GB2149255A

GB2149255A - Marine distress transmitter

Info

Publication number: GB2149255A
Application number: GB08329434A
Authority: GB
Inventors: Rolf Johannessen
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1983-11-03
Filing date: 1983-11-03
Publication date: 1985-06-05
Also published as: GB8329434D0; GB2149255B

Abstract

A marine distress transmitter in a "float-free" container (the nautical equivalent of the aeronautical "black box") has an automatic radio beacon and also contains a recording of voyage data including radar data. To reduce the amount of data to be stored for a voyage lasting weeks "significant data" is selected, for example only other vessel contacts which come within a predetermined range or which persist for a given time. All data is recorded in a temporary store and only significant data is transferred to a permanent store in the distress transmitter.

Description

SPECIFICATION Marine distress transmitter This invention relates to a marine distress transmitter for automatic broadcasting of distress radio signals in the event of a marine disaster.

It is now common practice for aircraft, particularly civilian passanger carrying aircraft, to be equipped with a so called "black-box" flight recorder in which data concerning each flight, e.g. instrumentation readings and cockpit voice communications, are recorded. The flight recorder is also equipped with a radio beacon which is automatically energised in the event of a crash, thus aiding its recovery by rescue teams. The recorded data is then available to investigators who need this information to determine the cause of the crash.

It is now proposed that a similar device be fitted to ships, with special adaptation for the nature and duration of sea voyages. Such a device will be required to monitor and record voyage data such as course and speed, vital instrumentation data, radio communications etc. It must also be designed in a form which is readily recoverable after an accident at sea.

Typically it will be enclosed in a container which will float free from a sinking ship and will withstand fire and/or other potential damage.

One important problem remains to be overcome. On aircraft the flight recorder is required to monitor and record data for a maximum of one day or so-most aircraft journeys being considerably less than this in duration.

Ships, however, are often at sea for a number of weeks without putting into a port. For a marine distress transmitter to function effectively it must therefore have the capability of recording data for a long period of time. This implies an extensive data storage capability.

One suggested requirement for a marine recorder is that it records, inter alia, "what is seen on the vessel's own radar screen". As an example, consider a radar having a 6' antenna operating in the X-band. It has a horizontal beamwidth of 1.2" and therefore some 300 bearing cells. A maximum range of 48 nautical miles uses a pulse length of 0.6 ,us corresponding to a range cell length of 300 feet, giving about 1000 range cells along a radius. Thus the total number of information cells per revolution would by 300 x 1000=3 X 105. At 22 RPM the number of cells scanned is 3X 105x22X60X24=9.5X 109per day. If relative tracks were to be calculated, a finer granularity may well be required and fractions of range cells and fractions of bearing cells could be needed.Obviously storage on this scale for, say, 21 consecutive days is impracticable. Some means of reducing the storage requirements is required if a practical marine recorder is to be constructed.

According to the present invention there is provided a marine distress transmitter having means for monitoring and recording passage data including radar information, the recording means including temporary storage means wherein all radar data is initially stored, means for evaluating said temporarily stored data according to predetermined criteria, permanent storage means and means for transferring to said permanent storage means only data from the temporary storage means which meets said predetermined criteria.

In this way a significant reduction can be effected in the amount of data to be recorded in the marine recorder forming part of the distress transmitter.

Several possibilities for reducing the volume of data to be permanently stored can be considered, of which the following are some examples.

If information stored from the ship's navigation sensors were to be relied upon to provide ship's position, the main value in radar data would be to determine the tracks of targets within a few miles of the ship. Thus it could ignore echoes at ranges greater than, say, 5 miles. While this provides a 5:1 saving it is noted that if the navigating officer switches his radar to a low range display scale the pulse width is also reduced (for the radar considered (Selenia) to a 0.06 ys width). Thus the range cell is shortened giving 10 times more cells per mile.

While many range cells will have clutter which comes and goes, fewer will have persistent echoes. It would therefore be practical to look out for such persistent targets and to store for each time of occurrence, bearing and range. Time of occurrence would be "rotations after last whole hour" needing 22 rpm X 60 = 1 320 states or 11 bits. Bearing would need 10 bits, range 11 bits, level 3 bits showing a total of 35 bits and some checking bits for each target.

Many of the persistent echoes can be tracked and found to pass the ship with a closest point of approach greater than some safe limit. As the distance between the vessels increases and the other vessel disappears outside radar range, all information about its past track can be rejected since no danger ever occurred.

For the temporary storage a large solid state semiconductor memory is preferred. This can be separate from the transmitter/recorder which requires to be as compact as possible and to have permanent storage which is not affected by being detached from the ship. A semiconductor memory provides rapid access and is particularly suited to data processing techniques such as the evaluation described above.

For the permanent storage varous possibilites exist. A magnetiseable steel wire recorder, such as is used in aircraft, is probably to be preferred. However other recording media, such as magnetic tape or even a magnetic disc can be considered; all are capable of long term non-volatile storage of large amounts of data.

The particular types of data store to be used for the temporary and permanent storage are readily available to those skilled in the art and in themselves form no part of the present invention. Likewise the data processing equipment required to evaluate and select the data to be transferred to the permanent store is readily designed by those skilled in the art.

Finally, the choice of which data sources to monitor and evaluate form no part of the present invention which is concerned only with the reduction in volume of the data that is being monitored for subsequent permanent storage.

The recording equipment is secured in a float-free container together with a radio beacon. The container further includes a means for automatically switching on the radio beacon when the container is removed from the ship and immersed in the sea. Such means, e.g. switches responsive to inversion of the container, or to immersion of the container in the sea, are readily designed by those skilled in the art.

Claims

1. A marine distress transmitter having means for monitoring and recording passage data including radar information, the recording means including temporary storage means wherein all radar data is initially stored, means for evaluating said temporarily stored data according to predetermined criteria, permanent storage means and means for transferring to said permanent storage means only data from the temporary storage means which meets said predetermined criteria.

2. A marine distress transmitter according to claim 1 wherein said evaluating means is arranged to reject radar information relating to other vessels the tracks of which do not come within a predetermined range of the ship.

3. A marine distress transmitter according to claim 1 or 2 wherein the evaluating means is arranged to determine persistant target echoes and to reject non-persistent echoes.

4. A marine distress transmitter according to claim 3 wherein the recording means is arranged to record for each persistent echo data relating to time of occurrence, bearing and range.

5. A marine distress transmitter according to any preceding claim further including an automatic radio beacon with means for energising said beacon when predetermined distress conditions occur.

6. A marine distress transmitter substantially as hereinbefore described.