A method for calculating the altitude of an aircraft, an altitude calculation program, and an aircraft having the same.

Abstract

To provide an altitude calculation method and an altitude calculation program for a flying object that can calculate the accurate altitude without any additional measuring device even in a place where there is no structure as a marker in the circumference or in a place where there is another flying object under the flying object, and the flying object with the same.SOLUTION: The present invention relates to an altitude calculation method for a flying object, and the altitude calculation method includes calculating the altitude of the flying object using information on the horizontal coordinates of the flying object, reception signal intensity of a radio signal and previously acquired altitude calculation supplementary information.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an altitude calculation technology for a flying object.

Background Art

[0002] In response to social issues such as the recent decline in the working population and decarbonization, diversification and multi-leveling are also required in the field of mobility. In particular, with the development of drone technology, the demand for air mobility for logistics and short- to medium-distance travel has been increasing, and the 3Dization of economic activities through the automation (unmanned operation) and high-speedization of flying objects is expected to be an essential technology for future sustainable development.

[0003] For the automation of a flying object, accurate identification of the current position is indispensable. In addition to satellite positioning such as GNSS (Global Navigation Satellite System), various methods such as pattern matching technology for searching for the corresponding position from the video from a camera mounted on the flying object have been studied. Regarding the altitude of a flying object, in addition to GNSS positioning, many flying objects can measure altitude using a barometer. However, since GNSS uses satellites for position calculation, it can calculate coordinates with high accuracy in the horizontal direction, but there is a problem that errors are likely to occur in the vertical coordinates. Also, since the amount of change in air pressure due to altitude is not large, it is difficult to measure precise altitude with a barometer.

[0004] In contrast, there is Patent Document 1 as the background art in this technical field. In Patent Document 1, it is disclosed that an image of the surroundings is taken from a camera mounted on a flying object, and the flying position of the flying object is estimated with higher accuracy based on a landmark structure.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] As described in Patent Document 1, it is conceivable to estimate the precise altitude based on images captured from a camera, using landmark structures as a reference. However, when operating aircraft in urban areas, such as air mobility vehicles, the take-off and landing ports are expected to be located on the rooftops of buildings. In this case, if there are no buildings taller than the building serving as the take-off and landing port, there are no landmark structures to use as altitude references, making it impossible to estimate the altitude by pattern matching and thus preventing the acquisition of an accurate altitude.

[0007] On the other hand, altitude measurement can be done by using a laser rangefinder to measure the distance to the ground. However, since air mobility may involve the simultaneous operation of multiple aircraft, it is conceivable that multiple aircraft may be waiting above the landing / takeoff port during takeoff and landing. In this case, if there are other aircraft below the aircraft, they will obstruct the laser rangefinder's ability to measure altitude. Furthermore, adding altitude measurement equipment such as laser rangefinders increases the aircraft's weight and costs.

[0008] In view of the above problems, the present invention aims to provide an altitude calculation method for an aircraft, an altitude calculation program, and an aircraft having the same, which can accurately calculate the altitude without additional measuring equipment, even in places where there are no landmark structures in the surrounding area or where there are other aircraft below the aircraft. [Means for solving the problem]

[0009] One example of the present invention is a method for calculating the altitude of an aircraft, which calculates the altitude of an aircraft using information on the horizontal coordinates of the aircraft, the received signal strength of a radio signal, and pre-obtained altitude calculation auxiliary information. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an altitude calculation method for an aircraft, an altitude calculation program, and an aircraft having the same, which can accurately calculate the altitude without additional measuring equipment even in places where there are no landmark structures in the surrounding area or where there are other aircraft below the aircraft. [Brief explanation of the drawing]

[0011] [Figure 1] This is a diagram showing the configuration of the altitude calculation system in Example 1. [Figure 2] This is a hardware configuration diagram of the aircraft in Example 1. [Figure 3] This is a functional configuration diagram of the aircraft in Example 1. [Figure 4] This figure shows the correspondence information between altitude and received signal strength in Example 1. [Figure 5] This is a processing flowchart of the altitude calculation unit in Example 1. [Figure 6] This diagram illustrates the method for calculating the altitude of an aircraft in Example 2. [Figure 7] This figure shows the base station information in Example 2. [Figure 8] This is a processing flowchart of the altitude calculation unit in Example 2. [Figure 9] This diagram illustrates the method for calculating the altitude of an aircraft in Example 3. [Figure 10] This figure shows the information regarding the change in received signal strength in Example 3. [Figure 11] This is a processing flowchart of the altitude calculation unit in Example 3. [Figure 12] This diagram illustrates the method for calculating the altitude of an aircraft in Example 4. [Figure 13] This figure shows the information corresponding to the amount of change in Example 4. [Figure 14] This is a processing flowchart of the altitude calculation unit in Example 4. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment

[0013] FIG. 1 is a configuration diagram of an altitude calculation system in this embodiment. In FIG. 1, the altitude calculation system includes aircraft 1a, 1b, 1c capable of wireless communication (hereinafter collectively referred to as aircraft 1), wireless base stations 2a, 2b (hereinafter collectively referred to as wireless base station 2 or base station 2) that perform wireless communication with aircraft 1, takeoff and landing ports 3a, 3b where aircraft 1 take off and land (hereinafter collectively referred to as takeoff and landing port 3), and a control system 4 that controls aircraft 1.

[0014] Aircraft 1 carries passengers and cargo from takeoff and landing ports 3 installed at various locations and flies to the destination, and lands at the takeoff and landing port 3 of the destination to transport people and cargo. The control system 4 obtains information such as the position, state, and destination of aircraft 1 within the jurisdiction, formulates instructions for safely operating all aircraft 1 within the airspace based on this information, and instructs each aircraft 1 using wireless communication. Each aircraft 1 operates in accordance with instructions from the control system 4 such as movement, standby, takeoff and landing.

[0015] FIG. 2 is a hardware configuration diagram of the aircraft in this embodiment. In FIG. 2, aircraft 1 includes a propulsion device 11 such as a motor and a rotor, which is an engine for moving the aircraft, a communication device 12 for communicating with the outside such as a control system, a sensor group 13 for measuring the attitude of the aircraft, a storage device 14 for recording necessary information, and a control device (computer) 15 for controlling each device. The control device 15 is composed of a CPU 21, a RAM 22, and a flash ROM (FROM) 23. The control device 15 executes various functions through software processing by interpreting the operation program by the CPU and the like.

[0016] FROM23 contains, as processing programs, a flight control program 24 that performs overall control of the aircraft, a position calculation program 25, and an altitude calculation program 26 that calculates the aircraft's current altitude. These processing programs are loaded into RAM22 and executed by CPU21. FROM23 may consist of a single memory medium as shown in the figure, or it may consist of multiple memory mediums. Furthermore, it may be a non-volatile memory medium other than flash ROM.

[0017] The flight control program 24 controls the propulsion system 11 based on measurement data from a group of sensors 13, such as a gyro sensor and an accelerometer, to control the attitude of the aircraft. The position calculation program 25 calculates the aircraft's current position using GNSS or the like. The flight control program 24 also notifies the air traffic control system 4, using the communication device 12, of the aircraft's position information, which is the result of the position calculation program 25 plus the altitude information calculated by the altitude calculation program 26, as well as information such as the destination recorded in the storage device 14, and receives instructions from the air traffic control system 4. The flight control program 24 also uses the propulsion system 11 to perform operations such as takeoff, landing, waiting in the air, and movement, in accordance with the instructions from the air traffic control system 4. The contents of this embodiment can also be executed when the aircraft is controlled by a pilot on board or by a remote pilot controlling it via wireless communication from a remote location.

[0018] Figure 3 is a functional configuration diagram of the aircraft in this embodiment. In Figure 3, the same reference numerals are used for components identical to those in Figure 2, and their descriptions are omitted. In Figure 3, the difference from the hardware configuration diagram in Figure 2 is that the control device 15 is configured as a flight control unit 16 that processes according to the flight control program 24 in Figure 2, a position calculation unit 17 that processes according to the position calculation program 25, and an altitude calculation unit 18 that processes according to the altitude calculation program 26.

[0019] Next, the altitude calculation method in this embodiment will be described. In this embodiment, the received signal strength of the wireless communication signal is measured and the accurate altitude is estimated by comparing it with a previously measured received signal strength distribution map of the relevant airspace. In this embodiment, the altitude of the aircraft is calculated at a specific received signal measurement location. For example, a location whose position is clearly known, such as above a takeoff and landing port, and where the wireless environment is stable, is set as the altitude calculation location.

[0020] At the altitude calculation location, the received signal strength from radio base stations at each altitude is measured in advance, and correspondence information (correspondence table) between altitude and received signal strength is created as auxiliary information for altitude calculation. If there are multiple base stations from which signals can be received, the correspondence information is created by combining them. An example of the correspondence information between altitude and received signal strength is shown in Figure 4. In Figure 4, the correspondence information 5 between altitude and received signal strength is listed for base stations A, B, and C.

[0021] Figure 5 is a processing flowchart of the altitude calculation unit showing the procedure for calculating the altitude of the aircraft in this embodiment. In Figure 5, when the aircraft calculates its own altitude, first Position calculation unit 17 The device moves to a predetermined received signal measurement location using the communication device 12 (Step S1). Next, at that location, the received signal strength of the radio signal from the base station 2 is measured using the communication device 12 (Step S2). For example, when using LTE (Long Term Evolution) as the wireless communication, the RSSI (Received Signal Strength Indicator) acquired by the receiving device during communication is used as the received signal strength. In this case, in order to improve the measurement accuracy, multiple measurements may be taken for the same base station, and the results may be statistically processed to determine the received signal strength. After the measurement, it is checked whether there are any unmeasured base stations that can still be received at that measurement point (Step S3), and if there are, the device switches to that base station (Step S4) and measures the received signal strength. If there are no base stations, the necessary statistical processing is performed on each measurement result, and the measurement results are recorded in the storage device 14 for each base station (Step S5).

[0022] Next, in step S6, the measurement result of the received signal strength is compared with the altitude and received signal strength information stored in the memory device 14 to find an altitude that closely matches the measurement result (step S7). Methods for determining whether there is a match include selecting the altitude that minimizes the sum of absolute errors with the received signal strength of each base station, or evaluating the magnitude of the error by weighting base stations with strong received signal strengths.

[0023] Thus, according to this embodiment, accurate altitude can be calculated even in locations where there are no landmark structures in the surrounding area or where other aircraft are below the aircraft. Furthermore, because wireless communication equipment is used, accurate altitude can be calculated without additional measuring devices. [Examples]

[0024] In Example 1, the altitude of the aircraft was calculated at a specific calculation location. In contrast, this example describes a method for calculating the altitude of an aircraft at any location. Figure 6 is a diagram illustrating the method for calculating the altitude of an aircraft in this example.

[0025] As a premise of this embodiment, the aircraft has in advance base station information in its storage device, which includes the horizontal coordinates of the radio base station, antenna installation height (H1), and transmission power strength information, as altitude calculation auxiliary information. An example of base station information is shown in Figure 7. In Figure 7, base station information 6 includes the position coordinates X, Y, Z and transmission power strength Tx for base stations A, B, and C.

[0026] In Figure 6, the horizontal distance (L1) between aircraft 1 and wireless base station 2 is calculated using base station information 6 and the aircraft's own position information measured by the aircraft. For example, if the coordinates of base station 2 are (x1, y1) and the coordinates of aircraft 1 are (x2, y2), the horizontal distance (L1) can be calculated using the following equation (1).

[0027] L1^2=(x1-x2)^2+(y1-y2)^2 ···(1) Next, the aircraft 1 measures the received signal strength from base station 2 at its position. The signal propagation distance is calculated from this received power strength measurement result and the transmitted power strength information of base station 2, and this is taken as the straight-line distance (L2) between base station 2 and aircraft 1. The magnitude of the attenuation of the radio signal with distance can be determined from Frith's transfer formula. In addition, in urban areas where there are obstacles between the base station and the aircraft, the propagation distance can be estimated using propagation models such as the Walfisch-Ikegami model. From L2 and L1 obtained above, the relative altitude (H2) between aircraft 1 and base station 2 is calculated using the following equation (2).

[0028] H2^2 = L2^2 - L1^2 ... (2) From this relative altitude (H2) and the antenna installation height (H1) from the base station 2's zero altitude position 30, the altitude of the aircraft from the zero altitude position 30 (H3) is calculated using the following equation (3).

[0029] H3 = H1 + H2 ... (3) Figure 8 is a processing flowchart of the altitude calculation unit showing the procedure for calculating the altitude of the aircraft in this embodiment. In Figure 8, the aircraft first Position calculation unit 17 The aircraft calculates its own position (step S21). Next, the aircraft uses the communication device 12 to measure the signal strength of the received signal from the radio base station at that position (step S22), and performs the necessary statistical processing to record it (step S23). Next, the altitude calculation unit refers to the received base station position information from the base station information in the memory device and calculates the horizontal distance (L1) between the base station and the aircraft using equation (1) (step S24).

[0030] Next, the altitude calculation unit calculates the straight-line distance between the base station and the aircraft from the measured received signal strength and the transmitted signal strength obtained from the base station information (step S25). Next, the altitude calculation unit calculates the relative altitude (H2) between the base station and the aircraft using equation (2) from the horizontal distance (L1) and straight-line distance (L2) obtained so far (step S26). Then, the altitude calculation unit calculates the altitude of the aircraft (H3) using equation (3) from the relative altitude (H2) and the base station antenna installation height (H1) described in the base station information (step S27). Alternatively, the above measurements may be performed on multiple receivable base stations, and the altitude of the aircraft may be calculated by statistical processing of the measurement results.

[0031] Thus, according to this embodiment, in addition to the effects of Embodiment 1, the altitude of the aircraft can be calculated at any location. [Examples]

[0032] This embodiment describes a method for calculating the altitude of an aircraft in an environment where the received signal strength changes significantly. Figure 9 is a diagram illustrating the method for calculating the altitude of an aircraft in this embodiment.

[0033] As a premise of this embodiment, the aircraft has in its memory device, as altitude calculation auxiliary information, received signal strength change information that records the change altitude (H4) at which the received signal strength from the radio base station changes and the amount of change. An example of received signal strength change information is shown in Figure 10. In Figure 10, received signal strength change information 7 has the change altitude at which the received signal strength changes and the amount of change for base stations A, B, and C.

[0034] In Figure 9, once the aircraft 1 reaches the area above the measurement location, it changes its altitude while receiving signals from the radio base station 2. At this time, if the received signal strength at the aircraft 1 changes significantly due to factors such as the presence of an obstruction 31 between the base station 2 and the aircraft 1, the amount of change is recorded. Based on this amount of change, the received signal strength change information 7 at that measurement point is referenced to determine the altitude at which the change occurs, and this is set as the aircraft's altitude.

[0035] Figure 11 is a processing flowchart of the altitude calculation unit showing the procedure for calculating the altitude of an aircraft in this embodiment. In Figure 11, the aircraft first moves to the received signal measurement location (step S31). Next, the aircraft uses the communication device 12 to measure the received signal strength from the base station at that location (step S32). From there, the aircraft descends (step S33), and the received signal strength is measured again at the position after the descent (step S34). The altitude calculation unit compares the received signal strength before and after this movement and checks whether it exceeds a predetermined conversion amount (step S35). If it does not exceed the limit, it descends further using that point as a reference point and repeats the same measurement and comparison. If the amount of change exceeds a predetermined value, the altitude calculation unit records the amount of change (step S36) and checks at what altitude such a change occurs by referring to the received signal strength change information 7 (step S37). Based on this, the altitude calculation unit calculates the altitude of the aircraft at that time (step S38). In this embodiment, the calculation of the aircraft's altitude is based on the premise that the received signal strength will change significantly in an environment where the received signal strength fluctuates greatly. Therefore, in step S35, it is assumed that at some altitude during the aircraft's descent, the amount of conversion of the received signal strength will exceed a predetermined value. However, assuming that the amount of change in the received signal strength does not exceed a predetermined value, in step S35, the system may perform a process to determine that altitude calculation is impossible if the aircraft's altitude falls below a predetermined level.

[0036] Thus, according to this embodiment, in addition to the effects of Examples 1 and 2, the accurate altitude of the aircraft can be calculated even in environments where the received signal strength changes significantly. [Examples]

[0037] This embodiment describes another method for calculating the altitude of an aircraft. Figure 12 is a diagram illustrating the method for calculating the altitude of an aircraft in this embodiment.

[0038] As a premise of this embodiment, the aircraft calculates altitude at a specific received signal measurement location. The aircraft also stores information in its memory regarding the correspondence between the change in received signal strength from the radio base station and the change in altitude, as altitude calculation auxiliary information at that measurement location. An example of change amount correspondence information is shown in Figure 13. In Figure 13, change amount correspondence information 8 shows the relationship between the change in altitude and the change in received signal strength for base stations A, B, and C.

[0039] In this embodiment, the relative change in altitude of the aircraft can be measured using an acceleration sensor or the like. In Figure 12, once the aircraft reaches the measurement point, it changes its altitude while receiving signals from the wireless base station. At this time, the aircraft also measures the change in altitude. The change in received signal strength when a predetermined altitude change is performed is then recorded. The altitude of the aircraft (H6) is calculated by referring to the change amount correspondence information 8 for this change in altitude (H5) and the change in received signal strength.

[0040] Figure 14 is a processing flowchart of the altitude calculation unit showing the procedure for calculating the altitude of an aircraft in this embodiment. In Figure 14, the aircraft first moves to a position where the received signal can be measured (step S41). Next, the aircraft uses the communication device 12 to measure the received signal strength from the base station at that position (step S42). From there, the aircraft descends by a predetermined amount of altitude change (H5) (step S43), and measures the received signal strength again at the position after the descent (step S44). The measurement results are recorded in the storage device 14 (step S45). The altitude calculation unit then refers the amount of change in the received signal strength before and after this movement to the change amount corresponding information 8 in the storage device 14 (step S46). If there is an altitude change corresponding to that change amount, that altitude is set as the aircraft altitude (H6) (step S47). At this time, the received signal strength may be measured for multiple base stations that can receive signals, and the altitude may be calculated based on the results. Also, if a change amount suitable for the change amount corresponding information 8 cannot be found in one measurement, it is possible to change the altitude and remeasure.

[0041] Thus, according to this embodiment, altitude is calculated using not only the change in received signal strength but also the change in altitude, resulting in a more accurate altitude calculation compared to Embodiment 1. Furthermore, since altitude can be calculated while descending, it has the advantage of being calculated during the landing sequence.

[0042] As illustrated above, the present invention utilizes existing wireless equipment used for communication to calculate altitude, enabling accurate altitude calculation without additional measuring devices. Therefore, resource utilization through the use of existing wireless equipment is possible, and the present invention contributes to waste reduction, particularly in relation to SDG 12, Responsible Consumption and Production, in order to achieve the Sustainable Development Goals (SDGs).

[0043] Furthermore, the present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Also, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of Symbols]

[0044] 1, 1a, 1b, 1c: Aircraft; 2, 2a, 2b: Radio base station (base station); 3, 3a, 3b: Takeoff / landing port; 4: Control system; 5: Correspondence information between altitude and received signal strength; 6: Base station information; 7: Receiving strength change information; 8: Change amount correspondence information; 11: Propulsion system; 12: Communication equipment; 13: Sensor group; 14: Memory device; 15: Control device; 16: Flight control unit; 17: Position calculation unit; 18: Altitude calculation unit; 30: Altitude zero position; 31: Obstruction

Claims

1. A method for calculating the altitude of an aircraft, Using the horizontal coordinate information of the aforementioned aircraft, the aircraft is moved to a specific horizontal coordinate position. The received signal strength of the radio signal is measured at the specific horizontal coordinate position. An altitude calculation method characterized by calculating the altitude of the aircraft based on the received signal strength and altitude calculation auxiliary information acquired in advance for the specific horizontal coordinate position.

2. In the method for calculating altitude according to claim 1, The aforementioned altitude calculation auxiliary information is correspondence information between altitude and received signal strength at a specific horizontal coordinate position, An altitude calculation method characterized by calculating the altitude of the aircraft from the received signal strength at a specific horizontal coordinate position and the correspondence information between altitude and received signal strength.

3. In the method for calculating altitude according to claim 1, The aforementioned altitude calculation auxiliary information is information relating the change in altitude at a specific horizontal coordinate position where the received signal strength changes, and the amount of that change. An altitude calculation method characterized by measuring the received signal strength of the radio signal in response to a change in the altitude of the aircraft at a specific horizontal coordinate position, and when the amount of change in the measured received signal strength exceeds the amount of change in the corresponding information, calculating the altitude of the aircraft from the change in the corresponding information in response to the amount of change.

4. In the method for calculating altitude according to claim 1, The aforementioned altitude calculation auxiliary information is correspondence information that shows the relationship between the amount of change in altitude and the amount of change in received signal strength at a specific horizontal coordinate position, An altitude calculation method characterized by measuring the received signal strength of the radio signal in response to a change in the altitude of the aircraft at a specific horizontal coordinate position, referring to the corresponding information based on the amount of change in the received signal strength of the radio signal in response to the measured change in altitude, and calculating the altitude of the aircraft from the altitude change in which the received signal strength changes.

5. An aircraft having a propulsion system for movement, a communication device for communicating with the outside world, a memory device, and a control device, The aforementioned storage device stores altitude calculation auxiliary information that has been previously acquired for a specific horizontal coordinate position. The control device is The propulsion system is controlled using the horizontal coordinate information of the aircraft to move the aircraft to the specific horizontal coordinate position. At the specific horizontal coordinate position, the received signal strength of the wireless signal is measured using the communication device. An aircraft characterized by calculating the altitude of the aircraft based on the received signal strength and the altitude calculation auxiliary information.

6. In the flying body according to claim 5, The aforementioned altitude calculation auxiliary information is correspondence information between altitude and received signal strength at a specific horizontal coordinate position, The control device is An aircraft characterized by calculating the altitude of the aircraft from the received signal strength at a specific horizontal coordinate position and the correspondence information between the altitude and the received signal strength.

7. In the aircraft described in Claim 5, The aforementioned altitude calculation auxiliary information is information relating the change in altitude at a specific horizontal coordinate position where the received signal strength changes, and the amount of that change. The control device is An aircraft characterized in that, at a specific horizontal coordinate position, the received signal strength of the radio signal is measured in response to a change in the altitude of the aircraft using the communication device, and when the amount of change in the measured received signal strength exceeds the amount of change in the corresponding information, the altitude of the aircraft is calculated from the change in altitude of the corresponding information in response to the amount of change.

8. In the flying vehicle according to Claim 5, The aforementioned altitude calculation auxiliary information is correspondence information that shows the relationship between the amount of change in altitude and the amount of change in received signal strength at a specific horizontal coordinate position, The control device is An aircraft characterized in that, at a specific horizontal coordinate position, the received signal strength of the radio signal in response to a change in the altitude of the aircraft is measured using the communication device, the corresponding information is referenced based on the amount of change in the received signal strength of the radio signal in response to the measured change in altitude, and the altitude of the aircraft is calculated from the change in altitude in which the received signal strength changes.

9. An altitude calculation program that causes a computer to perform the process of calculating the altitude of an aircraft, The aforementioned computer is equipped with a storage device for storing advanced calculation assistance information, The aforementioned altitude calculation program, The steps include: moving the aircraft to a specific horizontal coordinate position using the horizontal coordinate information of the aircraft; The steps include measuring the received signal strength of a radio signal at a specific horizontal coordinate position, An altitude calculation program characterized by causing the computer to perform the steps of calculating the altitude of the aircraft based on the received signal strength and the altitude calculation auxiliary information.

10. In the altitude calculation program according to claim 9, The aforementioned altitude calculation auxiliary information is correspondence information between altitude and received signal strength at a specific horizontal coordinate position, The aforementioned altitude calculation program, An altitude calculation program characterized by causing the computer to perform the steps of calculating the altitude of the aircraft from the received signal strength at the specified horizontal coordinate position and the correspondence information between the altitude and the received signal strength.

11. In the altitude calculation program according to claim 9, The aforementioned altitude calculation auxiliary information is information relating the change in altitude at a specific horizontal coordinate position where the received signal strength changes, and the amount of that change. The aforementioned altitude calculation program, An altitude calculation program characterized by causing the computer to perform the following steps: measure the received signal strength of the radio signal in response to a change in the altitude of the aircraft at a specific horizontal coordinate position; and when the amount of change in the measured received signal strength exceeds the amount of change in the corresponding information, calculate the altitude of the aircraft from the change in the corresponding information in response to the amount of change.

12. In the altitude calculation program according to claim 9, The aforementioned altitude calculation auxiliary information is correspondence information that shows the relationship between the amount of change in altitude and the amount of change in received signal strength at a specific horizontal coordinate position, The aforementioned altitude calculation program, An altitude calculation program characterized by causing the computer to perform the following steps: measure the received signal strength of the radio signal in response to a change in the altitude of the aircraft at a specific horizontal coordinate position; refer to the corresponding information based on the amount of change in the received signal strength of the radio signal in response to the measured change in altitude; and calculate the altitude of the aircraft from the change in altitude in which the received signal strength changes.

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