Abstract:
A marine locator device including: a light section including a visible light emitter and an infrared light emitter; a communication device operable to broadcast an information signal; a controller operable to communicate with and control the light section and the communication device; a power supply electrically connected with the light section, the communication device, positioning system, and a controller; and a positioning system configured to determine geographic coordinates of the device, wherein the controller is operable to communicate with and control the positioning system and to incorporate the geographic coordinates into the information signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a US national stage under 35 U.S.C. §371 of PCT/US2006/021960 filed Jun. 6, 2006, which in turn claims the benefit of priority from U.S. Provisional Application Ser. No. 60/687,588, filed on Jun. 6, 2005. These applications are herein incorporated by reference in their entirety. 

   TECHNICAL FIELD 
   This invention relates to locating a position in a body of water. 
   BACKGROUND 
   A person on the deck of a surface vessel risks falling overboard. Whether or not an overboard person survives in the water depends upon the ability to retrieve the person from the water before the person drowns or succumbs to other hazards (e.g., hypothermia). However, several factors can impede the location and rescue of a person in the water including poor visibility, rough sea states, and an inability to circle back to the person&#39;s position (particularly for large vessels) upon becoming aware of a “man overboard” condition. 
   To facilitate water rescue efforts, particularly in adverse conditions, marine location markers can be used to mark the approximate position of a person in the water. Marine location markers can be pyrotechnic devices that provide a signal, in the form of smoke and fire, to would-be rescue craft. Marine location markers can also be electronic devices configured to provide one or more signals including visual, audible, and position signals. By responding to the signal of the marine location markers, would-be rescue craft can localize search efforts to the area most likely to contain the person overboard, thereby improving the probability of rescue. 
   Marine location markers can also be useful in other applications requiring a reference to a specific point on a body of water. For example, marine location markers can be used to mark the boundary of a chemical spill in the water. The subsequent movement of the marine location marker provides an indication of the spread of the chemical spill. In another example, marine location markers can be used to mark the position of a rendezvous point for two vessels. In still another example, marine location markers can be used to mark the position of an object (e.g., lost cargo) in the water. 
   Current MK 25/MK 58 Marine Location Markers are devices designed to provide visual reference to a specific point at sea. The units contain red phosphorous, which is no longer produced in North America and must be acquired from overseas sources, and other chemicals, which are blended to form the compound necessary for the MK 58 and MK 25 candles to produce flame and smoke. These units require careful storage and disposal because of their pyrotechnic nature (e.g., phosphorous by nature can spontaneously ignite). 
   SUMMARY 
   Novel marine location devices and systems include a real-time locator, a Global Positioning System transponder and/or radio frequency beacon, a human visible light beacon, and an infrared light beacon. Signals from marine location devices to remote units can contain information specific to the marine location devices and their environment (e.g., location, water, temperature, sea state) and signals from remote units to marine location devices can control operation of the marine location devices. 
   In an aspect of the invention, a marine locator device includes a light section including a visible light emitter and an infrared light emitter; a communication device operable to broadcast an information signal; a controller operable to communicate with and control the light section and the communication device; a power supply electrically connected with the light section, the communication device, positioning system, and a controller; and a positioning system configured to determine geographic coordinates of the device, wherein the controller is operable to communicate with and control the positioning system and to incorporate the geographic coordinates into the information signal. 
   In an aspect of the invention, a marine locator system includes: a marine locator device and a remote unit. The marine locator device includes: a light section including a light emitter; a communication device operable to broadcast an information signal and to receive a control signal; a controller operable to communicate with and control the light section and the communication device; and a positioning system configured to determine geographic coordinates of the device, wherein the controller is operable to communicate with and control the positioning system and to incorporate the geographic coordinates into the information signal. The remote unit comprising a control signal generator and a transmitter. 
   In an aspect of the invention, a marine locator device includes: a substantially cylindrical watertight container approximately 21.7 inches long with an outer diameter of approximately 5 inches with a first end and a second end opposite the first end, the container including transparent portion on the first end, wherein a center of gravity of the device is closer to the second end of the container than to the first end of the container; a light section including a visible light emitter and an infrared light emitter; a two-way radio transceiver connected to the power supply and microcontroller and operable to broadcast an encrypted information signal beyond the watertight cylindrical container and further operable to receive an encrypted control signal generated by a remote unit; a microcontroller operable to communicate with and to control the operating states of the first light beacon, the second light beacon, and the two-way radio transceiver; a Global Positioning System receiver wherein the microcontroller is operable to communicate with and control the Global Positioning System receiver and to incorporate the geographic coordinates into the encrypted information signal, and a temperature sensor arranged to measure a temperature proportional to the temperature of water surrounding the watertight cylindrical container and to communicate the sensed temperature to the microcontroller. 
   Embodiments can include one or more of the following features. 
   In some embodiments, the communication device is further operable to receive a control signal from a remote unit. In some cases, the controller includes a decryption module operable to decrypt the control signal. In some cases, the controller is operable to stop the broadcast of the information signal in response to the control signal from the remote unit. In some cases, the controller is operable to switch between the visible light emitter and the infrared light emitter in response to the control signal from the remote unit. 
   In some embodiments, marine locator devices also include a substantially cylindrical container. In some cases, the container includes a transparent portion through which light from the light section is emitted, the transparent portion located at the first end of the container. In some cases, the container includes an interior cavity, the interior cavity extending axially within the container from a second end of the container that is opposite a first end of the container. The power supply can weigh at least 2 pounds and be positioned in the interior cavity such that a center of gravity of the device is closer to the second end of the container than to the first end of the container. A battery power supply can have a nominal voltage of 6 volts direct current with a capacity of 18-20 Amp-hours. 
   In some embodiments, marine locator devices also include a scuttling device operable to allow water into the container. In some cases, marine locator devices also include a timing mechanism operable to activate the scuttling device. In some cases, the scuttling device includes a solenoid. In some cases, the controller is operable to activate the scuttling device in response to a scuttling signal received through the communication device. The scuttling device can be a non-pyrotechnic scuttling device capable of activation to sink the marine locator device. 
   In some embodiments, the power supply has a nominal voltage of 6 volts direct current and a capacity of at least 15 ampere-hours. 
   In some embodiments, marine locator devices also include a temperature sensor arranged to measure a temperature proportional to the temperature of a body of water and/or a sea state sensor. 
   In some embodiments, marine locator devices also include an activation mechanism triggered by immersion in water and operable to activate the power supply and/or a manual activation mechanism operable to activate the power supply. 
   In some embodiments, marine locator devices also include a battery power supply that is switchable between the on and off states. The battery power supply can be switchable between the on and off states through manual operation, contact with water, or a control signal from a remote unit. 
   In some embodiments, the communication device broadcasts the information signal at fixed time intervals. In some cases, the information signal is encrypted. 
   In some embodiments, remote units also include a graphic user interface. Remote units can be operable to calculate the set and drift of marine locator devices and/or operable to calculate the course of intercept of the marine locator device. 
   Marine locator devices and systems as described herein can provide significant advantages including increased ease of manufacture and use and improved functionality. Marine locator device that do not use pyrotechnic signaling mechanisms can be less dangerous to manufacture, can have less stringent storage requirements, and can be less likely to pose personnel safety issues during and after use. For example, a marine locator device without pyrotechnic components that washes ashore after use does not contain a residue of compounds, such as red phosphorus, that might ignite as the device is being examined by a beach-goer. This also can lead to reduced certification requirements. For example, Hazards of Electromagnetic Radiation to Ordnance (HERO) or Weapon System Explosive Safety Review Board (WSESRB) certifications required before devices containing explosive/pyrotechnic material can be brought aboard US Navy ships can be avoided. 
   Global Positioning Systems and beacon lighting technologies can be combined to form a new marine location device. A Global Positioning System/Radio Beacon can provide pinpoint location of the marker while the infrared beacon feature more effectively enables a pilot&#39;s night time referencing with night vision goggles. Additional sensors can be included to provide information such as, for example, temperature and sea state, that can aid planning and prioritization of recovery efforts. Control of marine locator device components from a remote unit can provide increased operational security by minimizing emissions from the device to those necessary for recovery efforts and providing for a remote scuttling option. Control from a remote unit can also provide for increased operational effectiveness. For example, a marine locator device can be controlled to switch from visible light emission to infrared emission as a helicopter pilot using night vision goggles approaches. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  is a schematic of a marine locator system. 
       FIG. 2A  is a side cross-section of a marine locator device. 
       FIG. 2B  is an enlarged cross-section of a portion of the marine locator device of  FIG. 2A . 
       FIG. 3A  is a top view of the marine locator device of  FIG. 2  with a lid attached and covering a light section. 
       FIG. 3B  is a top view of the marine locator device of  FIG. 2  with the lid removed and exposing the light section. 
       FIG. 4  is a front view of a graphic user interface on a remote device. 
   

   Like reference symbols in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a locator system  10  includes a marine locator device  14  and a remote unit  18  on a control craft  22  (e.g., a ship, a boat, or a helicopter). Marine locator device  14  is deployed (e.g., thrown overboard, dropped from an aircraft) in the vicinity of an object or person  30  to be tracked in a body of water  34 . For example, marine locator device  14  can be dropped from a search and rescue aircraft in the vicinity that a person is observed in the ocean. Although the location of person  30  can change in the time between an initial sighting and the arrival of a recovery craft due to the effects of wind, waves, and currents, the location of marine locator device  14  deployed in vicinity of person  30  will experience similar movements due to the effects of these same forces. 
   Marine locator device  14  includes a light section  38 , a positioning system  42 , a temperature sensor  46 , and a transceiver  50 . Positioning system  42  calculates the geographic position (e.g., latitude and longitude) of marine locator device  14  based on position signals  62  from satellites  64 . Temperature sensor  46  measures the temperature of the water in which marine locator device  14  is deployed. Transceiver  50  broadcasts an information signal  72  including the geographic position of marine locator device  14  as well as output of temperature sensor  46 . The water temperature as measured by temperature sensor  46  can be used to estimate survival time of a person in the water. 
   As a recovery craft approaches the approximate location of marine locator device  14 , light section  38  emits a light signal  54  above a water surface  58  in response to a control signal  76  transmitted by remote unit  18  and received by transceiver  50 . Light signal  54  aids in final localization of the marine locator device  14  and can be particularly useful under conditions (e.g., during combat operations) when ongoing electronic emissions may be undesirable. In some cases, control craft  22  acts as the recovery craft. In some cases, the recovery craft and control craft  22  are separate units. 
   Remote unit  18  includes a remote transceiver  80  and a user interface  84 . Remote unit  18  is positioned aboard control craft  22 . Remote transceiver  80  is in communication with user interface  84  through a communication channel  88 . Remote transceiver  80  receives information signal  72  and transmits the information signal through communication channel  88  to user interface  84 . In response to information signal  72 , an operator  94  maneuvers control craft  22  in the direction of marine locator device  14 . Through user interface  84 , operator  94  generates control signal  76  to be broadcast from remote transceiver  80  to control the operation of marine locator device  14 . 
   Referring to  FIGS. 2A and 2B , marine locator device  14  includes a housing  96  to allow the marine locator device to withstand high-impact shocks or abrasion and cold or hot environmental conditions in storage or use without negatively impacting the performance of the device. Marine locator device  14  can be constructed to be of sufficient durability to withstand rough handling during storage and the impact forces during deployment and use. The durability will be accomplished by utilizing various material types and internal design features so that the marine locator device will operate as designed. In some embodiments, housing  96  is a cylindrical tube measuring approximately 21.7 inches (0.69 m) in length with an approximately 5-inch (12.7 cm) outer diameter to match the size envelope of an MK 58 MOD 1 Marine Location Marker (MK 58). This size combination allows marine locator device  14  to fit within current storage units used by the United States Navy, thereby facilitating the use of marine locator device  14  as a replacement for the MK 58. 
   Housing  96  is designed to allow the marine locator device  14  to withstand a launch from an aircraft (e.g., a fixed-wing aircraft flying at an altitude of 750 ft and a speed of 350 knots). Accordingly, housing  96  is a single piece with a top opening  100  and a bottom opening  104  made of a metal alloy, for example a corrosion resistant alloy such as aluminum, brass, plated steel, or stainless steel. For example, housing  96  may be formed using an extruded tube in a standard tube size (e.g., nominally 5.0 inches (12.7 cm) outer diameter with a wall thickness of between about approximately 0.0157 inch (0.4 millimeter) or 28-30 gauge standard steel) to minimize production costs and ensure production quality. Housing  96  can also be two or more pieces joined together to form a watertight seal. For example, pieces may be joined together using a weld, an adhesive, or an interference fit. Housing  96  can also be made of a high-impact plastic or other synthetic material such as nylon, polyvinyl chloride (PVC), or polycarbonates. 
   Crimps  108  are formed into housing  96 . Crimps  108  increase the ability of housing  96  to withstand stresses without substantially deforming. For example, in the embodiment shown, crimps  108  allow housing  96  to better resist buckling stress that may result from launching marine locator device  14  from a moving aircraft or ship. In other embodiments, crimps  108  may be configured in other directions to resist additional stresses experienced by marine locator device  14  in use. In still other embodiments, crimps  108  may allow housing  96  to be gripped more securely by a person handling marine locator device  14 . 
   The strength of housing  96  is reinforced by one or more support members  92  arranged along the inner surface of housing  96 . For example, for embodiments including housing  96  as a cylindrical tube, support members may be rings with outer diameters approximately equal to the inner diameter of the housing. In these embodiments, the support members may be arranged along the inner surface of the housing an interference fit. 
   Marine locator device  14  includes a power supply  112 . In the embodiment shown, power supply  112  is multiple batteries  114  arranged in a column coaxially aligned with the centerline axis  116  of housing  96 . Power supply  112  can be replaceable and/or can be rechargeable. For example, power supply  112  may be recharged with power supply  112  still contained within marine locator device  114 . As another example, power supply  112  may be removed from marine locator device  114  and subsequently recharged. 
   In some embodiments, including the embodiment shown, power supply  112  includes batteries  114  of a standard size. Configuring power supply  112  to operate on batteries  114  of a standard size minimizes the cost of power supply  112  and facilitates the procurement of replacements for batteries  114 . For example, batteries  114  are standard D-cell batteries. To facilitate the use of batteries  114  of a standard size, power supply  112  includes a battery tube plug  118 . In this embodiment, battery tube plug  118  holds batteries  114  in a fixed position within marine locator device  14  by preventing batteries  114  from moving along centerline  116 . To prevent short-circuiting of an electric circuit including power supply  112 , battery tube plug  118  is made of a non-conductive material (e.g., rubber or a similar synthetic material). 
   It should be appreciated that the range and operating time of marine locator device  14  will be proportional to the size (e.g. volume and weight) of power supply  112 . Thus, to maximize the range and operating time of marine locator device  14 , the size of power supply  112  should also be maximized. However, the upper end of the permissible size of power supply  112  may be limited by the desired weight, dimensions, and weight distribution of marine locator device  14 . In some embodiments, power supply  112  includes eight D-cell batteries arranged in a column. In some embodiments, power supply  112  occupies a volume of approximately 25.69 in 3  (421 cm 3 ) and weighs approximately 2.43 lb (1.1 kg). In some embodiments, the nominal voltage of power supply  112  is 6 volts direct current with a capacity of 18-20 Amp-hours. In some cases, batteries  114  are arranged electrically into two banks. 
   In many embodiments, power supply  112  is deactivated when marine locator device  14  is not in use. For example, power supply  112  may be in a deactivated state when marine locator device  14  is stored aboard a ship. This increases the probability that power supply  112  will be at or near its maximum state-of-charge when marine locator device  14  is deployed into the water. 
   In some embodiments, power supply  112  may be activated by a user through a manual operation—e.g., flipping a switch to complete an activation circuit. In other embodiments, power supply  112  may become activated when marine locator device  14  is immersed in water for more than a few seconds. For example, power supply  112  may become activated when a sufficient volume of water enters into a battery activation chamber to complete the power supply circuit. 
   A bottom end  120  of marine locator device  14  is opposite a top end  124  of the marine locator device. The weight of marine locator device  14  is distributed such that the center of gravity of the marine locator device is located on axis  116  of the marine locator device closer to bottom end  120  than to top end  124 . Although the orientation of marine locator device  14  is subject to environmental effects, the shape and location of the center of gravity bias the marine locator device towards an orientation in which bottom end  120  is below water and top end  124  above water when the marine locator device has been deployed. In particular, a weight  128  is fixed proximate to bottom end  124 . In some embodiments, the amount and position of weight  128  may be adjusted to allow the center of gravity of marine locator device  14  to match the center of gravity of the MK 58. It should be appreciated that if the physical dimensions and weight of the marine locator device  14  match those of the MK 58 then further matching the center of gravity of the MK 58 allows marine locator device  14  to exhibit the same aerodynamic characteristics as the MK 58. In some embodiments, components (e.g., power supply  112 ) are chosen and arranged to provide the desired weight and center of gravity without the use of weight  128 . 
   A bottom cap  132  is attached to bottom opening  104  of housing  96  to form a watertight seal, preventing water from entering marine locator device  14 . In some embodiments, a permanent weld produces a watertight seal between bottom cap  132  and bottom opening  104 . In other embodiments, the watertight seal between bottom cap  132  and bottom opening  104  is achieved by threading bottom cap  132  into the inner surface of housing  96 , thereby compressing an o-ring between the bottom cap and the housing to form a watertight seal. Other sealing mechanisms (e.g., gaskets) can also be used. 
   Removable plug  124  is removable to provide access to power supply  112 . For example, a user may remove removable plug  124  to replace or recharge power supply  112 . In one embodiment, removable plug  124  threads into bottom cap  132  to compress an o-ring between the removable plug and the bottom cap to form a watertight seal. In another embodiment, removable plug  124  may include a water soluble portion that dissolves after a period of exposure to water, allowing water to enter and sink marine location marker  14 . Some embodiments of marine locator device  14  without a removable power supply do not include removable plug  124 . 
   A portion of the volume of the marine locator device  14  includes filler material  140  such as a resilient, medium-density (˜3.6 pounds per cubic foot (57.67 kg/m 3 ) foam. In many embodiments, filler material  140  fills empty cavities within the marine locator device  14 . For example, in the embodiment shown, filler material  140  fills the annular cavity between power supply  112  and housing  96 , preventing power supply  112  from moving in the radial direction. In some embodiments, filler material  140  is of sufficient resilience to absorb shock and vibrations experienced by marine locator device  14 . In some embodiments, filler material  140  provides thermal insulation to allow the marine locator device  14  to operate in cold water. 
   In the embodiment shown, filler material  140  is biodegradable foam, for example a foam based on soy starch or corn starch (e.g., GreenCell®). In this embodiment, the biodegradable foam provides positive buoyancy to marine locator device  14  while the biodegradable foam is dry. However, the biodegradable foam begins to degrade and dissolve when it is exposed to water. Thus, when the watertight integrity of housing  96  is breached, the annular region once filled with filler material  140  becomes filled with water and the marine locator device  14  begins sinking. That is, in this embodiment, the marine locator device  14  can be scuttled by displacing filler material  140  with water such that the marine locator device becomes negatively buoyant. 
   Filler material  140  may be a combination of two or more types of foam. In some embodiments, a combination of foams with varying degrees of degradability in water are used for filler material  140 . In these embodiments, adjusting the volumetric fraction of slower-degrading foam relative to faster-degrading foam (e.g., Eco-Foam) changes the sinking time for marine locator device  14 . Thus, in these embodiments, the composition of filler material  140  may be adjusted to achieve a desired sinking time for marine locator device  14  (e.g., fifteen minutes after filler material  140  is first exposed to water). 
   Temperature sensor  46  of marine locator device  14  is a surface mounted thermistor or resistance temperature detector (RTD) probe permanently mounted to the inside skin of housing  96  in a location which is below the waterline of the marine locator device when deployed. Temperature sensor  46  thus measures the temperature on the inside of housing  96  as a proxy for the temperature of the water surrounding marine locator device  14 . The thermistor can be of the Negative Temperature Coeffecient (NTC) or Positive Temperature Coeffecient (PTC) type. This arrangement of the temperature probe does not require any protrusions beyond the surface of housing  96 , thus maintaining the surface characteristics desired for air launch. Some non-air launch embodiments include other temperature sensor configurations (e.g., temperature sensors with external probes to measure local water temperature directly or temperature sensors potted flush with the outer surface of marine locator device  14 ) and/or other temperature sensors (e.g., thermocouple). 
   Positioning system  42  and transceiver  50  of marine locator device  14  are incorporated with a microcontroller into an electronics package  144  mounted in housing  96 . The electronics of marine locator device  14  are encased in a shock-proof material (e.g., a urethane based, electronics grade potting material) so that the device handling, deployment, and environments encountered will not adversely affect the performance of the electronics and lighting located in the device. The microcontroller incorporated into electronics package  144  can be implemented through a combination of hardware and/or software components, modules, and tools. 
   In the illustrated embodiment, positioning system  42  and transceiver  50  are separate units that communicate with and are controlled by the microcontroller. In some alternate embodiments, the functions of positioning system  42  and transceiver  50  are features of the microcontroller itself. Electronics package  144  also provides encryption/decryption, timing, and activation/deactivation modules. These modules also can be implemented through a combination of hardware and/or software and can be separate units that communicate with and are controlled by the microcontroller or can be features of the microcontroller itself. 
   The encryption/decryption modules provide for secure transmissions when marine location device is being used in potentially hostile environments. However, the encryption/decryption modules can be deactivated when it is desired that anyone with a remote unit  18  be able read information signal  72  (e.g., when a civilian search and rescue operation is being conducted). In such instances, information signal  72  will be unencrypted but command functions of the microcontroller will be limited to remote units  18  with authorized access (e.g., verified with a password or requiring a specific encrypted control signal  76 ). Timing and activation/deactivation modules can provide for power conservation and security by turning off system components that are not being used and/or limiting active transmissions from marine locator devices  14 . 
   Positioning system  42  is a global positioning system (GPS) unit that includes a GPS antenna  148  mounted on electronics package  144 . In this embodiment, GPS antenna  148  is an antenna with a flat profile (e.g., a patch antenna). Use of a flat profile antenna maintains the surface characteristics desired for air launch. Transceiver antenna  152  similarly mounted on electronics package  144  is also a flat profile antenna for the same reason. Some non-air launch embodiments include other antenna configurations. 
   As discussed above, positioning system  42  calculates the geographic position (e.g., latitude and longitude) of marine locator device  14  based on position signals  62  from satellites  64 . The microcontroller receives position information from positioning system  42  and water temperature information from temperature sensor  46 . The microcontroller then uses transceiver  50 , under circumstances described in more detail below, to broadcast information signal  72  including the geographic position of marine locator device  14  and local water temperature. In some embodiments, other sensors (e.g., a sea state sensor) included in marine locator device  14  provide information to the microcontroller that can be included in information signal  72 . 
   Marine locator device  14  optionally includes a scuttling device  154  operable to breach the watertight integrity of housing  96  to sink the marine locator device. This can be desirable, for example, as a means of preventing the recovery of marine locator device  14  by unfriendly forces. In this embodiment, scuttling device  154  is a solenoid actuated valve in communication with and controlled by the microcontroller. Thus, marine locator device  14  can be scuttled, for example, a set period of time after deployment, as the power supply reaches a preset minimum level, or in response to a command included in control signal  76 . The use of a non-pyrotechnic scuttling device  154  reduces concerns associated with the storage and disposal of explosive material. In some embodiments designed for applications where on-command scuttling is not required, marine locator device  14  includes a water-soluble scuffling device which dissolves after immersion for a specific period of time. 
   Referring to  FIGS. 2A ,  2 B,  3 A, and  3 B, light section  38  includes a white light emitter  156  and an infrared emitter  160 . A protective cover  164  is mounted to adjacent to emitters  156 ,  160  against the inside surface of housing  96 . Protective cover  164  is fabricated from a clear high-impact resistant material such as acrylic, Lexan®, or other durable synthetic material that has high light transmission properties and is scratch/scuff resistant. Spacers  168  and gaskets  172  are located along the inner surface of housing  96  between protective cover  164  and electronics package  144  to help maintain the separation between the protective cover and the electronics package. Gaskets  168  are configured to prevent moisture intrusion into the device even when subjected to pressures of several times the normal operating conditions encountered and can be manufactured from rubber or synthetic material. In this embodiment, light emitters  156 ,  160  include appropriate spectrum frequency diodes focused parallel to axis  116  and toward top end  124  of marine locator device  14 . Relative to arrays of emitters, this configuration increases the likelihood that light will be visible to aerial searchers even in high sea states (e.g., the focused light is more likely to penetrate airborne water particles associated with large waves). However, omni-directional strobes may also be used in some configurations. In some embodiments, a single light emitter with switchable filters, in place of the multiple light emitters, is used to selectively emit visible or infrared light. 
   Referring to  FIGS. 2B and 3A , marine locator device  14  includes a lid  176  mounted on housing  96  over protective cover  164  to prevent damage to the protective cover during handling and storage. Lid  176  includes a pull-away cover  180  with an attached D-ring  184  to facilitate removal of the pull-away cover. In this embodiment, lid  176  is manufactured of a corrosion resistant metal such as, for example, stainless or plated steel sheet or aluminum alloy. However, in some embodiments, other materials such as, for example, impact resistant plastics are used. Similarly, some embodiments use other configurations of lids  176  (e.g., lids screwed onto threads machined in the outer surface of housing  96 ) or omit lids altogether. Lids  176  are removed prior to deployment of marine locator devices  14  (e.g., by air crew members loading the devices aboard a search and rescue aircraft or by shipboard lookouts prior to throwing a marine locator over the side in the vicinity of a person who has fallen overboard). Lids  176  can also be configured for automatic removal by a launch system as part of device deployment. 
   Referring to  FIG. 3B , white light emitter  156  and infrared emitter  160  are positioned on electronics package  144  in locations corresponding to the holes in existing MK-58 locator devices which are used for inflow of water and outflow of smoke and flames from these existing pyrotechnic-based locator devices. This positioning allows marine locator devices  14  to use housings produced for existing MK-58 locator devices. 
   Referring to  FIGS. 1 and 4 , user interface  84  of remote unit  18  of marine locator system  10  is a graphical user interface  188  that can be used to control marine locator device  14 . Remote unit  18  includes a processor that compares the geographic position of control craft  22  and/or the recovery craft (if a separate unit is being used to recover a person or object in the water) with the geographic location reported by marine locator device  14  through information signal  72 . Remote unit  18  is set to display the information reported by a specific marine locator device  14  or a set of specific marine locator devices. Remote units  18  can calculate and display the set and drift (e.g., the rate and direction of movement) of marine location devices  14  based on changes in reported position of the marine locator devices. 
   Graphical user interface  188  displays the bearing and range from control craft  22  to a marine locator device  14  designated as WALDOE 12345 both in text box  192  and in plot  196 . The bearing displayed can be relative bearing or true bearing. Graphical user interface  188  is configured to display the course and speed of control craft  22  as an arrow  200 . If a separate unit is being used recover the person or object in water, remote unit  18  can display the range and bearing of marine locator device  14  from the recovery craft rather than control craft  22  assuming that the position of the recovery craft (absolute or relative to the control craft) is known. If marine locator system  10  is being used to recover a person in the water and the time of water entry is known and entered into remote unit  18 , graphical user interface  188  displays time in the water as well as intercept time (e.g., the length of time it will take control craft  22  at present course and speed to reach marine locator device  14 ) and an estimated survival time based on the water temperature information transmitted by the marine locator device. Graphical user interface  188  also includes a touchscreen with buttons  204  to access menus controlling both remote unit  18  directly and marine locator device  14  via the selection of commands that will be included in control signal  76 . 
   For purposes of illustration, the operation of marine locator system  10  is described as applied to the recovery of a person in the water in an area where hostile forces are present. As discussed above, marine locator device  14  has various other applications including for example, marking the location of a person in the water during civilian search and rescue operations and marking the location of floating contraband that has been spotted by military or law enforcement personnel. Different configurations and operational uses of marine locator device  14  are appropriate for different applications. Accordingly, the method of operation described below is illustrative in nature and will be modified to fit actual applications. 
   In operation, marine locator device  14  will be loaded aboard a fixed wing aircraft (e.g., an F/A-18) prior to its launch as part of a search for a pilot downed in waters near an enemy coastline. Aircrew members loading marine locator device  14  will remove pull away cover  180  to prepare the marine locator device for deployment. Encrypted information signal and command signal settings on marine locator device  14  will be selected and the unit specific identifier of the marine locator device would be loaded into remote unit  18  as part of the preparation process. Upon sighting the downed pilot, the fixed wing aircraft will launch marine locator device  14  to land in the water in the vicinity of the downed pilot. 
   At this time, remote unit  18  will establish communications with marine locator device  14  and perform a system check on the marine locator device while the fixed wing aircraft is still on station and able to deploy a second marine locator device if necessary. After the system check, remote unit  18  will send control signal  76  placing marine locator device  14  in a passive mode (e.g., not transmitting information signal  72  or emitting light signals) while a recovery unit such as, for example, a helicopter moves towards the reported position. Marine locator device  14  can be set to periodically broadcast position updates or can be set to remain in passive mode until activated by a new control signal  76 . Both of these approaches reduce power usage of marine locator device  14  as well as limit emissions from the marine locator device that might attract the attention of hostile forces. Because both information signal  72  and control signal  76  are encrypted, the ability of hostile forces to access the position information contained in the information signal and/or to activate and control marine locator device  14  will be limited. 
   As the recovery unit approaches the general location of marine locator device  14 , remote unit  18  will send control signal  76  telling the microcontroller of marine locator device  14  to begin more frequent (e.g., continuous) transmission of information signal  72 . As the recovery unit approaches the specific location of marine locator device  14 , remote unit  18  can send control signal  76  commanding the microcontroller to stop transmitting information signal  72  and to activate light section  38  to provide of light signal  54  to guide the final approach of the recovery helicopter. If the pilot of the recovery helicopter is using nightvision goggles for night recovery, infrared emitter  160  will be activated. Alternatively, when nightvision goggles are not being used, white light will be used and emitter  156  will be activated. After arrival at the location of marine locator device  14 , the recovery craft will commence local search to find and recover the downed pilot. After recovery of the downed pilot, remote unit  18  will send control signal  76  commanding the microcontroller to activate scuttling device  154  thus allowing marine locator device  14  to fill with water and sink. 
   For some applications (e.g., small arm weapon targets and ship handling maneuvers), it is desirable for a marine location device to emit a steady display of smoke although a flame is not required. Smoke-generating marine location devices include environmentally friendly smoke-generating material (e.g., a mixture of chemicals such as potassium chlorate or potassium nitrate, sulfur, and sodium bicarbonate). The smoke-generating material can optionally include a coloring agent (e.g., dyes used for common firework art). The smoke-generating material is packed into device container with or in place of inert filler material with the duration of smoke controlled by the volume and weight of smoke-generating materials used. The ignition can be DC induced ignition (e.g., a electric match) from either a water activated battery or ignition button prior to manual launch. Smoke-generating marine location devices can include some or all of the features of the non-pyrotechnic embodiments described above. However, weight and volume requirements for smoke-generating material to generate smoke for a given duration can reduce the capacity of marine location devices to include all of the components of the non-pyrotechnic embodiments. Although containing pyrotechnic material, replacement of red phosphorus with environmentally friendly smoke-generating material can provide improvements in ease of manufacture, storage, and use. 
   A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. 
   For example, some marine locator device embodiments incorporate a sea-state sensor. Such a sea-state sensor can be of a mechanical or electronic nature with construction design features that shall detect and transfer motion information/data to the microcontroller. In some cases, a mechanical device includes a hollow tube or cylinder that will detect movement of a ball or roller inside the tube and estimate sea state based on the detected movements (e.g., inertia of the marine locator device causes a reaction to wave motion with the ball or roller making contact with each end of the tube in response to the wave-induced motion). Similarly, an electronic motion sensor located within the device could also be incorporated to provide the same sea-state data. 
   Accordingly, other embodiments are within the scope of the following claims.