GB2614250A

GB2614250A - Aerial imaging array

Info

Publication number: GB2614250A
Application number: GB2118729.9A
Authority: GB
Inventors: Hexter Rhys
Original assignee: HIDEF Aerial Surveying Ltd
Current assignee: HIDEF Aerial Surveying Ltd
Priority date: 2021-12-22
Filing date: 2021-12-22
Publication date: 2023-07-05
Also published as: WO2023118773A1

Abstract

An aerial imaging array includes at least two imaging devices 10 viewing downwards on a mount 20 attached to an aircraft 40. The imaging devices each have a field of view 30 and an image frame 60 with a vertical centreline 70 and a transverse centreline. They are positioned within the mount so that the projections of the vertical centrelines onto a horizontal plane are parallel and any gap between adjacent fields of view is less than a quarter of the width of the smaller of the adjacent fields of view. There may be a gap between adjacent fields of view. The centrelines of the viewing directions of imaging devices with adjacent fields of view may be at least 20 degrees apart. The imaging array may include first 90 and second 100 pairs of imaging devices. The first/second pair of imaging devices’ viewing directions may be tilted left/right by angles β,γ where β >20° and γ<β. The first pair of imaging devices’ viewing directions may be tilted left and right by angle β of more than 20° and the second pair of imaging devices’ viewing directions may be tilted left and right by angle γ<β.

Description

AERIAL IMAGING ARRAY

The present invention relates to an imaging array for aerial surveying, for use for example, but not exclusively, in the field of offshore environmental surveying.

In the field of offshore environmental surveying, it is often necessary to carry out surveys of large areas of open sea in a short period of time. The only feasible way to achieve this is to use an aircraft to deploy some means of implementing an environmental survey. In the past, such surveys have often utilised specially trained human observers, who identify and count observed creatures, such as sea birds and marine mammals. More recently these techniques have been replaced by technologies based on digital image capture.

Digital imaging survey technologies have many intrinsic advantages over visual observers: the surveys are repeatable and auditable; the aircraft can fly higher, increasing safety and enabling surveys over man-made constructions such as wind-farms. One feature of digital methods that can sometimes be a disadvantage is the binary cut-off between those areas that are observed (in-frame) and those that are not. This has an impact on detection rate and therefore the statistical analysis of tightly grouped objects such as some sea ducks, or pods of marine mammals. Visual surveys are able to pick out these larger groups at some distance and hence achieve better sensitivity.

WO 2013/054128 Al discloses an aerial imaging array comprising at least two imaging devices provided on a mount. The gap between adjacent fields of view is at least a quarter of the width of the smaller of the adjacent fields of view.

High Definition Imagery for Surveying Seabirds and Marine Mammals: A Review of Recent Trials and Development of Protocols by Chris B. Thaxter 8z Niall H.K. Burton, 2009, discloses a review of trials of high definition imagery technology in the monitoring and assessment of bird numbers at offshore sites.

The present invention provides an aerial imaging array comprising at least two imaging devices provided on a mount, attachable to an aircraft such that the imaging devices view downwards,

wherein each imaging device has a Field of view;

wherein each imaging device has an image frame and each image frame has a vertical centreline and a transverse centreline, and the imaging devices are posed within the mount such that the projections of the vertical centrelines onto a horizontal plane are substantially parallel, and wherein the imaging devices are arranged such that any gap between adjacent fields of view is less than a quarter of the width of the smaller of the adjacent fields of view.

Providing that the non-imaged gap between adjacent fields of view is less than a quarter of the width of the smaller of the adjacent fields of view allows the use of sensors which have more pixels while maintaining the image quality across the pixels For a given number of imaging devices, a greater swathe can be surveyed while maintaining image quality.

Embodiments of the invention will now be described, with reference to the accompanying drawings, in which: Fig. 1 is a plan view of an imaging array according to an embodiment of the invention; Fig. 2 is a side view of an imaging array according to an embodiment of the invention; Figs. 3 and 4 are, respectively, a plan view and a side view illustrating schematically the fields of view of the imaging array when mounted on a flying aircraft; Fig. 5 is a perspective view of an imaging array according to an embodiment of the invention; and Fig. 6 is a rear view of an imaging array according to an embodiment of the 30 invention.

Embodiments of the invention comprise an array of two or more imaging devices. In the preferred embodiment shown in the figures there are four imaging devices 10.

As shown in Figs. 1 and 2, the imaging devices 10 are arranged in a mount 20.

Figs. 3 and 4 illustrate the fields of view 30 of the imaging devices when the mount 20 is arranged such that the imaging devices 10 look downward from an aircraft 40. Each field of view 30 is a rectangular-section cone. The imaging devices may be arranged such that there is an un-imaged gap 50 between the adjacent fields of view 30. Alternatively, the imaging devices may be arranged such that there is no un-imaged gap between the adjacent fields of view 30. In this context, 'adjacent' refers to the nearest neighbouring field of view, though the fields of view are clearly not necessarily contiguous because there may be a gap therebetween. In other words, the fields of view do not overlap if there is a gap.

In the preferred embodiment, each imaging device has a sensor at an image plane, at which the image is detected as a rectangular (or square) image frame. Each image frame has a transverse centreline and a vertical centreline, each centreline dividing the image frame into halves. In Fig. 3, the projection of the image frame of each imaging device onto a horizontal surface (such as the ground or sea) beneath the aircraft is shown by the quadrilaterals 60. The distortion of the quadrilaterals 60 is exaggerated in Fig. 3; in practice they are all approximately rectangular and of substantially the same size. The projections of the respective 'vertical' centrelines are shown by the dotted lines 70. The imaging devices 10 are positioned within the mount 20 such that the projections of the vertical centrelines 70 are parallel to each other. In this context, the so-called 'vertical' centrelines are those running closest to the direction of flight or the aircraft.

In a preferred embodiment, each imaging device is orientated about its optical axis such that the projection of each vertical centreline 70 is parallel to the direction of flight of the aircraft, i.e. parallel to the longitudinal axis of the fuselage of the aircraft 40. In this way, objects in the center of the image frame appear to travel vertically through the frame as the aircraft flies forwards In the illustrated embodiment of the invention, the imaging devices 10 are positioned in the mount 20 such that they do not look directly downwards, but at a forward or backward looking angle a, as shown in Fig. 4. In this way, the images represent a partially side-on view of the animals rather than a top down view; this makes many creatures (animals/birds) easier to recognise.

Preferably, the mount 20 is provided with a rotation facility, such as a 'lazysusan' bearing 80, shown in Fig. 5, that enables the imaging devices 10 to be pointed consistently in the same direction (with respect to the ground) throughout a survey.

For example, the imaging devices can point forward when the aircraft is flying in a first direction; the aircraft then turns through 180 degrees to make a pass flying in the opposite direction, but the mount 20 is also rotated through 180 degrees so that the imaging devices point backwards relative to the aircraft, but still in the same direction relative to the ground as when flying in the first direction.

In a preferred embodiment, the imaging devices are digital video cameras. Use of such cameras can enable the wing motion of flying birds to be observed.

In one embodiment of the imaging array, four digital video cameras with identical sensors and lens arrangements form the imaging array. Optionally, the camera sensors each have a width of more than 2500 pixels, for example at least 3000 pixels, optionally at least 5000 pixels, and optionally 6250 pixels. As a result, if each pixel images a width of 2cm on the ground, then the image width is more than 50m, for example at least 60m, optionally at least 100m, and optionally 1 25m, The cameras are arranged in a mount positioned above a hole in the fuselage of a light aircraft 40.

The hole is sufficiently large that the cameras have an unobstructed view. The cameras and lenses are selected such that the image width on the ground when looking forwards is between 50m and 200m, preferably 125m, when the aircraft altitude is 500m. As indicated in Fig. 1, the cameras are arranged in two pairs 90, 100, one in front of the other. As shown in the drawings, optionally the left and right cameras of one pair of cameras 90 are tilted to the left and right respectively by an angle [3, shown in Fig. 6. In this context, tilting the camera refers, of course, to orientating the viewing direction of the camera in a particular direction (the viewing direction being the direction of the center of the field of view). The angle 13 is preferably more than 20 degrees and preferably at least 21 degrees. The angle j3 is preferably not more than 30 degrees. For example the angle 13 is preferably around 22.5 degrees. The cameras of the other pair 100 are tilted by an angle 7, where y is less than IS, as shown in Fig. 6.

Alternatively, one pair of cameras 90 are tilted to the left and the other pair of cameras 100 are tilted to the right. Within one pair of cameras 90, one may be tilted to the left by the angle 13 and the other may be tilted to the left by the angle y.

Within the other pair of cameras 100, one may be tilted to the right by the angle 13 and the other may be tilted to the right by the angle y.

In a preferred example, the angle a is between one quarter and one half of the angle 13, for example one third of 13, or approximately 7.5 degrees, such that any gaps between the fields of view of all adjacent cameras are approximately equal. In a preferred embodiment, the viewing directions of imaging devices providing adjacent fields of view are less than 25 degrees apart. In this specific example the viewing directions of imaging devices providing adjacent fields of view are 15 degrees apart i.e. -22.5 degrees, -7.5 degrees, +7.5 degrees and +22.5 degrees. In another example, the viewing directions of imaging devices providing adjacent fields of view are at least 20 degrees apart, or at least 21 degrees apart, e.g. -30 degrees, -10 degrees, +10 degrees and +30 degrees, or -33 degrees, -11 degrees, +11 degrees and +33 degrees. According to this embodiment, the cameras are tilted forwards by an angle a between 10 and 45 degrees, preferably 30 degrees. Each camera is orientated such that the projections of their centrelines 70 on the ground are parallel. The cameras have fields of view in which the distance on the ground between the projections of the centrelines is significantly greater than the image width A. Referring to Fig. 3, the gap B between adjacent fields of view is less than a quarter the width of one of the fields of view. The gap B between adjacent fields of view may be less than a quarter the width of the smaller of the fields of view. Optionally, the gap B between adjacent fields of view is at most 24%, or at most 22%, of the width of one of (e.g. the smaller of) the fields of view. Preferably the gap B between adjacent fields of view is at most a fifth the width of one of (e.g. the smaller of) the fields of view, and preferably at most a sixth the width of one of (e.g. the smaller of) the fields of view. Optionally the

is no gap between adjacent fields of view.

Providing that any non-imaged gap between adjacent fields of view is less than a quarter of the width of the smaller of the adjacent fields of view allows the use of sensors which have more pixels while maintaining the image quality across the pixels. Image sensors that have more pixels (e.g. more than 2500 pixels in width) are able to scan a wider area. This means that the outer portions of the outermost fields of view can have an angle to the ground (e.g. the sea surface) that is small enough for the image quality to degrade. For example, when the field of view is as great as about 45 degrees, then the images of the sea surface may stop penetrating the water column and objects submerged in the water may be undetectable in the camera images. This can undesirably bias the results of a survey carried out using the aerial imaging apparatus.

Optionally, the imaging devices are arranged such that the angle of the field of view from vertical is at most about 35 degrees. Optionally, the angle between adjacent cameras is less than 25 degrees.

For offshore applications, the angle a should be selected such that reflected light from the sun can be avoided. The angle a may also be selected to optimise the recognition of animals in which profile is a particularly important feature, e.g, birds distinctively with long necks or legs

Claims

CLAIMS1. An aerial imaging array comprising at least two imaging devices provided on a mount, attachable to an aircraft such that the imaging devices view downwards,wherein each imaging device has a field of view;wherein each imaging device has an image frame and each image frame has a vertical centreline and a transverse centreline, and the imaging devices are posed within the mount such that the projections of the vertical centrelines onto a horizontal plane are substantially parallel; and wherein the imaging devices are arranged such that any gap between adjacent fields of view is less than a quarter of the width of the smaller of the adjacent fields of view.
2. The imaging array according to claim 1, wherein the imaging devices are arranged such that there is a gap between adjacent fields of view.
3 The imaging array according to claim 1 or 2, wherein centrelines of the viewing directions of imaging devices providing adjacent fields of view are at least 20 degrees apart.
4. The imaging array according to any preceding claim, comprising a first pair of imaging devices and a second pair of imaging devices.
5. The imaging array according to claim 4, wherein the viewing directions of the imaging devices of the first pair are tilted left by an angle i3 and by an angle 7 respectively, and the viewing directions of the imaging devices of the second pair are tilted right by the angle f3 and the angle y respectively, wherein the angle 13 is more than 20 degrees and the angle 7 is less than f3.
6. The imaging array according to claim 4, wherein the viewing directions of the imaging devices of the first pair are tilted left and right respectively by an angle f3 more than 20 degrees, and the viewing directions of the imaging devices of the second pair are tilted left and right respectively by an angle y that is less than 13.
7. The imaging array according to claim 5 or 6, wherein the angle 7 is between one quarter and one half of the angle if
8. The imaging array according to any preceding claim wherein any gap between adjacent fields of view is at most 24% of the width of the smaller of the adjacentfields of view.
9. The imaging array according to any preceding claim wherein any gap between adjacent fields of view is at most a fifth of the width of the smaller of the adjacentfields of view.
10. The imaging array according to any preceding claim, wherein each imaging device has a width of more than 2500 pixels.
11. The imaging array according to any preceding claim, wherein said projection of each vertical centreline is substantially parallel to the direction of flight of the aircraft
12. The imaging array according to any preceding claim, wherein the viewing direction of each imaging device is tilted forward or backward by an angle of at least degrees from the vertical.
13. The imaging array according to any preceding claim, wherein the viewing direction of each imaging device is tilted forward or backward by an angle of not more than 45 degrees from the vertical
14. The imaging array according to any preceding claim comprising four imaging devices.
15. The imaging array according to any preceding claim, wherein the mount comprises a rotatable frame to which the imaging devices are attached to enable the imaging devices to be rotated collectively with respect to the aircraft.
16. The imaging array according to any preceding claim wherein each imaging device is a digital camera.