WO1989003050A1

WO1989003050A1 - Transmission system for radar derived positional data

Info

Publication number: WO1989003050A1
Application number: PCT/GB1988/000778
Authority: WO
Inventors: John Peter Millward
Original assignee: John Peter Millward
Priority date: 1987-09-28
Filing date: 1988-09-22
Publication date: 1989-04-06
Also published as: GB8722730D0; AU2487388A; GB2210528A

Abstract

A radar system is disclosed in which a ground radar station transmits positional data of detected objects and an aircraft receives the data and displays it on a screen, having firstly transformed the data so that the position of the host aircraft forms the centre of the display. The system therefore acts as if the host aircraft has its own radar apparatus. Because the display in the aircraft is centered on the host aircraft, it is far easier for the pilot to detect whether he is on a collision course with another aircraft than it is for an air traffic controller to detect whether two aircrafts on his screen are on a collision course.

Description

TRANSMISSION SYSTEM FOR RADAR DERIVED POSITIONAL DATA This invention relates to extended uses of radar.

Background to the Invention

With the increasing 'use of airspace, radar has played an increasingly important role in assisting prevention of mid-air collisions. The whole of the United Kingdom,, for example, is covered by ground radar down to an altitude of 3000 feet (about lOOOm) or less, and air traffic controllers monitor the one million or so aircraft movements per year in the UK on their radar screens and advise aircraft pilots by radio if the pilot is in radio contact, if there appears to the controller be a risk of collision so that evasive action can be taken. Therefore, aircraft pilots rely on their own sight, and on the air traffic controller's interpretation of his radar screen in avoiding collisions.

Figures 1A and IB of the drawings show schematically two slightly different displays on a ground radar screen. The centre of each screen C corresponds to the position of the ground radar transceiver. In each case the positions of two aircraft A, B are shown over five scans of the radar, for example A1A to A5A for aircraft A in Figure 1A. The paths AA, BA, AB and BB of the aircraft have been marked on the drawing, but this information would not be available to the .air traffic controller. Whereas paths AA and BA cross at point XA in Figure 1A and paths AB and BB cross at point XB in Figure IB, assuming that the two aircraft are at the same altitude and maintain their speeds and courses, the situation of Figure 1A will not result in a collision because aircraft B will reach the crossing point XA after aircraft A. However, in the case of Figure IB both aircraft will reach the crossing point XB at the same time. From a consideration of ten points on the radar screen, it requires great skill and experience on the part of the air traffic controller to perform a mental extrapolation and determine that evasive action is necessary in the case of the Figure IB situation, but not in the case of the Figure 1A situation. It must also be borne in mind that the radar displays of Figure 1 show very simple cases, and that in reality the screens may be displaying many other aircraft and other features over a typical radius of 30 miles (about 50 km), and the air traffic controller would not be in a position to judge that the two aircraft represented in Figure IB are possibly on a collision course until they appear on the screen much, closer than as shown in Figure IB.

Radar is not fitted to the majority of aircraft because it is expensive, bulky and heavy. Indeed,, it is believed that only a very few military aircraft are fitted with radar, and in those cases the radar has a limited scan.

An aircraft pilot's own sight is not at all reliable in detecting the risk of a mid-air collision. This is because, if two aircraft are on a collision course, assuming that both are flying at constant speed and bearing, then the first aircraft does not move across the field of view of the pilot of the second aircraft, but merely grows slowly in size, and it may not be until the last minute that the pilot of the second aircraft detects the presence of the first aircraft. Conversely, the second aircraft does not move across the field of view of the pilot of the first aircraft. Summary of the Invention

In accordance with one aspect of the invention, there is provided a radar system, comprising: a ground radar station for detecting the positions of objects relative thereto; a transmitter for transmitting data derived from the detected positions; and a mobile station operable to receive the transmitted data and to provide a signal dependent upon the path relative to the mobile station of an object detected by the ground station.

The signal may be a visual display of the path of the detected object or objects and/or an indication as to whether or not the path of any detected object appears to be on a collision or near-collision course with the mobile station.

Considering the case where such an apparatus is provided on aircraft A, Figures IC and ID show examples of displays which could be provided for the pilot or navigator corresponding to Figures 1A and^"IB, respectively, (but at half the scale) when the display is centred on the current position of aircraft A, that is position AC in Figure IC and position AD in Figure 5D. The successive positions B1C to B5C of aircraft B in Figure IC can easily be extrapolated to determine that aircraft B will pass behind aircraft A. However, the extrapolation performed in the case of Figure ID upon the points BID to B5D immediately shows that aircraft B is on a collision course with aircraft A, and therefore the pilot or navigator of aircraft A can simply see that evasive action needs to be considered. This is because he need make only a single extrapolation of direction, whereas, referring to Figures 1A and IB, the air traffic controller must make four extrapolations, i.e. of direction for each aircraft to obtain the crossing point and of speed and thus time for each aircraft to reach the crossing point.

According to another aspect of the invention, there is provided a ground radar station for detecting the positions of objects relative thereto, in combination with a transmitter for transmitting data derived from the detected positions.

According to a further aspect of the invention, there is provided a positional display apparatus comprising: means to receive positional data of an object in terms of one co-ordinate system; means to convert the positional data to being in terms of a further co-ordinate system relative to the position of the apparatus; and means to display the converted positional data.

According to yet another aspect of the invention, there is provided a radar system in which data from which a radar screen image could be constructed is transmitted, and in which an aircraft receives the data and constructs a radar screen image in which the image of the aircraft in the display remains stationary despite movement of the aircraft.

Specific Description

There follows a description by way of example of a specific embodiment of the present invention, reference being made to the accompanying drawings, in which:

Figures 1A and IB illustrate a conventional ground radar display;

Figures IC and ID illustrate a display which may be provided in an aircraft in accordance with the invention;

Figure 2 is a block diagram schematically illustrating radar station equipment; Figure 3 is a geometrical diagram used to explain the operation of an encoder in the radar station; Figure 4 shows a transmitted data format; Figure 5 is a block diagram schematically illustrating an apparatus for fitting to an aircraft; and

Figure 6 is an example of a display of the apparatus of Figure 5.

Referring to Figures 2 to 4, a ground radar transceiver 10 has an output serially supplying signals corresponding to the range R. and bearing

A. of N points (i = 1 to N) as displayed on the

radar screen. An encoder 12 receives the signals R.

A. and from those signals and the values of the

latitude X_Q and longitude Y_Q of the radar

transceiver calculates the latitude X. and longitude Y. of each of the N points and serially

supplies the X, , Y. signals to a buffer 14, where

they are temporarily stored. Once a full scan of the radar has been completed, a controller 16, causes a VHF radio transmitter 18 to package and transmit the data in the format shown in Figure 4. Each transmission begins with a predetermined start code, then the latitude and longitude of the radar transceiver and a predetermined separation code, then the latitude and longitude and a separation code for each point 1 to N, and then a predetermined end code. Transmissions are repeated at a predetermined rate of, for example, _L0 transmissions per minute, which conveniently corresponds to the usual scan rate of 10 scans per minute for most UK ground radar.

Referring now to Figure 5, the apparatus mounted in ^'the aircraft comprises a computer 20 which receives signals from a VHF radio receiver 22 and drives a liquid crystal panel display 24. The computer can also address and read a position data memory 26 and is associated with a keyboard 28 for manual data entry and control of the system.

In operation, the data transmitted by the ground transmitter for one scan is received by the receiver 22 and unpackaged, and the batch of data

X_n0,Ϋυ_n to X_Λn Y„n is stored in one of five sections of

the position memory 26. The batch of data for the next scan is stored in another one of the five sections of the memory 26, and so on. The memory 26 is cyclically refreshed so that it holds five batches of position data for the last five scans of the radar, and the computer memorises in which portion of the memory the most recent batch of data is held.

In order to initiate the system, the aircraft pilot or navigator enters via the keyboard 28 his estimated latitude X and longitude Y . The

computer then checks through the batch of data stored in the most recently refreshed portion of the position memory and determines which data pair X , Y corresponds most closely to the estimated

position X Y since it can be expected that

the position of the aircraft will correspond to one of the positions received from the ground radar. The position X , Y is stored. This process is

repeated with each received batch of data and the stage is reached where the apparatus:

a) has stored five batches of positional data; b) knows the order in which the batches have been stored; and c) knows which data pair in each batch corresponds its own position.

From the five pairs of ^• own-position data, the computer determines the average bearing of the host aircraft during the 5-scan period. The computer then performs a co-ordinate conversion process an each set of data. The conversion process has the following effects:

a) the co-ordinate system is rotated so that the average bearing of the aircraft over the 5-scan period becomes the y-axis of all of the data; b) the co-ordinate system is translated so that the own-position data pair in each of the five batches of data becomes the origin (X_, Y ) =

(0, 0) for that batch of data; and c) the co-ordinate system is expanded or contracted so that the scale of the image represented by the data is enlarged or made smaller in accordance with a factor which may be entered via the keyboard. The data as it is transformed is supplied to the display 24, where, for each data pair a point is displayed at co-ordinates on the display panel corresponding to the converted co-ordinates, the y-axis of the converted co-ordinate system (ie the aircraft bearing) corresponding to the vertical direction of the display panel and the origin αf the converted co-ordinate system corresponding to the centre of the display panel. Furthermore, the intensity and/or size of each displayed point is made to be dependent on the particular batch of data from which the point is derived, so that data from the most recent radar scan is brightest and/or largest and that from the earliest radar scan is dimmest and/or smallest. Thus, another aircraft moving relative to the host aircraft will be displayed as a row of five points having brightness and/or size increasing in the direction of travel of the other aircraft. It will be noted, however, that the host aircraft will be displayed as a single point on the display panel, because as a result of the conversion process the host aircraft's own position becomes the origin and centre of the screen for each batch of data. The display panel is updated every time a further batch of data is received.

Many modifications may be made to the ground and airborne apparatus described above.

For example, in the arrangement described above, the average bearing of the host aircraft over the last five-scan period is determined and continually updated. In addition, the speed and average bearing of the host aircraft may be calculated from the most recent two pairs of position co-ordinates, and an extrapolation process may be carried out using the speed and bearing in order to determine which data pair in the next batch of data is likely to represent the new position of the host aircraft. In initiating the system_/ the aircraft pilot or navigator may enter via the keyboard 28 his estimated bearing and speed, in addition to the estimated latitude and longitude.

Also, for example, in the embodiment described above, the bearing of the host aircraft is determined from the own-position co-ordinate pairs in the five batches of data. Since these five positions are close together, errors may be introduced, and, whilst these errors will not substantially affect the display of relative positions of other aircraft with respect to the host aircraft, rotational variations may be introduced in the display as between adjacent displayed images. Rather than calculating the bearing of the host aircraft, the bearing may b.e entered by the pilot or navigator via the keyboard and may be updated each time a change of course is made. Alternatively, if the host aircraft is fitted with a compass having an electrical output indicating the current bearing, that electrical output may be used to supply bearing information to the display apparatus.

In a development of the arrangement described above, the computer may be programmed to compare the position data in the five batches of data and to determine which position co-ordinate pairs in the batches relate to the same aircraft. Having done this the courses of all of the other aircraft are extrapolated and the computer determines whether any other aircraft is expected to collide with or come within a predetermined distance of the host aircraft. If so, this is indicated to the pilot or navigator, for example, by flashing on the display the points representing the aircraft causing the danger, by flashing a line indicating the other aircraft's course, and/or by a visual or audible alarm. Furthermore, the computer may determine the expected time to collision and cause the display to display that time.

In a further development, in the case where an aircraft is fitted with a transponder so that the ground radar installation can determine the altitude and/or an identity code of the aircraft, the altitude data and/or identity code data for the aircraft is included in the transmissions in the available space marked "blank" in Figure 4, and this additional data is stored in the memory 26 of the host aircraft. The computer then causes the display panel 24 to indicate adjacent the most recent position point for each aircraft the most recently received altitude and/or the identity code for that aircraft. Additionally, in the development described above of extrapolating each aircraft's course to determine whether there is a risk of collision, the altitude of the host aircraft may be input to the computer, for example, manually via the keyboard, from an onboard altimeter, or from the received data from the ground radar, and the differences between the altitudes of the host aircraft and the other aircraft may be taken into account in assessing the risk of collision. Moreover, the computer may be programmed not to display the locations of aircraft having more than a predetermined difference in altitude from that of the host aircraft so that .a less cluttered display may be provided. Furthermore, the altitude data or identity code of the host aircraft received from the ground radar may be compared with altitude data entered via the keyboard or from an onboard altimeter or with an identity code stored by the computer in checking that the computer has correctly identified from the received data that which relates to the host aircraft.

Other data may be displayed such as North-South and East-West cross-hairs through the centre point, range circles centred on the centre point of the display and digitally range-marked, such as "lOnm", "20nm", "30nm", and a digital indication of the host aircraft's current latitude and longitude. When more than one ground radar station provides the facility mentioned above, they may transmit on different frequencies, and the pilot or navigator of the host aircraft may tune to the desired frequency. Alternatively, the host aircraft may receive on two or more channels and the pilot or navigator may select whether to display the da£a from one ground radar station, the other, or both. Alternatively, the ground radar stations may all transmit on the same frequency, but with time-sequenced transmissions of the batches of data, so that no two adjacent stations transmit at the same time, and again the host aircraft may select which data from the various received transmissions to display.

The apparatus fitted to the aircraft may also be provided with a PROM containing information about the height and locations of high ground and structures in the area likely to be covered by the host aircraft, and this information may be displayed on the display panel in the appropriate location and marked with the relevant height. Also, the apparatus fitted to the aircraft may be provided with a PROM containing map data, and thus a map may also be diplayed on the display and may move across the display as the position of the host aircraft moves. The PROM may be arranged so that it is easily removable and can be replaced by a different PROM covering a different area. As an alternative to providing the display with the bearing of the host aircraft extending in the upward direction, the display may be provided with true north in the upward direction, and a bearing indicator may be provided to show the bearing of the host aircraft.

In a further development of this latter modification, the apparatus fitted to the aircraft has two modes, namely a "map mode" and a "flight mode". In the map mode, the display does not move so that it is centered on the position of the host aircraft, but instead it is movable under the direction of cursor keys of the keyboard 28, or alternatively an associated joystick control. Map mode is particularly useful in initiating the system when provided with the following facilities. The pilot adjusts the portion of the map which is displayed until it covers the area in which the host aircraft is located. The display then, therefore, shows the positions of aircraft, as transmitted by the ground radar station, moving relative to the ground. The pilot then enters his estimated position, speed and bearing . via the keyboard 28, and the estimated course of the host aircraft is then displayed on the screen, preferably in a different manner to the displayed courses determined from the data received from the ground radar, for example, as a series of five small circles rather than five dots. Assuming that the pilot's estimates are reasonably accurate, the simulated course will lie adjacent to (or be superimposed on), and move with the course of, the host aircraft as determined from the data received from the ground radar station. It is therefore a simple matter for the pilot to determine which of the courses displayed on the screen, as received from the ground radar station, corresponds to the course of the host aircraft. The pilot can then adjust his estimated position using the cursor controls or joystick control so that it generally coincides with the displayed course which he considers represents his own aircraft, and can then press a flight mode button on the keyboard. Once that is done, the computer 20 determines that the course of the aircraft received from ground radar which lies most closely adjacent to the pilot's estimated course is the course of the host aircraft and continues by forming the display in the manner described above with the position of the host aircraft centered on the display.

In a further modification of the arrangement described above, the current latitude and longitude of the host aircraft is stored once the aircraft has landed and the apparatus has been switched off (apart from the memory continuing to be powered by a back-up battery), and this information is then available to the pilot when he next switches on the apparatus ready for a further flight.

Most ground radar stations in the United Kingdom have a scan period of six seconds, and therefore if one batch of data is transmitted for each scan, the displayed five batches of data will represent the course of each aircraft over 24 seconds, and the relative speeds of the aircraft -can be determined from the spacings of the dots in the display. However, a few ground radar stations in the United Kingdom scan at a different rate, for example having a 10 second period. Ideally, therefore, some adjustment should be made so that, whichever type of station is transmitting, the display always displays the course of an aircraft over a predetermined period of time, and this is, of course, essential, if the display is displaying a mixture of data from two different ground radar stations operating at different rates. Such adjustment may either be made at the ground radar station so that a station scanning with a ten second period transmits as if it were scanning with a six second period. Alternatively, the adjustment may be made in the host aircraft.

Figure 6 illustrates a display incorporating some of the modifications or developments described above. The display has N-S, E-W cross-hairs 30; marked range-circles 32; a marker 36 at the top of the display showing the host aircraft's heading; and digital latitude, longitude and bearing information 38 of the host aircraft at the top-right corner of the display. An aircraft approaching from the East is on a collision course, and a warning line 40 indicating its course is flashing. An aircraft to the West-South-West has an altitude indication 42. A slower aircraft having closer spaced markings 44 to the South-South-East is turning to port.

Claims

1. A radar system, comprising: a ground radar statio for detecting the positions of objects relative thereto; a transmitter for transmitting data derived from the detected positions; and a mobile station operable to receive the transmitted data and to provide a signal dependent upon the path relative to the mobile station of an object detected by the ground station.

2. A system as claimed in claim 1, wherein the signal is a visual display of the path of the detected object.

3. A system as claimed in claim 1, wherein the signal is an indication as to whether or not the path of a detected object appears to be on a collision or near-collision course with the mobile station.

4. A ground radar station for detecting the positions of objects relative thereto, in combination wiith a transmitter for transmitting data derived from the detected positions.

5. A combination as claimed in claim 4, wherein the data is transmitted in terms of the position of a detected object relative to a standard co-ordinate system.

6. A combination as claimed in claim 5, wherein the data is transmitted in terms of the latitude and longitude of a detected object.

7. A combination as claimed in claim 4, wherein the transmitted data also includes data representing altitude of a detected object.

8. A positional display apparatus comprising: means to receive positional data of an object in terms of one co-ordinate system; means to convert the positional data to being in terms of a further co-ordinate system relative to the position of the apparatus; and means to display the converted positional data.

9. An apparatus as claimed in claim 8, further including means to store the positional data, the receiving means being arranged to receive updated positional data of the object, and the display means being arranged to display the stored data and the updated data after conversion by the converting means.

10. An apparatus as in claim 9, wherein the conversion means is operable to convert the updated data so that it is in terms of a co-ordinate system relative to a correspondingly updated position of the apparatus.

11. An apparatus as claimed in claim 10, and further comprising means to discriminate whether the positional data and the updated positional data are indicative of an object having a collision or near collision course towards the apparatus.

12. An apparatus as claimed in claim 8, wherein the positional data is received as part of a batch of positional data relating to a plurality of objects.

13. An apparatus as claimed in claim 12, and further comprising means to correlate data in the batch of data with updated data in the batch of updated data relating to the same object.

14. An apparatus as claimed in claim 13, wherein the discriminated data is displayed differently to the other data.

15. An apparatus as claimed of claim 8, wherein the conversion means is operable to rotate the co-ordinate system so that it is aligned with a direction of movement of the apparatus.

16. An apparatus as claimed in claim 8, further comprising means to vary the scale of said further co-ordinate system.

17. An apparatus as claimed in claim 8, wherein the display means comprises a screen, and the data is displayed on the screen by being positioned on the screen in correspondence with the converted co-ordinates of the data.

18. An apparatus as claimed in claim 8, further comprising means to store map data, and means to select an appropriate portion of the map data, the appropriate portion being displayed on the display means.

19. An apparatus as claimed in claim 8, wherein the apparatus has a further mode, in which positional data relative to the ground is displayed on the display means, and further comprising means to enter an estimated position, which is displayed on the display means for comparison with the received position or positions.

20. A radar system in which data from which a radar screen image could be constructed is transmitted, and in which an aircraft receives the data and constructs a radar screen image in which the image of the aircraft in the display remains stationary despite movement of the aircraft.