Abstract:
A portable seisgun device providing a consistent signal for detection with sensor arrays and geophones in the course of seismic studies, and a self-contained transport mechanism. The device comprises a main platform, a muffling skirt and a gun stock mounted on a dolly. The platform provides a safe place to operate the device. The skirt both reduces noise and contains debris. The firing barrel fires a shotgun shell into the ground, producing the seismic signal. Interchangeable barrels permit different types of ammunition to be used. The dolly acts as both infrastructure and transport for the device and additional equipment, including over rough terrain.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/384,455, filed Sep. 20, 2010. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Devices for generating a seismic impulse for study by geological scientists are known in the art. Most notably, a seismic shotgun (“seisgun”) was introduced as a portable, inexpensive source for shallow refraction or reflection surveying. The present disclosure is directed to an improved seisgun that is increasingly mobile, self-contained, affordable, and easy to operate and maintain in a variety of field conditions. 
     2. Background Art 
     The Betsy™ seisgun (Betsy Seisgun Inc., Tulsa, Okla.) has for some three decades represented the state of the art with respect to seismic shotgun devices. The Betsy™, described in U.S. Pat. Nos. 4,223,759, 4,334,591, 4,354,572, and 4,418,786 to Martin, and by Varsek and Lawton (J OURNAL OF THE  C ANADIAN  S OCIETY OF  E XPLORATION  G EOPHYSICISTS,  21:1, 1985), consists of a modified 21 mm (8 ga) industrial shotgun mounted vertically on a base muffle chamber. Slug cartridges are filed electrically and, as is well known in the art, the slug impacts the ground, perhaps in a bore hole of predetermined depth, resulting in a seismic pulse that is measurable using conventional detection means. 
     BRIEF SUMMARY OF THE INVENTION 
     Described herein is a portable seisgun device that safely provides a consistent seismic signal for detection with sensor arrays and geophones in the course of seismic studies, and also provides a transport mechanism for the geophone equipment, even over rough terrain. The device comprises a main platform, a muffling skirt and a gun stock mounted on a dolly. The skirt both reduces noise and contains debris; the platform provides a safe place to operate the device; and the firing barrel fires a shotgun shell into the ground, producing the seismic signal. The dolly acts as both infrastructure and transport for the device and additional equipment. 
     Safety is increased due to noise suppression and debris containment. Reliability is increased over existing devices. The device also allows for different penetration depths via the use of interchangeable firing barrels. The device is adapted to handle multiple gauges of ammunition for getting signals to different depths by utilizing interchangeable barrels, but when firing each gauge of shells it will produce a consistent result. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of the device. 
         FIG. 2  is a cutaway view of certain elements of the device. 
         FIG. 3  is a partial perspective view of certain elements of the device. 
         FIG. 4  is a partial side view of certain elements of the device. 
         FIG. 5   l  is perspective view of an element of the device. 
         FIG. 6  is a partial perspective view of an element of the device. 
         FIG. 7  is a partial perspective view of an element of the device. 
         FIG. 8  is a partial perspective view of certain elements of the device. 
         FIG. 9  is a cutaway view of an embodiment of the device. 
         FIG. 10  is a perspective view of an embodiment of the device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , seisgun device  10  is shown. Device  10  comprises a platform  12  having an upper surface  14  and a lower surface  16 . Platform  12  may be any type of resilient material, such as wood, fiberglass, or metal, and may be any thickness. Platform  12  is preferably optimized for weight and strength. 
     Located roughly centrally about platform  12  is an aperture  18 . As will be shown, upper surface  14  of platform  12  serves as the firing platform where one or more operators will stand and thus should be smooth, durable, and adapted for sure footing. Optionally, upper surface  14  may feature non-skid material  20 , which may be any tactile or coarse material such as conventional self-adhesive strips or non-slip tapes. Non-skid material  20  may be in any arrangement or pattern about platform  12 , including radially about aperture  18  as well as perimetric. 
     Extending upward from platform  12 , through aperture  18 , is an elongate stock  22  having a first end  24  and a second end  26  (obscured in  FIG. 1 ; see  FIG. 2 ). As illustrated in  FIG. 3 , aperture  18  is preferably adapted to receive stock  22 . For example, the outer diameter of stock  22  (or any protrusions thereon) may be slightly smaller than the inner diameter of the circular portion of aperture  18 . Correspondingly, any protruding or surface features on stock  22  are reflected in the outline of aperture  18  and/or are otherwise accommodated by its inner diameter. In an exemplary embodiment shown in  FIG. 3 , aperture  18  is roughly circular with a plurality of spaced apart, substantially radial projections  26 . Stock  22  has corresponding and complementary radial tabs  30 . Still referring to  FIG. 3 , secondary platform  32  is below, in a parallel plane to and spaced apart from platform  12 , defining an inter-platform space  34  therebetween. Secondary platform  32  is visible through aperture  18 , as shown. A secondary aperture  36  is located roughly centrally about secondary platform  32 , and corresponding roughly with the circular portion of aperture  18 . Secondary aperture  36  is preferably circular and similar in size to aperture  18 . Secondary aperture  36  preferably does not have any radial projections, which will be understood to restrict the downward travel of stock  22 . 
     As will be appreciated, second end  26  of stock  22  is inserted downward (direction of arrow  32 ) into and through aperture  18 . Tabs  30  line up with projections  28  of aperture  18 . Second end  26  of stock  22  will pass through secondary aperture  36 , but tabs  30  will not. Upon insertion, stock  22  may be rotated partially within inter-platform space  34  such that tabs  30  are no longer aligned with projections  28 , thereby preventing upward movement of stock  22  (opposite arrow  32 ) relative to platform  12  and thus retaining stock  22  in its vertical, upright position ( FIG. 1 ). Likewise, in order to remove stock  22  from platform  12 , stock  22  is rotated in an opposite direction within inter-platform space  34  until tabs  30  align with projections  28  and then lifted until clear. 
     Referring back to  FIG. 2 , first end  24  of stock  22  further comprises a firing mechanism  40  and at least one hand grip  42 . A pair of hand grips  42  perpendicularly opposed about stock  22  are preferred. Hand grips  42  aid in the rotation, insertion and removal of stock  22  as described above. 
     Firing mechanism  40  further comprises a trigger  44 . Trigger  44  is actuated by pressing it down. Optionally, firing mechanism comprises a safety  46 . Safety  46  may be any interlock or device capable of preventing the actuation of trigger  44 . In the exemplary embodiment depicted in  FIG. 4 , safety  46  comprises a member  48  that pivots about a pin  50  between a “fire” position  52  and a “safe” position  54 . In “safe” position  54 , member  48  frictionally engages both trigger  44  and first end  24  of stock  22 , thereby preventing trigger  44  from being depressed. 
     Referring back to  FIG. 2 , second end  26  of stock  22  further comprises a substantially cylindrical barrel  56  having a breech end  58  opposite a discharge end  6   o . Barrel  56  is detachably secured to stock  22 , as will be further discussed below. Breech end  58  is proximate second end  26  of stock  22 . As shown in  FIG. 5 , breech end  58  further comprises an annular seal  62 , such as an o-ring, that engages second end  26  of stock  22 . 
     Barrel  56 , preferably made of a sturdy, corrosion resistant material such as stainless steel, also comprises a centrally disposed, cylindrical channel (chamber)  64  disposed between the breech end  58  and discharge end  60 . The opening of chamber  64  at breech end  58  may also comprise an annular shelf  66 . 
     Turning to  FIG. 6 , chamber  64  is adapted to receive ammunition  68  such as a standard shotgun slug shell. Device  10  preferably has only a single-shot capacity, which will be appreciated to maximize safety to the operator as well as bystanders. As is well known in the art, and as illustrated in  FIG. 6 , conventional shotgun ammunition  68  comprises a shell case  70 , a rimmed brass cap  72 , and a primer  74  centrally located about the cap  72 , as well as gunpowder, wadding and the shot or slug disposed within shell case  70  (not shown). The primer  74 , upon being struck by a firing pin, explodes and ignites the gunpowder. The powder in turn burns and creates gas to propel the wadding and shot/slug forward. The wadding seals the gas behind the shot/slug. 
     It will be appreciated that the diameter of chamber  64  must correspond to the diameter of ammunition  68  (e.g., shell case) to be used. In order to retain the ammunition, the diameter of chamber  64  at breech end  58  must also be smaller than the diameter of the rim about the cap  72  of the shell  68 . Optionally, the rim of cap  72  may rest on annular shelf  66 . 
     Device  10  is adapted to be used with different gauge ammunition  68 . As is known in the art, ammunition  68  may vary in terms of both length and diameter, which might necessitate changes in the internal dimensions of chamber  64 . This may be accomplished by using a universal barrel  56 , or by using interchangeable, gauge-specific barrels  56 ,  56 ′. For example, barrel  56  may be adapted for conventional 12 ga. ammunition  68 , while a different barrel  56 ′ may be adapted for conventional 8 ga. ammunition  68 ′. 
     In order to accommodate interchangeability, second end  26  of stock  22  is adapted to releasably receive a barrel  56 . Barrel  56  may be retained frictionally and/or using any number of securing devices such as clamps, brackets or clips. Alternatively, the outer surface of barrel  56  and inner surface of second end  26  of stock  22  may be complementarily threaded. Regardless of the mechanism selected, interchangeability preferably permits the fast, convenient swapping of barrels  56 ,  56 ′ in the field and without tools or using only very simple hand tools. 
     In an exemplary embodiment shown in  FIG. 7 , approximately one half of second end  26  of stock  22  is notched out, thereby defining a receiving area  76 . At one end of receiving area  76  is breech (breech face)  78 . Centrally located about breech  78  is the aperture  80  through which firing pin  82  (only partially shown) extends upon the actuation of trigger  44  ( FIG. 7  shows the position of firing pin  82  during actuation of trigger  44 ). Between breech  78  and second end  26  is a raised surface  84 . Turning back to  FIG. 5 , barrel  56  may also comprise a circumferential groove  86 . It will be appreciated that groove  86  corresponds with and is complementary to raised surface  84 . 
     Because of the notch out in second end  26  of stock  22 , barrel  56  may slide directly down into receiving area  76  by lining up breech end  58  with breech  82 , and by lining up groove  86  with raised surface  84 . It will be appreciated that barrel  56  may not be inserted into receiving area  76  while trigger  44  is actuated. In yet another embodiment shown in  FIG. 8 , barrel  56  is frictionally retained in receiving area  76  by an angular locking bar  88  that is secured under tension at a first end  90  to stock  22  (such as by a fastener) and engages at a second end  92  under tension with circumferential groove  86  about barrel  56 . 
     Turning back to  FIG. 2 , an elongate firing pin (rod)  82  is disposed between firing mechanism  40  and barrel  56 , preferably centrally within the length of stock  22 . Firing rod  82  comprises a proximal end  94  (see also  FIG. 4 ) and a distal end  96  (see also  FIG. 7 ). Proximal end  94  is retained by a first spring  98  and is in physical communication with trigger  44  such that when spring  98  is at rest, trigger  44  is raised up and ready to receive a downward force. Distal end  96  is retained by a second spring  100  and when spring  100  is at rest, distal end  96  is suspended behind breech  78  (over the primer  74  of ammunition  68 , when device is loaded). 
     As shown in  FIGS. 1 and 9 , lower surface  16  of platform  12  is secured to a longitudinal support frame  102 . Support frame  102  preferably comprises a handle portion  104  at one end, a wheel assembly  106  opposite said handle portion  104 , and a base plate  108  that is substantially perpendicular to both platform  12  and support frame  102 . Preferably, wheel assembly  106  is opposite base plate  108  and comprises two, inflatable tires no mounted on wheels  112  about a single axle  114 . By way of example, support frame  102  could be a conventional hand truck, hand cart or hand dolly. As is well known in the art, hand trucks have perpendicular base plates that are mounted on the support frame opposite of the wheel assembly. It should be appreciated that the present disclosure includes a useful method for the conversion of an existing hand truck into a seismic shotgun device as described herein, as well as a kit for facilitating the same. 
     A skirt  116  is disposed below secondary platform  32 , proximate secondary aperture  36 . Skirt  116  is also secured to support frame  102 . Skirt  116  may be any hollow structure but is preferably lightweight and capable of suppressing both sound as well as physical debris such as earth, vegetation or water. By way of example, skirt  116  could be an automobile tire. Optionally, the interior surface of skirt  116  may further comprise a shock and/or sound deadening and/or dampening substance such as spray-on foam, insulation or the like. 
     Still referring to  FIG. 9 , it will be appreciated that the depth of penetration of second end  26  of stock  22  should be sufficient so as to dispose barrel  56  within the space  118  defined by skirt  116 . This will maximize the effectiveness of skirt  116  in containing both noise and debris. 
     Support frame  102  may be adapted to receive and releasably retain stock  22  when not in use for purposes of both storage and transportation. This adaptation may comprise one or more of the following: clamps, brackets, slots, grooves, channels, elastic members, recesses, hollowed-out portions, or any combination thereof. Furthermore, this adaptation may comprise physical modifications to the frame  102 , separate elements affixed to frame  102  such as a receiving block  128  (having an upward-facing cylindrical recess for receiving second end  26  of stock  22 ), a clip  130  (for engaging stock  22  proximate first end  24 ) or both. See also  FIG. 1 . 
     In any event, stock  22  is retained at the lower surface  16  of platform  12 , and it will be appreciated that the upper surface  14  of platform  12  remains clear for receiving and transporting other cargo  124 , such as measuring equipment, field gear or supplies, as illustrated in  FIG. 10 . Cargo  124  is also supported by base plate  108  and may be secured to device  10  via cargo straps  126 , such as conventional bungee cords or the like. It will be appreciated that device  10 , like many conventional hand trucks or dollies, may be transported over a variety of terrains, including unpaved and uneven surfaces. Given its configuration, device  10  is particularly well adapted for transport in a vertical or substantially vertical position. 
     Device  10  preferably comprises a shell removal tool  120  such as a rod. Tool  120  may be any elongated member capable of reaching into a spent ammunition shell  68  from discharge end  6   o  of barrel  56  and pushing shell  68  from chamber  64 . In a preferred embodiment, support frame  102  is adapted to receive and releasably retain tool  120  such as by a holder, bracket, sleeve, clip, channel or other means  122  that provides ready access and convenient storage. Alternatively, tool  120  may be fixed and stationary, which would require the user to place discharge end  6   o  of barrel  56  over tool  120  but would enable one-handed clearing of spent shells  68 . 
     In an exemplary embodiment, the use and operation of seisgun device  10  is as follows. The operator transports seisgun device  10  to a desired location. Field gear and supplies may be strapped to platform  12 , thereby maximizing portability. Locations are ordinarily prepared by digging a borehole; in many applications, a borehole having a depth of approximately 18 inches is appropriate. The desired ammunition type is selected based on parameters that are well known in the art. An exemplary type is a 12-gauge shotgun slug. 
     Device  10  is lowered into a horizontal position, and any cargo, gear or apparatus is removed. Stock  22  is removed from support frame  102 . Ammunition  68  is inserted by sliding the live shell into breech end  58  of barrel  56  until the rim  70  of the shell  68  engages the outer surface of breech end  58 . Barrel  56 , maintained with discharge end  60  pointing downward so as to retain shell  68  in place, is attached to second end  26  of stock  22 . Tabs  30  are aligned with projections  28 , and second end  26  of stock  22  is then inserted downward into aperture  18  and rotated within inter-platform space  34 . Safety  46  is disengaged and firing mechanism  40  is placed into fire position  52 . When it is determined by the operator to be safe to do so, trigger  44  is actuated. Trigger  44  may be actuated by any means capable of delivering a downward force, such as a light mallet blow or even the palm of the user&#39;s hand. 
     Ammunition  68  (i.e., the shot or slug contained within the shell) is dispensed into the borehole, resulting in the desired seismic activity to be monitored using conventional surface and subsurface detection equipment. Following firing, safety  46  is engaged, rendering firing mechanism  40  in the safe position  54 . Stock  22  is rotated in an opposite direction within inter-platform space  34  until tabs  3   o  are aligned with projections  28  of aperture  18 . Stock  22  is lifted and removed from platform  12 . Barrel  56  is removed form second end  26  of stock  22 . 
     Persons skilled in the art will understand that the discharge of shotgun ammunition will frequently result in the malformation of the spent shell. An expanded or irregular shell may not slide out of chamber  56  as readily as it was inserted. By inserting removal tool  120  into discharge end  6   o  of barrel  56 , spent ammunition  68  is removed. During transportation, stock  22  remains disengaged from device  10 . Preferably, stock  22  is secured about support frame  102  in a manner as described above. 
     Whereas, the present invention has been described in relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.