Navigation device, and method for determining a navigation solution

Abstract

The invention relates to a navigation device (100) comprising: an inertial measurement unit (110) which is suitable for generating inertial measurement data; and a speed measuring system (120) which is suitable for emitting at least one spatially focussed, preferably electromagnetic, wave at a predefined frequency and for receiving a frequency spectrum of the wave reflected from a reference object (200), in particular the earth's surface, wherein a Doppler shift of the predefined frequency makes it possible to determine a speed of the navigation device in the direction of radiation relative to the reference object (200). The navigation device (100) also has an estimation filter (130), in particular a Kalman filter, which is suitable for using the inertial measurement data generated by the inertial measurement unit (110) and the frequency spectrum received from the speed measurement system (120) as input data in order to determine a navigation solution of the navigation device (100) therefrom.

Description

[0001] Navigation device and method for determining a navigation solution

[0002] The present invention relates to a navigation device and a method for determining a navigation solution.

[0003] Inertial measurement units have long been used to create navigation solutions. In such inertial measurement units, measurement data from various inertial sensors, such as acceleration sensors or gyroscopes, are used to determine the movement of the measurement unit in space, i.e., to find a navigation solution for the inherently unknown three-dimensional navigation of the measurement unit in space.

[0004] The measured acceleration or angular rate values ​​represent second derivatives of the position with respect to time. Due to the integration of the measured values ​​with respect to time, which is necessary to determine the navigation solution, the navigation solution of a purely inertial measuring unit becomes increasingly inaccurate and thus less reliable over time.

[0005] It is known to circumvent this problem by comparing the inertial navigation solution with alternative position data at specific times to reduce accumulated errors. The state of the art here is to refer to global navigation satellite systems (GNSS), such as GPS, GLONASS, Galileo, and the like. These theoretically provide an exact position of the measuring unit or the vehicle carrying the measuring unit, which can be used to compensate for accumulating errors of the inertial measuring unit.

[0006] It is also known to combine GNSS signals and the measurement data from the inertial measurement unit in an estimation filter, which calculates (estimates) the next measured values ​​and / or satellite signals based on previously available data and then compares them with the actually measured data. If there is a discrepancy between the estimated and measured data, the assumed state, i.e., the navigation solution and the resulting location, is corrected.

[0007] The amount of measurement information that can be processed in the estimation filter can also be increased. For example, an additional control of altitude errors in aircraft by comparing them with the results of a barometric altitude measurement is known. Attempts to correct the inertial navigation solution independently of the availability of GNSS are also known. In addition to the combination of various sensors, such as barometers, magnetometers, odometers, and / or cameras, the use of a Doppler radar system has been proposed, which allows the system's velocity to be determined from the Doppler shift of radar waves reflected from the Earth's surface.Monitoring the speed, preferably in several independent viewing directions, allows a navigation solution independent of the inertial measurement, which can be used to control and correct the inertial navigation solution in the same way as the solution based on GNSS data.

[0008] However, the use of Doppler radar systems described above typically ignores the fact that, due to the actual physical conditions during radar measurement, the reflected signal not only exhibits a frequency shift, but also develops a frequency spectrum characteristic of the respective reflection situation. Rather, the focus has so far been on a Doppler shift, namely the main component of maximum intensity visible in the frequency spectrum. As a result, the navigation solutions calculated using Doppler radar systems do not achieve the required accuracy to compensate for, for example, the loss of a GNSS signal.

[0009] The object of the invention is therefore to provide a navigation device with an inertial measuring unit which can calculate a navigation solution using data generated by a speed measuring system, such as a Doppler radar system, which is sufficiently accurate to compensate for the temporary failure of a GNSS correction of the inertial measuring unit or to make the GNSS correction unnecessary.

[0010] This problem is solved by the subject matter of the independent claims.

[0011] In particular, a navigation device comprises an inertial measuring unit capable of generating inertial measurement data, and a speed measuring system capable of emitting at least one spatially focused, preferably electromagnetic, wave at a predetermined frequency and receiving a frequency spectrum of the wave reflected from a reference object, in particular the Earth's surface, wherein a Doppler shift of the predetermined frequency allows a speed of the navigation device in the emission direction relative to the reference object to be determined. The navigation device further comprises an estimation filter, in particular a Kalman filter, capable of using the inertial measurement data generated by the inertial measuring unit and the frequency spectrum received by the speed measuring system as input data in order to determine a navigation solution of the navigation device therefrom.

[0012] In the navigation device, inertial measurement data, such as acceleration and angular rate measurements, are input into an estimation filter in a conventional manner to generate a navigation solution. In addition, the estimation filter receives not only a single Doppler shift, i.e., a single velocity value per velocity measurement, but also the entire frequency spectrum of the reflected wave (or the equivalent intensity distribution in the time domain). This allows the estimation filter to utilize all the information contained in the reflected wave, thereby increasing the accuracy of the achievable navigation solution.

[0013] The estimation filter may be suitable for calculating an estimated received frequency spectrum for a next point in time based on the navigation solution determined on the basis of the input data received so far, comparing the frequency spectrum actually received by the speed measuring system at this next point in time with the estimated received frequency spectrum, and correcting the navigation solution based on deviations between the estimated and the actually received frequency spectrum, preferably in such a way that the deviations are reduced.

[0014] From the previously determined navigation solution, the spatial state of the navigation device can be determined. This, in turn, makes it possible to calculate the speed and direction of the speed measuring device relative to the reference object. This then results in an intensity distribution and a frequency spectrum of the reflected wave. By comparing this estimated frequency spectrum with the actually measured frequency spectrum, conclusions can be drawn about incorrect assumptions regarding the state variables and / or system equations used by the estimation filter. In particular, differences between the position and speed values ​​calculated by the estimation filter and the actual values ​​will be reflected in differences between the estimated and the actually measured frequency spectrum.Differences between estimated and actually measured frequency spectra can also occur in cases where the main component of maximum intensity visible in the frequency spectrum is the same in both spectra.

[0015] Thus, using the entire frequency spectrum provides a better indication of an erroneous navigation solution than using a single frequency component. The frequency spectrum therefore provides a reliable indication of such differences and can be used to improve the corrections to the state variables used by the estimation filter. This increases the reliability and accuracy of the navigation system.

[0016] The speed measurement system can be configured to radiate three spatially focused waves at a predetermined frequency, possibly different, onto the reference object. The main beam directions of the three spatially focused waves are linearly independent, and the estimation filter is configured to use the frequency spectra of the reflections of all three waves as input data. In this way, the motion in space can be recorded three-dimensionally using the speed measurement system. The frequency spectra obtained in this way are therefore particularly suitable for improving the navigation solution in three-dimensional space.

[0017] The navigation device can further comprise an evaluation unit capable of deriving state parameters from the received frequency spectrum that characterize the received frequency spectrum. In this case, the state parameters include, in addition to the Doppler shift and / or the resulting velocity relative to the reference object, other parameters that characterize the received frequency spectrum. The estimation filter is capable of using the state parameters as input data for determining the navigation solution.

[0018] Instead of using the entire frequency spectrum, it may be sufficient to characterize it using a set of parameters and enter these parameters into the estimation filter. For example, the Doppler shift of the emitted wave can be determined in a known manner from the main component of the frequency spectrum, i.e. the peak with the greatest intensity. In addition, other characteristic quantities are determined, such as the position of other peaks in the spectrum, the parameters of Gaussian fits at various peaks, the intensity distribution in the spectrum, the linewidth of various reflections, and the like. By selecting meaningful parameters, the determination of the navigation solution in the estimation filter can be made simpler and therefore faster. Since other parameters of the spectrum are taken into account in addition to the Doppler shift, the accuracy and reliability are increased compared to known systems.

[0019] The navigation device may also be capable of receiving signals from a global navigation satellite system (GNSS), and the estimation filter may be capable of using the GNSS signals as input data for determining the navigation solution. In this case, in addition to the inertial measurement data and velocity measurement data, GNSS position data is also available to support the navigation solution. This further increases the accuracy and reliability of the navigation solution.

[0020] The estimation filter can be used to determine the navigation solution based on the inertial measurement data and the GNSS signals when the GNSS signals are received, and based on the inertial measurement data and the received frequency spectrum when no GNSS signals can be received. The speed measurement data then serves to bridge a temporary failure of the GNSS signal. In this way, the inertial measurement data can be used to calculate a reliable navigation solution even when no GNSS position data is available, since the error accumulation can be kept within a sufficiently low range by relying on the frequency data.

[0021] The speed measurement system can be a radar system that emits electromagnetic waves in the radio range, i.e., a Doppler radar system. However, the speed measurement system can also be a lidar system that emits laser light. The wavelength can depend on the application and can be, for example, in the UV, visible, or IR range. However, in principle, speed measurement can be performed with any device that emits waves whose reflection can be measured. In addition to electromagnetic waves, and especially radar waves, to which this description primarily refers, sound waves can also be used.

[0022] An aircraft, in particular an autonomously flying aircraft, can be equipped with a navigation device as described above, wherein the aircraft is suitable for control based on the navigation solution generated by the navigation device. The aircraft can be suitable for use in urban airspace. Due to its high reliability and accuracy, the navigation device enables safer control of an aircraft, either by providing reliable information to a pilot in poor or limited visibility or by fully autonomous control of the aircraft based on the navigation solution.

[0023] A method for determining a navigation solution by means of a navigation device as described above comprises: generating inertial measurement data by the inertial measuring unit; emitting at least one spatially focused wave with a predetermined frequency by the speed measuring system; receiving a frequency spectrum of the wave reflected from a reference object, in particular the Earth's surface, by the speed measuring system, wherein a Doppler shift of the predetermined frequency allows a speed of the navigation device in the emission direction relative to the reference object to be determined; determining a navigation solution of the navigation device by the estimation filter by using the inertial measurement data generated by the inertial measuring unit and the frequency spectrum received from the speed measuring system as input data of the estimation filter.

[0024] The invention is described in detail below with reference to the figures. The following description is purely exemplary and should not be construed as limiting. The present invention is defined solely by the subject matter of the claims. It shows:

[0025] Fig. 1 is a schematic representation of a navigation device;

[0026] Fig. 2 shows a schematic representation of frequency spectra; Fig. 3 shows a schematic flow diagram of a calculation of navigation solutions;

[0027] Fig. 4 is a schematic representation of an aircraft with a navigation device;

[0028] Fig. 5 is a schematic representation of a parameterization of a frequency spectrum;

[0029] Fig. 6 is a further schematic representation of a navigation device; and

[0030] Fig. 7 is a schematic flow diagram of a method for determining a navigation solution.

[0031] Figure 1 schematically shows a navigation device 100 moving relative to a reference object 200. The navigation device 100 is attached, for example, to a vehicle, ie, an aircraft, land vehicle, or watercraft. The navigation device 100 is capable of determining its previous movements through space from measurement data, ie, the navigation device 100 determines a navigation solution based on its previous movements or the movements of the vehicle to which it is attached.

[0032] For this purpose, the navigation device 100 has an inertial measuring unit 110, a speed measuring system 120 and an estimation filter 130, which is optionally part of an evaluation unit 140 or is in data exchange with such an evaluation unit 140.

[0033] The inertial measuring unit 110 is suitable for generating inertial measurement data, i.e., measurement data caused by the inertia of the mass of the navigation device or its components with respect to movements in space. In particular, the inertial measuring unit 110 is suitable for measuring accelerations along at least one of the three spatial directions and angular rates of rotations about at least one of the three spatial axes. The inertial measuring unit 110 can be designed in a known manner, e.g., as a micro-electro-mechanical acceleration / angular rate sensor, a fiber gyroscope, or the like. The decisive factor here is that the inertial measuring unit 110 records measurement data that, in principle, allow the movements of the navigation device 100 in space to be calculated back, i.e., that allow a—albeit possibly inaccurate—navigation solution to be determined.

[0034] The speed measurement system 120 is capable of emitting at least one spatially focused, preferably electromagnetic, wave R at a predetermined frequency and receiving a frequency spectrum of the wave reflected from the reference object 200, preferably the Earth's surface. A Doppler shift of the predetermined frequency can then be used to determine the speed of the navigation device in the direction of emission relative to the reference object 200.

[0035] The speed measuring system 120 is thus suitable, in a manner known per se, for utilizing the Doppler effect to determine the relative movement between the navigation device 100 and the reference object 200 from the frequency of a reflected signal. The reference object 200 can be considered stationary with respect to the speeds of the navigation device. For example, the reference object 200 can be the earth's surface or an elevation on the earth's surface, such as a mountain, a building, or a tower, if the navigation device 100 is moving outdoors. However, the reference object 200 can also be a part of a building or a piece of furniture if the movement takes place inside a building or the like. In principle, the reference object 200 can also move itself.However, the navigation device 100 must then be provided with the navigation solution of the reference object 200 in order to determine its speed from the relative speed to the reference object.

[0036] The nature of the wave emitted by the speed measuring system 120 is, in principle, arbitrary and can be adapted to the intended use of the navigation device 100, as long as an emitted signal of a predetermined frequency makes it possible to determine a relative speed relative to the reflection source from the reflected signal via the Doppler effect. In the following, it is assumed that the speed measuring system 120 is a Doppler radar system that emits radar waves of a specific frequency. Lidar systems that emit a laser beam and capture the reflection of this beam are also conceivable. Sound waves can also be used.

[0037] However, the speed measuring system 120 does not measure a single reflection frequency corresponding to the emission frequency, shifted according to the Doppler effect. Rather, the emitted wave R is reflected at different angles by different objects. This results in different Doppler shifts for the different reflection angles, which are reflected as frequency components in the overall signal. The shape of the antenna pattern, the different distances to the reference object within the radar beam, and other effects can contribute to this. The frequency spectrum F of these various signals is generated from the temporal progression of the reflection intensity in the usual way, e.g., by a Fourier transform, such as a discrete Fourier transform or a fast Fourier transform.

[0038] An example of such a frequency spectrum is shown in Fig. 2. The upper image of Fig. 2 shows a frequency spectrum F in which the Doppler shift f is plotted against the intensity. Although the actual frequency shift is clearly visible at approximately 5 kHz, the frequency spectrum F also has other, clearly visible components. The lower part of Fig. 2 shows various components of the spectrum F that have been normalized to the same maximum value. In addition to the actual Doppler detection D, the frequency spectrum F also contains a component E that can be attributed to the distance and a component res that can be attributed to the radar cross section (res). The frequency spectrum F therefore contains a wealth of other information in addition to pure speed information.

[0039] For this reason, in the navigation device 100, not only the frequency shift of the transmission frequency or the corresponding speed information, but the entire frequency spectrum is made available to the estimation filter 130. The estimation filter 130, which may in particular be a Kalman filter, uses the inertial measurement data generated by the inertial measurement unit 110 and the frequency spectrum received by the speed measurement system 120 as input data to determine a navigation solution for the navigation device 100. The estimation filter 130 essentially operates in a conventional manner, i.e., based on known state values, states for the next period are estimated, which can then be compared with actually measured values.From this comparison, changes are made to the system state that bring the estimate into better agreement with the measured values, and the process is iterated.

[0040] This is illustrated by way of example in the flowchart of Fig. 3. After system initialization at S110, a navigation solution for the current period is calculated at S120, which specifies the movement of the navigation device 100, preferably in three-dimensional space. Based on this, the states for the next period are estimated at S130. These allow, among other things, the calculation of an expected frequency spectrum. At S140, a query is made as to whether a new frequency spectrum can be provided by the speed measuring system. If this is not the case (N), the method continues with step S120. If a new frequency spectrum is available (Y), the estimated spectrum is compared with the measured spectrum at S150, and the result of the comparison at S120 is incorporated into the calculation of the navigation solution.

[0041] The estimation filter 130 is therefore suitable for calculating an estimated received frequency spectrum for a next point in time based on the navigation solution determined on the basis of the input data received so far, for comparing the frequency spectrum F actually received by the speed measuring system at this point in time with the estimated received frequency spectrum, and for correcting the navigation solution based on deviations between the estimated and the actually received frequency spectrum, preferably in such a way that the deviations are reduced.

[0042] Processing the entire frequency spectrum F instead of just the strongest frequency component results in a parameter gain that enables a more precise verification of the states propagated based on the system equations. This increases the accuracy and reliability of the calculated navigation solution. Preferably, the speed measurement system 120 is capable of radiating three spatially focused waves with a possibly different, predetermined frequency onto the reference object 200, wherein the main beam directions of the three spatially focused waves are linearly independent. Such an arrangement is shown as an example in Fig. 4.

[0043] Here, an aircraft 300 carries the navigation device 100, which is equipped with a speed measurement system 120 configured as a Doppler radar system. The aircraft 300 can be a conventional aircraft such as an airplane or a helicopter. However, the aircraft 300 can also be an autonomously or semi-autonomously flying aircraft that navigates predominantly or exclusively using the navigation solution determined by the navigation device 100. In particular, the aircraft 300 can be suitable for use in urban areas.

[0044] Doppler radar, for example, transmits four radar waves R1, R2, R3, and R4 toward the Earth's surface, which are reflected from it. The radar waves R1, R2, R3, and R4 are preferably transmitted and received at separate times, are differently encoded, modulated, or have frequencies that differ so much that the received reflections can be assigned to the respective waves. Alternatively or additionally, the total spectrum of all reflections can also be further processed.

[0045] Of the four radar waves R1, R2, R3, and R4, three are linearly independent. Ideally, each triplet of radar waves is linearly independent. This allows movements in all three spatial directions to be read from the radar waves. It goes without saying that exactly three waves can be used instead of four, and that the use of more than four is also possible.

[0046] The estimation filter 130 uses the frequency spectra of the reflections of all electromagnetic waves as input data. This further expands the parameter space for the estimation filter 130, thereby further improving reliability and accuracy. In particular, by estimating and comparing a plurality of frequency spectra or their superposition(s), errors in the estimated states used can be more easily identified in the estimation filter 130, thus bringing the navigation solution into line with the actual movement. As shown in Fig. 1, the navigation device 100 can optionally have an evaluation unit 140 suitable for deriving state parameters from received frequency spectra that characterize the received frequency spectrum. The evaluation unit 140 can be a hardware or software component.For example, the evaluation unit 140 may be a computer, a processor, a circuit, or a program executed on one of these components.

[0047] The state parameters identified by the evaluation unit 140 include, in addition to the Doppler shift and / or the velocity derived therefrom relative to the reference object 200, further parameters characterizing the received frequency spectrum. The state parameters thus represent a characterization of the frequency spectrum F that lies between the full spectrum, i.e., the full information, and the velocity derived therefrom, i.e., the minimum information. In this way, fixed operating parameters can be provided to the estimation filter 130. This can reduce the computational effort for estimation and comparison compared to the full spectrum. On the other hand, the estimation filter 130 receives more information than the pure velocity information, which can improve the accuracy and reliability of the navigation solution.

[0048] An example of such a parameterization is shown in Fig. 2, where the entire spectrum was decomposed into individual components that parameterize the spectrum. Another example is shown in Fig. 5, in which two Gaussian curves were fitted to the spectrum F. Curve P1, with its mean and standard deviation, represents a parameterization of the Doppler shift. Curve P2, with its mean and standard deviation, represents a parameterization of the majority of the other causes of the spectrum shape. In this way, one can attempt to describe the complete spectrum essentially with a set of state parameters.

[0049] The estimation filter 130 is suitable for using these state parameters as input data for determining the navigation solution. This means that the entire spectra are no longer estimated and compared, but only the state parameters of the spectra. This reduces the computational effort and, due to the fact that a majority of parameters were derived from the frequency spectrum, still leads to a reliable and accurate solution.

[0050] As shown in Fig. 6, the navigation device 100 can also be suitable for receiving signals from a global navigation satellite system (GNSS) 400, e.g., via a communication unit 150. These GNSS signals can also be fed to the estimation filter 130 in a manner known per se, which then uses them to determine the navigation solution. This makes the navigation solution more accurate and reliable, since in addition to acceleration data (inertial measurement unit 110) and speed data (speed measurement system 120), position data (GNSS 400) is also available. This position data can be estimated in a manner known per se and compared with the actually measured position in order to correct the system equation or the navigation solution and align it with the actual movement.

[0051] The estimation filter 130 may be suitable for determining the navigation solution based on the inertial measurement data and the GNSS signals when the GNSS signals are received. This generates a reliable and accurate navigation solution according to typical requirements. However, if no GNSS signals can be received during a certain period of time, the estimation filter 130 determines the navigation solution based on the inertial measurement data and the received frequency spectrum.

[0052] This means that the frequency data is used to bridge a period in which GNSS reception is not possible. In this way, the navigation solution can be supported by measurement data that differs from the inertial measurement data and can therefore be kept within an accuracy range that meets typical requirements. In normal operation, i.e. when all measurement data (inertial measurement, speed determination, position determination) is available, a highly accurate and reliable navigation solution can be determined. If certain measurement data fail, such as the GNSS signal, the time until the quality of the navigation solution is no longer acceptable is extended, compared to conventional operation. This time is further increased by using information from the received frequency spectrum. This increases the reliability of the overall system, as GNSS failures can be compensated for.A method for determining a navigation solution using a navigation device 100 corresponding to the above description is shown schematically in Fig. 7. Here, at S210, inertial measurement data is generated by the inertial measurement unit 110.

[0053] At S220, the speed measuring system 120 emits at least one spatially focused, preferably electromagnetic, wave with a predetermined frequency.

[0054] At S230, a frequency spectrum of the wave reflected from a reference object 200, in particular the earth's surface, is received by the speed measuring system 120, wherein a Doppler shift of the predetermined frequency allows a speed of the navigation device 100 in the radiation direction relative to the reference object 200 to be determined.

[0055] At S240, a navigation solution of the navigation device 100 is determined by the estimation filter 130 by using the inertial measurement data generated by the inertial measurement unit 110 and the frequency spectrum received from the speed measurement system 120 as input data of the estimation filter 130.

[0056] In this way, a navigation solution can be generated in an accurate and reliable manner.

Claims

Claims 1. A navigation device (100), comprising: an inertial measuring unit (110) suitable for generating inertial measurement data; a speed measuring system (120) suitable for emitting at least one spatially focused, preferably electromagnetic, wave at a predetermined frequency and for receiving a frequency spectrum of the wave reflected from a reference object (200), in particular the Earth's surface, wherein a Doppler shift of the predetermined frequency allows a speed of the navigation device in the emission direction relative to the reference object (200) to be determined; and an estimation filter (130), in particular a Kalman filter, suitable for using the inertial measurement data generated by the inertial measuring unit (110) and the frequency spectrum received by the speed measuring system (120) as input data in order to determine a navigation solution of the navigation device (100) therefrom.

2. Navigation device (100) according to claim 1, wherein the estimation filter (130) is suitable for calculating an estimated received frequency spectrum for a next point in time on the basis of the navigation solution determined on the basis of the input data received so far, for comparing the frequency spectrum actually received by the speed measuring system at this next point in time with the estimated received frequency spectrum and for correcting the navigation solution based on deviations between the estimated and the actually received frequency spectrum, preferably in such a way that the deviations are reduced.

3. Navigation device (100) according to one of the preceding claims, wherein the speed measuring system (120) is adapted to radiate three spatially focused waves with a possibly different, predetermined frequency onto the reference object (200); the main beam directions of the three spatially focused waves are linearly independent; and the estimation filter (130) is adapted to use the frequency spectra of the reflections of all three waves as input data.

4. Navigation device (100) according to one of the preceding claims, further comprising: an evaluation unit (140) adapted to derive state parameters from the received frequency spectrum that characterize the received frequency spectrum; wherein the state parameters comprise, in addition to the Doppler shift and / or the velocity derived therefrom relative to the reference object, further parameters that characterize the received frequency spectrum; and the estimation filter (130) is adapted to use the state parameters as input data for determining the navigation solution.

5. Navigation device (100) according to one of the preceding claims; wherein the navigation device (100) is adapted to receive signals from a global navigation satellite system, GNSS, (400); and the estimation filter (130) is adapted to use the GNSS signals as input data for determining the navigation solution.

6. The navigation device (100) according to claim 5, wherein the estimation filter (130) is adapted to determine the navigation solution based on the inertial measurement data and the GNSS signals when the GNSS signals are received; and the estimation filter (130) is adapted to determine the navigation solution based on the inertial measurement data and the received frequency spectrum when no GNSS signals can be received.

7. Navigation device (100) according to one of the preceding claims, wherein the speed measuring system (120) is a radar system that emits electromagnetic waves in the radio range or a lidar system that emits laser light.

8. Aircraft (300), in particular autonomously flying aircraft (400), with a navigation device (100) according to one of the preceding claims, wherein the aircraft (300) is suitable for control based on the navigation solution.

9. A method for determining a navigation solution using a navigation device (100) according to claim 1, comprising: Generating inertial measurement data by the inertial measurement unit (110); Emitting at least one spatially focused, preferably electromagnetic, wave with a predetermined frequency by the speed measuring system (120); Receiving a frequency spectrum of the wave reflected from a reference object (200), in particular the earth's surface, by the speed measuring system (120), wherein a Doppler shift of the predetermined frequency allows a speed of the navigation device (100) in the radiation direction relative to the reference object (200) to be determined; Determining a navigation solution of the navigation device (100) by the estimation filter (130) by using the inertial measurement data generated by the inertial measurement unit (110) and the frequency spectrum received from the speed measurement system (120) as input data of the estimation filter (130).

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