Abstract:
Magnetic signature measurements are taken at various points corresponding to an original water depth beneath a ship. A computer processor receives and processes (i) this group of measured magnetic signature values and (ii) the designed magnetic signature value the sensing of which actuates the subject magnetic mine, implementing graph display management on a user interface display screen. According to the computer processing, some or all such measured magnetic signature values are extrapolated at different depths each greater than the original depth, thereby yielding several or many groups, each group being of extrapolated magnetic signature values associated with various points corresponding to the same depth, the groups collectively representing a three-dimensional arrangement of extrapolated magnetic signature values associated with various points corresponding to different depths. Each point is characterized as either actuating or non-actuating of the mine, and various perspectives of some or all such characterizations are displayed.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to magnetically responsive devices such as magnetic mines, more particularly to methods and apparatuses for evaluating the performance of a ship&#39;s degaussing system with respect to threats posed by magnetic mines that are situated in a marine environment. 
   A mine is an explosive device which is usually concealed either underground or underwater, and which is used primarily by military forces for defensive purposes. Mines typically are self-contained devices which include an explosive capability and a detonator (a firing mechanism for triggering the mine explosion), and which explode when touched by or approached by a target. “Minefields” are areas where mines have been placed. Generally there are two categories of mines, based on their situation, viz., “land mines” and “underwater mines” (synonymously referred to as “water mines,” “submarine mines,” “sea mines” or “naval mines”). 
   An underwater mine is a mine which is situated in or on water or contiguously with respect to water or which otherwise bears physical or functional relation to a water environment. A typical underwater mine comprises an explosive charge positioned underwater and set to fire in response to the presence of a marine vehicle (e.g., a ship or submarine) in contact therewith or in proximity thereto. Underwater mines are generally laid in the water for purposes of damaging or sinking ships or of deterring ships from entering an area. “Moored mines” are underwater mines having positive buoyancy, typically held below the water surface at a pre-selected depth by a mooring (e.g., cable) attached (e.g., tethered) to an anchor (e.g., on a sea bottom). “Bottom mines” are underwater mines having negative buoyancy and resting on a seabed (e.g., at the bottom of relatively shallow water). “Floating mines” are underwater mines that are not entirely underwater but are visible on the surface. 
   Underwater mines are triggered either by direct contact or by indirect influence. Typically, when an underwater mine is triggered, an expanding gas sphere caused by the explosion sends shock waves through the water, these shock waves having deleterious effects on the nearby target marine vessel. “Contact mines” are actuated as a result of physical contact between the target ship and the mine&#39;s casing or one or more of the mine&#39;s appendages (e.g., rods or antennae protruding from the mine&#39;s surface). “Influence mines” are actuated either as a result of sensing an “influence field” emanating from the target marine vessel, or as a result of the target marine vessel&#39;s intrusion within an “influence field” emanating from the mine. Generally, influence mines sense changes in physical patterns in surrounding water, such as pertaining to magnetic fields (“magnetic mines”), pressure change (“pressure mines”) or sound waves (“acoustic mines”). 
   U.S. Navy surface combatant ships are equipped with degaussing systems comprising a set of current-carrying coils which are adjusted to reduce the ship&#39;s magnetic field and thereby reduce it&#39;s vulnerability to the magnetic mine threat. Currently, performance of U.S. naval combatant degaussing systems is determined by recording the combatant&#39;s magnetic field at a Magnetic Silencing Facility (MSR), measuring the peak field, and adjusting degaussing coil currents to reduce this peak field to less than a specified level. 
   However, magnetic mines do not operate by measuring the peak value of a ship&#39;s magnetic field; rather, magnetic mines operate by measuring the rate of change of a ship&#39;s magnetic field. In addition, many mines measure the rate of change in the ship&#39;s horizontal magnetic fields to determine when to actuate. Current methods for measuring combatant degaussing system performance may not reflect the combatant&#39;s actual susceptibility to the magnetic bottom mine threat. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, it is an object of the present invention to provide an improved methodology for assessing the performance of a ship&#39;s degaussing system relative to underwater magnetic mine threat. 
   It is another object of the present invention to provide such a methodology wherein an improvement resides in the concordance of the performance assessment with the mine&#39;s designed criterion for actuation thereof. 
   In accordance with typical embodiments of the present invention, a method is provided for visually representing information pertaining to the threat to a vehicle of a magnetically responsive device of interest. The inventive method comprises the steps of: (a) determining a relationship, in a spatial region, between magnetic signature data and device actuation data; and, (b) effecting a display indicative of the relationship. The magnetic signature data pertains to the vehicle. The device actuation data pertains to the magnetically responsive device. 
   According to frequent practice of such inventive methodology, the magnetically responsive device is a magnetic mine. The device actuation data is mine actuation data. The magnetic signature data includes plural magnetic field values associated with the vehicle. The magnetic field values correspond to plural locations in the spatial region. Each magnetic field value corresponds to a different location in the spatial region. The mine actuation data includes plural mine actuation criteria associated with the magnetic mine. The actuation criteria correspond to plural locations in the spatial region. Each actuation criterion corresponds to a different location in the spatial region. The determination of a relationship between the magnetic signature data and the mine actuation data includes establishing a correlation, in the spatial region, between the magnetic field values and the mine actuation criteria. 
   According to typical inventive practice, each actuation criterion is used by the magnetic mine for the purpose of making a threshold determination of whether or not the magnetic mine actuates at that particular location—i.e., a threshold determination of actuation of the magnetic mine versus non-actuation of the magnetic mine at such location. Each actuation criterion includes consideration of at least one influence parameter, at least one of which is a magnetic influence parameter (i.e., pertains to magnetic field or magnetic signature). For instance, each actuation criterion can be based at least in part on a magnetic influence parameter pertaining to the magnetic field rate-of-change value. 
   Typically according to practice of the present invention, the vehicle is a nautical vehicle. The determination of a relationship between the magnetic signature data and the mine actuation data includes extrapolating plural measured magnetic field values associated with the nautical vehicle so as to obtain plural two-dimensional arrays of extrapolated magnetic field values. Each two-dimensional array corresponds to a different water depth which is greater than an initial water depth. The correlation is between the extrapolated magnetic field values and the mine actuation thresholds, a two-dimensional array of measured magnetic field values having been obtained at the initial water depth. According to some inventive embodiments, the determination of a relationship between the magnetic signature data and the mine actuation data includes obtaining the two-dimensional array of said measured magnetic field values. 
   In accordance with many embodiments of the present invention, a computer program product comprises a computer useable medium having computer program logic recorded thereon for enabling a computer system to display, on a display screen of said computer system, information pertaining to the vulnerability of a marine vessel to an underwater magnetic mine. The present invention&#39;s computer program logic comprises: (a) means for enabling the computer system to extrapolate magnetic signature measurement values, taken at various locations at a selected water depth, so as to obtain a three-dimensional matrix of magnetic signature extrapolation values existing at various locations at various water depths greater than the selected water depth; (b) means for enabling the computer system to relate a magnetic mine model to the three-dimensional matrix of magnetic signature extrapolation values, wherein the magnetic mine model includes a criterion for actuation of a magnetic mine for each of various locations, and wherein at each of various locations the magnetic signature extrapolation value is understood to either satisfy or not satisfy the magnetic mine actuation criterion; and, (c) means for enabling the computer system to render a graphical representation informative of the relation of the magnetic mine actuation criterion to the three-dimensional matrix of magnetic signature extrapolation values. According to typical such embodiments, the computer program logic further comprises means for enabling the computer system to adjust the number of magnetic signature measurement values prior to the extrapolation. 
   Many inventive embodiments provide apparatus comprising a machine having a memory. The machine contains a data representation pertaining to hazard posed to navigation by a magnetic water mine. The data representation is generated, for availability for containment by the machine, by the method comprising: (a) extrapolating measured magnetic field values to obtain a three-dimensional array of extrapolated magnetic field values; and, (b) associating the three-dimensional array with a model pertaining to actuation of the mine. The measured magnetic field values correspond to a shallowest water depth. The extrapolated magnetic field values correspond to at least two deeper water depths. Each extrapolated magnetic field value is defined as being either one (but not both) of the following: (i) a magnetic field value which does not actuate the mine; and, (ii) a magnetic field value which does actuate the mine (That is, in an exclusively disjunctive manner, each extrapolated magnetic field value is defined as meeting either condition “(i)” or condition “(ii)”). According to typical such embodiments, the inventive apparatus further comprises another machine for graphically representing at least one aspect of the association of the three-dimensional array with the model pertaining to mine actuation. 
   According to typical embodiments, the present invention&#39;s “Degaussing Vulnerability Display Program” enables the rapid determination of the performance of a surface combatant&#39;s degaussing system against the magnetic mine threat, with visualization of both the ship&#39;s magnetic signature and resulting mine actuation contours. The present invention&#39;s degaussing vulnerability display program provides a new metric for measuring degaussing system performance. Using accurate mine models and extrapolation techniques, the inventive program enables degaussing engineers at magnetic silencing facilities to rapidly compute and visualize a surface combatant&#39;s vulnerability to the magnetic mine threat. Moreover, the present invention admits of mine threat vulnerability assessment in terms of the specific kind of magnetic field phenomenon (e.g., rate of change of magnetic field) that, according to the design of a given magnetic mine, precipitates actuation of such given magnetic mine. 
   A “mine model” (also known as a “mine simulation”) is a representation of the decision-making process that a particular mine undergoes in order to determine whether or not to actuate under various circumstances. Typically, a mine model is a computer mine model (or computer mine simulation)—e.g., a software simulation of the process that an actual mine uses to determine when to actuate. A mine can use one influence signature, or a combination of plural influence signatures, in the mine&#39;s process of determining when to actuate. For example, an acoustic signature can be used together with a magnetic signature in the mine&#39;s detection-and-actuation process. Basically, any measurable signature emitted by a passing target can be used in the mine&#39;s detection-and-actuation process. For inventive embodiments which are practiced in association with plurally influenced devices, it is assumed that all other (e.g., non-magnetic) influence parameters are satisfied; that is, it is assumed that all influence parameters which are unrelated to the type(s) of influence parameter(s) with which the inventive embodiment is concerned (viz., magnetic influence parameters, which are influence parameters involving magnetic field or magnetic signature) are satisfied. 
   A magnetic mine model/simulation incorporates data obtained through testing of the magnetic mine of interest. Generally, a mine model/simulation is based upon experimentally obtained data concerning the behavior of the subject mine. The mine is tested by ascertaining how the mine reacts under various circumstances (e.g., at various distances from or locations relative to various stimuli). In particular, investigation involves when the mine actuates and when it does not under various conditions. In this manner, the investigators can rather accurately determine the mine&#39;s functional characteristics. The information thus learned can be used for computer modeling (computer simulating) the mine&#39;s behavior. 
   Techniques for testing mines and preparing computer models/simulations are well known in the pertinent arts. For instance, one who is ordinarily skilled in computational sciences (or a related mathematical, scientific or engineering discipline) and who is tasked with computer modeling/simulating a mine&#39;s behavior would be capable of applying his or her skill for such assignment. The inventive practitioner(s) may or may not have participated in mine testing and/or mine modelling/simulating; in any event, in the light of the instant disclosure, the inventive practitioner(s) will be capable of practicing the present invention. Ordinarily skilled artisan or artisans who read the instant disclosure will be capable of utilizing a mine model/simulation (e.g., in order to evaluate ship degaussing performance) in accordance with the present invention. 
   The term “mine model” as used herein refers to any model or simulation of or relating to a mine&#39;s behavior. A mine model is typically in computer software form. The term “magnetic mine” as used herein refers to any mine that is influenced by one or more phenomena involving magnetism, regardless of whether and to what extent the mine is influenced by one or more phenomena not involving magnetism (such as involving acoustics or pressure). The term “mine actuation criterion” as used herein refers to the standard, rule or test on which a mine (e.g., in its processing) bases its judgment or decision as to whether or not to actuate. A mine actuation criterion can be characterized by any degree of complexity and can include consideration of any singular or plural number of parameters (factors). 
   The present invention&#39;s degaussing vulnerability display program has several other features and advantages that are consistent with U.S. Navy goals. Firstly, input to the inventive program comes from the binary range data files collected by the U.S. Navy&#39;s magnetic silencing facilities; this will enable vulnerability of a ranged combatant to be determined quickly after ranging, either at the magnetic silencing facility or onboard the ranged ship—e.g., simply by copying the data file to a floppy disk and sending the disk to the ship. Furthermore, the inventive program is able to display onset-of-actuation contours at multiple depths in a plan view, allowing the user to select the depth of display. In addition, the inventive program is capable of displaying, in an elevation view, the overall onset-of-actuation curve for all depths at which actuation will occur. Moreover, the inventive program is very easy to use and is interactive, with quick as possible turn-around. Finally, the inventive program has an architecture which will allow new mine models to be added as new mines are exploited and new models developed. 
   This application bears some relation to the following pending U.S. nonprovisional patent applications, each of which is incorporated herein by reference: Ser. No. 09/746,535, filing date 21 Dec. 2000, (patent application) publication no. 2002/0080138 A1, publication date 27 Jun. 2002, invention entitled “Mine Littoral Threat Zone Visualization Program,” sole inventor Paulo Bertell Tarr; Ser. No. 09/721,998, filing date 27 Nov. 2000, invention entitled “Optimal Degaussing Using an Evolution Program,” joint inventors Paulo Bertell Tarr and Nevin D. Powell. 
   Other objects, advantages and features of this invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
   BRIEF DESCRIPTION OF THE APPENDICES 
   The following appendices, representative of computer code in accordance with the present invention, are hereby made a part of this disclosure: 
   Attached hereto marked “APPENDIX A” (2 pages) and incorporated herein by reference is a file entitled “dvd4Doc.h.txt,” which sets forth header code for the document code set forth in “APPENDIX B.” 
   Attached hereto marked “APPENDIX B” (9 pages) and incorporated herein by reference is a file entitled “dvd4Doc.ccp.txt,” which sets forth document code. 
   Attached hereto marked “APPENDIX C” (4 pages) and incorporated herein by reference is a file entitled “dvd4View.h.text,” which sets forth header code for the view code set forth in “APPENDIX D.” 
   Attached hereto marked “APPENDIX D” (63 pages) and incorporated herein by reference is a file entitled “dvd4View.ccp.txt,” which sets forth view code. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein like numbers indicate the same or similar components, and wherein: 
       FIG. 1  is a block-and-flow diagram of an embodiment of the “Degaussing Vulnerability Display Program” in accordance with the present invention. 
       FIG. 2  is a diagrammatic perspective representation of an embodiment of inventive practice in association with a ship such as shown in  FIG. 1 , particularly illustrating the inventive generation of a three-dimensional interrelationship between (i) calculated magnetic signature extrapolation values and (ii) known actuation characteristics of a given magnetic mine. 
       FIG. 3  is a conceptual representation including four two-dimensional arrays (in plan view) arranged in diagrammatical flow format, particularly illustrating how, in accordance with an embodiment of the present invention, a two-dimensional array of extrapolated signature value locations is interrelated with a particular mine&#39;s actuation properties so as to yield either actuation or non-actuation of the mine at each location of the two-dimensional array. 
       FIG. 4  is a diagrammatic perspective representation similar to that shown in  FIG. 2 , particularly illustrating the inventive generation of a three-dimensional magnetic mine vulnerability region (delimited by a three-dimensional mine actuation surface) located beneath the ship, such generation being based on a three-dimensional interrelationship such as shown in  FIG. 2 . 
       FIG. 5  is a block-and-flow diagram concordant with that shown in  FIG. 1 , particularly illustrating computer implementation of the present invention. 
       FIG. 6  is a pictorial representation of a computer user interface having an overview display window, wherein the display window is shown to include four visual displays, viz., a “Run Information” display, a “Magnetic Signature Profile” display, an “Actuation Contour” display and an “Actuation Curve” display. 
       FIG. 7  is the view of the computer user interface shown in  FIG. 6 , wherein the display window is shown to predominately include an enlarged version of the “Magnetic Signature Profile” display shown in  FIG. 6 , such magnetic signature profile display depicting a vertical “slice” of the ship&#39;s magnetic signature, such vertical slice extending longitudinally (from bow to stern). 
       FIG. 8  is the view of the computer user interface shown in  FIG. 6 , wherein the display window is shown to predominately include an enlarged version of the “Actuation Contour” display shown in  FIG. 6 , such actuation contour display depicting a horizontal slice of an actuation surface, such horizontal slice extending longitudinally (from bow to stern). 
       FIG. 9  is the view of the computer user interface shown in  FIG. 6 , wherein the display window is shown to predominately include an enlarged version of what is essentially the “Actuation Curve” display shown in  FIG. 2 , such actuation contour display depicting a vertical slice of an actuation surface, such vertical slice extending athwartship (from port to starboard). 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference is now made to  FIG. 1  through  FIG. 5 . A ship  10  has a degaussing system installed thereon, and is thus equipped with plural L-coils  80   L , plural A-coils  80   A  and plural M-Coils  80   M , such as shown in  FIG. 2 . 
   As shown in  FIG. 1 , ship  10  is “ranged” at a “Magnetic Silencing Facility” (“MSF”)  12 , using magnetic sensors (e.g., magnetometers)  11 . The magnetic field of ship  10  is recorded in a range file  14 . The inventive program (the present invention&#39;s “Degaussing Vulnerability Display Program”) reads the range file  14  into a signature array  16 . The inventive program “decimates” signature array  16  to a decimated signature array  18  which is suitable for extrapolation. Signature array  16  and decimated signature array  18  correspond to the same water depth. 
   When an underwater magnetic mine model  22  is selected, the decimated signature  18  is extrapolated to produce the ship&#39;s magnetic signatures  20  at deeper water depths. The extrapolated signatures  20   a ,  20   b ,  20   c  . . .  20   max  each represent a planar array of signature values at a particular water depth (e.g., the distance below the water surface w shown in  FIG. 2  and  FIG. 3 ), based on the configuration of the magnetic sensors  11  distributed below the ship  10  hull at magnetic sensing facility  12 . Each signature  20  is extrapolated from the planar signature array  16  derived from the range file  14  readings, such range file  14  readings having previously been taken (at a magnetic silencing facility  12 ) at a water depth shallower than that corresponding to any of the extrapolated signatures  20 . 
   As shown in  FIG. 1 , the combination of all of these signatures at varying water depths represents a three-dimensional array  200  of parallel planar arrays  20 . Each two-dimensional array  20  represents a kind of two-dimensional mathematical matrix of magnetic signature values, while the three dimensional array  200  represents a kind of three-dimensional mathematical matrix of magnetic signature values which is the aggregate of the plural two-dimensional arrays  20 . Extrapolated signatures  20  are processed in association with a mine model  22 , and the resulting actuation contour is stored in the actuation surface  25 . If the inventive program is directed to plural mine models  22 , each mine model  22  has its own actuation surface  25  associated therewith. 
   If any mine actuation has occurred at the extrapolation depth, the depth is incremented, the signature is extrapolated at the new depth, the signature is processed with the mine model, and the new actuation contour is added to the actuation surface. This process is repeated until a water depth is reached where actuation does not occur. At this point, all extrapolated signatures are in memory and any profile from any depth can be displayed in the program display  44 . The actuation surface is also complete at this point, so the actuation curve and any contour at any depth in the actuation surface can be displayed. 
   Particularly with reference to  FIG. 2  through  FIG. 4 , the inventive program associates the three-dimensional signature array  200  information with the mine model  22  information indicative of the magnetic actuation locations of a particular mine. Each two-dimensional signature array  20  has a mathematical array of signature values, each location  50  having its own corresponding signature value. The magnetic signature array  200  is processed using the mine model  22  to determine actuation surface  25 . The inventive program permits an association between these two groups of information in terms of a causal relationship between magnetic signature indicia and mine actuation. Magnetic signature array  200  and mine model  22  are inventively cohered so that, at any given location in the region of interest, a threshold determination is made of whether or not a particular mine model  22  mine is actuated. Regardless of the nature of mine model  22  in terms its mine actuation processing, the present invention can utilize mine model  22  so as to process the magnetic signature  200  information and thereby determine mine actuation locations. 
   In the world of mine warfare, there are many types of mines having diverse actuation “thought processes.” Mine actuation processing varies both in principle and complexity. Each mine&#39;s mine model  22  reflect that mine&#39;s actuation processing characteristics. For instance, let us take a relatively simple case wherein the actuation of a mine depends only on the rate-of-change (e.g., peak rate-of-change) of the magnetic field; that is, rate-of-change is the only factor (influence parameter) characterizing the mine&#39;s actuation processing. Then, the inventive association of mine model  22  with 3-D signature array  200  (which is the combination of individual 2-D signature arrays  20  wherein each location  50  has its own corresponding magnetic field/signature value) involves a less complicated determination of magnetic field rate-of-change at each location; in other words, according to the mine model  22 , magnetic field rate-of-change is the only condition that needs to be satisfied in order to result in mine actuation. In this example, at each location  50 , mine  22  is characterized by a minimum (threshold) magnetic field value above which (or at or above which) such mine  22  is actuated. Each location  50  is related with mine model  22  in terms of the mine&#39;s threshold magnetic field value so as to manifest whether or not this threshold magnetic field value is reached, and hence mine  22  actuates, at such location  50 . 
   As another example, let us take a more complicated case wherein a mine&#39;s actuation depends on plural influence parameters, among which is the ship&#39;s magnetic field/signature (e.g., rate-of-change); another influence parameter can be, e.g., the ship&#39;s acoustic signature. Since there are plural conditions (each condition pertaining to an influence parameter) precedent to mine actuation, the present invention&#39;s processing (whereby mine model  22  is used to process 3-D signature array  200  to determine mine actuation locations) must take every such condition into account; hence, for any given location, the inventive processing&#39;s determination of mine actuation-versus-non-actuation examines all such conditions and decides whether the magnetic signature information corresponding to such location results in mine actuation. The magnetic signature phenomenon/phenomena will not result in mine actuation unless every other influence parameter condition is satisfied. 
   Inventive practice can involve any among diverse magnetic and non-magnetic influence parameters. Examples of non-magnetic influence parameters are those involving sound and pressure. Examples of magnetic (magnetic signature/field) influence parameters, any one or more of which can be that influence parameter (or among those influence parameters) which is (are) pertinent to inventive practice, include the following: magnetic field (e.g., peak magnetic field); rate-of-change (e.g., peak rate-of-change) of the magnetic field (e.g., in a segment of the magnetic field); root mean square of the magnetic field; distance of the magnetic field from a desired goal magnetic field. Terms such as “magnetic field value” and “magnetic signature value” are used interchangeably herein, and broadly refer to any physical parameter or parameters that relate to magnetic field or magnetic signature, including but not limited to those mentioned hereinabove. Rate-of-change (e.g., peak rate-of-change) will be an influence parameter for many inventive embodiments. 
   Upon association of each of the 2-D magnetic field arrays  20  (shown in  FIG. 1 ) with the pertinent magnetic field/signature parameter of a given mine  22 , 2-D magnetic field arrays  20  (shown in  FIG. 1 ) become 2-D mine actuation arrays  24  (shown in  FIG. 2 ). That is, upon association of 3-D magnetic field array  200  (shown in  FIG. 1 ) with the pertinent magnetic field/signature parameter of a given mine  22 , 3-D magnetic field array  200  (which is a collection of 2-D magnetic field arrays  20 , as shown in  FIG. 1 ) becomes 3-D mine actuation array  240  (which is a collection of 2-D mine actuation arrays  24 , as shown in  FIG. 2 ). Thus, 2-D magnetic field arrays  20   a ,  20   b ,  20   c ,  20   d ,  20   e ,  20   f ,  20   g , . . . become 2-D mine actuation arrays  24   a ,  24   b ,  24   c ,  24   d ,  24   e ,  24   f ,  24   g , . . . respectively. 
   This correlation of the mine  22  actuation value(s) with 3-D magnetic field array  200 , thereby forming 3-D mine actuation array  240 , is best visualized conceptually in  FIG. 3 , wherein multiple circles each represent a particular “uncorrelated” location  50  in a particular 2-D magnetic field array  20 . Mine model  22  is inventively utilized so as to process the magnetic signature  200  information and determine, based on the mine&#39;s design, where such mine is actuated (e.g., explodes). Each uncorrelated location  50  is related with mine  22  in terms of the mine&#39;s actuation criterion at such location  50  so as to manifest whether or not this actuation criterion is met (and hence mine  22  actuates) at such location  50 . The graphical representation is thus informative in an exclusively disjunctive demarcating fashion, wherein each location manifests either a mine actuation condition or a mine non-actuation condition. Cumulative manifestations, at some or all locations, of this either/or condition can be represented visually using delineation and/or contrasting shading and/or contrasting coloring on the display screen of a computer display  44 . 
   When a given uncorrelated location  50  (shown as an empty circle, or circular outline) of 2-D signature array  20  is correlated with mine  22  actuation information, that location  50  becomes either actuated location  50   ACT  (shown as a solid black circle) or non-actuated location  50   NON  (shown as a solid gray circle). Therefore, a given 2-D mine actuation array  24  describes “actuation-versus-non-actuation” of a mine  22 , as 2-D mine actuation array  24  can include: (i) all actuated locations  50   ACT  and no non-actuated locations  50   NON , as shown in 2-D mine actuation array  24   ACT ; or, (ii) all non-actuated locations  50   NON  and no actuated locations  50   ACT , as shown in 2-D mine actuation array  24   NON ; or, (iii) some (one or more) actuated locations  50   ACT  and some (one or more) non-actuated locations  50   NON , as shown in 2-D mine actuation array  24   ACTNON . 
   Each 2-D mine actuation array  24  is characterized by a two-dimensional pattern of actuated locations  50   ACT  and/or non-actuated locations  50   NON . The combination of these individual two-dimensional array actuation-versus-non-actuation patterns yields a three-dimensional “actuation surface”  25  which bounds the three-dimensional “actuation region”  250  of three-dimensional space. Actuation region  250  represents the sum of all locations, relative to ship  10 , at which mine  22  will be actuated. Actuation surface  25  represents the outer boundary of this actuation region  250 . 
   The graphical representation shown in  FIG. 4  is one of many ways in which, according to the present invention, information indicative of actuation surface  25  (or actuation region  250 ) can be displayed for human visualization or comprehension. As elaborated upon hereinbelow with reference to  FIG. 6  through  FIG. 9 , the three-dimensional actuation surface  25  (or actuation region  250 ) can be displayed as a crosswise “slice” in any of multifarious orientations, such as that which is described by the following: (i) existing in a vertical geometric plane oriented longitudinally through the ship  10  at any of various selected locations (e.g., through the centerline) from bow to stern (in a manner akin to that which is shown in  FIG. 7 ); (ii) existing in a vertical geometric plane oriented transversely through the ship  10  at any of various selected locations (e.g., through the midline) from port to starboard (in a manner akin to that which is shown in  FIG. 9 ); or, (iii) existing in a horizontal geometric plane oriented at any of various selected water depths below the ship  10  (in a manner akin to that which is shown in  FIG. 8 ). 
     FIG. 5  facilitates understanding of how the present invention will typically be practiced in association with computer apparatus. Range information  14  is input into computer system  40  that includes processor  42  (which includes a computer memory) and display  44  (which includes a computer user interface). Computer system  40  (in particular, processor  42 ) uses a computer program product (which includes a recording medium) in accordance with the present invention. In accordance with the inventive program, processor  42 : assimilates range information  14  into 2-D signature array  16 ; decimates 2-D signature array  16  into decimated 2-D signature array  18 ; extrapolates decimated 2-D signature array  18  into plural extrapolated 2-D signature arrays  20  at various water depths, which together constitute 3-D extrapolated signature array  200 ; associates 2-D extrapolated signature arrays  20  (i.e., 3-D extrapolated signature array  200 ) with one or more mine model  22  actuation values, resulting in 2-D actuation arrays  24 , which together constitute 3-D actuation array  240 . Display  44  displays (e.g., on a display screen) information indicative of the association between extrapolated signature arrays  20  (3-D extrapolated signature array  200 ) and the mine model  22  actuation value(s). 
   Computer system  40  can be located onboard ship  10  and/or offboard/ashore, e.g., at a magnetic silencing facility  12 . Generally according to inventive practice, there will be a one-to-one correspondence between 2-D extrapolated signature arrays  20  and 2-D actuation arrays  24 . Depending on the inventive embodiment, the decimation step can be performed or skipped by processor  42 ; if such decimation is omitted, processor  42  extrapolates 2-D signature array  16  directly into plural extrapolated 2-D signature arrays  20  at various water depths (which together constitute 3-D extrapolated signature array  200 ). In accordance with various embodiments of the present invention, the computer system  40  operations can be performed for any number of mine models  22  corresponding to a diversity of mine types. 
   Now with reference to  FIG. 6  through  FIG. 9 , in accordance with a preferred embodiment of the present invention&#39;s degaussing vulnerability display program, a display  26  includes a window  28 . As shown in  FIG. 6 , window  28  is the overview display window  28   OV . Overview display window  28   OV  is divided into four window display quadrants, viz.: the run information display  30 ; the magnetic signature profile display  32 ; the actuation contour display  34 ; and, the actuation curve display  36 . 
   After the inventive program has been started and a range file selected, the run information is printed in the information display  30 , shown in  FIG. 6  in the upper left quadrant of overview display window  28   OV . This information includes filename, ship  10  name, magnetic silencing facility (MSF)  12  at which the file was created, ship  10  heading, longitudinal spacing of the magnetic signature profiles, ship  10  speed and mine type  22 . 
   As shown in  FIG. 6  (in the upper righthand quadrant of overview display window  28   OV ) and  FIG. 7 , the ship&#39;s magnetic signature  32 ′ is plotted in the magnetic signature profile display  32 , one longitudinal profile at a time. The rate-of-change of the magnetic signature profile can be displayed as well, by selecting “Rate of Change” from the “Signature” menu, or by pressing the d/dt button in the toolbar  38 . The rate-of-change  32 ″ is also shown (shown in gray) in the magnetic signature profile display  32 . 
   The magnetic signature component to display (vertical, longitudinal, or athwartship) can be selected from the axis pop-up menu in the signature menu, or by pressing the z, x, or y button in the toolbar  38 . Just above the signature profile display  32  is a slider  40 , which can be dragged with the mouse to select which signature profile appears in the signature profile display  32 . The signature profile display  32  defaults to the keel profile when a file is first opened. Bow and stern locations are, indicated on the signature profile plot, as well as the location of longitudinal mine actuation, if any. 
   Clicking on the signature profile display  32  in the overview display window  28   OV  (shown in  FIG. 6 ) zooms it to fill the window  28 , window  28  thereby becoming signature profile display window  28   32  (shown in  FIG. 7 ), which can be resized as desired. Clicking on the zoomed signature profile display  32  in the signature profile display window  28   32  returns the program&#39;s signature profile display window  28   32  to the overview display window  28   OV  shown in  FIG. 6 . 
   The onset-of-actuation contour display  34  shown in  FIG. 8  also appears in the lower righthand quadrant of the present invention&#39;s degaussing vulnerability display overview window  28   OV  shown in  FIG. 6 . Contour display  34  presents a plan view of the ship  10  and the magnetic silencing range, with ship outline, sensor locations and actuation locations, plotted for the selected depth. A depth slider  42  located just above the contour display  34  can be dragged with the mouse, to select any depths for which extrapolation and actuation have been completed. 
   The onset-of-actuation contour  34 ′ is displayed as a thick line, and the actuation contour  34 ″ for the selected magnetic signature component (vertical, longitudinal or athwartship) is displayed as a thin line. Clicking on the contour display  34  (in the upper righthand quadrant of overview display window  28   OV  shown  FIG. 6 ) zooms contour display  34  to fill the window as shown in  FIG. 8 , and contour display  34  can be resized as desired. Clicking on the zoomed contour display  34  shown in  FIG. 8  returns the practitioner to the overview display  28   OV  shown in  FIG. 6 . 
   The onset-of-actuation curve display  36 , shown in  FIG. 9 , also appears in  FIG. 6  (sans shading above onset-of-actuation curve  36 ′) in the lower lefthand quadrant of the overview degaussing vulnerability display  28   OV . Curve display  36  presents an elevation view of the ship and the magnetic silencing range, and extends from the water surface, down to the water depth for which the selected mine no longer actuates. During correlational (associative between signature  20  and mine  22 ) processing, the onset-of-actuation curve  36 ′ is displayed as a thick line. Once extrapolation and correlational processing have reached a water depth at which the mine  22  does not actuate, correlational processing stops and the onset-of-actuation curve  36 ′ is indicated in the curve display  36  by a filled closed planar geometric figure (e.g., a filled polygon), such as shown in  FIG. 9 . The actuation curve  36 ″ for the selected magnetic signature component (vertical, longitudinal, or athwartship) is obscured in  FIG. 9  but is more clearly displayed in  FIG. 6  as a thin black line. 
   The actuation contour  34  shown in  FIG. 8  and the actuation curve  36  shown in  FIG. 9  are but two examples of how mine actuation can be visualized in accordance with the present invention. The actuation contour  34  represents a horizontal longitudinal slice of an actuation surface, whereas the actuation curve  36  represents a transverse vertical slice of an actuation surface. According to inventive practice, the actuation surface “slice” (segment) can be oriented any which way. Actuation contour  34  and actuation curve  36  are two preferred orientation modes for rendering humanly comprehensible visuals. Another orientation mode which may be preferable in inventive practice for purposes of showing mine actuation is a longitudinal vertical slice, analogous to that which is depicted in the magnetic signature profile display shown in  FIG. 7 ; it is readily envisioned that a like graph can represent a longitudinal vertical slice of an actuation surface rather than a longitudinal vertical slice of a magnetic signature. 
   Similarly as may be performed for magnetic profile display  32  and actuation contour  34 , the practitioner can: click on actuation curve display  36  and thereby zooms it to fill window  28  (such as shown in  FIG. 9 ); resize actuation curve display  36  as desired; clicking on the zoomed curve display  36  (shown in  FIG. 9 ) to return to the overview display  28   OV  (shown in  FIG. 6 ). 
   Prior to processing, the longitudinal spacing of the magnetic signature profile data samples can be changed. This is done from the “Signature” menu, in the longitudinal spacing pop-up menu  39 . The initial spacing of the data varies with ship speed and range sampling rate. It is typically less than one foot between data samples in the longitudinal direction. The athwartship spacing depends on sensor spacing, which is twenty feet between sensors at the magnetic silencing facilities. 
   It is not necessary, albeit often preferable, to decimate range signature  16  array so as to become decimated signature array  18 . In other words, according to some inventive embodiments, the decimation step can be omitted, and the extrapolated signatures  20  can be taken directly from the range signature  16 . Nevertheless, in order to speed up the extrapolation process, the original range signature  16  data can be decimated by up to eighty-foot spacing between samples. This provides a very quick overview of onset of actuation, but may not be accurate. 
   For accurate processing, the data needs to be sampled at a rate which provides a good indication of local peak fields and signature shape. Depending upon the complexity of the ranged magnetic signature, this rate will vary, but can be quickly determined by trying different spacing and observing signature profile degradation. For accurate extrapolation, the longitudinal spacing should be no more than twenty feet. The selected spacing is printed in the run information display  30  quadrant of the overview display  28   OV  shown in  FIG. 6 . 
   The depth increment at which extrapolation and correlational mine processing occurs can be changed by selecting the water depth increment pop-up menu from the mines menu. According to this inventive embodiment, water depth increments from five (5) to twenty (20) feet can be selected. A depth increment of twenty feet will result in quicker completion of processing, but the five-foot increment will yield a more detailed actuation curve  32 , with more actuation contours  34 . 
   Ship speed can be changed by selecting the “Speed” pop-up menu from the “Mines” menu. According to this inventive embodiment, speeds of five to fifteen knots can be selected. The default speed is the speed at which the ship  10  was ranged at the magnetic silencing facility  12 . 
   Vulnerability computation according to the present invention begins when a mine model  22  is selected from the “Mines” menu. “Version 1.0” of the present invention&#39;s “Degaussing Vulnerability Display Program” includes two mine models  22 , viz., “FM1” and “FM2.” The sensitivity of both mines is set to maximum. When a mine  22  is selected for the first time after opening a binary range file, the magnetic signature is extrapolated to twenty (20) feet below the range depth. The extrapolated magnetic signature  20  is then processed by the selected mine model  22 , and the resulting actuation contour  32  is displayed, along with the actuation curve  34 , which are each complete only to the extrapolated water depth. 
   Once mine processing is complete, the water depth is incremented, the magnetic signature is extrapolated to the new depth and processed with the selected mine model  22 , and the new actuation contour  32  and actuation curve  34  are displayed. Processing continues in this fashion until a water depth is reached where mine  22  actuation no longer occurs. After this point is reached, all of the extrapolated signatures and actuation contours are in computer memory and can be reviewed by using the mouse to drag the water depth slider  42  (located above the actuation contour display  34 ) to display the actuation contour  34  and magnetic signature profile  32  at the desired water depth. 
   During extrapolation and mine processing, a progress box (not shown) appears above the actuation curve display  36 , indicating which stage of processing (e.g., the extrapolation stage versus the mine processing stage) the inventive program is in. A stop button is located within the progress box, to enable processing to be interrupted. The display window  28  cannot be closed, and the program cannot be exited, while processing is occurring. 
   The present invention&#39;s degaussing vulnerability display window  28  (whether overview display  28   OV , magnetic profile display  28   32 , actuation contour display  28   34  or actuation curve display  28   36 ) can be print-previewed and printed out in either portrait or landscape mode, using the “Page Setup,” “Print Preview,” and “Print” entries in the “File” menu. After processing is complete, the Degaussing Vulnerability Display program contains a set of extrapolated signatures, and an actuation surface for each mine model that has been selected. All of this data can be saved in a “Vulnerability” file, with a “.dvd” extension, using the “Save As” entry in the “File” menu. Once saved, vulnerability files can be re-opened for performing additional vulnerability studies at different ship speeds. These follow-on studies will be much quicker than the original processing, as the magnetic signature will not need to be extrapolated again. 
   The present invention&#39;s degaussing vulnerability display program was written by the inventor in the Microsoft® Visual C++® programming language, using the Microsoft Foundation Classes (MFC) and a set of degaussing classes. The MFC are a set of C++ classes which provide an application framework for windows programming in the Windows NT® and Windows 95® operating systems. The degaussing classes are encapsulations of data and algorithms which are commonly used in degaussing software programming. 
   Reference is now made to APPENDIX A, APPENDIX B, APPENDIX C and APPENDIX D. The computer code set forth in the appendices herein, representative of the present invention&#39;s software (written in C++), is characterized by a “document-view” architecture. That is, part of the inventive code handles the data that is involved, e.g., program initialization and data management; this part includes the “document code” and represents the “document” aspect of the inventive code. The other part of the inventive code handles the user interface; this part includes the “view code” and represents the “view” aspect of the inventive code. The inventive code is presented herein in the appendices in four sections, viz.: APPENDIX A, containing the header file for the document code; APPENDIX B, containing the document code file; APPENDIX C, containing the header file for the view code; and, APPENDIX D, containing the view code file. 
   The degaussing classes used in the design and implementation of the present invention&#39;s degaussing vulnerability display program include range data, signature, mine, actuation surface and display classes. The range data class opens a range data file, allocates enough computer memory to hold the data, and reads the data from disk into memory. The signature class holds a triaxial, uniformly sampled magnetic signature comprising multiple longitudinal profiles, and provides methods for decimating and extrapolating the signature, locating the keel profile, and compiling signature statistics. The mine classes encapsulate mathematical mine models which receive uniformly sampled data as input and output mine look and fire signals. The actuation surface class holds mine actuation location information for multiple depths. Finally, the display class encapsulates the data and algorithms necessary to draw the magnetic signature profiles, actuation contours and actuation curves, which are needed or desired for degaussing vulnerability display. 
   Mathematically, the extrapolation technique used in the inventive computer code embodiment set forth hereinabove, a generally preferred extrapolation technique for practice of the present invention&#39;s degaussing vulnerability display program, is known as “the solution of the Dirichlet problem for the plane.” This extrapolation technique allows calculation of the three components of the magnetic field of a ship (vertical, longitudinal and athwartship), when the vertical magnetic field has been measured by a magnetic range located between the ship and the calculation depth. This extrapolation technique is accurate at or below a distance equal to the largest spacing used in the data measurement grid. Since the magnetic range sensors are separated by twenty feet, the first extrapolation depth is always twenty feet below the range depth. 
   Onset of actuation for a particular mine is determined by applying all of the ship magnetic signature profiles to the selected mine model and noting where actuation occurs. The onset-of-actuation contour for a particular depth is determined by forming the union of the actuation contours at that depth, for the vertical, longitudinal and athwartship components of the magnetic signature at that depth. The onset-of-actuation curve is determined by forming the union of the actuation curves for the vertical, longitudinal and athwartship components of the magnetic signature. 
   Generally, a magnetic mine is a device having a magnetic detection component. Although inventive practice will typically involve magnetic mines, the present invention can be practiced in association with any magnetically responsive (e.g., magnetically actuated or magnetically activated or magnetically sensitive) system or devices, such as magnetic mines and magnetic detectors. Moreover, although inventive practice will more typically be concerned with vulnerability assessment of ships and other surface naval vessels, the present invention can be practiced whether the vehicle in question is a marine vehicle or land vehicle. Furthermore, it is not necessary, according to inventive practice, that the spatial region examined for vulnerability assessment lie entirely or mainly below the vehicle. For instance, a submarine may require vulnerability assessment with regard to magnetic devices located below, beside and/or above the submarine. In the light of the instant disclosure, the ordinarily skilled artisan will be capable of practicing the present invention with regard to diverse vehicles as well as diverse magnetic systems and devices. 
   Other embodiments of this invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Various omissions, modifications and changes to the principles described herein may be made by one skilled in the art without departing from the true scope and spirit of the invention which is indicated by the following claims.