Underwater monitoring device and underwater monitoring method

Abstract

This invention provides an underwater monitoring device and method that take reflected noise into consideration, are adaptable to various situations, and offer high measurement accuracy. [Solution] An underwater monitoring device 1 according to one aspect of the present invention comprises a light irradiation member 2 that irradiates visible laser light, a light receiving member 3 that receives reflected light R of the visible laser light irradiated by the light irradiation member, and a positional relationship changing member 4 that changes the positional relationship between the light irradiation member and the light receiving member. Another aspect of the present invention is an underwater monitoring device having a light irradiation member that irradiates visible laser light, a light receiving member that receives reflected light of the visible laser light irradiated by the light irradiation member, and a control member that controls the light irradiation member and the light receiving member, wherein multiple light receiving members are provided for a single light irradiation member, and the control member 5 selects the output of one of the multiple light receiving members.

Description

[Technical Field]

[0001] The present invention relates to an underwater monitoring apparatus and an underwater monitoring method. [Background Art]

[0002] As a technique for measuring an object (measurement target) located at a distant position, LiDAR (Light Detection and Ranging) using light is frequently used. LiDAR is a technique that irradiates a measurement target with light, measures the light reflected by scattering among the irradiated light, and performs various measurements based on information obtained from the measurement.

[0003] While LiDAR is generally often used on land, there is a demand to apply this LiDAR technology also underwater.

[0004] Techniques related to underwater LiDAR are described in, for example, Patent Document 1 and Non-Patent Document 1 below. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-open No. 2013-124882 [Non-Patent Documents]

[0006] [Non-Patent Document 1] https: / / www.spiedigitallibrary.org / journals / optical-engineering / volume-56 / issue-3 / 031212 / Underwater-three-dimentional-imaging-laser-sensor-with-120-deg-wide / 10.1117 / 1.OE.56.3.031212.pdf [Summary of Invention] [Problems that the invention aims to solve]

[0007] Incidentally, in actual underwater measurements, reflection noise is generated by various factors such as suspended and dissolved substances. Since the type and amount of these vary greatly depending on the measurement location, it is necessary to respond appropriately to these various situations.

[0008] However, the technologies described in Patent Document 1 and Non-Patent Document 1 both describe inventions that avoid the effects of underwater reflection noise through electronic circuit and software technologies. On the other hand, in underwater, it is necessary to detect weak reflected light from the object to be measured, so a highly sensitive photodetector, such as a SiPM (Silicon Photomultiplier), is used. When strong reflected light is incident on a SiPM, a phenomenon of signal saturation occurs. As will be described later, if the reflected noise light from noise-inducing objects melted or suspended in the water is very large, as shown in Figure 7, the underwater LiDAR is affected by this noise light component immediately after emitting the laser beam, and as shown in Figure 8, the output of the photodetector becomes saturated. If the object to be measured is in the region where saturation occurs, the reflected light received signal from the object to be measured itself is buried in the saturation region, making it difficult to use the reception method that sets a signal threshold as disclosed in the invention. Avoiding this effect requires ingenuity in the optical system and mechanism, but these prior examples have not adequately addressed this, and challenges remain in measurement accuracy. In other words, noise-inducing objects exist in water, either molten or suspended within it, and there remains a challenge in addressing the effects of reflected noise caused by reflected light when laser light is shone on these noise-inducing objects.

[0009] Therefore, in view of the above problems, the present invention aims to provide an underwater monitoring device and an underwater monitoring method that take reflected noise into consideration, can handle various situations, and have high measurement accuracy. [Means for solving the problem]

[0010] An underwater monitoring device according to one aspect of the present invention that solves the above problems comprises a light irradiating member that irradiates laser light in the visible region, a light receiving member that receives reflected light of the visible region laser light irradiated by the light irradiating member, and a positional relationship changing member that changes the positional relationship between the light irradiating member and the light receiving member.

[0011] Furthermore, although not limited to this viewpoint, the positional relationship changing member is preferably a distance adjusting member that changes the distance between the light irradiating member and the light receiving member.

[0012] Furthermore, although not limited to this viewpoint, the positional relationship changing member is preferably a rotating member that rotates the light-receiving member or the light-emitting member around the light-emitting member or the light-receiving member.

[0013] Furthermore, although not limited to this viewpoint, it is preferable that the optical axis of the light irradiating member and the optical axis of the light receiving member are not coaxial, resulting in a biaxial optical system.

[0014] Furthermore, an underwater monitoring device according to another aspect of the present invention is an underwater monitoring device having a light-emitting member that emits visible-range laser light, a light-receiving member that receives reflected light of the visible-range laser light emitted by the light-emitting member, and a control member that controls the light-emitting member and the light-receiving member, wherein multiple light-receiving members are provided for a single light-emitting member, and the control member selects the output of one of the multiple light-receiving members. [Effects of the Invention]

[0015] In summary, the present invention provides an underwater monitoring device and method that take reflected noise into consideration, can handle various turbidity conditions, and offer high measurement accuracy. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of an underwater monitoring device according to an embodiment. [Figure 2]It is a schematic diagram of the underwater monitoring device according to the embodiment when viewed from the front. [Figure 3] It is a schematic cross-sectional diagram of the underwater monitoring device according to the embodiment. [Figure 4] It is a functional block diagram of the underwater monitoring device according to the embodiment. [Figure 5] It is a diagram showing signal characteristics of reflected light in water with few noise-inducing objects according to the embodiment. [Figure 6] It is a schematic cross-sectional diagram of the coaxial optical system according to the embodiment. [Figure 7] It is a diagram explaining reflection noise caused by suspended matter and the like in water according to the embodiment. [Figure 8] It is a diagram showing signal characteristics with a saturated state of reflected light in water with many noise-inducing objects according to the embodiment. [Figure 9] It is a schematic diagram relating to the arrangement of a light irradiation member and a light receiving member of the underwater monitoring device according to the embodiment. [Figure 10] It is a diagram showing signal characteristics with reduced reflection noise in water containing a large amount of suspended matter and the like according to the embodiment. [Figure 11] It is a schematic diagram relating to the arrangement of a light irradiation member and a light receiving member of the underwater monitoring device according to the embodiment. [Figure 12] It is a schematic diagram of another example of a cross-section of the underwater monitoring device according to the embodiment. [Figure 13] It is a schematic diagram relating to reflected light from the light irradiation member and the light receiving member of the underwater monitoring device according to the embodiment. [Figure 14] It is a schematic diagram relating to reflected light from the light irradiation member and the light receiving member of the underwater monitoring device according to the embodiment. [Figure 15] It is a schematic diagram relating to reflected light from the light irradiation member and the light receiving member of the underwater monitoring device according to the embodiment. [Figure 16] It is a diagram explaining an example of scanning of light irradiated by the underwater monitoring device according to the embodiment. [Figure 17] It is a diagram showing a flow of peak determination processing of the underwater monitoring device according to the embodiment. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention can be implemented in many different forms and is not limited to the specific examples shown in the embodiments below.

[0018] Figure 1 is a schematic diagram of the underwater monitoring device (hereinafter referred to as "the device") 1 according to this embodiment; Figure 2 is a diagram showing the arrangement of the light irradiating member 2, light receiving member 3, etc., when the device 1 is viewed from the front; Figure 3 is a schematic diagram of the cross-section of the device 1; and Figure 4 is a functional block diagram of the device 1.

[0019] As described above, the device 1 comprises a light irradiation member 2 that irradiates a laser beam L in the visible region, a light receiving member 3 that receives the reflected light R of the visible region laser beam L irradiated by the light irradiation member 2, and a positional relationship changing member 4 that changes the positional relationship between the light irradiation member 2 and the light receiving member 3. The device 1 is a so-called LiDAR (Light Detection And Ranging) that measures distance by irradiating a measurement target with laser beam L, and moreover, it is a so-called two-axis optical system in which the optical axes of the light irradiation member 2 and the light receiving member 3 do not coincide.

[0020] In addition to the above configuration, the device 1 also includes a control member 5 that controls the light irradiation member 2 and the light receiving member 3. Furthermore, in the device 1, the light irradiation member 2, the light receiving member 3, the positional relationship changing member 4, and the control member 5 are housed in a sealed enclosure 6 to prevent water from entering. With this configuration, the device 1 can measure (monitor) the surrounding environment and the distance to the object to be measured.

[0021] As is clear from the description herein, the device 1 is a device used to measure the distance to an object to be measured (hereinafter referred to as "object to be measured") in water. The device 1 is not limited to this, and may be a device used for fixed-point observation by fixing it in one place in the water, or it may be an attachment device installed on a so-called underwater drone that is equipped with a power component such as a motor and can move freely in the water, or it may be combined with other components such as the power component of an underwater drone and become part of it, and housed integrally in a single housing.

[0022] As described above, the device 1 is equipped with a light irradiation member 2 and is capable of irradiating laser light L in the visible region. The light irradiation member 2 is not limited as long as it has the above functions, but it is preferably composed of a light source member 21, a collimator lens 221, an optical path adjustment member 22, and an optical scanning member 23. Specifically, the light irradiation member 2 of the device 1 emits light from the light source member 21, converts it into substantially parallel light with the collimator lens 221, adjusts the optical path of this light with the optical path adjustment member 22 and directs it into the optical scanning member 23, and the optical scanning member 23 changes the direction (optical axis) of the light over time, specifically by scanning it.

[0023] Furthermore, as described above, the light source member 21 of this device 1 is a member that can irradiate laser light L in the visible region, and is not limited as long as it has this function, but is preferably a laser diode (LD), fiber laser, etc., but is more preferably a laser diode from the viewpoint of simplicity, space saving, power saving, and miniaturization. Specifically, by using a laser diode, it is possible to irradiate the desired light in a simple manner, and even if a laser diode is installed for each desired wavelength, it can be made space-saving, and power consumption is reduced, which are the advantages.

[0024] Furthermore, it is preferable that the wavelength of the laser light emitted by the light source element 21 of this device 1 is in the visible region. This is because, within a wide wavelength range, light in the visible wavelength region is less likely to be absorbed by water. In other words, by using a wavelength in the visible region, it is possible to achieve accurate distance measurement in water without absorption even underwater. The wavelength in the visible region will be described later, but specifically, it is preferable that it be in the range of 360 nm to 830 nm.

[0025] Furthermore, the optical scanning member 23 of this device 1 is a member that can change the direction (optical axis) of the light incident from the optical path adjustment member 22 over time. The optical scanning member 23 is not limited to these, but examples include MEMS mirrors, polygon mirrors, etc. The actual scanning movement of the optical scanning member will be described separately.

[0026] Furthermore, it is preferable that the light irradiating member 2 and light receiving member 3 of this device 1 be housed within a cylindrical housing for the light irradiating member, comprising a light source member 21, an optical path adjustment member 22, and an optical scanning member 23. This allows for miniaturization while ensuring secure connections between each component. The cross-sectional view of the light irradiating member 2, light receiving member 3, and positional relationship changing member 4 in this case is shown in Figure 3 above.

[0027] Furthermore, the light-receiving member 3 of this device 1 receives the reflected light R of the visible-range laser light L emitted by the light-irradiating member 2. According to this device 1, the light emitted from the light-irradiating member 2 hits the object to be measured and is scattered, but a portion of it returns to the device 1 side as reflected light R. By detecting this light with the light-receiving member 3, it becomes possible to obtain the necessary information as shown in the following section.

[0028] Furthermore, the light-receiving member 3 of this device 1 is not limited as long as it has the above-described function, but it is preferable that it is configured to output an electrical signal based on the received light. Specifically, examples include optical elements such as a photoelectric conversion element 31, a bandpass filter 32 and a lens 33 arranged before the photoelectric conversion element 31. Here, the photoelectric conversion element 31 is not limited, but examples include a phototransistor, photodiode, phototube, photomultiplier tube, SiPM (Silicon Photomultiplier), etc. This allows the received laser light to be output as an electrical signal to the control member 5.

[0029] As mentioned above, the device 1 is equipped with a positional relationship changing member 4 that changes the positional relationship between the light irradiating member 2 and the light receiving member 3. By providing the positional relationship changing member 4, reflection noise can be reduced. The specific principle of this positional relationship changing member 4 will be explained below.

[0030] Generally, in an ideal state where no reflection noise is generated by reflected light, when the laser light emitted from the light irradiating member 2 strikes the object to be measured, is reflected light, and detected by the light receiving member 3, the signal characteristics will be as shown in Figure 5, for example.

[0031] However, in actual underwater environments, there are many dissolved or floating objects along the way, and when laser light strikes these objects, they also become reflected light and can contribute to reflected noise (these dissolved or floating objects in water are called "noise-inducing objects"). For example, when using a coaxial optical system as shown in Figure 6 (an optical system in which the optical axis of the light-emitting element and the optical axis of the light-receiving element coincide), no matter what direction the laser light L is scanned, a noise-inducing object N will be directly in front, as shown in Figure 7. As a result, reflected noise from the noise-inducing object N is detected by the light-receiving element 3 immediately after the laser light is emitted, and a saturation region (a region where the maximum value of receivable light is reached) is formed in the signal. Then, the signal of reflected light R from the object to be measured is buried within the signal of reflected noise, and it becomes impossible to observe the peak of this reflected light R. In other words, the method of detecting the signal by setting a signal threshold becomes unusable. An image of the signal in this case is shown in Figure 8.

[0032] However, by first offsetting the optical axis of the light-emitting member 2, i.e., the propagation axis (optical axis) of the laser light L, and the optical axis of the light-receiving member 3 to create a so-called two-axis optical system, even if reflected light R, which causes reflection noise, is generated by a noise-inducing object N immediately after irradiation of the laser light L, it is less likely to be incident on the light-receiving member 3, and the optical distance can be increased, thereby reducing reflection noise. An image of this case is shown in Figure 9. This figure shows an image when the laser light L emitted from the light-emitting member 2 is scanned from a2 to f2. In the case of a two-axis optical system as shown in this figure, firstly, the light-receiving member 3 and the light-emitting member 2 are located in different positions, and naturally, the angular range (field of view) in which reflected light R can be detected is offset from the scanning area of ​​the laser light emitted by the light-emitting member 2. Therefore, for example, if a noise-inducing object N is located on the optical axis in the direction of a2, the light will only enter the field of view of the light-receiving member 3 when it reaches position a1, which is the intersection of the edge of the field of view of the light-receiving member 3 and the optical axis of the light-emitting member 2. As a result, light from noise-inducing objects N located closer than a1 will not be detected by the light-receiving member 3. Similarly, reflected light from noise-inducing objects N located closer to the light-emitting member 2 than the intersections b1, c1, d1, e1, and f1 (each of which are points of intersection with the field of view boundary) will not be detected by the light-receiving member 3. In other words, a biaxial optical system can cut out reflected noise from nearby noise-inducing objects N that would be detected in a coaxial optical system. In particular, as we move from a2 to f2, the distance between the light-receiving member 3 and the intersections b1, c1, d1, e1, and f1 (each of which are points of intersection with the field of view boundary) increases, causing light attenuation, which in turn reduces the intensity of reflected noise and narrows the saturation region. In particular, since light attenuates with the square of its distance, the effect of distance is significant. As a result, it becomes possible to detect the peak of reflected light R from the object being measured without it being buried in the reflected noise signal. An illustrative diagram of this case is shown in Figure 10.

[0033] Furthermore, Figure 11 shows an image diagram where the distance D between the light irradiating member 2 and the light receiving member 3 is longer than in Figure 9. In this example, because the distance D is longer, the intersection point between the scanning area of ​​the light irradiating member 2 and the field of view of the light receiving member 3 is further away, and reflection noise can be further reduced. Specifically, a noise-inducing object N on the propagation axis of the laser light L irradiated by the light irradiating member 2 and heading towards a2' only enters the field of view of the light receiving member 3 when it reaches position a1', and can be detected as reflection noise. Reflection noise at positions closer than a1' is not detected. Similarly, a noise-inducing object N on the propagation axis of the laser light L heading towards b2' can only be detected when it reaches position b1', and will not be detected unless it is at a position further away from the light irradiating member 2. As a result, there is an advantage in that reflection noise can be reduced more significantly than in the example in Figure 9.

[0034] Furthermore, this device 1 is equipped with a positional relationship changing member 4 that changes the positional relationship between the light irradiating member 2 and the light receiving member 3. This allows for adjustment of the positional relationship between the light irradiating member 2 and the light receiving member 3, enabling detection of the optimal signal from reflected light R. Specifically, by positioning the light irradiating member 2 and the light receiving member 3 in close proximity, the scanning area of ​​the light irradiating member 2 and the field of view of the light receiving member 3 can be brought closer together, thereby securing a wider measurement range. However, as mentioned above, there is a risk of increased reflection noise. In contrast, by increasing the distance D between the light irradiating member 2 and the light receiving member 3, the overlap between the scanning area of ​​the light irradiating member 2 and the field of view of the light receiving member 3 is reduced, but as mentioned above, reflection noise can be significantly reduced. Therefore, the positional relationship changing member 4 can be used to identify the position with the best balance, thereby optimizing the setup.

[0035] Furthermore, as described above, the positional relationship changing member 4 is preferably a distance adjusting member that adjusts the distance D between the light emitting member 2 and the light receiving member 3. While not limited to such distance adjusting members, examples include a screw mechanism that connects screw shafts with screw grooves to both the light emitting member 2 and the light receiving member 3, and drives a fitting member such as a wheel or ball that engages with these screw shafts to adjust the distance between them; a cam mechanism that provides a cam between the light emitting member 2 and the light receiving member 3, and adjusts the distance D between them by rotating this cam; a linear guide rail mechanism; and a cylinder mechanism that connects cylinders to both the light emitting member 2 and the light receiving member 3, and adjusts the distance D between them by moving the piston of the cylinder back and forth.

[0036] Furthermore, in this device 1, the positional relationship changing member 4 may be a means for changing the positional relationship, as described above, a means for changing the distance between the light irradiating member 2 and the light receiving member 3, i.e., a distance adjustment member. However, it may also be a means for rotating the light receiving member 3 or the light irradiating member 2 around the light irradiating member 2 or the light receiving member 3, i.e., a rotating member. An image of this case is shown in Figure 12. By rotating as shown in this figure, the positional relationship between the light irradiating member 2 and the light receiving member 3 is changed, the measurement range is changed, and measurement under suitable conditions becomes possible. In particular, as described later, by fixing the light receiving member 3 in one position and performing a measurement, and then rotating and fixing the light receiving member 3 in another position and performing a measurement there, it is possible to obtain the same effect as when multiple light receiving members 3 are provided at a lower cost. However, if speed is required for measurement, it is preferable to have a configuration with multiple light receiving members 3 as described later. Furthermore, if the positional relationship changing member 4 is a rotating member, it is preferable that it has a drive member 41 that realizes rotational motion and a fixing member 42 that is rotated by the drive member 41 and fixed to the light receiving member 3, and in particular, it is preferable that it is configured to rotate around the light irradiating member 2. By doing so, it is easier to obtain the same effect as when multiple light receiving members 3 are provided, as described later. In this case, the drive member 41 is not particularly limited, but as described above, it is preferable that it is a motor such as a DC motor, AC motor, stepping motor, or servo motor that directly generates rotational motion.

[0037] Incidentally, in this device 1, instead of providing a positional relationship changing member 4, multiple light receiving members 3 that detect light in the same wavelength range may be provided for a single light irradiating member 2. This has advantages such as making it easier to find the signal peak when one light receiving member 3 has high reflection noise by receiving the reflected light R with the other light receiving member 3, and obtaining a wider measurement range. An illustrative diagram of this case is shown in Figures 13, 14, and 15, and the effects of the configuration shown in these figures will be explained. Note that in Figure 14, one light receiving member 3 is represented by a dotted line for illustrative purposes, and in Figure 15, the other light receiving member 3 is represented by a dotted line for illustrative purposes. In the example shown in these figures, two light receiving members 3 are arranged on opposite sides of a single light irradiating member 2 at the same distance from each other.

[0038] First, looking at Figure 13, although light-receiving members 3 are provided, their positions are different. Therefore, even if the field of view is the same, the range in which the reflected light R can be detected differs. By providing multiple light-receiving members 3, it is possible to combine these measurement ranges to measure a wider area. In particular, by combining regions with low reflection noise, it is possible to measure a wide area with low reflection noise. This principle will be explained in detail below.

[0039] Furthermore, focusing on Figure 14, the situation is almost the same as in Figure 9. Specifically, for example, if a noise-inducing object N is located on the optical axis in the direction of a2, the light will only enter the field of view of one of the light-receiving members 3 when it reaches position a1, which is the intersection of the edge of the field of view of one of the light-receiving members 3 and the optical axis of the light-emitting member 2. Therefore, light from noise-inducing objects N located closer than a1 will not be detected by one of the light-receiving members 3. Similarly, reflected light from noise-inducing objects N located closer to the light-emitting member 2 than b1, c1, d1, e1, and f1, which are the intersection points of each of the figures with the boundaries of the field of view, will not be detected by one of the light-receiving members 3. In other words, a biaxial optical system can cut out reflected noise from nearby noise-inducing objects N that would be detected in a coaxial optical system. Furthermore, as the signal moves from a2 to f2, the distance between the light-receiving element 3 and the intersection points b1, c1, d1, e1, and f1 (which are the boundaries of the field of view) increases, causing spectral attenuation. This reduces the intensity of the reflection noise and narrows the saturation region. The effect of distance is particularly pronounced because light attenuates with the square of its distance. As a result, it becomes possible to detect peaks in the reflected light R from the object being measured without them being buried in the reflection noise signal.

[0040] Furthermore, focusing on Figure 15, it is almost identical to Figures 14 and 9, except that it is symmetrical to Figure 14. That is, laser light L is irradiated from the light irradiating member 2 onto the object to be measured. Specifically, for example, if a noise-inducing object N is located on the optical axis in the direction of g2, the light will only enter the field of view of the other light-receiving member 3 when it reaches position g1, which is the intersection of the edge of the field of view of the other light-receiving member 3 and the optical axis of the light irradiating member 2. Therefore, light from noise-inducing objects N located closer than g1 will not be detected by the other light-receiving member 3. Similarly, reflected light from noise-inducing objects N located closer to the light irradiating member 2 than h1, i1, j1, k1, and l1, which are the intersections of each of these points with the boundary of the field of view in the figure, will not be detected by the other light-receiving member 3. In other words, reflected noise from nearby noise-inducing objects N that would be detected in a coaxial optical system can be cut out in a biaxial optical system. Furthermore, as the signal moves from g2 to l2, the distance between the intersection points h1, i1, j1, k1, and l1 (which are the boundaries of the field of view) and the other light-receiving element 3 increases. This causes spectral attenuation, which reduces the intensity of the reflection noise and narrows the saturation region. In particular, since light attenuates with the square of its distance, the effect of distance is significant. As a result, it becomes possible to detect the peak of the reflected light R from the object being measured without it being buried in the reflection noise signal.

[0041] As described above, by arranging multiple light-receiving members 3 with the light-emitting member 2 in between, the light is received by the light-receiving member 3 on the side with reduced reflection noise, and by combining these, a wider measurement range can be obtained. Specifically, for one of the light-receiving members 3, range A is the measurement range, while for the other light-receiving member 3, range B is the measurement range. The combined range C is the maximum measurement range. As for range D, which is the overlapping range of range A and range B, since this range can be measured by either one of the light-receiving members 3 or the other, the measurement result of one may be adopted, or the average of both measurement results may be adopted.

[0042] Furthermore, the control member 5 of this device 1 is electrically connected to the light irradiation member 2, the light receiving member 3, and the positional relationship changing member 4, and is a member for controlling them via the transmission and reception of electrical signals. This enables various processes and allows for highly accurate measurement of the distance to the object being measured.

[0043] As described above, Figure 4 shows the functional block of the control member 5 of the device 1. As shown in this figure, the control member 5 of the device 1 is composed of a light emission control signal generation unit 51, a drive signal generation unit 52, a flight time measurement unit 53, a position relationship change control unit 54, and a main control unit 55. In this example, the device 1 is connected to an external computer or the like by wire or wireless connection and receives commands from the operator of the device 1 to perform the desired processing.

[0044] The control member 5 of the device 1 is not limited as long as it has the above-described function and can be realized by various configurations, but for example, it is preferable to arrange resistors, capacitors, IC chips, etc. on a plastic substrate on which metal wiring is formed and connect them with the metal wiring. Furthermore, it is preferable that this printed circuit board is not only composed of a so-called gate array that performs predetermined processing, but also a programmable so-called FPGA (Field-Programmable gate array).

[0045] Furthermore, the light emission control signal generation unit 51 in the control member 5 of this device 1 generates a light emission control signal in response to an external command signal and outputs it to the light irradiation member 2, which then emits light based on this signal.

[0046] As is clear from the above description, the light emission control signal generated by this control member 5 is a signal input to the light irradiation member 2, more specifically to the light source member 21 of the light irradiation member 2. Based on this light emission control signal, the light source member 21 can emit a predetermined amount of light.

[0047] Furthermore, while the waveform of the light emission control signal is not limited as long as it emits light from the light source member 21 and achieves the effect of the device 1, it is preferable that it be a pulse-like waveform that occurs at regular intervals, as shown in this figure. This makes it possible to improve the peak value of the laser light, which has the effect of enabling accurate measurements in scenes with high turbidity.

[0048] Furthermore, the drive signal generation unit 52 in the control member 5 of this device 1 generates a drive signal, which is a signal for controlling the optical scanning member 23 in the optical irradiation member 2. The optical scanning member 23 is driven by the drive signal generation unit 52, making it possible to emit the laser light generated by the light source member 21 in the desired direction. The waveform of the drive signal can be adjusted as appropriate depending on the type of optical scanning member 23 used.

[0049] Furthermore, the control member 5 includes a time-of-flight measurement unit 53. The time-of-flight measurement unit 53 calculates time-of-flight data and distance data based on the electrical signal received from the light-receiving member 3. Theoretically, the time-of-flight data can be calculated as the difference between the time data when the light-irradiating member 2 irradiated light and the time data when the light-receiving member 3 received the light. In other words, "time-of-flight data" refers to data that contains information about the time the light traveled (time of flight). If this time-of-flight data is known, the round-trip flight distance data of the laser beam can be measured by multiplying this time-of-flight data by the speed of light data, which contains information about the speed of light (half of this distance is the distance between the device 1 and the object being measured). In other words, "distance data" refers to data that contains information about the distance between the device 1 and the object being measured, and includes information about half the product of the time-of-flight data value and the speed of light data value. Note that the device 1 is intended to be used in a medium, more specifically in water, and for more accurate measurement, it is preferable to use the speed of light data in the medium, more specifically in water. The acquired distance data is output to the main control unit 55.

[0050] Furthermore, the device 1 is equipped with a positional relationship change control unit 54. By including this positional relationship change control unit 54, it is possible to generate an electrical signal for driving the positional relationship change member 4 based on an electrical signal from the main control unit 55, specifically a control signal, and to control the positional relationship change member 4.

[0051] Furthermore, the main control unit 55 of this device 1 is connected to the light emission control signal generation unit 51, the drive signal generation unit 52, the flight time measurement unit 53, and the position relationship change control unit 54, and performs overall control, i.e., main control. The main control unit 55 has the function of a relay point that, for example, records distance data input from the flight time measurement unit 53 and outputs it to an externally connected computer or the like.

[0052] Furthermore, in this method, it is preferable to irradiate while scanning with visible laser light. Since the cross-sectional area of ​​the emitted laser light is a minute point region, even if the laser light is shone on the object to be measured, only the distance to the point where the light hits the object can be measured. Therefore, by irradiating while scanning, it becomes possible to measure distances over a wide area by determining the distances at multiple points, even though they are still points. This scanning can be achieved by the optical scanning member 23 described above.

[0053] While there are no particular limitations on the method of scanning light, examples include raster scanning and rotational scanning. However, considering cases where the common photodetector uses photoelectric conversion elements such as CCDs or CMOS, raster scanning is preferable because it corresponds to the cells arranged in a grid of photoelectric conversion elements, making it simpler. Figure 16 shows an example of raster scanning. In raster scanning, during scanning, the process starts from one corner (upper left in the figure, the intersection of the left vertical line and the upper horizontal line) and gradually moves downwards to the other vertical line (right vertical line) (moving from the upper horizontal line to the lower horizontal line) (this is called "one line"), then turns back and returns to the one vertical line (left vertical line), and then turns back again and repeats until it reaches the other corner (lower right in the figure, the intersection of the right vertical line and the lower horizontal line). This makes it possible to scan a certain area without any omissions. After reaching the other corner (bottom right in the diagram), the sensor returns linearly (in a non-emitting state) to the first corner (top left in the diagram), and then starts scanning again as the next frame (that is, the period from one corner to the other corner and back to the first corner constitutes one frame).

[0054] In summary, this device 1 provides an underwater monitoring device and method that take into account the turbidity of the water, can handle various turbidity conditions, and offers high measurement accuracy.

[0055] Furthermore, in this device 1, by combining the light-emitting member 2 and the light-receiving member 3, three-dimensional information with depth can be obtained from the distance information between this device 1 and the object to be measured.

[0056] Figure 17 shows the flow of the peak determination process performed by this device 1.

[0057] First, (A) determine whether or not there is a saturation region in the measured signal intensity. If there is no saturation region, the signal intensity waveform with the longest distance to the peak value (the one with the longest time to appear) is selected as the received signal from the object being measured, and the measurement is terminated. On the other hand, if there is a saturation region, proceed to the next determination process.

[0058] Next, (B) determine whether the signal has peak values ​​outside the saturation region. If there are peak values, the peak value with the longest distance outside the saturation region (the one with the longest time to appear) is used as the received signal from the object being measured, and the measurement is terminated. On the other hand, if there are no signal peak values ​​outside the saturation region, proceed to the next determination process.

[0059] Next, (C) check whether the distance between the light-emitting member and the light-receiving member has reached the mechanical limit. If it has not, widen the distance between the light-emitting member and the light-receiving member by a predetermined distance, and then return to the process described in (B) above. On the other hand, if the mechanical limit has been reached, the measurement is terminated because there is no object to be measured.

[0060] In (C) above, if the positional relationship changing member 4 is a rotating member, it is preferable that the above mechanical limit be a predetermined number of rotations or rotation angle. For example, it is preferable that the mechanical limit be 1 rotation or 360 degrees.

[0061] As described above, this device 1 can reduce reflected noise even when it would otherwise be obscured by it, thereby providing an underwater monitoring device and method that can handle various turbidity conditions and have high measurement accuracy. [Industrial applicability]

[0062] The present invention has industrial applicability as an underwater monitoring device and underwater monitoring method. [Explanation of Symbols]

[0063] 1. Underwater monitoring device 2. Light-irradiating component 21. Light source component 22. Optical path adjustment member 221 Lens 23. Optical scanning component 3. Light-receiving component 31. Photoelectric conversion element 32. Bandpass filter 33 lenses 4. Positional relationship changing component 5. Control component 51. Light emission control signal generation unit 52. Drive signal generation unit 53. Flight time measurement unit 54. Positional Relationship Change Control Unit 55. Main Control Unit 6. Cabinet N··Noise-inducing object L-Laser light R··Reflected light

Claims

1. A light-irradiating member that emits laser light in the visible region, A light-receiving member that receives reflected light of the visible-range laser light irradiated by the light-irradiating member, An underwater monitoring device comprising a positional relationship changing member for changing the positional relationship between the light irradiating member and the light receiving member.

2. The positional relationship changing member is, The underwater monitoring device according to claim 1, which is a distance adjustment member that changes the distance between the light irradiating member and the light receiving member.

3. The positional relationship changing member is, The underwater monitoring device according to claim 1, which is a rotating member that rotates the light-receiving member or the light-emitting member around the light-emitting member or the light-receiving member.

4. The underwater monitoring device according to claim 1, wherein the optical axis of the light irradiating member and the optical axis of the light receiving member are not coaxial biaxial optical system.

5. A light-irradiating member that emits laser light in the visible region, A light-receiving member that receives reflected light of the visible-range laser light irradiated by the light-irradiating member, An underwater monitoring device comprising a control member for controlling the light irradiation member and the light receiving member, Multiple light-receiving members are provided for each light-irradiating member. The control member is an underwater monitoring device that selects the output of one of the multiple light-receiving members.

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