Patent Publication Number: US-9405005-B1

Title: Automatic dependent surveillance broadcast (ADS-B) system for ownership and traffic situational awareness

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. provisional patent application Ser. No. 61/637,563 filed on Apr. 24, 2012, which is incorporated herein by reference. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The invention described hereunder was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law #96-517 (35 U.S.C. 202) in which the Contractor has elected not to retain title. 
    
    
     BACKGROUND 
     a. Field of Invention 
     The invention relates to aircraft telemetry and control systems suitable for use in an unmanned aerial system (UAS) and, more particularly, to an ADS-B architecture for use in both manned and unmanned aircraft that provides airborne or ground control station (GCS) pilots with enhanced ownship and traffic situational awareness. 
     b. Background of the Invention 
     The Federal Aviation Administration (FAA) promulgates both Visual flight Rules (VFR) and Instrument Flight Rules (IFR) for all manned aircraft. VFR regulations require a pilot to be able to see outside the cockpit, and to control the aircraft&#39;s attitude, navigate, and avoid obstacles and other aircraft. However, an airborne pilot&#39;s cockpit instrumentation offers very limited en-route and terminal surveillance to augment the pilot&#39;s situational awareness, and offers minimal information on surrounding traffic, nor any traffic alerts. 
     The dearth of situational information is even more pronounced for Unmanned Aerial Systems (UASs) such as drones, which have no onboard pilot to perform the see and avoid function. Currently, UASs can only fly domestically in our National Airspace System with a Certificates of Approval (COA) or Experimental Airworthiness Certificate issued by the FAA. The FAA will only issue these certificates if a qualified ground observer or qualified personnel in a manned chase aircraft can perform the See-And-Avoid (S&amp;A) function. 
     The demand for UASs is proliferating among the military, civil government, and private sectors due to significant improvements in their capabilities and performance. UAS-related research and innovation is driving the creation of companies and jobs, and UAS innovation has dramatically reduced the cost of aerial surveillance for law enforcement agencies and private companies. However, the proliferation of UASs is causing challenges as well. Without a regulatory framework, a large number of UASs in U.S. airspace would endanger commercial airlines and private aircraft. The FAA has not yet established Federal Aviation Regulations (FARs) for UASs to fly routinely in U.S. airspace. However, the FAA has been charged with developing a comprehensive plan for the integration of private UASs into U.S. airspace by late 2015. 
     It is reasonable to assume that any new FAA rules will impose requirements similar to manned aircraft. The FAA is mandating every aircraft operating within its airspace, where a transponder is currently required, to be equipped with Automatic dependent surveillance-broadcast (ADS-B) Out by Jan. 1, 2020. ADS-B is the satellite-based successor to radar. ADS-B makes use of GPS technology to determine and share precise aircraft location information, and streams additional flight information to the cockpits of properly equipped aircraft. ADS-B is a more reliable system for detecting and avoiding both cooperative aircraft and, importantly, non-cooperative aircraft such as parachutists, balloons, and manned aircraft without radios or navigation aids. Indeed, proposed FAR rules have been discussed. Any new FAA rules for UASs will inevitably impose strict standards for UASs, and is very likely to require some form of ADS-B-based collision avoidance technology. Unfortunately, current ADS-B Out lacks enhanced visual acquisition of real time traffic. Conventional ADS-B Out schema only transmit the immediate aircraft&#39;s position and velocity information automatically and periodically (at least once every second) without flight crew or operator intervention. Only air traffic controllers currently have information on surrounding aircraft positions, and the UAS&#39;s GCS has no information on surrounding aircraft or threats. Moreover, conventional aerospace telemetry networks require the use of efficient domain-specific protocols at the transport, network, and routing layers to protect against temporary loss of telemetry. However, the existing GCS devices (conventional computers) and services are based on legacy protocols such as wireless radio frequency communications via serial asynchronous protocols that serves as a conduit to assure the necessary UAS pilot situational awareness. ADS-B is susceptible to temporary loss of telemetry between the GCS, and if ADS-B data were to be transmitted using serial asynchronous or TCP/IP protocol it would be highly susceptible to telemetry loss. The loss of telemetry can occur from various factors such as simple line of sight distance, interference, to atmospheric disturbances. These constraints make conventional ADS-B ill-suited for remote-piloted UASs were situational awareness and conflict situational awareness is extremely limited. 
     One solution is for every GCS to transmit their UAS coordinates to air traffic control and let them consolidate and analyze all their data, inclusive of all UASs under their command. United States Patent Application 20100066604 by Limbaugh et al. (Kutta Technologies, Inc.) published Mar. 18, 2010 shows an unmanned aerial system (UAS) position reporting system in which an air traffic control reporting system (ATC-RS) receives position data of a UAS from its ground control station (GCS) and communicates the position of the UAS to a civilian air traffic control center (ATC) or to a military command through an ADS-B signal or through a TIS-B signal through the ADS-B and TIS-B transceiver. The ATC-RS is adapted to display the position of the UAS in the airspace on a display screen. This solution is cumbersome inasmuch as it requires four separate data transmissions to avoid a collision, and it is highly prone to temporary loss of telemetry. 
     A better solution is to use a UAS&#39;s ADS-B Out transceiver as a “repeater” to transmit not just the immediate aircraft discretes, but also other priority aircraft and ADS-B IN traffic information in the ADS-B telemetered signal. This way the GCS has all the data in one downlink. 
     U.S. Pat. No. 6,064,335 to Eschenbach (Trimble) issued May 16, 2000 shows a GPS based ADS-B system in which any properly equipped aircraft can know the position and heading of all neighboring aircraft. Each aircraft utilize GPS technology to determine its position and heading, and these discretes are transmitted to other ADS-B equipped aircraft, as well as ground control. Each aircraft in the vicinity would receive the GPS squitter and track the position and progress of neighboring aircraft, thus implementing a GPS squitter Traffic Alert and Collision Avoidance System (TCAS). Despite suggesting the repeater concept, the Trimble collision avoidance system only uses it to give a manned aircraft a way of visually cross-checking air traffic alerts from squitter avionics with air traffic controller communications. The suggested system is not adapted for use in a UAS and does not disclose a turnkey communication network between air and GCS. 
     What is needed is an ADS-B system that is more fully adapted for both airborne pilots and UAS pilots to provide a more comprehensive and failsafe detection and warning system to avoid accidents. Otherwise, impending FAA regulations are expected to severely limit the range and conditions under which UASs can operate. Disclosed herein is a system and method for ADS-B adapted for UASs to give them a new capability—to periodically transmit the ownship three-dimensional position and airspeed, as well as that of other surrounding aircraft in the vicinity, to the GCS and to use an ADS-B functional redundancy via a secure UDP/IP network link that is impervious to temporary telemetry loss for increased UAS situational awareness in uncertain environments. The system may also be deployed in the cockpit of conventional aircraft for enhanced ownship and traffic situational awareness of the airborne pilot. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an ADS-B system coupled to a manned or unmanned aerial vehicle for increased situational awareness and self-separation assurance including methods for ADS-B functional redundancy. 
     It is another object to provide an ADS-B system adapted for use in a UAS to provide increased situational awareness and a self-separation assurance system to avoid accidents. 
     It is another object of the invention to provide an UAS-ADS-B architecture that provides UAS GCS operators with comprehensive ownship and traffic situational awareness by inclusion of surrounding traffic information in the transmission of data through the GCS telemetry downlink using serial and/or a secure packet-based IP network to the GCS. 
     It is another object of the invention to provide an UAS-ADS-B architecture in which ADS-B data is received at a GCS via telemetry downlink, wherein a software lost-link detector senses a loss of telemetry link and compensates for temporary loss of telemetry between the GCS. 
     It is another object to provide methods for displaying ADS-B traffic information in three and four dimensions at the GCS using an industry standard Earth browser for the visual acquisition of traffic and situational awareness, and for consolidating the above-mentioned display with weather, restricted airspace, and satellite imagery information on the Earth browser for hazard avoidance. 
     It is another object to provide autonomous GCS software algorithms for traffic situation awareness and alerting of potential collisions or hazardous traffic situations, based on separation and collision zones surrounding the aircraft. 
     According to the present invention, the above-described and other objects are accomplished by providing an ADS-B system for increased situational awareness and self-separation assurance employing methods for ADS-B functional redundancy. The invention is especially suited (and is herein described) in the unmanned context in which a UAS is capable of telemetering the position of the “ownship” in addition to the location of surrounding aircraft, as well as FAA and other data, to a ground control station (GCS) in real time. At the UAS, the ADS-B system uses a Universal Access Transceiver (UAT) to receive air-to-air ADS-B In messages direct from aircraft nearby, as well as ADS-R and TIS-B messages from ground based transceivers. The ADS-B messages are received by UAT antennas and are processed by the ADS-B UAT as ADS-B/ADS-R/TIS-B message reports. The ADS-B message packets are transmitted to an ADS-B ground control station (GCS) laptop via a telemetry Radio Frequency datalink via serial asynchronous protocol. The transmitted message packets include heartbeat, ownship, and traffic reports. 
     The complete system architecture relies on an IP network background and incorporates redundancy via the internet. The ADS-B data is transmitted encrypted to the UAS GCS using UDP/IP protocol to meet FAA security data requirements. The GCS laptop employs “lost-link” detection software to sense any loss of telemetry link and to compensate. If the lost-link software senses a loss of telemetry link resulting from either the downlink telemetry between the UAS and the GCS being lost, or the data corrupted, the lost-link software automatically switches over to the FAA secure center data stream and provide near real time substitute data to the operator. The redundancy of data adds aircraft situational awareness even during the loss of telemetry. 
     The invention also provides a GCS architecture and geo-browser software application at the GCS that parses incoming ADS-B messages and converts the ADS-B data to a keyhole markup (KML) format for display purposes. The dynamic KML files are written to an industry Earth browser (Google Earth Pro® or the like), which reads the KML files and displays the ownship and traffic information spatially, providing 3D synthetic views of the UAS and its surroundings as well as projected future positions of the UAS and other aircraft. A key aspect of the visual display is that all traffic aircraft models are accompanied with 3D color-coded contrails as an aide to visual acquisition of traffic targets. The ownship data may be selectively overlayed with other downlink data such as weather, FAA Notice To Airmen (NOTAMS), keep out zones, and other relevant information. The consolidation of ADS-B information with telemetry communications allows real-time traffic information to be available to the UAS operator. 
     A novel algorithm is also proposed for traffic situation awareness and alerting of potential collisions or hazardous traffic situations. Automatic traffic alerts are generated based on separation and collision zones surrounding the aircraft, respectively. 
     The same geo-browser display provided at the GCS may be deployed in the cockpit of conventional aircraft for enhanced ownship situational awareness of the airborne pilot. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional aspects of the present invention will become evident upon reviewing the embodiments described in the specification and the claims taken in conjunction with the accompanying figures, wherein like numerals designate like elements, and wherein: 
         FIG. 1  is a block diagram of the overall system architecture. 
         FIG. 2  illustrates the ADS-B IN overview for processing ADS-B/ADS-R/TIS-B traffic reports. 
         FIG. 3  is a schematic block diagram illustrating the control interfaces of the ADS-B and GPI  7  transmission between the UAS aircraft  2  and the GCS  1 . 
         FIG. 4  illustrates an embodiment of the UAS-ADS-B unmanned aircraft system diagram for vehicle installation. 
         FIG. 5  shows a detailed schematic of the converter apparatus  24 . 
         FIG. 6  is a process low diagram of the software used at GCS  1  ADS-B laptop according to the present invention. 
         FIG. 7  is a diagram of the UAS-ADS-B functional redundancy architecture for loss link of vehicle telemetry. 
         FIG. 8  illustrates the detailed Loss Link module state machine diagram for the loss link checksum algorithm  42 . 
         FIG. 9  is a more detailed illustration of the UAS-ADS-B risk collision volumes  84 - 87  for detecting intruding aircraft, alerting, and displaying UAS  2  aircraft position for self-separation assurance. 
         FIGS. 10-14  illustrate the UAS-ADS-B synthetic display for exocentric (God&#39;s eye) and egocentric views and related functionality showing user controls and three dimensional display processing. 
         FIG. 15  illustrates the ADS-B system of  FIG. 1  adapted for a general aviation manned aerial vehicle  11  for increased situational awareness and self-separation assurance. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is a hardware and software architecture that integrates Automatic Dependence Surveillance Broadcast (ADS-B) surveillance technology to an unmanned aircraft system (UAS), with improved communications and sophisticated display capabilities to provide increased situational awareness and a self-separation assurance system to avoid accidents. The ADS-B system architecture is especially suited for UAS&#39; because it integrates: 1) UAS flight qualified customized ADS-B hardware; 2) wireless radio frequency telemetry for vehicle communications; 3) loss link functional redundancy of ADS-B/ADS-R/TIS-B data, special use airspace data, and hazardous weather data via secure internet communication; 4) a software architecture with novel algorithms for real-time ADS-B data integration, conflict detection and alerting, and control logic for loss of UAS telemetry link; and 5) a synthetic vision display using a fully-integrated geobrowser for three dimensional graphical representations for ownship and air traffic situational awareness. 
     The following is a list of acronyms used, which are used throughout the description of the preferred embodiment: 
     ADS-B Automatic Dependent Surveillance-Broadcast 
     IPv6 Internet Protocol version 6 
     GBT Ground Based Transceiver (ADS-B) 
     GCS Ground Control Station 
     GPS Global Positioning System 
     NACp Navigation Accuracy Category Position 
     NIC Navigation Integrity Category 
     SBS Surveillance Broadcasting Services (ADS-B) 
     TCP Transport Layer Protocol 
     TIS-B Traffic Information Services-Broadcast 
     UDP User Datagram Protocol 
     UAS Unmanned Aircraft System 
     UAT Universal Access Transceiver 
     WAAS Wide Area Augmentation System 
     In accordance with the invention, priority aircraft and ADS-B IN traffic information are included in the transmission of data through the telemetry communications to a remote ground control station (GCS). In addition to accurate location and UAS operational data, the inclusion of ADS-B information with telemetry communications allows real-time traffic information to be available to the UAS operator located at the GCS. Furthermore, the ADS-B data is displayed to the operator on an industry standard Earth browser to provide an enhanced visual display with three and/or four dimension trajectories for increased situation awareness and enhanced visual acquisition of traffic for conflict detection. This increased situational and traffic awareness is a preeminent attribute for successful UAS operations and greatly improves safety for the UAS, other aircraft in the area, and nearby ground facilities and personnel. The embodiments disclosed herein offer a new capability for ADS-B surveillance redundancy, the system provides for automatic internet connection to the FAA technology center and Surveillance Broadcasting Services in the event that the telemetry signal is lost. In this “lost link” scenario, ADS-B data from the FAA tech center sent via a secure IP network can be used to track the UAS until the primary signal can be recovered. 
       FIG. 1  is a block diagram of the system architecture, which includes an ADS-B Universal Access Transceiver (UAT)  3  mounted in the UAS  2 , and connected to a top-mounted UAT antenna  4 , a top-mounted GPS/WAAS antenna  5 , a bottom-mounted UAT antenna  8 , and an altitude encoder  6 . Note that UAS composite airframes require a metal ground plane of at least eight inches for the proper transmission and reception of ADS-B messages. This radio frequency (RF) ground plane may be installed beneath the airframe skin, or on the outside of the airframe. The UAS  2  is also equipped with an existing generic payload interface GPI  7  controller in communication with the UAT  3 . The GPI  7  is provided with a common payload communication interface in the UAS which includes a wireless (RF) telemetry link via Telemetry antenna  9  to GCS  1  for remote control of the UAS  2  via its mission computer, as well as for remote control of the mission payload(s) via GPI  7 . The GPI  7  is always transmitting for UAS  2  payload (ADS-B) operations and is the primary method of ADS-B transmission of data used herein. The GCS  1  and associated ground control equipment (to be described) allows an operator to interactively control both the mission payload functions as well as the control functions of the UAS  2 . 
     UAT  3  is preferably a Garmin® GDL 90 ADS-B universal access transceiver. The GDL 90 includes a built-in 15 channel GPS/WAAS receiver, and is certified to support a broad array of Automatic Dependent Surveillance-Broadcast (ADS-B) broadband services and is factory-configured to broadcast ownship position, velocity, projected track, altitude, and flight identification via RF communications (an RF data link on 978 MHz) to other ADS-B equipped aircraft in the vicinity, as well as to other ground-based transceivers maintained by the FAA. Alternatively, UAT  3  maybe a TSO certified Free Flight® RANGR universal access transceiver using the identical ADS-B message reports. The UAT  3  may also provide other ancillary functions, including storage and retrieval of UAS aircraft configuration data. GPS/WAAS antenna  5  is connected to the UAT  3  built-in 15 channel GPS/WAAS receiver. UAT antennas  4 ,  8  and GPS/WAAS antenna  5  are conventional components. The altitude encoder  6  is also a conventional component that produces digitized pressure information for determining the UAS&#39;  2  pressure altitude. 
     The UAT  3  is inherently capable of ADS-B Out broadcasts of ownship UAS ADS-B data. For this, the UAT  3  determines the UAS ownship position/velocity from a built-in fifteen (15) channel GPS/WAAS receiver in the UAT  3  transponder unit, receiving signals from GPS/WAAS antenna  5 . The UAT  3  inputs pressure/altitude from altitude encoder  6  to broadcast ownship pressure altitude information. The upper and lower UAT antennas  4 ,  8  provide line-of-sight transmission and reception of ADS-B broadcasts. The UAT  3  also receives a system maintenance input as required for the configuration and maintenance of the ADS-B system, and also receives pilot input from the Ground Control Station (GCS)  1 . 
       FIG. 2  is a block diagram of the ADS-B In system architecture. UAT  3  is inherently capable of ADS-B-In reception of air-to-air ADS-B messages direct from aircraft nearby and air-to-ground ADS-B/ADS-R/TIS-B messages from ADS-B ground based transceiver(s), though it is not inherently configured to re-transmit them. In accordance with the present invention, the air-to-air ADS-B In messages  13  from aircraft nearby and air-to-ground ADS-R  14  and TIS-B 15 messages from ADS-B ground based transceiver(s) are received and processed from encoded ADS-B Out transmission of other aircraft. More specifically as seen in  FIG. 2 , the ADS-B In messages are received by the UAT  3  via UAT antennas  4 ,  8  and are processed by the UAT  3  as ADS-B/ADS-R/TIS-B message reports. These ADS-B In message reports are temporarily stored by the UAT  3  and are encoded in the packet-based ADS-B messages and are sent via serial asynchronous communications to the GCS  1 . In general, the serial order sequence is ADS-B out ownship messages, which are sent and then followed by ADS-B In traffic message reports. 
     The UAT  3  is reprogrammed to do this for ADS-B Out/In by enabling both transmit (Tx) and receive (Rx) during initial setup installation using the provided instrument programming interface. Thus, the UAS  2  ADS-B Out UAT  3  transceiver effectively transmits not just the ownship UAS  2  discretes, but also other surrounding priority aircraft and ADS-B In traffic information, all in “consolidated” ADS-B message reports. This way the GCS  1  has all the data in one downlink. This process is detailed below in regard to  FIG. 3 . 
     The consolidated ADS-B Out and ADS-B In message packets are transmitted to the ADS-B Display  44  at GCS  1  using the existing UAS-ADS-B payload telemetry, e.g., GPI  7  via its conventional telemetry protocols (from the GPI port at 1 Hz via the existing Telemetry Radio Frequency datalink). In this case any of a variety of radio communications may be used including Ku Satellite Beyond line of sight, C-Band line of sight, and S-Band radio communications. However, bandwidth constraints of radio communications limit the amount of ADS-B messages for traffic and real-time weather information. As seen in  FIG. 3 , to improve the flow of data communications for a plurality of data rates and/or serial protocols, the present invention uses a dedicated converter  25  with memory buffers for the consolidated ADS-B Out and ADS-B In messages using UAS serial protocols via telemetry RF communications. Specifically, an RS-232/422 converter  25  is interposed between the UAT  3  and payload GPI  7  as described below, to convert between the data communication protocols of the UAT  3  ADS-B unit and the UAS  2  serial telemetry protocol. Similarly, the inverse RS-422/232 converter  24  is used at GCS  1  to convert between the data communication protocol of the UAS  2  and the Laptop serial protocol. The ownship ADS-B Out messages contain data such as ownship latitude, longitude, geometric altitude, velocity, heading, and accuracy metrics (compliant with standard GPS accuracy and integrity parameters: NACp, NIC, and SIL). In addition, the UAT  3  receives ADS-B In traffic reports for up to thirty two ADS-B or TIS-B targets, prioritized based on proximity to the ownship UAS. Each of the consolidated ADS-B Out message packets are encoded with a checksum to ensure the validity of the telemetry signal (as will be described), and are transmitted to GCS  1  via GPI  7  and/or via secure internet connectionless communications  27  using encrypted UDP/IP protocol (as will be described). 
     The GCS  1  is manned by a flight crew and controls/provides the operational status of the ADS-B UAS  2 . For this purpose GCS  1  includes a UAT control panel  42  connected to converter  24  and configured to transmit control messages to the UAT  3  via the GPI  7  telemetry protocols. A ground control station display  44  is connected to converter  24 , receives the consolidated ADS-B message packets and provides ADS-B status, and displays synthetic 3D/4D views of ownship and traffic information to the UAS pilot. The control station display  44  and UAT control panel  42  may be a conventional PC-based computer such as a laptop, with on-board display and network interface. Alternatively, the functional equivalent of the display  44  and control panel  42  may be provided to the pilot in the cockpit of conventional aircraft for enhanced ownship situational awareness of the airborne pilot. In the latter case, a conventional PC-based tablet computer is preferred, though a cockpit laptop will also suffice. 
     In the UAS context, GCS  1  allows an operator to fly the UAS  2  by remote control, and serves two important functions allocated to the UAS operator. The first is system monitoring: the human operator should be able to monitor the ADS-B system and ownship navigation. The second is traffic situational awareness: the human operator should be informed of traffic data and alerted. These functions model what the UAS-ADS-B system does to enable the proper system behavior. 
       FIG. 3  is a schematic block diagram illustrating the control interfaces of the ADS-B and GPI  7  transmission between the UAS aircraft  2  and the GCS  1 , as well as the details of the RS-232/422 conversion. The UAT  3  receives commands via the aircraft telemetry communications system (the existing UAS-ADS-B payload telemetry, e.g., via its GPI  7  port at 1 Hz using the existing Telemetry Radio Frequency datalink). The converter apparatus  25  (described below) converts between the data communication protocols of the UAT  3  ADS-B unit and the UAS  2  telemetry protocol and the reverse analogue converter  24  is used in GCS  1 . 
       FIG. 4  illustrates an embodiment of the UAS-ADS-B unmanned aircraft system diagram. It should be understood that specialized precautions must be employed to adapt the UAS  2  equipment to operations at high altitudes. For present purposes a heater was incorporated in UAT  3  and converter apparatus  25 , with temperature sensors to maintain temperature control to operate at unpressurized altitudes of 55,000 feet and temperatures of −55 degrees C. 
       FIG. 5  shows a detailed schematic of the converter apparatus  24  at the GCS  1 . The converter apparatus converts between the data communication protocols of the UAT  3  ADS-B unit and the UAS  2  telemetry protocol and is used in both the UAS  2  and GCS  1 . Converter apparatus  24  further comprises a baud rate converter  76  for changing the speed or baud rate of the data passing through, a power converter  78  for converting 28 vdc to 12 vdc, and an RS-232 to RS-422 converter  77  for changing the transmission protocol. All pinouts are given. 
     GCS  1  UAS-ADS-B Software Architecture 
     The UAS-ADS-B software resident at GCS  1  includes novel algorithms for ADS-B sensor processing, alerts, displays, and control logic for loss of UAS telemetry link. The software architecture core functionality comprises four software modules for translation, loss-link, self-separation, and synthetic display. The software architecture includes a translation module for generating KML scripts from the UAS-ADS-B data, a loss link redundancy module to compensate for loss link of telemetry, a separation assurance software module for traffic situation awareness and alerting of potential collisions or hazardous traffic situations, and a synthetic display management user-interface for managing the 3D/4D synthetic displays on ground control station display  44 . Each of these GCS software modules is described in more detail below. 
       FIG. 6  is a control flow diagram of the software architecture including translation module for generating KML scripts from the UAS-ADS-B data, and loss link redundancy module to compensate for loss link of telemetry, these two modules collectively providing the communication infrastructure for real-time correlation and track processing of ADS-B data. The software architecture uses threading and partitioning for the ownship and the traffic data reports to take maximum advantage of multiple quad-core processors. The software architecture includes a backup parallel design (the Loss Link software module which branches to the left) that must operate only after the radio telemetry communications has failed, and the Translation module which branches to the right. 
     Translation Module 
     Generally, the translation module parses all the message packets sent from the ADS-B UAT  3  and writes KML scripts that comprise models and trajectories for the ownship UAS  2 . Keyhole markup (KML) is a file format suitable for displaying geographic data in an Earth browser such as Google Earth, Google Maps, etc. A KML file is processed in much the same way that HTML (and XML) files are processed by web browsers. Each KML file becomes a layer to be used in the virtual globe. The UAS-ADS-B data gleaned from the KML scripts is overlayed on a 3D/4D geobrowser display (an Earth browser such as Google Earth™ Pro) to provide various synthetic views of the UAS  2  and its surroundings as described below, as well as projected future positions of the UAS and other aircraft. 
     More specifically, and with reference to  FIG. 6 , at step  30  a Master Serial scheduler  30  governs and schedules all thread processes within the system software, including thread processes for the Loss Link software module which branch to the left, and the Translation module which branches to the right. Once the software is started, all variables are initialized and static variables such as the mission flight plan and a checksum table are computed at steps  31 ,  32 , respectively. The flight plan contains a list of waypoints for the UAS  2  to fly. All flight plans (waypoints) are interpreted from a .txt formatted document generated by a mapping system of choice, such as Falcon View®, a mapping system created by the Georgia Tech Research Institute which displays various types of maps and geographically referenced overlays. A loss link failure test at step  42  (described below) is initialized to null. Once all preliminary operations are complete, the software creates a “serial monitor” thread which monitors and reads the desired serial port&#39;s binary data stream. This thread loops indefinitely at step  33 , and at step  34 ( a ) reads the desired serial (COM) port and writes all incoming data to a file in hexadecimal format at step  34 ( b ). This write-to-file method was employed to ensure no bytes from the serial stream are lost during data processing and to provide the capability to post-analyze historical flight data and/or replay. After the serial monitor thread is created at step  33 , the translation software begins an infinite looping sequence at step  35  until terminated by the user. During this looping sequence, the translation software opens the file currently being written at step  34   b  and continuously reads the hexadecimal bytes from the file, byte-by-byte, converting them to their decimal equivalent. Step  36  searches for the first instance of a heartbeat message (this provides a starting point for data processing) module. Upon finding it, then at step  47   a  the message identifier byte is stored and bytes are continued to be read. Once this file position is discovered, subsequent bytes are then used to populate temporary data arrays based on the current message identifier  47   b . Once an array is fully populated at step  37 , it is passed to a checksum function where the message integrity is validated. If the checksum fails, the message is discarded. If the checksum process passes, the array is then transferred to a series of thread functions corresponding to the current message identifier (e.g. heartbeat  38 , ownship, GPS altitude, or traffic report  39 ) and a new thread is born. These thread functions are responsible for reading and interpreting the bytes such that useful information can be provided to the flight crew at GCS  1 . While this information is being computed in the thread, the Master Serial program  30  continues to read bytes and populate other arrays. Once the Master Serial  30  has finished reading all current messages from the ADS-B, at step  45  it waits for the threads to join and return their data. This data is then placed into the proper location within a main dictionary. Within the dictionary, each aircraft is assigned its own unique location with ownship data always occupying the first index location. All aircraft are assigned their own unique International Civil Aviation Organization (ICAO) code and the dictionary is indexed by ICAO Code. The data is placed into the proper location within the main dictionary by searching until a match is found. If a match is found, the data returned from the telemetry processors will simply be appended to the matching ICAO code index. If no match is found, the data will be assigned a new position, unused within the dictionary. For the latitude, longitude, and altitude elements, the thirty most recent data points are stored (these are used to display the color-coded flight history, or “contrails” of a particular aircraft trajectory as described below). In order to provide pilots with the latest and most relevant data, each aircraft is also assigned a timeout parameter. This timeout parameter allows continuous monitoring of the age of the latest data entries and is used to delete any aircraft (hence removing it from the display) which has not received an update in at least 25 seconds. This timeout period requirement is consistent with the FAA TSO-195 standard to eliminate stale air traffic data or misleading information. After all active telemetry processing threads have joined and the data distribution process is complete, the program once again resumes and passes the updated dictionary to Keyhole Markup Language (KML) threads where the information is written in a KML format file at step  40 , the KML format being supported by the display software (e.g., Google® Earth). Unlike the threads which interpret and analyze bytes, the main software does not wait for the KML threads to join and terminate since they are able to operate asynchronously from the main program. User selected overlays  46  as well as status and traffic alert overlays (to be described) are applied as necessary. Further, these files at step  40  and  41  are overwritten at every instance since they are being continuously monitored for updates by the Google® Earth Pro software. 
     Loss Link Functional Redundancy 
     In the event that radio telemetry communication is lost with the ADS-B hardware on a UAS  2 , it becomes critical to acquire ADS-B data from an outside source to maintain an enhanced state of situational awareness. Although radio telemetry communications is nominally reliable loss link failure is a likelihood risk due to various factors such as simple line of sight distance, interference, and atmospheric disturbance. The software architecture uses a backup parallel design to automatically establish a connection with the FAA Technical Center and receive data via a UDP/IP Ethernet connection. To accomplish Loss Link functional Redundancy the present invention employs a redundant architecture and a lost link software module at GCS  1  for automatically arbitrating to a backup (redundant) ADS-B data stream upon loss link. 
       FIG. 7  is a diagram of the UAS-ADS-B functional redundancy architecture for loss link of vehicle telemetry  10 . With the UAS transmission of ADS-B broadcasts, ADS-B messages are received by one or more ADS-B ground based transceiver(s) within line-of-sight coverage. During a loss link scenario the lost link software module at GCS  1  automatically arbitrates to a backup (redundant) ADS-B data stream as illustrated in  FIG. 7  until the vehicle telemetry ADS-B data is received and checksum values match. The backup (redundant) ADS-B data stream may be the FAA Technical Center  26 , in which case each secure ADS-B data steam packet is received by the GCS  1  through a UDP/IP network link from the FAA Flight Monitor Server (FMS)  27  for UAS operator display  44 . This way, whenever telemetry  10  is lost between the UAS and GCS  1 , the loss link software module automatically and immediately processes the ADS-B data streamed from the FMS  27 . The FAA Flight Monitor Server  27  located at the William J. Hughes Technical Center  26  multi-streams the UAS ownship (ADS-B ICAO) and/or ADS-B/ADS-R/TIS-B/FIS-B traffic situational awareness data to the FMS  28  Real Time Tracking Surveillance (RTTS) module resident on the ADS-B laptop and/or local host server. The FMS  28  RTTS module decrypts the ADS-B data multi-steam packets. The GCS  1  ADS-B laptop parses and process the data for display, so that the UAS operator is properly informed of traffic data and alerted. In another embodiment ADS-B data from a commercial ITT SBS Surveillance and Broadcasting Services using a publish/subscribe method is directly streamed to GCS  1  ADS-B laptop via a secure UDP/IP network protocol and can be used to track the UAS  2  until the primary signal can be recovered. 
     The FAA flight monitor server  27 , located in the FAA Technical Center  26 , nationally provides a network infrastructure to receive ADS-B packets, encrypts the data, and rebroadcast all data as multicast UDP packets. The FMS  27  connection allows the GCS  1  to receive live ADS-B traffic data. The SBSS/SDP network architecture utilizes a predefined transport layer port number and network layer multicast IP addresses for each application service supported. Since up-to-date flight data is highly sensitive and the established communication protocol is UDP, network data broadcasts from the FAA Technical Center  26  are encrypted for network security. The payload ADS-B report packets are formatted and encoded by the FAA Category 033 (v3) format message structures defined in FAA NAS-IC82530001-01 Appendix B. The FMS-RTTS client/server  28  application by the FAA, which is hosted on a Laptop or Gateway server as an MS window based client, is able to decrypt and receive packets in the FAA&#39;s CAT  33  format. In the preferred embodiment the FMS RTTS client/server  28  application is hosted directly on the ADS-B Laptop  44 , thus ADS-B data streams can be received directly. 
     Referring to the loss-link (left-hand) side of  FIG. 6 , if the loss link module detects a loss link scenario the lost link software module begins an infinite looping sequence at step  43  until terminated by the user. During this looping sequence, the loss-link software automatically arbitrates to a backup (redundant) ADS-B data stream available over the UDP/IP port, reads it at step  44   a , and writes all incoming backup data to a file in hexadecimal format at step  44 ( b ), the backup data essentially becoming the surrogate for the translation software above beginning at step  36 . In the presently preferred embodiment, when the loss link module has detected a failure condition at step  42 , the software utilizes the JAVA “Socket” module to connect to the multicast IP address and associated port at step  44  wherein data will be received and written in the same manner as the serial connection in the main architecture  31 . Once connected, the socket behaves essentially like a file that can be read as at step  44 . The service volume IDs (IP addresses encoded in the form of 239.16x.yz.31) are known apriori. For illustration, the transport layer assigned port may be designated as 59950 and the multicast IP address is 239.161.yz.31 (i.e.LAX 26 SV). The LAX ADS-B UAT CAT  33  data stream will be routed from the ADS-B FMS  27  server via multicast IP to the FMS RTTS client/server  28  application, wherein the ADS-B data packets are decrypted on a gateway local host server network address (10.10.10.10) and then sent to the ADS-B Laptop  44  UDP/IP (10.10.10.xx) Ethernet port connection. The ADS-B Laptop IP network address herein (10.10.10.xx) cannot be 0, 10, or 255. The software searches for the unique ICAO code of the said UAS  2  in the ADS-B data-stream, if a key match is found the matching element (target address) has been found so its index, or position, velocity, altitude and service volume ID is parsed, the data returned will be appended to the matching ICAO code index, and processed for display. If radio telemetry communication is somehow recovered with the UAT  3  on the UAS  2 , the lost link software module automatically switches back to the nominal UAS transmission of ADS-B messages via vehicle telemetry. This method provides UAS-ADS-B functional redundancy for increased situational awareness, a critical attribute for safe UAS flight operations. 
     Loss Link Module 
       FIG. 8  illustrates the detailed Loss Link Module state machine diagram used at GCS  1  ADS-B laptop according to the present invention. In accordance with the invention, the reception of consecutive corrupted or no ADS-B messages are considered a loss link failure (off-nominal) condition. When consolidated ADSB Out and ADS-B In data is sent over the RF telemetry link(s) to the ADS-B Laptop  44  at GCS  1 , it is possible that external environmental factors will result in data corruption. In accordance with the invention the consolidated ADS-B Out and ADS-B In message packets are each encoded with checksum bits to ensure the integrity and validity (99.9% accuracy) of the ADS-B messages prior to transmission to the ADS-B Laptop  44  at GCS  1 . A conventional CRC binary checksum value is computed and appended to the end of each ADS-B Out and ADS-B In message, the checksum being the result of a binary long-division calculation computed from the message block of digital data. As the ADS-B message is received, a lost-link software module resident on ADS-B Laptop  44  re-calculates the checksum value from the message and compares it to the appended checksum value  48 . If the calculated checksum value matches the appended checksum value, the data is assumed correct for display  39 . If not, the entire message packet is discarded  49 . If the checksum does not match for a least five consecutive times and/or no message IDs are received, the Loss Link state machine transitions to the off nominal state  50  and loss link  42  is enabled to true. Basically, the lost-link module determines when the radio telemetry communications has failed and automatically arbitrates to a backup (redundant) data stream  44  as illustrated in  FIG. 6-7 , thereby providing redundancy for the ADS-B data. 
     Self-Separation Assurance Software Module 
       FIG. 9  is a more detailed illustration of the UAS-ADS-B risk collision volumes  84 - 87  for detecting intruding aircraft, alerting, and displaying UAS  2  aircraft position for self-separation assurance. The software is generally designed to detect intruding aircraft in terms of increasing threat risk and to display aircraft position. The objective of the self-separation assurance software module is to detect and alert UAS pilots of potential collisions or hazardous traffic situations. As shown in  FIG. 9  UAS-ADS-B risk collision volumes are used to establish increasing threat risk. Traffic alerts are based on separation and collision zones  84 ,  85 ,  86  &amp;  87  surrounding the UAS  2 , respectively. The self-separation assurance software module establishes a plurality of geometric and concentric collision zones  84 ,  85  . . . n about the moving UAS  2 , each representing the actual position of the UAS  2  within a region of interest. The regions of interest are pre-determined to allow self-separation via direct control by the UAS pilot, e.g., to allow the UAS  2  to be maneuvered within a sufficient timeframe to prevent activation of a collision avoidance maneuver while conforming to accepted air traffic separation standards. The collision zones  84 - 85 ,  86  . . . n are preferably cylindrical volumes, but may be spherical or ovoid. The outermost collision zone  84  establishes a 5 nautical mile (NM) separation threshold about the UAS  2  and if another aircraft/object breaches zone  84  a coded (yellow) aircraft symbol  81 , traffic alert, and aural alert is automatically generated. The next collision zone  85  establishes a 3 NM safety radius (minimum separation) about the UAS  2  and if another aircraft/object breaches zone  85  a coded (red) aircraft symbol  82 , traffic alert, and aural alert is automatically generated. The next collision zone  86  establishes a 1 NM collision avoidance threshold about the aircraft and if another aircraft/object breaches zone  86  a coded (red) aircraft symbol  83 , a near mid-air collision alert, and aural alert is automatically generated. The innermost collision zone  87  establishes a 1000′ diameter about the aircraft and if another aircraft/object breaches zone  87  a collision-imminent signal and aural alert is automatically generated. These auto-generated traffic alerts based on separation and collision zones  84 - 87  surrounding the aircraft are consistent with the recommendations of RTCA Special Committee  186 : “Application of Airborne Conflict Management: Detection, Prevention, &amp; Resolution.” RTCA/DO-263, December 2000. 
     Synthetic Display and Alerting 
     As stated above, the present invention provides various intuitive 3D/4D synthetic views of the UAS and its surroundings as well as projected future positions of the UAS and other aircraft. The design of this synthetic display user interface can be seen in  FIG. 10-14 . 
       FIGS. 10-14  illustrate the UAS-ADS-B synthetic display for exocentric (God&#39;s eye) and egocentric views and related functionality showing user controls and three dimensional display processing. The pilot may select from a plurality of viewpoints including God&#39;s Eye ( FIGS. 10-11 ), Chase ( FIG. 12 ), and Manual views ( FIG. 13 ) for the out-the-window view. The synthetic displays collectively keep the pilot aware of what the UAS  2  is going to do during flight. 
     As seen in  FIGS. 10-11 , a key aspect of the visual display is that all traffic aircraft models are accompanied with three-dimensional color-coded contrails to aide in the visual acquisition of traffic targets. Traffic contrails  69  are color-coded based on the relative altitude vertical separation distance between the object and the ownship. The 3-dimensional graphical representation of traffic models uses a plurality of airborne and/or surface vehicles; which are based on ADS-B aircraft identification and/or vehicle emitter types. The exocentric view or God&#39;s Eye viewpoints of  FIGS. 10-11  display ADS-B traffic on a plan view relative to own-ship, allowing the pilot to effectively gauge the traffic surrounding the ownship. This is well-suited for situational awareness. 
     ADS-B Status and Alerts 
     The ideal design incorporates salient indicators and unique display views to maintain the operator&#39;s situational awareness. The number of both intruders and threats is closely monitored and displayed to the pilot in an overlay located at the upper-right portion of the screen  57 . In order to alert users of system anomalies, the software also displays notifications pertaining to the status of the hardware. The salient indicators GPS Status  62 , ADSB status  60 , and Telemetry Status  61  indicate the following failure conditions: 
     GPS Invalid 
     GPS Failure 
     UAT Failure 
     Lost Link 
     The GPS status  62  is continuously monitored by analyzing the status byte located within each heartbeat message. A “GPS Invalid” overlay will first be displayed when the UAT  3  indicates that GPS data is invalid. The GPS icon in the display will also change from green to yellow during this time. Once the invalid status has been maintained for ten consecutive heartbeat messages, the “GPS Invalid” overlay is replaced by “GPS Fail” and (Red X screen) overlay. The GPS status icon also converts from yellow to red. If the status byte indicates valid GPS data at any time, the GPS overlays are removed and the status icon reverts to green, indicating a nominal state. 
     The ADS-B status  60  is also continuously monitored, a UAT Failure occurs if the UAT bit failure indication or if all communication with the ADS-B unit is lost for 10 consecutive seconds. This event can be attributed to a total hardware failure anywhere in the system. Once this condition is recognized, a “UAT Fail” overlay is displayed and the ADS-B icon  60  becomes red. Finally, the Lost Link status alert  61  is continuously monitored by the loss link module by analyzing invalid checksum operations. Corrupted ADS-B data or no data herein is considered a malfunction and the telemetry icon  61  becomes red. 
     Examining  FIG. 10 , an operating display in Manual View, it can be seen that there are currently a total of three real-time aircraft being tracked flying within the viewing limits. The position history is stored and displayed via color coded contrails. The target labeled “traffic  3 ”  54  has breached the 5 nautical mile separation threshold (outermost range ring) and is within 1000 feet of altitude causing a “Traffic Alert”  59  overlay to be displayed to the user. On the left of the display, all relevant ownship information  63  is visible with hardware status indicators located directly above. The current flight plan is also displayed  75 . Further, the image overlay  57  in the upper right corner currently recognizes three TIS-B targets, one ADS-B target, and one intruder  54 . In the manual view modality, the field of view limits can be manipulated to a worldwide view or to any user spatially oriented viewpoint. The ADS-B laptop display  44  herein is utilized for visual and/or aural display to the flight crew as well as for performing routine maintenance of the ADS-B system. 
       FIGS. 11-12  illustrate the UAS-ADS-B synthetic visuals for exocentric (God&#39;s eye) and egocentric views and related functionality showing user controls and three dimensional display processing. The ideal solution is to design the system in a way that keeps the pilot aware of what the aircraft is going to do during flight. The design implementation, for that reason, allows the user to select a plurality of viewpoints from God&#39;s Eye, Chase, and Manual views for the out-the-window view  64 . In addition, three concentric circles are drawn around the ownship; one at a radius of 10 nautical miles (magnetic compass), 5 nautical miles, and at 3 nautical miles  68 . This allows the operator to approximate the self-separation between the ownship and traffic. Finally, located at the far left  64  of the figure, it can be observed that the pilot has several viewing options as well as the capability of either enabling or disabling any of the programs features such as real-time weather, ADS-B ground stations, and satellite imagery. Geobrowser network links are used to link to a plurality of near real-time satellite information from the FAA, DOD, and NOAA to overlay satellite imagery. 
     Traffic for a plurality of targets can be selected at the far left  65  with the highest priority traffic ranked order from 1 to 32 relative to ownship. The selected traffic target displays the ADS-B surveillance information including ICAO, NIC, and NAC p    56 . Further, the traffic relative bearing, range, altitude, and vertical trend  54  are depicted to aid in visual acquisition. Finally, to improve pilot situational awareness, the surveillance information from nearby aircraft is continuously monitored and compared to the current ownship position. If any other aircraft&#39;s (e.g., 54) relative horizontal separation distance falls below 5 NM and reports vertical separation within 1000 feet of the current ownship position, the target is deemed an intruder and the pilot is alerted via a “Traffic Alert” overlay  59 . In this case the target&#39;s icon  54  changes color from blue to yellow on the display. In the event that the horizontal separation is less than 3 NM and the target reports an altitude within 500 feet, the target  54  becomes a threat and the pilot is notified via a flashing “Traffic Alert” overlay  59  and aural alert as well as a change of icon color from yellow to red. The traffic symbols for TIS-B are depicted as Icon based standard symbols from RTCA/DO-317A. 
       FIG. 12  is an egocentric “Chase” viewpoint, which attempts to give the pilot an intuitive 3-D visualization of the flight of the ownship. This lags the ownship and allows the pilot to see the entire UAS  2 , along with all traffic in the forward vicinity. This perspective viewpoint can be spatially oriented to a cockpit out-the-window view. 
       FIG. 13  is a manual or out-the-window view providing a panoramic display functionality using at least three cockpit displays. 
       FIG. 14  illustrates the UAS-ADS-B visualization from the God&#39;s Eye view including overlays for weather  70 , restricted airspace  71 , and ADS-B ground stations. By including network links to the FAA database, the display incorporates FAA airspace designations, ADS-B ground stations, satellite imagery, and real-time weather  70 , all of which are effectively seen when the user is in God&#39;s Eye View. 
     Flight Test Results 
     The above-described system has been deployed and tested on an Ikhana™ Predator-B UAS using Garmin&#39;s ADS-B capable GDL 90 installed in the forward avionics bay (depicted in  FIG. 4 ). For flight testing all RF transmission to the GCS  1  took place over the GPI  7  link. The FAA ADS-B streaming data was received as backup. The Ikhana™ Predator-B UAS underwent four highly successful flights as the first high performance large UAS integrated with ADS-B Out and ADS-B In functionality. The FAA monitored all flights and collected data for post-flight analysis. After viewing the results, it was found that the system performed exceptionally well, producing errors far below the mandated requirements. 
     This description of the present invention has been presented for purposes of illustration and description and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. For example, in another preferred embodiment, the UAS  2  can be outfitted with a dual link ADS-B device that transmits on 1090 Mhz and receives on both 1090 and 978 MHz. 
     In yet another embodiment, the components of the UAS  2  may be deployed in a surface vehicle. For example, an emergency response unit and/or and gas truck can be outfitted with portable ADS-B devices and portable UAT and GPS antennas as described above. 
     In yet another embodiment designed for manned aircraft, an iPad™ or other tablet or portable computer may be equipped with the same UAS-ADS-B software resident at GCS  1  for traffic situational awareness of the pilot.  FIG. 15  illustrates the ADS-B system of  FIG. 1  adapted for a general aviation manned aerial vehicle  11  for increased situational awareness and self-separation assurance. In this instance the GCS display  44  is replaced by one or more onboard portable tablet computers  80  having one or more processors using touch screen display(s) and interfaced as described previously. The tablet(s)  80  and control panel  42  are provided to the pilot in the cockpit of the conventional aircraft  11 , and are connected directly to the UAT  3  for enhanced ownship situational awareness of the airborne pilot. This embodiment also employs a dedicated converter  79  with memory buffers (similar to  25  described above) for converting the consolidated ADS-B Out and ADS-B In messages to the proper serial protocol of the tablet(s)  80  via direct serial communications. 
     It should be understood that various changes may be made in the form, details, arrangement and proportions of the components. Such changes do not depart from the scope of the invention which comprises the matter shown and described herein and set forth in the appended claims.