Patent Publication Number: US-9897417-B2

Title: Payload delivery

Description:
RELATED APPLICATIONS 
     This application is a national phase application filed under 35 USC § 371 of PCT Application No. PCT/EP2014/076539 with an International filing date of 4 Dec. 2014 which claims priority of GB Patent Application 1321548.8 filed 6 Dec. 2013 and EP Patent Application 13275298.1, also filed 6 Dec. 2013. Each of these applications is herein incorporated by reference in their entirety for all purposes. 
     FIELD OF THE INVENTION 
     The present invention relates to delivering payloads to targets. 
     BACKGROUND 
     Unmanned Air Vehicles (UAVs) are commonly used to perform a variety of tasks. Such tasks include performing wide area searches of areas, surveillance operations, delivery of payloads, etc. 
     Conventionally, procedures to be performed by a UAV in order to complete a task are determined by a human operator and typically involve the direct control, by the human operator, of the UAV and on-board sensors. Such procedures may include, for example, the remote flying of the UAV by the operator to follow a route, and/or the moving of on-board sensors etc. 
     Furthermore, typically data gathered by a UAV (e.g. using on-board sensor systems) is transmitted to an entity remote from the UAV for analysis. 
     However, the manual control of a UAV and the transmission of data gathered by that UAV tend to require relatively high band-width communication. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention provides a method for delivering a payload to a target, the payload being releasably attached to an unmanned aircraft (e.g. an unmanned autonomous aircraft). The method comprises: acquiring, by one or more processors, a position of the target on the ground; acquiring, by the one or more processors, parameter values relating to manoeuvrability of the aircraft; acquiring, by the one or more processors, one or more properties of the payload; acquiring, by the one or more processors, parameter values relating to environmental conditions in which the aircraft is flying; using the acquired target position, the acquired payload properties, and the acquired parameter values relating to the environmental conditions, determining, by the one or more processors, a position for the aircraft and a value for a velocity for the aircraft; using the determined position and velocity value, determining, by the one or more processors, a procedure for the aircraft; performing, by the aircraft, the determined procedure; and, at a point in the procedure that the aircraft has the determined position and is travelling at a velocity equal to the determined velocity value, releasing, by the aircraft, the payload. The determined position and a velocity for the aircraft are such that, were the aircraft to release the payload whilst located at the determined position and travelling at a velocity equal to the determined velocity value, the payload would land on the ground within a predetermined distance of the target. The determined procedure is such that, were the aircraft to perform that procedure, at at least one instance during the procedure, the aircraft would be located at the determined position and travelling at a velocity equal to the determined velocity value. 
     At the point at which it is released from the aircraft, the payload may have the same position and velocity as the aircraft. The payload will then be acted on by at least gravity, and wind. After being released by the aircraft, the payload may fall freely from the aircraft. The one or more processors may calculate a velocity and position at which the payload should be released from the aircraft so that, when acted upon by at least gravity and wind, the payload will fall from the aircraft, and travel (e.g. under the action of gravity and wind) to land at or proximate to the target. The position and velocity at which the payload should be released by the aircraft may be determined using a position of the target, properties of the payload, and the parameter values relating to environmental conditions, such as wind speed and direction. 
     The parameter values relating to environmental conditions in which the aircraft is flying may include a wind speed and direction with respect to the aircraft. Other parameters values may be used instead of or in addition to the wind speed and direction including, but not limited to, a times of day measurement, an assessment of weather conditions etc. 
     The step of acquiring the parameter values relating to environmental conditions in which the aircraft is flying may comprise measuring, by a sensor located on the aircraft, the parameter values. The sensor may be operatively coupled to the one or more processors such that the measured parameter values may be sent from the sensor to the one or more processors. 
     The one or more processors may be located on-board the aircraft. 
     The step of determining the procedure may comprise determining a route for the aircraft to follow and determining a velocity profile for the aircraft. The step of the performing, by the aircraft, the procedure may comprise the aircraft following the determined route in accordance with the determined velocity profile. 
     The properties of the payload may include a drag coefficient of the payload in air. The properties of the payload may include a specification that the payload is a steerable or guidable payload, and the method further may comprise, after the payload is released from the aircraft, steering or guiding the payload towards the target. 
     The parameter values relating to environmental conditions in which the aircraft is flying may include a measurement of wind speed and direction. 
     The step of acquiring the position of the target on the ground may comprise: acquiring, by the one or more processors, a range of motion of a sensor relative to the aircraft, the sensor being mounted on the aircraft; acquiring, by the one or more processors, positional information of an area of terrain; acquiring, by the one or more processors, parameter values relating to the manoeuvrability of the aircraft; using the acquired range of motion of the sensor, the acquired specification of the area of terrain, and the acquired parameter values relating to the manoeuvrability of the aircraft, determining, by the one or more processors, an initial procedure to be performed by the aircraft; performing, by the aircraft, the initial procedure; whilst the aircraft performs the initial procedure, capturing, by the sensor, a set of images; and processing the set of images to detect, within at least one of those images, the target and acquire the position of the target on the ground. The initial procedure may comprise the aircraft moving with respect to the area of terrain and the sensor moving with respect to the aircraft such that, for each point in the area of terrain, that point is coincident with a footprint of the sensor on the ground for at least some time during the initial procedure. Capturing the set of images may be performed such that, for every point in the area of terrain, that point is present within at least one of the images in the set. 
     Alternatively, the step of acquiring the position of the target on the ground may comprise: acquiring, by one or more processors, a range of motion of a sensor relative to the aircraft, the sensor being mounted on the aircraft; acquiring, by the one or more processors, a specification of a path along the ground; acquiring, by the one or more processors, parameter values relating to the manoeuvrability of the aircraft; using the acquired range of motion of the sensor, the acquired specification of the path, and the acquired parameter values relating to the manoeuvrability of the aircraft, determining, by the one or more processors, an initial procedure to be performed by the aircraft; performing, by the aircraft, the initial procedure; whilst the aircraft performs the initial procedure, capturing, by the sensor, a set of images; and processing the set of images to detect, within at least one of those images, the target and acquire the position of the target on the ground. The initial procedure may comprise the aircraft moving with respect to the path along the ground and the sensor moving with respect to the aircraft such that, for each point along the path, that point is coincident with a footprint of the sensor on the ground for at least some time during the initial procedure. Capturing the set of images may be performed such that each point along the path is present within at least one of the images in the set. 
     The step of acquiring the position of the target on the ground may comprise: acquiring, by one or more processors, a range of motion of a sensor relative to the aircraft, the sensor being mounted on the aircraft; acquiring, by the one or more processors, a position of an initial target on the ground; acquiring, by the one or more processors, parameter values relating to the manoeuvrability of the aircraft; using the acquired range of motion of the sensor, the acquired specification of the position of the initial target, and the acquired parameter values, determining, by the one or more processors, an initial procedure to be performed by the aircraft; performing, by the aircraft, the initial procedure; whilst the aircraft performs the initial procedure, capturing, by the sensor, a set of images; and processing the set of images to detect, within at least one of those images, the target and acquire the position of the target on the ground. The initial procedure may comprise the aircraft moving with respect to the initial target and the sensor moving with respect to the aircraft such that the initial target is wholly contained within a footprint of the sensor on the ground for the entire duration of the procedure. Capturing the images may be performed such that the whole of the initial target is present within each image in the set. 
     The step of processing the set of images to detect the target and acquire the position of the target on the ground may comprise: for each image in the set, determining, by the one or more processors, a set of properties of that image; performing, by the one or more processors, a target detection process on the set of images to detect one or more targets within the set of images; for a each detected target, determining, by the one or more processors, a set of properties of that target; transmitting, by a transmitter on-board the aircraft, for use by an entity remote from the aircraft, the determined image properties; transmitting, by the transmitter, for use by the entity, the determined target properties; by the entity remote from the aircraft, using the received image properties and target properties, identifying a region of interest on the ground; sending, from the entity to the aircraft, a request for image data relating to the region of interest; receiving, by a receiver on-board the aircraft, the request; in response to receiving the request, transmitting, by the transmitter, for use by the entity, the image data relating to the determined region of interest; and, by the entity remote from the aircraft, using the received image data, selecting a target and sending a specification of the selected target to the aircraft, the specification of the selected target including the position of that target on the ground. 
     The step of capturing the set of images may comprises, for each image: acquiring, by one or more processors, a specification of a region on the ground to be imaged; measuring, by a position sensor fixedly mounted to a rigid support structure, its position; measuring, by an orientation sensor fixedly mounted to the rigid support structure, its orientation; using the measured position and orientation and using the acquired region specification, determining, a position and orientation for the sensor, the sensor being fixedly mounted to the rigid support structure; controlling the aircraft and the orientation of the sensor on-board the aircraft such that the sensor has the determined position and orientation, thereby providing that a footprint of the sensor on the ground is coincident with the region on the ground to be imaged; and, when the sensor has the determined position and orientation, capturing, by the sensor, one or more images of the area of the ground within the sensor footprint. 
     In a further aspect, the present invention provides apparatus for delivering a payload to a target, the payload being releasably attached to an aircraft, the apparatus comprising: one or more processors configured to acquire a position of the target on the ground, acquire parameter values relating to manoeuvrability of the aircraft, acquire one or more properties of the payload, acquire parameter values relating to environmental conditions in which the aircraft is flying, using the acquired target position, the acquired payload properties, and the acquired parameter values relating to the environmental conditions, determine a position for the aircraft and a value for a velocity for the aircraft, and, using the determined position and velocity value, determine a procedure for the aircraft; means for controlling the aircraft to perform the determined procedure; and means for, at a point in the procedure that the aircraft has the determined position and is travelling at a velocity equal to the velocity value, releasing the payload from the aircraft. The determined position and a velocity value are such that, were the aircraft to release the payload whilst located at the determined position and travelling at a velocity equal to the determined velocity value, the payload would land on the ground within a predetermined distance of the target. The determined procedure is such that, were the aircraft to perform that procedure, at at least one instance during the procedure, the aircraft would be located at the determined position and travelling at a velocity equal to the determined velocity value. 
     In a further aspect, the present invention provides a program or plurality of programs arranged such that when executed by a computer system or one or more processors it/they cause the computer system or the one or more processors to operate in accordance with the method of any of the above aspects. 
     In a further aspect, the present invention provides a machine readable storage medium storing a program or at least one of the plurality of programs according to the preceding aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration (not to scale) showing a scenario; 
         FIG. 2  is a schematic illustration (not to scale) of an aircraft; 
         FIG. 3  is a schematic illustration (not to scale) of a sensor module; 
         FIG. 4  is a process flow chart showing certain steps of a process in which an imaging process is performed; 
         FIG. 5  is a schematic illustration (not to scale) showing the aircraft following a flight path defined by the waypoints; 
         FIG. 6  is a process flow chart showing certain steps in a first embodiment of the imaging process; 
         FIG. 7  is a schematic illustration (not to scale) of the aircraft performing a wide area search; 
         FIG. 8  is a process flow chart showing certain steps in a second embodiment of the imaging process; 
         FIG. 9  is a schematic illustration (not to scale) showing the aircraft performing a feature following process; 
         FIG. 10  is a process flow chart showing certain steps in a third embodiment of the imaging process; 
         FIG. 11  is a schematic illustration (not to scale) of the aircraft performing a surveillance operation; 
         FIG. 12  is a process flow chart showing certain steps of an image processing method; and 
         FIG. 13  is a process flow chart showing certain steps of a payload delivery process. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic illustration (not to scale) showing an example scenario  1  in which embodiments of an imaging process is to be implemented. 
     The scenario  1  comprises an aircraft  2  and a ground station  4 . 
     The aircraft  2  is described in more detail later below with reference to  FIG. 2 . 
     In the scenario  1 , as described in more detail later below as the aircraft  2  is airborne, systems on board the aircraft  2  capture high resolution visible band images of an area on the ground  8 . Processed image data is then sent from the aircraft  2  to the ground station  4  via a wireless communications link  6 . 
     In the scenario  1 , the ground station  4  is located on the ground  8  and is remote from the aircraft  2 . 
       FIG. 2  is a schematic illustration (not to scale) of the aircraft  2 . The imaging process performed by the aircraft  2  in this scenario  1  will be described in more detail later below with reference  FIG. 5 . 
     The aircraft  2  is an unmanned aircraft. The aircraft  2  comprises a sensor module  10 , a processor  12 , a storage module  14 , a plurality of aircraft subsystems (which are hereinafter collectively referred to as “the aircraft subsystems” and indicated in  FIG. 1  by a single box and the reference numeral  16 ), a transceiver  18 , and a payload  19 . 
     The sensor module  10  is described in more detail later below with reference to  FIG. 3 . In this embodiment, the sensor module  10  is connected to the processor  12  such that information may be sent between the sensor module  10  and the processor  12 . 
     In this embodiment, the processor  12  is configured to process information received by it as described in more detail later below. In addition to being connected to the sensor module  10 , the processor  12  is connected to the storage module  14  such that information may be sent from the processor  12  to the storage module  14  (for storage by the storage module  14 ) and such that information stored by the storage module  14  may be acquired by the processor  12 . The processor  12  is further connected to the aircraft subsystems  16  such that information may be sent between the processor and the aircraft subsystems  16 . The processor  12  is further connected to the transceiver  18  such that information may be sent between the processor  12  and the transceiver  18 . The processor  12  is further connected to the payload  19  such that information may be sent between the processor  12  and the payload  19 . 
     In this embodiment, the storage module  14  is configured to store information received from the processor  12 . 
     In this embodiment, the aircraft subsystems  16  include, but are not limited to, a propulsion system of the aircraft  2 , a power system of the aircraft  2 , a fuel system of the aircraft  2 , and a navigation system of the aircraft  2 . The propulsion system may, for example, include primary and auxiliary propulsion units for generating thrust and/or lift. In this embodiment, the propulsion system includes sensing apparatus from which data relating to the propulsion of the aircraft  2  (e.g. the aircraft&#39;s speed) may be acquired. The power system may comprise electrical power and power distribution systems for providing electrical power to other aircraft systems. In this embodiment, the power system includes sensing apparatus from which data relating to a state or operations of the power system may be acquired. The fuel system may comprise fuel storage (such as fuel tanks), monitoring (such as fuel level, temperature and/or pressure sensors), and distribution systems (such as supply lines). In this embodiment, the fuel system includes sensing apparatus from which data relating to the fuel system may be acquired. In this embodiment, the navigation system includes sensing apparatus for determining, at least, a global position of the aircraft  2  (e.g. a Global Positioning System receiver), an altitude of the aircraft  2 , and a heading of the aircraft  2 . 
     In this embodiment, the transceiver  18  is configured to receive information from an entity that is remote from the aircraft  2  and relay that information to the processor  12 . Also, the transceiver  18  is configured to transmit, for use by an entity that is remote from the aircraft  2 , information received by the transceiver  18  from the processor  12 . 
     In this embodiment, the payload  19  may be any appropriate type of load or cargo, such as a container containing food supplies or equipment. The payload  19  may be a lethal effector or a non-lethal effector. 
     In this embodiment, the processor  12  may operate so as to release the payload  19  from the aircraft in flight so that the payload  19  is free to move away from the aircraft  2 . In some embodiments, the payload  19  is a “dumb” payload. In some embodiments, the payload  19  is a steered payload and may be controlled, e.g. by the processor  12 , so as to change direction after it has been released from the aircraft  2 . In some embodiments, the payload  19  is a guided payload. In some embodiments, the payload  19  may include a parachute which may be deployed after the payload  19  is released from the aircraft  2  so as to slow the decent of the payload  19  from the aircraft  2  to the ground  8 . 
       FIG. 3  is a schematic illustration (not to scale) showing the sensor module  10 . In this embodiment, the sensor module  10  is detachable from the aircraft fuselage and may, e.g., be replaced by a further sensor module comprising a different type of sensor. 
     In this embodiment, the sensor module  10  comprises a camera  20 , an interface module  22 , a position and orientation module  24 , a rigid support structure  26 , and a moveable turret  28 . 
     In this embodiment, the camera  20  is a visible light detecting camera configured to capture visible light images as described in more detail later below. The camera  20  is mounted to the turret  28  such that, by moving or steering the turret  28 , the position and orientation of the camera  20  relative to the support structure  26  may be changed. In other words, by steering the turret  28 , the facing of the camera  20  may be changed. In this embodiment, the camera  20  is connected to the interface module  22  such that, as described in more detail later below, a control signal may be sent from the interface module  22  to the camera  20  and such that image data may be sent from the camera  20  to the interface module  22 . 
     In this embodiment, the interface module  22  is configured to process information received by the interface module  22  as described in more detail later below. In this embodiment, the interface module  22  is mounted to the support structure  26  such that the interface module  22  has a fixed position and orientation relative to the support structure  26 . In addition to being connected to the camera  20 , the interface module  22  is connected to the processor  12  such that information may be sent between the interface module  22  and the processor  12 . The interface module  22  is also connected to the position and orientation module  24  such that information may be sent between the interface module  22  and the position and orientation module  24 . 
     In this embodiment, the position and orientation module  24  comprises a position sensor  30  and an orientation sensor  32 . The position sensor  30  is configured to measure a global position of the position sensor  30 . The position sensor  30  may, for example, include a GPS receiver. The orientation sensor  32  is configured to measure an orientation of the orientation sensor  32 . The orientation sensor may, for example, include a compass. In this embodiment, the position and orientation module  24  is mounted to the support structure  26  such that the position sensor  30  and an orientation sensor  32  each have a fixed position and orientation relative to the support structure  26 . 
     In this embodiment, the turret  28  is a steerable sensor turret. The turret  28  is attached between the camera  20  and the support structure  26  such that, by steering the turret  28  such that, by steering the turret  28 , the facing of the camera  20  with relative to the support structure  26  may be altered. In this embodiment, the turret  28  is connected to the interface module  24  such that a control signal (i.e. a signal for steering the turret  28 ) may be sent from the interface module  24  to the turret  28 . The turret  28  is configured to operate in accordance with a received control signal. 
     In this embodiment the turret  28  is a gimballed sensor turret configured to allow for rotation of the camera  20  around multiple (e.g. two or three) orthogonal axes with respect to the support structure  26 . For example, the turret  28  may comprise three gimbals coupled together such that the pivot axes of the gimbals are orthogonal to one another. 
     In this embodiment, the rigid support structure  26  is fixedly attached to the fuselage of the aircraft  2 . The support structure  26  is resistant to bending and flexing as the aircraft  2  flies. 
     In some embodiments, the turret  28  is attached directly to the fuselage of the aircraft  2 , i.e. the rigid support structure  26  may be omitted. 
     In operation, as the aircraft  2  flies in the proximity of an area of terrain or a terrain feature, the camera  20  captures high resolution visible band images of that area of terrain or terrain feature, as described in more details later below. The area of terrain or terrain feature that is imaged using the camera  20  is hereinafter referred to as the “imaging target”. Data corresponding to the images captured by the camera  20  is sent from the camera  20  to the processor  12 . The processor  12  is used to perform an image processing method on the received data. 
     In this embodiment, during the image processing method, processed data is sent from the processor  12  to the storage module  14  where it is stored, as described in more detail later below. Also, processed data is sent from the processor  12  to the transceiver  18  where it is transmitted to the ground station  4 . 
       FIG. 4  is a process flow chart showing certain steps of a process performed by the entities in the scenario  1 . 
     At step s 2 , a specification of the imaging target that is to be imaged is provided to the aircraft  2 . In this embodiment, the specification of the imaging target is stored in the storage module  14 . In this embodiment, the specification of the imaging target is loaded onto the aircraft  2  prior to the aircraft  2  taking off. However, in other embodiments, the specification of the imaging target may be transmitted to the aircraft  2 , e.g. from the ground station  4 , while the aircraft  2  is airborne. 
     The imaging target may, for example, be specified using global coordinates (i.e. latitudes and longitudes). 
     At step s 4 , a specification of a volume of airspace in which the aircraft  2  is permitted to fly whilst imaging the imaging target is provided to the aircraft  2 . In this embodiment, the specification of the volume of airspace is stored in the storage module  14 . In this embodiment, the specification of the volume of airspace is loaded onto the aircraft  2  prior to the aircraft  2  taking off. However, in other embodiments, the specification of the volume of airspace may be transmitted to the aircraft  2 , e.g. from the ground station  4 , while the aircraft  2  is airborne. 
     The volume of airspace may, for example, be specified using global coordinates and altitudes. 
     At step s 6 , a sequence of waypoints is provided to the aircraft  2 . In this embodiment, a waypoint is a point in the air that the aircraft  2  is to fly through, or within a pre-determined distance of. The sequence of waypoints define a flight-path for the aircraft from the aircraft&#39;s take-off point, to a point within, or within a predetermined distance of, the volume of airspace specified at step s 4 . 
     In this embodiment, the specification of the sequence of waypoints is stored in the storage module  14 . In this embodiment, the specification of the sequence of waypoints is loaded onto the aircraft  2  prior to the aircraft  2  taking off. However, in other embodiments, the specification of the sequence of waypoints may be transmitted to the aircraft  2 , e.g. from the ground station  4 , while the aircraft  2  is airborne. 
     The sequence of waypoints may, for example, be specified using global coordinates and altitudes. In some embodiment, one or more of the waypoints may be a different type of point that can be used to define a route for the aircraft  2 . For example, in some embodiments, a waypoint is a point on the ground over which the aircraft  2  is to fly. 
     In this embodiment, steps s 2  to s 6  are performed prior to the aircraft  2  taking off. However, in other embodiments the data corresponding to one or more of the waypoints, the imaging target, and/or the volume of airspace may be provided to the aircraft  2  at a different time, for example when the aircraft  2  is airborne (in which case, this data may be provided to the aircraft  2  from the ground station  4  via the communications link  6 ). Thus, tasks can advantageously be uploaded whilst the aircraft  2  is airborne. Furthermore, tasks for the aircraft  2  can updated, modified, cancelled, replaced, added to etc. whilst the aircraft  2  is airborne. 
     At step s 8 , the aircraft  2  takes-off from the ground station  4 . 
     At step s 10 , the aircraft  2  follows the flight path defined by the sequence of waypoints stored in the storage module  14  until the aircraft  2  enters the volume of airspace. In this embodiment, the aircraft  2  is unmanned and autonomous. 
       FIG. 5  is a schematic illustration (not to scale) showing the sequence of waypoints  34  followed by the aircraft  2 . In this embodiment, the flight path  36  defined by the waypoints  34  is followed by the aircraft  2  until the aircraft  2  enters the volume of airspace  38 .  FIG. 5  further shows the imaging target  40 . 
     At step s 12 , upon entering the volume of airspace  38 , the aircraft performs an imaging process to capture images of the imaging target  40 . In this embodiment, the sensor module  10  captures images of the imaging target  40 . 
     A first embodiment of the imaging process is described in more detail later below with reference to  FIGS. 6 and 7 . 
     A second embodiment of the imaging process is described in more detail later below with reference to  FIGS. 8 and 9 . 
     A third embodiment of the imaging process is described in more detail later below with reference to  FIGS. 10 and 11 . 
     At step s 14 , the sensor module  10  sends the captured images to the processor  12 . 
     At step s 16  the processor  12  performs an image processing method on the received images. 
     An embodiment of an image processing method is described in more detail later below with reference to  FIG. 12 . 
     At step s 18 , the aircraft  2  completes its journey, for example, by returning to its launch-site (e.g. the ground station  4 ), for example, by following the flight path  36 . 
     Thus, a process in which an imaging process is performed is provided. 
     What will now be described is a first embodiment of an imaging process performed at step s 12 . 
     In this first embodiment, the imaging target  40  is a relatively large defined area of terrain. In the first embodiment, the imaging of the imaging target  40  comprises conducting a “wide area search” of the imaging target  40 . The terminology “wide area search” is used herein to refer to the reconnaissance of the imaging target  40  that includes taking images of the imaging target  40  such that each point in the imaging target  40  is contained in at least one of those images. In this embodiment, the relatively large defined area of terrain is such that the entirety of the area of terrain cannot be captured in a single image taken by the camera  20 . In this embodiment, a wide area search further comprises processing the captured images to detect targets of interest within those images. 
       FIG. 6  is a process flow chart showing certain steps in the first embodiment of the imaging process. 
     At step s 20 , the processor  12  acquires the specification for the imaging target  40  and the specification for the volume of airspace  38  that are stored in the storage module  14 . 
     In this embodiment, the specification of the imaging target  40  includes global positions of points along the border of the imaging target  40 , i.e. a definition of the border of the large defined area of terrain that is to be imaged. 
     At step s 22 , the processor  12  acquires current performance parameter values for the aircraft  2  from the aircraft subsystems  16 . Examples of appropriate aircraft performance parameter values include, but are not limited to, velocities at which the aircraft  2  is capable of travelling, altitudes at which the aircraft  2  is capable of travelling, and a turning radius for the aircraft  2   
     At step s 24 , the processor  12  acquires performance parameter values for the sensor module  10  from the interface module  22 . Examples of appropriate performance parameter values for the sensor module  10  include, but are not limited to, the frequency with which the camera  20  can capture images, a range of motion, or range of travel, of the turret  28  relative to the support structure  26 , and a maximum speed at which the turret  28  may move. 
     The range of motion of the turret  28  may specify a distance (linear and/or angular), relative to the support structure  26 , that the moveable turret  28  may travel while properly attached to the support structure  26 . The range of motion of the turret  28  may specify, for each of one or more axes (e.g. multiple orthogonal axes), an angular distance about that axis relative to the support structure  26  that the turret  28  is capable of moving. The range of motion of the turret  28  may define the range of possible positions and facings relative to the support structure  26  that the camera  20  may occupy by operation of the turret  28 . 
     In some embodiments, the aircraft  2  is required to perform the wide area search of the imaging target  40  within a pre-specified amount of time. In such embodiments, the processor  12  may also acquire a specification of this time period. 
     At step s 26 , using some or all of the information acquired at steps s 20 , s 22 , and s 24 , the processor  12  determines a route, hereinafter referred to as the “first route”, within the volume of airspace  38  for the aircraft  2 . The determined first route is such that, were the aircraft  2  to follow that route, the sensor module  10  would be capable of capturing images of the imaging target  40  such that each point in the imaging target  40  is contained within at least one of those images. 
     Further information about the first route determined by the processor  12  at step s 26  is described in more detail later below with reference to  FIG. 7 . 
     At step s 28 , the processor  12  determines an imaging schedule, hereinafter referred to as the “first imaging schedule”, for the sensor module  10 . In this embodiment, the first imaging schedule specifies a sequence of points along the first route and, for each of those points, one or more regions within the imaging target  40  of which the camera  20  is to capture an image. 
     In this embodiment, the first imaging schedule is such that, were the camera  20  to capture images in accordance with that imaging schedule, each point on the ground  8  within the imaging target  40  would be contained within at least one of the captured images (i.e. a wide area search of the imaging target  40  would be performed). 
     Each of the sequence of points along the first route may be specified, for example, by an aircraft position (e.g. as GPS coordinates and an altitude). Each of the regions within the imaging target  40  that the camera  20  is to capture an image of may be specified by GPS coordinates for that region. 
     Further information about the first imaging schedule is described in more detail later below with reference to  FIG. 7 . 
     At step s 30 , the processor  12  sends the first imaging schedule to the interface module  22  of the sensor module  10 . 
     At step s 32 , the aircraft  2  is controlled (e.g. by the processor  12 ) so as to follow the first route. 
     At step s 34 , as the aircraft  2  follows the first route, the interface module  22  acquires position and orientation measurements from the position and orientation module  24 . In particular, the interface module  22  acquires position measurements from the position sensor  30  and orientation measurements from the orientation sensor  32 . 
     In this embodiment, the position and orientation module  24  is fixed to the support structure  26 . Also, the turret  28  is fixed to the support structure  26 . Thus, using the acquired position and orientation measurements, and using a known positional relationship between the turret  28  and the position and orientation module  24 , and using the known orientation of the turret  28  relative to the support structure  26 , the interface module  22  is able to determine a current position and orientation for the camera  20 . 
     At step s 36 , using the determined current position and orientation of the camera  20  and using the first imaging schedule received from the processor  12 , as the aircraft  2  follows the first route, the interface module  22  controls the turret  28  and the camera  20  so as to capture images in accordance with the first imaging schedule. 
     For example, a step in the first imaging schedule may specify a region within the imaging target  40  of which an image is to be captured. Using specification of that region, the interface module  22  determines a position and orientation for the camera  20  that would provide that the specified region is wholly located in the camera&#39;s footprint on the ground  8 . When that step in the first imaging schedule is reached, the interface module  22  controls the turret  28  so that the camera  20  has the determined position and orientation. Once the camera  20  has the desired position and orientation, the interface module  22  controls the camera  20  to capture one or more images of the specified region. 
     Further information about the capturing of images performed at step s 36  is described in more detail later below with reference to  FIG. 7 . 
     At step s 38 , the camera  20  sends the captured images to the interface module  22 . 
     At step s 40 , the interface module  22  processes the received images so as to convert those images into a predetermined format (e.g. a standardised format) that is usable by the processor  12 . 
     After step s 40 , the method proceeds back to step s 14  of  FIG. 4 , at which point the interface module  22  sends the converted images to the processor  12 . 
     Thus, a first embodiment of the imaging process is provided. 
       FIG. 7  is a schematic illustration (not to scale) of the aircraft  2  performing a wide area search of the imaging target  40 , as described above with reference to  FIG. 6 . 
     In  FIG. 7 , the first route is indicated by the reference numeral  42 . The direction of travel of the aircraft  2  along the first route  42  is indicated in  FIG. 7  by arrow heads placed along the first route  42 . 
     Also, in  FIG. 7 , the region of the ground  8  that is able to be imaged by the camera  20  at a particular time-step is indicated by the reference numeral  44 . This region is referred to herein as the “camera footprint”. 
     In this embodiment, the size of the camera footprint  44  on the ground  8  at a particular time-step is dependent on the position and orientation of the camera  20  relative to the aircraft  2  (which may be controlled by controlling the turret  28 ), the position and orientation of the aircraft  2  (including the altitude of the aircraft  2  above the ground  8 ), and the surface relief of the ground  8  (information relating to which may, for example, be loaded onto the aircraft  2  prior to take-off). The size of the camera footprint  44  on the ground  8  at a particular time-step may be determined by the processor  12 . 
     In this embodiment, when viewed from above, the first route  42  is substantially S-shaped. The first route  42  comprises three parallel straight sections that are connected together by curved sections. In other embodiments, the first route  42  may have a different shape, for example, the first route  42  may include a different number of straight sections and curved sections. 
     As the aircraft  2  flies along the straight sections of the first route  42 , the camera footprint  44  is moved over the imaging target  40  in the direction of travel of the aircraft  2  (as indicated in  FIG. 7  by an arrow and the reference numeral  46 ). Also as the aircraft  2  flies along the straight sections of the first route  42 , the turret  28  may be controlled such that the camera footprint  44  is swept back and forth in a direction that is perpendicular to the direction of travel of the aircraft  2  (as indicated in  FIG. 7  by arrows the reference numerals  48 ). In this embodiment, the camera  20  is controlled so as to capture images of the imaging target  40  as the aircraft  2  flies along the straight sections of the first route  42 . Thus, as the aircraft flies along the straight section of the first route  42  a strip of the imaging target  40  is imaged. In this embodiment, for each straight section of the first route  42 , a length of the strip of the imaging target  40  that is imaged as the aircraft  2  flies along that straight sections is greater than or equal to the entire length of the imaging target  40 . 
     In this embodiment, the distance between a straight section of the first route  42  and a subsequent straight section of the first route  42  is such that the strip of the imaging target  40  that is imaged while the aircraft  2  flies along the straight section overlaps at least to some extent with the strip of the imaging target  40  that is imaged while the aircraft  2  flies along the subsequent straight section. 
     In this embodiment, the number of straight sections is such that the entirety of the imaging target  40  is imaged during the straight sections of the first route  42 . 
     In this embodiment, the curved sections of the first route  42  are sections at which the aircraft  2  turns, i.e. changes direction, between straight sections of the first route  42 . Preferably, the first route  42  is determined such that the number of turns the aircraft  2  has to make is minimised. In this embodiment, the radius of each of the curved sections, which is denoted in  FIG. 7  by double headed arrows and the reference numeral  49 , is dependent upon the minimum turn radius of the aircraft  2 . In particular, for each curved section of the first route  42 , the radius  49  of that curved section is greater than or equal to the minimum turn radius of the aircraft  2 . 
     By flying along the first route  42  and by controlling the turret  28 , the camera footprint  44  is moved over the entirety of the imaging target  40 . Thus, each point within the imaging target  40  is contained within at least one image taken by the camera  20 . 
     In other embodiments, the first route  42  has a different shape to that described above. Also, in other embodiments, the turret  28  is controlled so as to move the camera footprint  44  in a different way to that described above, while still providing that each point within the imaging target  40  is contained within at least one image captured by the camera  20  as the aircraft  2  follows the first route  42 . 
     In some embodiments, after following the first route  42  and imaging the entirety of the imaging target  40 , the processor  12  calculates a further first route and a further first imaging schedule. The further first route and the further first imaging schedule may be such that, were the aircraft  2  to follow the further first route and capture images in accordance with the further first imaging schedule, each point on the ground  8  within the imaging target  40  would be contained within at least one of the captured images (i.e. a further wide area search of the imaging target  40  would be performed). The images captured during the first imaging schedule may be registered with those captured during the further first imaging schedule. For example, the images captured during the first imaging schedule and the images captured during the further first imaging schedule may be transformed into a global coordinate system. An advantage provided by performing more than one wide area search of the imaging target  40  is that errors in determined geolocations of detected targets tend to be reduced. In particular, when determining a geolocation of a detected target from an image (e.g. as described in more detail later below), the uncertainty associated with that determined geolocation tends to be largest in the direction of travel of the aircraft  2  when that image was taken. Using more than one image to determine a geolocation of a detected target tends to advantageously decrease the associated uncertainty. Preferably, for each image used to determine a geolocation of a target, the direction that the aircraft  2  was travelling when that image was taken is different (for example, preferably perpendicular) to the direction that the aircraft  2  was travelling when each of the other images used to determine the geolocation of that target was taken. This may be provided by calculating the further first route in such a way that it is different to the first route  42 . For example, the further first route may be determined using a criterion that an overlap between the further first and the first route is minimised. 
     Advantageously, uncertainty associated with a geolocation of a point or region tends to be greatly reduced if the direction in which the aircraft flies while that region is imaged during the first imaging schedule is substantially perpendicular to a direction in which the aircraft flies while that region is imaged during the further first imaging schedule. Thus, in embodiments in which a target is detected in the images captured during the first imaging schedule, the uncertainty associated with the geolocation of that target tends to be greatly reduced if the direction in which the aircraft flies while that target is imaged during the first imaging schedule is substantially perpendicular to a direction in which the aircraft flies while that target is imaged during the further first imaging schedule. Thus, the further first route may be determined using the position of the target determined from the images captured during the first imaging schedule, such that the further first route is perpendicular to the first route at the points on those routes at which the target is imaged. 
     What will now be described is a second embodiment of an imaging process performed at step s 12 . 
     In this second embodiment, the imaging target  40  is a predefined elongate terrain feature such as a road, a river, or a canal. For convenience, the imaging target  40  may be considered to be a linear terrain feature. In other embodiments, the imaging target is a different linear target such as a border of a country or man-defined feature. In other embodiments, the imaging target  40  is a line along the ground defined by a human such as an operator of the aircraft  2 . In the second embodiment, the imaging of the imaging target  40  comprises performing a “feature following” process on the imaging target  40 . The terminology “feature following” is used herein to refer to the imaging of an elongate imaging target  40  along its entire length. In this embodiment, a feature following process is a process comprising taking images of the imaging target  40 , such that each point along the entire length of the elongate imaging target  40  is contained in at least one of those images. In this embodiment, a feature following process further comprises processing the captured images to detect targets of interest within those images. 
     In this embodiment, the imaging target  40  upon which the aircraft  2  is to perform the feature following process is a pre-specified feature, a specification of which is uploaded into the storage module  14  prior to the aircraft  2  taking off. However, in other embodiments, the imaging target  40  upon which the aircraft  2  is to perform the feature following process is a linear target that has been previously detected, for example, by performing the wide area search process (as described in more details above with reference to  FIGS. 6 and 7 ). 
       FIG. 8  is a process flow chart showing certain steps in the second embodiment of the imaging process. 
     At step s 42 , the processor  12  acquires the specification for the imaging target  40  and the specification for the volume of airspace  38  that are stored in the storage module  14 . 
     In this embodiment, the specification of the imaging target  40  includes global positions of points along the length of the linear imaging target  40 . 
     At step s 44 , the processor  12  acquires current performance parameter values for the aircraft  2  from the aircraft subsystems  16 . Examples of appropriate aircraft performance parameter values include, but are not limited to, velocities at which the aircraft  2  is capable of travelling, altitudes at which the aircraft  2  is capable of travelling, and a turning radius for the aircraft  2 . 
     At step s 46 , the processor  12  acquires performance parameter values for the sensor module  10  from the interface module  22 . Examples of appropriate performance parameter values for the sensor module  10  include, but are not limited to, the frequency with which the camera  20  can capture images, a range of motion of the turret  28 , and a maximum speed at which the turret  28  may move. 
     At step s 48 , using some or all of the information acquired at steps s 42 , s 44 , and s 46 , the processor  12  determines a route, hereinafter referred to as the “second route”, within the volume of airspace  38  for the aircraft  2 . The determined second route is such that, were the aircraft  2  to follow that route, the sensor module  10  would be capable of capturing images of the imaging target  40  such that each point along the length of the linear imaging target  40  is contained within at least one of those images. In this embodiment, the second route is such that, were the aircraft  2  to follow that route, the aircraft  2  would “follow” the imaging target  40  along its path. 
     Further information about the second route determined by the processor  12  at step s 48  is described in more detail later below with reference to  FIG. 9 . 
     At step s 50 , the processor  12  determines an imaging schedule, hereinafter referred to as the “second imaging schedule”, for the sensor module  10 . In this embodiment, the second imaging schedule specifies a sequence of points along the second route and, for each of those points, a point along the linear imaging target  40  upon which the footprint of the camera  20  on the ground  8  is to be centred. 
     In this embodiment, the second imaging schedule is such that, were the camera  20  to capture images in accordance with that imaging schedule, each point along the linear the imaging target  40  would be contained within at least one of the captured images. 
     Each of the sequence of points along the second route may be specified, for example, by an aircraft position (e.g. as GPS coordinates and an altitude). Each of the points along the length of the linear imaging target  40  upon which the camera footprint is to be centred may be specified by GPS coordinates for that region. 
     Further information about the second imaging schedule is described in more detail later below with reference to  FIG. 9 . 
     At step s 52 , the processor  12  sends the second imaging schedule to the interface module  22  of the sensor module  10 . 
     At step s 54 , the aircraft  2  is controlled (e.g. by the processor  12 ) so as to follow the second route. 
     At step s 56 , as the aircraft  2  follows the second route, the interface module  22  acquires position and orientation measurements from the position and orientation module  24 . In particular, the interface module  22  acquires position measurements from the position sensor  30  and orientation measurements from the orientation sensor  32 . 
     In this embodiment, the position and orientation module  24  is fixed to the support structure  26 . Also, the turret  28  is fixed to the support structure  26 . Thus, using the acquired position and orientation measurements, and using a known positional relationship between the turret  28  and the position and orientation module  24 , and using the known orientation of the turret  28  relative to the support structure  26 , the interface module  22  is able to determine a current position and orientation for the camera  20 . 
     At step s 58 , using the determined current position and orientation of the camera  20  and using the second imaging schedule received from the processor  12 , as the aircraft  2  follows the second route, the interface module  22  controls the turret  28  and the camera  20  so as to capture images in accordance with the second imaging schedule. 
     For example, a step in the second imaging schedule may specify a point along the linear imaging target  40  upon which the footprint of the camera  20  on the ground  8  is to be centred. Using the specification of that point, the interface module  22  determines a position an orientation for the camera  20  that would provide that the footprint of the camera  20  on the ground  8  is centred on that specified point. When that step in the second imaging schedule is reached, the interface module  22  controls the turret  28  so that the camera  20  has the determined position and orientation. Once the camera  20  has the desired position and orientation, the interface module  22  controls the camera  20  to capture an image of the imaging target  40 . The captured image is centred on the specified point along the linear imaging target  40 . 
     In this embodiment, an image of the imaging target  40  captured at the ith step of the second imaging schedule overlaps at least to some extent with an image of the imaging target  40  captured at the (i+1)th step of the second imaging schedule (if such an image is taken). Thus, each point along the length of the imaging feature  40  is contained in at least one image captured by the aircraft  2  during the feature following process. 
     Further information about the capturing of images performed at step s 58  is described in more detail later below with reference to  FIG. 9 . 
     At step s 60 , the camera  20  sends the captured images to the interface module  22 . 
     At step s 62 , the interface module  22  processes the received images so as to convert those images into the predetermined format that is usable by the processor  12 . 
     After step s 62 , the method proceeds back to step s 14  of  FIG. 4 , at which point the interface module  22  sends the converted images to the processor  12 . 
     Thus, a second embodiment of the imaging process is provided. 
       FIG. 9  is a schematic illustration (not to scale) showing a top-down view of the aircraft  2  performing a feature following process to image the linear imaging target  40 , as described above with reference to  FIG. 8 . 
     In this embodiment, the volume of airspace  38  in which the aircraft  2  is permitted to fly during the feature following process is defined with respect to the linear imaging feature  40 . For example, in embodiments in which the linear imaging target  40  is a border of a country, the aircraft  2  may only be permitted to fly in the airspace above one side of that linear feature. 
     In  FIG. 9 , the second route is indicated by the reference numeral  50 . The direction of travel of the aircraft  2  along the second route  50  is indicated in  FIG. 9  by arrow heads placed along the second route  50 . 
     As in  FIG. 7 , in  FIG. 9 , the camera footprint (i.e. the ground  8  that is able to be imaged by the camera  20  at a particular time-step) is indicated by the reference numeral  44 . 
     In this embodiment, the size of the camera footprint  44  on the ground  8  at a particular time-step is dependent on the position and orientation of the camera  20  relative to the aircraft  2  (which may be controlled by controlling the turret  28 ), the position and orientation of the aircraft  2  (including the altitude of the aircraft  2  above the ground  8 ), and the surface relief of the ground  8  (information relating to which may, for example, be loaded onto the aircraft  2  prior to take-off). The size of the camera footprint  44  on the ground  8  at a particular time-step may be determined by the processor  12 . 
     In this embodiment, the imaging target  40  is a linear feature. In this embodiment, when viewed from above, the shape of the second route  50  is substantially the same as that of the imaging target  40 . In effect, the aircraft  2  “follows” the path of the linear imaging target  40 . 
     In this embodiment, the second imaging schedule specifies a sequence of points (indicated by Xs in  FIG. 9 ) along the linear imaging feature  40 . The points X are points on the imaging target  40  upon which the camera footprint  44  is to be centred when images are captured. In this embodiment, the sequence of points X are determined by the interface module  22  dependent inter alia upon the size of the camera footprint  44  on the ground  8  such that, when the aircraft  2  follows the second route  50  and implements the second imaging schedule, each and every point along the entire length of the imaging target  40  is contained within at least one of the captured images. 
     In this embodiment, as the aircraft  2  follows the second route  50 , the camera footprint  44  is moved along the length of the imaging target  40 , and the turret  28  may be controlled, such that the camera footprint  44  is centred upon each of the points X in turn. When the camera footprint  44  is centred upon each point X, one or more images of the imaging target  40  are captured by the camera  20 . In this embodiment, the turret  28  may be controlled such that the camera footprint  44  is moved in the direction of travel of the aircraft  2 , and/or in a direction that is perpendicular to the direction of travel of the aircraft  2 . Such movement of the camera footprint  44  is indicated in  FIG. 9  by arrows and the reference numerals  52 ). 
     In this embodiment, the imaging target  40  comprises a curved portion along which multiple images are to be taken. This curved portion is indicated in  FIG. 9  by a dotted box and the reference numeral  54 . In this embodiment, the turning radius of the aircraft  2  is larger than the radius of curvature of the curved portion  54  of the imaging target  40 . Thus, the second route  50  includes a loop, which is indicated in  FIG. 9  by a dotted box and the reference numeral  56 . In this embodiment, a route contains a “loop” if, when viewed from a certain direction, e.g. from above, the route crosses itself at at least one point. In this embodiment, the loop  56  increases the length of time that the aircraft spends in the vicinity of the curved portion  54 , thereby allowing the aircraft  2  to image the curved portion in accordance with the second imaging schedule. 
     Preferably, the second route  50  is determined so as to minimise the number of loops  56 . In this embodiment, the radius  58  of the loop  56  is dependent upon the minimum turn radius of the aircraft  2 . In particular, the radius  58  is greater than or equal to the minimum turn radius of the aircraft  2 . 
     In other embodiments, the second route  50  has a different shape to that described above. Also, in other embodiments, the turret  28  is controlled so as to move the camera footprint  44  in a different way to that described above, while still providing that each point along the length of the imaging target  40  is contained within at least one image captured by the camera  20  as the aircraft  2  follows the second route  50 . 
     In some embodiments, after following the second route  50  and imaging the entirety of the imaging target  40 , the processor  12  calculates a further second route and a further second imaging schedule. The further second route and the further second imaging schedule may be such that, were the aircraft  2  to follow the further second route and capture images in accordance with the further second imaging schedule, each point on the ground  8  along the length of the linear imaging target  40  would be contained within at least one of the captured images (i.e. a further feature following process would be performed to image the image target  40 ). An advantage provided by performing more than one feature following process on the imaging target  40  is that errors in determined geolocations of detected targets tend to be reduced. In particular, when determining a geolocation of a detected target from an image (which is described in more detail later below), the uncertainty associated with that determined geolocation tends to be largest in the direction of travel of the aircraft  2  when that image was taken. Using more than one image to determine a geolocation of a detected target tends to advantageously decrease the associated uncertainty. Preferably, for each image used to determine a geolocation of a target, the direction that the aircraft  2  was travelling when that image was taken is different to the direction that the aircraft  2  was travelling when each of the other images used to determine the geolocation of that target was taken. 
     What will now be described is a third embodiment of an imaging process performed at step s 12 . 
     In this third embodiment, the imaging target  40  is point on the ground  8  or a relatively small area of terrain. In the third embodiment, the imaging of the imaging target  40  comprises conducting “surveillance” of the imaging target  40 . The terminology “surveillance” is used herein to refer to the reconnaissance of a target (e.g. a detected object) or a target area (i.e. a relatively small defined area of terrain). In this embodiment, surveillance is a process comprising taking images of the imaging target  40 , such that the entirety of the imaging target  40  is contained in each of those images. In this embodiment, surveillance further comprises processing the captured images to detect targets of interest within those images. 
     In some embodiments, the imaging target  40  upon which a surveillance process is performed may be a target that has been previously detected, for example, by performing the wide area search process (as described in more details above with reference to  FIGS. 6 and 7 ) or the feature following process (as described above with reference to  FIGS. 8 and 9 ). 
       FIG. 10  is a process flow chart showing certain steps in the third embodiment of the imaging process. 
     At step s 64 , the processor  12  acquires the specification for the imaging target  40  and the specification for the volume of airspace  38  that are stored in the storage module  14 . 
     At step s 66 , the processor  12  acquires current performance parameter values for the aircraft  2  from the aircraft subsystems  16 . Examples of appropriate aircraft performance parameter values include, but are not limited to, velocities at which the aircraft  2  is capable of travelling, altitudes at which the aircraft  2  is capable of travelling, and a turning radius for the aircraft  2   
     At step s 68 , the processor  12  acquires performance parameter values for the sensor module  10  from the interface module  22 . Examples of appropriate performance parameter values for the sensor module  10  include, but are not limited to, the frequency with which the camera  20  can capture images, a range of motion of the turret  28  (with respect to the aircraft fuselage), and a maximum speed at which the turret  28  may move. 
     In this embodiment, the aircraft  2  is required to perform surveillance of the imaging target  40  for a pre-specified amount of time. The processor  12  acquires a specification of this time period (e.g. which may have been loaded onto the aircraft  2  prior to take-off). 
     At step s 70 , using some or all of the information acquired at steps s 64 , s 66 , and s 68 , the processor  12  determines a route, hereinafter referred to as the third route, within the volume of airspace  38  for the aircraft  2 . Preferably, the third route is such that, were the aircraft  2  to follow that route, at each time step within the time period, the sensor module  10  would be capable of capturing an image containing the entirety of the imaging target  40 . 
     Further information about the third route is described in more detail later below with reference to  FIG. 11 . 
     At step s 72 , the processor  12  determines an imaging schedule, hereinafter referred to as the third imaging schedule, for the sensor module  10 . In this embodiment, the third imaging schedule specifies the time-steps of the time period and the imaging target  40 . 
     Each of the sequence of points along the third route may be specified, for example, by an aircraft position (e.g. as GPS coordinates and an altitude). The imaging target  40  of which the camera  20  is to capture an image at each time step of the time period may be specified by GPS coordinates for that target. 
     Further information about the third imaging schedule is described in more detail later below with reference to  FIG. 11 . 
     At step s 74 , the processor  12  sends the third imaging schedule to the interface module  22  of the sensor module  10 . 
     At step s 76 , the aircraft  2  is controlled (e.g. by the processor  12 ) so as to follow the third route. 
     At step s 78 , as the aircraft  2  follows the third route, the interface module  22  acquires position and orientation measurements from the position and orientation module  24 . In particular, the interface module  22  acquires position measurements from the position sensor  30  and orientation measurements from the orientation sensor  32 . 
     In this embodiment, the position and orientation module  24  is fixed to the support structure  26 . Also, the turret  28  is fixed to the support structure  26 . Thus, using the acquired position and orientation measurements, and using a known positional relationship between the turret  28  and the position and orientation module  24 , and using the known orientation of the turret  28  relative to the support structure  26 , the interface module  22  is able to determine a current position and orientation for the camera  20 . 
     At step s 80 , using the determined current position and orientation of the camera  20  and using the second imaging schedule received from the processor  12 , as the aircraft  2  follows the second route, the interface module  22  controls the turret  28  and the camera  20  so as to capture images in accordance with the third imaging schedule (i.e., at each time-step within the time period, capture one or more images that wholly contain the imaging target  40 ). 
     For example, for a time step in the time period, using the current position and orientation of the camera  20 , and using the specification of the imaging target  40 , the interface module  22  determines a position an orientation for the camera  20  that would provide that the imaging target  40  would be wholly located in the camera&#39;s footprint on the ground  8 . The interface module  22  then controls the turret  28  so that the camera  20  has the determined position and orientation. Once the camera  20  has the desired position and orientation, the interface module  22  controls the camera  20  to capture one or more images of the imaging target  40 . 
     Further information about the capturing of images performed at step s 80  is described in more detail later below with reference to  FIG. 11 . 
     At step s 82 , the camera  20  sends the captured images to the interface module  22 . 
     At step s 84 , the interface module  22  processes the received images so as to convert those images into the predetermined format that is usable by the processor  12 . 
     After step s 84 , the method proceeds back to step s 14  of  FIG. 4 , at which point the interface module  22  sends the converted images to the processor  12 . 
     Thus, a third embodiment of the imaging process is provided. 
       FIG. 11  is a schematic illustration (not to scale) of the aircraft  2  performing surveillance of the imaging target  40 , as described above with reference to  FIG. 10 . 
     In  FIG. 11 , the third route is indicated by the reference numeral  58 . The direction of travel of the aircraft  2  along the third route  58  is indicated in  FIG. 11  by arrow heads placed along the third route  58 . 
     As in  FIGS. 7 and 9 , in  FIG. 11 , the camera footprint (i.e. the ground  8  that is able to be imaged by the camera  20  at a particular time-step) is indicated by the reference numeral  44 . 
     In this embodiment, the size of the camera footprint  44  on the ground  8  at a particular time-step is dependent on the position and orientation of the camera  20  relative to the aircraft  2  (which may be controlled by controlling the turret  28 ), the position and orientation of the aircraft  2  (including the altitude of the aircraft  2  above the ground  8 ), and the surface relief of the ground  8  (which may, for example, be loaded onto the aircraft  2  prior to take-off). The size of the camera footprint  44  on the ground  8  at a particular time-step may be determined by the processor  12 . 
     In this embodiment, the third  58  route is such that, at each point along the third route  58 , the sensor module  10  on-board the aircraft  2  is able to capture an image that wholly contains the imaging target  40 . In this embodiment, the third route  58  is an “off-set loiter” whereby, at each point along the third route  58 , the distance between the aircraft  2  and the imaging target  40  is greater than or equal to a predetermined minimum distance. This predetermined minimum distance may, for example, be uploaded onto the aircraft  2  prior to the aircraft  2  taking off, and stored in the storage module  14 . An off-set loiter type route advantageously tends to reduce the likelihood of the aircraft  2  being detected by the entities at or proximate to the imaging target  40  compared to a type of route that permits the aircraft  2  to circle above the imaging target  40 . 
     In this embodiment, the third route  58  is a loop, i.e. a start point of the third route  58  has the same position as an end point of the third route  58 . Thus, the aircraft is able to “loiter” relative to the imagining target by following the loop. 
     Also, the third route  58  may be determined such that, for each point along the third route  58 , the distance between the aircraft  2  and the imaging target  40  is less than or equal to a predetermined maximum distance. This predetermined maximum distance may, for example, be uploaded onto the aircraft  2  prior to the aircraft  2  taking off, and stored in the storage module  14 . This predetermined maximum distance may be dependent upon the capabilities of the camera  20  such that, at each point along the third route  58 , the camera  20  is capable of capturing images of the imaging target  40 . 
     In this embodiment, the aircraft  2  comprises an exhaust from which, during flight, waste gases or air from an aircraft engine are expelled. The exhaust of the aircraft points in certain direction relative to the aircraft fuselage. The direction in which the exhaust of the aircraft  2  points is the direction in which waste gases from the engine are expelled. A specification of this direction may be acquired by the processor  12 , for example, from an aircraft subsystem  16  (e.g. a propulsion system). In this embodiment, the determination of the third route  58  comprises minimising the duration for which the exhaust of the aircraft  2  is directed towards the imaging target  40 . In other words, in this embodiment, the third route  58  is such that the length of time that the exhaust is directed towards the imaging target  40  during the third route  58  is minimised. The exhaust of the aircraft  2  tends to produce a high level of noise in the direction in which waste gases from the aircraft engine are expelled (compared to the level of noise in other direction). Also, the exhaust of the aircraft  2  tends to produce a high level of noise compared to other aircraft systems. In some situations, minimising the duration for which the exhaust is directed towards the imaging target  40  may minimise the level of aircraft noise experienced by entities at or proximate to the imaging target  40 . This tends to reduce the likelihood of the aircraft  2  being detected, as a result of the noise generated by the aircraft  2 , by the entities at or proximate to the imaging target  40 . 
     In this embodiment, the aircraft subsystems  16  include one or more sensors for measuring a speed and direction of wind relative to the aircraft  2 . Such measurements may be acquired by the processor  12 . In this embodiment, the determination of the third route  58  comprises using measurements of the wind relative to the aircraft  2  so as to provide that, at each point along the third route  58 , the aircraft  2  is downwind of the imaging target  40 . In other embodiments, wind measurements may be used to determine a route such that, at each point along that route, the wind does not carry sound generated by the aircraft  2  (e.g. by the aircraft engine or exhaust) towards the imaging target  40 . This tends to reduce the likelihood of the aircraft  2  being detected, as a result of the noise generated by the aircraft  2 , by the entities at or proximate to the imaging target  40 . 
     In some embodiments, the processor  12  uses wind measurements to determine the volume of airspace  38  in which the aircraft  2  is permitted to fly whilst following the third route  58 . For example, the volume of airspace  38  may be determined as a volume that is wholly downwind of the imaging target  40 . 
     In some embodiments, the processor  12  determines a position of the Sun relative to the aircraft  2 . This may be performed using a clock measurement, a measurement of the location of the aircraft  2 , and a measurement of the orientation of the aircraft  2 , each of which may be acquired by the processor  12 . In some embodiments, the determination of an aircraft route may comprise using the determined position of the Sun relative to the aircraft  2  to reduce glare in the images taken by the camera  20  and/or increase the likelihood of high quality images of the imaging target  40  being captured. In some embodiments, the determination of an aircraft route may comprise using the determined position of the Sun relative to the aircraft  2  to reduce the likelihood of the aircraft  2  being seen by a particular entity, for example, by positioning the aircraft  2  between the Sun and that entity. 
     What will now be described is an embodiment of the image processing method performed by the processor  12  at step s 16 . 
       FIG. 12  is a process flow chart showing certain steps of an embodiment of the image processing method. 
     At step s 86 , each image received by the processor  12  from the camera  20  is “geolocated”. The terminology “geolocate” is used herein to refer to a process by which the real-world position of an image is determined. 
     In this embodiment, geolocation of an image comprises determining the real-world coordinates of each corner of the image, thereby determining the location of the portion of the ground  8  contained within that image. The coordinates of a corner of an image are determined by the processor  12  using the location and orientation of the aircraft  2  when that image was taken, and using the position and orientation of the camera  20  with respect to the aircraft  2  when that image was taken. 
     The processor  12  may also estimate, for each image, an uncertainty associated with the geolocation information for that image. 
     The processor  12  may also determine, for each image, a time at which that image was captured. 
     At step s 88 , each image and respective geolocation information (i.e. real-world coordinates of the image corners) is stored in the storage module  14 . 
     At step s 90 , the processor  12  performs a target detection algorithm on the images of the imaging target  40  stored within the storage module  14 . The algorithm is performed to detect targets of interest (e.g. vehicles, buildings, people, etc.) within the images. 
     Any appropriate target detection algorithm may be used. For example, an algorithm that detects image features dependent on the contrast of those features in the image, or an edge detection algorithm may be used. 
     At step s 92 , for each image, and for each target detected in that image, the processor  12  determines a geolocation for that target. A geolocation for a target within an image may be determined using the geolocation information relating to that image and stored in the storage module  14 . 
     The processor  12  may also estimate, for each target, an uncertainty associated with the geolocation information for that target. The processor  12  may also determine, for each target, a time at which that the image of that target was captured. 
     At step s 94 , for each image, a list of the targets detected within that image and the corresponding geolocation information for the targets is compiled. 
     At step s 96 , the lists of the target (including the geolocation information for the detected targets) are stored in the storage module  14 . 
     At step s 98 , image property information (including the geolocation information of each of the images and, in some embodiments, information about the errors/uncertainty associated with that geolocation information and/or times at which each of the images were taken) is transmitted from the aircraft  2  to the ground station  4 , by the transceiver  18 , via the wireless communications link  6 . 
     At step s 100 , target property information (including the geolocation information for each of the detected targets and, in some embodiments, information about the errors/uncertainty associated with that geolocation information and/or times at which images of each of the targets were taken) is transmitted from the aircraft  2  to the ground station  4 , by the transceiver  18 , via the wireless communications link  6 . 
     In this embodiment, only information relating to certain properties of the images/targets is transmitted to the base station from the aircraft  2 , not the images themselves. Thus, the amount of data transmitted to the ground station  4  at steps s 98  and s 100  tends to be small relative to the amount of data that would be transmitted were the images themselves transmitted. 
     In this embodiment, as more images of the imaging target  40  are captured by the camera  20  and processed by the processor  12 , targets detected in different images are associated together (i.e. assumed to be the same) if the geolocations of those targets are the same or within a pre-defined distance of one another. A geolocation of a target may be determined using the geolocations of that target in each of the different images in which that target is detected. For example, the geolocation of a target may be determined as the average (or centre of mass) of the geolocations of that target determined from each of the different images in which that target was detected. This process of associating together targets with the same or sufficiently similar geolocation information advantageously tends to reduce the uncertainly about a detected target&#39;s true geolocation. 
     Thus, in this embodiment, geolocation information for detected targets is continuously updated during the imaging of the imaging target  40 . Updated information may be continuously sent from the aircraft  2  to the ground station  4 . 
     In some embodiments, as more images of the imaging target  40  are captured by the camera  20 , those images may be registered together. 
     At step s 102 , the information sent to the ground station  4  at steps s 98  and s 100  is displayed to an operator at the ground station  4  (e.g. target locations may be displayed on a map on a display screen). Time and date information for an image (specifying when an image was taken) may also be displayed to the operator. 
     At step s 104 , the operator selects a particular target of interest (e.g. by selecting that target on the display screen). In this embodiment, this generates a request for an image of the selected target to be returned to the ground station  4 . 
     The operator may request that a certain type of image is returned to the ground station  4 . For example, the operator may request a cropped image (i.e. a sub-image) containing a certain target, or a compressed version of an entire camera image containing that target. 
     At step s 106 , the ground station  4  sends the generated request to the transceiver  18  of the aircraft  2 . The transceiver  18  relays the request to the processor  12 . 
     At step s 108 , the processor  12  processes the received request and retrieves, from the storage module  14 , one or more images containing the target specified in the request (i.e. the particular target that was selected by the operator at step s 104 ). 
     At step s 110 , the processor  12  processes the retrieved image such that an image corresponding to the operator&#39;s request is produced. 
     At step s 112 , the transceiver  18  transmits the produced image to the ground station  4  via the wireless communications link  6 . 
     At step s 114 , the image received at the ground station  4  is displayed to the operator for analysis. 
     Thus, the image processing method performed at step s 16  of the trajectory planning algorithm is provided. 
     In this embodiment, after a target has been detected by performing the imaging process described above with reference to  FIGS. 4 to 12 , a payload delivery process is performed so as to deliver the payload  19  to a detected target. In other embodiments, a different process (e.g. a different payload delivery process) is performed after a target has been detected. 
       FIG. 13  is a process flow chart showing certain steps of an embodiment of a payload delivery process. 
     At step s 116 , the operator located at the ground station  4  identifies a target to which the payload  19  is to be delivered. The target to which the payload  19  is to be delivered is hereinafter referred to as the “payload target”. For example, at step s 114  of the above described imaging process, the operator analyses the displayed images and selects a target within the displayed images as being the payload target. 
     At step s 118 , the ground station  4  sends a geolocation of the payload target to the transceiver  18  of the aircraft  2 . The transceiver  18  relays this target specification to the processor  12 . In other embodiments, a target identifier may be sent to the aircraft  2  and the processor  12  may determine/acquire a geolocation for that specified target using information stored in the storage module  14 . 
     At step s 120 , the processor  12  acquires current aircraft parameter values for the aircraft  2  from the aircraft subsystems  16 . Examples of appropriate aircraft parameter values include, but are not limited to, velocities at which the aircraft  2  is capable of travelling, altitudes at which the aircraft  2  is capable of travelling, and a turning radius for the aircraft  2 . In this embodiment, the aircraft subsystems  16  include one or more sensors for measuring a speed and direction of wind relative to the aircraft  2 . Such measurements are also acquired by the processor  12 . 
     At step s 122 , the processor  12  acquires values of one or more parameters relating to the payload  19 . In this embodiment, the processor  12  acquires values for the mass of the payload  19  and a drag coefficient for the payload  19  in air (or other value indicative of the drag that would be experienced by the payload  19  were the payload  19  to be released from the aircraft  2 ). In this embodiment, the processor further acquires other properties of the payload  19  such as the type of payload  19 , whether or not the payload  19  is a dumb payload, a steered payload, a guided payload, or another type of payload, and whether or not the payload includes a parachute. The processor  12  may also acquire, e.g. from the storage module  14  or from the payload  19 , a specification of a distance from the payload target within which the payload  19  is to land on the ground  8 . 
     At step s 124 , using some or all of the information acquired by the processor  12  at steps s 118 -s 122 , the processor  12  determines a location and a velocity, which are hereinafter referred to as the “payload release location” and “payload release velocity” respectively. The payload release location may be specified by a geolocation and an altitude. The payload release velocity may be specified by an aircraft heading and an aircraft speed. In this embodiment, the payload release location and payload release velocity are such that, were the aircraft  2  to release the payload  19  whilst located at the payload release location and travelling with the payload release velocity, the payload  19  would land on the ground  8  within the pre-specified distance of the payload target. 
     In some embodiments, for example in embodiments in which the payload is a steered or guided payload, the payload release location is a volume of airspace in which the payload may be released (and subsequently steered or guided, e.g. by the processor  12 , towards the payload target). In such embodiments, the payload release velocity may be a range of velocities. 
     At step s 126 , using the determined payload release location and using measurements of the aircraft&#39;s current position and orientation, the processor  12  determines a route from the aircraft&#39;s current location to the payload release location. This determined route will hereinafter be referred to as the fourth route. 
     At step s 128 , using the determined fourth route, the payload release velocity and using a measurement of the aircraft&#39;s current velocity, the processor  12  determines a velocity profile for the aircraft  2  along the along the fourth route. In this embodiment, the velocity profile is such that, were the aircraft  2  to travel along the fourth route with the determined velocity profile, the aircraft  2  would arrive at the payload release location travelling at the payload release velocity. 
     At step s 130 , the aircraft  2  is controlled (e.g. by the processor  12 ) so as to follow the fourth route in accordance with the determined velocity profile. 
     At step s 132 , when the aircraft  2  reaches the payload release location, the processor  12  releases the payload  19  from the aircraft  2 . At the payload release location the aircraft is travelling at the payload release velocity. 
     At step s 134 , after being release from the aircraft  2 , the payload  19  travels towards the payload target, and land on the ground  8  within the pre-specified distance of the payload target. Thus, the payload  19  is delivered to the payload target. 
     Thus, a payload delivery process is provided. 
     An advantage provided by the above described system and method is that a route that is to be followed by the aircraft is determined on-board the aircraft. Also, the aircraft may be controlled so as to follow the determined route by systems located on-board the aircraft. Thus, the aircraft tends to be capable of acting autonomously, i.e. without receiving instructions or control signals from the ground station. 
     A further advantage provided by the above described system and methods is that task information, including task parameters, can be uploaded to the aircraft whilst the aircraft is on the ground (i.e. prior to take off), or whilst the aircraft is airborne, thereby allowing for the updating of task parameters after take-off. Furthermore, certain of the task parameters can advantageously be measured/determined using other systems on-board the aircraft. For example, an aircrafts Global Positioning System (GPS), or the aircraft&#39;s avionic or fuel systems etc. can be used to determine parameters such as the location and orientation of the aircraft, the time of day, and/or how much fuel/time is left to complete a task. 
     An advantage provided by the above described sensor module is that measurements taken by the position and orientation module may be used to accurately determine a position and orientation of the camera. This tends to be due to the position and orientation module and the turret to which the camera is mounted having a fixed position and orientation with respect to one another as a result of being attached to the rigid structure. The determined position and orientation of the camera tend to be more accurate than those that may be produced using conventional systems, for example, those systems in which position and orientation measurements of an aircraft are used to determine a position and orientation of a camera mounted to that aircraft. Accurate position and orientation measurements of the camera tend to facilitate in the accurate control of the camera. Furthermore, geolocations of the images produced by the camera, and geolocations for targets detected in those images, tend to be more accurate than those produced using conventional imaging systems. 
     A further advantage provided by the above described sensor module is that the sensor module is modular. The interface module, in effect, isolates the processor from the detailed implementation of the camera and the position and orientation module. The processor sends imaging commands to the interface module and, in response, receives image data in a predetermined format. The control of the camera and turret is entirely performed by the interface module. 
     In the above embodiments, the communications link between the processor and the interface module is standardised. 
     In some embodiments, an operator may replace a sensor module that includes one type of imaging sensor with a sensor module that includes a different type of imaging sensor. In other words, a sensor module that includes one type of imaging sensor may be removed from the aircraft and a sensor module that includes a different type of imaging sensor may be installed in its place. As the communications link between the processor and the interface module is standardised across all such sensor modules, updates to other aircraft systems (such as the processor) tend not to be required. Sometime after being installed on an aircraft, the interface module of a sensor module may send certain sensor module parameters (such as sensor types, range of motion etc.) to the processor. 
     In the above embodiments, the sensor module includes the turret. However, in other embodiments, the sensor module does not include that turret. Thus, when replacing a first sensor module with a second sensor module, the first sensor module may be removed from the turret and the second sensor module may be attached to the turret in its place. 
     Advantageously, using the above described system and methods, the aircraft tends to be capable of performing a wide area search of a given area of terrain. The wide area search of the given area of terrain may be performed autonomously by the aircraft. The wide area search of the given area of terrain advantageously tends to facilitate the detection of targets within that area of terrain. Furthermore, advantageously, the wide area search may be performed such that a number of criteria are satisfied (e.g. such that the number of turns performed by the aircraft while performing the wide area search is minimised). 
     Advantageously, using the above described system and methods, the aircraft is able to follow (for example, fly above) an elongate portion of terrain, and capture images along the entire length of that elongate portion of terrain. The feature following process may be performed autonomously by the aircraft. The feature following process advantageously tends to facilitate the detection of targets along the length of the elongate region of terrain. Furthermore, advantageously, the aircraft may follow the elongate portion of terrain even if the elongate portion of terrain includes bends or curves that have a radius of curvature that is smaller than the turning radius of the aircraft. This tends to be provided by including one or more loops in the aircraft&#39;s route. 
     Advantageously, using the above described system and methods, the aircraft tends to be capable of performing surveillance of a target on the ground. The surveillance may be performed autonomously by the aircraft. The surveillance of a target advantageously tends to facilitate the detection of other targets at or proximate to target under surveillance. For example, if the target under surveillance is a building, the above described surveillance process may be performed to detect (and subsequently identify) people of vehicles entering or leaving that building. In some embodiments, the surveillance of a target may be performed to detect actions performed by that target. For example, if the target under surveillance is a vehicle, the above described surveillance process may be performed to detect when that vehicle moves, and where that vehicle moves to. 
     Advantageously, the surveillance process may be performed such that a noise signature of the aircraft experienced at or proximate to the target under surveillance tends to be minimised. This advantageously tends reduce the likelihood of the aircraft being detected by entities located at or proximate to the target under surveillance. 
     An advantage provided by performing the above described image processing method is that, unless otherwise instructed, the aircraft only transmits image properties (i.e. image geolocation and the associated uncertainty etc.), and the properties of any detected targets. In other words, unless such data is requested, complete image data is not transmitted from the aircraft to the ground station. The image/target property data tends to be a much smaller amount than complete image data. Thus, bandwidth requirements of communications between the aircraft and the ground station tend to be reduced. 
     Furthermore, only the image data of particular interest to an operator at the ground station (i.e. only cropped sub-images or compressed images that are requested by the operator) are transmitted to the ground station for analysis. This further tends to provide that bandwidth requirements of communications between the aircraft and the ground station are reduced. Moreover, since relatively useless and/or redundant information is not transmitted to the operator for analysis, the analysis by the operator tends to be easier and/or more efficient. 
     A further advantage provided by the above described image processing method is that image information and information about any detected targets (e.g. geolocation etc.) tends to be continuously updated as more images are taken by the aircraft. This advantageously tends to reduce uncertainty in the information provided to the ground station. Thus, more accurate results tend to be produced compared to conventional image processing techniques. 
     Advantageously, the above described payload delivery process may be used to deliver a payload to a target. The aircraft tends to be capable of delivering the payload to its intended target autonomously. Environmental conditions, such as wind speed and direction, and also the presence of terrain features (such as lakes, rivers, mountains, etc.) may advantageously be taken into account during the payload delivery process. Advantageously, the processor tends to be capable of determining an optimum aircraft position and velocity for payload release. 
     Apparatus, including the processor and/or the interface module, for implementing the above arrangement, and performing the above described method steps, may be provided by configuring or adapting any suitable apparatus, for example one or more computers or other processing apparatus or processors, and/or providing additional modules. The apparatus may comprise a computer, a network of computers, or one or more processors, for implementing instructions and using data, including instructions and data in the form of a computer program or plurality of computer programs stored in or on a machine readable storage medium such as computer memory, a computer disk, ROM, PROM etc., or any combination of these or other storage media. 
     It should be noted that certain of the process steps depicted in any of the flowcharts and described herein may be omitted or such process steps may be performed in differing order to that presented herein and shown in the Figures. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally. 
     In the above embodiments, the imaging process is implemented by an unmanned air vehicle. However, in other embodiments a different type of vehicle is used. For example, in other embodiments, an unmanned land-based vehicle, or a semi-autonomous or manned aircraft is used. 
     In the above embodiments, a single vehicle images a single imaging target. However, in other embodiments a plurality of vehicles is used. Also, in other embodiments, there is a plurality of different imaging targets. 
     In the above embodiments, the camera is a visible band camera. However, in other embodiments, a different type of sensor is used. For example, an infrared camera, an ultra-violet camera, a range sensor, or an ultrasound sensor may be used. In some embodiments, the sensor module includes more than one type of sensor. 
     In the above embodiments, the flight path that the aircraft follows from the ground station to the volume of airspace is defined by a sequence of waypoints. However, in other embodiments the flight path may be defined in a different way, for example, using a sequence of aircraft headings and corresponding flight durations. In other embodiments, the aircraft may be controlled by a human operator until the aircraft arrives at a point in the volume of airspace. 
     In the above embodiments, the processor determines the route that the aircraft is to follow to perform an imaging process in response to the aircraft entering the volume of airspace. However, in other embodiments, the processor determines the route when a different set of criteria have been satisfied. For example, in other embodiments the route for the imaging process is determined by the processor when the aircraft is at a specific location, within a pre-determined distance of a specific location, or at a certain time of day. 
     In the above embodiments, a volume of airspace is defined in which the aircraft is permitted to fly whilst performing the imaging process. However, in other embodiments no such volume is defined. For example, in other embodiments the aircraft is allowed to fly anywhere during the imaging process. In some embodiments, a minimum distance that the aircraft must be from the imaging target while performing the imaging process is implemented. In some embodiments, a maximum distance that the aircraft may be from the imaging target while performing the imaging process is implemented. 
     A route that the aircraft is to follow to perform an imaging process may be any shape. Furthermore, a route may depend on any appropriate criteria or measurements instead of or in addition to those mentioned above. For example, a requirement that the aircraft remains substantially at certain compass bearing from the area of terrain may be implemented. 
     In the above embodiments, the aircraft performs a single imaging process. However, in other embodiments a different number of imaging processes are performed. One or more of the performed imaging processes may be different to one or more of the other imaging processes that are performed. For example, in some embodiments, one or more wide area searches and/or one or more feature following processes may be performed to detect a target within a certain region. One or more surveillance operations may then be performed on the detected target. 
     In the above embodiments, during the information processing process, data is transmitted to the ground station from the aircraft for analysis by an operator. However, in other embodiments, data is transmitted from the aircraft to a different entity, for example, an entity that is remote from the aircraft such as a different aircraft. In some embodiments, data is transmitted from the processor for use by other systems on-board the aircraft. In some embodiments transmitted data is for another purpose instead of or in addition to analysis by an operator (e.g. for use as an input to a further process). 
     In the above embodiments, a payload delivery process is performed to deliver a single payload to a single target. However, in other embodiments, the payload delivery process may be performed to deliver a different number of payloads to a different number of targets. In some embodiments, there may be a plurality of different types of payloads. 
     In the above embodiments, the payload delivery process is performed to deliver a payload to a target that has been detected by performing the process of  FIG. 4 . However, in other embodiments, the payload delivery process is performed to deliver a payload to a target that has been detected using a different process.