Unmanned airborne ground penetrating radar system and inspection method for dam hidden danger detection

Abstract

Disclosed are an unmanned airborne ground penetrating radar system and an inspection method for a dam hidden danger detection, including an unmanned aerial vehicle (UAV) system; the UAV system includes an unmanned aerial vehicle, a sensor platform, a radar platform, a forward-looking laser rangefinder and a ground penetrating radar; the sensor platform is installed on the UAV, and the forward-looking laser rangefinder is installed on the sensor platform, and the radar platform is installed on the UAV at one side of the sensor platform; moreover, the ground penetrating radar is installed on the radar platform, and a variable polarization ground penetrating radar antenna array is arranged in the ground penetrating radar; the variable polarization ground penetrating radar antenna array includes a substrate, and a plurality of groups of orthogonal dual-polarization Vivaldi antenna transmitting subarrays and receiving subarrays are mounted on the substrate.

Claims

1. An unmanned airborne ground penetrating radar system for a dam hidden danger detection, comprising an unmanned aerial vehicle system, wherein the unmanned aerial vehicle system comprises an unmanned aerial vehicle, a sensor platform, a radar platform, a forward-looking laser rangefinder and a ground penetrating radar; the sensor platform is installed on the unmanned aerial vehicle, and the forward-looking laser rangefinder is installed on the sensor platform, and the radar platform is installed on the unmanned aerial vehicle at one side of the sensor platform; and the ground penetrating radar is installed on the radar platform, and a variable polarization ground penetrating radar antenna array is arranged in the ground penetrating radar; the variable polarization ground penetrating radar antenna array comprises a substrate, orthogonal dual-polarization Vivaldi antenna transmitting subarrays and orthogonal dual-polarization Vivaldi antenna receiving subarrays; the orthogonal dual-polarization Vivaldi antenna transmitting subarrays and the orthogonal dual-polarization Vivaldi antenna receiving subarrays are mounted on the substrate; each of the orthogonal dual-polarization Vivaldi antenna transmitting subarrays and the orthogonal dual-polarization Vivaldi antenna receiving subarrays comprises an orthogonal dual-polarization Vivaldi antenna array element; the orthogonal dual-polarization Vivaldi antenna array elements of the orthogonal dual-polarization Vivaldi antenna transmitting subarrays and a feed network form a 2×2 antenna array, the orthogonal dual-polarization Vivaldi antenna array elements of the orthogonal dual-polarization Vivaldi antenna receiving subarrays and another feed network form another 2×2 antenna array; and four transmitting antennas work simultaneously and four receiving antennas work simultaneously; each orthogonal dual-polarization Vivaldi antenna array element comprises: two Vivaldi antennas disposed on the substrate, and polarization modes of the two Vivaldi antennas are vertical polarization and horizontal polarization respectively; and each of the two Vivaldi antennas comprises: a dielectric substrate, disposed on the substrate; wherein the dielectric substrate comprises a first surface and a second surface parallel to each other, the first surface comprises: a first area and a second area, boundaries between the first area and the second area comprises: two exponential curves symmetrical with a center line of the dielectric substrate; a conductor patch, covering the first area of the first surface of the dielectric substrate; an opening slot with a horn-shaped opening, defined by the conductor patch and corresponding to the second area of the first surface of the dielectric substrate; wherein two edges of the opening slot coincide with the two exponential curves; a microstrip line, disposed on the second surface of the dielectric substrate and configured to connect a coaxial cable; and a stripline, disposed on the second surface of the dielectric substrate and connected to the microstrip line; the two Vivaldi antennas of the orthogonal dual-polarization Vivaldi antenna array element are placed orthogonally in a cross to form a crossed balun feed structure, and in the crossed balun feed structure, the stripline of one of the two Vivaldi antennas is connected to the second surface of the other one of the two Vivaldi antennas, thereby energy from the microstrip line to the stripline of the one Vivaldi antenna is coupled to the first surface of the other Vivaldi antenna to form radiation through the second surface of the other Vivaldi antenna; when the two Vivaldi antennas in each orthogonal dual-polarization Vivaldi antenna array element simultaneously transmit signals with an equal amplitude and a phase difference of 90°, circularly polarized electromagnetic waves are transmitted from the orthogonal dual-polarization Vivaldi antenna transmitting subarrays to the orthogonal dual-polarization Vivaldi antenna receiving subarrays, and a mixed polarization detection mode of “circularly polarized transmission-linearly polarized reception” is formed; and when the two Vivaldi antennas in each orthogonal dual-polarization Vivaldi antenna array element transmit signals with an equal amplitude and a phase difference of 0° in time sharing, horizontal or vertical polarized electromagnetic waves are respectively transmitted from the orthogonal dual-polarization Vivaldi antenna transmitting subarrays to the orthogonal dual-polarization Vivaldi antenna receiving subarrays, and a detection mode of “linearly polarized transmission-linearly polarized reception” is formed.

2. An inspection method of the unmanned airborne ground penetrating radar system for the dam hidden danger detection according to claim 1, comprising: step 1: starting the sensor platform, wherein the sensor platform is internally provided with an inclination angle control algorithm with an adaptive speed; and step 2: controlling an angle between the laser rangefinder and a traveling plane by the inclination angle control algorithm with the adaptive speed according to the speed of the unmanned aerial vehicle, and keeping the angle constant during a traveling of the unmanned aerial vehicle to adapt to an attitude advance control of the unmanned aerial vehicle on the plane where the ground penetrating radar antenna array is located in a dam hidden danger detection task under different flight speed conditions.

3. The unmanned airborne ground penetrating radar system for a dam hidden danger detection according to claim 1, wherein the horn-shaped opening faces toward a maximum radiation direction of the Vivaldi antenna.

4. The unmanned airborne ground penetrating radar system for a dam hidden danger detection according to claim 1, wherein in the crossed balun feed structure, the microstrip line of the one Vivaldi antennas is connected to the coaxial cable to receive the energy, the microstrip line transmits the energy to the stripline, the stripline extends to a fan-shaped branch on the second surface of the other Vivaldi antenna, the fan-shaped branch disposed on the second surface of the other Vivaldi antenna is coupled with slot lines of the opening slot of the first surface of the other Vivaldi antenna to form the radiation.

5. The unmanned airborne ground penetrating radar system for a dam hidden danger detection according to claim 1, wherein the dielectric substrates of the two Vivaldi antennas of the orthogonal dual-polarization Vivaldi antenna array element are placed orthogonally in a cross to form a cross-shaped dielectric substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic structural diagram of an unmanned airborne ground penetrating radar according to the application.

(2) FIG. 2 is a schematic structural diagram of a variable polarization ground penetrating radar antenna array according to the application.

(3) FIG. 3 is a schematic diagram of a Vivaldi antenna array element structure according to the application.

(4) FIG. 4 is a schematic diagram of a crossed balun feed structure according to the application.

(5) FIG. 5 is a schematic diagram of an orthogonal dual-polarization Vivaldi antenna transmitting subarray structure according to the application.

(6) FIG. 6 is a schematic diagram of a geometric relationship calculation of an inspection method according to the application.

(7) FIG. 7 is a schematic diagram of an inspection method of an unmanned airborne ground penetrating radar system for the dam hidden danger detection according to the application.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(8) In order to deepen an understanding of the application, the application is further described below with embodiments. The embodiments are only used to explain the application and do not constitute a limitation on a scope of protection of the application.

(9) As shown in FIGS. 1-6, this embodiment proposes an unmanned airborne ground penetrating radar system for a dam hidden danger detection, including an unmanned aerial vehicle (UAV) system; the UAV system includes an unmanned aerial vehicle 1, a sensor platform 2, a radar platform 3, a forward-looking laser rangefinder 4 and a ground penetrating radar 5; the sensor platform 2 is installed on the UAV 1, the forward-looking laser rangefinder 4 is installed on the sensor platform 2, and the radar platform 3 is installed on the UAV 1 at one side of the sensor platform 2. Moreover, the ground penetrating radar 5 is installed on the radar platform 3, and a variable polarization ground penetrating radar antenna array is arranged in the ground penetrating radar 5; the sensor platform 2 controls the forward-looking laser rangefinder 4 to have a constant angle with respect to a flight plane of the UAV 1, so that the sensor platform 2 senses a change of a front terrain in advance and realizes an advance control; the radar platform 3 receives a reading of the forward-looking laser rangefinder 4, and angles of the ground penetrating radar 5 in a traveling direction and a vertical direction are controlled on the radar platform 3, so that the ground penetrating radar 5 is parallel to a ground to ensure an imaging stability; and the UAV 1 calculates a flight trajectory according to data of the forward-looking laser rangefinder 4 to achieve a terrain following.

(10) The variable polarization ground penetrating radar antenna array includes a substrate 6, a plurality of groups of orthogonal dual-polarization Vivaldi antenna transmitting subarrays 7 and orthogonal dual-polarization Vivaldi antenna receiving subarrays 8 are mounted on the substrate 6, and corresponding feed networks are also included; the plurality of groups of orthogonal dual-polarization Vivaldi antenna transmitting subarrays 7 each includes two groups of orthogonal Vivaldi antenna array elements 9, a cross-shaped dielectric substrate 10, a gradual opening slot 11, conductor patches 12 and a crossed balun feed structure 13; the gradual opening slot 11 formed by two exponential curves symmetrical about a center line of the substrate 6 is arranged on an upper surface of the cross-shaped dielectric substrate 10 to form a horn-shaped opening facing a maximum radiation direction of a Vivaldi antenna 14, and the upper surface part except the gradual opening slot 11 is covered by the conductor patches 12; each orthogonal dual-polarization Vivaldi antenna transmitting subarray 7 also includes a corresponding feed structure and a Wilkinson power divider, which are used to transmit and receive vertically polarized and horizontally polarized electromagnetic waves respectively, so that a combined detection size of dam hidden dangers is small, and a rapid detection with the UAV 1 is facilitated.

(11) Each orthogonal dual-polarization Vivaldi antenna transmitting subarray 7 or each orthogonal dual-polarization Vivaldi antenna receiving subarray 8 is composed of orthogonal dual-polarization Vivaldi antenna array elements 9 and the feed network to form a 2×2 antenna array, in which four groups of transmitting antennas work simultaneously and four groups of receiving antennas work simultaneously. A gain and a directivity of an antenna system are enhanced and a detection depth of the ground penetrating radar is improved by superposing the electromagnetic waves generated by different array elements in a same polarization mode in time and space.

(12) Each orthogonal dual-polarization Vivaldi antenna array element 9 is composed of two groups of Vivaldi antennas 14 which are placed orthogonally in a cross, and polarization modes of the two groups of Vivaldi antennas 14 are vertical polarization and horizontal polarization respectively.

(13) As shown in FIG. 4, the crossed balun feed structure 13 is a mutual feed structure in which a microstrip line-stripline 15 on the Vivaldi antenna 14 in each orthogonal dual-polarization Vivaldi antenna array element 9 is connected to a back of the Vivaldi antenna 14 orthogonal to the microstrip line-stripline 15 in the subarray, and energy is coupled to an upper surface slot line 16, so that an upper surface feed line of the antenna feeds the other orthogonal antenna. The crossed balun feed structure 13 consists of the microstrip line-stripline 15 on the antenna array element in the subarray and a double-sided slot line structure on the other antenna array element in the subarray. The microstrip line on each antenna array element is connected with a coaxial cable and transmits the energy to the stripline; the stripline extends to a fan-shaped branch on the surface of the other orthogonal antenna array element at an end, and couples the energy to the upper surface slot line of the other orthogonal antenna to form an effective radiation on the antenna, thus forming the crossed balun feed structure 13. A signal fed to one antenna array element in the dual-polarization Vivaldi antenna subarray forms the effective radiation on the other antenna array element placed orthogonal to the antenna array element.

(14) The structure of each orthogonal dual-polarization Vivaldi antenna transmitting subarray 7 is shown in FIG. 5. The main structure is two Vivaldi antennas 14 placed in a cross array, and the maximum radiation direction of the Vivaldi antennas 14 is along an intersecting axial direction. A feed mode of each orthogonal dual-polarization Vivaldi antenna subarray 8 is a variable polarization feed mode, which controls each orthogonal dual-polarization Vivaldi antenna transmitting subarray and receiving subarray 7. Each transmitting subarray adopts a multi-polarization mode variable feed, and each receiving subarray adopts a horizontal and vertical dual-channel receiving; when the two groups of Vivaldi antennas 14 in each orthogonal dual-polarization Vivaldi antenna array element 9 simultaneously transmit the signals with an equal amplitude and a phase difference of 90°, circularly polarized electromagnetic waves are transmitted, and a mixed polarization detection mode of “circularly polarized transmission-linearly polarized reception” is formed; when the two groups of Vivaldi antennas 14 in each orthogonal dual-polarization Vivaldi antenna array element 9 transmit the signals with the equal amplitude and the phase difference of 0° in time sharing, horizontal or vertical polarized electromagnetic waves are respectively transmitted, and a “linearly polarized transmission-linearly polarized reception” is formed, and fully-polarized detection modes of “horizontal-horizontal, horizontal-vertical, vertical-horizontal, vertical-vertical” are realized. When a trend of the dam hidden dangers is unclear, a multi-polarization detection may realize a fast and accurate detection.

(15) In this embodiment, an advanced terrain perception is realized by adopting an advanced detection layout strategy based on a multi-sensor, and an all-terrain near-ground following of the ground penetrating radar 5 under an ultra-low altitude condition is realized by a double closed-loop attitude control mode based on an adjustment of the angle and a speed by the radar platform 3 with multi-sensor information fusion.

(16) As shown in FIG. 7, an inspection method of an unmanned airborne ground penetrating radar system for a dam hidden danger detection includes following steps:

(17) Step 1: starting the sensor platform 2, and the sensor platform 2 is internally provided with an inclination angle control algorithm with an adaptive speed; and

(18) Step 2: controlling an angle between the laser rangefinder and a traveling plane by the inclination angle control algorithm with the adaptive speed according to the speed of the UAV 1, and keeping the angle constant during a traveling of the UAV 1 to adapt to an attitude advance control of the UAV 1 on the plane where the ground penetrating radar 5 antenna array is located in a dam hidden danger detection task under different flight speed conditions.

(19) The specific steps of the Step 1 and the Step 2 are as follows: the UAV 1 receives x.sub.0, y.sub.0 and z.sub.0, where x.sub.0=x.sub.goal and y.sub.0=y.sub.goal are horizontal coordinates of a target, and z.sub.0=h, h is a relative ground height to be controlled; when the UAV 1 takes off, the sensor platform 2 is vertically downward, and an altitude is raised to h; the angle

(20) $\theta ={\tan }^{-1}\frac{v\times t_z}{h}$
between the sensor platform 2 and the flight plane of the UAV is adjusted, and the UAV flies to the target, where v is a horizontal speed and t.sub.z is a vertical reaction time; the higher the speed of the UAV 1 in a flight process, the longer the horizontal distance d.sub.g is needed to adjust the altitude, and the longer the vertical reaction time t.sub.z is needed; because in a long survey line inspection process, a constant speed flight is generally adopted, the horizontal speed v is given, the reasonable vertical reaction time v.sub.z is calculated through a vertical speed v.sub.z of an aircraft; the angle θ between the forward-looking laser rangefinder 4 and the traveling plane is calculated by

(21) $\theta ={\tan }^{-1}\frac{v\times t_z}{h},$
and θ is controlled to remain unchanged by the sensor platform 2 during the traveling process; the radar platform 3 keeps the readings of the two radar side laser rangefinders consistent all the time during the traveling process, as shown in FIG. 6, so that the ground penetrating radar 5 is kept relatively parallel to the ground in the vertical direction of the traveling direction; when a height change is detected, the coordinates P.sub.i+1 of the measuring point are determined, the slope

(22) $\alpha =\arctan \frac{1_{\mathrm{laser}}^i-1_{\mathrm{laser}}^{i+1}.Math.\sin \theta }{v\Delta t-1_{\mathrm{laser}}^i-1_{\mathrm{laser}}^{i+1}.Math.\cos \theta },$
a deflection angle

(23) $\gamma =\arctan \frac{\mathrm{laser}2-\mathrm{laser}3}{w}$
and the height change Δz=h×secα−l.sub.laser×sin θ in a Y-axis direction of the ground penetrating radar are determined; laser is the distance from the target point to the aircraft measured by the laser rangefinder, laser2 and laser3 are the distances from a measured surface measured by laser rangefinder sensors on both sides of the ground penetrating radar 5, and w is the distance between the laser rangefinder sensors on both sides of the ground penetrating radar 5; and Δt=1/f, where f is a sampling frequency of the forward-looking laser rangefinder 4; the radar platform 3 controls the inclination angle of the ground penetrating radar 5 in the traveling direction to be a and the inclination angle γ in the y axis direction to be by adopting a double-closed-loop control mode based on the angle and speed, so that the ground penetrating radar 5 is always kept parallel to the ground;

(24) the coordinates x.sub.i+1, y.sub.i+1, z.sub.i+1 of the measuring point are calculated, where
x.sub.i+1=d.sub.g×cos φ+x.sub.i
y.sub.i+1=d.sub.g×sin φ+y.sub.i, where φ is a yaw angle of a flight direction of UAV 1, d.sub.g=l.sub.laser×cos θ, and z.sub.i+1=z.sub.i+Δz, and h may be kept at the measuring point; the UAV 1 moves to x.sub.i+1, y.sub.i+1, z.sub.i+1 until the UAV 1 reaches the position, and then continue to move to x.sub.0, y.sub.0, and controls the vertical speed during a movement:

(25) $v_z=\frac{z_{i+1}-z_{current}}{z_{i+1}-z_i}\times v_{z\_\max },$  where z.sub.current is a current altitude, and v.sub.z_max is an upper speed limit of the UAV 1 in the vertical direction; if another altitude change is detected, steps S4-S6 are repeated; and the UAV 1 stops when the UAV 1 reaches x.sub.0, y.sub.0.

(26) The above shows and describes a basic principle, main features and advantages of the application. It should be understood by those skilled in the art that the application is not limited by the above-mentioned embodiments. The above-mentioned embodiments and descriptions only illustrate principles of the application. Without departing from a spirit and a scope of the application, there are various changes and improvements of the application, all of which fall within the scope of the claimed application. The scope of the application is defined by the appended claims and their equivalents.