WO2015170078A2

WO2015170078A2 - Tethered aerial platform and aerial observation system

Info

Publication number: WO2015170078A2
Application number: PCT/GB2015/051271
Authority: WO
Inventors: Stuart David GAIR
Original assignee: Spillconsult Limited
Priority date: 2014-05-05
Filing date: 2015-05-01
Publication date: 2015-11-12
Also published as: WO2015170078A3; GB2527736A; GB201407903D0

Abstract

An aerial observation system is described and comprises a tethered aerial platform and a plurality of ground-based monitoring devices. The aerial platform carries a payload comprising a plurality of fixed focal length cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for transmitting, independently to each of the plurality of ground-based monitoring devices, a data signal comprising image data captured by one or more of the plurality of cameras. Each ground-based monitoring device is independently operable to select and display an image area of interest from the image data contained in the data signal. By utilising fixed focal length cameras instead of the normal (but much heavier, more delicate and more power-hungry) pan, tilt and zoom cameras conventionally used in such application, sensor payload on the balloon can be reduced, robustness can be increased, and battery life improved. Moreover, multiple users are able to independently access different fields of view simply by selecting different image areas out of the image data transmitted (potentially to all base stations) from the aerial platform.

Description

Tethered Aerial Platform and Aerial Observation System

Field of the invention

The present invention relates to a tethered aerial platform, and to an aerial observation system. Embodiments of the present invention relate to wireless multi-camera aerial observation.

Background to the invention

Aerial observation provides a top-down view of a large coverage area on the Earth's surface, and can be used for many applications, ranging from security to oil spill detection. Various different airborne platforms can be used to carry the cameras and other sensor equipment required for aerial observations. These include unmanned airborne platforms such as drones and UAVs, aerostats (balloons), kites and kytoons (hybrid balloon-kites such as the Allsopp Helikite). Many application require a low-cost, robust and continuous use aerial surveillance system, for long term surveillance of a defined area. For example this is very useful for oil spill management, where it is not cost effective to use helicopters for long periods and drones/UAV's are not robust enough. A kytoon, such as the Helikite (stable combination of balloon/kite) provides an excellent platform, as they can float/fly stably above the area you want to scan for long periods. A kytoon is a tethered platform, which may be fixed either to a static point on the ground or to a mobile structure such as a maritime vessel.

Existing kytoon based observation platforms are provided with pan and tilt camera systems to enable an operator, connected to the camera system by a bidirectional communications link, to target the camera to any area of interest within the coverage area of the platform. The use of pan and tilt cameras creates a problem of complexity/cost and weight. Also, a pan and tilt camera only captures the limited viewing area it is pointed at. Use of such a platform requires continuous manual operation of the pan and tilt camera by the operator, and for the operator to spot the right thing to point the camera at, making it easy to miss vital information, which could be in a blind spot.

Embodiments of the present invention seek to address these problems.

Summary of the invention

According to an aspect of the present invention, there is provided an aerial observation system comprising a tethered aerial platform and a plurality of ground-based monitoring devices, the aerial platform carrying a payload comprising a plurality of fixed focal length cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for transmitting, independently to each of the plurality of ground-based monitoring devices, a data signal comprising image data captured by one or more of the plurality of cameras; wherein each ground-based monitoring device is independently operable to select and display an image area of interest from the image data contained in the data signal.

By utilising fixed focal length cameras instead of the normal (but much heavier, more delicate and more power-hungry) pan, tilt and zoom cameras conventionally used in such application, sensor payload on the balloon can be reduced, robustness can be increased, and battery life improved. Simplifying the imaging equipment is counter-intuitive for an application where the general trend is for providing operators with greater control in controlling a viewing area (conventionally achieved by uplink control of the pan, tilt and zoom cameras). It has however been recognised that this functionality can be achieved just as well by providing high resolution, wide angle, fixed focal length cameras and conducting pan, tilt and zoom functionality at a ground based device. Moreover, this also allows multiple users to independently access different fields of view simply by selecting different image areas out of the image data transmitted (potentially to all base stations) from the aerial platform. This is in contrast to the conventional method in which a single operator controls the operation of the pan, tilt and zoom cameras, precluding other users from viewing a different imaging area. Furthermore, each independent base station need not be aware of data access by another base station.

While image areas of interest could simply be selected from thumbnails, preferably each ground based monitoring device is operable to digitally pan, tilt and zoom the image area by selecting for display different parts of the image data contained in the data signal. This provides the user of each base station with the same functionality as if they were controlling a pan, tilt and zoom camera on board the aerial platform. More preferably, the plurality of cameras each have a respective different coverage area, and the coverage areas of the plurality of cameras substantially meet or overlap, and wherein each ground-based monitoring device is operable to generate and display an image of an area of interest which spans two or more adjacent coverage areas by combining image data in the data signal originating from two or more of the cameras. This enables the base station to treat the entire coverage area as a single image. Preferably, at least three fixed focal length camera are used, providing substantially 360° coverage of the area around and below the aerial platform.

Preferably, the payload comprises a telemetry unit, the telemetry unit determining the current position and heading of the aerial platform and generating telemetry data therefrom, the telemetry data being transmitted in the data signal along with the image data. More preferably, the telemetry data indicates a direction in which each of the plurality of cameras is looking. This makes it possible for the base station to display the image data and any other sensor data along with other information (e.g. viewing directions and locations) of value in interpreting the sensor data. Preferably, the telemetry unit or the ground-based monitoring device triggers an alert in the event that the aerial platform exceeds or drops below a predetermined altitude.

Preferably, the plurality of cameras are Internet Protocol (IP) cameras and the communication means communicates the data signal to the ground-based monitoring devices using an IP communications link.

While embodiments of the present invention may be applied to a variety of different aerial observation systems, preferably the tethered aerial platform is a balloon or a kite- stabilised balloon (kytoon).

In some cases, the payload may comprise one or more non-optical sensors and the data signal comprises the sensor outputs of the non-optical sensors.

In some cases the communication means is responsive to uplink commands to selectively activate and deactivate (or switch between active and low power states) ones of the plurality of cameras. In this way, battery life can be conserved by only keeping active cameras which are currently in use. This is an exception to the generally one-way communication scheme, in which generally there is no need to control the camera due to the facility to perform image area selection (e.g. pan, tilt and zoom) digitally at the base station. According to another aspect of the present invention, there is provided a tethered aerial platform carrying a payload, the payload comprising a plurality of cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for wirelessly transmitting a data signal comprising image data captured by one or more of the plurality of cameras; wherein the tethered aerial platform is a kytoon, and the centre of gravity of the payload is substantially directly underneath or behind the centre of aerostatic lift of the kytoon. This has been found to cause the kytoon to adopt substantially the same pitch angle irrespective of whether there is significant airflow past the kytoon.

According to another aspect of the present invention, there is provided a tethered aerial platform carrying a payload, the payload comprising a plurality of cameras mounted at selected positions about the aerial platform, communication means connected to the plurality of cameras for transmitting a data signal comprising image data captured by one or more of the plurality of cameras, and a battery; wherein the tethered aerial platform is a kytoon comprising a balloon part and a kite part mounted beneath the balloon part, wherein the communication means and the battery are mounted to the kite part at a position substantially adjacent to and beneath the balloon part. This, along with the provision of cameras directly mounted to and around the outside of the balloon part of the kytoon, has been found to improve the stability of the kytoon compared with prior art arrangements in which the payload has been hung well below the balloon part of the kytoon.

According to another aspect of the present invention, there is provided a tethered aerial platform carrying a payload, the payload comprising a plurality of cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for transmitting a data signal comprising image data captured by one or more of the plurality of cameras; wherein the tethered aerial platform is a kytoon comprising a balloon part and a kite part mounted beneath the balloon part, wherein the kite part defines a keel of the tethered aerial platform extending along the underneath of the balloon part, and wherein a first part of the payload is mounted to one side of the keel and a second part of the payload is mounted to the other side of the keel. This results in a more event weight distribution laterally, lessening the degree to which the kytoon may skew to one side.

The first part of the payload may comprise a battery and the second part of the payload may comprise a communications hub for connecting the cameras to a wireless transceiver of the communication means. Preferably the first and second parts of the payload, located respectively either side of the keel, are approximately equal in mass, which helps to keep the kytoon level.

According to another aspect of the present invention there is provided a tethered aerial platform carrying a payload, the payload comprising a plurality of cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for transmitting a data signal comprising image data captured by one or more of the plurality of cameras; wherein the cameras each comprise a mounting plate and a camera part which extends out from the mounting plate, and wherein the aerial platform comprises pockets shaped to receive the mounting plates of the cameras, each pocket having an aperture through which the camera part protrudes. This arrangement is secure enough to retain a simple fixed focal length camera in place against the outer surface of the balloon part of the kytoon, but permits the cameras to be installed and removed very quickly.

Preferably, the mounting plate and the inside of the pocket are shaped to match each other to inhibit rotation of the camera with respect to the pocket. Preferably, the pocket is formed from a flap, fixed along one edge, which folds over the camera and is secured over the camera using a releasable fixing. Preferably, the backing plate is generally square and comprises cut-outs or indentations along each side to increase the flexibility of the backing plate. This, along with a generally curved shape, helps the backing plate to conform to the balloon. Preferably, the camera and a cable for connecting the camera to the

communications unit are formed as a single waterproof unit. Preferably, the cable is received within a sleeve which extends from the pocket to a position proximate the communications unit.

According to another aspect of the present invention, there is provided an aerial observation system comprising a tethered aerial platform as defined above, and a plurality of ground-based monitoring devices, the cameras of the aerial observation platform being fixed focal length cameras mounted at selected positions about the aerial platform, the

communication means being operable to transmit, independently to each of the plurality of ground-based monitoring devices, a data signal comprising image data captured by one or more of the plurality of cameras; wherein each ground-based monitoring device is independently operable to select and display an image area of interest from the image data contained in the data signal.

Embodiments of the present invention use a multitude of simple fixed cameras placed on the Kytoon (e.g. Helikite) in positions chosen to cover a desired view angle, thereby creating continuous real-time capture of the required area. Certain aspects of the present invention may not be limited to a Helikite-type platform, but this are used as an example embodiment.

Aerial observation platforms (e.g. balloons, kite-stabilised balloons) are often used for easy and relatively low-cost access to a height from which a remotely-operated camera can be used to relay images. There are no known systems which provide a number of separate users access to multiple cameras (e.g. covering 360 degree vision) on the same platform. Using digital pan, tilt and zoom methods on wide-angle camera images, it is possible to provide independent control of the image area viewed for many users. By utilising simple fixed focal length cameras and securing them and supporting electronics, batteries and communication equipment in the novel manner described herein, it is possible to provide an elegant, robust and easily stowed arrangement for the airborne system (compared to bulky pan-tilt control mechanisms).

While in a related (but different) field remote controlled balloons have previously been provided with multiple camera systems to provide an all-round view to assist with flying the balloon, such all-round static cameras have not previously been utilised to define a viewing area for surveillance purposes which can be shared wirelessly to multiple base stations. Detailed description

The invention will now be described by way of example with reference to the following Figures in which:

Figures 1A to 1 C schematically illustrate a kytoon-based aerial observation platform according to an embodiment of the invention;

Figure 2 schematically illustrates a network arrangement for the aerial observation platform of Figure 1 ;

Figure 3 schematically illustrates the electronics configuration of the sensor and communications system on-board the aerial observation platform;

Figure 4 schematically illustrates the electronics configuration of a base station for viewing the camera and sensor outputs of the aerial observation platform;

Figures 5 to 8 schematically illustrate fields of view for cameras disposed on the aerial observation platform;

Figure 9 schematically illustrates an example user interface for a base station device viewing the camera and sensor outputs of the aerial observation platform;

Figure 10 schematically illustrates a desired weight distribution for the aerial observation platform of Figure 1 ;

Figure 1 1 schematically illustrates a pocket for removably securing the

communications hub to the aerial observation platform;

Figure 12 is an exploded schematic view of a camera for mounting to the aerial observation platform;

Figures 13A and 13B provide further views of the camera of Figure 12 when assembled;

Figure 14 schematically illustrates a mounting pocket and camera arrangement suitable for mounting cameras to an aerial observation platform; and

Figure 15 schematically illustrates cable layouts for connecting the cameras to a communications hub mounted to the keel of an aerial observation platform.

Referring to Figures 1A to 1 C, a multiple camera and communications system arrangement is shown to be mounted on an aerial observation platform 1. The aerial observation platform 1 is a kytoon, that is a combination balloon and kite structure such as the Helikite, designed and manufactured by Allsopp Helikites Limited. As can be seen from Figure 1 A, the kytoon comprises a kite part 3 which is mounted beneath the balloon part 2. The kytoon remains airborne in a variety of wind conditions by virtue of the aerostatic lift provided by the balloon part 2 and the aerodynamic lift provided by the kite part 3.

Moreover, the kite part 3 retains the aerial observation platform in a relatively constant heading with respect to a current direction of airflow past the kytoon (i.e. the wind direction). A set of cameras 4 are mounted on and around the balloon part 2 of the aerial observation platform 1. These are connected to a main hub 5, which in this example comprises a wireless transceiver, control electronics, and connection ports for the cameras 4, all housed within an IP67 rated case. Camera Ethernet cables run from the cameras 4 to the main hub 5 between an inner skin and an outer skin of the balloon part 2 of the kytoon. The main hub 5 is connected to a set of planar aerials 6, permitting wireless communication with ground- based devices. However, it is also possible to use a transceiver with a built-in antenna. Referring to Figure 1 B, the cameras 4 can be seen to comprise a camera support (mounting) plate 7 which includes holes which are used to stitch it to the outer skin of the kytoon.

Referring to Figure 1C, the cameras 4 can be seen to comprise an IP High Definition camera which is attached to the support plate 7 by way of a ball joint, permitting the camera to be pointed in a range of different directions. While the cameras 4 are static during operation of the airborne platform, the cameras 4 are able to be manually adjusted on the ground to ensure that the desired field of view is achieved for each camera (preferably resulting in a full 360° view around and beneath the kytoon when it is in operation).

Referring to Figure 2, a private cloud-in-the-sky network is shown to provide access to cameras and other sensors (on the periphery of the cloud) with users connecting to the cloud using a base station or the Internet. Other possible sensors may include (but are not limited to) particle sensors, IR cameras, UV sensors, noise monitoring sensors, radiation sensors. Sensor outputs included in data signal and provided to base stations, which display the sensor outputs in an appropriate way. The airborne platform 1 can be seen from Figure 2 to carry IP cameras 4 and the hub 5. For the purposes of Figure 2, a wireless modem 8 is shown separately from the hub 5, but could be provided as a single unit. The wireless modem 8 is able to transmit image data (which may be static images or video images) to various base stations 9. To provide a 360° field of view, a number (typically four, but may be 3 to 6 or an even greater number) of wide-angle cameras 4 are mounted around the periphery of the aerial platform 1. The cameras 4 are arranged to transmit their video information via a standard communications link (e.g. Internet Protocol, over wireless internet) to one or many Base Stations 9 via either multiple IP sessions or using a broadcast protocol such as IP Multicasting. The camera images are broadcast and picked up by one or more ground-based computers containing a wireless modem. The images are of sufficiently high quality to enable pan-and-zoom operations to be carried out digitally at the base station, removing the need for a mechanical pan-tilt mechanism, and for a zoom lens. The multiple camera transmissions enable multiple base stations to receive all views, giving an all-round viewing capability for all users, independently of each other.

Referring to Figure 3, a more detailed block diagram of the airborne components are shown. In Figure 3, the cameras 4 are shown to be connected to an Ethernet switch 5a of the hub 5 by RJ45 connectors. The Ethernet switch 5a is also connected to a telemetry unit 5b, again using an RJ45 connector. The Ethernet switch 5a is also connected to the WiFi modem 8, again using an RJ45 connector. The WiFi modem 8 forms part of a further electronics module comprising a battery 10 and antenna 11.

Referring to Figure 4, a block diagram of a base station 9 is shown. The base station

9 comprises an antenna 21 for receiving the wireless transmission from the antenna 1 1 of the airborne system. The antenna 21 is connected to a wireless card 23, which is in turn connected to a computer module 25 using a PCI-e connection. The computer module 25 may be a conventional computer (processor, motherboard and associated components). The computer module 25 is connected to a memory module 29 which stores image data and metadata received from the airborne system, and is also connected to a display module 27 which is used to display the image data and any other sensor data, along with a user interface which can be navigated by a user to control the display of the image data and sensor data.

To build the airborne system, various off-the-shelf components may be used for the wireless IP cameras, the wireless modem, the Ethernet switch and the Lithium battery power supply. Optionally, a sensor and control system can be added, providing GPS position, magnetic heading, and means to selectively turn cameras on and off on the airborne platform to conserve battery life. In this way, a typical mission with 4 cameras can have a 10-hour battery life if a 22Ah battery is used.

By using multiple fixed IP cameras on a kite-stabilised balloon, together with pan-tilt features on plural independent base stations (in order to achieve and navigate a desired field of view), it is possible to combine miniaturised elements of network devices to provide this type of operation in a sufficiently light package, and to design software to enable users to pan and zoom under their own, independent control.

In this way, it is possible to provide an aerial surveillance system that can be used for various purposes, such as to trace oil spills on the ocean surface.

The aerial platform provides a remote surveillance unit which is able to communicate with a base unit on (for example) a skimmer support boat. The remote surveillance unit is in the present case a kytoon (Helikite) with several cameras and electronics for wireless communications with the base unit. Video feed and pictures from the remote unit are sent to the base unit which is based on a computer with a touch screen, but provided in a rugged case. Communications between the remote unit and the base unit may be achieved by setting up a local area network (LAN) in which a base station can access each camera by their unique IP address. In addition to the downlink information, uplink control to a camera (for example to deactivate it to save battery life, or conversely to reactivate it) can be achieved by sending commands to its IP address. A multicast system can be established using this LAN, which allows multiple base stations to view video/image/telemetry from the remote unit.

Several cameras (usually 3-6 cameras) may be used on the platform, potentially providing an all-round view. This increased field of view provides a significant advantage compared to a single-camera solution because it can provide a simultaneous 360° field of view from the remote unit. Also, mechanical arrangements for mount/tilt mechanisms on board the aerial platform are not necessary, which reduces the payload weight and opens the possibility of the cameras being rolled up with the kite for storage (due to the smaller size and less fragile nature of fixed focal length (non-zoom) cameras). The field of view can also be increased by using a lens with short focal length.

Figures 5 to 8 demonstrate some possible camera arrangements and the coverage areas which they provide. Referring to Figure 5, a plan view from the ground below the kytoon shows the overlapping camera angles (fields of view) of the cameras 4. In Figure 5 cameras are shown to be provided at the front, rear and to either side of the kytoon, each camera having a field of view at 90° from the adjacent cameras (that is, looking forward, backwards and directly to either side). It can be seen that, beyond a certain distance from the kytoon, complete horizontal coverage is provided outwardly of the kytoon. Referring to Figure 6, a front view of the kytoon is provided, demonstrating that vertically coverage is provided from just below the horizon, to directly downwards. It can be seen that the cameras in this case are mounted to either side of the balloon part of the kytoon, near or adjacent to the bottom of the balloon part of the kytoon. Here, a blind spot would occur directly underneath the kytoon, but this may be acceptable for some applications. Referring to Figure 7, a more distant view of the front of the kytoon demonstrates that it is possible to set up the camera arrangement to achieve a complete view of the ground, if this is required (in the case of Figure 7 this is shown to be the case at an altitude of 400ft from the ground). Referring to Figure 8, a side view of the kytoon shows that the kytoon is inclined with respect to the horizon. In particular the front of the balloon (left hand side of Figure 8) is inclined upwards of the horizon, and as a result the front camera is positioned underneath the nose of the balloon. The rear of the balloon (right hand side of Figure 8) is inclined downward of the horizon, and as a result the rear camera is positioned higher up on the rear

(approximately half way up the balloon). Both the front and rear cameras have a vertical field of view which starts just below the horizon and extends downwards to the vertical or near vertical. As with Figures 6 and 7, the cameras in Figure 8 can be configured to avoid a blind spot.

For the use of a software zoom on a high definition wide-angle image to be practical, the angle resolution should be similar to that available on a standard surveillance camera with a standard field of view. The BTC-40 microUAV camera has a 40 degree field and a 752x582 sensor, giving 0.053 degrees per pixel. To cover 120 degrees field of view a bigger sensor is required with a horizontal resolution of at least three times 582, giving a minimum of 1746. Typical resolutions available are 1.2MPix (1280x960) (not sufficient), and 3MPix (2048x 1536) (acceptable) and 5MPix (2580x1290) (better than acceptable). The video resolution 1080p is a 1920x1080 image, which is also acceptable.

Video and image downlink and control uplink between the sensor payload and base unit is achieved using wireless. In order to cope with high definition video feed from several cameras (1080p), which will have a downlink speed requirement of the order of 5Mb/s per camera, a WiFi-n link, capable of over 100Mb/s is used between two units.

Each camera unit includes a HD camera module, and an Ethernet adapter (and preferably a temperature sensor which triggers the camera to switch off if it gets too hot). A lightweight and low power camera module such as those using an Omnivision CCD sensor may be suitable. The camera module should preferably be sealed in a water-proof enclosure.

The electronics module 5 contains the Ethernet switch and telemetry unit. The Ethernet switch needs (in this example) at least 5 ports: 3 cameras minimum, 1 telemetry, and 1 wifi-n access point. If more cameras are required, an extra or larger Ethernet switch can be used to accommodate additional IP devices.

The telemetry unit 5b comprises a GPS module, compass, an accelerometer, a temperature sensor, and an Ethernet adapter. It also include power distribution and current monitoring electronics, particularly useful so that subsystems can be controlled and shut down remotely.

The system may be powered by a 12V 22Ah Tracer battery to provide extra power consumption when more cameras are used. The Wifi-n access point is (in the present example) included in this module. The antenna used for WFi-n connections is (again, in the present example) attached to this module. A fully managed wireless access point with triple antenna ports is beneficial in order to maximise the data rate using the wireless-n standard.

A balloon deflation device can be used to bring down the kytoon in case it is lost from its tether. Note that for an oil-spill use the GPS unit will need to be programmed to alert if a given altitude is exceeded (the usual GPS trigger is a change in location).

It will be appreciated that the aerial platform may be required to operate on its battery for an extended period, and that changing the battery requires the platform to be reeled in, thereby halting operations. In order to maximise the period of operation, a power scheduling scheme to put unused cameras in a low power (or deactivated) state may be used, reducing the total power consumption. The base unit may be used by sailors on a skimmer boat. It comprises a touch screen, a computer module running Windows, and additional peripherals. The electronic components are preferably assembled in a ruggedized case to protect against physical and water damage. The base unit can be powered via the boat's mains or a battery.

Referring to Figure 9, an example user interface 50 is shown, in which a main view

52 is provided of an area of interest to the user. The user is able to use a control panel to zoom (+/- buttons), tilt and pan (directional buttons) the area of interest. These operations are carried out digitally, and may utilise image data from one or more of the cameras. With more than one camera being used, it is possible to provide a 360° view from the remote unit. Still images from cameras around the airborne platform can be 'stitched' together using image-processing software to give 360 degree view. Other functions may also be controlled, such as frame rate and switching between video and still images. A preview area 54 is provided which allows the user to see a reduced-size image or thumbnail of the views from other cameras. In the present case four cameras are represented in the preview area, corresponding to a nose camera, a tail camera, a port camera and a starboard camera. A telemetry area 56 is also provided which sets out the current heading, altitude and position (latitude and longitude) of the kytoon. For each camera a heading (that is, the direction in which that camera is looking) may be calculated from the platform heading and displayed in association with the view from the camera, so that the user is aware of the direction in which they are looking when using that view. In additional to these elements, physical interface elements such as a power button, power socket, and video output are accessible and water proofed.

The screen size for the display module 27 should preferably be 9"-12" and provide a high brightness to cope with outdoors use. The base station may have a remote access ability to allow a PC/laptop to view the payload video feed. The base station may be operable to record metadata and image data and other sensor data together - to provide a log for later reviewing offline. The metadata (added by the telemetry unit) may include time and date information used to generate the log, so that sensor data can be tracked over time.

In some cases the base station may be able to provide all or a subset of the data signal received from the balloon to another device. The base station in this case could provide restricted access to the data acquired by the sensor payload on the balloon. For example, the base station may encrypt parts of the data signal before transmitting it to another device. Only devices with an appropriate decryption key will then be able to access the decrypted parts of the data signal. Access to the data signal may also be restricted by permitting only certain devices to establish a communications session with the balloon.

Referring to Figure 10, the mass distribution of the sensor payload is illustrated, in particular with the layout and weight balance set to control the flight angle. In particular, Figure 10 shows the kytoon 1 attached to the ground via a tether 100. An ideal pitch angle e for the kytoon is shown with respect to the horizon. This pitch angle is achieved by the kytoon by default when there is wind present due to the respective aerostatic and

aerodynamic lift contributions of the balloon and kite parts. However, in the absence of wind the kytoon may adopt a different pitch angle due to the absence of aerodynamic lift. This is undesirable because it will alter the fields of view of the cameras. It has been found that by positioning the centre of gravity of the sensor payload, that is, the cameras, the hub, the modem, the battery and so on, (substantially) directly underneath, or just behind (with respect to the nose to tail axis of the kytoon) the centre of aerostatic lift of the kytoon, the ideal pitch angle can be made to be substantially the same irrespective of whether the kytoon is flown in windy or still conditions. In this way, careful positioning of the main components can be used to control weight distribution to maximise stability of the Helikite in flight and maintain the correct pitch in all wind speeds. In general terms, an even mass distribution for the cameras is achieved by positioning them on and around the balloon, while a suitable centre of mass for the remainder of the sensor (including communications) payload is achieved by positioning these elements appropriately on the kite part of the kytoon.

Referring to Figure 1 1 , a pouch 110 for carrying the hub is shown on one side of the keel (formed along the base of the balloon by the upper part of the kite). A similar pouch is provided the other side of the keel to carry the battery and modem. A small aperture through the keel (between and joining the two pouches) connects the battery and modem to the hub. By positioning these elements of the sensor payload right under the balloon part, this helps avoid impact with the ground during launch, which is a problem which other kytoon based products suffer from. In addition, more conventional designs hang a sensor payload (e.g. cameras and communication unit) underneath the kytoon, which generates a pendulum effect causing the kytoon to sway. By siting these components on the balloon itself

(cameras) and immediately beneath the balloon on the kite part (battery, hub, modem, telemetry), these problems can be alleviated.

Referring to Figure 12, an exploded view of a camera 4 is provided. The camera 4 is shown to comprise a mounting plate 42, a rear container hemisphere 44, a front container hemisphere 46 and an O-ring 48. The optical and electronics elements of the camera (no shown are mounted inside the container hemispheres 44, 46, and a cable is potted into the rear container hemisphere 44 to provide a watertight seal. The camera and cable can therefore be considered as a single waterproofed unit. The other end of the cable is provided with a waterproof connector, which can be connected to any of the camera connectors on the hub. The front container hemisphere 46 is then fitted to the rear container hemisphere 44 and is then inserted into the tubular part of the mounting plate 42. The O- ring 48 then secures the two hemispheres within the tubular part of the mounting plate 42. Due to the substantially spherical shape of the camera container, it can be rotated into a desired position by a user. It will be understood that this structure effectively houses the camera components within a ball joint itself. Figures 13A and 13B provide an external view and a cross sectional view (respectively) of the camera 4 in its assembled state. It can be seen from these Figures that the plate 42 is slightly curved, in order to conform to the surface of the balloon.

Referring to Figure 14, it is shown that the cameras 4 fit in a simple flap 120 on the outside of the balloon, which includes a hole that fits over the camera ring, and Velcro 130 around the edge to hold the flap down over the camera, and form a secure pouch. Whilst this is secure in use, it takes seconds to fit or remove. The built-in camera mount backing plate serves to spread the weight of the camera over the balloon surface, and provides good stability against the flexible and easily depressed surface of the balloon. It is also designed intentionally to be flexible (thinness of material and indented shape midway along edges) and includes rounded bead edges, which all help to protect the delicate balloon material. The camera mount backing plate is additionally square shaped to locate it in the square pouch, preventing it from turning (rotating) in use, which would cause the image deviate from horizontal. The cable 140 to/from the camera 4 runs from the pocket inside the outer cover, which helps to prevent the camera 4 from falling should it escape from the pouch.

Referring to Figure 15, the layout of cables 150, in pockets 160 sewn in behind an outer covering, are shown. The balloon can be seen to include sleeved cable pockets to guide the cable, which could be located on the outside of the main outer protective fabric, or the inside of the outer protective fabric. These sleeves start from a simple hole in the back of the camera pouch and exit through a simple hole in the skin above the hub pouch.

Excess cable length can then sit behind the hub pouch 170, where they can be connected to hub, easily accessed via a Velcro flap on the back of the hub pouch.

In the present example, in addition to an (inner) lightweight helium balloon membrane, an outer protective balloon skin is present, made from lightweight "ripstop" parachute or spinnaker type material. This is very useful for mounting all the features such as the various pouches, cable pockets etc., although it would be possible to create a similar arrangement on the surface of the standard helium membrane, where a less rugged, lighter weight (and cheaper) version might be required.

The attachment structures described above provide for simple rigging and operation with all components easy to fit, remove and swap out at any time. In particular, with such an arrangement, assembly requires the following simple procedure:

1. Slide the hub and battery into each of their pouches. 2. Pull up each camera flap, insert camera cable connector into hole and push all the way down sleeve, until it emerges just above the hub.

3. Position camera below flap, lower flap and press down Velcro.

4. Attach all the connectors on the back of the hub and close pouches.

Disassembly can be achieved simply by following the above steps in reverse.

Alternatively the cameras, cabling, hub and battery can also optionally be left in place and packed up with the balloon on deflation, to go in a bag for storage or transport. It has been found that the cable sleeves are important to prevent loose cables from becoming tangled with the balloon, which would prevent re-inflation.

Preferably, waterproofing (IP68 rating) should be provided for all weather operation, with the waterproof hub, connected to cameras with waterproof connectors, mounted in a shower proof bag on the side of the Helikite keel, with the access openings at the rear of the pouch - offering additional protection.

From the above, it will be understood that the present invention offers a number of benefits. For example, the system supports simple "inflate and go" operation, which is fast to rig and easy to understand/use. Secondly, the system is robust and stable in operation, with good protection from impacts and from weather. Thirdly, an all-round view is provided, which allows customer to specify a viewing envelope on a per balloon basis by varying the quantity and position of cameras during balloon build. Fourthly, flexibility of viewing on the ground is provided, with ability to receive on multiple base stations, and intuitive touchscreen interface that allows user to simply navigate and zoom in on specific part of overall view.

It will be appreciated that embodiments of the present invention could be utilised in a variety of different applications. In addition to spotting and tracking oil spills, these may include road safety (monitoring traffic and/or road conditions for example), and surveillance by police and other emergency services. Security firms may benefit from the invention for handling security at events such as festivals, theme parks, sports venues etc. In these contexts multiple organisations can access data from the same cameras, independently of each other and without knowledge of each other.

In the context of oil spill monitoring, different users (of separate base stations) may be command staff overseeing the operation, responders handling specific aspects of the operation, and multiple vessels looking at different regions within the overall coverage area serviced by the aerial platform. The coverage area may vary substantially depending on the nature of the application, typically ranging for a few miles up to a few tens of miles.

Claims

An aerial observation system comprising a tethered aerial platform and a plurality of ground-based monitoring devices, the aerial platform carrying a payload comprising a plurality of fixed focal length cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for transmitting, independently to each of the plurality of ground-based monitoring devices, a data signal comprising image data captured by one or more of the plurality of cameras; wherein each ground-based monitoring device is independently operable to select and display an image area of interest from the image data contained in the data signal.

An aerial observation system according to claim 1 , wherein each ground based monitoring device is operable to digitally pan, tilt and zoom the image area by selecting for display different parts of the image data contained in the data signal. An aerial observation system according to claim 1 or claim 2, wherein the plurality of cameras each have a respective different coverage area, and the coverage areas of the plurality of cameras substantially meet or overlap, and wherein each ground- based monitoring device is operable to generate and display an image of an area of interest which spans two or more adjacent coverage areas by combining image data in the data signal originating from two or more of the cameras.

An aerial observation system according to any preceding claim, comprising at least three fixed focal length camera providing substantially 360° coverage of the area around and below the aerial platform.

An aerial observation system according to any preceding claim, wherein the payload comprises a telemetry unit, the telemetry unit determining the current position and heading of the aerial platform and generating telemetry data therefrom, the telemetry data being transmitted in the data signal along with the image data.

An aerial observation system according to claim 5, wherein the telemetry data indicates a direction in which each of the plurality of cameras is looking.

An aerial observation system according to claim 5 or claim 6, wherein the telemetry unit or the ground-based monitoring device triggers an alert in the event that the aerial platform exceeds or drops below a predetermined altitude.

An aerial observation system according to any preceding claim, wherein the plurality of cameras are Internet Protocol (IP) cameras and the communication means communicates the data signal to the ground-based monitoring devices using an IP communications link.

9. An aerial observation system according to any preceding claim, wherein the tethered aerial platform is a balloon or a kite-stabilised balloon.

10. An aerial observation system according to any preceding claim, wherein the payload comprises one or more non-optical sensors and the data signal comprises the sensor outputs of the non-optical sensors.

1 1. An aerial observation system according to any preceding claim, wherein the

communication means is responsive to uplink commands to selectively activate and deactivate ones of the plurality of cameras.

12. A tethered aerial platform carrying a payload, the payload comprising a plurality of cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for wirelessly transmitting a data signal comprising image data captured by one or more of the plurality of cameras; wherein the tethered aerial platform is a kytoon, and the centre of gravity of the payload is substantially directly underneath or behind the centre of aerostatic lift of the kytoon. 13. A tethered aerial platform carrying a payload, the payload comprising a plurality of cameras mounted at selected positions about the aerial platform, communication means connected to the plurality of cameras for transmitting a data signal comprising image data captured by one or more of the plurality of cameras, and a battery;

wherein the tethered aerial platform is a kytoon comprising a balloon part and a kite part mounted beneath the balloon part, wherein the communication means and the battery are mounted to the kite part at a position substantially adjacent to and beneath the balloon part.

14. A tethered aerial platform carrying a payload, the payload comprising a plurality of cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for transmitting a data signal comprising image data captured by one or more of the plurality of cameras; wherein the tethered aerial platform is a kytoon comprising a balloon part and a kite part mounted beneath the balloon part, wherein the kite part defines a keel of the tethered aerial platform extending along the underneath of the balloon part, and wherein a first part of the payload is mounted to one side of the keel and a second part of the payload is mounted to the other side of the keel.

15. A tethered aerial platform according to claim 14, wherein the first part of the payload comprises a battery and the second part of the payload comprises a communications hub for connecting the cameras to a wireless transceiver of the communication means.

16. A tethered aerial platform carrying a payload, the payload comprising a plurality of cameras mounted at selected positions about the aerial platform and communication means connected to the plurality of cameras for transmitting a data signal comprising image data captured by one or more of the plurality of cameras; wherein the cameras each comprise a mounting plate and a camera part which extends out from the mounting plate, and wherein the aerial platform comprises pockets shaped to receive the mounting plates of the cameras, each pocket having an aperture through which the camera part protrudes.

17. A tethered aerial platform according to claim 16, wherein both the mounting plate and the inside of the pocket are shaped to match each other to inhibit rotation of the camera with respect to the pocket.

18. A tethered aerial platform according to claim 16 or claim 17, wherein the pocket is formed from a flap, fixed along one edge, which folds over the camera and is secured over the camera using a releasable fixing.

19. A tethered aerial platform according to any one of claims 16 to 18, wherein the

backing plate is generally square and comprises cut-outs or indentations along each side to increase the flexibility of the backing plate.

20. A tethered aerial platform according to any one of claims 16 to 19, wherein the

camera and a cable for connecting the camera to the communications unit are formed as a single waterproof unit.

21. A tethered aerial platform according to claim 20, wherein the cable is received within a sleeve which extends from the pocket to a position proximate the communications unit.

22. An aerial observation system comprising a tethered aerial platform according to any one of claims 12 to 21 , and a plurality of ground-based monitoring devices, the cameras of the aerial observation platform being fixed focal length cameras mounted at selected positions about the aerial platform, the communication means being operable to transmit, independently to each of the plurality of ground-based monitoring devices, a data signal comprising image data captured by one or more of the plurality of cameras; wherein each ground-based monitoring device is

independently operable to select and display an image area of interest from the image data contained in the data signal.

23. An aerial observation system or tethered aerial platform substantially as hereinbefore described with reference to the accompanying drawings.