Atmospheric refractive index correction method for frequency modulation laser interference ranging

Abstract

The invention relates to the technical field of frequency modulation laser ranging, in particular to an atmospheric refractive index correction method for frequency modulation laser interference ranging, which can correct the change of a frequency-distance relationship caused by the change of an atmospheric refractive index, finally obtain an actual distance value and improve the accuracy of frequency modulation laser ranging. According to the invention, the temperature, humidity and atmospheric pressure of the environment are collected in real time, and the refractive index of each time of distance measurement is calculated by using the corrected Edlen formula, so that the influence of environmental factors on the light propagation speed can be accurately considered; calculation is carried out by using the relationship between the frequency after the refractive index correction and the distance, so that the distance measurement error caused by the change of the refractive index can be obviously reduced, and the overall precision of distance measurement is improved.

Description

Technical Field

[0001] The invention relates to the technical field of frequency modulated laser ranging, and in particular to a method for correcting atmospheric refractive index in frequency modulated laser interferometry ranging. Background Art

[0002] The frequency modulated laser interferometer ranging technology detects and calculates the frequency of the echo beat frequency signal generated by the distance through linear modulation of the laser light frequency and coherent detection, and then obtains the distance value of the measured target, as shown in formula (1):

[0003]

[0004] Where T is the sweep period, B is the sweep bandwidth, c is the speed of light, and f IF is the frequency of the beat signal. As mentioned above, optical distance measurement is essentially the measurement of optical path. R in the above formula is actually the optical path. With the change of atmospheric refractive index, the optical path corresponding to the same physical distance must be different. The relationship between optical path R, distance L and refractive index n is shown in formula (2). If the refractive index change is not corrected, it will be difficult to obtain an accurate distance value:

[0005] R=n×L (2)

[0006] In summary, frequency modulated laser ranging is a coherent laser ranging technology that achieves accurate distance measurement through linear modulation of laser light frequency and coherent detection. It has the advantages of low laser peak power and high measurement accuracy. In frequency modulated laser ranging technology, the distance information of the target can be obtained by measuring the frequency of the beat signal returned by the target containing distance information. Therefore, when measuring the distance, the relationship between the beat signal frequency and the measured distance must be calibrated in advance. Optical ranging is essentially a measurement of the optical path. However, when the atmospheric refractive index changes, the optical path at the same distance will also change, resulting in a large ranging error. At present, the refractive index correction methods for ranging systems are mostly concentrated in the field of interferometers. The interferometer ranging method and the frequency modulated laser ranging method are quite different in principle, and their refractive index correction methods cannot be used for frequency modulated laser ranging. Summary of the invention

[0007] In view of this, the present invention provides a method for correcting the atmospheric refractive index of frequency modulated laser interferometer ranging, which can correct the change of "frequency-distance relationship" caused by the change of atmospheric refractive index, and finally obtain the actual distance value, thereby improving the accuracy of frequency modulated laser ranging.

[0008] To achieve the above purpose, the technical solution of the present invention is as follows:

[0009] The present invention provides a refractive index correction method for a frequency modulated laser ranging system, comprising the following steps: calibrating the frequency-distance relationship of the frequency modulated laser ranging system under laboratory conditions to obtain a frequency f under a refractive index n1 condition. IF Relationship k1 with distance L;

[0010] During the ranging process, the temperature T, humidity F and atmospheric pressure P of the ranging environment are collected in real time, and the refractive index n2 at each ranging is calculated according to the modified Edlen formula;

[0011] Frequency f under refractive index n2 IF -distance L relationship is calculated to obtain the relationship between frequency and distance after refractive index correction, and the corrected distance value is obtained by multiplying it with the interference signal frequency.

[0012] The temperature T, atmospheric pressure P and humidity F of the laboratory environment are collected, and the refractive index in the laboratory environment is calculated according to the modified Edlen formula; the modified Edlen formula takes into account the influence of temperature T, atmospheric pressure P and humidity F on the atmospheric refractive index.

[0013] Among them, k2 = k1 × n1 / n2 is used to calculate the frequency f under the refractive index n2 condition. IF -distance L relationship k2 is calculated to obtain the relationship between frequency and distance after refractive index correction.

[0014] Among them, the refractive indices n1 and k1 are recorded as system parameters in the system distance measurement software; the system distance measurement software automatically reads and records the temperature T, atmospheric pressure P and humidity F data collected by the environmental sensor, as well as the calculated refractive index, and automatically performs refractive index correction and distance calculation based on these data.

[0015] Where, the frequency f under the refractive index n1 condition is IF The relationship between k1 and the distance L is as follows: L = k1 × f IF .

[0016] Beneficial effects:

[0017] 1. The present invention collects the temperature, humidity and atmospheric pressure of the environment in real time, and uses the modified Edlen formula to calculate the refractive index at each distance measurement, so as to accurately consider the influence of environmental factors on the light propagation speed; and uses the frequency-distance relationship after the refractive index correction for calculation, so as to significantly reduce the distance measurement error caused by the refractive index change, thereby improving the overall accuracy of the distance measurement.

[0018] 2. The present invention is applicable to distance measurement requirements under different environmental conditions. Whether it is a laboratory environment or a complex outdoor environment, the accuracy of distance measurement can be ensured by correcting the refractive index in real time, and the distance measurement parameters can be automatically adjusted according to environmental parameters, with strong adaptability.

[0019] 3. The present invention can record the refractive index n1 and k1 as system parameters in the system distance measurement software, and recalculate the refractive index n2 and the frequency-distance relationship k2 each time the distance is measured, so as to ensure the stability of the distance measurement system at different time points. This dynamic correction mechanism helps to reduce the distance measurement fluctuation caused by changes in environmental factors and improve the stability and reliability of the distance measurement results.

[0020] 4. The refractive index correction method of the present invention eliminates the linear error of distance measurement caused by the change of refractive index, and finally obtains the actual distance value, thereby improving the accuracy of frequency modulated laser distance measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the ranging error curve before and after the refractive index correction according to the embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0023] The present invention proposes a refractive index correction method for frequency modulated laser interferometer ranging, which improves the accuracy and environmental adaptability of frequency modulated laser ranging. In the method of the present invention, it is necessary to calculate the atmospheric refractive index. First, the environmental temperature T, atmospheric pressure P and humidity F of the environment are obtained by using an environmental sensor, and the atmospheric refractive index at the measurement time is calculated based on the corrected edlen formula. The specific implementation process of the correction method of the present invention is as follows:

[0024] First, the frequency-distance relationship of the frequency modulated laser ranging system is calibrated under laboratory conditions to obtain the frequency f under the refractive index n1 condition. IF The relationship k1 with the distance L is as follows:

[0025] L=k1×f IF (3)

[0026] Optical distance measurement is essentially the measurement of the optical path, which is the distance R and the interference frequency f. IF If there is an inherent relationship k between them, then

[0027] R=k×f IF (4)

[0028] According to the refractive index formula, we have

[0029] R=L×n1 (5)

[0030] Combining formulas (3) to (5), we have:

[0031] k=k1×n1 (6)

[0032] Similarly, under the condition of refractive index n2, we have:

[0033] k=k2×n2 (7)

[0034] According to formula (6) and (7), we get:

[0035] k2=k1×n1 / n2 (8)

[0036] According to formula (8), the corrected frequency-distance relationship under any refractive index condition can be obtained.

[0037] The present invention formulates the refractive index correction process as follows:

[0038] Step 1: Calibrate the frequency-distance relationship of the frequency modulated laser ranging system under laboratory conditions to obtain the frequency f under laboratory environmental conditions. IF -distance L relationship k1. The temperature, atmospheric pressure and humidity of the laboratory environment are collected by environmental sensors, and the refractive index n1 in the laboratory environment is calculated using the modified Edlen formula.

[0039] Step 2: Record the refractive index n1 and k1 as system parameters in the system distance measurement software.

[0040] Step 3: When the ranging system performs ranging, it uses environmental sensors to collect the temperature, humidity and atmospheric pressure of the environment in real time, and uses the modified Edlen formula to calculate the refractive index n2 for each ranging.

[0041] Step 4: Use the above formula (8) to calculate the frequency f under the refractive index n2 condition IF -distance L relationship k2 is calculated to obtain the relationship between frequency and distance after refractive index correction, and the corrected distance value is obtained by multiplying it with the interference signal frequency.

[0042] The distance measurement error before and after refractive index correction in the range of 2.7m to 30m is as follows Figure 1 As shown, it can be seen that the distance measurement linear error caused by the refractive index change is eliminated by using the refractive index correction method proposed in the present invention.

[0043] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A refractive index correction method for a frequency modulated laser ranging system, characterized in that: The following steps are involved: Under laboratory conditions, the frequency-distance relationship of the frequency modulated laser ranging system is calibrated to obtain the frequency f under the refractive index n1 condition. IF Relationship k1 with distance L; During the ranging process, the temperature T, humidity F and atmospheric pressure P of the ranging environment are collected in real time, and the refractive index n2 at each ranging is calculated according to the modified Edlen formula; Frequency f under refractive index n2 IF -distance L relationship is calculated to obtain the relationship between frequency and distance after refractive index correction, and the corrected distance value is obtained by multiplying it with the interference signal frequency.

2. The refractive index correction method according to claim 1, characterized in that: The temperature T, atmospheric pressure P and humidity F of the laboratory environment are collected, and the refractive index in the laboratory environment is calculated according to the modified Edlen formula; the modified Edlen formula considers the influence of temperature T, atmospheric pressure P and humidity F on the atmospheric refractive index.

3. The refractive index correction method according to claim 1 or 2, characterized in that: Using k2 = k1 × n1 / n2, the frequency f under the condition of refractive index n2 is IF -distance L relationship k2 is calculated to obtain the relationship between frequency and distance after refractive index correction.

4. The refractive index correction method according to claim 3, characterized in that: The refractive indices n1 and k1 are recorded as system parameters in the system distance measurement software; the system distance measurement software automatically reads and records the temperature T, atmospheric pressure P and humidity F data collected by the environmental sensor, as well as the calculated refractive index, and automatically performs refractive index correction and distance calculation based on these data.

5. The refractive index correction method according to claim 3, characterized in that: Frequency f at refractive index n1 IF The relationship between k1 and the distance L is as follows: L = k1 × f IF .

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