Particle detection device, particle detection method, and particle detection program

Abstract

To provide a particle detection device capable of identifying a localized position of a target particle.SOLUTION: The particle detection device has: emission means 2 for emitting pulsed light in a predetermined space; light receiving means 3 for receiving pulsed light reflected by particles S floating in the predetermined space; a detection unit 4 for detecting that a target particle, as one of the particles S, exists at a localized position with high density in an emission direction of the pulsed light; and a storage unit 5 for storing the output of the detection unit 4. The detection unit 4 converts a distance to the particle S on the basis of a time difference between the emission of the pulsed light and its reception by the light receiving unit 3 to integrate count values based on the intensity of reflected light received by the light receiving unit 3 corresponding to the distance into a line graph, compares it sequentially with a first line graph which is a reference line graph 5a stored in the storage unit 5 when the target particle does not exist, and detects that the target particle exists at the localized position with high density when a convex increase area exceeds a reference value at the localized position in the first line graph.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a particle detection device, a particle detection method, and a particle detection program that can identify the location of target particles, such as particles related to smoke resulting from a fire, that have a particle diameter smaller than that of ordinary particle dust, locally and with high density. [Background technology]

[0002] Patent Document 1 discloses a fire detector that is installed in a predetermined space with the center of the ceiling as a fixed point, as a fire detector for detecting particles of interest floating in a room as a closed space, for example. Patent Document 2 discloses an optical fire detector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 57-188213 [Patent Document 2] Japanese Patent Publication No. 2020-038203 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, it is difficult to detect smoke caused by small particles due to an early stage fire at a position away from the fire detector installed at a specific fixed position.

[0005] Furthermore, in Patent Document 2, it is difficult to identify the local position where the particle of interest is generated in the direction of light emission from the light source, and detection including positions on a line or a plane is not possible.

[0006] An object of the present invention is to solve the above-mentioned problems and to provide a particulate body detection device, a particulate body detection method, and a particulate body detection program that can identify a local position where a target particulate body is occurring in the emission direction of pulsed light.

[0007] Furthermore, the present invention aims to provide a small industrial lidar as a novel particulate detection device. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a particulate body detection device comprising: emission means for emitting pulsed light into a predetermined space at predetermined intervals; light receiving means for receiving the pulsed light reflected by a particle of interest floating in the predetermined space; and a detection unit for detecting the presence of the particle of interest at a high density at a local position in the emission direction of the pulsed light, wherein the detection unit stores a first line graph as a reference, converts the distance to the particle of interest based on the time difference between the emission of the pulsed light and the reception of the pulsed light by the light receiving means, and generates a line graph of count values based on the intensity of the reflected light of the light receiving means corresponding to the distance, successively compares the latest line graph with the first line graph, and determines that the particle of interest is in an abnormal state where it is present at a high density at the local position when the increased area at the local position compared to the first line graph exceeds a reference value.

[0009] Furthermore, a particulate body detection method according to the present invention includes a server that stores a first line graph serving as a reference, emits pulsed light into a predetermined space at predetermined intervals, receives the pulsed light reflected by particulate bodies floating in the predetermined space, and detects that particulate bodies of interest are present at a high density at a local position in the emission direction of the pulsed light, the server comprising the steps of: converting a distance to the particulate body in the absence of the particulate body of interest based on a time difference between emission and reception of the pulsed light; and storing a latest line graph in which count values based on the intensity of reflected light corresponding to the distance are plotted as a line graph; and determining, when an increased area at the local position in the latest line graph exceeds a reference value relative to the first line graph, that an abnormal state exists in which the particulate body of interest is present at a high density at the local position. The present invention is characterized by comprising:

[0010] Furthermore, a particulate matter detection program according to the present invention includes a server that stores a first line graph serving as a reference, and when emitting pulsed light into a predetermined space at predetermined intervals, receiving the pulsed light reflected by particulate matter floating in the predetermined space, and detecting that particulate matter of interest is present at a high density at a local position in the direction of emission of the pulsed light, the program has the server execute at least the following steps: converting the distance to the particulate matter of interest that would occur if the particulate matter of interest were not present based on the time difference between emission and reception of the pulsed light, and storing a latest line graph in which count values based on the intensity of reflected light corresponding to the distance are plotted as a line graph; and detecting that the particulate matter of interest is present at a high density at the local position in the latest line graph when an increased area at the local position in the latest line graph exceeds a reference value. [Effects of the Invention]

[0011] The particulate body detection device, particulate body detection method, and particulate body detection program of the present invention are capable of detecting fires and the like in tunnels not based on fixed-point detection but on line or surface detection, and are capable of identifying positions where target particulate bodies are locally present in high density in the direction of emission of pulsed light, and of detecting the occurrence of fires and the like early on without false detection. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an overall configuration diagram according to an embodiment of the present invention; [Figure 2] 10 is a graph showing count values based on the intensity of reflected light as a function of the distance to a particle when the particle of interest does not exist. FIG. [Figure 3] 10 is a graph showing the attenuation rate and transmittance based on the reflected light intensity according to the distance to a particle when a particle of interest is present. FIG. [Figure 4] 10 is a graph showing the attenuation rate and transmittance when the convex increasing area is steep and when it is gradual at a local position. FIG. [Figure 5] FIG. 10 is a graph showing the attenuation rate and transmittance, representing the time elapsed since the increased area of the convex shape exceeded a reference value. [Figure 6] FIG. 10 is an explanatory diagram of a specific embodiment. [Figure 7] FIG. 1 is an illustration of particle detection via the Internet. [Figure 8] FIG. 10 is a flowchart for detecting the presence of a particle of interest. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below based on the illustrated embodiments.

[0014] (Particle detection device) 1 shows a particulate matter detection device 1 according to an embodiment of the present invention. The particulate matter detection device 1 is provided with an emission means 2 that emits pulsed light to a particulate matter S to be detected, and the emission means 2 is equipped with a scanning mechanism 2a. The device is also provided with a light receiving means 3 that receives reflected light from the particulate matter S at a light receiving section, and the output of the light receiving means 3 is connected to a detection section 4, and the output of the detection section 4 is connected to a memory section 5 and an output section 6. The memory section 5 is configured to store a reference line graph 5a, a previous line graph 5b, and a reference value Do of the increased area D.

[0015] When pulsed light is emitted from the emitting means 2 toward particulate matter S floating in a predetermined space, the pulsed light reflected by the particulate matter S is received by the light receiving means 3. As particulate matter S, in addition to dust, which is a normal airborne particle, particulate matter of interest may be, for example, particulate matter with a particle size smaller than that of normal particulate matter, such as smoke caused by a fire. Note that smoke is a state in which solid or liquid particles are suspended in gas, and the composition of smoke ranges from water vapor to harmful particulate matter such as dioxins.

[0016] Furthermore, examples of the above-mentioned specified space include roofed spaces such as inside tunnels for automobiles or railways, tunnels at construction sites, and indoor parking lots, as well as enclosed spaces such as inside buildings such as houses, gymnasiums, exhibition halls, and factories, and inside other ships.

[0017] The pulsed light source of the emitting means 2 may be a laser light source such as a semiconductor laser, i.e., a laser diode (LD), or a light source such as an LED, whose wavelength is 300 nm to 1700 nm, from just before visible light to infrared light. The pulsed light may be, for example, one that repeatedly outputs pulsed light with a pulse width of 10 nS and a frequency of 200 Hz to 1 MHz. The wavelength of the light source is not limited to a single wavelength, and may be multiple wavelengths.

[0018] The pulsed light from the emitting means 2 can be scanned one-dimensionally or two-dimensionally using a scanning mechanism 2a, and can be, for example, a laser beam emitted horizontally or a laser LIDAR beam scanned within a horizontal plane. The latter can be applied to small industrial LIDARs.

[0019] In the detection unit 4, the distance to the particle body S, for example, within 300 m, is converted based on the time difference between the emission of the pulsed light from the emission means 2 and its reception by the light receiving means 3, and the count value of the pulsed light based on the reflected light intensity of the light receiving means 3 according to the distance is detected as a line graph.

[0020] If there are no particles S of interest, such as smoke from a fire, the latest line graph will be the same as the line graph for the past time period, and an output will be obtained with the horizontal axis representing distance L and the vertical axis representing count values, as shown in the graph diagram of Figure 2. The count values on the vertical axis are calculated by counting the output from the light receiving means 3 in the detection unit 4 as the number of particles S based on the reflected light intensity when the pulsed light emitted from the emitting means 2 at predetermined intervals exceeds a threshold. The obtained count values serve as indicators for detecting the presence or absence of particles of interest and the amount thereof.

[0021] The detection frequency of the count value of the reflected light from these particles of interest decreases in proportion to the square of the distance. Therefore, the pre-calibration count threshold, which is the curve shown in Figure 2, is the threshold for the detected count value when the density of the particles of interest is the same. If this pre-calibration count threshold is multiplied by a coefficient proportional to the square of the distance and expressed as a transmittance (attenuation rate), a linear threshold that is constant with respect to the distance is obtained. By multiplying the detected count value by a coefficient proportional to the square of the distance, a post-calibration transmittance threshold can be used, for example, with a transmittance of 98% per meter, as shown in Figure 2.

[0022] This calibrated transmittance threshold is the base of the convex increased area D described below, and in the graphs shown in Figures 3 and 4, the left vertical axis represents the attenuation rate obtained by multiplying the detected count value by the calibrated coefficient, while the right vertical axis represents the transmittance obtained by multiplying the detected count value by the calibrated coefficient. For attenuation rates and transmittances that do not reach the calibrated transmittance threshold, the detection of particles S is treated as noise.

[0023] The output of the detection unit 4 is stored in the storage unit 5 as the latest detected line graph and is compared with a first line graph that serves as a reference. This first line graph is the reference line graph 5a or the immediately preceding line graph 5b, where the reference line graph 5a is a line graph having the calibrated transmittance threshold value shown in Fig. 2, and the immediately preceding line graph 5b is the immediately preceding line graph created by aggregating pulsed light for a aggregation time period, which will be described later.

[0024] The storage unit 5 also stores a reference value Do of the locally convex increased area D for the reference line graph 5a or the immediately preceding line graph 5b, and the detection unit 4 sequentially compares the first line graph with the reference line graph 5a or the immediately preceding line graph 5b, and detects when the latest line graph is a graph like that shown in Figure 3, which is different from Figure 2, that is, when the convex increased area D with the calibrated transmittance threshold as its base exceeds the reference value Do, indicating an abnormal state. Whether or not this reference value Do has been exceeded is determined taking into account the elapsed time, as shown in Figure 5, which will be described later.

[0025] In Figure 3, when an abnormal state is detected at a distance of approximately 20 m for a predetermined period of time, for example, three consecutive counting periods, in which the increased area D of the convex shape with the corrected transmittance threshold as its base exceeds the reference value Do, it is determined that a particle S has been detected.

[0026] On the other hand, if the increased area D of the convex shape with the corrected transmittance threshold at a distance of around 40 m as its base exceeds the reference value Do, but no abnormal state in which the reference value Do is exceeded consecutively for multiple counts over the aggregation time, it is not determined in Figure 3 that the abnormality occurrence threshold has been exceeded.

[0027] By adjusting the reference value Do, it may be determined that the abnormality threshold is met even if the increased area D of the convex shape having the corrected transmittance threshold as its base exceeds the reference value Do only once. The reference value Do may be a minute value.

[0028] When the convex increased area D at a local position described in Figure 3 exceeds the reference value Do, the increased area D may have a steep shape, or the increased area D may have a gradual shape in which the base of the increased area D expands flatly at a predetermined rate centered on the local position.

[0029] Furthermore, as shown in Figure 4, there may be cases where the base of the convex increased area D at a local position expands at a predetermined rate around the local position, and the height of the convex increased area D also increases at a predetermined rate around the local position.

[0030] In addition, if the increased area D has a steep convex shape, the particle of interest is light relative to the surrounding atmosphere, and if the increased area D has a gradual, flat shape, the particle of interest is heavy relative to the surrounding atmosphere.The state of the particle of interest relative to the surrounding atmosphere can be determined from the shape of the increased area D.

[0031] Regarding the output unit 6, whether or not a particle of interest S is present at a high density in a localized location, and the extent of its presence, can be displayed by a warning or alarm that appeals to human senses such as sight or hearing.If a detection terminal such as that shown in Figure 7 described below is used, the warning or alarm can be displayed on the display screen.

[0032] (Relationship between distance and reflected light intensity for the same particle) Here, when the pulsed light is reflected by a particle S floating in a position where the distance L is small, i.e., a nearby position, the solid angle seen by the light receiving unit of the light receiving means 3 is large, and therefore a high intensity of the reflected light is obtained. On the other hand, when the pulsed light is reflected by a particle S floating in a position where the distance L is large, i.e., a distant position, the solid angle seen by the light receiving unit of the light receiving means 3 is small, and therefore the intensity of the reflected light is low. In other words, for particle S, which are floating particles with a particle diameter of several tens of μm, particle S in a nearby position will strongly reflect light, and particle S in a distant position will weakly reflect light. (Relationship between particle size and reflected light intensity at the same distance) In addition, when the radius of the particle S is r, the scattered light intensity of the particle S is 1 / 4πr, which is the reciprocal of the surface area of the sphere. 2 Therefore, the reflected light intensity is higher for a target particle having a small particle diameter, such as a particle S related to smoke from a fire, than for a normal particle S, such as dust, at the same distance.

[0033] That is, when there is a particle S of interest that is different from ordinary dust, for example smoke from a fire with a particle diameter smaller than that of dust, a situation can be recognized as a graph as shown in Fig. 3, which is differentiated from the graph in Fig. 2. In other words, it is possible to detect the presence of a particle S of interest, for example smoke from a fire with a particle diameter smaller than that of dust, at a local position where the increased area of the convex shape exceeds the reference value Do.

[0034] With regard to the diameter of the particles S, while normal dust has a diameter of 10 μm to 100 μm, smoke from a fire has a diameter smaller than 10 μm, for example, 2.5 μm or less for M2.5, so when smoke from a fire occurs, the intensity of the reflected light received by the light receiving means 3 increases.

[0035] (Example) 6 is an explanatory diagram of a more specific embodiment. If the pulse width of the pulsed light from the emitting means 2 is 10 nS, the pulsed light will travel 1.5 m in 5 nS. For example, if the pulsed light is reflected by the particle S at a point 1.5 m away, it will be received as reflected light 10 nS after traveling 3 m. Similarly, if the pulsed light is reflected by the particle S at a point 3 m away, it will be received as reflected light 20 nS after traveling 6 m.

[0036] If the maximum length of a closed space such as a tunnel is, for example, 750 m, the pulsed light will travel 750 x 2 = 1500 m before it is reflected by particle S at the maximum length and received, so the elapsed time required for pulsed light with a pulse width of 10 nS to travel 1500 m is 5 μS.

[0037] With regard to this light reception, the presence or absence of reflected light whose reflected light intensity exceeds a threshold is detected 10 times every 1 nS during a 10 nS time period during which light is emitted at a predetermined distance.

[0038] 6, since the pulsed light reaches a distance of 1.5 m between 5 nS and 15 nS after light emission, 10 detections of particles S at a distance of 1.5 m are performed between 10 nS and 20 nS after light emission. Since the light reaches a distance of 3 m between 10 nS and 20 nS after light emission, 10 detections of particles S at a distance of 3 m are performed between 20 nS and 30 nS after light emission. Then, 10 detections of particles S are performed for each 1.5 m increase in distance up to the maximum length of 750 m.

[0039] Here, the emission interval is set so that the time period during which light is reflected and received by the particle S at a maximum distance of 750 m does not overlap with the time period during which light is reflected and received by the particle S at a distance of 1.5 m in the next pulse emission.

[0040] In this way, whether or not the reflected light intensity exceeds the threshold is detected every 10 nS after light emission, such as in the time period 10 nS to 20 nS after light emission, the time period 20 nS to 30 nS after light emission, and so on, and a count value based on the reflected light intensity when the threshold is exceeded is displayed. This count value is not based on a single pulse of light, but on multiple pulses of light pulses; for example, the light emission interval in Figure 6 is 10 nS, and 10,000 pulses of light pulses are counted over 1 second (1,000 mS). The curve of the pre-calibration count threshold shown in Figure 2 fluctuates depending on this counting time.

[0041] On the analysis screen, the calibrated transmittance threshold is used as the base, and by detecting whether the increased area D exceeds the reference value Do, the generation of smoke particles S due to a fire can be detected early. As shown in Figure 5, if the increased area D exceeds the reference value Do over multiple consecutive time periods, it can be determined that a fire has occurred.

[0042] That is, if the transmittance obtained by multiplying the detected count value by the calibrated coefficient exceeds the calibrated transmittance threshold value over multiple consecutive distances, and the increased area D exceeds the reference value Do with the calibrated transmittance threshold value as the base, an abnormality is detected. If an abnormality occurs continuously over multiple consecutive time periods, it can be determined that a fire has occurred.

[0043] As mentioned above, the counting time is set to, for example, one second, and a reference value judgment is performed on the counted values. If an abnormal state in which the increased area D exceeds the reference value Do is detected a predetermined number of times during the counting time, for example, three consecutive seconds, which is three times, it is determined that a fire has occurred.

[0044] Here, a reflector with a known reflectance of scattered light is placed at the position of the maximum length of 750 m described above, and the transmittance of the particle detection device can be calculated using the reflector as a reference based on the intensity of light received by the light receiving means 3. That is, if the emission intensity of the pulsed light is Po, the transmittance is T, the reflectance of the reflector is Ro, and the intensity of light received by the light receiving means 3 is P, the transmittance T can be calculated by P = Po x T x R x T. Thus, while conventional smoke detectors were capable of detection at a transmittance of 90% to 95%, the detection device of this embodiment is capable of detection at a transmittance of 98%.

[0045] (Particle detection method) 1 to 3, the particle detection method includes an emission step by emission means 2 that emits pulsed light in a predetermined space, a light receiving step by light receiving means 3 that receives the pulsed light reflected by particles S floating in the predetermined space, and a detection step by detection unit 5 that detects that particles of interest, as particles S, are present at a high density at a local position in the emission direction of the pulsed light. The detection step converts the distance to the particle S based on the time difference between the emission of the pulsed light and the reception by the light receiving means 3, and creates a line graph based on the reflected light intensity obtained by the light receiving means 3 corresponding to this distance. The line graph is then sequentially compared with a first line graph in storage unit 5 when the particle of interest, S, is not present. If the area D of the convex increase at the local position relative to the first line graph exceeds a reference value Do, it is detected that the particle of interest is present at a high density at the local position.

[0046] FIG. 7 is an explanatory diagram of a particle detection method using a server and multiple lightweight, portable mobile devices, such as smartphones, as the particle detection device 1 of FIG. 1. The latest line graph detected by the detection device is transmitted to a server via the Internet. The server stores a reference line graph 5a or a previous line graph 5b, which are sequentially compared with the latest line graph. By sequentially comparing the reference line graph 5a or the previous line graph 5b with the latest line graph, if the increased area D of the convex shape with the calibrated transmittance threshold as its base exceeds a reference value Do, the presence of a particle of interest S at a local location can be detected. It is also possible to transmit data detected by the detection device to a server, which generates a latest line graph, which can be sequentially compared with the reference line graph 5a or the previous line graph 5b.

[0047] FIG. 8 shows a flowchart for detecting a particle of interest according to the present invention, as described with reference to FIGS. 1 to 7. Step S1 shows a step in which light is emitted from the emitting means 2 on the premise that it will be received by the light receiving means 3, and in step S2, the first line graph described above is stored. In step S3, the latest line graph is detected and compared with the first line graph. Furthermore, in step S4, it is determined whether the increased area D of the convex shape integrated over time shown in FIG. 5, with the calibrated transmittance threshold as the base, exceeds a reference value Do.

[0048] If the reference value Do is exceeded, in step S5, an output is made that the particle of interest is present within a predetermined distance, and if a detection terminal shown in Fig. 7 is used, this is output on the display screen of the detection terminal. If the reference value Do is not exceeded in step S4, the process waits until the reference value Do is exceeded. Here, artificial intelligence AI may be used in at least one of steps S2 to S4.

[0049] (Variation) In addition to the uses mentioned above, the present invention can be used for atmospheric measurements such as aerosols, typhoons, heavy rain, lightning strikes, tornadoes, and heavy rain; dust detection; detection of specific gas leaks such as hydrogen gas; environmental measurements such as radioactivity measurement and radioactive material detection; industrial measurements such as natural gas detection; automatic driving in environments with poor visibility such as fog; and other applications to bioterrorism.

[0050] The particulate body detection device, particulate body detection method, and particulate body detection program of the present invention are capable of detecting fires in tunnels and the like not based on fixed-point detection but on line or surface detection, and are capable of identifying the position in the direction of light emission where the particle body of interest is locally present at a high density, and of detecting the occurrence of a fire or the like early on without false detection.

[0051] Furthermore, by using the particulate detection device, the particulate matter of interest is particulate matter S related to smoke caused by a fire, which has a particle diameter smaller than that of ordinary particulate matter, dust, and it can be determined that a fire has occurred when the increased area of the convex shape in the detection unit 4 exceeds a reference value over a predetermined period of time. This has the advantage of enabling early detection of particulate matter S at low concentrations in fires, including fire sites, for example, as a disaster prevention measure.

[0052] The particulate body detection device further includes a first line graph that is a reference line graph 5a that uses an average of multiple lines graphed under the condition that the area of the convex increase at a local position does not exceed a reference value, or a previous line graph 5b that is graphed under the condition that the area of the convex increase at a local position does not exceed a reference value. In this way, in the former case, the reference line graph 5a can be used as a stable reference, and in the latter case, the previous line graph 5b can be used as the latest reference.

[0053] Furthermore, the particulate matter detection device may use laser light emitted in the horizontal direction as the pulsed light, or laser lidar light scanned within a horizontal plane, thereby allowing for a simple arrangement of the particulate matter detection device. [Explanation of symbols]

[0054] 1. Particle detection device 2 Emission means 3 Light receiving means 4. Detection unit 5 Storage section 6 Output section D Increased area L distance S particle body

Claims

1. an emission means for emitting pulsed light at predetermined intervals in a predetermined space; a light receiving means for receiving the pulsed light reflected by a particle of interest floating in the predetermined space; a detection unit for detecting that the particle of interest is present at a high density at a local position in the emission direction of the pulsed light, the detection unit stores a first line graph as a reference, converts the distance to the particle of interest based on the time difference between the emission of the pulsed light and the reception of the light by the light receiving means, and generates a line graph of the count value based on the intensity of the reflected light by the light receiving means according to the distance; The latest line graph is successively compared with the first line graph, and if the increased area at the local position relative to the first line graph exceeds a reference value, it is determined that the particle of interest is present at a high density at the local position, indicating an abnormal state.

2. the first line graph has a post-calibration transmittance threshold, which is a threshold of a straight line that is constant with respect to distance, obtained by multiplying a pre-calibration count threshold according to distance, which is a curve, by a coefficient proportional to the square of the distance, based on reception of the pulsed light for a total time including a large number of times of the pulsed light; The particle detection device according to claim 1, wherein the detection unit sequentially compares the latest line graph, which represents the transmittance by multiplying the count value obtained by aggregating the received pulsed light during the aggregation time by the coefficient, with the first line graph, and determines that the abnormal state exists when the increased area of the convex shape in the line graph, which has the calibrated transmittance threshold as its base, exceeds the reference value.

3. 3. The particulate detection device according to claim 2, wherein the detection unit determines that a fire has occurred when the increased area exceeds the reference value for a predetermined number of times during the counting time.

4. 4. The particulate body detection device according to claim 2, wherein the detection unit determines a state of the target particle relative to a surrounding atmosphere from the shape of the increased area of the convex shape.

5. 5. The particle detection device according to claim 4, wherein when the convex increasing area is a steep shape, the particle of interest is light relative to the surrounding atmosphere, and when the convex increasing area is a gradual shape that spreads out in a flat plane, the particle of interest is heavy relative to the surrounding atmosphere.

6. 4. The particulate detection device according to claim 2, wherein the pulsed light is a laser light emitted in a horizontal direction or a laser lidar light scanned within a horizontal plane.

7. A particulate matter detection method comprising: a server that stores a first line graph serving as a reference; emitting pulsed light into a predetermined space at predetermined intervals; receiving the pulsed light reflected by particulate matter floating in the predetermined space; and detecting that particulate matter of interest is present at a high density at a local position in the direction of emission of the pulsed light, the method comprising: the server converts the distance to the particle when the particle of interest does not exist based on the time difference between the emission and reception of the pulsed light, and stores an updated line graph in which count values based on the intensity of the reflected light corresponding to the distance are plotted as a line graph; determining that the particle of interest is present at a high density at the local position when the increased area at the local position in the latest line graph exceeds a reference value with respect to the first line graph; A method for detecting a particulate object, comprising:

8. a server that stores a first line graph as a reference, emitting pulsed light into a predetermined space at predetermined intervals, receiving the pulsed light reflected by particles floating in the predetermined space, and detecting that particles of interest are present at a high density at a local position in the direction of emission of the pulsed light, a step of converting the distance to the particle when the particle of interest is not present based on the time difference between the emission and reception of the pulsed light, and storing in the server an updated line graph in which count values based on the intensity of the reflected light corresponding to the distance are plotted as a line graph; detecting that the particle object of interest is present at a high density at the local position when an increased area at the local position in the latest line graph exceeds a reference value with respect to the first line graph; A particle detection program characterized by executing at least the following.

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