Geostationary Observation System

Abstract

To improve the precision of an azimuth angle of a visual line vector when conducting optical observation from an observation satellite of a stationary orbit.SOLUTION: A stationary observation system 200 includes: an observation satellite 100 launched into a stationary orbit and flying in the sky of an observation zone; an optical observation device which is provided in the observation satellite 100 in order to conduct visible light observation with respect to each observation zone in the observation zones; a position database 213 which indicates a position of a landmark of at least one of an eastern island, a western island, a southern island and a northern island in the observation zone; and an azimuth angle database 214 which indicates an azimuth angle from a position of the observation satellite 100 in the sky of the observation zone to a position of the landmark.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] This disclosure relates to observations from geostationary orbit. [Background technology]

[0002] Research is being conducted on geostationary observation systems that use optical observation equipment to conduct continuous observations from geostationary orbit. With improvements in development technology, it is expected that optical observation equipment for satellites will be able to capture images with a swath of about 100 kilometers at a resolution of a few meters from a geostationary orbit at an altitude of about 36,000 kilometers. An optical observation device equipped with a two-dimensional visible light detector captures an image of one scene, then rotates its line of sight vector to capture images of adjacent areas, repeatedly, thereby obtaining wide-area observation data. The high resolution of optical observation equipment is an advantage, but because there are a large number of scenes to be imaged, it takes time to obtain wide-area observation data.

[0003] The means for moving the line of sight vector include a means for providing an optical observation device with a field of view changing device, and a means for moving the attitude of the observation satellite itself. High-resolution optical observation equipment has a large effective aperture diameter, and the field-of-view changing device also becomes large. Therefore, a means of changing the attitude of the observation satellite itself is rational. When the line of sight vector is shifted by changing the attitude of the observation satellite itself, the observation satellite's attitude is shifted by driving an actuator such as a momentum wheel, and the fluctuation in the observation satellite's attitude is stopped by braking control. Then, imaging is performed. Therefore, it takes time to shift the line of sight vector.

[0004] Patent Document 1 discloses a system for observing a target area using a constellation of observation satellites. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-126876 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to improve the accuracy of the azimuth angle of the line of sight vector when optical observation is performed from an observation satellite in geostationary orbit. [Means for solving the problem]

[0007] The stationary observation system of the present disclosure comprises: An observation satellite that is placed in a geostationary orbit and flies over the observation area, an optical observation device provided on the observation satellite for performing visible light observation of each observation area within the observation region; a location database indicating the location of a landmark on at least one of the easternmost island, westernmost island, southernmost island, and northernmost island in the observation area; an azimuth angle database indicating azimuth angles from the position of the observation satellite to the position of the landmark in the sky above the observation area; Equipped with. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to improve the accuracy of the azimuth angle of the line of sight vector when performing optical observation from an observation satellite in geostationary orbit. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a configuration diagram of an observation satellite 100 according to the first embodiment. [Figure 2] FIG. 1 is a diagram showing an entire observation area 111 according to the first embodiment. [Figure 3] FIG. 2 is a diagram showing the easternmost observation area 112 and the western adjacent area 113 according to the first embodiment. [Figure 4] FIG. 1 is a diagram showing an observation area 110 according to the first embodiment. [Figure 5]FIG. 11 is a diagram showing the easternmost observation area 112 and the western adjacent area 113 according to the second embodiment. [Figure 6] FIG. 11 is a configuration diagram of a stationary observation system 200 according to a third embodiment. [Figure 7] FIG. 10 is a configuration diagram of an observation satellite 100 according to a third embodiment. [Figure 8] FIG. 11 is a diagram showing an observation area 110 according to the third embodiment. [Figure 9] 11 is a table showing the location of each island in the observation area 110 according to the third embodiment. [Figure 10] FIG. 10 is a configuration diagram of a stationary observation system 200 according to a fourth embodiment. [Figure 11] FIG. 13 is a configuration diagram of a stationary observation system 200 according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the embodiments and drawings, the same or corresponding elements are denoted by the same reference numerals, and the description of elements denoted by the same reference numerals as elements already described will be omitted or simplified as appropriate.

[0011] Embodiment 1 A configuration for capturing wide-area images from an artificial satellite will be described with reference to FIGS. 1 to 4. FIG.

[0012] ***Configuration Description*** The configuration of the observation satellite 100 will be described with reference to FIG. The observation satellite 100 is an artificial satellite (geostationary satellite) that is placed in a geostationary orbit, and flies in the geostationary orbit above an observation area 110. A specific example of the observation satellite 100 is a meteorological satellite.

[0013] The observation satellite 100 is equipped with an optical observation device 101. "Observation" corresponds to "imaging." The optical observation device 101 performs visible light observation of each observation region within the observation area 110. In visible light observation, images are taken by detecting visible light. The optical observation device 101 includes a visible light detector. The visible light detector includes a plurality of aligned visible light detection elements. The visible light detector is also called a visible light detection sensor. Specifically, the optical observation device 101 includes a two-dimensional visible light detector. The two-dimensional visible light detector includes a plurality of visible light detection elements arranged two-dimensionally. Observation data is obtained by visible light observation using the optical observation device 101. The observation data corresponds to image data showing the observation area.

[0014] The observation satellite 100 has a function for changing the direction of the line-of-sight vector of the optical observation device 101 . For example, the observation satellite 100 is equipped with a field of view changing device. The field of view changing device changes the field of view direction of the optical observation device 101. The field of view direction corresponds to the direction of the line of sight vector. A specific example of the field of view changing device is a driving mirror. For example, the observation satellite 100 is equipped with an attitude control device. The attitude control device controls the attitude of the observation satellite 100. By changing the attitude of the observation satellite 100, the direction of the line of sight vector of the optical observation device 101 can be changed. A specific example of the attitude control device is a reaction wheel.

[0015] The observation satellite 100 uses an optical observation device 101 to capture images of an entire observation area 111 within an observation region 110 from a geostationary orbit. A specific example of the observation area 110 is the land and territorial waters of Japan. The entire observation area 111 is a wide observation range made up of a plurality of observation areas. The observation area 110 and the entire observation region 111 include land (earth surface) and ocean (sea surface).

[0016] ***Explanation of Operation*** The wide-area imaging method is a method for imaging the entire observation area 111, and corresponds to the operation procedure of the observation satellite 100. First, the observation satellite 100 directs the line-of-sight vector of the optical observation device 101 toward one of the north and south ends of the easternmost row of the entire observation area 111. Specifically, the line-of-sight vector of the optical observation device 101 is directed toward the northern end of the easternmost row of the entire observation area 111. However, the line-of-sight vector of the optical observation device 101 may also be directed toward the southern end of the easternmost row of the entire observation area 111. Thereafter, the observation satellite 100 repeatedly moves the line-of-sight vector of the optical observation device 101 in the forward direction between north and south, and the optical observation device 101 repeatedly takes images. Specifically, the forward direction is from north to south. However, the forward direction may also be from south to north. This operation is called "forward imaging." After the forward imaging, the observation satellite 100 shifts the line of sight vector of the optical observation device 101 to the west. This operation is called "westward line of sight shift." After the westward line of sight shift, the observation satellite 100 repeatedly shifts the line of sight vector of the optical observation device 101 in the north-south reverse direction, and the optical observation device 101 repeats imaging. This operation is called "reverse direction imaging." After the backward imaging, the observation satellite 100 performs a westward line of sight movement. The observation satellite 100 and the optical observation device 101 then repeat the process of taking a forward image, moving the line of sight to the west after taking the forward image, taking a backward image, and moving the line of sight to the west after taking the backward image until the entire observation area 111 has been photographed from the eastern end to the western end. In this way, the entire observation area 111 is photographed.

[0017] The wide-area imaging method will be specifically described with reference to FIGS.

[0018] In FIG. 2, each square represents the field of view of the optical observation device 101, that is, the imaging range per one shot. The entire observation area 111 is a collection of squares with bold frames. Of the entire observation area 111, the row at the eastern end is called the easternmost observation area 112. Of the entire observation area 111, the row adjacent to the west side of the easternmost observation area 112 is referred to as the western adjacent area 113. Of the entire observation area 111, the westernmost row is called the westernmost observation area 114.

[0019] FIG. 3 shows the easternmost observation area 112 and the adjacent area 113 to the west. The observation satellite 100 repeatedly changes the line-of-sight vector of the optical observation device 101 until the field of view of the optical observation device 101 moves from the northernmost to the southernmost end of the easternmost observation area 112. In other words, the observation satellite 100 moves the line-of-sight vector of the optical observation device 101 in the latitudinal direction (southward). During this time, the optical observation device 101 repeatedly takes images. The observation satellite 100 then moves the field of view of the optical observation device 101 from the southernmost end of the easternmost observation area 112 to the southernmost end of the adjacent observation area to the west (west-side adjacent area 113). In other words, the observation satellite 100 moves the line-of-sight vector of the optical observation device 101 in the longitude direction (westward). Thereafter, the observation satellite 100 repeatedly changes the line-of-sight vector of the optical observation device 101 until the field of view of the optical observation device 101 moves from the southernmost to the northernmost end of the observation area adjacent to the west. In other words, the observation satellite 100 moves the line-of-sight vector of the optical observation device 101 in the latitudinal direction (northward). During this time, the optical observation device 101 repeatedly takes images. After that, the observation satellite 100 moves the field of view of the optical observation device 101 from the northernmost end of the observation area adjacent to the west to the northernmost end of the observation area adjacent to the west. In other words, the observation satellite 100 moves the line-of-sight vector of the optical observation device 101 in the longitude direction (westward). The observation satellite 100 and the optical observation device 101 repeat the process of taking images and moving the line of sight vector in the latitudinal direction and moving the line of sight vector to the adjacent observation area to the west until the field of view of the optical observation device 101 moves to the westernmost end of the entire observation area 111.

[0020] ***Supplement to the first embodiment*** The first embodiment will be supplemented with reference to FIG. The greater the difference in azimuth angle of the line-of-sight vector before and after movement, the longer it takes to move the line-of-sight vector. Therefore, it is rational to select a wide-area imaging method that minimizes the amount of movement of the line-of-sight vector. Furthermore, considering that the altitude of the sun changes while wide-area observation data is being acquired, it is rational to observe in order starting from the observation area with the most favorable sunlight conditions.

[0021] For example, assume that the two-dimensional visible detector of the optical observation device 101 can capture an image of a 100 km x 100 km range from a geostationary orbit, and that the optical observation device 101 acquires wide-area observation data of Japan and the surrounding oceans. Japan's land area is approximately 380,000 square kilometers, its territorial waters are approximately 430,000 square kilometers, its contiguous zone is approximately 320,000 square kilometers, and its exclusive economic zone (including the extended continental shelf) is approximately 4.05 million square kilometers, totaling approximately 5.18 million square kilometers. The area of ​​one image is 10,000 square kilometers (= 100 km x 100 km), so by simple calculation, approximately 500 images would be required. When observing the area around 35 degrees north latitude from a geostationary orbit, the number of images captured is expected to decrease due to the strabismus effect of the line of sight vector. However, it will take several days just to capture the entire area.

[0022] Assuming that it takes an average of one minute to capture an image and change the line of sight vector, it will take 500 minutes to capture 500 images, which means it will take about 8.3 hours. When a two-dimensional visible light detector observes a daylight area, there is not enough time to observe it from 8:00 AM to 4:00 PM. In addition, the time periods before 8:00 AM and after 4:00 PM are not suitable for observation using visible light because the Earth's surface is dark due to the low altitude of the sun.

[0023] The Earth rotates 15 degrees longitude-wise every hour. In other words, the Earth rotates 120 degrees longitude-wise every 8 hours. Therefore, the latitude at which sunlight shines from the zenith at noon moves 120 degrees from east to west. The difference in longitude between the easternmost and westernmost points of Japan is about 30 degrees, which is equivalent to the movement of the sun in the longitude direction for two hours. Therefore, if imaging from east to west takes a total of about eight hours, four hours before noon and four hours after noon, the solar altitude at the easternmost point will be equivalent to 9 a.m., and the solar altitude at the westernmost point will be equivalent to 3 p.m. This leaves about two hours of leeway for the time required for imaging and changing the line of sight vector. Conversely, if imaging is conducted from west to east over a total of approximately eight hours around noon, the solar altitude at the westernmost point will be equivalent to 7:00 a.m., and the solar altitude at the easternmost point will be equivalent to 5:00 p.m. Therefore, visible observations will be conducted under dark conditions.

[0024] ***Effects of the First Embodiment*** Conventional meteorological satellites are equipped with optical observation equipment using two-dimensional infrared detectors. Conventional meteorological satellites repeatedly take images and change their line-of-sight vector in an east-west direction from the northernmost point of the entire observation area, and then repeatedly take images and change their line-of-sight vector in an east-west direction for the adjacent observation area to the south, repeating this process until they reach the southernmost point of the entire observation area. Conventional meteorological satellites acquire observation data day and night by detecting infrared rays, so this wide-area imaging method is rational. On the other hand, the observation satellite 100 is equipped with an optical observation device 101 that uses a two-dimensional visible light detector. Because the sunlit area on the Earth's surface moves from east to west over time, the observation satellite 100 captures images sequentially from east to west. This allows for a longer period of time in a day for capturing images of the Earth's surface. As a result, observation data can be acquired over a wider area. Furthermore, observation data over a wider area can be acquired with little change in the angle of incidence of sunlight on the monitored object. Furthermore, the observation satellite 100 limits the movement of the line-of-sight vector of the optical observation device 101 to the adjacent area, which reduces fluctuations in the azimuth angle of the line-of-sight vector, thereby shortening the observation time.

[0025] Embodiment 2 The embodiment in which the one-dimensional visible light detector is used will be described with reference to FIG. 5, focusing mainly on the differences from the first embodiment.

[0026] ***Configuration Description*** The observation satellite 100 includes an optical observation device 101, as in the first embodiment. However, the visible light detector of the optical observation device 101 is a one-dimensional visible light detector. The one-dimensional visible light detector includes a plurality of visible light detection elements arranged in one dimension.

[0027] ***Explanation of Operation*** A wide-area imaging method will be described. First, the observation satellite 100 directs the line-of-sight vector of the optical observation device 101 toward one of the north and south ends of the easternmost row of the entire observation area 111. Specifically, the line-of-sight vector of the optical observation device 101 is directed toward the northern end of the easternmost row of the entire observation area 111. However, the line-of-sight vector of the optical observation device 101 may also be directed toward the southern end of the easternmost row of the entire observation area 111. Thereafter, the optical observation device 101 of the observation satellite 100 captures images while the line-of-sight vector of the optical observation device 101 moves in the forward direction, north to south. Specifically, the forward direction is from north to south. However, the forward direction may also be from south to north. This operation is called "forward imaging." After the forward imaging, the observation satellite 100 moves the line of sight vector of the optical observation device 101 to the west. This operation is called "westward line of sight movement." After the westward line of sight shift, the observation satellite 100 moves the line of sight vector of the optical observation device 101 in the north-south reverse direction, while the optical observation device 101 takes images. This operation is called "reverse direction imaging." After the backward imaging, the observation satellite 100 performs a westward line of sight movement. The observation satellite 100 and the optical observation device 101 then repeat the process of taking a forward image, moving the line of sight to the west after taking the forward image, taking a backward image, and moving the line of sight to the west after taking the backward image until the entire observation area 111 has been photographed from the eastern end to the western end. In this way, the entire observation area 111 is photographed.

[0028] The wide-area imaging method will be specifically described with reference to Fig. 5. The one-dimensional visible detector of the optical observation device 101 has 16 visible detection elements arranged in a horizontal row. The observation satellite 100 continues to change the line-of-sight vector of the optical observation device 101 until the field of view of the optical observation device 101 moves from the northernmost to the southernmost point of the easternmost observation area 112. In other words, the observation satellite 100 moves the line-of-sight vector of the optical observation device 101 in the latitudinal direction (southward). During this time, the optical observation device 101 continues to take images. The observation satellite 100 then moves the field of view of the optical observation device 101 from the southernmost end of the easternmost observation area 112 to the southernmost end of the adjacent observation area to the west (west-side adjacent area 113). In other words, the observation satellite 100 moves the line-of-sight vector of the optical observation device 101 in the longitude direction (westward). After that, the observation satellite 100 continues to change the line-of-sight vector of the optical observation device 101 until the field of view of the optical observation device 101 moves from the southernmost to the northernmost end of the observation area adjacent to the west. In other words, the observation satellite 100 moves the line-of-sight vector of the optical observation device 101 in the latitudinal direction (northward). During this time, the optical observation device 101 continues to take images. After that, the observation satellite 100 moves the field of view of the optical observation device 101 from the northernmost end of the observation area adjacent to the west to the northernmost end of the observation area adjacent to the west. In other words, the observation satellite 100 moves the line-of-sight vector of the optical observation device 101 in the longitude direction (westward). The observation satellite 100 and the optical observation device 101 repeat the process of taking images and moving the line of sight vector in the latitudinal direction and moving the line of sight vector to the adjacent observation area to the west until the field of view of the optical observation device 101 moves to the westernmost end of the entire observation area 111.

[0029] ***Effects of the Second Embodiment*** Two-dimensional image observation data is obtained by capturing images while moving a one-dimensional visible detector in a direction perpendicular to the pixel row. This method is called push-broom imaging. By using a one-dimensional visible light detector, it is possible to capture images of the observation area while changing the azimuth angle of the observation satellite 100 at a substantially constant speed. Therefore, compared to the first embodiment in which a two-dimensional visible light detector is used, the second embodiment can shorten the time required to brake and stop the movement of the line-of-sight vector. In the second embodiment, similar to the first embodiment, the effect of the sunlit area with the change in time can be obtained by capturing images in order from east to west.

[0030] Embodiment 3 A mode for improving the accuracy of the azimuth angle of the line of sight vector in the optical observation device 101 will be described below with reference to Figs. 6 to 9, mainly in terms of the differences from the first and second embodiments.

[0031] ***Configuration Description*** The configuration of the stationary observation system 200 will be described with reference to FIG. The geostationary observation system 200 includes an observation satellite 100 and a ground system 210 .

[0032] The configuration of the observation satellite 100 will be described with reference to FIG. The observation satellite 100 includes an optical observation device 101, an attitude control device 102, a propulsion device 103, a satellite control device 104, a communication device 105, and a power supply device 106.

[0033] The optical observation device 101 is as described in the first embodiment.

[0034] The attitude control device 102 is a device for controlling the attitude elements of the observation satellite 100, such as the attitude and angular velocity of the observation satellite 100. The attitude control device 102 changes each attitude element in a desired direction. Alternatively, the attitude control device 102 maintains each attitude element in a desired direction. The attitude control device 102 includes an attitude sensor, an actuator, and a controller. The attitude sensor includes a gyroscope, an earth sensor, a sun sensor, a star tracker, a thruster, and a magnetic sensor. The actuator includes an attitude control thruster, a momentum wheel, a reaction wheel, and a control moment gyro. The controller controls the actuator according to measurement data from the attitude sensor or various commands from the ground system 210. The attitude control device 102 can be used to change the azimuth angle of the line of sight vector of the optical observation device 101 .

[0035] The propulsion device 103 is a device that provides thrust to the observation satellite 100 and changes the speed of the observation satellite 100. Specifically, the propulsion device 103 is an electric propulsion device. For example, the propulsion device 103 is an ion engine or a Hall thruster.

[0036] The satellite control device 104 is a computer equipped with a processing circuit that controls each device of the observation satellite 100. For example, the satellite control device 104 controls each device in accordance with various commands transmitted from the ground system 210.

[0037] The communication device 105 is a communication device for communicating with the ground system 210. For example, the communication device 105 receives various commands from the ground system 210. The communication device 105 also transmits observation data obtained by the optical observation device 101 to the ground system 210.

[0038] The power supply unit 106 includes a solar cell, a battery, a power control device, and the like, and supplies power to each device of the observation satellite 100 .

[0039] Returning to FIG. 6, the configuration of the ground system 210 will be described. The ground system 210 includes a communication device 211 , a satellite control device 212 , a position database 213 , and an azimuth angle database 214 .

[0040] The communication device 211 communicates with the observation satellite 100. Specifically, the communication device 211 transmits various commands to the observation satellite 100. The communication device 211 also receives observation data transmitted from the observation satellite 100.

[0041] The satellite control device 212 is a computer equipped with hardware such as a processing circuit and an input / output interface. The satellite control device 212 generates various commands to control the observation satellite 100. The satellite control device 212 also analyzes the observation data obtained from the observation satellite 100. The position database 213 and the azimuth angle database 214 are used in generating various commands and analyzing observation data.

[0042] The location database 213 indicates the locations of landmarks on at least one of the easternmost island, westernmost island, southernmost island, and northernmost island in the observation area 110 .

[0043] The azimuth angle database 214 indicates the (absolute) azimuth angles of landmarks.

[0044] The processing circuits provided in the satellite control unit 212 and the satellite control unit 104 will now be described. The processing circuitry may be dedicated hardware or may be a processor that executes a program stored in a memory. In the processing circuit, some functions may be realized by dedicated hardware and the remaining functions may be realized by software or firmware, i.e., the processing circuit may be realized by hardware, software, firmware, or a combination thereof. Dedicated hardware may be, for example, a single circuit, a complex circuit, a programmed processor, parallel programmed processors, an ASIC, an FPGA, or a combination thereof. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array.

[0045] Specific examples of the position database 213 and the azimuth angle database 214 will be described with reference to FIGS. Figure 8 shows an observation area 110. The observation area 110 includes Japan's land and territorial waters. The easternmost island is Minamitorishima, the westernmost island is Yonagunijima, the southernmost island is Okinotorishima, and the northernmost island is Etorofujima. Figure 9 shows the locations of Minamitorishima, Yonagunijima, Okinotorishima, and Etorofu Island. The locations (coordinate values) are expressed in longitude and latitude. The location database 213 indicates the locations of landmarks on Minamitorishima, Yonagunijima, Okinotorishima, and Etorofu Island. For example, the landmarks may be natural features, man-made objects, or coastal features. The azimuth angle database 214 indicates the azimuth angle of the line-of-sight vector of the optical observation device 101 relative to the landmarks at the easternmost, westernmost, southernmost, and northernmost ends of the island. The azimuth angle is expressed as an azimuth angle and an elevation angle.

[0046] ***Explanation of Operation*** A method for adjusting the line-of-sight vector will now be described. First, the satellite control device 212 generates a command indicating the relative position of the landmark and transmits the command to the observation satellite 100 via the communication device 211. The satellite control device 104 receives the command via the communication device 105. Next, the satellite control device 104 directs the line-of-sight vector of the optical observation device 101 toward the landmark based on the relative position of the landmark. Next, the optical observation device 101 captures images of the landmarks and generates observation data. Next, the satellite control device 104 transmits the observation data to the ground system 210 via the communication device 105. The satellite control device 212 receives the observation data via the communication device 211.

[0047] Next, the satellite control device 212 calculates the position of the landmark by analyzing the observation data. The calculated position is called the measured position. Specifically, the satellite control device 212 visualizes the observation data obtained through visible light observation and calculates the measurement position within the image of the landmark that appears in the image. The position coordinates of the landmark are known. Position coordinates refer to coordinate values. At this time, the satellite control device 212 extracts the azimuth angle of the line-of-sight vector at the moment when the point corresponding to the pixel at the top, bottom, left, and right edge of the image obtained from the observation data is captured, from telemetry information related to the attitude control of the observation satellite 100. The extracted azimuth angle of the line-of-sight vector is treated as the measurement position of the point corresponding to the pixel at the top, bottom, left, and right edge. Furthermore, the satellite control device 212 analyzes the difference in the azimuth angle of the line-of-sight vector that was changed before the image was captured so that the landmark appears in the image. As a result, the satellite control device 212 calculates the azimuth angle of the line-of-sight vector at the moment when the landmark was captured.

[0048] Next, the satellite control device 212 calculates the error in the line of sight vector of the optical observation device 101 based on the difference between the measured position of the landmark and the position of the landmark shown in the position database 213. The calculated error is called the adjustment amount. The position database 213 indicates in advance the azimuth angle of the line-of-sight vector for capturing an image of a landmark. Therefore, if there is no error in the line-of-sight vector, the landmark should appear at the center of an image captured with the landmark at the center. However, if the landmark appears at a position away from the center of the image, it is determined that this is due to an error in the azimuth angle. Therefore, the satellite control device 212 evaluates the difference between the measured position and the landmark position indicated in the position database 213 as the difference in the landmark position in the image, and calculates the azimuth angle error as an adjustment amount by converting the position difference into an azimuth angle difference.

[0049] Next, the satellite control device 212 generates a command indicating the amount of adjustment and transmits the command to the observation satellite 100 via the communication device 211. The satellite control device 104 receives the command via the communication device 105.

[0050] Then, the satellite control device 104 adjusts the azimuth angle of the line-of-sight vector of the optical observation device 101 according to the amount of adjustment. The adjustment eliminates errors in the azimuth angle of the line-of-sight vector, improving the accuracy of the azimuth angle of the line-of-sight vector, and as a result, improving the accuracy of the measurement position when capturing an image of an arbitrary imaging target other than a landmark.

[0051] For optical observation equipment, the accuracy of the azimuth angle of the line-of-sight vector is referred to as the "pointing direction determination accuracy." The accuracy of the pointing direction determination is degraded by the accuracy of the attitude sensor equipped on the geostationary satellite, which is a factor of error.The pointing direction determination accuracy is also degraded by the thermal deformation of the geostationary satellite (and optical observation equipment) due to temperature changes in geostationary orbit, which is a factor of error. The accuracy of determining the pointing direction can be improved by eliminating error factors by using the coordinate values ​​of known landmarks as a reference when observing the Earth's surface. However, when observing a moving object such as a ship on the ocean, if there is an error in the azimuth angle of the line of sight vector, there is a risk of losing sight of the moving object even when trying to track it. Therefore, the coordinate values ​​of known landmarks in marine monitoring are recorded in a database. For example, the landmarks are the geographical features, man-made objects, or coastal shapes of Minamitorishima (the easternmost island), Yonagunijima (the westernmost island), Okinotorishima (the southernmost island), and Etorofujima (the northernmost island). These landmarks serve as markers in the observation data obtained by imaging. Furthermore, in ocean monitoring, the azimuth angles of known landmarks relative to the observation satellite 100 are recorded in a database. The azimuth angles are expressed as azimuth angles and elevation angles.

[0052] ***Effects of the Third Embodiment*** According to the third embodiment, it is possible to improve the accuracy of the azimuth angle of the line of sight vector in the optical observation device 101.

[0053] ***Supplement to embodiment 3*** The observation satellite 100 may include a position database 213 and an azimuth angle database 214 . The satellite control device 104 may calculate the measured positions of the landmarks and the adjustment amount of the line of sight vector.

[0054] Embodiment 4 The following describes the mode for measuring the position of an object, mainly focusing on the differences from the third embodiment, with reference to FIG.

[0055] ***Configuration Description*** The configuration of the stationary observation system 200 will be described with reference to FIG. The ground system 210 further includes a position measurement device 215 .

[0056] Like the satellite control device 212, the position measurement device 215 is a computer equipped with hardware such as a processing circuit and an input / output interface. The position measurement device 215 measures the position of the imaged object (imaged object) by analyzing the observation data obtained from the observation satellite 100. A specific example of the imaged object is a moving body such as a ship. In measuring the position of the imaged object, a position database 213 and an azimuth angle database 214 are used.

[0057] ***Explanation of Operation*** A method for measuring the position of an imaged object will now be described. The position measurement device 215 calculates the position of an object imaged by the optical observation device 101 based on the difference between the azimuth angle of the landmark and the azimuth angle of the line-of-sight vector of the optical observation device 101 at the time of image capture, and the position of the landmark.

[0058] For example, the position of the captured object is calculated as follows. First, the satellite control device 104 directs the line-of-sight vector of the optical observation device 101 toward the observation area. Next, the optical observation device 101 captures an image of the observation area and generates observation data. Next, the satellite control device 104 directs the line-of-sight vector of the optical observation device 101 toward the landmark based on the azimuth angle of the landmark. At this time, the azimuth angle of the line-of-sight vector of the optical observation device 101 is the same as the azimuth angle of the landmark. Next, the optical observation device 101 captures images of the landmarks and generates observation data. Next, the satellite control device 104 transmits the observation data of the observation area, the observation data of the landmarks, and the azimuth data to the ground system 210 via the communication device 105. Next, the satellite control device 212 receives the observation data of the observation area, the observation data of the landmarks, and the azimuth data via the communication device 211. Next, the satellite control unit 212 visualizes the observation data obtained through visible light observation and extracts the azimuth angle of the line-of-sight vector at the moment when the point corresponding to the pixel at the top, bottom, left, or right edge of the image is captured from telemetry information related to the attitude control of the observation satellite 100. The extracted azimuth angle of the line-of-sight vector is treated as the measurement position of the point corresponding to the pixel at the top, bottom, left, or right edge. Next, the satellite control device 212 transmits to the position measurement device 215 information on the observation data of the imaged observation area, with the measurement positions of the points corresponding to the pixels at the top, bottom, left, and right ends, and information on the observation data of the imaged landmark, with the measurement positions of the points corresponding to the pixels at the top, bottom, left, and right ends. Next, the position measurement device 215 calculates the measurement position of the azimuth angle of the landmark from the received image. Because the position coordinates of the landmark are known, if the measured position in the image deviates from the expected position, this is due to an error in the azimuth angle of the line of sight vector. Therefore, the position measurement device 215 calculates the amount of adjustment of the azimuth angle based on the difference from the azimuth angle of the landmark whose position coordinates are known. Next, the position measurement device 215 selects an object to be imaged as a position measurement target from the image of the observation area, and calculates the azimuth angle at which the object was imaged. Next, the position measurement device 215 adjusts the azimuth angle at which the imaged object was captured using the adjustment amount of the azimuth angle of the landmark. If the landmark is captured after the observation area is captured, the azimuth angle error of the observation satellite 100 equipped with the optical observation device 101 will be the same. Therefore, the error in the azimuth angle at which the observation area is imaged is eliminated by using the same adjustment amount as that of the azimuth angle of the landmark whose position coordinates are known. In this way, the position measurement device 215 calculates the position of the captured object present in the observation area based on the observation data of the observation area, the observation data of the landmarks, and the azimuth angle difference data.

[0059] ***Features of the Fourth Embodiment*** The optical observation device 101 observes the moving object and then captures an image of the landmark. The position measurement device 215 measures the position of the moving object based on the difference in azimuth angle of the shifted line-of-sight vector.

[0060] When tracking a ship (distressed or suspicious ship) discovered in the vast ocean, it is difficult to measure the ship's position if there are no landmarks in the ocean. In addition, there is a large position error due to errors in the line-of-sight vector of a geostationary satellite. In this case, by capturing an image of the landmark after capturing an image of the ship, the position of the ship can be measured with high accuracy.

[0061] ***Effects of the Fourth Embodiment*** According to the fourth embodiment, the position of the imaging object can be measured with high accuracy.

[0062] ***Supplement to the fourth embodiment*** The observation satellite 100 may be equipped with a position measurement device 215. That is, the observation satellite 100 may calculate the position of the imaged object.

[0063] Embodiment 5. The manner in which a moving object is observed will be described with reference to FIG. 11, focusing mainly on the differences from the first to fourth embodiments.

[0064] ***Configuration Description*** The configuration of the stationary observation system 200 will be described with reference to FIG. The ground system 210 further includes a mobile database 216 . The mobile object database 216 indicates, for each mobile object, an identifier and a location at each time.

[0065] ***Explanation of Operation*** A method for observing a moving object will be explained. The satellite control device 104 directs the line-of-sight vector of the optical observation device 101 toward the position of the observation target based on the position of the observation target, the positions of the landmarks, and the azimuth angles of the landmarks. The optical observation device 101 then captures an image of the observation target. A specific example of the observation target is a moving body such as a ship.

[0066] The relative azimuth angle is an azimuth angle derived as the difference between the azimuth angle of the line-of-sight vector at the moment when the observation target is imaged and the azimuth angle of the line-of-sight vector at the moment when the landmark is imaged. The amount of adjustment for the azimuth angle is derived by the position measurement device 215 of the fourth embodiment, and errors in the line of sight vector of the landmark are eliminated. Therefore, if the satellite control device 104 commands the azimuth angle of the line of sight vector using the relative azimuth angle from the landmark and captures an image of the observation target, errors in the line of sight vector are eliminated, and the observation target can be reliably captured.

[0067] For example, a moving object is observed as follows: The satellite control unit 212 retrieves the last location information of the mobile from the mobile database 216 . The satellite control device 212 calculates the relative azimuth angle of the moving body at the last position of the moving body based on the last position of the moving body, the positions of the landmarks, and the azimuth angles of the landmarks. The satellite control device 212 generates a command indicating the azimuth angle of the moving body after adding the landmark adjustment amount to the relative azimuth angle of the moving body to eliminate the error in the line of sight vector (adjusted rearward azimuth angle), and transmits the command to the observation satellite 100 via the communication device 211. The satellite control device 104 receives the command via the communication device 105. The satellite control device 104 directs the line-of-sight vector of the optical observation device 101 toward an observation region including the last position of the moving object, based on the adjusted rearward direction angle of the moving object. The optical observation device 101 captures an image of an observation area and generates observation data. If the time elapsed since the time of the moving object's last position is short, the moving object is present in the observation area.

[0068] ***Features of the Fifth Embodiment*** The mobile object database 216 records the ID and location coordinates of the mobile object together with time information. The optical observation device 101 captures an image by moving the line of sight vector to the periphery of the position coordinates last updated at the request of the user.

[0069] When tracking a ship (distressed or suspicious ship) found in the vast ocean, it is difficult to measure the ship's position if there are no landmarks in the ocean. In addition, there is a large position error due to the error in the line-of-sight vector of the geostationary satellite. At this time, calibration can be performed by repeatedly capturing images of landmarks (artificial or natural objects) and the ship. The location coordinates of a vessel with a registered ID, measured by a satellite positioning system or other means, are registered in a database. In other words, changes in location coordinates as the vessel moves are recorded. If a vessel goes missing due to a maritime accident or distress, the vessel can be found in a short time by searching the area around its last recorded location coordinates.

[0070] ***Effects of the Fifth Embodiment*** According to the fifth embodiment, a moving object can be observed.

[0071] Embodiment 6 The following describes the mode of correcting the azimuth angle of the line-of-sight vector, focusing mainly on the differences from the first to fifth embodiments.

[0072] ***Configuration Description*** The configuration of the stationary observation system 200 is the same as that in the third to fifth embodiments.

[0073] ***Explanation of Operation**** A method for calibrating the line-of-sight vector will now be described. If there is no error in the landmark's line of sight vector, the imaged landmark will appear in the expected position specified by the line of sight vector command. However, if there is an error in the line of sight vector, the position in the image will deviate from the expected position. The value obtained by converting the image position error into the line of sight vector azimuth angle is the adjustment amount. The method for eliminating line of sight vector errors is as shown in embodiment 3. Furthermore, once the adjustment amount is calculated, if an error is added to the azimuth angle of the landmark's line-of-sight vector over time, that error will later become a measurement error in the position of the observation target. Specifically, the main cause of azimuth angle errors is the temporal change in the line-of-sight vector due to thermal deformation caused by changes in the daily sunlight environment and thermal deformation caused by changes in the angle of incidence of sunlight on the orbital plane over the course of a year. Therefore, images of the landmarks are taken several times a day to measure the daily fluctuations in the landmark's azimuth angles, and the trend of the daily fluctuations in the amount of adjustment is recorded in a database. Similarly, the annual fluctuations in the landmark's azimuth angles are measured, and the trend of the seasonal fluctuations in the amount of adjustment is recorded in a database. The diurnal and seasonal variations in thermal deformation over time are highly reproducible. Therefore, the daily and annual trends in the error of the line-of-sight vector's azimuth angle can be calibrated based on the trends in the diurnal and seasonal variations of the landmarks. Specifically, the adjustment amount for the season and time when the observation target is imaged is corrected by referring to the trend of daily fluctuations in the landmark adjustment amount and the trend of seasonal fluctuations in the landmark adjustment amount. In this way, the satellite control device 104 corrects the azimuth angle of the landmark in accordance with at least one of the daily variation trend and the seasonal variation trend. Then, based on the corrected azimuth angle, the satellite control device 104 corrects the azimuth angle when measuring the position coordinates of an object whose position coordinates are unknown.

[0074] ***Features of the Sixth Embodiment*** For observation satellites flying in geostationary orbit, the direction of sunlight incident on them rotates once around the north-south axis in one day. Therefore, the direction of sunlight incident on them changes over time, which can cause thermal deformation due to temperature changes, which can change the azimuth angle of the line-of-sight vector. By observing the landmark multiple times per day, the diurnal variation of the azimuth angle can be calibrated. If the azimuth angle fluctuates due to seasonal changes, the seasonal variation in the azimuth angle can be calibrated by observing the landmark multiple times throughout the year.

[0075] When measuring the position of an object to be imaged or observed, the accuracy of the position measurement is improved by calibrating the azimuth angle of a landmark that serves as a reference.

[0076] ***Effects of the Sixth Embodiment*** According to the sixth embodiment, the azimuth angle of the line-of-sight vector can be corrected to improve the accuracy of position measurement.

[0077] ***Supplementary explanation of implementation form*** Each embodiment is an example of a preferred embodiment and is not intended to limit the technical scope of the present disclosure. Each embodiment may be implemented in part or in combination with other embodiments. [Explanation of symbols]

[0078] 100 Observation satellite, 101 Optical observation equipment, 102 Attitude control device, 103 Propulsion device, 104 Satellite control device, 105 Communication equipment, 106 Power supply unit, 110 Observation area, 111 Entire observation area, 112 Easternmost observation area, 113 Western adjacent area, 114 Westernmost observation area, 200 Geostationary observation system, 210 Ground system, 211 Communication equipment, 212 Satellite control equipment, 213 Position database, 214 Azimuth angle database, 215 Position measurement equipment, 216 Mobile object database.

Claims

1. An observation satellite that is placed in a geostationary orbit and flies over the observation area, an optical observation device provided on the observation satellite for performing visible light observation of each observation area within the observation region; a location database indicating the location of a landmark on at least one of the easternmost island, westernmost island, southernmost island, and northernmost island in the observation area; an azimuth angle database indicating azimuth angles from the position of the observation satellite to the position of the landmark in the sky above the observation area; a position measurement device that calculates the position of an image captured by the optical observation device based on the difference between the azimuth angle of the landmark and the azimuth angle of the line-of-sight vector of the optical observation device at the time of image capture, and the position of the landmark; A geostationary observation system comprising:

2. a satellite control device that directs the line-of-sight vector of the optical observation device to the position of the observation target based on the position of the observation target, the position of the landmark, and the azimuth angle of the landmark; 2. The geostationary observation system of claim 1.

3. The satellite control device corrects the azimuth angle of the landmark in accordance with at least one of a daily variation trend and a seasonal variation trend, and corrects the azimuth angle when measuring the position coordinates of an object whose position coordinates are unknown, based on the corrected azimuth angle.

2. The geostationary observation system of claim 1.

Images