WO2005064559A1

WO2005064559A1 - Tracking apparatus

Info

Publication number: WO2005064559A1
Application number: PCT/GB2004/005450
Authority: WO
Inventors: Christine Anne Edwards; Peter Eric Hall
Original assignee: Christine Anne Edwards; Peter Eric Hall
Priority date: 2003-12-30
Filing date: 2004-12-29
Publication date: 2005-07-14
Also published as: GB0330133D0; GB2409778A

Abstract

A tracking apparatus for use in locating a person who has fallen overboard in provided. The apparatus comprises a base unit and a personal unit. Global position satellite data is used to calculate a distance and bearing between the locations of the two units.

Description

TRACKING APPARATUS

This invention relates to a tracking apparatus for use in locating a person who has fallen overboard.

BACKGROUND OF THE INVENTION

In recent years, concentrated focus on safety issues in the maritime world by the appropriate regulating bodies has resulted in the conception of, and introduction of, a worldwide automated safety system: the Global Maritime Distress and Safety System (GMDSS) . This system supercedes manual systems operated by coastguards and rescue services. Its automated nature makes search-and-rescue missions more effective, and enables mariners to help themselves more efficiently in an emergency.

At sea, an ever-present hazard is the possibility of a boat's crew member falling overboard (known as Person Overboard, POB) . A POB has more chance of survival if rescued as soon as possible, and that means being picked up by the boat nearest him - probably the boat he fell from. The rescue depends upon the seamanship of the captain and remaining crew.

Two methods of automated-assisted POB rescue are personal and larger Emergency Position Indicating Radio Beacons (EPIRBs) and personal proximity detectors .

Personal EPIRBs are small radio beacons, designed to be worn by the crew. They can be automatic or manual. They broadcast an alarm on the international distress frequency, in order to alert the Emergency Services and initiate a Search-and-Rescue operation. A rescue helicopter receives the signal (if it is in range) and can follow its direction to the POB. It is possible to buy a direction finder for an EPIRB working on the inshore 121.5MHz distress frequency that is based on a boat, but the direction finding equipment cost is high, and it only gives an approximate bearing to the casualty.

There are also larger EPIRBs that transmit on 406.025MHz, usually known as 406MHz EPIRBs. These are more sophisticated devices that are mandatory for merchant vessels operating in GMDSS designated areas A2 to A4 (A2 is 20/30 miles to 150 miles off shore, A3 is beyond 150 miles, A4 is Polar regions) . These devices have the ship identity encoded into them and alert shore based services via COSPAS SARSAT satellites. Some yachts carry the 406MHz EPIRB.

Personal proximity detectors are small electronic devices worn by the crew that are constantly monitored by a fixed unit on board the boat. When a crew member moves outside of a pre-determined range, an on-board alarm is sounded. Some systems interface to the ship' s GPS receiver and log the boat's position at that moment, and this is taken to be the position that the crew member fell overboard.

US Patent No US6222484 describes a personal emergency location system using a personal global position system (GPS) in which a personal unit transmits a personal position to a base unit on a vessel. A disadvantage of this system is that a personal antenna must be deployed in order to successfully transmit the personal location to the base unit. SUMMARY OF THE INVENTION

According to the invention there is provided a tracking apparatus comprising: a personal unit comprising a personal GPS receiver, a personal microprocessor, a personal RF transmitter; a base GPS receiver; a base unit comprising a base RF receiver, a base microprocessor; and a visual display; and in which upon activation of the personal unit the personal GPS receiver is arranged to receive GPS satellite signals and calculate a personal location; the personal microprocessor is arranged in operation to receive the personal location from the personal GPS receiver; and generate an encoded signal in dependence upon said location; and the personal RF transmitter is arranged to transmit said encoded signal; the base GPS receiver is arranged to receive GPS satellite signals and calculate a base location; the base microprocessor is arranged in operation to receive the base location from the base GPS receiver; the base RF receiver is arranged to receive said encoded signal; and the base microprocessor is arranged upon receipt of said encoded signal to decode said encoded signal to determine said personal location; and determine a bearing and distance in dependence upon said personal location and said base location; and display said bearing and distance on said visual display.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a system that says ^ΛI have fallen in the water and I am at this position - come and get me via this route' . This is intended to aid the remaining crew members recover a casualty quickly with the minimum of additional stress. In UK latitudes there are many factors that affect survival, the main ones being shock, hypothermia, and the ability to remain afloat and breathe. It is possible that by the time the shore based emergency services have been alerted and arrive, the casualty is dead. The tracking system of the invention tracks a crew member who has fallen overboard and displays the recovery information relative to the boat.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which, Figure 1 illustrates a tracking apparatus in accordance with the present invention; Figure 2 illustrates a personal unit in accordance with the present invention; Figures 2a and 2b illustrate a front view and a side view of a preferred embodiment of the personal unit; Figure 2c and 2d illustrate automatic orientation of the personal unit using a rotatable float; Figure 3 illustrates a base unit in accordance with the present invention; Figure 4 illustrates a preferred visual display unit; Figure 5 illustrates a preferred format for encoding a signal; and Figure 6 illustrates a preferred embodiment of a protocol for communicating between a personal unit and a base unit.

Referring now to Figure 1 a tracking apparatus comprises a personal unit 10 worn by a crew member 100 and a base unit 20 on board a vessel 200. When the crew member 200 falls overboard (a POB situation) the tracking system is activated. A GPS signal 201, 202 is received by the personal unit and by the base unit from a number of satellites 203 (of which only one is shown) and these signals are used to determine their locations

Referring now to Figure 2 the personal unit 10 comprises a GPS Antennae 1, a GPS receiver 2. An activation switch 3 may be activated in the event of a POB situation either manually or by use of an immersion sensor. The personal unit may be powered up manually without raising the alarm.

Figure 2a and 2b illustrate a preferred embodiment of the personal unit 10.

The personal unit 10 is thin so it can be stored in the folds of a self or manually inflated lifejacket. Ideally the personal unit is released automatically by the inflation of the lifejacket causing ejection of the unit, this is advantageous if the person is unconscious when entering the water. When the lifejacket inflates, the personal unit is released, but is tethered to the crew member by a lanyard 33 as illustrated in Figure 2c. In the case of crew members who do not wear lifejackets, the unit could be worn in a belt pouch, but would then need to be manually released.

The main body of the unit 20 excluding antennae 6 (described later) is around the size of^" a mobile phone (approx 12cm x 8cm) . The unit may be marked with a unique personal identifier 35. The antennae 1 is a helical GPS antenna.

The unit has a rotatable float 34. When the unit is released into the water, the float rotates as illustrated diagrammatically in Figure 2d to place the antennae in the correct orientation. The float rotates to become horizontal in the water, and the unit rotates in the float by virtue of a weight at the bottom) A battery 36 can act as the a weight (or keel) to aid correct orientation of the antennae.

Optional features of the unit include a small strobe 31 to aid casualty recovery at night, a Transmit / Receive LED indicator 32 to give the casualty confidence that the unit is working, and he/she will be rescued.

The unit may be marked with a unique personal identifier 35.

The GPS receiver unit 2 determines the personal location and sends the personal location in the form of GPS data (data encoded to the NMEA 0183 standard) to a microprocessor 4 which encodes the GPS data to provide an encoded signal. It will be appreciated that functionality of the microprocessor 4 could be incorporated into a microprocessor which is internal to the GPS receiver. If this is the case then the personal location may be sent in the form of binary data, or by means of a variable in the program code. A transmitter 5 transmits the encoded signal via the antenna 6 at regular intervals. To remain within the allowable transmitter power band of the frequency bands to be used, a quarter wave dipole antenna is used on both the personal and base units. The details of encoding the signal are described later with reference to Figure 5.

Referring now to Figure 3, the base unit 20 comprises a receiver 22 which receives the encoded signal via antennae 21. The base unit antenna is mounted as high as possible on the vessel 200 in order to have, as far as is possible, an unobstructed 360 degree coverage.

When the base unit 20 receives the signal, it raises an alarm both audio (loud bleeping) and visual (flashing light) , microprocessor 23 decodes the signal and calculates a distance and bearing in dependence upon the personal location, and a base location determined by use of a base GPS signal 24. The base unit 20 sends the calculated distance and bearing continuously to a visual display, known as a cockpit repeater (a preferred cockpit repeater is illustrated in Figure 4. ) .

An alarm unit is a small low cost unit, capable of producing an audio and visual alarm that are moveable and can be mounted at strategic points around the vessel. These units can also show the current state of the communication between the casualty and the ship by means of a binary indicator. The alarm will be capable of being turned off, whether the casualty is rescued or not, by manual or automatic means or combination of both.

The distance and bearing are calculated using the personal location transmitted by the personal unit. If the signal is lost, either due to being blocked by waves, or by being out of range, or if the signal is continuously corrupt for a defined period of time, then the base unit reverts to calculating distance and bearing using Mead-reckoning' . Some transceivers have the ability to monitor received signal strength, so the signal reaching the limits of its range can be detected. An ACK / NAK protocol (described later) defines data transmission intervals and timeout periods, so if no signals or only corrupted signals are detected over a defined period, the POB is deemed to be out of range. Dead- reckoning' means taking a logged pattern of positions, determining the pattern of movement, and predicting this into the future. No tidal correction is used, in general the tidal drift will have been established by the time the signal is lost. However, in an improved version, tidal tables can be utilised to predict a POB position.

The crew are therefore assisted in the POB recovery by being shown the direction in which to steer, and how far away the casualty is. It is an advantage if they are using equipment (the cockpit repeater) which is used frequently in sailing the boat, and so the crew are thoroughly familiar with it.

Lack of familiarity with boat safety equipment is a major problem. In the embodiment of the invention described, in an emergency, the crew will use familiar equipment mounted in the correct place, displaying familiar data that is to be used for the rescue. There is nothing new to learn, and therefore no time-consuming hesitation and uncertainty.

The base unit interfaces to the boat's existing equipment: the boat's GPS receiver, and the boat's cockpit repeater, using the standard NMEA 0183 protocol to communicate with them. In normal conditions, the unit merely forwards the boat's GPS data to the cockpit repeater. In an emergency, it replaces some of the boat's GPS data with calculated data, which it forwards to the cockpit repeater.

There are a number of factors that affect the personal position calculated by a GPS receiver. Some, such as delays induced by the earth's atmosphere are constant for all makes of GPS receiver. Other factors which may affect the calculated position are the algorithms used to convert the time delays to a position, and most critical, an ellipsoid used to approximate the surface of the earth. Two identical GPS receivers using different ellipsoids in their calculations may generate positions differing by hundreds of meters. Therefore to eliminate extra potential errors arising from using different GPS receivers (the base unit's GPS receiver and the personal unit' s GPS receiver) it may prove necessary to install an identical GPS receiver in each of the base and personal unit.

The method for encoding the transmitted signal, and the protocol using for signal transmission will now be described.

Radio waves do not propagate very far through water. If a person falls in the water in heavy seas, he will be rising and falling with the waves, and sometimes the body of the wave will be between him and the boat, blocking reception of his signal by the boat.

The POB is potentially out of sight of the receiving unit for a considerable period of time, especially if the antenna on the boat is mounted in a low position. Assuming that the period between waves is 5 seconds, and that line of sight between the two antennae occurs for 1 second, then there is an 80% chance that the antennae do not 'see' each other.

Another consideration is the amount of time taken to physically transmit the POB position. The longer it takes to transmit this data, the greater the chance that some of the transmission will be lost as the POB sinks into a trough. A message that contains all the information needed is typically 65 bytes long. (The NMEA protocol defines the format, but the length of the message can vary according to the positional accuracy used. Typically between two and six decimal places of minutes are used). The transmission rate, 4.8K bits per second, is quite low. If the Crew Unit transmits a 65 byte message, it will take 149 ms .

It is not possible to continuously re-transmit POB positions and assume that some will be received by the boat because there are rules for the frequencies which are used, most of which impose a maximum of 10% duty cycle. Furthermore constant retransmission would also be very inefficient for power consumption.

According to the invention the essential details of the message are encoded into an encoded signal. This compresses - li ¬

the transmission time of the message to a few milliseconds. For an example see encoding illustrated in Figure 5. This reduces the message to 16 bytes. Transmission time for this is shown in the following table

Transmission Speed Time 4.8Kbρs 33.328 ms .

9.6Kbps 16.664 ms .

19.2Kbps 8.332 ms . 38.4Kbps 4.116 ms .

Due to increased bandwidth, the transmitted data range decreases as the speed increases. In the embodiment described a checksum is also used and the ACK/NAK (acknowledgement/negative acknowledgement) protocol mentioned earlier is used in the communications between the base unit and the personal unit as follows.

After the personal transmitter on the POB sends the encoded signal. One of three things may happen:

1. The POB is in the trough of a wave so the boat does not receive the message. The transmitter times out waiting for an ACK / NAK and re-transmits the message.

2. The boat receives the message but the Checksum does not match with the received calculation, therefore the message has been corrupted. The boat transmits a ^ΛNAK' and on reception of the ^λNAK' the POB retransmits the message immediately. If the POB is now in a trough and does not receive the ^ΛNAK' it times out as in case 1. 3. The boat receives the message and the checksum computes correctly. The boat transmits an ACK' acknowledging correct receipt of the message. The POB ceases transmission until the next message. If the POB is now in a trough and does not receive the ^λNAK' it times out as in case 1 and will retransmit this data, but the important thing is that the message has got through. The receiver on the boat will discard duplicate messages.

Figure 6 illustrates operation of the protocol during transmission in heavy seas.

The data required is latitude, longitude and time. It is preferable to avoid using floating point numbers due to the different representations between different processors. The format used in this embodiment of the invention is shown in Figure 5.

It is possible to determine the period of the waves, and thus when the POB is on the crest of a wave, which is an optimum position for line-of-sight transmission to the boat. This information can be determined by analysing the pattern of transmissions not acknowledged against those that are acknowledged by the base unit.

Preferably the transmitted power of the personal unit is controlled in a variable manner by software. This allows us the option of transmitting at low power initially when the crew member is near to the vessel . By monitoring the received signal strength (assuming the vessel is transmitting at constant power) , or by using the number of NAKs (not acknowledge) received as part of the communications protocol, the personal unit transmitter power can be optimised to the range of the vessel, thus conserving battery power.

Reducing the retry rate can further enhance this power conservation if no ACK or NAK is received from the vessel for a defined period, indicating that the vessel is out of range of the personal unit.

The personal unit must be small enough to be worn in a number of ways (pendant, wristwatch) without impeding movement. If the unit is fitted into a wristwatch. case, it could also function as a very accurate watch.

The personal unit may be built into a self-inflating lifebelt or buoyancy aid. The personal unit may be combined with a strobe light, which can be incorporated in a self-inflating lifejacket, or attached to the crew or worn by the crew in some other way.

The personal unit must be small enough to be unobtrusive, yet still be able to transmit enough signal power to be received at a reasonable distance.

The personal unit could have rechargeable batteries or replaceable batteries. Rechargeable batteries are environmentally friendly, cheaper over the long-term, and a wind up charger could be provided to eliminate the need for a power source and thus extend the range. However, rechargeable batteries deteriorate over time, gradually holding less and less charge. With replaceable batteries, the charge is always known and definite. The personal unit has a self diagnostic function as follows: Processor self test Code Checksum Transceiver Check Watchdog Timer Start Manual Override Check Immersion Sensor Check GPS self test Data from GPS check

The base unit also has a self-diagnostic function as follows

Processor self test

Code Checksum Transceiver Check

NMEA 0183 interface checks

Audio alarm check

Visual Alarm Check

Watchdog Timer Start Control Panel Checks

Internal GPS self test

Data from Internal GPS check.

The base unit plus personal unit(s) can be tested as a complete system, simulating an emergency.

The tracking apparatus is capable of dealing with multiple casualties in the water. The personal unit allows signals to be transmitted every n seconds where n is the maximum number of crew or units. For example if the POB position were transmitted no later than every 10 seconds, this allows up to 10 units to transmit in a staggered manner. The personal unit uses the GPS time stamp to determine when to transmit. A simple selection on the base unit allows one POB position to be displayed or for the unit to cycle through multiple casualties .

Other methods of dealing with multiple causalities include • use different channels for each personal unit • stagger the transmission time by a value determined by a unique personal unit identifier and allow the protocol to handle any clashes • use the base unit processor to determine the time interval to be used for example by determining how many casualties there are by counting the different personal unit identifiers, allocating a time interval for transmission to each one, and transmitting the appropriate time interval to each personal unit.

The transmitter range is set by the worst case situation, which is considered to be a large racing yacht losing crew overboard when on a spinnaker run in strong winds. By the time the spinnaker is dropped they could be a mile away from the casualty. If the casualty does go out of range, the receiving system software will predict drift by dead- reckoning, from the received information before loss of signal, and generate the estimated position of the POB.

Transmission uses one of the licence free bands for communications of 433MHz or 868MHz. Another option is to modulate the GPS signal into the 121.5MHz signal of an EPIRB, thus combining the ability to be found by a helicopter with the local rescue function. The tracking apparatus may have any of the following additional functionality. Transmission of an emergency signal through the Digital Selective Calling (DSC) facility of the VHF radio. Immobilisation of the Auto—pilot and or the engine in the event of an emergency. Other sensors may also be used for example a motion sensor (horizontal and/or vertical motion) or a heat sensor.

The base unit may have a 'locate unit' function using the unique identifier of a personal unit, where the position of an identified personal unit is obtained from the personal unit and is displayed. Also a 'locate all units' function may be provided where all units' positions and identities are displayed cyclically. It would then be possible to calculate and display bearing and distance to the unit(s) for example they could be displayed on a schematic or map.

It will be appreciated that the functionality of the base unit could be implemented by a suitably programmed conventional personal computer (PC) .

Claims

1. A tracking apparatus comprising: a personal unit comprising a personal GPS receiver, a personal microprocessor, a personal RF transmitter; a base GPS receiver; a base unit comprising a base RF receiver, a base microprocessor; and a visual display; and in which upon activation of the personal unit the personal GPS receiver is arranged to receive GPS satellite signals and calculate a personal location; the personal microprocessor is arranged in operation to receive the personal location from the personal GPS receiver; and generate an encoded signal in dependence upon said location; and the personal RF transmitter is arranged to transmit said encoded signal; the base GPS receiver is arranged to receive GPS satellite signals and calculate a base location; the base microprocessor is arranged in operation to receive the base location from the base GPS receiver; the base RF receiver is arranged to receive said encoded signal; and the base microprocessor is arranged upon receipt of said encoded signal to decode said encoded signal to determine said personal location; and determine a bearing and distance in dependence upon said personal location and said base location; and display said bearing and distance on said visual display.

2. A tracking apparatus according to claim 1, in which said personal unit further comprises a personal RF receiver, and said base unit further comprises a base RF transmitter, and in which the base RF transmitter is arranged to send an acknowledgement upon receipt of said encoded data and the personal transmitter is arranged to periodically transmit said encoded data until the personal RF receiver receives said acknowledgement.

3. A tracking apparatus according to claim 2, in which the base microprocessor is arranged to determine whether a received signal is corrupt and in which the base RF transmitter is arranged to transmit a negative acknowledgement upon receipt of a. corrupt signal, and in which upon receipt of a negative acknowledgement said RF transmitter is arranged to retransmit said encoded data.

4. A tracking apparatus according to any one of the preceding claims, in which said personal unit further comprises an immersion sensor and in which the personal unit is activated upon immersion in water.

5. A tracking apparatus according to any one of the preceding claims, in which the personal unit is activated manually.

6. A tracking apparatus according to any one of the preceding claims in which said encoded signal is transmitted at 433MHz or 868MHz.

7. A tracking apparatus according to any one of the preceding claims in which said encoded signal is modulated onto a 121.5MHz signal.

8. A tracking apparatus according to any one of the preceding claims in which said visual display is arranged in normal operation to display course and bearing to a predetermined waypoint, and in which upon activation of the personal unit the visual display unit displays course and bearing to the personal location.

9. A tracking apparatus according to any one of the preceding claims, in which said encoded signal includes a unique personal identifier in dependence upon the identity of the personal unit.

10. A tracking apparatus according to any one of the preceding claims in which the personal unit is arranged to perform a self test upon receipt of a self test request.

11. A tracking apparatus according to any one of the preceding claims in which the Base unit is arranged to perform a self test upon receipt of a self test request.

12. A tracking apparatus according to any one of the preceding claims in which after activation of the personal unit, when the base unit fails to receive an encoded signal within a predetermined time frame the base microprocessor is arranged to calculate a predicted personal location in dependence upon a recent personal location.

13. A tracking apparatus according to any one of the preceding claims in which the base unit is arranged to calculate the distance and bearing to a particular personal unit on request.

14. A tracking apparatus according to claim 13, in which the base unit is arranged to calculate the distance and bearing to a plurality of personal units on request.