Patent Publication Number: US-2023156519-A1

Title: Communication volume control device, communication volume control method, andrecording medium with program recorded therein

Description:
TECHNICAL FIELD 
     The present disclosure relates to a communication volume control device, a communication volume control method, and a program. 
     BACKGROUND ART 
     A system that collects road images captured by a vehicle and monitors a road status is known. 
     For example, PTL 1 discloses a technique in which a plurality of vehicles mounted with drive recorders are caused to travel, and road images to be captured by each vehicle and information on image capturing such as a time, a position, and the like are transmitted as image information to an analysis device via a communication network. The data analysis device uses the received image information to analyze a road status. The technique of PTL 1 may be used by a road manager of a disaster-stricken area to grasp road conditions allowing travel through the disaster-stricken area for evacuation and safe movement of residents in the disaster-stricken area during a disaster. 
     During a disaster, a communication band in the disaster-stricken area may become overwhelmed due to an increase in communication caused by safety confirmation and information collection not only by disaster victims, but also by people outside the disaster-stricken area, or further, caused by a power outage, a disaster at a base station, or the like. When the communication band is in such an overwhelmed state, it is difficult for an information processing device to receive image information, including images from vehicles. 
     In response, PTL 2 discloses a technique for reducing a communication volume (information volume) by only transmitting image information showing unusual behavior, for example, sharp turning, repeated braking, a sudden decrease in speed, or the like from vehicles to a data analysis device. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] WO 2015/129045 A 
         [PTL 2] JP 2019-160199 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the technique of PTL 2, there is a possibility that information necessary for responding during a disaster may be insufficient, or a large amount of image information not related to damage conditions of a disaster-stricken area may be transmitted. Therefore, with the technique of PTL 2, an operator of the information processing device cannot quickly acquire the information necessary for responding during the disaster in the disaster-stricken area. 
     An object of the present disclosure is to provide a communication volume control device, a communication volume control method, and a program capable of solving the above-described problems by suppressing the occurrence of data communication congestion when a disaster occurs and allowing the acquisition of information necessary for responding to a disaster in a disaster-stricken area. 
     Solution to Problem 
     A communication volume control device according to one aspect of the present disclosure, includes: an acquisition means configured to acquire, when a disaster occurs, target area information indicating a target area expected to be impacted by the disaster that has occurred; and an instruction means configured to instruct a plurality of imaging devices, which are mounted to each of a plurality of moving bodies and which transmit monitoring information related to captured images to a monitoring device at a predetermined timing, to adjust a communication volume based on the target area information when transmitting the monitoring information to the monitoring device from the imaging devices. 
     A communication volume control method according to one aspect of the present disclosure includes: acquiring, when a disaster occurs, target area information indicating a target area expected to be impacted by the disaster that has occurred; and instructing a plurality of imaging devices, which are mounted to each of a plurality of moving bodies and which transmit monitoring information related to captured images to a monitoring device at a predetermined timing, to adjust a communication volume based on the target area information when transmitting the monitoring information to the monitoring device from the imaging devices. 
     A recording medium according to one aspect of the present disclosure records a program caused to execute a process including: acquiring, when a disaster occurs, target area information indicating a target area expected to be impacted by the disaster that has occurred; and instructing a plurality of imaging devices, which are mounted to each of a plurality of moving bodies and which transmit monitoring information related to captured images to a monitoring device at a predetermined timing, to adjust a communication volume based on the target area information when transmitting the monitoring information to the monitoring device from the imaging devices. 
     Advantageous Effects of Invention 
     An effect of the present disclosure is to suppress the occurrence of data communication congestion when a disaster occurs and allow the acquisition of information necessary for responding to a disaster in a disaster-stricken area. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram illustrating an outline of a monitoring system  10  according to a first example embodiment. 
         FIG.  2    is a block diagram illustrating an example of a configuration of the monitoring system  10  according to the first example embodiment. 
         FIG.  3    is an example of a table illustrating a relationship between a disaster classification and a hazard map according to the first example embodiment. 
         FIG.  4    is an example of a hazard map indicating an area in which a mudslide is expected, according to the first example embodiment. 
         FIG.  5    is an example of a hazard map indicating an area in which flooding damage caused by an overflowing river is expected, according to the first example embodiment. 
         FIG.  6    is an example of a hazard map indicating an area in which damage caused by a volcanic eruption is expected, according to the first example embodiment. 
         FIG.  7    is an example of a hazard map indicating an area in which damage caused by a tsunami is expected, according to the first example embodiment. 
         FIG.  8    is a flowchart illustrating a communication volume reduction process according to the first example embodiment. 
         FIG.  9    is an example of a map showing a target area according to the first example embodiment. 
         FIG.  10    is a block diagram illustrating an example of another configuration of the monitoring system  10  according to the first example embodiment. 
         FIG.  11    is an example of disaster information when the disaster classification is an earthquake, according to a second example embodiment. 
         FIG.  12    is an example of disaster information when the disaster classification is a tsunami, according to the second example embodiment. 
         FIG.  13    is an example of disaster information when the disaster classification is typhoon/heavy rain, according to the second example embodiment. 
         FIG.  14    is an example of disaster information when the disaster classification is an eruption, according to the second example embodiment. 
         FIG.  15    is a flowchart of a communication volume reduction process according to the second example embodiment. 
         FIG.  16    is a block diagram illustrating an example of a configuration of a communication volume control device  1  according to a third example embodiment. 
         FIG.  17    is a block diagram illustrating an example of a hardware configuration of a computer  500 . 
     
    
    
     EXAMPLE EMBODIMENT 
     The example embodiments will be described in detail with reference to the drawings. The same reference numerals are given to the same constituent elements in each of the drawings and each of the example embodiments described in the description, and descriptions thereof will be omitted as appropriate. 
     First Example Embodiment 
     A first example embodiment will be described. The present example embodiment will be described on the assumption that imaging devices are mounted to vehicles, which are a type of moving body. 
     First, a configuration of a monitoring system according to the first example embodiment will be described.  FIG.  1    is a schematic diagram illustrating an outline of a monitoring system  10  according to the first example embodiment. In reference to FIG.  1 , the monitoring system  10  includes a plurality of imaging devices  20 _ 1 ,  20 _ 2 , . . .  20 _N (N represents a natural number) (hereinafter also collectively referred to as imaging devices  20 ), a communication volume control device  30 , a monitoring device  40 , and a plurality of vehicles  50 _ 1 ,  50 _ 2 , . . .  50 _N (N represents a natural number) (hereinafter also collectively referred to as vehicles  50 ). 
     In the monitoring system  10 , the imaging devices  20 _ 1 ,  20 _ 2 , . . .  20 _N are mounted to each of the vehicles  50 _ 1 ,  50 _ 2 , . . .  50 _N belonging to an institution that manages roads, for example, a local government body, a road management company, or the like. In the monitoring system  10 , the communication volume control device  30 , the monitoring device  40 , and the imaging devices  20 _ 1 ,  20 _ 2 , . . .  20 _N are connected in such a way as to be communicable, for example, via a communication network. 
     The communication volume control device  30  and the monitoring device  40  are arranged, for example, at a road management department of the above-described institution. The communication volume control device  30  and the monitoring device  40  may be arranged at a place other than the road management department of the above-described institution. In this case, the communication volume control device  30  and the monitoring device  40  may be enabled by a cloud computing system. 
     A case in which the imaging devices  20  are mounted to the vehicles  50  in the present example embodiment will be described. In this case, the imaging devices  20  may be, for example, drive recorders mounted to a vehicle. The imaging devices  20  may be mounted to another moving body such as a bicycle, a drone, or the like, or a person may carry the imaging devices  20  while walking. An image capturing device is not limited to the moving bodies, but may be a fixed/fixed point camera installed on a traffic light or the like. 
     Next, a configuration of each device will be described with reference to  FIG.  2   .  FIG.  2    is a block diagram illustrating an example of a configuration of the monitoring system  10  according to the first example embodiment. 
     (Configuration of Imaging Devices) 
     As illustrated in  FIG.  2   , the imaging devices  20  include an imaging unit  21 , a time acquisition unit  22 , a position acquisition unit  23 , a storage unit  24 , a transmission unit  25 , and a transmission control unit  26 . 
     The imaging unit  21  captures a periphery of the vehicles  50 . The imaging unit  21  captures a periphery of the vehicles  50  at predetermined intervals while the vehicles  50  travel on a road. The images obtained by image capturing may or may not include images of peripheral roads, such as forward of the vehicles  50  and the like. The images obtained by image capturing are images of a periphery of moving bodies when the imaging devices  20  are mounted to all of the moving bodies, and the images are of a periphery of a person when the imaging devices  20  are carried by the person. 
     The time acquisition unit  22  acquires a time of image capturing by the imaging unit  21  (hereinafter also referred to as an image capturing time). For example, the time acquisition unit  22  may acquire the image capturing time from the time (system clock) managed by the imaging devices  20  in conjunction with the image capturing of the imaging unit  21 . The time acquisition unit  22  outputs the image capturing time to the imaging unit  21 . 
     The position acquisition unit  23  acquires a position captured by the imaging unit  21  (hereinafter also referred to as an image capturing position). For example, the position acquisition unit  23  may be configured in such a way as to acquire the image capturing position in conjunction with the imaging capturing of the imaging unit  21 . The position acquisition unit  23  outputs, for example, the image capturing position to the imaging unit  21 . The position acquisition unit  23  is, for example, a global positioning system (GPS) receiver, and may be included in the imaging unit  21 , or may be a separate unit. 
     The imaging unit  21  acquires the image capturing time from the time acquisition unit  22 , acquires the image capturing position from the position acquisition unit  23 , and stores the captured images in the storage unit  24  as the monitoring information in association with the image capturing time and the image capturing position. 
     The storage unit  24  stores vehicle identifiers (IDs). The storage unit  24  also stores the monitoring information. The storage unit  24  is, for example, a random access memory (RAM). 
     The transmission unit  25  acquires the monitoring information from the storage unit  24  and transmits it to the monitoring device  40  via a communication network. The monitoring information may be transmitted, for example, in a mode in which the monitoring information including the images is transmitted each time an image is captured, or in a mode in which the monitoring information including each of one or more images captured in each period is transmitted at each predetermined period. A communication volume of the monitoring information transmitted by the transmission unit  25  is controlled by the transmission control unit  26 . 
     The transmission control unit  26  controls the communication volume of the monitoring information transmitted from the transmission unit  25 . When the transmission control unit  26  receives an instruction from the later-described communication volume control device  30  to reduce the communication volume of the monitoring information to be transmitted (hereinafter also referred to as a communication volume reduction instruction), it reduces the communication volume of the monitoring information to less than a normal state (before a disaster has occurred). For example, during a normal state, the transmission control unit  26  causes the transmission unit  25  to transmit the above-described monitoring information including the vehicle IDs, the images, the image capturing time, and the image capturing position as is. When the communication volume is reduced, the transmission control unit  26  causes the transmission unit  25  to transmit the above-described monitoring information excluding the images. The transmission control unit  26  may also change a frame rate or a bit rate of the images to reduce the communication volume instead of excluding the images from the monitoring information to reduce the communication volume. 
     (Configuration of Communication Volume Control Device) 
     The communication volume control device  30  includes a storage unit  31 , a disaster classification acquisition unit  32 , an area specifying unit  33 , and a transmission instruction unit  34 . The area specifying unit  33  is an example embodiment of an acquisition unit in the present disclosure. The transmission instruction unit  34  is an example embodiment of an instruction unit in the present disclosure. Some or all of the constituent elements of the communication volume control device  30  may be enabled by a cloud computing system, as described above. For example, the storage unit  31 , the area specifying unit  33 , and the transmission instruction unit  34  may be arranged on a cloud, and the disaster classification acquisition unit  32  may be arranged at a road management department. 
     The storage unit  31  stores a classification of the disaster that has occurred acquired by the disaster classification acquisition unit  32 . Examples of the disaster classification include earthquake, tsunami, typhoon/heavy rain, and eruption. 
     The storage unit  31  is loaded in advance with hazard maps of predetermined areas based on the disaster classification.  FIG.  3    is an example of a table illustrating a relationship between a disaster classification and a hazard map according to the first example embodiment. In reference to  FIG.  3   , it is illustrated that, for example, a mudslide hazard map is used when the disaster classification is earthquake. Details of the hazard maps will be described later. 
     The disaster classification acquisition unit  32  acquires the classification of the disaster that has occurred from, for example, an external source such as a meteorological agency or the like. The disaster classification acquisition unit  32  may acquire the classification of the disaster that has occurred from an input by an operator or the like via an input device (not illustrated). The disaster classification acquisition unit  32  causes the storage unit  31  to store the acquired disaster classification. 
     The area specifying unit  33  acquires the classification of the disaster that has occurred from the storage unit  31 . The area specifying unit  33  acquires the hazard map from the storage unit  31  based on the acquired disaster classification and the table illustrating a relationship between a disaster classification and a hazard map. The area specifying unit  33  specifies an area in which damage caused by the disaster is expected, that is, an area to which the monitoring information should be transmitted as a priority (hereinafter also referred to as a target area), from the acquired hazard map. The area specifying unit  33  outputs information on a target area to the transmission instruction unit  34 . The area specifying unit  33  may acquire the hazard map from an external database or a website of a public institution (such as a meteorological agency, a prefectural government, or the like) via a communication network. 
     The transmission instruction unit  34  transmits the communication volume reduction instruction to the vehicles  50  located outside the target area based on the information on the target area output from the area specifying unit  33 . The communication volume reduction instruction is an instruction to reduce the communication volume of the monitoring information to less than before the disaster (a normal state). 
     The transmission instruction unit  34  transmits, for example, the communication volume reduction instruction to all of the communicable vehicles  50  by specifying the target area. In this case, the imaging devices  20  of each vehicle  50  determine whether the vehicles  50  are located outside the target area, and reduce the communication volume when they are located outside the target area. 
     The transmission instruction unit  34  may extract the vehicles  50  located outside the target area based on the monitoring information, and transmit the communication volume reduction instruction to the vehicles  50 . The vehicles  50  located outside the target area are extracted based on the image capturing position included in, for example, the monitoring information stored in a storage unit  41  of the monitoring device  40 . 
     (Configuration of Monitoring Device) 
     The monitoring device  40  includes the storage unit  41  and a display control unit  42 . 
     The storage unit  41  stores the monitoring information received from the imaging devices  20 . 
     The display control unit  42  acquires, for example, the monitoring information of a position specified by an operator from the storage unit  41  and causes a display device (not illustrated) to display the images included in the monitoring information. The display control unit  42  may acquire the monitoring information from the storage unit  41  and display a mark indicating the presence of the monitoring information from the vehicles  50  at a location associated with the image capturing positions included in the monitoring information on the hazard map, and it may also cause the display device (not illustrated) to display the mark. 
     Next, the hazard maps based on the disaster classifications will be described. 
       FIG.  4    is an example of a hazard map indicating an area in which a mudslide is expected, according to the first example embodiment. Mudslides occur after heavy rain or an earthquake. Therefore, a hazard map such as is illustrated in  FIG.  4    is used when the disaster classification is typhoon/heavy rain or earthquake. In reference to  FIG.  4   , in the case of a mudslide, an area (position) indicated by a black dot such as is illustrated in an area A indicates that a mudslide is likely to occur. 
       FIG.  5    is an example of a hazard map indicating an area in which flooding damage caused by an overflowing river is expected, according to the first example embodiment. A hazard map such as is illustrated in  FIG.  5    is used when the disaster classification is typhoon/heavy rain. In reference to  FIG.  5   , in the case of an overflowing river, an area with heavy shading such as is shown in an area B 1  indicates that an amount of flooding damage is greater than that in an area with light shading, such as is shown in an area B 2 . 
       FIG.  6    is an example of a hazard map indicating an area in which damage caused by a volcanic eruption is expected, according to the first example embodiment. A hazard map such as is illustrated in  FIG.  6    is used when the disaster classification is eruption. In reference to  FIG.  6   , in the case of a volcanic eruption, an area with heavy shading such as is shown in an area C 1  indicates that an amount of damage caused by the eruption is greater than that in an area with light shading, such as is shown in an area C 2 . 
       FIG.  7    is an example of a hazard map indicating an area in which damage caused by a tsunami is expected, according to the first example embodiment. A hazard map such as is illustrated in  FIG.  7    is used when the disaster classification is tsunami. In reference to  FIG.  7   , in the case of a tsunami, an area with heavy shading such as is shown in an area D 1  indicates that an amount of damage caused by the tsunami is greater than that in a lightly shaded area, such as is illustrated in an area D 2 . 
     As illustrated above, depending on the disaster classification, a hazard map in which areas are split into levels based on a magnitude of the expected damage is created. It is possible to use these hazard maps with the approval of hazard map creators, such as a local government body or the like. 
     Next, operation of the first example embodiment will be described. 
     (Communication Volume Reduction Process) 
     A communication volume reduction process of the monitoring system  10  will be described with reference to  FIGS.  8  to  12   . 
       FIG.  8    is a flowchart illustrating a communication volume reduction process according to the first example embodiment. The communication volume reduction process may be executed, for example, automatically when a disaster occurs, or it may be executed based on an instruction from an operator or the like. The following process of step S 101  to step S 104  is a process performed in the communication volume control device  30 . The following process of step S 105  to step S 108  is a process performed in the imaging devices  20  of the vehicles  50 . 
     The disaster classification acquisition unit  32  of the communication volume control device  30  acquires the classification of the disaster that has occurred from an external website of a meteorological agency or the like and stores it in the storage unit  31  (step S 101 ). The disaster classification acquisition unit  32  acquires, for example, heavy rain as the classification of the disaster that has occurred from the meteorological agency. 
     The area specifying unit  33  acquires a hazard map based on the disaster classification in reference to the classification of the disaster that has occurred stored in the storage unit  31 . (Step S 102 ). For example, when the classification of the disaster that has occurred is heavy rain, the area specifying unit  33  acquires the mudslide hazard map (see  FIG.  4   ) and a flooding hazard map (see  FIG.  5   ) based on the table showing a relationship between a disaster classification and a hazard map split by disaster (see  FIG.  3   ). 
     The area specifying unit  33  specifies an area in which damage is expected indicated in the acquired hazard map as the target area (step S 103 ). For example, in reference to the flooding hazard map of  FIG.  5   , the area specifying unit  33  sets the area with heavy shading (an area in which an expected level of flooding damage is high) such as is illustrated in the area B 1  and the area with light shading (an area in which an expected level of flooding damage is medium) such as is illustrated in the area B 2  as the target area. 
     The transmission instruction unit  34  transmits the communication volume reduction instruction to the vehicles  50  located outside the target area (step S 104 ). The transmission instruction unit  34  transmits the communication volume reduction instruction to all of the communicable vehicles  50  by specifying the target area. For example, the transmission instruction unit  34  transmits the communication volume reduction instruction specifying the area B 1  and the area B 2  as the target area. 
     When the transmission control unit  26  in the imaging devices  20  of the each vehicle  50  receives the communication volume reduction instruction from the transmission instruction unit  34  of the communication volume control device  30  (step S 105 ), the vehicles  50  determine whether a host vehicle is located outside the target area (step S 106 ). The transmission control unit  26  determines whether the host vehicle is located outside the target area based on, for example, map information stored in advance in the storage unit  24  or the like and the position of the host vehicle acquired by the position acquisition unit  23 . 
     When the host vehicle is located outside the target area (step S 106 /Yes), the transmission control unit  26  reduces the communication volume to less than a normal state when transmitting the monitoring information (step S 107 ). When the host vehicle is located in the target area (step S 106 /No), the transmission control unit  26  keeps the communication volume to that of a normal state when transmitting the monitoring information (step S 108 ). 
     For example, the vehicles  50  located outside the area B 1  and the area B 2  transmit the monitoring information excluding the images to the monitoring device  40 . The vehicles  50  located in the area B 1  and the area B 2  transmit the monitoring information including the images to the monitoring device  40 . 
     Thereafter, the process from step S 104  is repeatedly executed at a predetermined time interval in the communication volume control device  30 . The process in step S 105  to step S 108  is repeatedly executed in the imaging devices  20  of the each vehicle  50  each time the communication volume reduction instruction is received. 
     Through this, from the time a disaster occurs, for the target area, the monitoring information including the images is stored, and for the areas other than the target area, the monitoring information not including the images is stored in the storage unit  41 . 
     A display example displayed on the display device by the display control unit  42  will be described with reference to  FIG.  9   .  FIG.  9    is an example of a map showing the target area according to the first example embodiment. In the example of  FIG.  9   , the target area in an area that is a current position is shown using shading, and an area outside the target area is shown with a blank background. On the map of  FIG.  9   , a road through which the vehicles  50  have passed after the disaster occurs are indicated by a thick line. In reference to  FIG.  9   , a road R 1  through which the vehicles  50  have passed in the target area and a road R 2  through which the vehicles  50  have passed outside the target area are illustrated. The vehicles  50  passing at each position on the roads is detected by receiving the monitoring information including the positions. 
     When an operator of the monitoring device  40  references images of a position a in the target area, for example, the display control unit  42  acquires the images of the position a stored in the storage unit  31  of the communication volume control device  30  to display on the display device in response to the operator clicking on the position a. In the example of  FIG.  9   , images of peripheral roads of the vehicles  50  located at the position a are displayed as the images of the position a. 
     When the operator of the monitoring device  40  references images of a position b outside the target area, outside the target area, no images are transmitted from the vehicles  50  and no images are present in the monitoring device  40  after the disaster occurs. Therefore, when the operator references the images of the position b outside the target area, for example, based on the monitoring information related to the position b (vehicle ID, position, and time), the display control unit  42  may request the vehicles  50  having the vehicle ID to transmit the images at the position b to the monitoring device  40  in response to the operator clicking on the position b. The display control unit  42  may also display the images at the position b transmitted from the vehicles  50  on the map. 
     The operation of the first example embodiment is thereby completed. 
     In the first example embodiment, the communication volume control device  30  and the monitoring device  40  have been configured to be arranged at a road management department, however as illustrated in  FIG.  10   , the communication volume control device  30  and the imaging devices  20  may be mounted to the vehicles  50 . 
     The communication volume control device  30  and the monitoring device  40  may be included in one device, or the communication volume control device  30  and the imaging devices  20  may be included in one device. 
     In the first example embodiment, the area specifying unit  33  specified the area in which damage was expected indicated in the acquired hazard map as the target area. The area specifying unit  33  is not limited hereto but may specify an area in which an expected level of damage is equal to or more than a predetermined value as the target area from among the areas in which damage is expected, and the transmission instruction unit  34  may transmit the communication volume reduction instruction to the vehicles  50  located outside the target area. The transmission instruction unit  34  may transmit a communication volume reduction instruction to the vehicles  50  to change a reduction amount of the communication volume based on the expected level of damage (a degree of impact of a disaster) in the target area. In this case, the transmission instruction unit  34  decreases, for example, the reduction amount of the communication volume the higher the expected level of damage. 
     In the first example embodiment, the monitoring information has been configured to include images, however it is not limited hereto. In respect of the monitoring information, the communication volume from the vehicles  50  outside the target area may be reduced in the target area and outside the target area, and images may be excluded. 
     Next, an effect of the first example embodiment will be described. 
     According to the first example embodiment, the occurrence of data communication congestion when a disaster occurs is suppressed and information necessary for responding to a disaster in a disaster-stricken area can be acquired. The reason is due to the following. The area specifying unit  33  of the communication volume control device  30  acquires the hazard map indicating the area in which the damage of the disaster that has occurred is expected. This is because the transmission instruction unit  34  instructs the imaging devices of the vehicles outside the target area to reduce the communication volume when transmitting the monitoring information to the monitoring device from the imaging devices to less than before the disaster occurred, with the area in which the damage of the disaster is expected set as the target area based on the acquired hazard map. 
     Second Example Embodiment 
     A second example embodiment will be described. 
     The second example embodiment differs from the first example embodiment in that it uses disaster information including a degree (level) of disaster for each area based on the disaster classification, instead of the hazard map. 
     The configuration of the monitoring system in the second example embodiment is the same as the configuration of the monitoring system  10  according to the first example embodiment ( FIG.  2   ). However, in the second example embodiment, the actions of the storage unit  31 , the disaster classification acquisition unit  32 , and the area specifying unit  33  are different. For the second example embodiment, only the parts differing from those of the first example embodiment will be described, with reference to  FIG.  2   . 
     The storage unit  31  stores the monitoring information received from the imaging devices  20 . The storage unit  31  stores the disaster information acquired by the disaster classification acquisition unit  32 . The disaster information includes the degree (level) of disaster and the areas based on the disaster classifications. 
     The disaster information will be described with reference to  FIGS.  11  to  14   .  FIG.  11    is an example of disaster information when the disaster classification is earthquake, according to the second example embodiment. In reference to  FIG.  11   , the disaster information related to an earthquake may include, for example, an area A that is a seismic source, a magnitude, and a seismic intensity of each area a to e as the degree (level) of disaster. 
       FIG.  12    is an example of disaster information when the disaster classification is tsunami, according to the second example embodiment. In reference to  FIG.  12   , the disaster information related to a tsunami may include, for example, forecast areas f to j in which tsunami damage is expected and a wave height in each of the forecast areas as the degree (level) of disaster. 
       FIG.  13    is an example of disaster information when the disaster classification is typhoon/heavy rain, according to the second example embodiment. In reference to  FIG.  13   , the disaster information related to a typhoon/heavy rain may include, for example, areas k to o in which damage is expected, in addition to an expected rainfall amount and a wind speed in each of the areas as the degree (level) of disaster. 
       FIG.  14    is an example of disaster information when the disaster classification is eruption, according to the second example embodiment. In reference to  FIG.  14   , the disaster information related to an eruption may include, for example, an eruption alert level as the degree (level) of disaster and target areas to be alerted. 
     These types of disaster information are illustrative examples according to the present example embodiment and are not limited to the above-described examples. For example, the disaster information related to a typhoon/heavy rain may further include areas in which damage caused by an overflowing river is expected. 
     The disaster classification acquisition unit  32  acquires the disaster information on a disaster that has occurred from, for example, an external source such as a meteorological agency or the like. Since there are cases where the disaster information is updated as needed, the disaster classification acquisition unit  32  may acquire the disaster information periodically. 
     The area specifying unit  33  acquires disaster information in which the degree (level) of disaster is equal to or more than a predetermined threshold value from the storage unit  31 . The disaster information in which the degree (level) of disaster is equal to or more than the predetermined threshold is disaster information including areas in which the degree (level) of disaster is equal to or more than the threshold. For example, when the disaster information is earthquake, it includes areas in which shaking at a seismic intensity equal to or more than 5 has been observed. The area specifying unit  33  does not acquire the disaster information when there is no disaster information in which the degree (level) of disaster is equal to or more than the predetermined threshold in the storage unit  31 . 
     The area specifying unit  33  specifies an area included in the acquired disaster information as a target area. 
     Next, operation of the second example embodiment will be described. 
     A communication volume reduction process in the monitoring system according to the second example embodiment will be described.  FIG.  15    is a diagram illustrating a flowchart of the communication volume reduction process according to the second example embodiment. 
     The disaster classification acquisition unit  32  acquires the disaster information from an external site such as a meteorological agency or the like and stores it in the storage unit  31  (step S 201 ). The area specifying unit  33  references the disaster information stored in the storage unit  31  and determines whether there are any areas in which the degree (level) of disaster is equal to or more than the threshold (step S 202 ). In a case where there is an area in which the degree (level) of disaster is equal to or more than the threshold (step S 202 /Yes), the area specifying unit  33  specifies the area as the target area (step S 203 ). In the case where the disaster information is earthquake (see  FIG.  11   ) and the threshold is set to a seismic intensity of 5, the area specifying unit  33  specifies the area c and the area d as the target area. 
     Thereafter, the process from step S 204  is repeatedly executed at a predetermined time interval in the communication volume control device  30 . The process in step S 205  to step S 208  is repeatedly executed in the imaging devices  20  of the each vehicle  50  each time the communication volume reduction instruction is received. 
     When there are no areas in which the degree (level) of disaster is equal to or more than the threshold (step S 202 /No), the area specifying unit  33  ends the communication volume reduction process. 
     The operation of the second example embodiment is thereby completed. 
     In the second example embodiment, the disaster information based on the disaster classification is used instead of the hazard maps, however an area in which an abnormality is detected using data from a satellite may be set as the target area. A method of detecting an abnormality from satellite data may be, for example, a method of comparing data from before a disaster with current data to confirm flooding or a building collapse from a data difference on a time axis. The detailed disaster information may be acquired by performing image analysis on all or some (conditions may be further narrowed down by area, time, or the like) images among the images and satellite data acquired in a target information area. 
     The target area may be configured in such a way as to be specified based on an area in which a communication environment has suddenly deteriorated, instead of the disaster information. This is because in this case, it is considered that in an area in which a communication environment has suddenly deteriorated, it is likely that some problem has occurred due to a disaster. A sudden deterioration of the communication environment is detectable when, for example, a difference between a communication volume before the deterioration of a communication environment and the current communication volume exceeds a predetermined threshold. 
     Instead of the disaster information, in case where a significant degree of acceleration in a vertical direction has been simultaneously detected from sensors (not illustrated) in the imaging units  21  of the plurality of vehicles  50 , when an earthquake has occurred in an area near to where each of the plurality of vehicles is located, the area may be specified as the target area. 
     Next, an effect of the second example embodiment will be described. 
     According to the second example embodiment, the occurrence of data communication congestion during a disaster is suppressed and information necessary for responding to a disaster in a disaster-stricken area can be acquired. The reason is due to the following. The area specifying unit  33  of the communication volume control device  30  acquires disaster information indicating an area in which a disaster has occurred. This is because the transmission instruction unit  34  instructs the imaging devices of the vehicles outside the target area to reduce the communication volume to less than before the disaster occurred when transmitting the monitoring information to the monitoring device from the imaging devices, with the area in which the disaster has occurred set as the target area based on the acquired disaster information. 
     Third Example Embodiment 
     A third example embodiment will be described. 
       FIG.  16    is a block diagram illustrating an example of a configuration of the communication volume control device  1  according to the third example embodiment. 
     The communication volume control device  1  includes an acquisition unit  2  and an instruction unit  3 . When a disaster occurs, the acquisition unit  2  acquires the target area information indicating a target area expected to be impacted by the disaster that has occurred. The instruction unit  3  instructs the plurality of imaging devices, which are mounted to each of a plurality of moving bodies and which transmit monitoring information related to captured images to the monitoring device at a predetermined timing, to adjust the communication volume based on the target area information when transmitting the monitoring information to the monitoring device from the imaging devices. 
     The acquisition unit  2  corresponds to the area specifying unit  33  according to the first example embodiment and the second example embodiment. The instruction unit  3  corresponds to the transmission instruction unit  34  according to the first example embodiment and the second example embodiment. 
     According to the third example embodiment, the occurrence of data communication congestion during a disaster is suppressed and information necessary for responding to a disaster in a disaster-stricken area can be acquired. The reason is due to the following. When a disaster occurs, the acquisition unit  2  of the communication volume control device  1  acquires the target area information indicating the target area expected to be impacted by the disaster that has occurred. This is because the instruction unit  3  instructs the imaging devices to adjust the communication volume when transmitting the monitoring information to the monitoring device from the imaging devices based on the target area information. 
     (Hardware Configuration) 
     In each of the above-described example embodiments, each constituent element of each device (the imaging devices  20 , the communication volume control device  30 , the monitoring device  40 , and the like) indicate a functional unit block. Some or all of the each component of the each device may be enabled by any combination of a computer  500  and a program. 
       FIG.  17    is a block diagram illustrating an example of a hardware configuration of the computer  500 . In reference to  FIG.  17   , the computer  500  includes, for example, a central processing unit (CPU)  501 , a read only memory (ROM)  502 , a random access memory (RAM)  503 , a program  504 , a storage device  505 , a drive device  507 , a communication interface  508 , an input device  509 , an output device  510 , an input/output interface  511 , and a bus  512 . 
     The program  504  includes instructions for enabling each function of the each device. The program  504  is loaded in advance in the ROM  502 , the RAM  503 , or the storage device  505 . The CPU  501  enables the each function of the each device by executing the instructions included in the program  504 . For example, the CPU  501  of the communication volume control device  30  executes the instructions included in the program  504  to enable functions of the disaster classification acquisition unit  32 , the area specifying unit  33 , and the transmission instruction unit  34 . For example, the RAM  503  of the communication volume control device  30  may store data of the storage unit  31 . 
     The drive device  507  performs reading and writing of a recording medium  506 . The communication interface  508  provides an interface with a communication network. The input device  509  is, for example, a mouse, a keyboard, or the like, and receives information input from an operator or the like. The output device  510  is, for example, a display, and outputs (displays) information to the operator or the like. The input/output interface  511  provides an interface with peripheral devices. The bus  512  connects each constituent element of the pieces of hardware. The program  504  may be provided to the CPU  501  via a communication network, or may be loaded in advance to the recording medium  506  to be read by the drive device  507  and provided to the CPU  501 . 
     The hardware configuration illustrated in  FIG.  17    is an example, and constituent elements other than these may be added, or some constituent elements may be excluded. 
     There are various modification examples for methods of enabling the each device. For example, the each device may be enabled by any combination of computers and programs each differing for the each constituent element. A plurality of constituent elements included in the each device may be enabled by any combination of one computer and programs. 
     A part or all of the each constituent element of the each device may be enabled by a general-purpose or dedicated circuitry, which includes a processor and the like, or a combination thereof. The circuitry may be configured by a single chip, or it may be configured by a plurality of chips connected via a bus. A part or all of the each constituent element of the each device may be enabled by a combination of the above-described circuitry or the like and programs. 
     When a part or all of the each constituent element of the each device is enabled by a plurality of computers, circuitry, and the like, the plurality of computers, circuitry, and the like may be concentratedly arranged or dispersedly arranged. 
     The communication volume control device  30  may be arranged in the vehicles  50 , or it may be arranged in a different place to the vehicles  50  and connected to the imaging devices  20  via a communication network. 
     Although the present disclosure has been described with reference to the example embodiments, the present disclosure is not limited to the example embodiments. Various modifications capable of being understood by those skilled in the art can be made to the configuration and the details of the present disclosure within the scope of the present disclosure. The configurations in each of the example embodiments can be combined with one another in so far as they do not depart from the scope of the present disclosure. 
     Some or all of the above-described example embodiments may be described such as in the following supplementary notes, however they are not limited to the following. 
     (Supplementary Note 1) 
     A communication volume control device including: 
     an acquisition means configured to acquire, when a disaster occurs, target area information indicating a target area expected to be impacted by the disaster that has occurred; and 
     an instruction means configured to instruct a plurality of imaging devices, which are mounted to each of a plurality of moving bodies and which transmit monitoring information related to captured images to a monitoring device at a predetermined timing, to adjust a communication volume based on the target area information when transmitting the monitoring information to the monitoring device from the imaging devices. 
     (Supplementary Note 2) 
     The communication volume control device according to Supplementary Note 1, wherein the target area information includes information indicating a degree of impact of the disaster for each area, and 
     the instruction means is configured to instruct the imaging devices of the moving bodies, which pass through areas in which a degree of impact of the disaster is smaller for each area, to reduce the communication volume to less than before the disaster occurred when transmitting the monitoring information to the monitoring device from the imaging devices. 
     (Supplementary Note 3) 
     The communication volume control device according to Supplementary Note 1 or 2, wherein the target area information is information to be specified from a hazard map indicating areas in which damage from the disaster is expected for each disaster classification, and 
     the instruction means instructs the imaging devices of the moving bodies outside a target area to reduce the communication volume by setting the areas in which damage from the disaster is expected and which are indicated by the hazard map associated with the classification of the disaster that has occurred as the target area. 
     (Supplementary Note 4) 
     The communication volume control device according to any one of Supplementary Notes 1 to 3, wherein the hazard map indicates areas in which damage from the disaster is expected and an expected level of damage in the areas, and 
     the instruction means instructs the imaging devices of the moving bodies outside an area in which the expected level of damage in respect of the disaster that has occurred in the hazard map is equal to or more than a predetermined value to reduce the communication volume. 
     (Supplementary Note 5) 
     The communication volume control device according to Supplementary Note 1 or 2, wherein the target area information is information to be specified from disaster information generated when a disaster occurs and which indicates an area in which the disaster has occurred, and 
     the instruction means instructs the imaging devices of the moving bodies outside the target area to reduce the communication volume by setting the areas in which the disaster has occurred indicated by the disaster information acquired in respect of the disaster that has occurred set as the target area. 
     (Supplementary Note 6) 
     The communication volume control device according to Supplementary Note 5, wherein the disaster information indicates areas in which damage has occurred and a level of damage in the areas, and 
     the instruction means instructs the imaging devices of the moving bodies outside an area in which the level of damage that has occurred is equal to or more than a predetermined value in the disaster information to reduce the communication volume. 
     (Supplementary Note 7) 
     The communication volume control device according to any one of Supplementary Notes 1 to 6, wherein the monitoring information includes images and an image capturing position of the images, and 
     when instructed to reduce the communication volume, the imaging devices exclude the images from the monitoring information when transmitting to the monitoring device. 
     (Supplementary Note 8) 
     The communication volume control device according to Supplementary Note 7, wherein the monitoring device displays a map indicating the image capturing position included in the monitoring information received from the imaging devices in different modes for when the monitoring information includes the images and when the monitoring information does not include the images. 
     (Supplementary Note 9) 
     The communication volume control device according to Supplementary Note 7, wherein the monitoring device displays images related to the monitoring information received from the imaging devices when the images are included in the monitoring information including a specified imaging capturing position, and when there is a request to display the images when images are not included, makes a request to the imaging devices, which are a transmission source of the monitoring information including the image capturing position, and displays the images received from the imaging devices in response to the request. 
     (Supplementary Note 10) 
     A communication volume control method including: 
     acquiring, when a disaster occurs, target area information indicating a target area expected to be impacted by the disaster that has occurred; and 
     instructing a plurality of imaging devices, which are mounted to each of a plurality of moving bodies and which transmit monitoring information related to captured images to a monitoring device at a predetermined timing, to adjust a communication volume based on the target area information when transmitting the monitoring information to the monitoring device from the imaging devices. 
     (Supplementary Note 11) 
     A recording medium with a program recorded therein, wherein the program is caused to execute a process including: 
     acquiring, when a disaster occurs, target area information indicating a target area expected to be impacted by the disaster that has occurred; and 
     instructing a plurality of imaging devices, which are mounted to each of a plurality of moving bodies and which transmit monitoring information related to captured images to a monitoring device at a predetermined timing, to adjust a communication volume based on the target area information when transmitting the monitoring information to the monitoring device from the imaging devices. 
     REFERENCE SIGNS LIST 
     
         
           1 ,  30  Communication volume control devices 
           2  Acquisition unit 
           3  Instruction unit 
           10  Monitoring system 
           20  Imaging devices 
           21  Imaging unit 
           22  Time acquisition unit 
           23  Position acquisition unit 
           24 ,  31 ,  41  Storage units 
           32  Disaster classification acquisition unit 
           33  Area specifying unit 
           34  Transmission instruction unit 
           40  Monitoring device 
           42  Display control unit 
           50  Vehicles 
           500  Computer 
           501  CPU 
           502  ROM 
           503  RAM 
           504  Program 
           505  Storage device 
           506  Recording medium 
           507  Drive device 
           508  Communication interface 
           509  Input device 
           510  Output device 
           511  Input/output interface 
           512  Bus