Patent Publication Number: US-2021174080-A1

Title: Information processing apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a technique for detecting growth conditions of crops. 
     BACKGROUND 
     A technique for detecting growth conditions of crops is known. JP-2017-15527A discloses a technique for detecting growth conditions of a wide range of crops using a state detection sensor provided in an unmanned aircraft. 
     When an index (e.g., NDVI) indicating the growth conditions of a crop is obtained based on an image shot from the sky using an aircraft such as a drone, it is likely that as the shooting range is increased, although the flight time is shortened, the accuracy of the obtained index decreases. 
     Therefore, an object of the present invention is to improve the accuracy of an index indicating the growth conditions of a crop obtained from a shot image while reducing the flight time of an aircraft that shoots the crop. 
     SUMMARY OF INVENTION 
     In order to achieve the above-described object, the present invention provides an information processing apparatus that includes: an image acquisition unit that acquires an image of a crop region that is shot by an aircraft that includes a shooting function; a calculation unit that calculates, based on the acquired image, an index indicative of growth conditions of a crop in the image; and an instruction unit that, in a case where in a portion of the crop region the calculated index is less than an index threshold, instructs the aircraft to shoot the portion with an increased resolution or a narrowed shooting range. 
     According to the present invention, it is possible to improve the accuracy of an index indicating the growth conditions of a crop obtained from a shot image while reducing the flight time of an aircraft that shoots the crop. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating an overall configuration of an agriculture support system, in accordance with the present invention. 
         FIG. 2  is a diagram illustrating a hardware configuration of a server apparatus, in accordance with the present invention. 
         FIG. 3  is a diagram illustrating a hardware configuration of a drone, in accordance with the present invention. 
         FIG. 4  is a diagram illustrating a configuration of functions realized by the agriculture support system, in accordance with the present invention. 
         FIG. 5  is a diagram illustrating an example of a method of shooting a field, in accordance with the present invention. 
         FIG. 6  is a diagram illustrating an example of an NDVI map in units of pixels, in accordance with the present invention. 
         FIG. 7  is a diagram illustrating an example of an NDVI map in units of regions, in accordance with the present invention. 
         FIG. 8  is a diagram illustrating an example of a flight path of a second shooting flight, in accordance with the present invention. 
         FIG. 9  is a diagram illustrating an example of a second NDVI map in units of regions, in accordance with the present invention. 
         FIG. 10  is a diagram illustrating an example of operating procedures of the apparatuses in recording processing, in accordance with the present invention. 
         FIG. 11  is a diagram illustrating a configuration of functions realized in a modification, in accordance with the present invention. 
         FIG. 12  is a diagram illustrating an example of an accuracy table, in accordance with the present invention. 
         FIG. 13  is a diagram illustrating an example of a threshold table, in accordance with the present invention. 
         FIG. 14  is a diagram illustrating an example of another accuracy table, in accordance with the present invention. 
         FIG. 15  is a diagram illustrating an example of sectional regions regarding which the shooting region is the same, in accordance with the present invention. 
         FIG. 16  is a diagram illustrating a configuration of functions realized in a modification, in accordance with the present invention. 
         FIG. 17  is a diagram illustrating an example of a threshold table, in accordance with the present invention. 
         FIG. 18A  is a diagram illustrating an example of an NDVI map in units of regions in a modification, in accordance with the present invention. 
         FIG. 18B  is a diagram illustrating an example of the NDVI map in units of regions in the modification, in accordance with the present invention. 
         FIG. 18C  is a diagram illustrating an example of the NDVI map in units of regions in the modification, in accordance with the present invention. 
         FIG. 18D  is a diagram illustrating an example of the NDVI map in units of regions in the modification, in accordance with the present invention. 
         FIG. 19  is a diagram illustrating an example of a threshold table, in accordance with the present invention. 
         FIG. 20A  is a diagram illustrating an example of the NDVI map in units of regions in the modification, in accordance with the present invention. 
         FIG. 20B  is a diagram illustrating an example of the NDVI map in units of regions in the modification, in accordance with the present invention. 
         FIG. 20C  is a diagram illustrating an example of the NDVI map in units of regions in the modification, in accordance with the present invention. 
         FIG. 20D  is a diagram illustrating an example of the NDVI map in units of regions in the modification, in accordance with the present invention. 
         FIG. 21  is a diagram illustrating an example of a threshold table, in accordance with the present invention. 
         FIG. 22  is a diagram illustrating an example of an altitude table, in accordance with the present invention. 
         FIG. 23  is a diagram illustrating an example of correction, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     1. Embodiment 
       FIG. 1  is a diagram illustrating an overall configuration of agriculture support system  1  according to an embodiment. Agriculture support system  1  is a system for supporting a person who works in a field (place where crops such as rice and vegetables are grown) by utilizing an index indicating the growth conditions of a crop. The index indicating the growth conditions is an index indicating one of or both of the degree of advancement in the growth stage of the crop (e.g., whether or not the period is appropriate for harvesting) and the conditions (also referred to as an activity level) such as a size and whether or not a disease is present. 
     In the present embodiment, an NDVI (Normalized Difference Vegetation Index), which will be described later, is used, and an index indicating the growth conditions of a crop in a field is calculated using an image of the field that is shot from the sky by an aircraft. The aircraft is not specifically limited as long as being able to shoot a field, and a drone is used in the present embodiment. Agriculture support system  1  includes network  2 , server apparatus  10 , and drone  20 . 
     Network  2  is a communication system including a mobile communication network, the Internet, and the like, and relays the exchange of data between devices accessing that system. Network  2  is accessed by server apparatus  10  through wired communication (or wireless communication), and by drones  20  through wireless communication. 
     Drone  20  is an aircraft that is a rotary-wing aircraft that includes one or more rotors and flies by rotating those rotors, in the present embodiment. Drone  20  includes a shooting function of shooting a field from the sky while flying. Drone  20  is carried to the field by a farmer who is the user of agriculture support system  1 , and performs flying and shooting as a result of the farmer performing an operation to start a shooting flight. Server apparatus  10  is an information processing apparatus that performs processing relating to supporting a worker. 
     Server apparatus  10  performs processing of calculating the above-described NDVI from a video of the field shot by drone  20 , for example. The NDVI indicates the growth conditions of the crop by a numerical value using a property that green leafs of plants absorb a large amount of red visible light and reflect a large amount of light having a wavelength in the near infrared region (0.7 μm to 2.5 μm). A worker can determine the timings of performing water sprinkling, fertilizer application, pesticide application, and the like to crops of the field in which the worker performs work with reference to the growth conditions indicated by the NDVI. 
       FIG. 2  is a diagram illustrating the hardware configuration of server apparatus  10 . Server apparatus  10  is a computer that includes the following apparatuses, namely processor  11 , memory  12 , storage  13 , communication apparatus  14 , input apparatus  15 , output apparatus  16 , and bus  17 . The term “apparatus” used here can be replaced with “circuit”, “device”, “unit”, or the like. One or more of each apparatus may be included, and some apparatuses may be omitted. 
     Processor  11  controls the computer as a whole by running an operating system, for example. Processor  11  may be constituted by a central processing unit (CPU) including an interface with peripheral apparatuses, a control apparatus, a computation apparatus, registers, and the like. Additionally, processor  11  reads out programs (program code), software modules, data, and the like from storage  13  and/or communication apparatus  14  into memory  12 , and then executes various types of processes in accordance therewith. 
     There may be one, or two or more, processors  11  that execute the various types of processes, and two or more processors  11  may execute various types of processes simultaneously or sequentially. Processor  11  may be provided as one or more chips. The programs may be transmitted from a network over an electrical communication line. 
     Memory  12  is a computer-readable recording medium, and may be constituted by at least one of ROM (Read Only Memory), EPROM (Erasable Programmable ROM), EEPROM (Electrically Erasable Programmable ROM), RAM (Random Access Memory), and so on, for example. Memory  12  may be called a “register”, “cache”, “main memory” (a main storage apparatus), or the like. Memory  12  can store the aforementioned programs (program code), software modules, data, and the like. 
     Storage  13  is a computer-readable recording medium, and may be constituted by at least one of an optical disk such as a CD-ROM (Compact Disc ROM), a hard disk drive, a flexible disk, a magneto-optical disk (e.g., a compact disk, a digital versatile disk, or a Blu-ray (registered trademark) disk), a smartcard, flash memory (e.g., a card, a stick, or a key drive), a Floppy (registered trademark) disk, a magnetic strip, and the like. 
     Storage  13  may be called an auxiliary storage apparatus. The aforementioned storage medium may be a database, a server, or another appropriate medium including memory  12  and/or storage  13 , for example. Communication apparatus  14  is hardware for communicating between computers over a wired and/or wireless network (a transmission/reception device), and is also called a network device, a network controller, a network card, a communication module, and the like, for example. 
     Input unit apparatus  15  is an input device that accepts inputs from the exterior (e.g., a keyboard, a mouse, a microphone, a switch, a button, a sensor, or the like). Output apparatus  16  is an output device that makes outputs to the exterior (e.g., a display, a speaker, or the like). Note that input apparatus  15  and output apparatus  16  may be configured integrally (e.g., a touchscreen). The apparatuses such as processor  11  and memory  12  can access each other over bus  17 , which is used for communicating information. Bus  17  may be constituted by a single bus, or may be constituted by buses that differ among the apparatuses. 
       FIG. 3  illustrates the hardware configuration of drone  20 . Drone  20  is a computer including the following apparatuses, namely processor  21 , memory  22 , storage  23 , communication apparatus  24 , flight apparatus  25 , sensor apparatus  26 , shooting apparatus  27  and bus  28 . The term “apparatus” used here can be replaced with “circuit”, “device”, “unit”, or the like. One or more of each apparatus may be included, and some apparatuses may be omitted. 
     Processor  21 , memory  22 , storage  23 , communication apparatus  24 , and bus  28  are the same types of hardware as those having the same names that are shown in  FIG. 2  (performance and specification need not be the same). Communication apparatus  24  can also perform, in addition to wireless communication with network  2 , wireless communication with other drones. Flight apparatus  25  is an apparatus that includes a motor, a rotor, and the like and causes the drone to fly. Flight apparatus  25  can cause the drone to move in all directions, to stop (hovering), and the like, in the air. 
     Sensor apparatus  26  is an apparatus including a sensor group that obtains information necessary for flight control. Sensor apparatus  26  includes a position sensor that measures the position (latitude and longitude) of the drone, a direction sensor that measures the direction the drone is facing (a forward direction is defined for the drone, and the forward direction is the direction the drone is facing), an altitude sensor that measures the altitude of the drone, a speed sensor that measures the speed of the drone, and an inertial measurement unit (IMU) that measures the 3-axis angular velocity and the three directional acceleration. 
     Shooting apparatus  27  is a so-called digital camera that includes a lens, an image sensor, and the like, and records an image shot using the image sensor as digital data. This image sensor has a sensitivity to light having a wavelength in the near infrared region that is needed for calculating the NDVI, in addition to visible light. Shooting apparatus  27  whose shooting direction is fixed is attached to a lower portion of the casing of the drone (drone  20 ), and shoots a vertically downward direction while the drone is flying. Also, shooting apparatus  27  includes an auto focus function, but does not include a zoom function (that is, the angle of view is fixed) in the present embodiment. 
     Note that server apparatus  10 , drones  20 , and so on may be configured including hardware such as microprocessors, DSPs (Digital Signal Processors), ASICs (Application Specific Integrated Circuits), PLDs (Programmable Logic Devices), FPGA (Field Programmable Gate Arrays), and the like, and some or all of the function blocks may be realized by that hardware. For example, processor  11  may be provided as at least one of these types of hardware. 
     A program provided in the present system is stored in server apparatus  10  and drone  20  that are included in agriculture support system  1 , and a function group described below is realized by a processor of each apparatus controlling the units by executing the program. 
       FIG. 4  illustrates a functional configuration realized by agriculture support system  1 . Server apparatus  10  includes crop image acquisition unit  101 , index calculation unit  102 , index map generation unit  103 , growth information recording unit  104 , and flight instruction unit  105 . 
     Drone  20  includes flight control unit  201 , flight unit  202 , sensor measurement unit  203 , and shooting unit  204 . Flight control unit  201  controls the flight of the drone when shooting of a field is performed. Flight control unit  201  stores field range information (e.g., information regarding latitude and longitude that indicate outer edges of the field) that indicates the geographic range of a field that a farmer who is the user has registered in advance, for example, and performs control of causing the drone to fly in a flight path so as to thoroughly fly above the entirety of the field at a fixed altitude based on the field range information. 
     The flight path in this case is a path of flying, in the case of a rectangular field, for example, by drawing a wavelike trajectory from one side of the field to the other side that opposes the one side. In addition thereto, the path may be a path of flying by drawing a spiral trajectory, in which the flight is first performed along the outer edges of the field, after completing one round, the path is shifted inside and next one round is performed, and this operation is repeated. That is, the flight path needs only be a flight path of thoroughly flying the entirety of the field. Flight unit  202  has a function of causing the drone to fly, and in the present embodiment, causes the drone to fly by operating the motor, the rotor, and the like included in flying apparatus  25 . 
     Sensor measurement unit  203  performs measurement by the sensors (position sensor, direction sensor, altitude sensor, speed sensor, and inertial measurement unit) included in sensor apparatus  26 , and repeatedly measures the position, direction, altitude, speed, angular velocity, and acceleration of the drone at predetermined time intervals. Sensor measurement unit  203  supplies the sensor information indicating the measured position, direction, altitude, speed, angular velocity, and acceleration to flight control unit  201 . Flight control unit  201  controls flight unit  202  based on the supplied sensor information, and causes the drone to fly along the above-described flight path. 
     Sensor measurement unit  203  supplies the sensor information indicating the measured position, direction, altitude, and speed to shooting unit  204 . Shooting unit  204  has a function of shooting a subject using a shooting apparatus  27 , and is an example of a “shooting function” of the present invention. When flight control unit  201  performs control so as to fly above a field, shooting unit  204  shoots the field as the subject. Shooting unit  204  shoots regions in which crops grow in the field (crop region). The image shot by shooting unit  204  is an example of an “image of a crop region” of the present invention. 
     The image sensor of shooting apparatus  27  has a sensitivity to light having a wavelength in the near infrared region, as described above, and therefore each pixel that forms a still image shot by shooting unit  204  is represented by, along with a pixel value (R) indicating red visible light, a pixel value (IR) indicating the light having a wavelength in the near infrared region. Shooting unit  204  shoots a plurality of still images so as to include all of the regions in the field based on the supplied sensor information. 
       FIG. 5  illustrates an example of a field shooting method. In  FIG. 5 , a path B 1  is shown when drone  20  flies above a field A 1  by drawing a wavelike trajectory. Shooting unit  204  calculates a shooting range (field range included in the angle of view) of the field (altitude at 0 m) from the altitude indicated by the sensor information and the angle of view of shooting apparatus  27 . Also, shooting unit  204  performs next shooting when the ratio of the overlapped area between the current shooting range obtained by the speed and direction indicated by the sensor information and the previous shooting range (e.g., the percentage of the overlapped area when the area of the shooting range is defined as 100%) has decreased below a threshold value. 
     Shooting unit  204  first shoots, in the example in  FIG. 5 , a shooting region C 1 , and then shoots a shooting region C 2  that overlaps the shooting region C 1  by a small amount. Also, shooting unit  204  notifies flight control unit  201  of the size of the calculated shooting range when the drone (drone  20 ) makes a turn. Flight control unit  201  makes a turn by shifting the path by an overlapped distance such that the shooting ranges of the notified size overlap such as shooting regions C 4  and C 5  in  FIG. 5 , for example. 
     Shooting unit  204  obtains still images by shooting regions C 1  to C 32  shown in  FIG. 5  by repeating shootings using this method, that is, shooting unit  204  shoots a plurality of still images whose shooting ranges overlap by a small amount. Note that in the example in  FIG. 5 , the field A 1  has a size and a shape such that a plurality of shooting ranges are appropriately included, but the field may not have such a size and shape. In this case, all of the regions in the field can each be included in at least one still image by performing shooting by increasing the overlapped portion between the shooting ranges or including the outside area of the field. 
     Note that the shooting method used by shooting unit  204  is not limited thereto. For example, if the flight speed and flight altitude when performing shooting are determined, the time intervals at which the shooting ranges overlap as shown in  FIG. 5  can be calculated in advance, and therefore the shooting need only be performed in such time intervals. Also, if the field map and the shooting positions are determined in advance, shooting unit  204  need only perform shooting when flying over the predetermined positions. 
     In addition thereto, a known method of shooting the ground using a drone may be used. The operations of the units included in drone  20  are started as a result of the farmer performing an operation to start flying. When the units start operating, drone  20  flies over the field in a set flight path, and shooting unit  204  repeatedly performs shooting, as described above. Shooting unit  204 , upon performing shooting, creates image data indicating the shot still image and shooting information regarding the shooting (information indicating the position, orientation, altitude, and time when the shooting is performed), and transmits the image data to server apparatus  10 . 
     Crop image acquisition unit  101  of server apparatus  10  acquires, by receiving the transmitted image data, the still image indicated by the image data as a crop region image shot by drone  20 . Crop image acquisition unit  101  is an example of an “image acquisition unit” of the present invention. Also, crop image acquisition unit  101  also acquires shooting information indicated by the received image data, and supplies the shooting information to index calculation unit  102  along with the acquired still image. 
     Index calculation unit  102  calculates an index indicating the growth conditions of a crop shot in the image based on the image of the crop region acquired by crop image acquisition unit  101 . Index calculation unit  102  is an example of a “calculation unit” of the present invention. Index calculation unit  102  calculates the above-described NDVI as the index indicating the growth conditions. Index calculation unit  102  calculates the NDVI by substituting the above-described red pixel value (R) and pixel value (IR) of light having a wavelength in the near infrared region in an equation of NDVI=(IR−R)/(IR+R), for each pixel of the still image, for example. 
     Index calculation unit  102  generates index information indicating the calculated NDVI in association with a pixel ID indicating the corresponding pixel, and supplies the index information to index map generation unit  103  along with the shooting information. The index information and the shooting information are supplied every time a crop region image is acquired, that is, drone  20  shoots a field image. Index map generation unit  103  generates an index map indicating the growth conditions of crops in the field based on the index (NDVI) calculated by index calculation unit  102 . 
     The index map is information representing the index (NDVI) in each position or region in the field on the map. First, index map generation unit  103  generates an NDVI map in units of pixels representing the NDVI in the position in the field corresponding to each pixel. 
       FIG. 6  illustrates an example of the NDVI map in units of pixels. In the example in  FIG. 6 , an NDVI map M 1  of the field A 1  shown in  FIG. 5  in units of pixels is shown. 
     The NDVI map M 1  is a rectangular map having a pixel D 1  at the upper left corner, a pixel D 2  at the lower left corner, a pixel D 3  at the upper right corner, and a pixel D 4  at the lower right corner, at the corners. “0.3” shown in the pixel D 1  is the NDVI in the pixel, at the upper left corner, of the image of the shooting region C 1  at the upper left corner shown in  FIG. 5 , and “−0.5” shown in the pixel D 2  is the NDVI in the pixel, at the lower left corner, of the image of the shooting region C 4  at the lower left corner shown in  FIG. 5 . 
     “0.2” shown in the pixel D 4  is the NDVI in the pixel, at the lower right corner, of the image of the shooting region C 29  at the lower right corner shown in  FIG. 5 , and “0.3” shown in the pixel D 3  is the NDVI in the pixel, at the upper right corner, of the image of the shooting region C 32  at the upper right corner shown in  FIG. 5 . Pixels indicating an overlapped portion of adjacent shooting regions are included in the NDVI map M 1 . Index map generation unit  103 , with respect to each of these pixels, uses an average value of the NDVI of the pixel (pixel indicating the same point in the field A 1 ) that is calculated from still images obtained by shooting the shooting regions. 
     The NDVI map M 1  is completed by drone  20  having shot the shooting region C 32  and the units performing the above operations. Index map generation unit  103  generates, in the present embodiment, an NDVI map in units of regions indicating the growth conditions of the crop in each of the plurality of regions obtained by sectioning the field A 1 , from the NDVI map M 1  in units of pixels that has been generated in this way. 
       FIG. 7  shows an example of the NDVI map in units of regions. In the example in  FIG. 7 , sectional regions E 1  to E 32  corresponding to the shooting region C 1  to C 32  shown in  FIG. 5  are shown. 
     Each sectional region is applied with a pattern according to the size of the NDVI average value. For example, the sectional regions E 1 , E 2 , and E 8  are applied with a pattern indicating that the NDVI average value is 0.6 or more. Similarly, the sectional regions E 7 , E 9 , and the like are applied with a pattern indicating that the NDVI average value is 0.2 or more and less than 0.6, and the sectional regions E 3 , E 4 , and the like are applied with a pattern indicating that the NDVI average value is −0.2 or more and less than 0.2. 
     Index map generation unit  103  supplies the generated NDVI map in units of pixels and NDVI map in units of regions to growth information recording unit  104  in association with the shooting information, and the shooting date and time of the images from which these maps are generated. Growth information recording unit  104  records these index maps generated by index map generation unit  103  as the growth information (information indicating the growth conditions of a crop) described above. 
     Growth information recording unit  104  retains the recorded growth information in a state in which the user (farmer) can read (being put on a web page that is accessible by a URL (Uniform Resource Locator) that the user is notified of, for example). The recorded growth information can also be downloaded from a terminal that is used by the user. The user downloads the growth information, confirms the change in the growth conditions in the field A 1 , and uses for determining the periods of performing farm work such as water sprinkling, fertilizer application, pesticide application, harvesting, and the like. 
     Index map generation unit  103  supplies the generated NDVI map in units of regions to flight instruction unit  105 . The supplying of the NDVI map is performed after ending shooting of all the shooting regions, that is, after the first shooting is ended. Flight instruction unit  105  makes an instruction regarding a second shooting flight to drone  20  that has ended the first shooting. Flight instruction unit  105  is an example of an “instruction unit” of the present invention. 
     Specifically, if a portion regarding which the index calculated by index calculation unit  102  is less than a predetermined threshold (index threshold) (this portion is also referred to as a “low index region” in the following) is present in the crop region, flight instruction unit  105  instructs drone  20  to shoot the low index region while increasing the resolution of the crop image. The NDVI calculated regarding the low index region indicates that the growth of the crop is delayed. 
     However, an error may occur in the NDVI depending on the shot image, and therefore does not necessarily indicate that the growth of the crop is actually delayed. Therefore, flight instruction unit  105  makes an instruction of performing a second shooting while increasing the resolution of the crop image such that an image with which the NDVI can be calculated at a higher accuracy can be shot. The resolution of a crop image is represented by the number of pixels representing a unit area (e.g., one square meter) of the crop region in an image of the crop region in which crops are grown, for example. 
     As the resolution of the crop image decreases, the number of pixels showing a crop and a substance other than the crop (such as soil, water surface, and the like) in a mixed manner increases, and therefore the accuracy of the NDVI value calculated from light reflected from the crop decreases. In contrast, as the resolution of the crop image increases, the number of pixels showing only the crop increases, and therefore the accuracy of the NDVI value increases. In the present embodiment, if a region regarding which the NDVI average value is less than 0.2 (index threshold described above) is present in the sectional regions shown in the supplied NDVI map, flight instruction unit  105  determines that the sectional region is the low index region. 
     In the example in  FIG. 7 , the NDVI average values of the sectional regions E 3 , E 4 , E 5 , E 6 , E 12 , E 13 , and E 27  are less than 0.2, and therefore flight instruction unit  105  determines that low index regions are present in the crop region. In the present embodiment, flight instruction unit  105  makes an instruction to shoot the low index region while performing a flight at an altitude lower than that when the image from which the index of the low index region has been calculated has been shot. As the flight altitude is reduced, the shooting range becomes narrower, and the number of pixels representing a unit area of the crop region increases, and as a result, the resolution of the above-described crop image increases. Accordingly, making an instruction to perform a flight at a low altitude is also making an instruction to shoot the low index region while increasing the resolution. 
     Specifically, flight instruction unit  105  generates a flight path that passes above all of the sectional regions indicated as the low index regions in the supplied NDVI map in units of regions and returns to the shooting start point at an altitude lower than that at the first shooting. Also, flight instruction unit  105  transmits the instruction data for instructing the flight through the generated flight path and performing shooting of the sectional regions that are low index regions, that is, for instructing a second shooting flight, to drone  20 . 
     Note that flight instruction unit  105 , upon determining that no low index region is present in the crop region, transmits instruction data for instructing to make a flight through a flight path for returning to base, that is, for directly returning to the shooting start point (return to base flight) to drone  20  instead of instructing the second shooting flight. When the first shooting flight is ended, flight control unit  201  of drone  20  stands by (makes hovering) at an end position (above the shooting region C 32  in the example in  FIG. 5 ), and waits for instruction data from server apparatus  10 . 
     Note that, if the waiting time exceeds a predetermined time, flight control unit  201  may transmit requesting data for requesting an instruction to server apparatus  10 . In this case, flight instruction unit  105  transmits, to drone  20 , instruction data if the determination regarding the low index region has been completed, and transmits instruction data for instructing a return to base flight if not, for example. Flight control unit  201 , upon receiving the instruction data, causes the drone to fly to the shooting start point through the flight path indicated by the instruction data. 
       FIG. 8  shows an example of the flight path in the second shooting flight. In the example in  FIG. 8 , drone  20  flies from the sectional region E 32  shown in  FIG. 7  to the sectional region E 27 , which is a low index region, and flies above the sectional region E 27 . Here, in the second shooting flight, the flight altitude is lowered, and therefore the shooting range is reduced to a quarter of that in the first flight, for example. 
     Therefore, flight instruction unit  105  instructs a shooting flight for shooting each divided region by flying over each of the divided regions obtained by dividing the sectional region E 27  into four. Flight instruction unit  105  instructs a shooting flight through a flight path B 2  that similarly passes over other sectional regions that are low index regions. Flight control unit  201  causes the drone to fly through this flight path B 2 , and shooting unit  204  shoots these sectional regions, and as a result, images obtained by shooting each sectional region that is a low index region is acquired by crop image acquisition unit  101 . 
     Thereafter, calculation of the index (NDVI) by index calculation unit  102  and the generation of an index map by index map generation unit  103  are performed. Here, index map generation unit  103  may generate an index map indicating the growth conditions for each shot divided region, but generates an index map indicating the growth conditions for each sectional region, similarly to the first shooting, in order to make the comparison with the index map generated only by the first shooting easy. 
     When the second shooting described above has been performed, the resolution of the crop image increases, and therefore it is possible that the sectional region determined as a low index region in the first shooting is determined not as the low index region, as a result of an NDVI representing a more actual state being calculated. 
       FIG. 9  shows an example of the second NDVI map in units of regions. In the example in  FIG. 9 , an NDVI map M 3  is illustrated in which the sectional regions E 3 , E 6 , and E 27  determined as the low index regions in  FIG. 7  are changed to sectional regions that are determined not as the low index regions. 
     Growth information recording unit  104  records the second NDVI map in units of pixels and the second NDVI map in units of regions as the growth information. Here, growth information recording unit  104  overwrites the growth information generated in the first shooting (e.g., NDVI map M 2  in units of regions shown in  FIG. 7 ) with the growth information generated in the second shooting (e.g., NDVI map M 3  in units of regions shown in  FIG. 9 ) (both pieces of information may be recorded without performing overwriting). With this, only the growth information whose accuracy is higher is recorded. 
     The apparatuses included in the agriculture support system  1  performs recording processing of recording crop growth information based on the configuration described above. 
       FIG. 10  shows an example of the operating procedure of each apparatus in the recording processing. This operating procedure is started by the user performing an operation to start the shooting flight of drone  20  as a trigger. First, drone  20  (flight control unit  201 , flight unit  202 , and sensor measurement unit  203 ) starts flying above the field based on the stored field range information (step S 11 ). 
     Next, drone  20  (shooting unit  204 ) starts the shooting of each shooting region from above the field (step S 12 ), generates image data indicating the shot still image and the shooting information (information indicating the position, orientation, and altitude when shooting is performed) every time the shooting is performed, and transmits the image data to server apparatus  10  (step S 13 ). Server apparatus  10  (crop image acquisition unit  101 ) acquires the still image indicated by the transmitted image data as the crop region image (step S 14 ). 
     Next, server apparatus  10  (index calculation unit  102 ) calculates the index (NDVI) indicating the growth conditions of the crop shot in the image based on the acquired crop region image (step S 15 ). Next, server apparatus  10  (index map generation unit  103 ) generates the index map indicating the growth conditions of the crop in the field based on the calculated indices (step S 16 ). Next, server apparatus  10  (growth information recording unit  104 ) records the generated index map as the growth information (step S 17 ). 
     Next, server apparatus  10  (flight instruction unit  105 ) determines whether or not a low index region is present in the crop region based on the index map generated in step S 16  (step S 21 ). If it is determined that a low index region is not present in step S 21  (NO), server apparatus  10  ends this operating procedure. If it is determined that a low index region is present in step S 21  (YES), server apparatus  10  (flight instruction unit  105 ) transmits instruction data for making an instruction to shoot the low index region while increasing the resolution to drone  20  (step S 22 ). 
     Drone  20  (flight control unit  201 , flight unit  202 , and sensor measurement unit  203 ) starts a second flight according to the instruction indicated by the transmitted instruction data (step S 23 ). Next, drone  20  (shooting unit  204 ) starts the second shooting (step S 24 ), generates image data every time shooting is performed, and transmits the image data to server apparatus  10  (step S 25 ). Server apparatus  10  (crop image acquisition unit  101 ) acquires the still image indicated by the image data transmitted second time as the crop region image (step S 26 ). 
     Next, server apparatus  10  (index calculation unit  102 ) calculates the second index (NDVI) based on the acquired crop region image (step S 27 ). Next, server apparatus  10  (index map generation unit  103 ) generates a second index map based on the calculated indices (step S 28 ). Also, server apparatus  10  (growth information recording unit  104 ) records the generated second index map as the growth information (step S 29 ), and ends this operating procedure. 
     As the flight altitude when field shooting is performed increases, the shooting range increases and the flight time can be shortened. On the other hand, as the shooting range increases, the resolution of the crop image decreases, and the accuracy of the NDVI decreases. In the present embodiment, as a result of shortening the flight time of drone  20  that shoots the crops by increasing the flight altitude in the first shooting, and increasing the resolution of the crop image in the second shooting, the accuracy of the NDVI obtained from the shot images can be increased. 
     If there is a puddle in the field or the field is a rice paddy, sunlight reflected on a water surface is incident on the lens of the digital camera, which may be a factor of incurring an error when the NDVI is calculated due to extremely bright pixels being included in the shot image. This reflected light is incident not only from direction in which the sun is present viewed from drone  20 , but also from various directions if the water surface waves. In the present embodiment, the shooting range is narrowed by reducing the flight altitude in the second shooting relative to the first shooting, and therefore the amount of reflected light that is incident on the lens decreases, and in this regard as well, the accuracy of the NDVI can be increased. 
     2. Modifications 
     The embodiment described above is merely an example of implementation of the present invention, and may also be modified as follows. Also, the embodiment and the modifications may be combined as necessary. In this case, implementation may be performed after the modifications are prioritized (after ranking, that is to say determining, which of the modifications is prioritized when competing events occur when the modifications are implemented). 
     Also, as a specific combination method, modifications that use different parameters for obtaining a common value or the like (a value, a change amount, an index or the like, e.g., an index threshold, its change amount, accuracy of the NDVI, or the like) may be combined, and the common value or the like may be obtained by using these parameters together, for example. Also, one value or the like may be obtained by adding separately obtained values following some rule. Also, when these operations are performed, different weights may be given to the parameters to be used. 
     2-1. Sectional Region 
     In the embodiment, index map generation unit  103  uses the region corresponding to a shooting range as the sectional region, and generates an NDVI map in units of regions, but the sectional region is not limited thereto. For example, a plurality of shooting ranges may be handled as one sectional region, or a region corresponding to a divided region obtained by dividing one shooting region into a plurality of pieces may be handled as the sectional region. Also, the shapes and sizes of the sectional regions may be the same or not the same. 
     2-2. Index Accuracy 
     In the embodiment, the index threshold is fixed, but the index threshold may be dynamically changed. 
       FIG. 11  illustrates the functional configuration realized by this modification.  FIG. 11  illustrates server apparatus  10   a  including index accuracy determination unit  106  in addition to the units shown in  FIG. 4 . 
     Index accuracy determination unit  106  determines the accuracy of an index calculated by index calculation unit  102 . Index accuracy determination unit  106  is an example of a “determination unit” of the present invention. Pixel values (IR, R) used for calculating the NDVI are supplied from index calculation unit  102  to index accuracy determination unit  106 , for example. Index accuracy determination unit  106  determines the index accuracy based on the size of the supplied pixel values. 
     For example, in the case of IR=20 and R=10, and in the case of IR=200 and the R=100 as well, the NDVI is 10/30 or 100/300, and is 0.333 . . . . If an error of 10 occurs in each of these pixel values, in the case of IR=30 and IR=20, NDVI=10/50=0.2, and in the case of IR=210 and R=110, NDVI=100/320=0.312 . . . . In this way, regarding the NDVI, as the pixel values of IR and R decrease, a small error in these pixel values appear as a larger error in the NDVI. 
     Index accuracy determination unit  106  determines the accuracy using an accuracy table in which an average value of the pixel values of IR and R is associated with the NDVI accuracy. 
       FIG. 12  shows an example of the accuracy table. In the example in  FIG. 12 , the average values of the pixel values of “less than Ave1”, “Ave1 or more and less than Ave2”, and “Ave2 or more” are respectively associated with the NDVI accuracies of “low”, “medium”, and “high”. 
     Index accuracy determination unit  106  determines the accuracy associated with the average value of the supplied pixel values in the accuracy table, as the accuracy of the index calculated by index calculation unit  102 . In this case, index accuracy determination unit  106  determines that the larger the average value of the supplied pixel values is, the higher the NDVI accuracy is. Index accuracy determination unit  106  notifies the flight instruction unit  105  of the accuracy determined in this way. 
     Flight instruction unit  105  uses a larger value as the index threshold, as the accuracy determined by index accuracy determination unit  106  decreases. Flight instruction unit  105  determines the index threshold using a threshold table in which the index accuracy is associated with the index threshold.  FIG. 13  shows an example of the threshold table. In the example in  FIG. 13 , the NDVI accuracies of “high”, “medium”, and “low” are respectively associated with the index thresholds of “Th 1 ”, “Th 2 ”, and “Th 3 ” (Th 1 &lt;Th 2 &lt;Th 3 ). 
     Flight instruction unit  105  determines the index threshold associated with the accuracy notified from index accuracy determination unit  106  in the threshold table as the index threshold used when determining whether or not a low index region is present. Flight instruction unit  105  notifies index map generation unit  103  of the determined index threshold. Index map generation unit  103  generates an NDVI map in units of regions in which the sectional regions regarding which the NDVI is less than the notified index threshold are shown, and supplies the NDVI map to flight instruction unit  105 . 
     Flight instruction unit  105  determines whether or not a low index region is present using the NDVI map in units of regions that is supplied in this way, and thereafter makes instructions similarly to the embodiment. In this way, in this modification, when the NDVI accuracy to be calculated is estimated to be low, the determination that the second shooting is to be performed is easier to be made by increasing the index threshold. Accordingly, compared with the case where the index threshold is fixed, growth information indicating more accurate growth conditions can be recorded. 
     On the other hand, in this modification, when the NDVI accuracy to be calculated is estimated to be high, the determination that the second shooting is to be performed is not easily made by decreasing the index threshold. Accordingly, compared with the case where the index threshold is fixed, the time needed to shoot the crop region can be reduced while suppressing the reduction of accuracy of the growth information. Note that the determination method of the index accuracy is not limited to the above-described method, and a method of making determination based on the difference from an index calculated in the past may also be used, for example. 
     In this case, the NDVI map in units of regions is supplied to index accuracy determination unit  106  from index map generation unit  103 . Index accuracy determination unit  106  reads out the NDVI map in units of regions recorded regarding the same field as the supplied NDVI map from growth information recording unit  104 . Index accuracy determination unit  106  calculates, for each sectional region, the difference between the average value of the indices of the sectional region shown in the NDVI map that is recorded when the previous shooting has been performed and the average value of the indices of the sectional region shown in the NDVI map that is generated in this shooting, and calculates the average value of the differences, for example. 
     Index accuracy determination unit  106  determines the accuracy using an accuracy table in which the average value of the differences is associated with the NDVI accuracy. 
       FIG. 14  shows another example of the accuracy table. In the example in  FIG. 14 , the average values of the differences of “less than Dif1”, “Dif1 or more and less than Dif2”, and “Dif2 or more” are respectively associated with the NDVI accuracies of “high”, “medium”, and “low”. Index accuracy determination unit  106  determines that the larger the calculated average value of the differences is, the lower the NDVI accuracy is, by using this accuracy table. 
     Thereafter, flight instruction unit  105  determines whether or not a low index region is present while using a larger value as the index threshold, as the accuracy determined by index accuracy determination unit  106  decreases, similarly to the above-described method. In this case as well, compared with the case where the index threshold is fixed, growth information indicating more accurate growth conditions can be recorded, and the time needed to shoot the crop region can be reduced while suppressing the reduction of accuracy of the growth information. 
     Also, when a sectional region that is smaller than the shooting region is used, as described in the above modification, a method of determining the index accuracy based on the degree of separation from the center of the shot image may also be used. In this case, index map generation unit  103  supplies the NDVI map in units of regions and information indicating the sectional regions regarding which an image used to calculate the NDVI is the same to index accuracy determination unit  106 . Index accuracy determination unit  106  determines that the NDVI accuracy of each sectional region included in the supplied NDVI map decreases as the distance of the sectional region from the center of the shot image increases. 
       FIG. 15  shows an example of the sectional regions regarding which the shooting region is the same. In  FIG. 15 , sectional regions Elli to E 119  are shown that are arranged in three columns vertically and three rows horizontally. In this case, index accuracy determination unit  106  determines that the NDVI accuracy at the sectional region E 115  at the center is “high”, the NDVI accuracies of the sectional regions E 112 , E 114 , E 116 , and E 118  that are horizontally and vertically adjacent to the sectional region E 115  are “medium”, and the NDVI accuracies of the sectional regions E 111 , E 113 , E 117 , and E 119  positioned at the corners are “low”. 
     In an image shot by a digital camera such as shooting apparatus  27 , the difference from the original image increases as separating from the center of the screen caused by phenomena such as barrel distortion in which peripheral portions of the screen bulges, pincushion distortion in which peripheral portions of the screen sink in a pincushion shape, and vignetting in which peripheral portions of the screen darkens. Therefore, as a result of determining the NDVI accuracies as in the example in  FIG. 15 , the determination that the second shooting is to be performed is easier to be made with respect to the sectional regions whose accuracy is low, and therefore growth information indicating more accurate growth conditions can be recorded. 
     2-3. Possible Flight Distance 
     A method different from the above-described modification may be used as a method of dynamically changing the index threshold. 
       FIG. 16  shows a functional configuration realized by this modification. In  FIG. 16 , server apparatus  10   b  including distance information acquisition unit  107  is shown in addition to the units shown in  FIG. 4 . Distance information acquisition unit  107  acquires information indicating a remaining possible flight distance of drone  20 . Distance information acquisition unit  107  is an example of a “distance acquisition unit” of the present invention. 
     Regarding the remaining possible flight distance, when the possible flight distance when a battery is 100% charged is 3000 m, if the remaining battery capacity is 50%, 1500 m is taken as the remaining possible flight distance, for example. In this modification, when drone  20  enters a state of waiting for instruction data after ending the first shooting, sensor measurement unit  203  measures the remaining battery capacity, and shooting unit  204  transmits remaining capacity data indicating the remaining battery capacity when transmitting image data. 
     Distance information acquisition unit  107  stores, in advance, the possible flight distance when the battery of drone  20  is 100% charged, and acquires the distance by multiplying the possible flight distance by the ratio of the remaining capacity indicated by the transmitted remaining capacity data as the information indicating the remaining possible flight distance. Distance information acquisition unit  107  supplies distance information indicating the acquired remaining possible flight distance to flight instruction unit  105 . Flight instruction unit  105  uses a larger value as the index threshold, as the possible flight distance indicated by the distance information acquired by distance information acquisition unit  107  increases. 
     Flight instruction unit  105  determines the index threshold using a threshold table in which the possible flight distance is associated with the index threshold. 
       FIG. 17  shows an example of the threshold table. In the example in  FIG. 17 , the possible flight distances of “less than Dis1”, “Dis1 or more and less than Dis2”, and “Dis2 or more” are respectively associated with index thresholds of “Th 1 ”, “Th 2 ”, and “Th 3 ” (Th 1 &lt;Th 2 &lt;Th 3 ). 
     Flight instruction unit  105  determines a low index region regarding which second shooting is to be performed using the index threshold associated, in the threshold table, with the possible flight distance indicated by the distance information supplied from distance information acquisition unit  107 , and makes an instruction to shoot the determined low index region. Accordingly, as the remaining possible flight distance when the first shooting is ended increases, the areas regarding which second shooting is to be performed increases, and therefore the flight distance of the second shooting flight tends to increase. As a result, although the remaining battery capacity when the second shooting flight is ended decreases, a large number of images with high accuracy can be shot in an amount corresponding to the increased flight distance, and as a result, growth information indicating more accurate growth conditions can be recorded. 
     Note that the method of acquiring the distance information is not limited to the method described above. For example, the configuration may be such that drone  20  calculates a remaining possible flight distance from the remaining capacity of the battery of the drone, and distance information acquisition unit  107  acquires the calculated possible flight distance. Also, remaining capacity information indicating the remaining battery capacity may be used as the distance information, without calculating the possible flight distance. In this case, flight instruction unit  105  may determine the index threshold using a threshold table in which the remaining capacity information is associated with the index threshold. Also, in addition thereto, information indicating the wind speed and the wind direction of the area including the field may also be used as the distance information. 
     In this case, flight instruction unit  105  divides the flight path of the second shooting flight by the direction, and corrects the possible flight distance considering the influence of the wind on the flight in each direction (decreases in the case of an against wind, and increases in the case of a following wind), for example. Flight instruction unit  105  determines the low index regions regarding which second shooting is to be performed using the index threshold that is associated with the corrected possible flight distance in the threshold table. Accordingly, a situation in which the remaining battery capacity becomes insufficient does not easily occur in the second shooting flight, compared with a case where information regarding the wind is not considered. 
     2-4. Density of Low Index Region 
     A method different from the above-described modifications may be used as the method of dynamically changing the index threshold. In this modification, index map generation unit  103  generates the NDVI map in units of regions using a provisional threshold as the index threshold. 
       FIGS. 18A to 18D  show examples of the NDVI map in units of regions of this modification. In  FIGS. 18A to 18D , sectional regions (low index region) regarding which the NDVI is less than the index threshold are applied with a pattern. In the example in  FIG. 18A , sectional regions E 5 , E 15 , and E 27  are low index regions, and in the example in  FIG. 18B , sectional regions E 6 , E 12 , and E 14  are low index regions. Index map generation unit  103  supplies the NDVI map in units of regions that is generated using the provisional threshold to flight instruction unit  105 . 
     When a provisional threshold is determined as the index threshold, flight instruction unit  105  uses a larger value as the index threshold in place of the provisional threshold, as the positional deviation of portions (low index regions) regarding which the index is less than the provisional threshold increases. Flight instruction unit  105  determines the size of the positional deviation as follows, for example. Flight instruction unit  105  determines a region surrounded by a rectangular that circumscribes all of the low index regions (a region F 1  in  FIG. 18A , and a region F 2  in  FIG. 18B ), and calculates the density of the low index region in this region. 
     In the case of the region F 1 , the density is 3/18=1/6, and in the case of the region F 2 , the density is 3/6=1/2. Flight instruction unit  105  determines that the larger the value of this density is, the more the low index regions are concentrated in a specific region, that is, the larger the positional deviation of the low index regions is. Flight instruction unit  105  determines the index threshold using a threshold table in which a value (deviation value) indicating the positional deviation of the low index regions is associated with the index threshold. 
       FIG. 19  shows an example of the threshold table. In the example in  FIG. 19 , deviation values of “less than 0.25”, “0.25 or more and less than 0.5”, and “0.5 or more” are respectively associated with index thresholds of “Th 1 ”, “Th 2 ”, and “Th 3 ” (Th 1 &lt;Th 2 &lt;Th 3 ). Flight instruction unit  105  determines the low index regions that are to be shot in the second shooting using the index threshold associated with the density value (deviation value) in the threshold table in place of the provisional threshold, and makes an instruction to shoot the determined low index regions. 
     If the index threshold is increased relative to the provisional threshold, the low index region is likely to extend to the surrounding area. For example, assume that a sectional region adjacent to a low index region that is determined when the provisional threshold is used becomes a low index region.  FIG. 18C  shows an NDVI map when the low index regions shown in  FIG. 18A  extend to adjacent sectional regions, and  FIG. 18D  shows an NDVI map when the low index regions shown in  FIG. 18B  extend to adjacent sectional regions. 
     In the example in  FIG. 18A , since the positional deviation of the low index regions is small, gaps remain between low index regions even if new low index regions are added, as shown in  FIG. 18C . On the other hand, in the example in  FIG. 18B , since the positional deviation of the low index regions is large, new low index regions increase so as to fill the gaps, and the low index regions become continuous, as shown in  FIG. 18D . As a result, in the example in  FIG. 18D , the flight distance in the second shooting flight is small, compared with the example in  FIG. 18C . 
     In this way, the larger the positional deviation of the low index region is, the more the increase in the flight distance when the index threshold is increased can be suppressed. In this modification, compared with the case where the index threshold is changed without considering the positional deviation of the low index regions, in the second shooting flight, the remaining battery capacity is effectively utilized while suppressing excessive consumption of the battery, and as a result, growth information indicating more accurate growth conditions can be recorded. 
     Note that the deviation value is not limited to the value described above. For example, the average value of the distances between one low index region and another low index region (as this value decreases, distances between low index regions decrease, and the positions are concentrated, that is, the positional deviation is large), may also be used as the deviation value. In addition thereto, any value may be used as long as the value indicates the positional deviation of the low index regions. 
     2-5. Size of Detour 
     As the method of dynamically changing the index threshold, a method different from those of the modifications described above may also be used. In this modification, similarly to the above-described modifications, index map generation unit  103  first generates an NDVI map in units of regions using a provisional threshold as the index threshold. 
       FIGS. 20A to 20D  show examples of the NDVI map in units of regions of this modification. In  FIGS. 20A to 20D , sectional regions (low index regions) regarding which NDVI is less than the index threshold are applied with a pattern. In the example in  FIG. 20A , sectional regions E 12  and E 21  are low index regions, and in the example in  FIG. 20B , sectional regions E 9  and E 24  are low index regions. Index map generation unit  103  supplies the NDVI map in units of regions that is generated using the provisional threshold to flight instruction unit  105 . 
     Flight instruction unit  105  uses a larger value as the index threshold in place of the provisional threshold, as the distance decreases between a path of drone  20  toward a scheduled landing point when the provisional threshold is determined as the index threshold and a portion whose NDVI is less than the provisional threshold. Flight instruction unit  105  provisionally determines, in the examples in  FIGS. 20A to 20D , a path B 3  from above a sectional region E 32  directly toward a sectional region E 1  as the path toward the scheduled landing point. Flight instruction unit  105  calculates the distance between the provisionally determined path B 3  and the low index regions. 
     Flight instruction unit  105  calculates, in the example in  FIG. 20A , the sum of distances L 1  and L 2  between the path B 3  and the low index regions E 12  and E 21 , and in the example in  FIG. 20B , the sum of distances between the path B 3  and the low index regions E 9  and E 24  as 0 (since the path B 3  passes through both of the low index regions). Flight instruction unit  105  determines the index threshold using a threshold table in which the distance between a provisionally determined path and low index regions is associated with the index threshold. 
       FIG. 21  shows an example of the threshold table. In the example in  FIG. 21 , the distances of “L 21  or more”, “L 11  or more and less than L 21 ”, and “less than L 11 ” are respectively associated with index thresholds of “Th 1 ”, “Th 2 ”, and “Th 3 ” (Th 1 &lt;Th 2 &lt;Th 3 ). Flight instruction unit  105  determines the low index regions that are to be shot in the second shooting using the index threshold associated with the density value in the threshold table in place of the provisional threshold, and makes an instruction to shoot the determined low index regions. 
     As the above-described shift distance increases, the distance of detour that is to be made separating from the path B 3  that is provisionally determined in the second shooting flight increases.  FIG. 20C  shows a flight path B 4  of the second shooting flight when the index threshold is increased and the low index regions shown in  FIG. 20A  have extended, and  FIG. 20D  shows a flight path B 5  when the index threshold is increased and the low index regions shown in  FIG. 20B  have extended. 
     If the index threshold is increased in each of the cases shown in  FIGS. 20A and 20B  without considering the size of detour, the possibility of the battery is to be depleted increases, because the distance is large when a flight is made through the flight path B 4  compared with the case of making a flight through the flight path B 5 . In this modification, the index threshold is decreased as the shift distance increases, as described above, and as a result, a situation does not easily occur in which the remaining battery capacity is not sufficient in the second shooting flight by not allowing the low index regions to extend when the shift distance is large, compared with the case of not considering the size of the shift distance. 
     2-6. Flight Altitude at Low Altitude 
     In the embodiment, flight instruction unit  105  makes an instruction to reduce the flight altitude in the second shooting flight than that of the first shooting flight. Flight instruction unit  105  may make a more detailed instruction regarding the flight altitude in the second shooting flight. Specifically, flight instruction unit  105  may make an instruction to maintain the altitude at a height corresponding to the crop type or more when performing a low-altitude flight. 
     Flight instruction unit  105  determines the flight altitude in the second flight shooting using an altitude table in which the crop type is associated with the flight altitude. 
       FIG. 22  shows an example of the altitude table. In the example in  FIG. 22 , the crop type of “cabbage, radish, etc.”, “rice, wheat, etc.”, and “corn, sugarcane, etc.” are respectively associated with the flight altitudes of “H 1 ”, “H 2 ”, and “H 3 ” (H 1 &lt;H 2 &lt;H 3 ). In this altitude table, the smaller the height of the crop is, the lower flight altitude is associated therewith. 
     In this modification, the user registers, in advance, the type of crop that is grown in each field, and flight instruction unit  105  stores the registered crop type in association with a field ID for identifying the field. Shooting unit  204  of drone  20  adds the field ID to image data, and transmits the image data. Index map generation unit  103  generates the NDVI map in association with the field ID, and supplies the NDVI map to flight instruction unit  105 . 
     Flight instruction unit  105  reads out the crop type stored in association with the field ID that is associated with the NDVI map, when making an instruction of the second shooting flight based on the supplied NDVI map, and makes an instruction to fly at a flight altitude that is associated with the crop type in the altitude table. In the altitude table, for each of a plurality of crops, the lowest flight altitude is determined, of the flight altitudes at which the crop will not fall by the wind caused by the rotors of drone  20  (downwind). 
     For example, a method of making a flight always at a flight altitude H 3  that is highest in the altitude table is conceivable in order to merely ensure that any type of crop will not fall. In contrast, if the method of this modification is used, the resolution of a crop image is increased by reducing the flight altitude as far as possible while ensuring that the crop will not fall by the downwind, and therefore the growth information indicating more accurate growth conditions can be recorded. 
     Note that, in the example in  FIG. 22 , a crop having a lower height is associated with a lower flight altitude, but there is no limitation thereto, and a crop type that has a high height but is strong against a wind may be associated with a low flight altitude. In other words, a flight altitude need only be associated at which, when a flight is performed at the flight altitude instructed by flight instruction unit  105 , the crop will not fall by the downwind. 
     2-7. Index Correction 
     The index obtained by the first shooting may be corrected using the index having a high accuracy obtained in the second shooting. In this modification, index calculation unit  102  first, similarly to the embodiment, calculates the NDVI of a portion that is a low index region in the first shooting, based on the image shot by drone  20  in the second shooting flight in accordance with the instruction made by flight instruction unit  105 . 
     Index calculation unit  102  corrects the NDVI with respect to the entirety of the image that has been previously shot, according to the difference between the NDVI calculated in this way and the NDVI calculated previously regarding the low index region. Index calculation unit  102  calculates, for each low index region, the difference between the NDVI calculated in the first shooting and the NDVI calculated in the second shooting, and calculates the average value of the differences with respect to all of the low index regions, for example. This average value of the differences indicates the tendency of the difference between the first NDVI and the second NDVI having a higher accuracy. 
     Index calculation unit  102  performs correction such that, using the average value of the differences as the correction value, the correction value is added to the NDVI (NDVI that is the index threshold or more) of each sectional region regarding which the second shooting is not performed. 
       FIG. 23  shows an example of the correction. In  FIG. 23 , NDVIs of eight low index regions (regions surrounded by thick lines) that are calculated in the first and second shootings are respectively shown. 
     In this example, from the first shooting to the second shooting, 0.0 changes to −0.1 (difference: −0.1), −0.3 changes to −0.3 (difference: 0.0), 0.1 changes to 0.2 (difference: +0.1), −0.4 changes to −0.3 (difference: +0.1), −0.3 changes to −0.2 (difference: +0.1), 0.1 changes to 0.2 (difference: +0.1), and −0.2 changes to −0.1 (difference: +0.1), −0.1 changes to 0.1 (difference: +0.2). 
     The average value of the differences in this case is +0.6/8=+0.075. Index calculation unit  102  calculates the value obtained by adding 0.075 to the NDVI of each of the sectional regions other than the low index regions as the corrected NDVI. According to this modification, the NDVI value in the sectional region with respect to which the second shooting, in which the resolution of the crop image is increased relative to the first shooting, is not performed can be approximated to a correct value, compared with the case where the above-described correction is not performed. 
     2-8. Removal of Reflected Light 
     Index calculation unit  102  calculates the NDVIs regarding all of the pixels in the embodiment, but there is no limitation thereto. For example, there are cases where pixels indicating reflected light of sunlight are included in the image, as described above, and therefore the configuration may be such that index calculation unit  102  does not calculate the NDVI with respect to such an image. 
     In this modification, index calculation unit  102  calculates the NDVI by removing pixels, of the pixels of the image of the crop region acquired by crop image acquisition unit  101 , whose brightness is a predetermined criterion or more. Each pixel is represented by, in addition to the pixel value (IR) indicating the light having a wavelength in the near infrared region, pixel values (R, G, and B) respectively indicating red, green, and blue, which are three primary colors of the visible light. Index calculation unit  102  determines that the pixel having pixel values of the three primary colors respectively higher than thresholds is a pixel whose brightness is the predetermined criterion or more, for example. 
     As a result of index calculation unit  102  calculating the NDVIs regarding the pixels obtained by removing the pixels determined in this way, the accuracy of the calculated NDVIs can be increased, relative to the case where the pixels representing reflected light are not removed. Note that, although pixel values of G and B are not needed for calculating the NDVI, as a result of shooting light of these colors, pixels whose R, G, and B pixel values are all high, that is, pixels representing reflected light whose color is close to white can be more appropriately removed. 
     2-9. Zoom 
     Flight instruction unit  105  makes an instruction to increase the resolution of the crop image by performing a low-altitude flight relative to the first shooting, in the embodiment, but the method of increasing the resolution is not limited thereto. When shooting apparatus  27  of drone  20  includes a zoom lens for causing the focal distance to change, flight instruction unit  105  makes an instruction to shoot a low index region while increasing the focal distance relative to that when the image with respect to which an index of the low index region has been calculated has been shot. 
     When the focal distance is increased, the shooting region narrows, and the number of pixels representing a unit area of the crop region increases, and as a result, the resolution of the above-described crop image increases. Therefore, making an instruction to increase the focal distance is equivalent to make an instruction to shoot the low index region while increasing the resolution. In this modification as well, similarly to the embodiment, as a result of increasing the resolution of the crop image in the second shooting, the accuracy of the NDVI obtained from the shot image can be increased. 
     Note that when, as in the embodiment, only a low-altitude flight is instructed, shooting apparatus  27  need only include a single focus lens, and therefore the weight of drone  20  can be reduced relative to the case of using a zoom lens. Also, there is a tendency that a bright image can be shot with a fixed focal lens, and the pixel value increases relative to the case of using the zoom lens, and as a result, the accuracy of the NDVI can be increased, as described with reference to  FIG. 11 . 
     2-10. Shooting Range 
     Flight instruction unit  105  makes an instruction to increase the resolution of the crop image, in the embodiment, but there is no limitation thereto, and flight instruction unit  105  may also make instruction to shoot the low index region while reducing the shooting range, although the resolution of the crop image is not changed. 
     In this case, it is assumed that shooting apparatus  27  of drone  20  includes, outside of the lens, a shutter that can be opened and closed, and can change the angle of view by changing the opening degree of the shutter while not changing the focal distance (an image in which the portion hidden by the shutter is blackened is shot). By merely narrowing the shooting range in this way, the number of pixels that represents the reflected light (sunlight reflected by a water surface) decreases, and therefore the accuracy of the calculated NDVI can be increased. 
     2-11. Index Representing Growth Conditions 
     The NDVI is used as the index representing the growth conditions, in the embodiment, but there is no limitation thereto. For example, a leaf color value (value indicating the leaf color), a vegetation rate (occupancy rate of the vegetation region per unit area), SPAD (chlorophyll content), a plant height, a number of stems, or the like may also be used. In other words, any value may be used as the index representing the growth conditions, as long as the value represents the growth conditions of a crop, and the value can be calculated from a shot image of the crop region. 
     2-12. Aircraft 
     Although the embodiment describes using a rotary wing-type aircraft as an aircraft that carries out autonomous flight, the aircraft is not limited thereto. For example, the aircraft may be a fixed-wing aircraft, or may be a helicopter-type aircraft. Additionally, autonomous flight functionality is not necessary, and for example, a radio-controlled (wirelessly-operated) aircraft, which is operated remotely by an operation manager, may be used, as long as the aircraft can fly in allocated flight airspace during in allocated permitted flight period. 
     2-13. Apparatuses that Realize Units 
     The apparatuses that realize the functions shown in  FIG. 4  and the like may be different from those shown in the diagrams. For example, the drone may include all of or some of the functions included in the server apparatus, and the drone may calculate the index, record the growth information, and make an instruction of the second shooting flight by itself. 
     In this case, the processor of the drone is an example of an “information processing apparatus” of the present invention. Also, the functions of the server apparatus may be realized by a user terminal (a notebook PC, a smartphone, or the like) used by the user. In this case, the user terminal is an example of the “information processing apparatus” of the present invention. Also, the operations performed by each function may be performed by another function, or by a new function. For example, the operations performed by index calculation unit  102  (calculation operation of the index) may be performed by index map generation unit  103 . 
     Also, the operations performed by index map generation unit  103  may be divided, and the function of generating a first NDVI map and the function of generating a second NDVI map may be newly provided, for example. Also, the functions included in the server apparatus may be realized by two or more apparatuses. In other words, as long as the agriculture support system realizes these functions as a whole, the number of apparatuses included in the agriculture support system is not limited. 
     2-14. Category of the Invention 
     The present invention may be understood as an information processing apparatus such as the server apparatus described above, an aircraft such as a drone (the drone may also act as the information processing apparatus), as well as an information processing system such as the agriculture support system including those apparatuses and the aircraft. The present invention can also be understood as an information processing method for implementing the processing executed by the respective apparatuses, as well as a program for causing a computer that controls the respective apparatuses to function. The program may be provided by being stored in a recording medium such as an optical disk or the like, or may be provided by being downloaded to a computer over a network such as the Internet and being installed so as to be usable on that computer. 
     2-15. Processing Sequences, Etc. 
     The processing sequences, procedures, flowcharts, and the like of the embodiments described in the specification may be carried out in different orders as long as doing so does not create conflict. For example, the methods described in the specification present the elements of a variety of steps in an exemplary order, and the order is not limited to the specific order presented here. 
     2-16. Handling of Input/Output Information, Etc. 
     Information and the like that has been input/output may be saved in a specific location (e.g., memory), or may be managed using a management table. The information and the like that has been input/output can be overwritten, updated, or added to. Information and the like that has been output may be deleted. Information and the like that has been input may be transmitted to other apparatuses. 
     2-17. Software 
     Regardless of whether software is referred to as software, firmware, middleware, microcode, hardware description language, or by another name, “software” should be interpreted broadly as meaning commands, command sets, code, code segments, program code, programs, sub programs, software modules, applications, software applications, software packages, routines, subroutines, objects, executable files, execution threads, sequences, functions, and so on. 
     Additionally, software, commands, and so on may be exchanged over a transmission medium. For example, when software is transmitted from a website, a server, or another remote source using hardwired technologies such as coaxial cable, fiber optic cable, twisted pair cabling, or digital subscriber line (DSL), and/or wireless technologies such as infrared light, radio waves, or microwaves, these hardwired technologies and/or wireless technologies are included in the definition of “transmission medium”. 
     2-18. Information and Signals 
     The information, signals, and so on described in the specification may be realized using any of a variety of different techniques. For example, data, instructions, commands, information, signals, bits, symbols, chips, and so on that may be referred to throughout all of the foregoing descriptions may be realized by voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, photo fields or photons, or any desired combination thereof. 
     2-19. Systems and Networks 
     The terms “system” and “network” used in the specification can be used interchangeably. 
     2-20. Meaning of “Based On” 
     The phrase “based on” used in the specification does not mean “based only on” unless specifically mentioned. In other words, the phrase “based on” means both “based only on” and “based at least on”. 
     2-21. “And” and “Or” 
     In the specification, with respect to configurations that can be realized both as “A and B” and “A or B”, a configuration described using one of these phrases may be used as a configuration described by the other of these phrases. For example, if the phrase “A and B” is used, “A or B” may be used as long as implementation is possible without conflicting with the other phrase. 
     2-22. Variations, Etc. On Embodiment 
     The embodiment described in the specification may be used alone, may be combined, or may be switched according to how the invention is to be carried out. Additionally, notifications of predetermined information (e.g., a notification that “X is true”) are not limited to explicit notifications, and may be carried out implicitly (e.g., the notification of the predetermined information is not carried out). 
     Although the foregoing has described the present invention in detail, it will be clear to one skilled in the art that the present invention is not intended to be limited to the embodiments described in the specification. The present invention may be carried out in modified and altered forms without departing from the essential spirit and scope of the present invention set forth in the appended scope of patent claims. As such, the descriptions in the specification are provided for descriptive purposes only, and are not intended to limit the present invention in any way. 
     REFERENCE SIGN LIST 
     
         
         
           
               1  Agriculture support system 
               10  Server apparatus 
               20  Drone 
               101  Crop image acquisition unit 
               102  Index calculation unit 
               103  Index map generation unit 
               104  Growth information recording unit 
               105  Flight instruction unit 
               106  Index accuracy determination unit 
               107  Distance information acquisition unit 
               201  Flight control unit 
               202  Flight unit 
               203  Sensor measurement unit 
               204  Shooting unit