Differential navigation and data fusion communication method of unmanned aerial vehicle airborne gravity and magnetic system

Abstract

This invention discloses a differential navigation and data fusion communication method for an UAV airborne gravity and magnetic system, relating to the field of airborne geophysical exploration technology. The method constructs a dual-mode GNSS positioning architecture of "real-time differential + offline differential": the real-time differential channel directly connects ephemeris data to the gravimeter's internal satellite board via an independent antenna for real-time timing, marking, and integrated navigation during flight; the offline differential channel records the raw ephemeris and pseudoranges of the aircraft rover and ground base station for post-processing differential analysis to obtain trajectory data with centimeter / decimeter-level accuracy. Simultaneously, this invention designs a standardized data protocol frame to achieve the fusion encapsulation of GNSS and magnetic data, and employs a transparent data link with a communication distance ≥100km and bandwidth ≥4Mbps to achieve beyond-line-of-sight telemetry and remote control. This invention can simultaneously meet the dual requirements of real-time navigation and high-precision post-processing calculations, ensuring the spatiotemporal consistency of gravity and magnetic data, and effectively expanding the operational radius of UAV geological exploration.

Description

Technical Field

[0001] This invention relates to the field of airborne geophysical exploration technology, and in particular to a differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) airborne gravity and magnetic system. Background Technology

[0002] In the field of airborne geophysical exploration, the use of UAVs equipped with gravity and magnetic measurement systems for geological surveys places extremely high demands on the accuracy of navigation and positioning and the spatiotemporal synchronization of data.

[0003] Airborne gravity measurements require the precise extraction of the acceleration (especially vertical acceleration) of the flight vehicle to separate gravity anomalies caused by geological bodies from the total gravity signal. Existing technologies suffer from the following main shortcomings: 1. Insufficient positioning accuracy. The single-point positioning accuracy of a simple Global Navigation Satellite System (GNSS) is only at the meter level, which cannot meet the centimeter / decimeter level dynamic displacement accuracy required for gravimeter calculations, resulting in large errors in gravity anomaly calculations.

[0004] 2. Difficulty in time synchronization. Gravity and magnetic data need to be strictly aligned with high-precision timestamps and location information. If there are delays or deviations in GNSS time synchronization or data labeling, it will lead to spatial misalignment during subsequent data processing, affecting the accuracy of geological interpretation.

[0005] 3. The need for both real-time and post-processing coexists but is difficult to balance. Gravimeters require real-time differential signals during flight for integrated navigation and flight control guidance, but the final calculation of gravity anomalies relies on high-precision offline differential analysis afterward. Existing systems often struggle to simultaneously achieve seamless switching and data fusion between these two modes.

[0006] 4. Bottlenecks exist in long-distance data transmission. Geological exploration often requires operations in areas far from ground stations (50-60km or more), and real-time transmission of critical equipment status or partial measurement data is necessary. Existing data transmission links have limited transmission distance and insufficient bandwidth, failing to meet the monitoring needs of beyond-line-of-sight operations. Summary of the Invention

[0007] To achieve the above objectives, this invention provides a differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) airborne gravity and magnetic system, comprising: A dual-mode differential GNSS positioning architecture is constructed, which includes a real-time differential channel and an offline differential channel; The real-time differential channel is as follows: a GNSS antenna is independently installed on the top of the UAV body and directly connected to the satellite board inside the gravimeter via an radio frequency cable. This allows the gravimeter to receive real-time ephemeris data through the GNSS antenna during flight, which is used for internal clock timing and marking, as well as for combined navigation calculation with the inertial measurement unit, and to output single-point positioning data with time stamps in real time. The offline differential channel is as follows: the UAV flight parameter recorder records the raw satellite observation data of the aircraft rover station throughout the flight, and at the same time, a ground base station is deployed and the raw ephemeris and pseudorange of the ground base station are recorded synchronously. After the flight mission is completed, the raw data of the aircraft rover station and the ground base station are imported into the differential processing software for post-processing differential processing to calculate the position and velocity data with centimeter / decimeter accuracy and retain the time stamp. The magnetic measurement system is connected to the flight control system via a serial communication interface to acquire GNSS data. The UTC time, latitude and longitude, differential status, PDOP accuracy factor, and sea level height information are encapsulated in binary using a standardized data protocol frame. This allows the magnetic field data collected by the magnetometer to be automatically aligned with the received GNSS timestamp internally, forming a standard data stream containing time, position, and magnetic field value. Beyond-line-of-sight communication is achieved using a transparent data link with a communication distance of ≥100km and a bandwidth of ≥4Mbps. The downlink transmits the working status, remaining fuel, and aircraft position telemetry information of the gravity and magnetic equipment back to the ground station, while the uplink supports the ground station in sending commands over long distances to control the start-up, shutdown, or parameter adjustment of the gravity and magnetic equipment.

[0008] Preferably, the gravimeter is a VGS gravimeter, the GNSS antenna is a TB2611-KT type antenna, and the radio frequency cable is a TNC-JW3 / dual-head unidirectional JC195 waterproof-1M type radio frequency cable.

[0009] Preferably, the magnetic force measurement system is connected to the flight control system through a pre-reserved obstacle avoidance radar communication interface, and the connector of the obstacle avoidance radar communication interface is a DB9 female connector.

[0010] Preferably, the frame header of the standardized data protocol frame is 0xEB 0x90 and the frame tail is 0xED 0x03; wherein the scaling factor for latitude and longitude is 1e7, the scaling factor for sea level height is 0.01, and the scaling factor for PDOP precision factor is 0.1.

[0011] Preferably, the serial communication interface is an RS232 serial communication interface with a baud rate of 9600bps. Data is transmitted in byte format, with each byte including 1 start bit, 8 data bits, 1 odd parity bit, and 1 stop bit. The data transmission frequency is 2 frames per second.

[0012] Preferably, the gravimeter obtains flight power through a pre-installed photoelectric power supply 1 interface on the aircraft. The connector of the photoelectric power supply 1 interface is an XT60 female connector, with a power supply voltage of DC28V and a power of 420W. The starting current of the gravimeter is 25A, and the steady-state current is 10A.

[0013] Preferably, after the helicopter lands, the gravimeter is powered by a ground power source connected to the ground measurement panel, ensuring uninterrupted power supply for 24 hours.

[0014] Preferably, the magnetic force measurement system is powered by a unified power supply module with an input power of 200W and outputs including: AGS-863 UAV magnetic compensation recorder DC24~28V / 56W, Cs-3 magnetometer DC24~35V / 2A, and fluxgate DC28V / 0.3A.

[0015] Preferably, the ground station of the transparent data link is based on a Windows system, uses a laptop computer as the ground station terminal, and connects an external data link radio to complete beyond-line-of-sight flight monitoring.

[0016] Preferably, the UAV is a helicopter-type UAV, the gravimeter is installed in the original counterweight position in the instrument compartment of the nose, the probe of the magnetic force measurement system is installed under the belly of the UAV, the probe is 5400mm long, the distance from the nose of the UAV is greater than 3.1m, and the lowest point of the probe is 630mm from the ground.

[0017] The beneficial effects of this invention are: 1. High-precision positioning required for gravity calculation was achieved. Through a dual-mode differential architecture of "real-time coarse guidance + post-calculation fine analysis", the real-time requirements of flight control were met, and post-processing differential processing achieved centimeter / decimeter-level trajectory accuracy, providing key data support for high-precision gravity anomaly extraction.

[0018] 2. It ensures the spatiotemporal consistency of gravity and magnetic data. A separate antenna provides high-precision time synchronization and marking for the gravimeter, while a standardized serial port protocol injects GNSS timestamps into the magnetometer data stream, ensuring strict temporal and spatial alignment of the gravity and magnetic data and significantly reducing the difficulty and error of data processing.

[0019] 3. It expands the operational radius of UAV geological exploration. The 100km-level, 4Mbps bandwidth transparent data link extends the monitoring range from line-of-sight to beyond line-of-sight, solving the monitoring challenges during long survey lines (50-60km) and improving the safety and reliability of mission execution.

[0020] 4. Meets the ground maintenance needs of special equipment. The design of the ground power supply interface solves the special requirement of 24-hour uninterrupted power supply for the gravimeter, ensuring the continuity of the equipment clock and the stability of the reference, and avoiding recalibration and clock drift problems caused by power outages and restarts.

[0021] 5. Improved system integration and reliability. Communication via reserved interfaces on the flight controller avoids large-scale cable modifications; standardized data protocols reduce parsing errors between different devices; and clearly defined power supply interfaces and cables reduce the risk of electromagnetic interference and power failure. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the steps of the method of the present invention. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0025] Example 1: System Overall Architecture This embodiment provides a differential navigation and data fusion communication method for an airborne gravity and magnetic system suitable for helicopter-type unmanned aerial vehicles.

[0026] This invention constructs a dual-mode GNSS positioning architecture of "real-time differential + offline differential".

[0027] The real-time differential channel uses a direct hardware connection: a GNSS antenna (model: TB2611-KT) is independently mounted on the top of the UAV and directly connected to the satellite board inside the VGS gravimeter via an RF cable (TNC-JW3 / dual-head unidirectional JC195 waterproof-1M). During flight, the gravimeter receives real-time ephemeris data through this independent channel for high-precision timing and marking of the internal clock, as well as for combined navigation calculations with the inertial measurement unit. It outputs real-time single-point positioning data with time stamps to assist the flight control in maintaining the flight path.

[0028] The offline differential channel employs a data recording method: the UAV flight parameter recorder records the raw satellite observation data (including raw ephemeris and pseudorange) of the aircraft rover station throughout the entire flight; simultaneously, a ground base station is deployed to record the raw ephemeris and pseudorange of the ground base station. After the flight mission, the raw data from the aircraft rover station and the ground base station are imported into specialized software for differential processing, calculating latitude, longitude, altitude, and velocity data with centimeter / decimeter accuracy, and retaining precise time stamps for use in post-processing of gravity and magnetic data.

[0029] Example 2: Multi-source data fusion communication protocol This embodiment details the specific implementation of the data fusion and communication protocol.

[0030] The magnetic measurement system (AGS-863) connects to the flight control system via an RS232 serial communication interface, acquiring GNSS data using the flight control system's reserved "obstacle avoidance radar communication" interface (DB9 female connector). The serial communication baud rate is 9600bps, and all data is transmitted in byte format. Each byte includes 1 start bit, 8 data bits, 1 odd parity bit, and 1 stop bit, with a data transmission frequency of 2 frames per second.

[0031] This invention designs a standardized GNSS data protocol frame for data encapsulation. The frame header is 0xEB0x90, and the frame trailer is 0xED 0x03. The frame structure includes the following key fields: UTC time (UINT32, accuracy 1s), latitude (INT32, scale factor 1e7, range -90 to 90 degrees), longitude (INT32, scale factor 1e7, range -180 to 180 degrees), differential status (UINT8, 0 indicates invalid, 2 indicates valid), number of satellites used for positioning (UINT8), PDOP accuracy factor (UINT8, scale factor 0.1), sea level altitude (INT32, scale factor 0.01), radio altitude (INT32, scale factor 0.01), radio altitude status (UINT8), frame count (UINT8, range 0 to 255), and checksum (UINT8).

[0032] The magnetic field data collected by the magnetometer is automatically aligned internally with the received GNSS timestamps to form a standard data stream containing time, location, and magnetic field values, which is then stored locally.

[0033] Example 3: Beyond-line-of-sight transparent data link system This embodiment illustrates the implementation of a beyond-line-of-sight communication link.

[0034] To address the monitoring needs of long-distance geological exploration operations, this invention adds a transparent data link with a communication distance of ≥100km and a bandwidth of ≥4Mbps to replace the original short-range data transmission (P900).

[0035] The transparent data link supports bidirectional communication. Downlink telemetry: Key telemetry information such as the operating status of the gravity and magnetic field equipment (power supply voltage, temperature, data recording status), remaining fuel, and aircraft position are transmitted back to the ground station via a high-speed link. Uplink command: Supports the ground station to send commands over long distances to control the start, stop, or parameter adjustment of the gravity and magnetic field equipment.

[0036] The ground station is based on a Windows system and uses a laptop as the ground station terminal, connected to an external data link radio, to complete beyond-visual-range flight demonstrations and real-time monitoring.

[0037] Example 4: Uninterruptible Power Supply and Interface Definition This embodiment illustrates the specific implementation method of the power supply system.

[0038] To ensure the continuous operation of the gravimeter (which requires 24-hour uninterrupted power supply) during the pre-flight calibration and post-flight data download phases, this invention designs two sets of power supply logic: flight power supply and ground power supply.

[0039] Flight power supply: During flight, the VGS gravimeter is powered through the reserved "Photoelectric Power Supply 1" (XT60 female connector, 28V / 420W) interface on the aircraft. The starting current is 25A and the steady-state current is 10A.

[0040] Ground power supply: After the helicopter lands, the ground power supply is connected to the ground panel to continue powering the gravimeter, ensuring that its internal clock and sensors continue to operate and meeting the requirement of uninterrupted power supply 24 hours a day.

[0041] The other "Photoelectric Power Supply 2" interface supplies power to the power module of the magnetic measurement system. The power module has an input power of 200W and outputs including: AGS-863 UAV magnetic compensation recorder DC24~28V / 56W, Cs-3 magnetometer DC24~35V / 2A, and fluxgate DC28V / 0.3A.

[0042] Example 5: Equipment Installation and Layout This embodiment illustrates how each device is installed on the drone.

[0043] The gravimeter is installed in the original counterweight (electro-optical pod) location within the nose instrument bay. The VGS gravimeter is secured to its shock-absorbing base via four M10 mounting holes using three brackets. Each bracket is fixed to the fuselage via three mounting holes at the top, and a fairing covers the bottom to maintain a seal within the nose instrument bay. The closest distance between the gravimeter and the fuselage is greater than 20mm, and the distance between the gravimeter's mounting interface and the fuselage is greater than 110mm. The gravimeter's main unit measures 267mm × 255mm × 270mm and weighs 15kg.

[0044] The real-time differential channel GNSS antenna (TB2611-KT) is independently installed on the top of the drone body and is directly connected to the internal satellite board of the gravimeter via an RF cable (TNC-JW3 / Dual-headed unidirectional JC195 waterproof-1M).

[0045] The magnetic measurement system's probe is installed under the fuselage. The probe integrates a Cs-3 magnetometer, fluxgate magnet, probe housing, and connecting cables, with a total length of 5400mm. It consists of two sections: the middle section is 3800mm long and has a diameter ranging from 116mm to 160mm, with an overall weight of 29kg. The probe is positioned 5100mm from the rotor's center of gravity and 3400mm from the nose, with its lowest point 630mm from the ground. The probe is secured to the landing gear by two brackets and held in place by a tie rod, with the probe tilted upwards at a 5° angle to prevent it from touching the ground during takeoff and landing.

[0046] The AGS-863 UAV magnetic compensation recorder measures 327mm×124mm×194mm and weighs 7kg. It is installed on the right side of the support rod on the belly of the drone and the equipment support plate is fixed through the bolt holes of the probe bracket. The equipment is placed on the vibration damper and is damped by a flexible metal ring.

[0047] Example 6: Flight Calibration Test Verification This embodiment verifies the technical effectiveness of the present invention through flight calibration tests.

[0048] According to the error calibration requirements of airborne gravity and magnetic detection systems, the system upon which the method of this invention relies needs to complete the following flight calibration tests: Aeromagnetic compensation flight: Conducted in a rectangular area with sides of approximately 20 km and an altitude of 2000–3000 m. Flights were performed in four different headings: 0°, 90°, 180°, and 270°. For each heading, the aircraft performed a series of maneuvers: level flight, wing yaw (±10°), level flight, nose pitch (±5°), level flight, fuselage sideslip (±5°), and level flight again. Each maneuver was repeated five times consecutively, with a level flight time of approximately 10 seconds. This was used to acquire information about the impact of magnetic interference fields from the aircraft and its onboard equipment on magnetic measurement results and to calculate compensation coefficients.

[0049] Repeated line flight: Select an area with obvious gravity and magnetic anomalies, design a measurement line of about 50km in length, and conduct multiple round trip measurements. The number of effective repeated measurement lines should not be less than 6, which is used to verify the stability and accuracy of the airborne gravity and magnetic equipment.

[0050] Flight at different speeds: Flights were conducted at speeds of 20 km / h, 40 km / h, 60 km / h, 80 km / h, and 100 km / h along repeating lines to study the effects of different flight speeds on the spatial resolution of gravity anomalies.

[0051] Gentle undulation flight: Gentle undulation flight is conducted on repeating lines with an ascent and descent angle not exceeding 5° to test the effect of flight undulation on the airborne gravimeter.

[0052] Experimental results show that, through the dual-mode differential positioning architecture of this invention, the real-time differential channel provides reliable navigation data for flight control during flight, and post-flight offline differential processing achieves trajectory accuracy at the centimeter / decimeter level; strict spatiotemporal alignment of GNSS data and magnetic data is achieved through standardized data protocol frames; and beyond-line-of-sight flight monitoring is realized through a 100km-level transparent data link. The gravity and magnetic equipment operated stably and recorded complete data in all flight sorties, verifying the effectiveness and reliability of the technical solution of this invention.

[0053] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system, characterized in that, include: A dual-mode differential GNSS positioning architecture is constructed, which includes a real-time differential channel and an offline differential channel; The real-time differential channel is as follows: a GNSS antenna is independently installed on the top of the UAV body and directly connected to the satellite board inside the gravimeter via an radio frequency cable. This allows the gravimeter to receive real-time ephemeris data through the GNSS antenna during flight, which is used for internal clock timing and marking, as well as for combined navigation calculation with the inertial measurement unit, and to output single-point positioning data with time stamps in real time. The offline differential channel is as follows: the UAV flight parameter recorder records the raw satellite observation data of the aircraft rover station throughout the flight, and at the same time, a ground base station is deployed and the raw ephemeris and pseudorange of the ground base station are recorded synchronously. After the flight mission is completed, the raw data of the aircraft rover station and the ground base station are imported into the differential processing software for post-processing differential processing to calculate the position and velocity data with centimeter / decimeter accuracy and retain the time stamp. The magnetic measurement system is connected to the flight control system via a serial communication interface to acquire GNSS data. The UTC time, latitude and longitude, differential status, PDOP accuracy factor, and sea level height information are encapsulated in binary using a standardized data protocol frame. This allows the magnetic field data collected by the magnetometer to be automatically aligned with the received GNSS timestamp internally, forming a standard data stream containing time, position, and magnetic field value. Beyond-line-of-sight communication is achieved using a transparent data link with a communication distance of ≥100km and a bandwidth of ≥4Mbps. The downlink transmits the working status, remaining fuel, and aircraft position telemetry information of the gravity and magnetic equipment back to the ground station, while the uplink supports the ground station in sending commands over long distances to control the start-up, shutdown, or parameter adjustment of the gravity and magnetic equipment.

2. The differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system according to claim 1, characterized in that, The gravimeter is a VGS gravimeter, the GNSS antenna is a TB2611-KT type antenna, and the RF cable is a TNC-JW3 / dual-head unidirectional JC195 waterproof-1M type RF cable.

3. The differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system according to claim 1, characterized in that, The magnetic force measurement system is connected to the flight control system through the obstacle avoidance radar communication interface reserved by the flight control system. The connector of the obstacle avoidance radar communication interface is a DB9 female connector.

4. The differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system according to claim 1, characterized in that, The standardized data protocol frame has a frame header of 0xEB 0x90 and a frame tail of 0xED 0x03; the latitude and longitude scaling factor is 1e7, the sea level height scaling factor is 0.01, and the PDOP precision factor scaling factor is 0.

1.

5. The differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system according to claim 1, characterized in that, The serial communication interface is an RS232 serial communication interface with a baud rate of 9600bps. Data is transmitted in bytes, and each byte includes 1 start bit, 8 data bits, 1 odd parity bit, and 1 stop bit. The data transmission frequency is 2 frames / second.

6. The differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system according to claim 1, characterized in that, The gravimeter obtains flight power through the onboard pre-installed photoelectric power supply 1 interface. The connector of the photoelectric power supply 1 interface is an XT60 female connector, with a power supply voltage of DC28V and a power of 420W. The starting current of the gravimeter is 25A, and the steady-state current is 10A.

7. The differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system according to claim 6, characterized in that, After the helicopter lands, it connects to a ground power source via a ground-based panel to continue supplying power to the gravimeter, ensuring uninterrupted power supply 24 hours a day.

8. The differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system according to claim 1, characterized in that, The magnetic force measurement system is powered by a unified power module with an input power of 200W and outputs including: AGS-863 UAV magnetic compensation recorder DC24~28V / 56W, Cs-3 magnetometer DC24~35V / 2A, and fluxgate DC28V / 0.3A.

9. The differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) gravity and magnetic system according to claim 1, characterized in that, The ground station of the transparent data link is based on the Windows system, uses a laptop computer as the ground station terminal, and connects an external data link radio to complete beyond-line-of-sight flight monitoring.

10. A differential navigation and data fusion communication method for an unmanned aerial vehicle (UAV) airborne gravity and magnetic system according to any one of claims 1 to 9, characterized in that, The drone is a helicopter-type drone. The gravimeter is installed in the original counterweight position in the instrument compartment of the nose. The probe of the magnetic force measurement system is installed under the belly of the drone. The probe is 5400mm long and is more than 3.1m away from the nose. The lowest point of the probe is 630mm from the ground.

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