) are correctly reflected. 
     (Example 5) Example in which Two Acoustic Wave Receiving Sections a and b are Disposed at Opposed Positions on a Straight Line with an Acoustic Wave Transmitting Section Located at the Intermediate Position Therebetween, One Acoustic Wave Receiving Section c is Disposed on an Axis Orthogonal to the Straight Line, and Further, Acoustic Wave Receiving Sections d and e are Disposed at the Intermediate Positions Between the Straight Line and the Respective Orthogonal Axes 
     This example has a configuration using five acoustic wave receiving sections a to e. 
     The five acoustic wave receiving sections a to e detect wind speeds in different directions. Five black vectors depicted in (Example 5) of  FIG. 7  have lengths corresponding to the wind speeds in the respective directions analyzed on the basis of signals detected by the respective acoustic wave receiving sections a to e. 
     One white vector depicted in  FIG. 2  is generated by combining the five vectors. 
     In the white vector, the actual wind direction (=direction of the vector) and the actual wind speed length of the vector) are correctly reflected. 
     Since analysis results of more acoustic wave receiving sections are used in the manner explained above, analysis of a wind speed and a wind direction can be carried out with higher precision. 
     The eight acoustic wave receiving sections a to n are disposed in eight directions about the acoustic wave transmitting section located at the center, as in the configuration previously explained with reference to  FIG. 4 , signals received by the respective acoustic wave receiving sections a to h are analyzed, and the analysis results are combined, whereby an analysis result of a wind speed and a wind direction can be obtained with higher precision. 
     Next, a sequence of measuring a wind speed and a wind direction of the present second embodiment will be explained with reference to a flowchart depicted in  FIG. 8 . It is to be noted that processes following this flow can be executed according to a program stored in a storage section, not depicted in  FIG. 5 , of the wind direction-and-wind speed measuring device  200  and under control of a control section (data processing section) equipped with a CPU or the like having a program execution function. Steps of the flow depicted in  FIG. 8  will be explained in order. 
     (Step S 201 ) 
     First, at step S 201 , in a state where an output of a measurement acoustic wave from the acoustic wave transmitting section  208  is halted, A/D conversion is performed on acoustic waves, that is, noise received by one or plural acoustic wave receiving sections  202 . 
     This step is executed by the acoustic wave receiving section  202 . 
     (Step S 202 ) 
     Next, at step S 202 , the frequency spectrum of the noise received and A/D-converted at step S 201  is analyzed. 
     This step is executed by the signal analyzing section  203 . 
     The signal analyzing section  203  performs signal processing such as FFT (fast Fourier transform) to analyze the frequency spectrum and the signal level of the noise. 
     (Step S 203 ) 
     Next, at step S 203 , it is determined that a measurement acoustic wave characteristic is having, as a main bandwidth, a frequency bandwidth with a relatively low intensity among the frequency components constituting the noise, and a measurement acoustic wave having the determined characteristic is generated. 
     This step is executed by the signal selecting section  206  and the acoustic wave generating section  207 . 
     The signal selecting section  206  determines the measurement acoustic wave characteristic on the basis of the result of the noise analysis at step S 202 . That is, the signal selecting section  206  determines, as the measurement acoustic wave characteristic, a low-intensity (level) signal component (frequency component) among the signal components (frequency components) of the noise, and causes the acoustic wave generating section.  207  to generate a measurement acoustic wave signal having the determined frequency component. 
     (Step S 204 ) 
     Next, at step S 204 , the measurement acoustic wave generated by the acoustic wave generating section  207  is outputted through the acoustic wave transmitting section  208 . 
     (Step S 205 ) 
     Next, at step S 205 , A/D conversion is performed on acoustic wave signals received by the plural acoustic wave receiving sections  202 . 
     This step is executed by the plural acoustic wave receiving sections  202 . 
     It is to be noted that, in the acoustic wave signals received by the plural acoustic wave receiving sections  202 , the measurement acoustic wave outputted from the acoustic wave transmitting section.  208  and noise are mixed. 
     (Step S 206 ) 
     Next, at step S 206 , the frequency spectrum of each of the acoustic wave signals received by the plural acoustic wave receiving sections  202  is analyzed. 
     This step is executed by the signal analyzing section  203 . 
     The signal analyzing section.  203  performs signal processing such as FFT (fast Fourier transform) to anal frequency spectrum and the signal level of each of the received acoustic waves (measurement acoustic wave signals+noise). 
     (Step S 207 ) 
     Next, at step S 207 , the propagation time and the frequency variation of each of the acoustic waves received by the plural acoustic wave receiving sections  202  are analyzed. 
     This step is executed by the propagation time measuring section  204  and the signal analyzing section  203 . 
     The propagation time measuring section  204  and the signal analyzing section  203  analyze the propagation time and the frequency variation of only an acoustic wave having a frequency component around a frequency region (frequency fx in FIG. corresponding to the measurement acoustic wave. 
     That is, the propagation time and the frequency variation of only an acoustic wave signal that has a frequency component close to the frequency component of the measurement acoustic wave outputted through the acoustic wave transmitting section  208  at step S 204  are analyzed. As a result of this process, the analysis can be carried out while the effect of the noise is reduced. 
     (Step S 208 ) 
     Next, at step  3208 , a wind speed on a straight line connecting the acoustic wave transmitting section to each of the acoustic wave receiving sections is calculated on the basis of the analysis result analyzed at step S 207  on the propagation times and the frequency variations of the acoustic waves received by the plural acoustic wave receiving sections  202 . 
     This step is executed by the wind direction-and-wind speed calculating section  205 . 
     The wind direction-and-wind speed calculating section  205  calculates a wind speed on a straight line connecting the acoustic wave transmitting section to each of the acoustic wave receiving sections by using the propagation time reported by the propagation time measuring section  204  and the frequency variation reported by the signal analyzing section  203 . 
     This step corresponds to the process of calculating the black vectors, which has been explained with reference to  FIGS. 6 and 7 . 
     That is, this step corresponds to a process of calculating black vectors having, in different directions, respective lengths corresponding to the wind speeds on straight lines connecting the acoustic wave transmitting section to the corresponding acoustic wave receiving sections. 
     (Step S 209 ) 
     Finally, at step S 209 , the final and actual wind speed and wind direction are calculated. 
     This step is also executed by the wind direction-and-wind speed calculating section  205 . 
     The wind direction-and-wind speed calculating section  205  generates a combined vector (the white vector depicted in  FIG. 6 or 7 ) by combining the vectors (black vectors depicted in  FIG. 6 or 7 ) having respective lengths corresponding to the wind speeds in plural different directions calculated at step S 208 , that is, the wind speeds on plural different straight lines connecting the acoustic wave transmitting section to the corresponding acoustic wave receiving sections. 
     The length of the combined vector represents the actual wind speed in the measured space, and the direction of the combined vector represents the actual wind direction in the measured space. 
     Since the processes following the flowchart depicted in  FIG. 8  are executed, a measurement acoustic wave having a frequency characteristic of including few noise components can be used to obtain a wind speed and a wind direction with hi precision. 
     [3. Process of Selecting Measurement Acoustic Wave] 
     As previously explained, the wind speed measuring device according to the present disclosure sets, as a measurement acoustic wave, an acoustic wave signal having a particular frequency bandwidth the intensity of which is low in the frequency bandwidth constituting noise. 
     That is, the signal selecting section  106  depicted in  FIG. 1  and the signal selecting section  206  depicted in  FIG. 5  each determine, as a measurement acoustic wave characteristic, a low-intensity (level) signal component (frequency component) among the signal components (frequency components) of the noise, cause the acoustic wave generating section  107  or  207  to generate a measurement acoustic wave signal having the determined frequency component, and outputs the measurement acoustic wave signal through the acoustic wave transmitting section  108  or  208 . 
     An example of selecting a measurement acoustic wave by means of a signal selecting section will be explained with reference to  FIG. 9 . 
     Similarly to  FIG. 2  which has been explained above,  FIG. 9  depicts a noise analysis result (noise spectrum) obtained by the signal analyzing section  103  of the wind speed measuring device  100  depicted in  FIG. 1 , for example. The horizontal axis indicates a frequency. The vertical axis indicates a signal intensity. The frequency components of noise include various frequency components ranging from a low frequency to a high frequency. However, the level of the signal intensity varies without being uniform over the frequencies. 
     One example of a process of selecting a measurement acoustic wave by means of a signal selecting section will be explained. 
     First, search is conducted in a region from a predetermined first frequency (fa) to a predetermined second frequency (fb) in the noise spectrum depicted in  FIG. 9 , and a frequency at which the signal intensity becomes minimum is detected. In the example depicted in  FIG. 9 , the frequency (fx) is detected. 
     The frequency (fx) is selected as a frequency for a measurement acoustic wave. 
     It is to be noted that, in a case where plural frequencies at which the signal intensity becomes minimum are detected within the search range from the predetermined first frequency (fa) to the predetermined second frequency (fb), a priority selection order is previously determined such that, for example, a high frequency side one is selected. 
     Another example of determining a frequency for a measurement acoustic wave will be explained. 
     In this example, first, a predetermined first signal intensity (L 1 ) is previously determined as a signal intensity of a noise level allowable in a frequency bandwidth that matches a frequency bandwidth selected for a measurement acoustic wave. 
     Next, as in the aforementioned example, a predetermined frequency search width from the second frequency (fb) to the first frequency (fa) is searched, and a frequency that is first detected to be lower than the predetermined first signal intensity (L 1 ) is selected. In this case, full search in the range from the first frequency to the second frequency does not need to be conducted so that the speed of the signal selection processing can be increased. 
     The signal intensity of a measurement acoustic wave may be set to an outputtable maximum value. However, when the signal intensity is set to a value obtained by adding the predetermined second signal intensity (L 2 ) to the noise signal intensity of the selected frequency (fx), power consumption of the acoustic wave transmitting section can be suppressed. 
     In the manner described so far, for example, the signal selecting section  106  depicted in  FIG. 1  and the signal selecting section  206  depicted in  FIG. 5  each select a measurement acoustic wave such that the effect of noise can be avoided. 
     [4. Configuration and Processes of Wind Direction-And-Wind Speed Measuring Device that is Mounted on Mobile Body] 
     Next, a configuration and processes of a wind direction-and-wind speed measuring device that is mounted on a mobile body of various types including a vehicle and a drone will be explained. 
     For example, a wind direction and a wind speed are measured with a wind direction-and-wind speed measuring device  250  mounted on a vehicle  240 , as depicted in  FIG. 10 . In this case, the wind direction-and-wind speed measuring device  250  measures a wind direction and a wind speed that are different from those observed in a still state. That is, to the observed wind, a wind according to a movement speed and a movement direction of the vehicle  240  has been added. 
     Here, observation data obtained by observing a wind direction and a wind speed to which the effect of wind according to a movement speed and a movement direction of a mobile body such as the vehicle  240  has been added is defined as “data on the wind direction and the wind speed to the air.” 
     Meanwhile, observation data obtained by observing a wind direction and a wind speed in a still state is defined as “data on the wind direction and the wind speed to the ground.” 
     When a wind direction and a wind speed are measured with the wind direction-and-wind speed measuring device  200  of the second embodiment which has been explained with reference to  FIG. 5 , mounted on the vehicle  240 , as depicted in  FIG. 10 , the values of the wind direction and the wind speed calculated by the wind direction-and-wind speed calculating section  205  of the wind direction-and-wind speed measuring device  200  depicted in  FIG. 5  are the “data on the wind direction and the wind speed to the air.” 
     That is, the “data on the wind direction and the wind speed to the ground,” which corresponds to a wind direction and a wind speed observed in a still state, is not be calculated. 
     Hereinafter, a third embodiment having a configuration in which both “data on the wind direction and the wind speed to the air” that is about a wind direction and a wind speed to which an effect of a wind according to a movement speed and a movement direction of a mobile body have been added, and “data on the wind direction and the wind speed to the ground” that is about a wind direction and a wind speed observed in a still state can be calculated, will be explained. 
       FIG. 11  is a block diagram depicting a configuration of the wind direction-and-wind speed measuring device  250  according to the third embodiment of the present disclosure. Similarly to the wind direction-and-wind speed measuring device  200  according to the second embodiment which has been explained with reference to  FIG. 5 , the wind direction-and-wind speed measuring device  250  includes the control section  201 , the acoustic wave receiving sections  202   a  to  h , the signal analyzing section  203 , the propagation time measuring section  204 , the wind direction-and-wind speed calculating section.  205 , the signal selecting section  206 , the acoustic wave generating section  207 , and the acoustic wave transmitting section  208 , as depicted in  FIG. 11 . 
     In addition to these constituents, the wind direction-and-wind speed measuring device  250  according to the third embodiment depicted in  FIG. 11  further includes a GNSS reception section  251 , an acceleration sensor  252 , and a to-ground wind direction-and-wind speed calculating section  253 . 
     A process using the control section  201  to the acoustic wave transmitting section  208  is similar to that of the second embodiment which has been explained with reference to  FIG. 5 . However, the wind direction-and-wind speed calculating section  205  calculates a wind direction and a wind speed by adding the effect of a wind according to a movement Speed and a movement direction of a mobile body, that is, calculates “data on the wind direction and the wind speed to the air.” 
     The “data on the wind direction and the wind speed to the air” calculated by the wind direction-and-wind speed calculating section  205  is outputted to the to-ground wind direction-and-wind speed calculating section  253 . The to-ground wind direction-and-wind speed calculating section.  253  calculates “data on the wind direction and the wind speed to the ground,” that is, calculates a wind direction and a wind speed in a still state, by using the “data on the wind direction and the wind speed to the air” calculated by the wind direction-and-wind speed calculating section  205  and using information inputted from the GNSS reception section  251  and the acceleration sensor  252 . 
     The GNSS reception section  251  is a global positioning system (Global Navigation Satellite System) and measures the current position through a positioning process using a satellite. 
     The GNSS reception section  251  acquires the current position of a mobile apparatus such as a vehicle equipped with the wind direction-and-wind speed measuring device  250  and outputs information regarding the acquired current position to the to-ground wind direction-and-wind speed calculating section  253 . 
     Further, the acceleration sensor  252  detects the acceleration of the mobile apparatus such as the vehicle equipped with the wind direction-and-wind speed measuring device  250  and outputs information regarding the detected acceleration to the to-ground wind direction-and-wind speed calculating section  253 . It is to be noted that the acceleration sensor  252  generates time-series data on the acceleration, that is, generates information regarding an acceleration variation on a time axis, and outputs the information to the to-ground wind direction-and-wind speed calculating section  253 . 
     The to-ground wind direction-and-wind speed calculating section  253  acquires the acceleration information (time-series data) inputted from the acceleration sensor  252  and calculates the movement speed and the movement direction of the mobile apparatus such as the vehicle equipped with the wind direction-and-wind speed measuring device  250 . 
     Alternatively, the to-ground wind direction-and-wind speed calculating section  253  calculates the movement speed and the movement direction of the mobile apparatus such as the vehicle equipped with the wind direction-and-wind speed measuring device  250 , on the basis of time-series data on the current position of the mobile apparatus inputted from the GNSS reception section  251 . 
     The to-ground wind direction-and-wind speed calculating section  253  calculates the movement speed and the movement direction of the mobile apparatus such as the vehicle equipped with the wind direction-and-wind speed measuring device  250 , by using at least, either the information inputted from the acceleration sensor  252  or the information inputted from the GNSS reception section  251 . 
     Moreover, the to-ground wind direction-and-wind speed calculating section  253  acquires the “data on the wind direction and the wind speed to the air” calculated by the wind direction-and-wind speed calculating section  205 . On the basis of the movement speed and the movement direction of the mobile apparatus obtained by calculation based on the information inputted from the acceleration sensor  252  or the GNSS reception section  251 , and on the basis of the “data on the wind direction and the wind seed to the air,” the to-ground wind direction-and-wind speed calculating section  253  calculates “data on the wind direction and the wind speed to the ground,” that is, “data on the wind direction and the wind speed to the ground” corresponding to the wind direction and the wind speed observed in a still state. 
     The correspondence between the “data on the wind direction and the wind speed to the air” and the “data on the wind direction and the wind speed to the ground” will be explained with reference to  FIG. 12 . 
       FIG. 12  depicts 
     a wind direction-and-wind speed vector to the air, 
     a wind direction-and-wind speed vector to the ground, and 
     a movement vector of a mobile apparatus. 
     The length of each of the vectors represents the wind speed or the speed of the mobile apparatus. The direction of each of the vectors corresponds to the wind direction or the movement direction of the mobile apparatus. 
     It is to be noted that the wind direction-and-wind speed vector to the air is equivalent to a combined vector of a wind direction-and-wind speed vector  1  and a wind direction-and-wind speed vector  2 , as depicted in  FIG. 12 . 
     As understood from  FIG. 12 , when the movement vector of the mobile apparatus is added to the wind direction-and-wind speed vector to the air, the wind direction-and-wind speed vector to the ground can be calculated. 
     It is to be noted that the wind direction-and-wind speed calculating section  205  of the wind direction-and-wind speed measuring device  250  depicted in  FIG. 11  calculates a wind direction and a wind speed corresponding to the wind direction-and-wind speed vector to the air depicted in  FIG. 12 . 
     The to-ground wind direction-and-wind speed calculating section  253  receives the “data on the wind direction and the wind speed to the air” calculated by the wind direction-and-wind speed calculating section  205 , that is, data on the wind direction and the wind speed indicated by the wind direction-and-wind speed vector to the air depicted in  FIG. 12 . 
     Furthermore, the to-ground wind direction-and-wind speed calculating section  253  calculates data on the movement direction and the movement speed with respect to a movement phase indicated by the movement vector of the mobile apparatus depicted in  FIG. 12 , on the basis of the movement speed and movement direction of the mobile apparatus obtained by calculation based on the information inputted from the acceleration sensor  252  or the GNSS reception section  251 . 
     At last, the to-ground wind direction-and-wind speed calculating section  253  calculates data which the wind direction-and-wind speed vector to the ground depicted in  FIG. 12  has, that is, calculates the wind direction and the wind speed in a still state, by using data included in the two vectors 
     the wind direction-and-wind speed vector to the air and 
     the movement vector of the mobile apparatus. 
     In the manner described so far, the wind direction-and-wind speed measuring device  250  depicted in  FIG. 11  can calculate both “data on the wind direction and the wind speed to the air,” which is data on a wind direction and a wind speed to which the effect of a wind according to a movement speed and a movement direction of a mobile body has been added, and “data an the wind direction and the wind speed to the ground,” which is data on a wind direction and a wind speed observed in a still state. 
     [5. Configuration Example of Measuring Wind Direction and Wind Speed in 3D Space] 
     Next, a configuration example of measuring a wind direction and a wind speed in a 3D space will be explained. 
     The wind speed measuring device  100  which has been explained with reference to  FIG. 1  can detect, by means of one acoustic wave transmitting section and one acoustic wave receiving section, a wind speed on a straight line connecting the acoustic wave transmitting section and the acoustic wave receiving section. 
     In addition, for example, in a case where plural acoustic wave receiving sections are disposed around one acoustic wave transmitting section, as depicted in  FIG. 4  explained above, the wind direction-and-wind speed measuring device  200  which has been explained with reference to  FIG. 5  can analyze not only a wind speed but also a wind direction by analyzing acoustic waves received by the respective acoustic wave receiving sections. 
     However, in the configuration depicted in  FIG. 4 , the one acoustic wave transmitting section and the plural acoustic wave receiving sections are all disposed on a single plane. With such a configuration, a wind direct on and a wind speed can be detected only on plane, that is, the two-dimensional plane. 
     A configuration in which wind directions and wind speeds in every direction in a 3D space can be detected will explained with reference to  FIG. 13 . 
       FIG. 13  depicts an arrangement configuration example of acoustic wave transmitting sections and acoustic wave receiving sections that are con g red to be able to detect wind directions and wind speeds in every direction in a 3D space. 
     In this configuration, an acoustic wave transmitting sect P disposed at the center of a rectangular plane A, acoustic wave receiving sections a to d are disposed at the four vertexes of the plane A, in addition, an acoustic wave transmitting section is disposed at the center of a plane B that is orthogonal to the plane A, and acoustic wave receiving sections c to f are disposed at the four vertexes of the plane B. 
     This example corresponds to a configuration obtained by combining two sets disposed so as to be orthogonal to each other, the two sets each being obtained by providing four acoustic wave receiving sections to the wind direction-and-wind speed measuring device  200  depicted in  FIG. 5  explained as the second embodiment. In the configuration depicted in  FIG. 13 , the two acoustic wave receiving sections c and d, which are located on the contact line of the two wind direction-and-wind speed measuring devices that are disposed so as to be orthogonal to each other, are shared. 
     It is to be noted that a process of transmitting an acoustic wave from the acoustic wave transmitting section P and a process of transmitting an acoustic wave from the acoustic wave transmitting section Q are performed in time division to avoid interference. Alternatively, the processes are performed by using different frequencies. 
     With the configuration depicted in  FIG. 13 , a wind direction and a wind speed on the plane A and a wind direction and a wind speed on the plane B can be separately calculated. Information regarding the two wind directions and information regarding the two wind speeds are combined so that a true wind direction and a true wind speed in the 3D space can be calculated. 
     A specific example is depicted in  FIG. 14 . 
     A wind direction-and-wind speed vector a depicted in  FIG. 14  indicates a wind direction (direction of the vector) and a wind speed (length of the vector) on the plane A. 
     On the other hand, a wind direction-and-wind speed vector indicates a wind direction (direction of the vector) and a wind speed (length of the vector) on the plane B. 
     These two vectors are combined to obtain a 3D-space wind direction-and-wind speed vector depicted in  FIG. 14 . 
     The 3D-space wind direction-and-wind speed vector indicates a true wind speed and a true wind speed in the 3D space. 
     In the aforementioned manner, the acoustic wave transmitting section and plural the acoustic wave receiving sections are disposed so as not to be located on a single plane. Accordingly, a wind direction-and-wind speed measuring device capable of detecting a wind direction and a wind speed in a 3D space can be realized. 
     [6. Hardware Configuration Example of Wind Speed Measuring Device] 
     Next, a hardware configuration example of the wind speed measuring device according to the present, disclosure will be explained with reference to  FIG. 15 . 
     A CPU (Central Processing Unit)  301  functions as a data processing section that executes various types of processes according to a program stored in a ROM (Read Only Memory)  302  or a storage section  308 . For example, the CPU  301  executes the processes following any one of the sequences explained in the aforementioned embodiments. The program or data which is executed by the CPU  301  is stored in a RAM (Random Access Memory)  303 . The CPU  301 , the ROM  302 , and the RAM  303  are mutually connected via a bus  304 . 
     The CPU  301  is connected to an input/output interface  305  via the bus  304 . An input section  306  including various switches, a keyboard, a touch panel, a mouse, a microphone, and the like, and an output section  307  including a display, a loudspeaker, and the like are connected to the input/output interface  305 . 
     It is to be noted that an acoustic wave receiving section, an acceleration sensor, a GNSS reception section, etc., are included in the input section  306 . In addition, an acoustic wave transmitting section is included in the output section  307 . 
     The storage section  308  connected to the input/output interface  305  includes a hard disk, for example, and stores the program which is executed by the CPU  301  and various data. A communication section  309  functions as a transmission/reception section for data communication over a network such as the internet or a local area network and communicates with an external apparatus. 
     A drive  310  that is connected with the input/output interface  305  drives a removable medium  311  such as a magnetic disk, an optical disk, a magneto-optical disk, or a semiconductor memory such as a memory card so that data recording or data reading is carried out. 
     [7. Conclusion of Configurations According to Present Disclosure] 
     The embodiments of the present disclosure have been explained above in detail with reference to the particular embodiments. However, it is obvious that a person skilled in the art can make modification or substitution on the embodiments within the gist of the present disclosure. That is, the present invention has been disclosed in a form of exemplifications, and thus, should not be limitedly interpreted. In order to assess the gist of the present disclosure, the claims should be considered. 
     It is to be noted that the technology disclosed herein also may have the following configurations. 
     (1) 
     A wind speed measuring device including: 
     an acoustic wave transmitting section that transmits a measurement acoustic wave; 
     an acoustic wave receiving section that receives the measurement acoustic wave transmitted from the acoustic wave transmitting section; 
     a signal selecting section that determines a characteristic of the measurement acoustic wave outputted from the acoustic wave transmitting section; and 
     a wind speed calculating section that calculates a wind speed by analyzing a signal received by the acoustic wave receiving section, in which 
     the signal selecting section selects, as the measurement acoustic wave outputted from the acoustic wave transmitting section, an acoustic wave that mainly includes a low-intensity frequency bandwidth selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. 
     (2) 
     The wind speed measuring device according to (1), in which 
     the signal selecting section selects, as the measurement acoustic wave, an acoustic wave that mainly includes a frequency bandwidth having an intensity equal to or lower than a predetermined threshold and selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. 
     (3) 
     The wind speed measuring device according to (2), in which 
     the signal selecting section sets a signal intensity of the measurement acoustic wave to an intensity that is higher than the threshold by a predetermined intensity. 
     (4) 
     The wind speed measuring device according to any one of (1) to (3), in which 
     the wind speed calculating section calculates a wind speed on the basis of a propagation time that is taken for the measurement acoustic wave to travel along a path from the acoustic wave transmitting section to the acoustic wave receiving section. 
     (5) 
     The wind speed measuring device according to any one of (1) to (4), in which 
     the wind speed calculating section calculates a wind speed on the basis of a frequency variation that occurs during a time taken for the measurement acoustic wave to travel along a path from the acoustic wave transmitting section to the acoustic wave receiving section. 
     (6) 
     The wind speed measuring device according to any one of (1) to (5), in which 
     the plural acoustic wave receiving sections are disposed at different relative positions with respect to the acoustic wave transmitting section, and 
     the wind speed calculating section functions as a wind direction-and-wind speed calculating section to calculate a wind direction as well as a wind speed by analyzing signals received by the respective plural acoustic wave receiving sections. 
     (7) 
     The wind speed measuring device according to (6), in which 
     the wind direction-and-wind speed calculating section
         analyzes the signals received by the respective plural acoustic wave receiving sections,   calculates plural wind speeds on plural straight lines connecting the acoustic wave transmitting section to the corresponding acoustic wave receiving sections, and   calculates a wind direction on the basis of information regarding the plural calculated wind speeds in different directions.
 
(8)
       

     The wind speed measuring device according to (6) or (7), in which 
     the wind direction-and-wind speed calculating section calculates a final wind speed and a final wind direction by combining vectors that have respective lengths designed to indicate plural wind speeds on plural straight lines connecting the acoustic wave transmitting section to the corresponding acoustic wave receiving sections. 
     (9) 
     The wind speed measuring device according to claim any one of (6) to (8), in which 
     the acoustic wave receiving sections are disposed at an equal distance from the acoustic wave transmitting section. 
     (10) 
     The wind speed measuring device according to (9), in which 
     the acoustic wave receiving sections are disposed such that an equal space is provided between the adjacent acoustic wave receiving sections. 
     (11) 
     The wind speed measuring device according to any one of (6) to (10), further including: 
     a to-ground wind direction-and-wind speed calculating section that calculates to-ground wind direction-and-wind speed information which indicates a wind direction and a wind speed in a still state, in which 
     the to-ground wind direction-and-wind speed calculating section
         receives to-air wind direction-and-wind speed information which indicates a wind direction and a wind speed which are calculated by the wind direction-and-wind speed calculating section of the wind speed measuring device mounted on a mobile apparatus and which include an effect of wind caused by movement of the mobile apparatus, and   calculates the to-ground wind direction-and-wind speed information by using the to-air wind direction-and-wind speed information and information regarding a movement speed and a movement direction of the mobile apparatus.
 
(12)
       

     The wind speed measuring device according to (11), in which 
     the to-ground wind direction-and-wind speed calculating section calculates the movement speed and the movement direction of the mobile apparatus by using current position information inputted from a GNSS reception section mounted on the mobile apparatus or acceleration information inputted from an acceleration sensor. 
     (13) 
     The wind speed measuring device according to any one of (1) to (12), in which 
     the plural acoustic wave receiving sections are disposed at different relative positions with respect to the acoustic wave transmitting section, 
     the acoustic wave transmitting section and the plural acoustic wave receiving sections are disposed so as not to form a single plane, and 
     the wind speed calculating section functions as a wind direction-and-wind speed calculating section to calculate a wind speed and a wind direction in a three-dimensional space by analyzing signals received by the respective plural acoustic wave receiving sections. 
     (14) 
     The wind speed measuring device according to (13), in which 
     plural sets each including one acoustic wave transmitting section and plural acoustic wave receiving sections that are disposed on a single plane are combined such that the sets are designed not in parallel with one another. 
     (15) 
     The wind speed measuring device according to (13) or (14), in which 
     the wind speed measuring device has a configuration obtained by combining sets each including one acoustic wave transmitting section and plural acoustic wave receiving sections that are disposed on a single plane such that the sets are orthogonal to each other. 
     (16) 
     A wind speed measuring method which is executed by a wind speed measuring device, the method including: 
     a signal selecting step in which a signal selecting section determines a characteristic of a measurement acoustic wave outputted from an acoustic wave transmitting section; 
     a step in which the acoustic wave transmitting section transmits the measurement acoustic wave; 
     a step in which an acoustic wave receiving section receives the measurement acoustic wave transmitted from the acoustic wave transmitting section; and 
     a step in which a wind speed calculating section calculates a wind speed by analyzing a signal received by the acoustic wave receiving section, in which 
     in the signal selecting step, 
     an acoustic wave is selected as the measurement acoustic wave outputted from the acoustic wave transmitting section, the acoustic wave mainly including a low-intensity frequency bandwidth selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. 
     (17) 
     A program for causing a wind speed measuring device to execute a wind speed measuring process, the program being configured to cause the wind speed measuring device to execute: 
     a signal selecting step of causing a signal selecting section to determine a characteristic of a measurement acoustic wave outputted from an acoustic wave transmitting section; 
     a step of causing the acoustic wave transmitting section to transmit the measurement acoustic wave; 
     a step of causing an acoustic wave receiving section to receive the measurement acoustic wave transmitted from the acoustic wave transmitting section; and 
     a step of causing a wind speed calculating section to calculate a wind speed by analyzing a signal received by the acoustic wave receiving section in which 
     in the signal selecting step, 
     an acoustic wave is selected as the measurement acoustic wave outputted from the acoustic wave transmitting section, the acoustic wave mainly including a low-intensity frequency bandwidth selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. 
     Further, a series of the processes explained herein can be executed by hardware, software, or a complex configuration thereof. In a case where the processes are executed by software, a program having a sequence of the processes recorded therein can be executed after being installed into a memory of a computer incorporated in dedicated hardware, or can be executed after being installed into a general-purpose computer capable of various processes. For example, such a program may be previously recorded in a recording medium. The program can be installed into the computer from the recording medium. Alternatively, the program can be received over a network such as a LAN (Local Area Network) or the internet and be installed into a recording medium such as an internal hard disk. 
     It is to be noted that the processes described herein are not necessarily executed in the described time-series order, and the processes may be executed parallelly or separately, as needed or according to the processing capacity of a device to execute the processes. Further, in the present description, a system refers to a logical set configuration including plural devices, and the devices in the configuration are not necessarily included in the same casing. 
     INDUSTRIAL APPLICABILITY 
     As explained so far, a device capable of measuring d wind speed and a wind direction with high precision while reducing the effect of ambient noise can be realized according to the configuration of one embodiment of the present disclosure. 
     Specifically, for example, the device includes an acoustic wave transmitting section that transmits a measurement acoustic wave, an acoustic wave receiving section that receives the measurement acoustic wave transmitted from the acoustic wave transmitting section, a signal selecting section that determines a measurement acoustic wave characteristic, and a wind speed calculating section that calculates a wind speed by analyzing a signal received by the acoustic wave receiving section. The signal selecting section selects, as the measurement acoustic wave, an acoustic wave that mainly includes a low-intensity frequency bandwidth selected from a noise signal which the acoustic wave receiving section receives when the measurement acoustic wave is not transmitted. Alternatively, the plural acoustic wave receiving sections are disposed at different relative positions with respect to the acoustic wave transmitting section, and the wind speed calculating section functions as a wind direction-and-wind speed calculating section to calculate a wind direction as well as a wind speed by analyzing signals received by the respective plural acoustic wave receiving sections. 
     With the present configuration, a device capable of measuring a wind speed and a wind direction with high precision while reducing the effect of ambient noise can be realized. 
     REFERENCE SIGNS LIST 
     
         
         
           
               100  Wind speed measuring device 
               101  Control section 
               102  Acoustic wave receiving section 
               103  Signal analyzing section. 
               104  Propagation time measuring section 
               105  Wind speed calculating section. 
               106  Signal selecting section 
               107  Acoustic wave generating section 
               108  Acoustic wave transmitting section. 
               200  Wind direction-and-wind speed measuring device 
               201  Control section 
               202  Acoustic wave receiving section 
               203  Signal analyzing section 
               204  Propagation time measuring section 
               205  Wind direction-and-wind speed calculating section 
               206  Signal selecting section 
               207  Acoustic wave generating section 
               208  Acoustic wave transmitting section 
               230  Vehicle 
               250  Wind direction-and-wind speed measuring device 
               251  CNSS reception section 
               252  Acceleration sensor 
               253  To-ground wind direction-and-wind speed calculating section 
               301  CPU 
               302  ROM 
               303  RAM 
               304  Bus 
               305  input/output interface 
               306  input section 
               307  Output section 
               308  Storage section 
               309  Communication section 
               310  Drive 
               311  Removable medium