Millimeter wave imaging limit detection distance calculation method and system

Abstract

The invention discloses a millimeter wave imaging limit detection distance calculation method and system, and belongs to the technical field of millimeter wave remote sensing and detection. The problem that the millimeter wave imaging limit detection distance cannot be determined in the existing complex detection environment is solved. A brightness temperature difference formula of a target object at a limit distance in a current observation scene is established; an object with a known distance in the limit detection range of the millimeter wave imaging system is selected for detection, and a short-distance object brightness temperature difference formula is established; carrying out short-distance actual measurement by adopting a millimeter wave imaging system of which the limit distance is to be determined, and substituting a short-distance brightness temperature difference formula into a limit distance brightness temperature difference formula to obtain a relational expression between the brightness temperature difference and the detection distance d; adjusting the value of the detection distance d in the relational expression of the brightness temperature difference and the detection distance d according to the fixed step length until the brightness temperature difference is smaller than or equal to the brightness temperature sensitivity value of the millimeter wave imaging system, and obtaining the limit detection distance of the millimeter wave imaging system. The method is used for determining the limit detection distance of the millimeter wave imaging system.

Description

Technical Field

[0001] The invention belongs to the technical field of millimeter wave remote sensing and detection. Background Art

[0002] The millimeter wave imaging system achieves remote sensing and detection of the target objects and scenes by receiving the spontaneous or reflected millimeter wave thermal radiation of the target material. The short wavelength of millimeter waves gives it unique advantages in imaging resolution and penetration. In different scenarios, this technology has the advantages of all-day and all-weather operation, strong concealment, little interference from clutter, and low power consumption. Therefore, it has been widely used in important fields such as human security inspection, sea surface target detection, medical imaging, atmospheric remote sensing, industrial detection, and military detection.

[0003] The detection distance of the millimeter wave imaging system refers to the maximum distance at which the system can effectively detect the target object and generate a clear image. Its numerical value is affected by multiple factors, including transmission power, receiving sensitivity, antenna gain, atmospheric attenuation and environmental conditions. Under ideal conditions, the detection distance of millimeter wave imaging can reach hundreds of meters or even thousands of meters. In complex actual scenes, shorter detection distances can be measured through multiple experiments, but in applications such as sea surface target detection, the detection distance is required to be far, and the conditions of the detection scene are relatively complex. It is difficult to measure real data in actual scenes. In the simulation test stage, most of the data are obtained by theoretical derivation and empirical formulas. In order to make the results more realistic and accurate, the close-range measured detection data in the same scene is linked to the long-range detection capability evaluation. How to accurately determine the limit detection distance in a complex environment is a difficult problem today. The existing methods usually use multiple tests to achieve it, but this method has the problems of large computational complexity and low efficiency of repeated tests. In addition, multiple tests are not suitable for some complex environments. Summary of the invention

[0004] The present invention aims to solve the problem that the limit detection distance of millimeter wave imaging cannot be determined under the existing complex detection environment, and now provides a method and system for calculating the limit detection distance of millimeter wave imaging.

[0005] The method for calculating the limit detection distance of millimeter wave imaging of the present invention comprises:

[0006] Step 1: Establish a formula for the brightness temperature difference at the target object at the limit detection distance under the current observation scene;

[0007] Step 2: Select an object with a known distance within the limit detection range of the millimeter wave imaging system for detection, and establish a formula for the brightness temperature difference of a close-range object;

[0008] Step 3: Use the millimeter wave imaging system with the limit distance to be determined to perform actual close-range measurement, substitute the close-range brightness temperature difference formula into the limit detection distance brightness temperature difference formula, and obtain the relationship between the brightness temperature difference and the detection distance d;

[0009] Step 4: Adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step size until the brightness temperature difference is less than or equal to the brightness temperature sensitivity value of the millimeter wave imaging system, and obtain the limit detection distance of the millimeter wave imaging system.

[0010] Furthermore, in the present invention, in step 1, the formula for the brightness temperature difference at the limit distance in the current observation scene is:

[0011]

[0012] Among them, θ 1 and θ 2 are the 3dB beamwidths of the E and H planes of the detector antenna, △T is the brightness temperature difference of the object received at the detector, and T B-obj0 To detect the original brightness temperature of the object, T B-bac0 is the background original brightness temperature of the detected object, α is the atmospheric radiation attenuation rate between the detected object and the detector, S A is the projected area of ​​the object, and d is the distance from the object to the detector.

[0013] Furthermore, in the present invention, in step 2, the brightness temperature difference formula of the object at a close distance includes the brightness temperature difference formula when the detector antenna beam projection area is smaller than the target object and the brightness temperature difference formula when the beam projection area is greater than or equal to the target object.

[0014] In this embodiment, the two cases are the brightness temperature difference when the projection area of ​​the detector antenna beam is smaller than the target object and the brightness temperature difference when the projection area of ​​the beam is greater than or equal to the target object. According to the actual measurement conditions, any one of the cases is selected for measurement.

[0015] Furthermore, in the present invention, the original brightness temperature difference formula of the object when the beam projection area is smaller than the target object is:

[0016] T B-bac0 -T B-obj0 =ΔT 1 α 1

[0017] Among them, α 1 is the atmospheric attenuation rate from the object to the detector when the beam projection area is smaller than the target object area, △T 1 It is the measured brightness temperature difference between the target and the background at the detector when the beam area is smaller than the target object area.

[0018] Furthermore, in the present invention, the original brightness temperature difference formula of the object when the beam projection area is greater than or equal to the target object is:

[0019] T B-bac0 -T B-obj0 =ΔT 2 α 2 ·[π·d 0 2 tan(θ 1 / 2)·tan(θ 2 / 2)] / S A

[0020] Among them, α 2 is the atmospheric attenuation rate from the object to the detector when the beam projection area is larger than the target object area, d 0 is the actual measurement distance at close range, △T 2 is the brightness temperature difference when the beam diameter is larger than the target object diameter.

[0021] Furthermore, in the present invention, in step 3, the relationship between the brightness temperature difference and the detection distance d includes:

[0022] When the beam projection area is smaller than the target object projection area, the relationship is:

[0023]

[0024] When the beam projection area is larger than the target object projection area, the relationship is:

[0025]

[0026] Furthermore, in the present invention, in step 4, the MPM atmospheric model is used to adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step size until the brightness temperature difference ΔT is less than or equal to the brightness temperature sensitivity value ΔT of the millimeter wave imaging system. sys The detection distance d obtained is the limit detection distance of the millimeter wave imaging system.

[0027] Millimeter wave imaging limit detection distance estimation system, including:

[0028] The module for establishing the formula of the brightness temperature difference at the extreme distance is used to establish the formula of the brightness temperature difference at the extreme distance under the current observation scene;

[0029] A module for establishing a close-range brightness temperature difference formula is used to select two objects with known distances within the limit detection range of the millimeter wave imaging system for detection, and to establish a close-range brightness temperature difference formula using detection parameters;

[0030] A module for establishing the relationship between brightness temperature difference and detection distance, which is used to substitute the brightness temperature difference formula of the short distance into the brightness temperature difference formula of the extreme distance to obtain the relationship between the brightness temperature difference and the detection distance d;

[0031] The limit detection distance calculation module uses the MPM atmospheric model to adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step size until the brightness temperature difference is less than the temperature-brightness difference sensitivity value of the millimeter wave imaging system, thereby obtaining the limit detection distance of the millimeter wave imaging system.

[0032] By utilizing the brightness temperature data measured at close range, the present invention avoids the need for repeated complex inter-surface ray tracing calculations required by traditional methods while ensuring the accuracy of calculations. Instead, it only needs to calculate the atmospheric attenuation rate between the object and the detector. Since inter-surface ray tracing iterations are completely avoided, the amount of calculation is reduced by three orders of magnitude compared to traditional methods, from several hours to tens of seconds. This effectively improves the accuracy of determining the detection distance limit of millimeter-wave imaging in complex detection environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of the method of the present invention;

[0034] Figure 2 is a schematic diagram of a millimeter wave imaging observation scene involved in an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of a millimeter wave imaging model when the beam is smaller than the target object at a close distance involved in an embodiment of the present invention;

[0036] Figure 4 A schematic diagram of a millimeter wave imaging model when the beam is larger than the target object at a close distance involved in an embodiment of the present invention;

[0037] Figure 5 A diagram for calculating the area of ​​a ship in an embodiment of the present invention;

[0038] Figure 6 This is a close distance 2km disembarkation-sea surface brightness temperature map in an embodiment of the present invention;

[0039] Figure 7 is an apparent brightness temperature diagram of a critical distance antenna in an embodiment of the present invention;

[0040] Figure 8 A critical distance noise map in an embodiment of the present invention;

[0041] Fig. 9 is a brightness temperature variation curve at a critical distance in an embodiment of the present invention;

[0042] Fig.10 The figure is a functional block diagram of the system of the present invention. DETAILED DESCRIPTION

[0043] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0044] Specific implementation method 1: refer to Figure 1 Specifically describing this embodiment, the method for calculating the limit detection distance of millimeter wave imaging described in this embodiment includes:

[0045] Step 1: Establish a formula for the brightness temperature difference at the target object at the limit detection distance under the current observation scene;

[0046] Step 2: Select an object with a known distance within the limit detection range of the millimeter wave imaging system for detection, and establish a formula for the brightness temperature difference of a close-range object;

[0047] Step 3: Use the millimeter wave imaging system with the limit distance to be determined to perform actual close-range measurement, substitute the close-range brightness temperature difference formula into the limit detection distance brightness temperature difference formula, and obtain the relationship between the brightness temperature difference and the detection distance d;

[0048] Step 4: Adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step size until the brightness temperature difference is less than or equal to the brightness temperature sensitivity value of the millimeter wave imaging system, and obtain the limit detection distance of the millimeter wave imaging system.

[0049] The present invention can quickly deduce the system's limit distance through iteration through brightness temperature data at close range, which not only ensures the imaging quality, but also provides a scientific basis for system design, promotes technical standardization, enhances the comparability between different systems, and promotes technical exchanges and cooperation within the industry. In addition, detection distance evaluation also helps to reasonably configure components during system integration and reduce costs. At the same time, it predicts the performance of the system under different environmental conditions and provides optimal solutions for diversified application scenarios, thereby promoting the widespread application and continuous progress of millimeter wave imaging technology in security, traffic monitoring, medical imaging and other fields. The close distance described in the present invention is an object that can be detected by millimeter wave imaging in actual measurement, and its detection distance is determined according to the actual detection environment. The close-range detection data is used to obtain the brightness temperature difference formula when the projection area of ​​the detector antenna beam is less than the target object and the brightness temperature difference formula when the projection area of ​​the beam is greater than or equal to the target object.

[0050] Furthermore, in the present invention, in step 1, the formula for the brightness temperature difference at the limit distance in the current observation scene is:

[0051]

[0052] Among them, θ 1 and θ 2 are the 3dB beamwidths of the E and H planes of the detector antenna, △T is the brightness temperature difference of the object received at the detector, and T B-obj0 To detect the original brightness temperature of the object, T B-bac0 is the background original brightness temperature of the detected object, α is the atmospheric radiation attenuation rate between the detected object and the detector, S A is the projected area of ​​the object, and d is the distance from the object to the detector.

[0053] Furthermore, in the present invention, in step 2, the brightness temperature difference formula of the object at a close distance includes the brightness temperature difference formula when the detector antenna beam projection area is smaller than the target object and the brightness temperature difference formula when the beam projection area is greater than or equal to the target object.

[0054] In this embodiment, there are two cases: the brightness temperature difference formula when the detector antenna beam projection area is smaller than the target object and the brightness temperature difference formula when the beam projection area is greater than or equal to the target object. According to the actual measurement conditions, any one of the cases is selected for measurement.

[0055] Furthermore, in the present invention, the original brightness temperature difference formula of the object when the beam projection area is smaller than the target object is:

[0056] T B-bac0 -T B-obj0 =ΔT 1 α 1

[0057] Among them, α 1 is the atmospheric attenuation rate from the object to the detector when the beam projection area is smaller than the target object area, △T 1 It is the measured brightness temperature difference between the target and the background at the detector when the beam area is smaller than the target object area.

[0058] Furthermore, in the present invention, the original brightness temperature difference formula of the object when the beam projection area is greater than or equal to the target object is:

[0059] T B-bac0 -T B-obj0 =ΔT 2 α 2 ·[π·d 0 2 tan(θ 1 / 2)·tan(θ 2 / 2)] / S A

[0060] Among them, α 2is the atmospheric attenuation rate from the object to the detector when the beam projection area is larger than the target object area, d 0 is the actual measurement distance at close range, △T 2 is the brightness temperature difference when the beam diameter is larger than the target object diameter.

[0061] Furthermore, in the present invention, in step 3, the relationship between the brightness temperature difference and the detection distance d includes:

[0062] When the beam diameter is smaller than the target object diameter, the relationship is:

[0063]

[0064] When the beam diameter is larger than the target object diameter, the relationship is:

[0065]

[0066] Furthermore, in the present invention, in step 4, the MPM atmospheric model is used to adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step size until the brightness temperature difference ΔT is less than or equal to the brightness temperature sensitivity value ΔT of the millimeter wave imaging system. sys , the detection distance d obtained at this time is the limit detection distance of the millimeter wave imaging system.

[0067] Millimeter wave imaging limit detection distance estimation system, including:

[0068] The limit distance brightness temperature difference formula establishment module 1 is used to establish the limit distance brightness temperature difference formula under the current observation scene;

[0069] A close-range brightness temperature difference formula establishment module 2 is used to select two objects with known distances within the limit detection range of the millimeter wave imaging system for detection, and establish a close-range brightness temperature difference formula using detection parameters;

[0070] A module 3 for establishing the relationship between brightness temperature difference and detection distance is used to substitute the brightness temperature difference formula of the short distance into the brightness temperature difference formula of the extreme distance to obtain the relationship between the brightness temperature difference and the detection distance d;

[0071] The limit detection distance calculation module 4 uses the MPM atmospheric model to adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step size until the brightness temperature difference is less than the temperature-brightness difference sensitivity value of the millimeter wave imaging system, thereby obtaining the limit detection distance of the millimeter wave imaging system.

[0072] In an exemplary embodiment of the present invention, a millimeter wave imaging detection distance extrapolation equivalent method is provided, which can apply the brightness temperature difference measured at a close distance to the MPM atmospheric model through computer iteration to obtain the farthest detection distance, eliminating a large number of image simulation processes and greatly reducing simulation time. Please refer to Figure 2 In this exemplary embodiment, the millimeter wave imaging equivalent extrapolation method comprises the following steps:

[0073] Step S1: Obtain the area of ​​the observed target object and the brightness temperature calculation formula under the long-distance observation scene. The model is simplified as follows: Figure 2 Considering the background weighting and atmospheric radiation, the relationship between the original brightness temperature difference at the target object and the measured brightness temperature difference at the radiometer is obtained.

[0074] Step S2: The formula for obtaining the brightness temperature difference at close distance is discussed in two cases, and the original brightness temperature difference at the target is obtained from the brightness temperature difference measured at close distance.

[0075] Step S3: Substitute the original brightness temperature difference into the brightness temperature difference calculation formula of the observed scene to obtain the relationship between the brightness temperature difference and the detection distance d.

[0076] Step S4: Take the initial value of d as the initial detection distance of the short distance, and continuously increase d to iterate the value of ΔT, and compare it with the sensitivity K. As d increases, ΔT decreases. When the value of ΔT is less than the sensitivity K, the corresponding d is the farthest detection distance.

[0077] The above method can quickly predict and calculate the farthest distance of millimeter wave imaging detection. Compared with the method of generating simulated images to predict the farthest detection distance, this method uses the brightness temperature difference within the short distance within the detection range of the system to bring in the brightness temperature difference at the extreme distance, and calculates the brightness temperature difference value instead of image generation, which significantly reduces the calculation amount and calculation time of image generation pixels and improves the prediction efficiency.

[0078] Embodiments for detecting ships in combination with specific sea surface scenes;

[0079] The cargo ship on the sea surface is taken as the detection target object, the infinite calm sea surface is taken as the detection background, and the initial imaging distance is 2 kilometers. Firstly, the relationship between the original brightness temperature difference at the target object and the measured brightness temperature difference at the radiometer is obtained.

[0080] Then, the projected area of ​​the ship on the sea surface was measured to be 1.5024e+04m 2 At a detection distance of 2 km, the beam projection area is 3.798e+06m 2 , which is smaller than the projected area of ​​the target object, so the formula for the original brightness temperature difference between the ship and the sea surface at a detection distance of 2 kilometers is T B-bac0 -T B-obj0 =ΔT 1 α 1 , the atmospheric attenuation coefficient α is calculated according to the atmospheric MPM model 1 The target brightness temperature of the ship on the sea surface is calculated by using the ray tracing algorithm. The target brightness temperature prediction parameters are shown in Table 1. The ship-sea surface brightness temperature prediction results are shown in Table 1. Figure 6 shown.

[0081] Table 1:

[0082]

[0083]

[0084] According to the budget results, the original brightness temperature difference is T B-bac0 -T B-obj0 =61.7721, ΔT=47.4670, which is greater than the sensitivity of 0.3. According to step S3, the formula for the brightness temperature difference at any distance d is:

[0085] The detection distance d increases from the initial value of 2km, and increases by 1km each time. The value of △T corresponding to d is calculated by the formula of brightness temperature difference at close range, and compared with the sensitivity K=0.3. When △T is greater than K, d is increased by 1, and the new △T value is calculated. As d increases, △T decreases continuously. When d is 154km, △T is 0.30042; when d is 155km, △T is 0.2966, which is less than 0.3. Therefore, 154km is the critical distance, that is, the farthest distance detected.

[0086] Figure 7 This is the antenna apparent brightness temperature map at the critical distance (154 km) in the embodiment of the present invention. It can be seen from the figure that the brightness temperatures of the ship and the sea surface at 154 km are very close, but the position of the ship can still be distinguished. Due to the existence of system noise, the system noise is added to the antenna apparent brightness temperature map, and the result is as follows Figure 8 As shown, it is difficult to distinguish the difference in brightness temperature between the ship and the sea surface with the naked eye.

[0087] Further, in Figure 8 The horizontal line where the ship is located is selected to analyze the temperature difference between the ship and the sea surface. The results are as follows: Fig. 9 As shown. The smooth change of the curve indicates the brightness temperature of the sea surface, and the protrusion is the brightness temperature of the ship. The △T in the figure is 0.395K, which is close to 0.3K, which shows that the equivalent calculation method is feasible.

[0088] The detection distance of the millimeter wave imaging system of the present invention directly affects its imaging quality and application effect. Through the evaluation method, the performance characteristics of the system under different environmental conditions and target conditions can be identified, providing a scientific basis for system design and optimization. Due to its strong penetration and good anti-interference ability, millimeter wave technology is widely used in security, traffic monitoring, medical imaging and other fields. Studying the detection distance evaluation method can clarify its applicability and limitations in different application scenarios and promote its application in new fields. The present invention establishes a unified millimeter wave imaging system detection distance evaluation standard, which is conducive to scientific comparison between different systems, promotes technical exchanges and cooperation within the industry, and promotes technological progress. Understanding the detection distance of millimeter wave imaging helps to reasonably configure modules and components in system integration and design, ensure optimal performance in target detection and imaging, and reduce development and implementation costs. Millimeter wave imaging systems may work under different environmental conditions. The detection distance evaluation method can help researchers understand and predict the performance of the system under various climate, weather and lighting conditions, so as to facilitate the selection of the best solution for different application scenarios.

[0089] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A method for calculating the limit detection distance of millimeter wave imaging, characterized in that: include: Step 1: Establish a formula for the brightness temperature difference at the target object at the limit detection distance under the current observation scene; Step 2: Select an object with a known distance within the limit detection range of the millimeter wave imaging system for detection, and establish a formula for the brightness temperature difference of a close-range object; Step 3: Use the millimeter wave imaging system with the limit distance to be determined to perform actual close-range measurement, substitute the close-range brightness temperature difference formula into the limit detection distance brightness temperature difference formula, and obtain the relationship between the brightness temperature difference and the detection distance d; Step 4: Adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step size until the brightness temperature difference is less than or equal to the brightness temperature sensitivity value of the millimeter wave imaging system, and obtain the limit detection distance of the millimeter wave imaging system.

2. The method for calculating the limit detection distance of millimeter wave imaging according to claim 1, characterized in that: In step 1, the formula for the brightness temperature difference at the limit distance in the current observation scene is: Where θ1 and θ2 are the 3 dB beam widths of the E and H planes of the detector antenna, respectively; △T is the brightness temperature difference of the object received at the detector; T B-obj0 To detect the original brightness temperature of the object, T B-bac0 is the background original brightness temperature of the detected object, α is the atmospheric radiation attenuation rate between the detected object and the detector, S A is the projected area of ​​the object, and d is the distance from the object to the detector.

3. The method for calculating the limit detection distance of millimeter wave imaging according to claim 2, characterized in that: In step 2, the brightness temperature difference formula of the object at close distance includes the brightness temperature difference formula when the projection area of ​​the detector antenna beam is smaller than the target object and the brightness temperature difference formula when the projection area of ​​the beam is greater than or equal to the target object.

4. The method for calculating the limit detection distance of millimeter wave imaging according to claim 3 is characterized in that: The original brightness temperature difference formula of the object when the beam projection area is smaller than the target object is: T B-bac0 -T B-obj0 =ΔT1·α1 Among them, α1 is the atmospheric attenuation rate from the object to the detector when the beam projection area is smaller than the target object area, and △T1 is the measured brightness temperature difference between the target and the background at the detector when the beam area is smaller than the target object area.

5. The method for calculating the limit detection distance of millimeter wave imaging according to claim 3 or 4, characterized in that: The formula for the original brightness temperature difference of an object when the beam projection area is greater than or equal to the target object is: T B-bac0 -T B-obj0 =ΔT2·α2·[π·d0 2 ·tan(θ1 / 2)·tan(θ2 / 2)] / S A Among them, α2 is the atmospheric attenuation rate between the object and the detector when the beam projection area is larger than the target object area, d0 is the measurement distance in actual close-range measurement, and △T2 is the brightness temperature difference when the beam diameter is larger than the target object diameter.

6. The method for calculating the limit detection distance of millimeter wave imaging according to claim 5, characterized in that: In step 3, the relationship between the brightness temperature difference and the detection distance d includes: When the beam diameter is smaller than the target object diameter, the relationship is: When the beam diameter is larger than the target object diameter, the relationship is:

7. The method for calculating the limit detection distance of millimeter wave imaging according to claim 6, characterized in that: In step 4, the MPM atmospheric model is used to adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step size until the brightness temperature difference △T is less than or equal to the brightness temperature sensitivity value △T of the millimeter wave imaging system. sys The detection distance d obtained is the limit detection distance of the millimeter wave imaging system.

8. The millimeter wave imaging limit detection distance estimation system is characterized by: include: The module (1) for establishing the formula of the brightness temperature difference at the extreme distance is used to establish the formula of the brightness temperature difference at the extreme distance under the current observation scene; A close-range brightness temperature difference formula establishment module (2) is used to select two objects with known distances within the limit detection range of the millimeter wave imaging system for detection, and establish a close-range object brightness temperature difference formula using detection parameters; A module (3) for establishing the relationship between brightness temperature difference and detection distance is used to substitute the brightness temperature difference formula at a short distance into the brightness temperature difference formula at a limit distance to obtain the relationship between the brightness temperature difference and the detection distance d; The limit detection distance calculation module (4) uses the MPM atmospheric model to adjust the value of the detection distance d in the relationship between the brightness temperature difference and the detection distance d according to a fixed step length until the brightness temperature difference is less than the temperature-brightness difference sensitivity value of the millimeter wave imaging system, thereby obtaining the limit detection distance of the millimeter wave imaging system.

Images