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FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to the field of excavation and, more particularly, to a system and process for acquiring geological and positional data, and for controlling an excavator in response to the acquired data.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various types of excavators have been developed to excavate a predetermined site or route in accordance with a particular manner of excavation. One particular type of excavator, often referred to as a track trencher, is typically utilized when excavating long continuous trenches for purposes of installing and subsequently burying various types of pipelines and utility conduits. A land developer or contractor may wish to excavate several miles or even hundreds of miles of terrain having varying types of unknown subsurface geology.  
           [0003]    Generally, such a contractor will perform a limited survey of a predetermined excavation site in order to assess the nature of the terrain, and the size or length of the terrain to be excavated. One or more core samples may be analyzed along a predetermined excavation route to better assess the type of soil to be excavated. Based on various types of qualitative and quantitative information, a contractor will generally prepare a cost budget that forecasts the financial resources needed to complete the excavation project. A fixed cost bid is often presented by such a contractor when bidding on an excavation contract.  
           [0004]    It can be appreciated that insufficient, inaccurate, or misleading survey information can dramatically impact the accuracy of a budget or bid associated with a particular excavation project. An initial survey, for example, may suggest that the subsurface geology for all or most of a predetermined excavation route consists mostly of sand or loose gravel. The contractor&#39;s budget and bid will, accordingly, reflect the costs associated with excavating relatively soft subsurface soil. During excavation, however, it may instead be determined that a significant portion of the predetermined excavation route consists of relatively hard soil, such a granite, for example. The additional costs associated with excavating the undetected hard soil are typically borne by the contractor. It is generally appreciated in the excavation industry that such unforeseen costs can compromise the financial viability of a contractor&#39;s business.  
           [0005]    Various methods have been developed to analyze subsurface geology in order to ascertain the type, nature, and structural attributes of the underlying terrain. Ground penetrating radar and infrared thermography are examples of two popular methods for detecting variations in subsurface geology. These and other non-destructive imaging analysis tools, however, suffer from a number of deficiencies that currently limit their usefulness when excavating long, continuous trenches, or when excavating relatively large sites. Further, conventional subsurface analysis tools typically only provide an image of the geology of a particular subsurface, and do not provide information regarding the structural or mechanical attributes of the underlying terrain which is critical when attempting to determine the characteristics of the soil to be excavated.  
           [0006]    There is a need among developers and contractors who utilize excavation machinery to minimize the difficulty of determining the characteristics of subsurface geology at a predetermined excavation site. There exists a further need to increase the production efficiency of an excavator by accurately characterizing such subsurface geology. The present invention fulfills these and other needs.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is an excavator data acquisition and control system and process for characterizing the subsurface geology of an excavation site, and for utilizing the acquired data to optimize the production performance of an excavator. A geologic imaging system and a geographic positioning system are employed to initially survey a predetermined excavation site or route. A geologic characterization unit may also be employed to enhance the geologic imaging data. The acquired data are processed to provide detailed geologic and position data for the excavation site and utilized by a main control unit to optimize excavator production performance. In one embodiment, the main control unit accesses a geologic filter database, which includes geologic profile data for numerous types of geology, when analyzing unknown subsurface geology. Removing geological filter data content corresponding to known geology from the acquired geologic imaging data provides for immediate recognition of unknown and suspect subsurface objects. The geologic imaging system preferably includes a ground penetrating radar system having a plurality of antennas oriented in an orthogonal relationship to provide three-dimensional imaging of subsurface geology. Correlation software is employed to correlate acquired geologic image data to historical excavator production performance data to characterize the structural mechanics of subsurface geology. Accurate geographic mapping of an excavation site is provided by the geographic positioning system which preferably includes a mobile transponder mounted to an excavator and a plurality of ground-based transponders. In one embodiment, signals transmitted by one or more Global Positioning System (GPS) satellites are utilized together with reference signals produced by a plurality of ground-based transponders. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a side view of one embodiment of an excavator, termed a track trencher, including a ditcher chain trenching attachment;  
         [0009]    [0009]FIG. 2 is a generalized system block diagram of a track trencher embodiment of an excavator;  
         [0010]    [0010]FIG. 3 is an illustration of a main user interface for controlling a track trencher excavator, for viewing acquired geological and position data, and for interfacing with various electronic and electromechanical components of the excavator;  
         [0011]    [0011]FIG. 4 is a system block diagram of a main control unit (MCU) of a novel excavator data acquisition and control system;  
         [0012]    [0012]FIG. 5 is a system block diagram of a geologic data acquisition unit (GDAU) of a novel excavator data acquisition and control system;  
         [0013]    [0013]FIG. 6 is plot of reflected source electromagnetic signals received by a ground penetrating radar system using a conventional single-axis antenna system;  
         [0014]    [0014]FIG. 7 is a system block diagram of a geographic positioning unit (GPU) of a novel excavator data acquisition and control system;  
         [0015]    [0015]FIG. 8 is a system block diagram of an excavator control unit (ECU) of a novel excavator data acquisition and control system;  
         [0016]    [0016]FIG. 9 is a block diagram of various databases and software accessed and processed by the main control unit (MCU);  
         [0017]    [0017]FIG. 10 is an illustration of a predetermined excavation site having a heterogenous subsurface geology;  
         [0018]    [0018]FIG. 11 is an illustration of a survey profile in chart form obtained for a predetermined excavation route using a novel geologic data acquisition unit (GDAU) and geologic positioning unit (GPU);  
         [0019]    [0019]FIG. 12 is an illustration of an estimated excavation production profile in chart form corresponding to the survey profile chart of FIG. 11;  
         [0020]    [0020]FIG. 13 is an illustration of a predetermined excavation site having a heterogenous subsurface geology and an unknown buried object;  
         [0021]    [0021]FIG. 14 is an illustration of a conventional single-axis antenna system typically used with a ground penetrating radar system for providing two-dimensional subsurface geologic imaging;  
         [0022]    [0022]FIG. 15 is an illustration of a novel antenna system including a plurality of antennas oriented in an orthogonal relationship for use with a ground penetrating radar system to provide three-dimensional subsurface geologic imaging;  
         [0023]    [0023]FIG. 16 is an illustration of a partial grid of city streets and an excavator equipped with a novel excavator data acquisition and control system employed to accurately map a predetermined excavation site; and  
         [0024]    FIGS.  17 - 20  illustrate in flow diagram form generalized method steps for effecting a novel excavator data acquisition and control process. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    The novel excavator data acquisition and control system and process provides for a substantial enhancement in excavation efficiency and project cost estimation by the acquisition and processing of geological, geophysical, and geographic position information for a particular excavation site. The operation of an excavator is preferably optimized by modifying excavator operating parameters based on acquired survey data and input commands received from an operator of the excavator. The accuracy of estimating the resources and costs associated with excavating a particular excavation site is significantly increased by providing a computational analysis of the acquired survey data prior to initiating excavation of the site, thereby substantially reducing a contractor&#39;s risk of misquoting the costs associated with a particular excavation project due to a lack of accurate and detailed information regarding the geology of the subject excavation site.  
         [0026]    The advantages and features of a novel excavator data acquisition and control system and process will generally be discussed with reference to one particular type of excavator, termed a track trencher. It is to be understood, however, that a track trencher represents only one of many embodiments of an excavator that may be equipped with a novel excavator data acquisition and control system as disclosed hereinbelow. As such, the advantages and features of the disclosed novel system and process are not limited to application in connection with a track trencher.  
         [0027]    Referring now to the figures and more particularly to FIG. 1, there is shown an illustration of one embodiment of an excavator well-suited for incorporating a novel data acquisition and control system. A track trencher excavator, shown in FIGS. 1 and 2, typically includes an engine  36  coupled to a right track drive  32  and a left track drive  34  which together comprise the tractor portion  45  of the track trencher  30 . An excavation attachment  46 , usually coupled to the front of the tractor portion  45 , typically performs a specific type of excavating operation.  
         [0028]    A ditcher chain  50 , or other excavation attachment, is often employed to dig trenches of varying width and depth at an appreciable rate. The ditcher chain  50  generally remains above the ground in a transport configuration  56  when maneuvering the trencher  30  around an excavation site. During excavation, the ditcher chain  50  is lowered, penetrates the ground, and excavates a trench at the desired depth and speed while in a trenching configuration  58 . Another popular trenching attachment, termed a rock wheel in the art, may be controlled in a manner similar to that of the ditcher chain  50 . A track trencher  30  is well-suited for efficiently excavating a trench along a predetermined excavation route for the purpose of installing various types of pipelines and utility conduits.  
         [0029]    In FIG. 3, there is illustrated a main user interface  101  of a track trencher  30 . Propulsion and steering of a track trencher  30  when operating in a transport mode is generally controlled by manipulating the left and right track levers  64  and  66  which respectively control actuation of the left and right track drives  34  and  32 . Moving the right track lever  66  forward, for example, generally causes the right track drive  32  to operate in a forward direction and, depending on the relative velocity of the left track drive  34 , steers the track trencher  30  to move in either a left or right direction. Reversing the right track drive  32  is generally accomplished by pulling the right track lever  66  backwards, thereby causing the right track drive  32  to operate in a reverse direction. Propulsion of the left track drive  34  is accomplished in substantially the same manner as that previously described with regard to the right track drive  32 . Thus, both propulsion and steering are generally controlled by the track levers  64  and  66  of a track trencher  30 . Alternatively, the main user interface  101  may be configured to provide for independent steering and propulsion of the left and right track drives  34  and  32 , respectively.  
         [0030]    It is often desirable to maintain the engine  36  at a constant, optimum output level during excavation which, in turn, allows the attachment  46  to operate at an optimum excavating output level. A prior art control panel typically includes a plurality of controls and switches, including a speed range switch, RPM knob, steering trim knob, and propel trim knob, all of which must typically be adjusted during normal trenching operation to maintain the engine at the desired engine output level when encountering variable attachment  46  loading, and to steer the track trencher  30  in a desired direction. Additionally, a pair of right and left pump potentiometers typically require adjustment and readjustment to equilibrate the operational characteristics of the left and right pumps  38  and  40 .  
         [0031]    A significant disadvantage of a conventional track trencher control panel concerns a requirement that the operator must generally react quickly to changes in engine  36  loading, typically by first determining the appropriate switch to adjust and then the degree of switch adjustment. Typically, minor propulsion modifications are made by adjusting the propel trim knob. Moderate changes to the propulsion level of the track trencher  30  are generally effected by adjusting the RPM knob. A major modification to the propulsion level of the track trencher  30  is typically accomplished by switching the speed range switch from a high setting to either a medium or low setting, and once again adjusting the propel trim knob and RPM knob in order to avoid stalling out the engine  36 .  
         [0032]    The novel data acquisition and control system and process obviates the requirement of continuous manual adjustment and readjustment of a plurality of control switches, knobs, and levers. Instead, an intelligent excavation control unit (ECU) is employed to continuously monitor a network of sensors that transduce various excavator functions into electrical signals, and processes these and other electrical signals to optimize the steering and excavating performance of the excavator, with only minimal intervention by an excavator operator. An enhanced user-interface communicates pertinent excavator performance information, as well as geological and geographical position data, to an operator preferably over a display, such as a liquid crystal display or a cathode ray tube display, for example. A keyboard and other levers and switches are provided on the user-interface to communicate with the data acquisition and control system, and control the operation of the excavator.  
         [0033]    Data Acquisition and Control System  
         [0034]    Turning now to FIG. 4, there is illustrated a novel data acquisition and control system shown in system block diagram form. In broad and general terms, the system shown in FIG. 4 significantly enhances the operation of an excavator by the acquisition of geological, geophysical, and position information regarding a particular excavation site, and by employing this information to enhance excavation efficiency. The acquisition of such pertinent excavation site data substantially reduces the risk involved in estimating the cost and scheduling of a particular excavation project. Real-time acquisition of geographical position data provides for precision mapping of an excavated area to accurately identify the location and depth of, for example, buried pipelines and utility conduits installed at the excavation site. These and other significant advantages and features are provided by the novel excavator data acquisition and control system and process as discussed in greater detail hereinbelow.  
         [0035]    Referring to FIG. 4 in greater detail, the primary processing component of the novel data acquisition and control system is a main control unit (MCU)  250 , which preferably includes a central processing unit (CPU)  264 , Random-Access-Memory (RAM)  266 , and non-volatile memory  286 , such as Electrically Erasable Programmable Read-Only-Memory (EEPROM). The MCU  250  preferably includes appropriate input and output ports to communicate with a number of other sub-systems that acquire various types of data, process such data, and interface with the control system of an excavator to moderate and optimize the excavation process. A main user interface (MUI)  101  is preferably situated in proximity to an operator seat mounted to the excavator, and provides a means for communicating with the main control unit  250 . An excavator control unit (ECU)  255  communicates with the main control unit  250  and is responsive to operator inputs received from the main user interface  101  to cooperatively control the operation of the excavator. A computer or programmable controller  182  is preferably incorporated as a component of the excavator control unit  255  to control and moderate excavator function.  
         [0036]    The movement and direction of an excavator is preferably monitored and, if desired, moderated by a geographic positioning unit (GPU)  254 . The geographic positioning unit  254  preferably includes a mobile transponder mounted to the excavator and one or more reference transponders. Position reference signals produced by the reference transponders are processed by a CPU  270  of the geographic positioning unit  254  into geographic position data, such as latitude, longitude, and elevation data, and displacement data from one or more reference locations, for example.  
         [0037]    An important component of the novel data acquisition and control system concerns a geophysical data acquisition unit (GDAU)  256 , which acquires various types of geological and geophysical data for a particular excavation site. In one embodiment, the geophysical data acquisition unit  256  may be decoupled from the main control unit  250  to provide for initial surveying of a predetermined excavation site. After performing the initial survey, the data acquired by the geophysical data acquisition unit  256  is preferably downloaded into the RAM  266  or EEPROM  268  of the main control unit  250 . Alternatively, the geophysical data acquisition unit  256  is preferably coupled to the excavator and directly to the main control unit  250  to provide real-time acquisition of geological, geophysical, and position data during excavation. In yet another embodiment, initial surveying of an excavation site provides for the acquisition of pertinent geological, geophysical, and position data which is downloaded to the main control unit  250  upon completion of the initial survey. An onboard geophysical data acquisition unit  256 , which preferably includes the components used in the initial survey, provides for real-time data acquisition which may be used in conjunction with the data acquired from the initial survey to optimize excavator production performance. The geophysical data acquisition unit  256  preferably includes a CPU  276 , RAM  278 , and EEPROM  280 .  
         [0038]    Among the various types of data acquired by the geophysical data acquisition unit  256 , data pertaining to the specific geology at the excavation site, in addition to the physical characteristics of such geology, are of particular importance when optimizing the production performance of an excavator, and when estimating the cost and resource allocation of a particular excavation project. A geologic imaging unit (GIU)  258  is preferably coupled to the geophysical data acquisition unit  256  to provide information concerning the particular geology associated with an excavation site. Various geophysical characteristics associated with a particular geology at the excavation site are preferably determined by a geophysical characterization unit (GCU)  260 . An auxiliary user interface (AUI)  262  is preferably coupled to the geophysical data acquisition unit  256  to provide local viewing of acquired data and images, and to provide a means for an operator to communicate with the geophysical data acquisition unit  256 . The auxiliary user interface  262  is particularly useful in connection with an embodiment in which the geophysical data acquisition unit  256  is decoupled from the main control unit  250  to perform an initial survey of an excavation site. It is noted that RS-232 communication lines provide sufficient bandwidth for effecting communication between the electronic units and instruments of the novel data acquisition and control system.  
         [0039]    Geophysical Data Acquisition Unit (GDAU)  
         [0040]    As shown in FIG. 5, the geophysical data acquisition unit  256  preferably includes a geologic imaging unit  258  and a geophysical characterization unit  260 . The geophysical characterization unit  260  preferably includes a number of geophysical instruments which provide a physical characterization of the geology for a particular excavation site. A seismic mapping module  286  includes an electronic device consisting of multiple geophysical pressure sensors. A network of these sensors are arranged in a specific orientation with respect to the excavator, and are situated so as to make direct contact with the ground. The network of sensors measures ground pressure waves produced below the excavator and in the trench walls produced by the excavator. Analysis of ground pressure waves received by the network of sensors provides a basis for determining the physical characteristics of the subsurface at the excavation site. This data is preferably processed by the CPU  276  of the geophysical data acquisition unit  256  or, alternatively, by the CPU  264  of the main control unit  250 .  
         [0041]    A point load tester  288  may be employed to determine the geophysical characteristics of the subsurface at the excavation site. The point load tester  288  preferably employs a plurality conical bits for the loading points which, in turn, are brought into contact with the ground to test the degree to which a particular subsurface can resist a calibrated level of loading. The data acquired by the point load tester  288  provides information corresponding to the geophysical mechanics of the soil under test. This data may also be transmitted to the geophysical data acquisition unit  256  for storage in the RAM  278  or EEPROM  280 .  
         [0042]    The geophysical characterization unit  260  preferably includes a Schmidt hammer  290 , which is a geophysical instrument that measures the rebound hardness characteristics of a sampled subsurface geology. Other geophysical instruments may also be employed to measure the relative energy absorption characteristics of a rock mass, abrasivity, rock volume, rock quality, and other physical characteristics that together provide information regarding the relative difficulty associated with excavating a given geology. The data acquired by the Schmidt hammer  290  is also preferably stored in the RAM  278  or EEPROM  280  of the geophysical data acquisition unit  256 .  
         [0043]    The geologic imaging unit  258  preferably includes a ground penetrating radar system (GPRadar)  282  and an antenna system  284 . The GPRadar system  282  cooperates with the antenna system  284  to transmit source electromagnetic signals into the subsurface of an excavation site. The source electromagnetic signals penetrate the subsurface and are reflected back to the antenna system  284 . The reflected source electromagnetic signals received by the antenna system  284  are amplified and conditioned by the GPRadar system  282 . In one embodiment, analog reflected source electromagnetic signals processed by the GPRadar system  282  are preferably digitized and quantized by a quantizer  281 . In another embodiment, a digitizing GPRadar system  282  performs analog-to-digital conversion of the reflected source electromagnetic signals. The digitized radar data acquired by the geologic imaging unit  258  is preferably stored in RAM  278  or non-volatile EEPROM  280  memory in the geophysical data acquisition unit  256 .  
         [0044]    Referring now to FIG. 6, there is illustrated a visual illustration of typical geologic imaging data acquired from a GPRadar System  282  employing a conventional single-axis antenna system  284 . In FIG. 6, there is plotted GPRadar system  282  data acquired over a test site having five different man-made hazards buried at a depth of approximately 1.3 meters in sandy soil with a water table located at a depth of approximately four to five meters. It is noted that the data illustrated in FIG. 6 is representative of data typically obtainable by use of a PulseEKKO  1000  system manufactured by Sensors and Software, Inc. using conventional single-axis 450 MHz center frequency antennas. Other GPRAdar systems  282  which may be suitable for this application include SIR System-2 and System-10A manufactured by Geophysical Survey Systems, Inc. and model 1000B STEPPED-FM Ground Penetrating Radar manufactured by GeoRadar, Inc.  
         [0045]    Each of the buried hazards illustrated in FIG. 6 has associated with it a characteristic hyperbolic time-position curve. The apex of the characteristic hyperbolic curve provides an indication of both the position and the depth of a buried hazard. It can be seen from the graph of FIG. 6 that each of the buried hazards is located approximately 1.3 meters below the ground surface, with each of the hazards being separated from adjacent hazards by a horizontal distance of approximately five meters. The GPRadar System  282  data illustrated in FIG. 6 represents geological imaging data acquired using a conventional single-axis antenna system and, as such, only provides a two-dimensional representation of the subsurface being surveyed. As will be discussed in greater detail hereinbelow, a novel antenna system  284  comprising multiple antennas arranged in an orthogonal orientation provides for an enhanced three-dimensional view of the subsurface geology associated with a particular excavation site.  
         [0046]    Geographic Positing Unit (GPU)  
         [0047]    Turning now to FIG. 7, there is illustrated in greater detail a geographic positioning unit  254  that provides geographic position information regarding the position, movement, and direction of an excavator over an excavation site. In one embodiment, the geographic positioning unit  254  communicates with one or more external reference signal sources to determine information regarding the position of an excavator relative to one or more known reference locations. The relative movement of an excavator over a specified excavation route is preferably determined by the CPU  270  of the geographic positioning unit  254 , and stored as position data in RAM  272  or EEPROM  274 .  
         [0048]    In another embodiment, geographic position data for a predetermined excavation route is preferably acquired prior to excavating the route. This position data may be uploaded into a navigation controller  292  which cooperates with the main control unit  250  and the excavator control unit  255  to provide autopilot-like control and maneuvering of the excavator over the predetermined excavation route. In yet another embodiment, position data acquired by the geographic positioning unit  254  is preferably communicated to a route mapping database  294  which stores the position data for a given excavation site, such as a grid of city streets or a golf course under which various utility, communication, plumbing, and other conduits are buried. The data stored in the route mapping database  294  may be subsequently used to produce a survey map that accurately specifies the location and depth of various utility conduits buried in a specified excavation area.  
         [0049]    In one embodiment, a global positioning system (GPS)  296  is employed to provide position data for the geographic positioning unit  254 . In accordance with a U.S. Government project to deploy twenty-four communication satellites in three sets of orbits, termed the Global Positioning System (GPS) or NAVSTAR, various signals transmitted from one or more GPS satellites may be used indirectly for purposes of determining positional displacement of an excavator relative to one or more known reference locations. It is generally understood that the U.S. Government GPS satellite system provides for a reserved or protected band and a civilian band. Generally, the protected band provides for high-precision positioning to an accuracy of approximately one to ten feet. The protected band, however, is generally reserved exclusively for military and governmental surveillance purposes, and is modulated in such a manner as to render it virtually useless for civilian applications. The civilian band is modulated so as to significantly decrease its usefulness in high-accuracy applications. In most applications, positional accuracies of approximately one hundred to three hundred feet are typical using the civilian band.  
         [0050]    The civilian GPS band, however, can be used indirectly in relatively high-accuracy applications by using one or more civilian GPS signals in combination with one or more ground-based reference signal sources. By employing various known signal processing techniques, generally referred to as differential global positioning system (DGPS) signal processing techniques, positional accuracies on the order of one foot or less are achievable. As shown in FIG. 7, the global positioning system  296  utilizes a signal produced by at least one GPS satellite  302  in cooperation with signals produced by at least two base transponders  304 , although use of one base transponder  304  may be satisfactory in some applications. Various known methods for exploiting differential global positioning signals using one or more base transponders  304 , together with a GPS satellite signal  302  and a mobile GPS receiver  303  mounted to the excavator, may be employed to accurately resolve excavator movement relative to base transponder  304  reference locations using a GPS satellite signal source.  
         [0051]    In another embodiment, a ground-based positioning system may be employed using a range radar system  298 . The range radar system  298  preferably includes a plurality of base radio frequency (RF) transponders  306  and a mobile transponder  308  mounted to the excavator. The base transponders  306  emit RF signals which are received by the mobile transponder  308 . The mobile transponder  308  preferably includes a computer that calculates the range of the mobile transponder  308  relative to each of the base transponders  306  through various known radar techniques, and then calculates its position relative to all base transponders  306 . The position data acquired by the range radar system  298  is preferably stored in the RAM  272  or EEPROM  274  of the geographic positioning unit  254 .  
         [0052]    An ultra-sonic positioning system  300 , in another embodiment, may be employed together with base transponders  310  and a mobile transponder  3 l 2  mounted to the excavator. The base transponder  310  emits signals having a known clock timebase which are received by the mobile transponder  312 . The mobile transponder  312  preferably includes a computer which calculates the range of the mobile transponder  312  relative to each of the base transponders  310  by referencing the clock speed of the source ultrasonic waves. The computer of the mobile transponder  312  also calculates the position of the excavator relative to all of the base transponders  310 . It is to be understood that various other known ground-based and satellite-based positioning systems may be employed to accurately determine excavator movement along a predetermined excavation route.  
         [0053]    Excavator Control Unit (ECU)  
         [0054]    Referring now to FIG. 8, there is illustrated a system block diagram of an excavator control unit (ECU)  255  which communicates with the main control unit (MCU)  250  to coordinate the operation of an excavator. In accordance with an embodiment of the track trencher excavator  30  illustrated in FIGS. 1 and 2, the left track drive  34  typically comprises a left track pump  38  coupled to a left track motor  42 , and the right track drive  32  typically comprises a right track pump  40  coupled to a right track motor  44 . Left and right track motor sensors  198  and  192  are preferably coupled to the left and right track motors  42  and  44 , respectively. The left and right track pumps  38  and  40 , deriving power from the engine  36 , preferably regulate oil flow to the left and right track motors  42  and  44  which, in turn, provide propulsion for the left and right track drives  34  and  32 . The excavation attachment  46  preferably comprises an attachment motor  48  and an attachment control  98 , with the attachment  46  preferably deriving power from the engine  36 . A sensor  186  is preferably coupled to the attachment motor  46 . Actuation of the left track motor  42 , right track motor  44 , and attachment motor  48  is monitored by sensors  198 ,  192 , and  186  respectively. The output signals produced by the sensors  198 ,  192 , and  186  are communicated to the computer  182 .  
         [0055]    In response to steering and propel control signals respectively produced by the steering control  92  and propel control  90 , the computer  182  communicates control signals, typically in the form of control current, to the left and right track pumps  38  and  40  which, in turn, regulate the speed at which the left and right track motors  42  and  44  operate. The left and right track motor sensors  198  and  192  communicate track motor sense signals to the computer  182  indicative of the actual speed of the left and right track motors  42  and  44 . Similarly, an engine sensor  208 , coupled to the engine  36 , provides an engine sense signal to the computer  182 , thus completing a closed loop control system for the tractor drive portion  45  of a track trencher  30 . Those skilled in the art will recognize that various known computer configurations will provide a suitable platform for effectuating propulsion and steering changes of a track trencher  30  in response to the propel and steering signals produced by the propel and steering controls  90  and  92 .  
         [0056]    The excavation attachment  46  portion of a track trencher  30  includes an attachment motor  48 , attachment control  98 , and at least one attachment sensor  186 . The attachment motor  48  preferably responds to instructions communicated to the attachment control  98  from the computer  182 . The actual output of the attachment motor  48  is monitored by the attachment sensor  186 , which produces an attachment sense signal received by the computer  182 .  
         [0057]    In one embodiment, the left and right track motor sensors  198  and  192  are of a type generally referred to in the art as magnetic pulse pickups, or PPUs. The PPUs  198  and  192  transduce track motor rotation into a continuous series of pulse signals, wherein the pulse train preferably represents the frequency of track motor rotation as measured in revolutions-per-minute. When a transport mode of travel is selected, the propel control  90  preferably produces a transport propel control signal which is representative of a target velocity for the left and right track motors  42  and  44 , typically measured in revolutions-per-minute. Conversion of the transport propel signal into a target track motor velocity may be accomplished by the propel control  90  itself or, preferably, by the computer  182 . The computer  182  typically compares the left and right track motor sense signals respectively produced by the left and right PPU sensors  198  and  192  to the target track motor propulsion level represented by the transport propel signal. The computer  182  communicates the appropriate pump control signals to the left and right track pumps  38  and  40  in response to the outcome of the comparison to compensate for any deviation between the actual and target track motor propulsion levels.  
         [0058]    A display  73  is coupled to the computer  182  or, alternatively, to the main control unit  250 , and preferably communicates messages indicative of operating status, diagnostic, calibration, fault, safety, and other related information to an operator. The display  73  provides quick, accurate, and easy-to-understand information to an operator by virtue of the interpretive power of the computer  182  which acquires and processes data from a plurality of track trencher sensors, and various geological and geophysical instruments. Geologic imaging data and related geophysical information, for example, is visually displayed on the display  73 . Further, information regarding the position of the excavator as it traverses along a predetermined excavation route, as well as signal quality information received from the geographic positioning unit  254 , is displayed on the display  73 . A keyboard  75  is also provided on the main user interface  101  to permit an operator to communicate with the excavator control unit  255  and the main control unit  250 .  
         [0059]    Main Control Unit (MCU)  
         [0060]    Turning now to FIG. 9, there is illustrated a block diagram of various databases and software that are utilized by the main control unit (MCU)  250  when accessing and processing geological, geophysical, position, and operational data associated with surveying and excavating a selected excavation site. The data acquired by the geophysic data acquisition unit  256 , for example, is preferably stored in a database  326 , which includes a GPRadar database  328 , a geologic filter database  330 , and a geophysics database  332 . The GPRadar system  282  data, as previously discussed, is preferably digitized and stored in the GPRadar database  328  in a suitable digital format appropriate for correlation to data stored in other system databases. A geologic filter database  330 , as will be discussed in greater detail hereinbelow, includes filtering data produced by correlating GPRadar data to corresponding excavator production data stored in the excavation performance database  324 . Correlation and optimization software  320  performs the correlation of GPRadar data to actual excavator production data to develop an array of adjustable geologic digital filters that can be effectively overlaid with real-time acquired geologic image data to exclude or “filter out” verified geology data, thus leaving unverified images representative of one or more buried hazards. By way of further illustration, a particular type of soil produces a characteristic return radar image which can be correlated with excavator production data acquired by the excavator control unit  255 . Excavating through granite, for example, produces a characteristic return radar image that can be correlated to various excavator operation parameters, such as excavation attachment motor  48  speed, engine  36  loading, and left or right track motor  42  and  44  velocity changes.  
         [0061]    An “excavation difficulty” parameter or set of parameters are preferably computed based on the excavator operating parameters. The “excavation difficulty” parameters are then associated with the characteristic reflected radar image data corresponding to a particular geology, such as granite, for example. An array of “excavation difficulty” filter parameters and associated reflected radar image data values are preferably developed for a wide range of soil and rock, and stored in the geologic filter database  330 .  
         [0062]    An excavation statistics database  316  preferably receives data files from the correlation and optimization software  320  and compiles statistical data to reflect actual excavator production performance relative to specific geology, maintenance, and equipment variables. In one embodiment, GPRadar data and geophysical data is acquired by the geophysic data acquisition unit  256  during an initial survey of a predetermined excavation route. This data is preferably uploaded to the excavation statistics database  316  prior to excavating the predetermined route. The data stored in the excavation statistics database  316  can be viewed as a production estimate in the sample geology based on past excavator production performance.  
         [0063]    The main control unit  250  also executes ECU control software  318  which receives data files from the correlation and optimization software  320  and input commands received from the main user interface  101 . The ECU control software  318  compiles a current operation standard for operating the excavator over the course of the predetermined excavation route. If input data received from the main user interface  101  causes a modification in the operation standard, the ECU control software  318  computes modified excavator operational instructions which are transmitted to the main control unit  250  and the excavator control unit  255  which, in turn, modifies the operation of the excavator in response to the modified operation standard.  
         [0064]    A maintenance log memory  314  preferably includes non-volatile memory for storing various types of excavator maintenance information. An elapsed time indicator is preferably included in the maintenance log memory  314  which indicates the total elapsed operating time of the excavator. At predefined operating time values, which are preferably stored in the maintenance log memory  314 , the excavator operator is prompted by the main user interface  101  that scheduled service is required. Verification of scheduled service, the type of service, the date of service, and other related information is preferably input through the main user interface  101  for permanent storage in the maintenance log memory  314 . In one embodiment, the maintenance log memory  314  preferably includes a table of factory designated operational values and ranges of operational values associated with nominal excavator operation. Associated with each of the operational values and ranges of values is a status counter which is incremented upon each occurrence of excavator operation outside of the prescribed values or range of values. The status counter information is useful in assessing the degree to which an excavator has been operated outside factory specified operational ranges, which is particularly useful when determining the appropriateness of warranty repair work.  
         [0065]    Geologic Surveying and Imaging  
         [0066]    In general operation, as shown in FIG. 10, a predetermined excavation route is preferably initially surveyed using the geographic positioning unit  254  and the geophysic data acquisition unit  256 . In one embodiment, the geographic positioning unit  254  and geophysic data acquisition unit  256  are positioned in a transport cart  340  which is pulled along the predetermined excavation route by a vehicle  342 . In the illustrative example shown in FIG. 10, the excavation route is a county road under which a utility conduit is to be installed. As the transport cart  340  is pulled along the roadway  344 , data received from the geologic imaging unit  258  is acquired for the purpose of determining the soil properties of the subsurface below the roadway  344 . Concurrently, geographic position data is acquired by the geographic positioning unit  254  as the vehicle  342  and transport cart  340  traverse the roadway  344 . As such, specific geologic data obtained from the geologic imaging unit  258  may be correlated to specific geographic locations along the roadway  344 .  
         [0067]    The geologic imaging unit  258  preferably includes a GPRadar system  282  which is typically calibrated to penetrate to a pre-established depth associated with a desired depth of excavation. Depending on the pre-determined excavation depth, various types of soil and rock may be encountered along the predetermined excavation route. As shown in FIG. 10, a layer of road fill  346 , which lies immediately below the roadway  344 , has associated with it a characteristic geologic profile GP 1  and a corresponding geologic filter profile GF 1  which, as previously discussed, represents a correlation between excavation production performance data to reflected radar image data for a particular soil type. As the transport cart  340  traverses the roadway  344 , various types of soil and subsurface structures are detected, such as a sand layer  354 , gravel  352 , bedrock  350 , and native soil  348 , each of which has a corresponding characteristic geologic profile and geologic filter profile.  
         [0068]    Upon completion of the initial survey, the data acquired and stored in the geophysic data acquisition unit  256  and geographic positioning unit  254  is preferably downloaded to a separate personal computer (PC)  252 . The PC  252  preferably includes excavation statistics software and an associated database  316  to correlate the acquired survey data with historical excavator production performance data to produce an estimation as to expected excavator performance over the surveyed route. The performance estimates may further be used as a basis for computing the time and cost involved in excavating a particular area based on actual geological data and historical production performance data.  
         [0069]    After completion of the initial survey, the geophysic data acquisition unit  256  is preferably coupled to the main control unit  250  on the excavator prior to initiating excavation along the surveyed route. During excavation, as previously discussed, the various databases containing geological, geophysical, position, and excavator operating performance data are processed by the main control unit  250 . The main control unit  250 , in cooperation with the excavator control unit  255 , adjusts the operation of the excavator as it traverses and excavates along the surveyed route to optimize excavation.  
         [0070]    Referring now to FIG. 11, there is illustrated an example of a survey profile obtained by transporting the geophysic data acquisition unit  256  and geographic positioning unit  254  along a predetermined excavation route. It is noted that in this illustrative example, the length of the excavation route is defined as the distance between Location L 0  and Location L 5 . A corresponding estimated excavation production profile for the predetermined excavation route is shown in FIG. 12.  
         [0071]    Referring to FIG. 11 in greater detail, distinct changes in subsurface geological characteristics can be observed at locations L 1 , L 2 , L 3 , and L 4 , which are associated with corresponding changes in the “excavation difficulty” parameter plotted along the Y-axis of the survey profile chart. Between locations L 0  and L 1 , for example, the geologic profile GP 1    362  of the subsurface has associated with it a corresponding excavation difficulty parameter of D 1 . The geologic imaging data at L 1  indicates a transition in the subsurface geology to soil having a geologic profile of GP 2    364  and a corresponding excavation difficulty parameter of D 2 , thus indicating a transition to relatively softer soil.  
         [0072]    The estimated excavation production profile data shown in FIG. 12 indicates a corresponding transition from an initial production profile PP 1    372  to another production profile PP 2    374  at location L 1 . It is noted that the rate of excavation is plotted along the Y-axis of the excavation production profile chart. Based on the survey profile data for the subsurface geological characteristics between locations L 0  and L 2 , it can be seen that an initial excavation rate R 1  is estimated for the portion of the predetermined excavation route between locations L 0  and L 1 , and an increased excavation rate of R 2  between excavation route locations L 1  and L 2  due to the lower excavation difficulty parameter D 2  associated with geologic profile GP 2    364 . It can be seen that a similar relationship exists between a particular excavation difficulty parameter and its corresponding estimated excavation rate parameter.  
         [0073]    In general, excavation difficulty parameters of increasing magnitude are associated with corresponding excavation rate parameters of decreasing magnitude. This generalized inverse relationship reflects the practical result that excavating relatively hard soil, such as granite, results in a relatively low excavation rate, while excavating relatively soft soil, such as sand, results in relatively high excavation rates. It is noted that associated with each particular geologic profile (GP X ) and production profile (PP X ), there exists a corresponding excavation time, such as excavation time T 1  associated with geologic profile GP 1    362  and production profile PP 1    372 . As such, a total estimated excavation time for a particular predetermined excavation route can be obtained by summing each of the individual excavation time parameters T 1  through T N .  
         [0074]    The survey profile data of FIG. 11 associated with geologic profile GP 4    368  between excavation route locations L 3  and L 4  indicates a discontinuity at this location. The excavation production profile data of FIG. 12 corresponding to this portion of the predetermined excavation route indicates a corresponding discontinuity in the excavation rate estimation which is shown diverging toward zero. The data for this portion of the predetermined excavation route indicates the existence of extremely tough soil or, more likely, a man-made hazard, such as a concrete or steel pipeline, for example. Further investigation and surveying of the specific area may be warranted, which may require removal of the hazard or modification to the predetermined excavation route.  
         [0075]    A more realistic geologic profile for a particular length of the predetermined excavation route is illustrated as geologic profile GP 5    370  shown between excavation route locations L 4  and L 5 . The excavation difficulty parameter for this geologic profile results in an averaged parameter of D 5 . Accordingly, an averaged excavation rate of R 5  may be appropriate when excavating this portion of the predetermined route. Alternatively, the excavation rate associated with the production profile PP 5    380  may be moderated by the excavator control unit  255  to optimize the excavation rate based on such fluctuations in excavation difficulty. It is understood that the ability of an excavator to respond to such fluctuations in excavation rate is generally limited by various mechanical and operational limitations.  
         [0076]    Turning now to FIG. 13, there is illustrated a heterogeneous composition of differing soil types over a predetermined excavation route having a predefined distance of L S . The soil in region  1 , for example, has a geologic profile of GP 1  and a corresponding geologic filter profile of GF 1 . Each of the other soil types illustrated in FIG. 13 has a corresponding geologic profile and geologic filter profile value. It is assumed that the geologic filter database  330  contains geologic filter data for each of the regions  1 ,  2 ,  3  and  4  illustrated in FIG. 13. A significant advantage of the novel hazard detection process performed by the geophysic data acquisition unit  256  concerns the ability to quickly detect the existence of an unknown buried structure  401 . The correlation and optimization software  320  executed by the main control unit  250  preferably filters out known geology using a corresponding known geologic filter profile to exclude the known or verified geology data from data associated with a survey scan image. Filtering out or excluding the known or verified geology data results in imaging only unverified buried structures  401 . By excluding known geological data from geologic imaging survey scan data, unknown or suspect buried structures are clearly recognizable.  
         [0077]    Referring now to FIG. 14, there is illustrated a conventional antenna configuration for use with a ground penetrating radar system. Generally, a single-axis antenna, such as the one illustrated as antenna-A  382  oriented along the Z-axis, is employed to perform multiple survey passes  384  when attempting to locate a potential buried hazard  386 . Generally, a ground penetrating radar system has a time measurement capability which allows measuring of the time for a signal to travel from the transmitter, bounce off a target, and return to the receiver. This time function can be calibrated to the velocity of a specific subsurface condition in order to measure distance to a subsurface object or horizon. Calculations can be used to convert this time value to a distance measurement that represents the depth of the target based upon field determined values for characteristic soil properties, such a dielectric and wave velocity through a particular soil type. A simplified technique that can be used when calibrating the depth measurement capabilities of a particular ground penetrating radar system involves coring a sample target, measuring its depth, and relating it to the number of nanoseconds it takes a wave to propagate.  
         [0078]    After the time function capability of the ground penetrating radar system provides an operator with depth information, the radar system is moved laterally in a horizontal (X) direction, thus allowing for the construction of a two-dimensional profile of a subsurface. By performing multiple survey passes in a series of parallel lines  384  over a particular site, a buried hazard  386  may be located. It can be appreciated, however, that the two-dimensional imaging capability of a conventional antenna configuration  382  can result in missing a buried hazard  386 , particularly when the hazard  386  is parallel to the direction of a survey pass  384 .  
         [0079]    A significant advantage of a novel geologic imaging antenna configuration  284  provides for three-dimensional imaging of a subsurface as shown in FIG. 15. A pair of antennas, antenna-A  388  and antenna-B  390 , are preferably employed in an orthogonal configuration to provide for three-dimensional imaging of a buried hazard  386 . It is noted that the characteristic hyperbolic time-position data distribution, as shown in two-dimensional form in FIG. 6 by use of a conventional single-axis antenna, may instead be plotted as a three-dimensional hyperbolic shape that provides width, length, and breadth dimensions of a detected buried hazard  386 . It is further noted that a buried hazard  386 , such as a drainage pipeline, which runs parallel to the survey path  392  will immediately be detected by the three-dimensional imaging GPRadar system  282 . Respective pairs of orthogonally oriented transmitting and receiving antennas are preferably employed in the antenna system  284  of the geological imaging unit  258 .  
         [0080]    Excavation Site Mapping  
         [0081]    Turning now to FIG. 16, there is illustrated an excavator  410  performing an excavation operation along a city street  420  of a city street grid  422 . An important advantage of the novel geographic positioning unit  254  of the excavator  410  concerns the ability to accurately navigate along a predetermined excavation route, such as a city street  420 , and to accurately map the excavation route in a route mapping database  294  coupled to the geographic positioning unit  254 . It may be desirable to initially survey a city street grid  422  for purposes of accurately establishing an excavation route for each of the applicable city streets  420  comprising the city street grid  422 , for example. This data is preferably loaded into the navigation controller  292  of the geographic positioning unit  254 .  
         [0082]    As the excavator  410  progresses along the excavation route defined for each of the city streets  420 , actual position data is acquired by the geographic positioning unit  254  and stored in the route mapping database  294 . Any deviation from the predetermined excavation route stored in the navigation controller  292  is accurately recorded in the route mapping database  294 . Upon completion of an excavation effort, the data stored in the route mapping database  294  may be downloaded to a PC  252  to construct an “as built” excavation map of the city street grid  422 .  
         [0083]    Accordingly, an accurate survey map of utility or other conduits installed along the excavation route mav be constructed from the route mapping data and subsequently referenced by workers desiring to gain access to, or avoid, the buried conduits. It is to be understood that excavating one or more city streets for the purpose of installing utility conduits as shown in FIG. 16 is provided for illustrative purposes, and does not represent a limitation on the application of the geographic positioning and route mapping capability of the novel excavator data acquisition and control system.  
         [0084]    Still referring to FIG. 16, accurate navigation and mapping of a prescribed excavation route may be accomplished by a global positioning system  296 , range radar system  298  or ultrasonic positioning system  300 , as discussed previously with respect to FIG. 7. An excavator data acquisition and control system utilizing a GPS  296  configuration preferably includes first and second base transponders  404  and  408  together with one or more GPS signals received from a corresponding number of GPS satellites  302 . A mobile transponder  402 , preferably mounted to the excavator  410 , is provided for receiving the GPS satellite signal  412  and base transponder signals  414  and  418  respectively transmitted from the base transponders  404  and  408 . As previously discussed, a modified form of differential GPS positioning techniques may be employed to enhance positioning accuracy to one foot or less.  
         [0085]    In another embodiment, a ground-base range radar system  298  includes three base transponders  404 ,  408 , and  406  and a mobile transponder  402  mounted to the excavator  410 . It is noted that a third ground-based transponder  406  may be provided as a backup transponder for a system employing a GPS satellite signal  412  in cases where a GPS satellite signal  412  transmission is temporarily terminated. Position data is preferably processed and stored by the geographic positioning unit  254  using the three reference signals  414 ,  416 , and  418  received from the three ground-based radar transponders  404 ,  406 , and  408 . An embodiment employing an ultrasonic positioning system  300  would similarly employ three base transponders,  404 ,  406 , and  408  together with a mobile transponder  402  mounted to the excavator  410 .  
         [0086]    Eacavator Data Acquisition and Control Process  
         [0087]    Turning now to FIGS.  17 - 20 , there is illustrated in flowchart form generalized process steps associated with the novel excavator data acquisition and control system and process. Initially, as shown in FIG. 17, a number of ground-based transponders are positioned at appropriate locations along a predetermined excavation route at step  500 . The geophysic data acquisition unit  256  and geographic positioning unit  254  are then situated at an initial location L 0  of the excavation route at step  502 . The geologic imaging unit  258 , geophysical characterization unit  260 , and geographic positioning unit  254  are then initialized or calibrated at step  504 . After initialization, the geophysic data acquisition unit  256  and geographic positioning unit  254  are transported along the excavation route, during which GPRadar, position, and geophysical data is acquired at steps  506 ,  508 , and  510 . The data acquired by the GPRadar system  282  is preferably digitized and quantized at step  512 . Data acquisition continues at step  516  until the end of the excavation route is reached, as at step  518 . The acquired data is then preferably downloaded to a PC  252  or directly to the main control unit  250 .  
         [0088]    At step  530 , shown in FIG. 18, excavation statistical software is preferably executed on the data acquired during the excavation route survey. At step  532 , historical excavator production data is transferred from the excavation statistics database  316  to the PC  252 . The data acquired during the survey is also loaded into the PC at step  534 . The excavation statistical software then performs a correlation between the acquired GPRadar data and the historical excavator production data step  536 .  
         [0089]    In one embodiment, correlation between GPRadar data and historical production data is accomplished by use of various known matrix manipulation techniques. A historical production data matrix is preferably produced at step  538  by correlating geologic image data (ID X ) with corresponding excavator production data (PD X ). A correlation value (CV XX ) is produced corresponding to each pair of geologic image data and production data parameters. The correlation value CV 22 , for example, is a correlation value associated with a statistical correlation between geologic image data parameter ID 2  and excavator production data parameter PD 2 . Associated with each geologic image data parameter is an associated time parameter and location parameter, such as T 1  and L 1  associated with geologic image data parameter ID 1 . It can be seen that correlation values associated with a plurality of geologic image data and production data parameter pairs can be produced for time and position increments along a predetermined excavation route.  
         [0090]    At step  540 , actual geologic image data is acquired over the excavation route and preferably processed as a matrix of discrete geologic image data for corresponding discrete time and location distance increments. At step  542 , the matrices produced at steps  538  and  540  are manipulated to produce a correlation matrix in which an estimated or projected production data parameter (PD XX ) is associated with a pair of corresponding actual geologic image data (ID X ) and correlation value (CV X ) parameter pairs. For example, an estimated production data parameter PD 3  is associated with actual geologic image data parameter ID 3  and correlation value parameter CV 3 . It is noted that each of the estimated production data parameters is associated with a corresponding time and distance location increment.  
         [0091]    The estimated production performance parameters for a particular excavation route are computed at step  550  as shown in FIG. 19. The total estimated time (ET T ) to excavate the entire excavation route can be estimated by summing the discrete time increments T 1  through T N . The operational costs associated with excavating the predetermined excavation route can be determined by summing the operational costs associated with each of the discrete portions along the route. The estimated labor costs (LC T ) can be estimated by multiplying the total estimated excavation time (ET T ) by the total man hour cost per hour. An estimation of the grand total of costs (GT E ) can be determined by summing all of the production costs and labor costs associated with excavating the entire route.  
         [0092]    At step  552 , the estimated excavator operation parameters are computed. For the portion of the excavation route defined between reference location L 0  and L 1 , for example, the estimated production data may indicate an optimal left track velocity (V L ) of 125 feet per minute (FPM) and a right track velocity (V R ) of 125 FPM. Further, the estimated production data may suggest an optimal excavation attachment speed of approximately 110 RPM and a target engine speed of 2.250 RPM. It is noted that the left and right track velocities V L  and V R  of 125 FPM, respectively, represents straight tracking by the excavator along the excavation route.  
         [0093]    It can be seen that along the excavation route defined between location L 1  and L 2 , it is indicated that the excavator is steering in a right direction since the left track velocity V 1  of 230 FPM is greater than the right track velocity V R  of 150 FPM. Also, it is indicated that the excavating attachment speed is increasing to 130 RPM, and that the target engine speed is increasing to 2.400 RPM, thus indicating the presence of relatively softer soil within the region defined between locations L 1  and L 2 . Along the excavation route defined between locations L 2  and L 3 , it is indicated that the excavator is again tracking in a straight direction and at a relatively slow velocity of 60 FPM, thus indicating the presence of relatively hard subsurface soil. A corresponding slower excavating attachment speed of 100 RPM and lower target engine speed of 2,100 RPM are indicated due to the slower excavator velocity.  
         [0094]    At step  560 , as shown in FIG. 20, the estimated excavation operating parameters produced at step  552  are loaded into the main control unit  250 . Excavation is initiated beginning at reference location L 0  at step  562 . At step  564 , the main control unit  250  monitors the excavator operational parameters, and out-of-range conditions are recorded in the maintenance log memory  314 . Actual production performance parameters are acquired by the excavator control unit  255 , at step  568 , and transferred to the main control unit  250 . Any inputs received from the main user interface  101  are also transferred to the main control unit at step  570 . If the actual production performance parameters received from the excavator control unit  255  differ by a predetermined amount from the estimated excavation operation parameters, as tested at step  572 , the main control unit  250  optimizes the estimated parameters at step  574 , and transmits the optimized parameters to the excavator control unit  255  to effect the necessary changes to excavator operation at step  576 . Excavation continues at step  578  until the end location of the predetermined excavation route is reached at step  580 , after which the excavation operation is terminated as at step  582 .  
         [0095]    It will, of course, be understood that various modifications and additions can be made to the preferred embodiments discussed hereinabove without departing from the scope or spirit of the present invention. Accordingly, the scope of the present invention should not be limited by the particular embodiments discussed above, but should be defined only by the claims set forth below and equivalents of the disclosed embodiments.

Summary:
A portable structure supports a subsurface imaging system and is moveable over a given imaging site. At least a first antenna of a plurality of antennae is oriented in a manner differing from an orientation of a second antenna of the plurality of antennae, such as the first antenna being orientated substantially orthogonal to the second antenna. The antennae may operate in a bi-static mode. Transmitter and receiver circuitry, coupled to the antennae, respectively generates electromagnetic probe signals and receives electromagnetic return signals resulting from the probe signals. A processor processes the received electromagnetic return signals. A display may be provided as part of the subsurface imaging system and/or as part of a processing system separate from the subsurface imaging system which processes the received electromagnetic return signals. The processor can generate two-dimensional and/or three-dimensional detection data using the received electromagnetic return signals.