Abstract:
A brightness time change of the target object is analyzed and a periodic brightness change is extracted. By the matching with a database which includes data of a candidate of the target object, the features of the target object are estimated. If even the brightness data can be acquired even if the resolution of the optical observation is low, the features and states of the target object can be estimated.

Description:
TECHNICAL FIELD 
       [0001]    The present invention is related to a monitoring system and a monitoring method. 
       BACKGROUND ART 
       [0002]    Even if a defect has occurred after launching an artifact such as an artificial satellite from the ground, it is extremely difficult or impossible to perform maintenances such as direct inspection of the state of the artifact, investigation of a cause and a repairing. Of the artifacts, there is one which has a checking function and a backup function. However, a support by ground staffs through the communication with a ground station is basically needed for the above maintenances. Especially, when the defect has occurred in the communication function of the artifact, the ground staffs cannot know even the current situation of the artifact. 
         [0003]    However, there is a case where it is possible to know the state of the artifact even partially, by optically observing the artifact which orbits the earth, from the ground. 
         [0004]      FIG. 1  is a diagram conceptually showing a system which optically observes the artifact orbiting the earth from the ground.  FIG. 1  shows an optical observation system  10 , a low earth orbit  11 , a low earth orbit satellite  12 , a medium earth orbit  13 , a medium earth orbit satellite  14 , a geostationary orbit  15 , a geostationary orbit satellite  16  and an observation range  17 . The low earth orbit  11  shows 80 km to 2000 km, the medium earth orbit  13  shows 2000 km to 35000 km, and the geostationary orbit  15  shows about 35000 km to 37000 km. 
         [0005]    In an example of  FIG. 1 , the optical observation system  10  is arranged on the ground. The substantial observation range  17  of a general optical observation system  10  covers the so-called low earth orbit  11 , namely, the low earth orbit satellite  12  which orbits the earth above about thousands of kilometers from the ground. However, the resolution necessary to confirm the shape and attitude of the geostationary orbit satellite cannot be achieved, even if it is tried to observe the so-called geostationary orbit satellite  16  which orbits the earth on the so-called geostationary orbit  15  above about 36000 kilometers from the ground by the optical observation system  10  on the ground. 
         [0006]    In conjunction with the above description, Patent Literature 1 (JP 2002-220098A) discloses a method of detecting an object (debris and so on the geostationary orbit) which conducts a specific movement on the celestial. In the method of detecting according to Patent Literature 1, the object which conducts the specific movement is detected from image data obtained through an exposure period from a time t 0  to a time t T , by driving a telescope in a predetermined drive method in the astronomical observation. In this detecting method, when it is supposed that the observation object is observed at a point P x  of the image at an exposure start time t 0 , the trajectory of the object from the time t 0  to the time t T  is calculated on the image data and image data on the trajectory is added. 
       CITATION LIST 
       [0007]    [Patent literature 1] JP 2002-220098A 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is to provide a monitoring system and a monitoring method which can estimate the features and states of a target object orbiting the earth, when the target object is optically observed from the ground, even if the orbit of the target object is the geostationary orbit or above. Other objects and new features will become clear from the description and the attached drawings. 
         [0009]    According to an embodiment, the monitoring system includes an optical observation system and a data processing system. Here, the optical observation system optically observes a target object as an artifact which orbits the earth. The data processing system analyzes a brightness time change of the target object based on the observation result, extracts a periodic brightness change of the target object, and estimates the state of the target object. 
         [0010]    According to an embodiment, the monitoring method includes optically observing a target object as an artifact which orbits the earth, analyzing a brightness time change of the target object based on the observation result, and extracting a periodic brightness change of the target object based on the analysis result. 
         [0011]    According to the embodiments, the features and state of the target object can be estimated, when the brightness data of the target object can be acquired even if the resolution of the optical observation is low because a distance to the target object is too far. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagram showing a conventional system which optically observes an artifact which orbits the earth from the ground. 
           [0013]      FIG. 2  is a block diagram schematically showing the configuration example of a monitoring system according to the present invention. 
           [0014]      FIG. 3  is a flow chart showing the configuration example of a monitoring method of the present invention. 
           [0015]      FIG. 4A  is a graph showing an example of a brightness time change in the present invention. 
           [0016]      FIG. 4B  is a graph showing an example when frequency filtering processing is performed to the brightness time change in the present invention. 
           [0017]      FIG. 5A  is a graph showing a principle of extraction of a periodic brightness change in the present invention. 
           [0018]      FIG. 5B  is another graph showing the principle of extraction of the periodic brightness change in the present invention. 
           [0019]      FIG. 6A  is a diagram showing an example of shape data of a target object which has been stored in a light curve estimation database of the present invention. 
           [0020]      FIG. 6B  is a diagram showing another example of reflection characteristic data of the target object which has been stored in the light curve estimation database of the present invention. 
           [0021]      FIG. 6C  is a diagram showing another example of attitude data of the target object which has been stored in the light curve estimation database of the present invention. 
           [0022]      FIG. 7A  is a graph showing an example of the extraction result of the periodic brightness change in the present invention. 
           [0023]      FIG. 7B  is a graph showing an example of a detected extraordinary event in the periodic brightness change obtained in the present invention. 
           [0024]      FIG. 7C  is a diagram showing an example of a cause of the detected extraordinary event in the periodic brightness change obtained in the present invention. 
           [0025]      FIG. 7D  is a graph showing another example of the detected extraordinary event in the periodic brightness change obtained in the present invention. 
           [0026]      FIG. 7E  is a diagram showing another example of a cause of the detected extraordinary event in the periodic brightness change obtained in the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    Hereinafter, a monitoring system and a monitoring method according to embodiments of the present invention will be described below with reference to the attached drawings. 
       First Embodiment 
       [0028]      FIG. 2  is a block diagram showing a configuration example of the whole of monitoring system according to a first embodiment of the present invention. Referring to  FIG. 2 , the configuration of the monitoring system in the present embodiment will be described. 
         [0029]    As shown in  FIG. 2 , the monitoring system includes a bus  21 , an optical observation system  22  and a data processing system  23 . 
         [0030]    The optical observation system  22  has an adaptive optics unit  221 . 
         [0031]    The data processing system  23  has a processing section  231 , which includes an analyzing section  2311 , a frequency filtering section  2312  and an extracting section  2313 . 
         [0032]    The data processing system  23  further has a storage section  232 , which has a fixed star database  2321 , a space object database  2322 , a light curve estimation database  2323  and an important monitoring object database  2324 . 
         [0033]    The fixed star database  2321  stores data of fixed stars whose brightness can be used as a reference. The space object database  2322  stores data of artifacts which orbit the earth. The light curve estimation database  2323  stores data showing a relation of a feature of a periodicity of the brightness time change, i.e., a periodic brightness change, a shape and attitude of each of target objects, and a feature of a reflectivity of each of surface materials. The important monitoring object database  2324  stores a list of objects determined as important monitoring objects of the target objects and various data of them. 
         [0034]    The connection relation of the components shown in  FIG. 2  will be described. The bus  21  is connected with the optical observation system  22  and the data processing system  23 . In other words, the optical observation system  22  and the data processing system  23  can communicate with each other freely through the bus  21 . 
         [0035]    The operation of each of the components shown in  FIG. 2  will be described. 
         [0036]    The optical observation system  22  is installed on the ground and optically observes the sky. The adaptive optics unit  221  removes an influence of the atmosphere from the monitoring result of the optical observation system  22  by optical compensation. 
         [0037]    The processing section  231  executes a predetermined program which is supplied from the storage section  232  and an input unit  24 , to realize various functions. Note that in order to realize the various functions, the processing section  231  may refer to various data supplied from the storage section  232  and the input unit  24  and may use a part of the storage section  232  as a memory area. 
         [0038]    As one function of the processing section  231 , the analyzing section  2311  receives data acquired from the optical observation system  22  through the bus  21 . In order to make a fixed star and a target object clear, the analyzing section  2311  carries out a matching operation of each data by using the fixed star database  2321 . After that, the analyzing section  2311  analyzes brightness time changes of the target object and a reference fixed star. 
         [0039]    As one function of the processing section  231 , the frequency filtering section  2312  removes an influence of the atmosphere by carrying out the frequency filtering processing to data showing a brightness time change obtained optically from the target object. 
         [0040]    as one function of the processing section  231 , the extracting section  2313  extracts a periodicity of the brightness data based on the result of the analysis. 
         [0041]    The input unit  24  inputs a selected observation object and so on. Also, the input unit  24  may input various programs to be executed by the processing section  231  from a predetermined recording medium. 
         [0042]    The output unit  25  outputs the result of monitoring, extraction, and analysis by the optical monitoring system. 
         [0043]      FIG. 3  is a flow chart showing an overall operation example of the monitoring method of present invention. With reference to  FIG. 3 , the monitoring method of the present invention, i.e. the operation of the monitoring system of the present invention will be described. 
         [0044]    The flow chart shown in  FIG. 3  contains three processes roughly. In a first process S 1 , an observation instruction is issued. In a second process S 2 , an optical observation is carried out. In a third process S 3 , data processing is carried out. 
         [0045]    The first process S 1  contains three steps of the flow chart shown in  FIG. 3 . At a step S 11  of the first process, a target object is selected. At a step S 12  of the first process, the space object database  2322  is referred to. At a step S 13  of the first process, the coordinate data of the target object is extracted. 
         [0046]    The second process S 2  contains two steps of the flow chart shown in  FIG. 3 . At a step S 21  of the second process, the target object is monitored by the optical observation system  22  using the adaptive optics unit  221 . At a step S 22  of the second process, an observation image is acquired. 
         [0047]    The third process S 3  contains 13 steps of the flow chart shown in  FIG. 3 . At a step S 31  of the third process, the matching of the observation image to the fixed star database  2321  is carried out. At a step S 32  of the third process, the brightness time change of the target object is plotted. At a step S 33  of the third process, the brightness time change of the reference fixed star is plotted. At a step S 34  of the third process, the brightness time change of the target object is corrected. At a step S 35  of the third process, the frequency filtering processing is carried out. At a step S 36  of the third process, brightness data of the target object is extracted. At a step S 37  of the third process, the periodicity of brightness time change of the target object is extracted. As this result, whether or not the attitude control of the target object is being carried out can be estimated, and when the attitude control is not carried out, the target object can be considered to be not operated. The subsequent steps are different based on whether or not the target object is a new observation object. In case of the object (hereinafter, to be referred to as a “new object” or “unknown object”) for which the extraction of the brightness data has not been carried out so far, at a step S 38  of the third process, comparison with the light curve estimation database  2323  is carried out. At a step S 39  of the third process, the shape, the attitude, and the surface material of the target object are estimated. At a step S 310  of the third process, the target object is registered on the space object database  2322 . In case of the object (known object) for which the extraction of the brightness data has been carried out so far, at a step S 311  of the third process, comparison with the data acquired at previous times is carried out. At a step S 312  of the third process, occurrence or non-occurrence of an extraordinary event of the target object is detected. At a step S 313  of the third process, when the occurrence of the extraordinary event is detected at the step S 312  of the third process, the target object is registers on the important monitoring object database  2324 . 
         [0048]    The first process S 1  to third process S 3  are executed in this order. Also, each of the step S 11  to the step S 13  of the first process, the step S 21  to the step S 22  of the second process, and the step S 31  to the step S 37  of the third process is executed in this order. The processing contents differ depending on the new (unknown) object or the known object, in the step S 38  to the step S 310  and the step S 311  to the step S 313 . The above steps will be described in detail. 
         [0049]    At the step S 11  of the first process, the target object is selected. The selection may be carried out by a user of the monitoring system or the data processing system  23  may carry out according to a predetermined condition and a predetermined list. Here, the predetermined list and the predetermined condition may be contained in the space object database  2322  or may be contained in the important monitoring object database  2324 . 
         [0050]    At the step S 12  of the first process, the data processing system  23  refer to the space object database  2322  to acquire various data required to optically observe the selected target object from the ground. It is especially desirable that data indicating on what orbit the selected target object is orbiting the earth is contained in this data. Note that the selected target object may be a new object which is unregistered to the space object database  2322 . 
         [0051]    At the step S 13  of the first process, the processing section  231  extracts or calculates coordinate data of a position of the selected target object used when the selected target object is optically observed, from the various data acquired at the step S 12  of the first process. At this time, it is desirable to calculate a time zone in which the optical observation system  22  can observe the selected target object, in addition to the coordinates data 
         [0052]    At the step S 21  of the second process, the optical observation system  22  optically observes the target object. At that time, for the purpose to remove an influence of the atmosphere, the adaptive optics unit  221  is sometimes used. 
         [0053]    At the step S 22  of the second process, the optical observation system  22  acquires an image. This observation may be supported by the processing section  231 . Also, it is desirable that this observation of the same target object is repeated regularly or irregularly. 
         [0054]    At the step S 31  of the third process, the processing section  231  refers to the fixed star database  2321  which is previously stored in the storage section  232 . In this case, it is especially desirable that the processing section  231  specifies a fixed star near the target object in the image which has acquired at the step S 22  of the second process, and acquires various data of the specified fixed star. For example, it is desirable that the various data include coordinate data of the fixed star, a direction of the fixed star when being seen from the earth, a magnitude of the fixed star, an apparent brightness of the fixed start, and a period of light variation when the fixed star is a variable star in the comparable form with the observation result of the target object. 
         [0055]    At the step S 32  of the third process, the processing section  231  plots data showing a time change of estimated brightness of the target object. A graph may be produced in which the estimated brightness of the target object and an elapse of the time are plotted on the 2-dimensional coordinate system as an example of such data. However, an influence of the fluctuation of atmosphere which is not possible to correct by the adaptive optics unit  221  and noise data derived from the observation environment and so on are sometimes contained in the data obtained at this step. 
         [0056]    At the step S 33  of the third process, the brightness time change of a reference fixed star is plotted by the processing section  231 . 
         [0057]      FIG. 4A  is a graph showing an example of the plotting result of the brightness time change in the present invention. In the graph shown in  FIG. 4A , the horizontal axis shows time and the vertical axis shows the estimated brightness of the target object. 
         [0058]    At the step S 34  of the third process, the processing section  231  compares the estimated brightness of the target object plotted at the step S 32  of the third process and the brightness of the reference fixed star plotted at the step S 33  of the third process to determine a rate of the brightness time change which is regarded as the influence of the atmosphere and the influence of the observation environment. Thus, the processing section  231  corrects the brightness of the target object based on the rate of the brightness time change. 
         [0059]    At the step S 35  of the third process, the frequency filtering section  2312  applies predetermined frequency filtering processing to the data produced at the step S 34  of the third process, to classify the brightness data of the target object and the brightness data derived from things other than the target object. 
         [0060]      FIG. 4B  is a graph showing an example of the frequency filtering of the brightness in the present invention. The graph shown in  FIG. 4B  is identical to a result when the frequency filtering section  2312  applied the following changes to the graph shown in  FIG. 4A . That is, the plot data is classified to a first group  41 , a second group  42  and a third group  43  based on brightness ranges, and the plot data which belong to the first group  41  and the third group  43  are shown in white. In an example shown in  FIG. 4B , it is estimated that the second group  42  is the brightness data of the target object, and the plot data belonging to the first group  41  and the third group  43  are estimated to be noise data. 
         [0061]    At the step S 36  of the third process, the analyzing section  2311  removes the noise data from the data produced at the step S 34  of the third process of  FIG. 3  according to the classification carried out at the step S 35  of the third process, to extract the brightness data of the target object. 
         [0062]    At the step S 37  of the third process, the extracting section  2313  extracts the periodicity from the time change of the estimated brightness of the target object. Whether or not an attitude control of the target object is being carried out can be checked based on the extraction result, and it is possible to estimate that the target object is in the operation state when the attitude control is being carried out. 
         [0063]      FIG. 5A  is a graph showing the principle of extracting the periodicity of time change of the brightness in the present invention. In the graph shown in  FIG. 5A , the horizontal axis shows time and the vertical axis shows the estimated brightness of the target object. In an example shown in  FIG. 5A , a set of a large mountain and a small mountain shows a rotation period of the target object. 
         [0064]      FIG. 5B  is a different graph showing the principle of extracting the period of time change of the brightness in the present invention. In an example of the graph shown in  FIG. 5B , the horizontal axis shows time and the vertical axis shows the estimated brightness of the target object. Moreover, a first attitude  51 , a second attitude  52 , a third attitude  53 , a fourth attitude  54  and a fifth attitude  55  of the target object are shown in  FIG. 5B . These attitudes show the attitudes of the target object at the time which the target object is imaged. 
         [0065]    In an example shown in  FIG. 5B , the brightness increases in the second attitude  52  and the fourth attitude  54  in which the width of the target object is maximum. On the contrary, the brightness decreases in the first attitude  51 , the third attitude  53  and the fifth attitude  55  in which the width of the target object is minimized. 
         [0066]    As shown in the example of  FIG. 5B , when the target object rotates while the target object orbits the earth, the brightness of the target object in the view from the ground changes depending on the attitude of the target object, i.e. a phase of the rotation movement. The reason is in that a rate of an area of a portion, which reflects the sun light and so on well, of the surface of the target object changes according to the rotation of the target object. The period of this change of brightness substantively coincides with the rotation period. 
       Second Embodiment 
       [0067]    The process from the step S 11  of the first process to the step S 37  of the third process, of the plurality of processes in the monitoring method of the present invention, has been described as the first embodiment. The subsequent portion will be described as a second embodiment. Because the configuration of the monitoring system in the second embodiment is same as that of the first embodiment, the detailed description is omitted. 
         [0068]    At the step S 38  of the third process, the processing section  231  compares the brightness of the target object extracted at the step S 37  of the third process and data stored in the light curve estimation database  2323  of the storage section  232  when the data obtained about the target object is unregistered to the space object database  2322 , i.e. when a new object is observed. Specific examples of the contents of the light curve estimation database  2323  will be described with reference to  FIG. 6A  to  FIG. 6C . Note that the examples shown in  FIG. 6A  to  FIG. 6C  are schematically showing to simplify the description. The light curve estimation database  2323  is produced actually based on the optical measurement and the result of computer simulation. 
         [0069]      FIG. 6A  is a diagram showing an example of the shape data of the target object which is contained in the light curve estimation database  2323  in the present invention.  FIG. 6A  contains a cylindrical shape  61 , a first graph  611  corresponding to the cylindrical shape  61 , a rectangular parallelepiped shape  62  and a second graph  621  corresponding to the rectangular parallelepiped shape  62 . The first graph  611  shows an example of a pattern of the brightness time change estimated when the target object has the cylindrical shape  61 . In the same way, the second graph  621  shows an example of a pattern of the brightness time change estimated when the target object has the rectangular parallelepiped shape  62 . 
         [0070]      FIG. 6B  is a diagram showing another example of the reflection characteristic data of the target object which is contained in the light curve estimation database  2323  in the present invention.  FIG. 6B  contains a first graph  63  corresponding to a predetermined first material and a second graph  64  corresponding to a predetermined second material. The first graph  63  shows an example of the brightness time change pattern estimated when the surface of the target object is formed of the first material. In the same way, the second graph  64  shows an example of the brightness change pattern estimated when the surface of the target object is formed of the second material. 
         [0071]      FIG. 6C  is a diagram showing an example of the attitude data of the target object which is contained in the light curve estimation database  2323  in the present invention.  FIG. 6C  contains a first attitude  65  in which the target object of the cylindrical shape rotates around a line symmetrical axis, a first graph  651  corresponding to the first attitude  65 , a second attitude  66  in which the target object rotates around a line orthogonal to the line symmetrical axis, and a second graph  661  corresponding to second attitude  66 . The first graph  651  shows an example of the brightness change pattern estimated when the target object rotates around the line symmetrical axis. In the same way, the second graph  661  shows an example of the brightness change pattern estimated when the target object rotates around the orthogonal to the line symmetrical axis. 
         [0072]    At the step S 39  of the third process, the processing section  231  calculates the matching between the observation result of the brightness time change of the target object and data of the light curve estimation database  2323 , and estimates the features of the target object such as the shape, the attitude and the surface material based on the matching result. The estimation which is based on the examples of  FIG. 6A  to  FIG. 6C  will be described below. 
         [0073]    Based on the example shown in  FIG. 6A , the shape of the target object is more similar to the cylindrical shape  61 , when the amplitude of the brightness change is larger and an average is smaller. Also, it is possible to estimate that the shape of the target object is more similar to the rectangular parallelepiped shape  62 , when the amplitude of the brightness change is smaller and the average is larger. 
         [0074]    Based on the example shown in  FIG. 6B , the surface reflection characteristics of the target object are more similar to that of the first material, when the amplitude of the brightness time changes is larger. Also, it is possible to estimate that the surface reflection characteristic of the target object is similar to that of the second material, when the amplitude of the brightness changes is smaller. 
         [0075]    Based on the example shown in  FIG. 6C , the attitude of the target object is more similar to the first attitude, when the amplitude of the brightness time change is smaller and the period of the brightness time changes is longer. Oppositely, it is possible to estimate that the attitude of the target object is more similar to the second attitude, when the amplitude of the brightness time change is larger and the period of the brightness time changes is shorter. 
         [0076]    Actually, in the light curve estimation database  2323 , it is possible to carry out more detailed matching by using more measurement values or simulation results, so that it becomes able to more specifically estimate and narrow down the shape of the target object. 
         [0077]    At the step S 310  of the third process, the processing section registers the result estimated at the step S 39  of the third process on the space object database  2322  of the storage section  232 . 
       Third Embodiment 
       [0078]    The processing to the step S 310  of the third process of the plurality of steps contained in the monitoring method of the present invention has been described as the first embodiment or the second embodiment. The subsequent steps will be described as a third embodiment. Note that the monitoring system of the present invention to be used at the present embodiment is the same as that of the first embodiment. Therefore, further detailed description is omitted. 
         [0079]    At the step S 311  of the third process, when the target object have already registered on the space object database  2322 , i.e. when the known object has been observed once again, the processing section  231  compares the estimated brightness of the object body extracted at the step S 37  of the third process and the brightness data registered on the space object database  2322  of the storage section  232 . 
         [0080]    At the step S 312  of the third process, when there is a difference from the brightness information registered on the space object database  2322 , the processing section  231  detects an extraordinary state as shown in  FIG. 7  and can carry out the estimation. 
         [0081]    At the step S 313  of the third process, the known object from which an extraordinary event can be detected at the step S 312  of the third process is registered on the important monitoring object database  2324  of the storage section  232  so as to continuously monitor the object. The extraordinary event which can be detected will be described by using two examples. 
         [0082]    A first example will be described with reference to  FIG. 7A  to  FIG. 7C .  FIG. 7A  is a graph showing an example of a usual extraction result of the periodic brightness change in the present invention.  FIG. 7B  is a graph showing an example of an extraordinary event which occurs in the periodic brightness change which can be detected in the present invention. 
         [0083]    In two graphs shown in  FIG. 7A  and  FIG. 7B , the horizontal axis shows time and the vertical axis shows brightness. In the graph shown in  FIG. 7A , the brightness continues to periodically change to show the usual state of the target object. Oppositely, in the graph shown in  FIG. 7B , the amplitude of the brightness values changes greatly from the way. The processing section  231  detects such a change to be extraordinary and outputs the result to the output unit  25 . 
         [0084]      FIG. 7C  is a diagram showing an example of an extraordinary cause that the periodic brightness change detected in the present invention occurs. Alien substance  72  is orbiting around the target object  71  in the example shown in  FIG. 7C . When this alien substance  72  has begun to orbit around the target object  71 , the brightness of the target object  71  is more strongly observed due to the reflection light from the alien substance  72 , and oppositely, the brightness of the target object  71  is more weakly observed by blocking the light by the alien substance  72 . That is, the possibility that the extraordinary cause in the example shown in  FIG. 7B  is a phenomenon in an example shown in  FIG. 7C  can be estimated. 
         [0085]    A second example will be described with reference to  FIG. 7A ,  FIG. 7D  and  FIG. 7E .  FIG. 7D  is a graph showing another extraordinary example in which the periodic brightness change occurs which can be detected in the present invention. 
         [0086]    In the graph shown in  FIG. 7D , the horizontal axis shows time and the vertical axis shows brightness. In the graph shown in  FIG. 7D , the brightness average decreases greatly from the middle of the observation. The processing section  231  detects such a change as an extraordinary event, and outputs the result to the output unit  25 . 
         [0087]      FIG. 7E  is a diagram showing another example of an extraordinary cause by which the periodic brightness change occurs which can be detected in the present invention. In an example shown in  FIG. 7E , the target object  73  damages partially through the crash with an alien substance  74 . In this example, a part of a solar panel having an especially large area is damaged in the target object  73 . Therefore, the brightness of the target object  73  is greatly weakly observed since the crash. That is, the extraordinary cause in the example shown in  FIG. 7D  is estimated to be possibly a phenomenon in the example shown in  FIG. 7E . 
         [0088]    Although two extreme examples for simplification are described above, it actually become possible to estimate the detailed causes by using the monitoring system and the monitoring method according to the present invention by storing more causalities in the database previously. 
         [0089]    As above, the present invention accomplished by the inventor has been specifically described with reference to the embodiments. However, the present invention is not limited to the embodiments and various modifications are possible in a range not deviating from the scope of the present invention. Also, the above-mentioned embodiments can be freely combined with each other be freely in the range without contradicting technically. 
         [0090]    This application claims a priority based on a Japanese Patent Application No. JP 2014-083695. The disclosure thereof is incorporated herein by reference.