Abstract:
A GNSS system in combination with a hydraulically-actuated, airborne dispenser for a dry material crop dusting system to optimize the distribution of dry materials over a particular tract of land. A GNSS subsystem is included using at least one GNSS antenna and one GNSS receiver located on the aircraft. The aircraft is equipped with an electronic/hydraulic crop dusting subsystem connected to a GNSS CPU. The GNSS ranging signals received by the antennas are processed by a receiver and processor system for determining the vehicle&#39;s position and dynamic attitude in three dimensions (3D). A graphical user interface (GUI) placed in the vehicle will give the driver a real-time view of his or her current bearing as well as a calculated “optimal path” based on calculations and variable data, such as wind speed and direction, material moisture content, altitude, air speed and other conditions. The system is adapted for operation in a differential GNSS (DGNSS) mode utilizing a base station at a fixed location.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to and claims priority in U.S. Provisional Patent Application Ser. No. 61/252,994, filed Oct. 19, 2009, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to aircraft guidance and control with differential global navigation satellite systems (DGNSSs), and in particular to a DGNSS-based system and method for optimizing crop dusting with dry materials. 
         [0004]    2. Description of the Related Art 
         [0005]    GNSS guidance and control are widely used for vehicle and personal navigation and a variety of other uses involving precision location in geodesic reference systems. GNSS, which includes the Global Positioning System (GPS) and other satellite-based positioning systems, can achieve greater accuracy with known correction techniques, including a number of commercial satellite based augmentation systems (SBASs). 
         [0006]    Aircraft are often used to spray and dust croplands, forests and other land areas with chemicals, fertilizers, seeds, water, fire suppressants and other materials. These materials may be liquid or solid. An important objective in spraying and dusting crops and in aerial firefighting is even coverage without gaps or overlaps. Another major objective is avoiding exclusion areas, which can be located internally within a field or forest being treated, or externally beyond its borders. Dry materials are typically dropped from fixed and rotary wing aircraft using spreaders. These spreaders clamp to a gate box at the base of a hopper located inside of the fuselage. As the gate box is opened, material flows from the hopper into the spreader and is pushed out behind the aircraft by air passing through the spreader. Historically these systems had to be operated manually, but methods now exist that will allow these systems to operate electronically and/or hydraulically via switches in the cockpit. However, precise distribution control presents challenges with existing equipment. 
         [0007]    Aircraft can use venturi spreaders to distribute seed, dusting material, and other chemicals. Venturi spreaders clamp to a gate box at the base of a hopper. As the adjustable door of the gate box opens, seeds, chemicals and other materials from the hopper fall into the venturi spreader and airflow through the spreader distributes it. The amount the door is opened determines the material flow rate. Optional agitators to help material exit the hopper and gate box assembly can also be included. 
         [0008]    Ideally the material being dropped from the aircraft will entirely cover the property being targeted while avoiding exclusion areas. However, factors such as the altitude of the aircraft, the ground speed of the aircraft, temperature, humidity, moisture content of the material and ambient wind speed and direction can affect the results. Flying too high or too low can distort the swath of the spread and result in misapplication of the material. Guidance systems, such as DGNSS, combined with electronic controllers for the spreading equipment, can optimize crop dusting. 
         [0009]    Aerial photography, videography, surveying and telemetry procedures commonly require accurate navigation and aircraft locating equipment and methods in order to achieve optimum results. Flight guidance has also been automated with autopilots, automatic landing systems, navionics and other equipment. Such procedures can benefit from accurate GNSS-based control systems and methods. 
         [0010]    DGNSS can utilize satellite based augmentation systems (SBAS), including the Wide Area Augmentation System (WAAS) (U.S.), and similar systems such as EGNOS (European Union) and MSAS (Japan). When accomplished with two or more antennas at a fixed spacing, an angular rotation may be computed using the position differences. In an exemplary embodiment, two antennas placed in the horizontal plane may be employed to compute a heading (rotation about a vertical axis) from a position displacement. Heading information, combined with position, provides the feedback information desired for a proper control of the vehicle direction. 
         [0011]    Another benefit achieved by incorporating a GNSS-based heading sensor is the elimination or reduction of drift and biases resultant from a gyro-only or other inertial sensor approach. Yet another advantage is that heading may be computed while movable equipment is stopped or moving slowly, which is not possible in a single-antenna, GNSS-based approach that requires a velocity vector to derive a heading. Yet another advantage of incorporating a GNSS-based heading sensor is independence from a host vehicle&#39;s sensors or additional external sensors. Thus, such a system is readily maintained as equipment-independent and may be moved from one vehicle to another with minimal effort. 
         [0012]    An example of a GNSS is the Global Positioning System (GPS) established by the United States government, which employs a constellation of 24 or more satellites in well-defined orbits at an altitude of approximately 26,500 km. These satellites continuously transmit microwave L-band radio signals in two frequency bands, centered at 1575.42 MHz and 1227.6 MHz, denoted as L1 and L2 respectively. These signals include timing patterns relative to the satellite&#39;s onboard precision clock (which is kept synchronized by a ground station) as well as a navigation message giving the precise orbital positions of the satellites, an ionosphere model and other useful information. GPS receivers process the radio signals, computing ranges to the GPS satellites, and by triangulating these ranges, the GPS receiver determines its position and its internal clock error. 
         [0013]    In standalone GPS systems that determine a receiver&#39;s antenna position coordinates without reference to a nearby reference receiver, the process of position determination is subject to errors from a number of sources. These include errors in the GPS satellite&#39;s clock reference, the location of the orbiting satellite, ionosphere-induced propagation delay errors, and troposphere refraction errors. 
         [0014]    To overcome these positioning errors of standalone GPS systems, GPS applications have been improved and enhanced by employing a broader array of satellites such as GNSS and WAAS. For example, see commonly assigned U.S. Pat. No. 6,469,663 to Whitehead et al. titled Method and System for GPS and WAAS Carrier Phase Measurements for Relative Positioning, dated Oct. 22, 2002, the disclosures of which are incorporated by reference herein in their entirety. Additionally, multiple receiver DGPS has been enhanced by utilizing a single receiver to perform differential corrections. For example, see commonly assigned U.S. Pat. No. 6,397,147 to Whitehead titled Relative GPS Positioning Using A Single GPS Receiver With Internally Generated Differential Correction Terms, dated May 28, 2002, the disclosures of which are incorporated by reference herein in their entirety. 
         [0015]    Heretofore there has not been available a GNSS system and method for guiding aircraft to optimize various procedures, including the spreading of solid material accurately on a predetermined area within relatively precise boundaries while avoiding exclusion areas with the advantages and features of the present invention. 
       SUMMARY OF THE INVENTION 
       [0016]    In practice, an exemplary embodiment of the present invention uses a GNSS system(s) in combination with a hydraulically-actuated, airborne dispenser for a dry material crop dusting system to optimize the distribution of dry materials over a particular tract of land. The system is applicable to agriculture, but is not limited to that purpose. The system includes a GNSS subsystem with at least one GNSS antenna and one GNSS receiver located on the aircraft. The system also includes an electronic/hydraulic crop dusting subsystem connected to the GNSS. The GNSS ranging signals received by the antennas are processed by a receiver and processor system for determining the vehicle&#39;s position and dynamic attitude in three dimensions (3D). A graphical user interface (GUI) placed in the vehicle will give the driver a real-time view of his or her current bearing as well as a calculated “optimal path” based on calculations and variable data, such as wind speed and direction, material moisture content, altitude, air speed and other conditions. 
         [0017]    Information that GNSS can provide to the pilot of an aircraft includes not only the current position, but extends to providing the pilot with knowledge of the ideal flight path to provide relatively even distribution of dry material over the desired tract of land. An integrated system will use the GNSS system to control the gate box of the hydraulic crop dusting system. The GNSS guidance system will recognize the ideal time to open or close the gate, how far to open the gate and how much to alter the gate opening during flight based on fluctuations in ground speed. The gate positions can also change automatically based on data entered into a pre-designed map of varying rates. The opening and changing of gate positions are intended to achieve a continual optimal desired output while the guidance system is ensuring an even distribution of the dry material. Other exemplary embodiments include an aerial camera for photography or videography, a telemetry device, a laser altimeter and components, including software, for aerial mapping and surveying. Automatic and assisted landing functions can be accomplished with the DGNSS-based control system supplemented with the laser altimeter. 
         [0018]    An ideal function of the present invention is to gather information using an aircraft and a dry gate device and to save this information into a profile to be used during later dusting/spreading sessions over the same piece of land. This profile information will be used to calibrate a gate box assembly and control system as well as the GNSS guidance system. Information stored in the profile will include gate box metering data, GNSS flight path data, and visual imaging or telemetry data gathered by an included camera and/or telemetry device. A crop dusting control system aspect of the present invention includes a GNSS subsystem connected to a controller and providing georeference guidance and positioning, and a bulk material dispensing subsystem connected to the controller and selectively and variably discharging dry material with real-time feedback signals indicating actual discharge rates. A tracking aspect of the present invention uses GNSS with the vehicle controller for tracking. An imagery aspect of the present invention uses pre-existing or new, real-time images captured by an onboard camera device and precisely matched with georeference coordinates. A comprehensive system for GNSS-controlling vehicle navigation and material discharge flow control comprises another aspect of the present invention and uses various sensors as input devices and actuators. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
           [0020]      FIG. 1A  is an isometric view of a crop-dusting aircraft showing conventional X, Y and Z axes corresponding to roll, pitch and yaw rotation. 
           [0021]      FIG. 1B  is a schematic diagram of an airborne flow control system using DGNSS embodying an aspect of the invention in a crop dusting aircraft. 
           [0022]      FIG. 2  is a block diagram of the control system in an airborne solid material crop dusting distribution system. 
           [0023]      FIG. 3  is an isometric view of a venturi spreader and a dry materials hopper, which are installed in the crop dusting aircraft. 
           [0024]      FIG. 4  is an isometric view of the aircraft, particularly showing the material distributing components of the flow control and spreader system and the hydraulic subsystem. 
           [0025]      FIG. 5  is a block diagram of the electronic control components of the flow control and spreader system and their connection with the DGNSS rover system. 
           [0026]      FIG. 6  is a top plan view of the crop-dusting aircraft in operation applying material to a field by overflying a coverage pattern consisting of parallel swaths. 
           [0027]      FIG. 7  is a block diagram of a crop dusting control system comprising an alternative embodiment of the present invention, including a sub-tank within a primary tank. 
           [0028]      FIG. 8  is a diagram of an aircraft control system comprising an alternative embodiment of the present invention and including a laser altimeter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     I. Introduction and Environment 
       [0029]    As required, detailed aspects of the present invention are disclosed herein; however, it is to be understood that the disclosed aspects are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art how to variously employ the present invention in virtually any appropriately detailed structure. 
         [0030]    Global navigation satellite systems (GNSSs) are broadly defined to include GPS (U.S.), Galileo (Europe, proposed), GLONASS (Russia), Beidou/Compass (China, proposed), IRNSS (India, proposed), QZSS (Japan, proposed) and other current and future positioning technology using signals from satellites, with or without augmentation from SBAS or terrestrial reference correction sources. Inertial navigation systems (INS) include gyroscopic (gyro) sensors, accelerometers and similar technologies for providing output corresponding to the inertia of moving components in all axes, i.e. through six degrees of freedom (positive and negative directions along longitudinal X, transverse Y and vertical Z axes). Yaw, pitch and roll refer to moving component rotation about the Z, Y and X axes respectively. Said terminology will include the words specifically mentioned, derivatives thereof and words of similar meaning. 
         [0031]    Disclosed herein in an exemplary embodiment is a sensor system for vehicle control and guidance. The sensor system utilizes at least one GNSS carrier phase differenced antenna to derive attitude information, herein referred to as a GNSS attitude system. Moreover, the GNSS attitude system may optionally be combined with one or more rate gyro(s) used to measure turn, roll or pitch rates and to further calibrate bias and scale factor errors within these gyros. In an exemplary embodiment, the rate gyros and the GNSS receiver/antenna are integrated together within the same unit, to provide multiple mechanisms to characterize a vehicle&#39;s motion and position to make a robust vehicle steering control mechanism. 
         [0032]    Without limitation on the generality of useful applications of the present invention, an exemplary application of the DGNSS optimized crop dusting control system  2  (crop dusting system) comprises a crop dusting aircraft  4 , the receiver unit  12 , a master antenna  6  and optional slave antennas  8 ,  10 , a gate box control unit  30  and a SBAS  7  such as WAAS. The rover receiver unit  12  is comprised of a clock  16 , a central processing unit (CPU)  18 , a GNSS graphical user interface (GUI)  20 , a master rover receiver  14 , an optional slave rover receiver  22 , an antenna switch control  24 , and an orientation device  26 . The CPU  18  is electrically connected to the gate box control unit  30 , which is comprised of a gate box controller  38  and a gate box control display  40 . DGNSS accuracy is created by using SBAS  7  (e.g. WAAS) corrections in combination with the above-mentioned GNSS equipment. An optional camera/telemetry device  28  is connected to the CPU  18  and provides photography, videography and related optical and other telemetry functions, such as surveying topography and image capture for monitoring, recording and analyzing aerial procedures for direct georeferencing to 3-D digital models, such as the Google Earth model. 
       II. Crop Dusting Control System  2   
       [0033]    The exemplary purpose of the present invention is to gather data while flying over a specific piece of land. Information to be gathered includes visual image data and/or telemetry data, flight path information based on GNSS data points, and the rate of dry material being dropped from a dry gate mechanism. This data will be saved to a profile based on the material used and the land being flown over. Additional data may be input into said profile from external data sources, such as the internet or manually by a programmer or end-user. The goal of this combination of data is to increase the accuracy of dropping material over a piece of land from an aircraft for agricultural or other purposes. 
         [0034]    Referring to the drawings more detail, the reference numeral  2  generally designates the crop dusting control system. The crop dusting control system  2  is comprised generally of a crop-dusting aircraft  4 , a GNSS-based aircraft control subsystem  9  and a gate box control system  11 . The GNSS-based control subsystem is comprised of: antennas  6 ,  8 ,  10 ; additional flight instruments; the receiver unit  12 ; and the GUI  20 . The gate box control system is comprised of a gate box control unit  30 , an internal hopper  42 , a gate box assembly  64 , and a spreader  62 . 
         [0035]      FIG. 1A  represents an isometric view of a crop-dusting aircraft  4 . Roll refers to an aircraft turning about the X-axis. Pitch refers to an aircraft turning about the Y-axis. Yaw refers to an aircraft turning about the Z axis. This is graphically displayed in  FIG. 1  and these terms are used throughout in such a manner. 
         [0036]      FIG. 1B  represents a schematic diagram of a crop-dusting aircraft  4  and indicates the various elements of the crop dusting system  2 , including the aircraft control subsystem  9  and the gate control subsystem  11 . 
         [0037]    The GNSS system is comprised of the external antennas and the internal components including a receiver unit  12 . The master rover antenna  6  and the two optional slave antennas  8 ,  10  can be placed externally on the aircraft  4 . The example shown in  FIG. 1B  displays the optional slave antennas  8 ,  10  located on the tail (e.g., horizontal stabilizer) of the aircraft  4  with the master antenna  6  located near the cockpit. This arrangement is exemplary only, and other arrangements of one or more antenna(s) may be implemented and connected to the receiver unit  12 . Additional slave antennas may also be placed on the aircraft for increased accuracy and allow for the calculation of wind speed and direction. The various antennas receive satellite positional data, including each individual antenna&#39;s geo-reference DGNSS-determined location, and report this information to the rover receiver unit  12 . Having more than one antenna on the aircraft allows more detailed positional information about the vehicle to be transmitted. With three antennas, a complete six-degrees-of-freedom vector 3D attitude solution can be determined by the GNSS positioning system, allowing the system to track the yaw, pitch, and roll of the aircraft. Suitable receiver units are available from Hemisphere GPS, LLC of Calgary, Alberta, Canada and Scottsdale, Ariz., and can be based on Crescent single frequency or Eclipse dual frequency receiver technology. 
         [0038]    The master rover receiver  14  and the optional slave rover receiver  22  receive positional data from at least one antenna  6 ,  8 ,  10  on the aircraft, as well as from an SBAS  7 . As stated above regarding the slave antennas, the slave receiver  22  is an optional device that increases the positional accuracy of the entire system. The CPU  18  processes all information received by the master and slave rover receivers  14 ,  22  and compiles this data with information it may receive from other optional flight instruments. Through a combination of the clock  16 , CPU  18 , the orientation device  26 , and other optional flight instruments, information is displayed to the pilot through the GUI  20  located in the cockpit of the aircraft  4 . The GUI  20  provides information to the pilot graphically and allows the pilot to input commands directly into the GUI  20 , which are read and processed by the CPU  18 . Commands entered by the pilot are communicated to the crop dusting system  2  through the CPU  18 . The system also contains the antenna switch control  24 , which enables switching among the antennas  6 ,  8 ,  10  for selective or sequenced input to the receivers  14 ,  22 . The CPU  18  can be programmed for switching among the antennas  6 ,  8 ,  10  via the switch control  24 . Also contained within the receiver unit  12  is a wide area network (WAN) antenna  90  which can access long-distance wireless WAN networks and connect the pilot to the internet. 
         [0039]    Information displayed to the pilot on the GUI  20  will include the aircraft&#39;s dynamic operating characteristics such as current speed, altitude, heading, yaw, pitch, and roll. Additionally, the pre-programmed flight path over the selected tract of land will be displayed with the position of the aircraft  4  dynamically displayed in real-time, providing the pilot with a flight path that will produce optimal application of the dry crop dusting material. The GNSS system  9  will also notify the pilot when the aircraft  4  is deviating from the ideal path as calculated by the crop dusting system  2 . Ideal speeds for making sweeping turns will also be displayed, giving the pilot an opportunity to anticipate each turn. 
         [0040]    The WAN antenna  90  is able to connect to a nearby WAN or local area network (LAN). This connection to the internet will give the pilot (or driver in the case of adapting the present invention to a ground vehicle) internet capabilities which will allow the pilot to access specific websites containing recently updated photographs of the land to be dusted or surveyed. Information that can be gleaned from such a map includes field water data, the location of obstacles where dry material should not be spread, and other relevant data necessary for accurate and complete coverage of dry material. 
         [0041]    Data generated by the various sub-systems of the aircraft can be automatically sent over the WAN from the local WAN antenna  90  to a computer on the ground via the internet. This information can then be used to track the aircraft as it currently flies, to determine where a past aircraft has flown, or simply to monitor the various sub-systems. The CPU  18  connects to said WAN antenna and provides any and all relevant data requested by the user on the ground regarding the various systems and sub-systems of the overall crop dusting control system  2 . 
         [0042]    The optional camera/telemetry device  28  can facilitate a variety of procedures and operations. For example, real-time video images of fields, forests and other fly-over land and marine images can be captured for processing by the CPU  18 , thus providing visual records of operations. Such records can be uploaded to a server for further analysis and record-keeping. Aircraft equipped with the control system  2  can receive such photographic and geographic data for use in subsequent operations. For example, imagery can be made available for a next day&#39;s operations, or with even shorter turnaround. Such visual records can be matched with Google Earth data as mentioned below by an automatic geo-referencing process to generate pre-planned flight paths based on recent land data retrieved by fly-overs. Moreover, telemetry procedures such as topographical mapping, mineral surveying and other aerial operations can be facilitated with suitable RF, IR, optical, sonar, radar and other telemetry means. 
         [0043]    Providing up-to-date visual data and accurate information about water and mineral data would be extremely important in the agricultural field. There is a need in the industry for updated visual field data quickly and often. With the internet connection allowed by the WAN antenna  90 , an aircraft outfitted with the present invention can perform a fly-over of a particular piece of land and gather image data with the connected camera/telemetry device  28 . These images can immediately be sent over the network to whomever requested those photos, and the user on the ground can compare the images and setup a pre-planned flight path on a ground computer. This flight path can then be sent to the pilot who will then perform a job of dusting the area chosen by the user on the ground. Optionally, unmanned aerial vehicles (UAVs) can be used to daily or weekly perform large-scale sweeping flights over varying areas of land to gather image data. This data can be uploaded to a server accessible on the internet whereby paid subscribers can retrieve relevant and up-to-date image data on their particular piece of land by entering in geo-reference information. 
         [0044]    Even more simply, the camera or telemetry device  28  can be used to determine and account for altitude and wind drift calculations. Using simple image recognition the system can pick out a single point in an image and track its movement so as to determine aircraft altitude depending on how fast the tracked object moves through the frame. Determining the angle of movement relative to the orientation of the airplane can be used to determine cross wind. Combined with GNSS positional data, all positional information likely required by the CPU to calculate when and where dry material should be dropped onto a field should be readily available from the onboard equipment. 
         [0045]    The gate control system  11  is comprised of the controller unit  30 , the gate box assembly  64  and connected components. The gate box control unit  30  contains the electrical gate box controller  38  and the electrically connected gate box GUI  40 . The gate box control display  40  is similar to the GNSS GUI  20  in that it displays graphically information related to the gate control unit  11  to the pilot. The pilot can optionally enter commands into the gate box control display  40  which will send signals to the gate box controller  38  to open or close the gate box assembly  64 . It should be noted that a non-graphical user interface can be installed in place of the gate box GUI  40 . 
         [0046]    The gate box controller  38  is also electrically connected with the CPU  18 , which is in constant communication with the GNSS-based control subsystem  9 . This allows the CPU  18  to autonomously control the opening and closing of the gate box assembly  64  based on GNSS positional data. This combination of positional data, gate box control and a pre-planned flight path allows the pilot to optionally hand over all crop dusting control to the CPU while the pilot focuses on the task of flying the plane along the desired path. If the pilot wishes to regain manual control over the gate box assembly  64 , the pilot interrupts the auto-control of the gate box controller  38  via the gate box GUI  40 . 
         [0047]    The gate control system  11  includes a “soft close” feature whereby the final closing of the gate box assembly  64  is controlled via a proportional-integral-derivative (PID) control feature or function and algorithm, which can be programmed into the gate box control unit  30  and/or the CPU  18 . The PID soft close control is effective during the final portion of the gate closing motion and “softly” closed the gates just enough to prevent further material flow. In particular, the soft close control avoids “overclosing” the gates with greater force and movement than is necessary. Overclosing the gates tends to delay reopening because the actuator mechanism must overcome the greater force and the moving parts must travel further. Prompt system reactions upon crossing boundaries between different application rate zones are helpful in applying material. 
         [0048]    The two displays, the GNSS GUI  20  and the gate controller display  40 , are available to the pilot in the aircraft  4  cockpit and allow the pilot to make on-the-fly changes to the crop dusting system control  2 , or to merely adjust the aircraft&#39;s course to maintain the calculated optimal course. The two displays are electrically connected to the gate controller  38  and the CPU  18 , which are also electrically connected. Information sent to the gate controller  38  by the gate box control display  40  is also processed by the CPU  18  and stored in memory. 
         [0049]      FIG. 2  shows a box diagram and the connections between the GNSS sub-system  9 , the gate control sub-system  11 , and the gate hydraulic sub-system  80 . Electrical control signals are processed back and forth between the CPU  18  and the gate box controller  38 , with each providing constant feedback to one another. An additional feedback loop exists between the gate box controller  38  and a gate box assembly sensor  28 . The feedback mechanism shall be any suitable mechanism for the purposes of transmitting information from the sensor to the controller  38 . The sensor  36  may be a mechanical sensor, an optical sensor, or any sensor suitable for determining the rate of flow of material exiting the gate box  64  at any time. The dry material path  32  exits the hopper and enters the gate box, which is controlled by the several other systems combined. As the gate box assembly  64  is opened or closed, material will exit the gate box at a faster or slower rate which will then be picked up by the sensor  36 . This information is returned to the gate box controller  38  and in turn the CPU  18  and is stored as metering information to the profile of the present job. 
         [0050]      FIG. 3  displays the venturi spreader  62  and the gate box assembly  64  that attach to the aircraft  4 . One example of such a spreader and gate box assembly combination is that manufactured by Transland Inc. of Wichita Falls, Tex. As an example, a typical Transland spreader  62  and gate box assembly  64  is further comprised of a spreader tubular connection  66 , a gate box tubular connection  68 , some variety of spreader latch arm  70 , a gate box structural bar  72  and connected flexible arms  74 . In one such variety of spreader and gate box combination, the spreader latch arms  70  or similar connecting devices connect to the gate box structural bar  72  a similar device. The flexible arms  74  in the present example allow the structural bar  72  to be positioned to accept a variety of spreaders  62 . 
         [0051]      FIG. 4  shows the spreader  62  and the gate box assembly  64  mounted on the aircraft  4  and fed by the internal aircraft hopper  42 , which can be filled with dry material  44  for spreading by the spreader  62 . It should be noted that this material may not exit uniformly from the spreader as indicated. Depending on the wind conditions and the tilt of the aircraft  4 , the material  44  may drift a significant amount in the wind. Knowing the aircraft&#39;s altitude, wind speed, and wind direction can help the CPU  18  calculate such material drift and adjust the flight path accordingly. The CPU  18  working with the gate box controller  38  could signal the controlling hopper valves to open or close early or late depending on the wind and altitude. Additionally,  FIG. 4  shows the internal components of the hydraulic subsystem  80 . The hydraulic subsystem  80  is further comprised of a hydraulic reservoir  82 , a pump  84 , a control valve  86  and an actuator  88 . The hydraulic actuator  88  can comprise a piston-and-cylinder unit or a hydraulic motor. These components are controlled by the gate box controller  38 . The hydraulic subsystem  80  actuates the gate box assembly  64 . A hydraulic subsystem can be preferred over an electrical servo subsystem for speed and accuracy. 
         [0052]    The internal hopper  42  supplies the dry material to the gate box assembly  64 . The gate box assembly  64  is opened and closed using the above-mentioned hydraulic subsystem  80 . As the gate opens, dry material exits the hopper  42  and enters the gate box assembly  64 . Air passing through the spreader  62  pulls the dry material out of the spreader and the spread material  44  disburses evenly through the air as it falls on the ground below. 
         [0053]      FIG. 5  is a block diagram of the crop dusting control system  2  showing the receiver unit  12  and the CPU  18  combined in a single unit  12 / 18 , with appropriate I/O connections.  FIG. 5  also shows the electrical, hydraulic and mechanical I/O connections for the gate box controller  38 . An application of the present invention is to optimize the spread of dry material over a particular piece of land. The system  2  obtains DGNSS data from the rover receiver unit  12 , processes all relevant data through its CPU  18 , and determines when to open or close the gate box assembly  64 , and by how much. The gate box controller  38  operates the gate box assembly  64 . The gate box controller  38  then communicates with the hydraulic subsystem  80  whereby the gate box assembly  64  is opened or closed. Feedback from the gate box assembly  64  is transmitted to the gate box controller  64  via a push/pull encoder cable  76 , which is physically pushed or pulled as the gate moves, actuating an encoder  78  located within the gate box controller  64 . The gate box controller  64  is calibrated to determine the gate position, and this information is transmitted to the CPU  18  for further analysis. 
         [0054]      FIG. 6  is a top plan view of a crop-dusting aircraft  4  dusting a desired tract of land in parallel swaths. Contour or curved swaths can also be accommodated. For example, U.S. patent application Ser. No. 11/184,657 entitled Adaptive Guidance System and Method discloses accommodating various field configurations using straight-line (A-B) and contour swathing patterns, and is incorporated herein by reference. Tract border  46  information can be input to the CPU  18  of the crop dusting control system  2  pre-flight, and the gate controller  38  will shut the gate box assembly  36  when the CPU  18  determines that further dusting will fall outside of the border of the tract. The dusted rows  48  and the undusted rows  50  are displayed in  FIG. 6  as well. The rows  56  will remain uniform as long as the pilot, or autopilot linked to the control system  2 , guides the aircraft  4  along the displayed optimal path  52 . Including topographical information from Google Earth allowing three-dimensional positional information can increase uniformity in applying materials. Certain areas may be designated as “no spray zones”  54  for a number of reasons, including crop differences, soil differences, property boundaries, moisture levels, wind drift concerns, livestock, bodies of water, roadways, etc. The spraying or dusting control system  2  can be programmed to discontinue material distribution during flyover of these particular areas. Additionally, several government agencies, such as the U.S. Forest Service and the U.S.D.A., are currently in the process of creating Google Earth files. The files being created by these agencies can be used to further designate “no spray zones” and help to define large areas where spraying or dusting is common while precisely delineating private and federally-protected lands. 
         [0055]    Precise location and altitude variables are automatically obtained by the DGNSS portion of the crop dusting system  2 , processed by the CPU  18 , and instructions are automatically passed on to the gate box controller  38 . Variables that are input into the system manually to increase accuracy and optimization include, but are not limited to, wind speed, material type, and the spread density required. Additionally, boundary information regarding the specific tract of land to be dusted must necessarily be defined to the CPU for it to determine when the gate must be closed and when it should be reopened. Such boundary information can also be acquired through connections with the Google Earth program, as described in more detail below. Alternatively, the gate controller may be controlled manually via the gate box control display  40 . 
         [0056]    A pre-planned path can be programmed into the CPU which defines where the aircraft  4  should fly. This pre-planned path can be based on only data points or it can be introduced through common mapping programs such as Google Earth, a product of Google Inc. of Mountain View, Calif. By creating new Google Earth files with positioning information, the CPU can take DGNSS position information of the aircraft and overlay that information onto the Google Earth map to determine precise positional information. The DNGSS control subsystem  9  is designed to interact with planned advances in Google Earth software that will allow positional data to include Z-axis topography to further optimize position tracking and field spraying. Thus, if the land below the aircraft varies in height, the aircraft can automatically adjust its altitude as need to avoid irregular field spraying or dusting. 
         [0057]    The preferred embodiment of the present invention is designed to incorporate KML reference data used in conjunction with Google Earth. KML is a file format used to display geographic data in an Earth browser such as Google Earth and Google Maps. By using KML code, pilots or agricultural planners can use the Google Earth interface to add ground overlays, placemarks and other geographic data to the Google Earth interface, and save this as KML reference data which can then be shared with other pilots or agricultural planners for future use on a particular site. This reference data can then be incorporated into the pre-planned flight path over a particular tract of land. Alternatively, a map can be provided to the pilots via the GUI mentioned above wherein the Google Earth interface is overlaid with the flight plan and the pilot can visualize the flight pattern needed to cover the field. 
         [0058]    Said pre-planned flight path can also be created based on imaging taken by the aircraft on previous flights. Image data can be geo-referenced automatically using a program like Google Earth. The user may then overlay flight path information or field data onto the digital map, or may place reference points directly into the program and export a data file that can be used to preload the CPU  18  with information pertinent to the job to be performed at the field site. This information may include flight path routes, water data, crop zone layouts, and where not to dump dry material on the ground below. 
         [0059]    In another alternative use of the invention, the crop dusting control system  2  can be used to carry large amounts of water or chemicals, either solid or liquid, for the purpose of putting out large forest fires. Data from Google Earth created by such agencies as the U.S. Forest Service will allow such fire-fighting aircraft to quickly upload a pre-planned map of an area and even update that map with target fire-control zones. Since the system  2  can recognize data that already exist in a three-dimensional form within Google Earth, valuable time is saved, and highly precise flight plans can be created quickly and easily. 
       III. Alternative Embodiments 
       [0060]      FIG. 7  is a block diagram showing a tank control system  102  comprising an alternative embodiment of the present invention. The relationship between the hopper  142 , the gate box assembly  164 , and the spreader  162  as defined above is modified with the addition of a sub-tank  104  located within a main tank/hopper  142 . The sub-tank  104  can be filled with a concentrated chemical, whereas the main tank  142  can be filled with water for mixing with the concentrate in desired proportions. Both the internal sub-tank  104  and the hopper  142  feed into the gate box assembly, (or in the case of liquid application, into a sprayer assembly). The flow of material  108  and the flow of concentrated chemical  110  from the sub-tank  104  must pass through electrically controlled valves  106 . These valves are electrically connected to the gate box controller  138 , which determines how much of either product is introduced into the gate box assembly  164 . Said gate box controller  138  is in constant communication with the GNSS CPU  118  and so gate box controls can be based off of positional information or other data known to the CPU. The concentrated solution mixes with the material from the hopper  142  inside the gate box assembly  164 . The mixed material flow  112  is then passed along to the spreader  162 . From here, the mixed material is discharged at  144 . The advantages of such an embodiment are that the entire hopper load of spreading material, e.g. water, avoids contamination with chemical, and the entire hopper  142  does not have to be cleaned and sterilized of the chemical after the load is spread over a field. The sub-tank can be individually flushed or otherwise cleaned to remove chemical residue. Moreover, disposing of certain chemicals is regulated and involves significant expense, which can be minimized by isolating such materials in the sub-tank  104 . 
         [0061]      FIG. 8  shows an aircraft control system  202  comprising another alternative embodiment of the invention wherein a laser altimeter  228  is connected to an internal CPU  218  of a receiver unit  212 . A GNSS receiver unit  212  is connected to antennas  206 ,  208 ,  210 . As stated above, the slave antennas are optional, but additional antennas increase GNSS positional accuracy. A master rover receiver  214  and an optional slave rover receiver  222  receive positional data from the at least one antenna on the aircraft, as well as from an SBAS  207 . A CPU  218  processes all information received by the master and slave rover receivers  214 ,  222  and compiles this data with information it receives from the laser altimeter  228  and other flight instruments. Through a combination of the clock  216 , CPU  218 , an orientation device  226 , the laser altimeter  228 , and other flight instruments, information is displayed to the pilot through the GUI  220  located in the cockpit of the aircraft  204 . The GUI  220  provides information to the pilot graphically and allows the pilot to input commands directly into the GUI  220  which are read and processed by the CPU  218 . The system  202  also includes an antenna switch control  224 . A gate box control subsystem  11  such as that described above can optionally be utilized with the control system  204 . 
         [0062]    Although DGNSS systems are ideal and highly accurate when dealing with generally planar, two-dimensional coordinate systems, they are not as accurate when dealing with z-axis attitude for vehicles such as aircraft (e.g., X and Y). For this reason, altimeters are still used rather than relying on DGNSS alone. A laser altimeter  228  may be accurate to the centimeter level. Combining the altimeter  228  with the DGNSS system and a dual-frequency receiver such as the Eclipse receiver available from Hemisphere GPS can provide ideal approach vectors for use with the above-mentioned Google Earth mapping applications. 
         [0063]    Using input variables such as wind speed, wind direction, desired spread density and material type, altitude, roll, pitch and yaw the crop dusting control system CPU  18  determines how much to open or close the gate box assembly  64 . These variables, when changed, will also change the rate at which dry material must be dropped out of the plane. As the aircraft&#39;s flight path changes, the crop dusting control system  2  receives the constantly updating DGNSS data and the CPU  18  recalculates how open the gate box assembly  64  must be to maintain optimal material coverage. This same principal applies as the aircraft  4  approaches the tract border. For example, the faster the flight of the aircraft  4 , the sooner the controller  18  must shut the gate box assembly  64 . The inclusion of an optional laser altimeter  228  can enable more accurate flight plan following, for example using Google Earth information from planned future advances to include Z-axis topography, and allowing for a completely three-dimensional flight plan to be created prior to the aircraft taking off. Although the above generally represents an exemplary embodiment of the invention, it is to be understood that the invention can be embodied in various forms, and is not to be limited to the examples discussed above. For example, the system could be implemented to work with a material spreader designed for use with helicopter crop dusting equipment. 
         [0064]    It is to be understood that while certain aspects of the disclosed subject matter have been shown and described, the disclosed subject matter is not limited thereto and encompasses various other embodiments and aspects