Method and device for monitoring water content of surface layer of core wall of dam based on unmanned aerial vehicle

Abstract

The present application relates to the technical field of earth-rock dam monitoring, in particular to a dam core wall surface water content monitoring method and device based on a UAV, which is suitable for earth-rock dam construction period core wall filling water content quality control, wherein the method comprises: using a UAV carrying an L-band dual-polarized microwave radiometer to non-contact scan the dam core wall surface to shallow layer to obtain a brightness temperature sampling sequence; converting the true projection position of each brightness temperature sampling point in the brightness temperature sampling sequence to a dam body independent coordinate system to obtain brightness temperature data in the coordinate system; obtaining actual volume water content data of the dam core wall surface to shallow layer to calibrate the Topp model on site to establish a quantitative inversion relationship between brightness temperature and volume water content, and using the same to perform inversion to obtain volume water content spatial distribution results. Thus, the influence mechanism of core wall material properties on L-band microwave radiation characteristics is not clear, and existing soil moisture inversion models are difficult to be directly applied.

Description

Technical Field

[0001] This invention relates to the field of earth-rock dam monitoring technology, and in particular to a method and device for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles (UAVs). Background Technology

[0002] Earth-rock dams are one of the most widely used dam types in my country's dam engineering. The core wall, as the core seepage prevention structure of an earth-rock dam, directly affects the safety and stability of the entire dam. The moisture content of the core wall is a key parameter affecting its mechanical properties and seepage prevention effect. When the moisture content is too low, the core wall soil is prone to cracking due to drying shrinkage, forming seepage channels; when the moisture content is too high, it may lead to increased pore water pressure inside the core wall, inducing hydraulic fracturing and other damage, endangering dam safety. For a long time, dam safety monitoring in my country has mainly relied on manual inspections and automated systems composed of fixed instruments (such as piezometers, displacement gauges, and strain gauges). However, this traditional monitoring method has significant shortcomings in monitoring the moisture content of the core wall during the construction and operation periods: embedded instruments are destructive monitoring methods, and the instrument installation itself disturbs the core wall soil; the instrument deployment density is limited, making it difficult to obtain spatial distribution information of the moisture content on the core wall surface; and some facilities experience aging after long-term operation, affecting the reliability and comprehensiveness of the monitoring results.

[0003] Passive microwave remote sensing is one of the most effective methods for monitoring soil moisture content. Compared to infrared and visible light, microwaves have the advantages of longer wavelengths and stronger penetration. Compared to active microwave radar, passive microwave radiometers have advantages such as larger monitoring area, shorter cycle time, less susceptibility to surface roughness, and greater sensitivity to moisture. Among various microwave frequency bands, the L-band is widely recognized as the optimal band for passive microwave remote sensing to retrieve soil moisture due to its longer wavelength, stronger penetration, and high sensitivity to moisture. Studies have shown that the penetration depth of L-band microwaves in soil can vary significantly with different medium conditions, reaching tens of centimeters when soil moisture is low, thus effectively reflecting the volumetric water content information within a certain depth range of the medium layer. Based on this physical characteristic, countries in Europe and America have launched L-band passive microwave remote sensing satellites such as SMOS (Soil Moisture and Ocean Salinity) and SMAP (Soil Moisture Active Passive), achieving routine global-scale observation of surface soil moisture. However, the spatial resolution of spaceborne passive microwave radiometers is usually limited (on the order of tens of kilometers), making it difficult to meet the needs of fine-grained monitoring of small and medium-scale engineering targets such as dam core walls.

[0004] In recent years, the fusion technology of UAVs and L-band microwave radiometers has provided a new technical approach to solving the aforementioned problems. UAV platforms are characterized by their maneuverability and ability to plan routes on demand. They can carry lightweight L-band microwave radiometers at low altitudes, thereby obtaining spatial resolution far exceeding that of satellites (reaching tens of meters or even meters), and are unaffected by cloud cover, enabling all-weather operation. Existing research has shown that L-band passive microwave radiometers carried by UAVs can effectively acquire high-resolution brightness and temperature information of the Earth's surface, and use this information to retrieve surface soil moisture. The accuracy of this retrieval has been preliminarily verified in different land cover types such as farmland, shrubland, and bare soil. However, in the specific application scenario of monitoring surface water content in dam core walls, the influence mechanism of core wall material characteristics (such as compaction degree, particle size distribution, and clay mineral composition) on L-band microwave radiation characteristics remains unclear. Existing soil moisture retrieval models are difficult to apply directly, and there is a lack of dedicated monitoring devices and supporting retrieval methods for dam core walls. Summary of the Invention

[0005] This invention provides a method and device for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles (UAVs), in order to solve the problems that the influence mechanism of the core wall material characteristics on the L-band microwave radiation characteristics is still unclear and that existing soil moisture inversion models are difficult to apply directly.

[0006] A first aspect of the present invention provides a method for monitoring the surface water content of the core wall of a dam based on an unmanned aerial vehicle (UAV), comprising the following steps: A drone equipped with an L-band dual-polarized microwave radiometer was used to perform non-contact scanning of the core wall of the target dam from the surface to the shallow layer in order to obtain a brightness temperature sampling sequence. Geometric projection correction is performed on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projection position of each sampling point on the ground. The actual projected positions of each sampling point on the ground are transformed into the dam body independent coordinate system to obtain the brightness temperature data in the dam body independent coordinate system. The actual volumetric water content data from the surface to the shallow layer of the core wall of the target dam were obtained and the pre-constructed Topp model was calibrated on-site to establish a quantitative inversion relationship between brightness temperature and volumetric water content. The brightness temperature data in the independent coordinate system of the dam body is inverted using the quantitative inversion relationship between brightness temperature and volumetric water content to obtain the spatial distribution of volumetric water content from the surface to the shallow layer of the dam core wall.

[0007] Optionally, the non-contact scanning of the target dam core wall surface to shallow layers using a UAV equipped with an L-band dual-polarized microwave radiometer to obtain a brightness temperature sampling sequence includes: Obtain the flight log of the UAV equipped with an L-band dual-polarized microwave radiometer; Using the timestamp of the L-band dual-polarized microwave radiometer as the primary time stamp, the flight log is interpolated to each radiometer sampling time to obtain the initialized UAV equipped with the L-band dual-polarized microwave radiometer. The UAV equipped with an L-band dual-polarization microwave radiometer, after initialization, performs a non-contact scan of the core wall of the target dam from the surface to the shallow layer to obtain a brightness temperature sampling sequence, wherein the brightness temperature sampling sequence includes a horizontal polarization brightness temperature sampling sequence and a vertical polarization brightness temperature sampling sequence.

[0008] Optionally, the step of performing geometric projection correction on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projected position of each sampling point on the ground includes: The real-time latitude and longitude, attitude angle and flight altitude information of the UAV equipped with an L-band dual-polarized microwave radiometer are obtained. Convert the real-time latitude and longitude into a plane coordinate system; Based on the planar coordinate system, and in conjunction with the attitude angle and the flight altitude information, geometric projection correction is performed on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projection position of each sampling point on the ground.

[0009] Optionally, the step of transforming the actual projected positions of each sampling point on the ground to the dam body independent coordinate system to obtain brightness temperature data in the dam body independent coordinate system includes: By using the four corner control points pre-positioned on the dam, an independent coordinate system for the dam body is constructed; Two-dimensional similarity transformation or affine transformation is used to transform the actual projection position of each sampling point on the ground to the independent coordinate system of the dam body, so as to obtain the brightness temperature data in the independent coordinate system of the dam body.

[0010] Optionally, the step of obtaining the actual volumetric water content data from the surface to shallow layers of the target dam core wall and performing on-site calibration and correction of the pre-constructed Topp model to establish a quantitative inversion relationship between brightness temperature and volumetric water content includes: The surface to shallow layers of the core wall of the target dam were measured in real time using a time domain reflectometer to obtain actual volumetric water content data. The Topp model was calibrated on-site using the actual volumetric water content data to obtain a corrected Topp model. A quantitative inversion relationship between brightness temperature and volumetric water content is established based on the radiation propagation equation and the modified Topp model.

[0011] A second aspect of the present invention provides a device for monitoring the surface water content of a dam core wall based on an unmanned aerial vehicle (UAV), comprising: The scanning module is used to perform non-contact scanning of the surface to shallow layers of the core wall of the target dam using a UAV equipped with an L-band dual-polarized microwave radiometer, in order to obtain a brightness temperature sampling sequence. The correction module is used to perform geometric projection correction on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projection position of each sampling point on the ground. The conversion module is used to convert the actual projection position of each sampling point on the ground to the dam body independent coordinate system to obtain the brightness temperature data in the dam body independent coordinate system. The calibration module is used to obtain the actual volumetric water content data from the surface to the shallow layer of the core wall of the target dam and to perform on-site calibration of the pre-constructed Topp model in order to establish a quantitative inversion relationship between brightness temperature and volumetric water content. The inversion module is used to invert the brightness temperature data in the independent coordinate system of the dam body using the quantitative inversion relationship between the brightness temperature and the volumetric water content, so as to obtain the spatial distribution of volumetric water content from the surface to the shallow layer of the dam core wall.

[0012] Optionally, the scanning module includes: The first acquisition unit is used to acquire the flight log of the UAV equipped with an L-band dual-polarized microwave radiometer. The interpolation unit is used to interpolate the flight log to each radiometer sampling time according to time, using the timestamp of the L-band dual-polarized microwave radiometer as the main time stamp, so as to obtain the initialized UAV equipped with the L-band dual-polarized microwave radiometer. The scanning unit is used to perform non-contact scanning of the surface to shallow layers of the core wall of the target dam using the UAV equipped with the initialized L-band dual-polarization microwave radiometer, so as to obtain a brightness temperature sampling sequence, wherein the brightness temperature sampling sequence includes a horizontal polarization brightness temperature sampling sequence and a vertical polarization brightness temperature sampling sequence.

[0013] Optionally, the correction module includes: The second acquisition unit is used to acquire the real-time latitude and longitude of the UAV equipped with an L-band dual-polarized microwave radiometer, as well as the attitude angle and flight altitude information during the flight process. A conversion unit is used to convert the real-time latitude and longitude into a plane coordinate system; The correction unit is used to perform geometric projection correction on each brightness temperature sampling point in the brightness temperature sampling sequence based on the plane coordinate system and in combination with the attitude angle and the flight altitude information, so as to obtain the true projection position of each sampling point on the ground.

[0014] Optionally, the conversion module includes: The first building unit is used to construct an independent coordinate system for the dam body by utilizing the four corner control points pre-laid on the dam. The second conversion unit is used to convert the actual projection position of each sampling point on the ground to the independent coordinate system of the dam body by using two-dimensional similarity transformation or affine transformation, so as to obtain the brightness temperature data in the independent coordinate system of the dam body.

[0015] Optionally, the calibration module includes: The measurement unit is used to perform real-time measurements on the surface to shallow layers of the core wall of the target dam using a time-domain reflectometer to obtain actual volumetric water content data. The calibration unit is used to calibrate the Topp model on-site using the actual volumetric water content data to obtain a corrected Topp model. The second building unit is used to establish a quantitative inversion relationship between the brightness temperature and the volumetric water content based on the radiation propagation equation and the modified Topp model.

[0016] The method and device for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles (UAVs) proposed in this invention can quickly acquire high-resolution spatial distribution information of the surface water content of the core wall in a non-destructive and non-contact manner. It overcomes the limitations of traditional buried monitoring methods in terms of destructiveness and insufficient spatial coverage, and provides a brand-new technical solution for compaction quality control during dam construction and health assessment of the seepage prevention body during operation. It is applicable to engineering scenarios such as earth-rock dams, asphalt core wall dams, or clay core wall dams that require process control of water content, and is especially suitable for construction conditions where traditional point measurement is inefficient, has limited coverage, and cannot meet the requirements for rapid rectification.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 A flowchart illustrating a method for monitoring the surface water content of a dam core wall based on an unmanned aerial vehicle (UAV) according to an embodiment of the present invention; Figure 2 This is a block diagram of a device for monitoring the surface water content of a dam core wall based on an unmanned aerial vehicle (UAV) according to an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures: 20- Monitoring device for surface water content of dam core wall based on UAV, 201- Scanning module, 202- Correction module, 203- Conversion module, 204- Calibration module, 205- Inversion module. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] The following describes a method and apparatus for monitoring the surface water content of a dam core wall based on an unmanned aerial vehicle (UAV) according to an embodiment of the present invention, with reference to the accompanying drawings. Addressing the issues mentioned in the background section regarding the unclear mechanism of influence of core wall material properties on L-band microwave radiation characteristics in the specific application scenario of monitoring the surface water content of a dam core wall, the inability to directly apply existing soil moisture inversion models, and the lack of dedicated monitoring devices and supporting inversion methods for dam core walls, the present invention provides a method for monitoring the surface water content of a dam core wall based on an UAV. In this method, a UAV equipped with an L-band dual-polarized microwave radiometer first performs a low-altitude scan of the surface to shallow water content of the dam core wall along a fixed flight path. Then, the radiometer data, flight log data, and ground-based TDR (Time Domain Reflectometry) measured data are unified into the same time and coordinate framework. The actual landing point corresponding to each brightness temperature sample is obtained through attitude projection correction. The Topp model is calibrated on-site using the ground-based TDR measured points, and then tau-omega... The water content of the core wall was inverted using a microwave radiation transfer model and a modified Topp dielectric model. Finally, the spatial distribution map of the water content of the dam core wall, a list of abnormal areas, and construction rectification suggestions were output in the dam-independent coordinate system.

[0022] Specifically, Figure 1 This is a flowchart illustrating a method for monitoring the surface water content of a dam core wall based on an unmanned aerial vehicle (UAV) according to an embodiment of the present invention.

[0023] like Figure 1 As shown, the method for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles includes the following steps: In step S101, a UAV equipped with an L-band dual-polarized microwave radiometer is used to perform a non-contact scan of the surface to shallow layers of the core wall of the target dam to obtain a brightness temperature sampling sequence.

[0024] In some embodiments, a UAV equipped with an L-band dual-polarized microwave radiometer is used to perform non-contact scanning of the surface to shallow layers of the core wall of a target dam to obtain a brightness temperature sampling sequence, including: Obtain the flight logs of a drone equipped with an L-band dual-polarized microwave radiometer; Using the timestamp of the L-band dual-polarized microwave radiometer as the primary time stamp, the flight log is interpolated to each radiometer sampling time to obtain the initialized UAV equipped with the L-band dual-polarized microwave radiometer. The UAV equipped with an L-band dual-polarization microwave radiometer was initialized and used to perform non-contact scanning of the core wall of the target dam from the surface to the shallow layer to obtain a brightness temperature sampling sequence, which includes a horizontal polarization brightness temperature sampling sequence and a vertical polarization brightness temperature sampling sequence.

[0025] It should be noted that the embodiments of the present invention employ a multi-rotor unmanned aerial vehicle (UAV). This UAV not only carries an L-band dual-polarization microwave radiometer, but also includes an onboard positioning and attitude information recording unit, a ground-based time domain reflectometer (TDR) for water content measurement, and an RTK (Real-Time Kinematic) or total station for control point measurement. The L-band dual-polarization microwave radiometer is typically a PoLRa3.x model, which outputs vertical polarization brightness temperature (TBV) and horizontal polarization brightness temperature (TBH) data. The onboard positioning and attitude information recording unit records information such as latitude, longitude, altitude, speed, yaw angle, pitch angle, and roll angle. The TDR is responsible for obtaining the true volumetric water content values ​​at representative locations.

[0026] In actual operation, after the UAV equipped with the L-band dual-polarized microwave radiometer PoLRa3.x is powered on, it automatically performs GPS locking and time synchronization, outputs radiometer data files stored in .dat format and corresponding GPS / flight log files, and then uses the timestamp of the L-band dual-polarized microwave radiometer as the main time stamp to interpolate the flight log to each radiometer sampling time according to the time, so that the position, attitude and velocity information of the UAV equipped with the L-band dual-polarized microwave radiometer after initialization corresponds one-to-one with the brightness temperature sample.

[0027] Furthermore, using an initialized UAV equipped with an L-band dual-polarization microwave radiometer, a single flight with an integration time of 0.3s was conducted to perform a non-contact scan of the target dam core wall from the surface to the shallow layer. The initialized UAV equipped with the L-band dual-polarization microwave radiometer first reads the matched load, cold load, and original voltage of the polarization channel; then, based on the cold load file and the internal reference temperature, gain, bias, and cable loss corrections were performed to obtain two brightness temperature sampling sequences: initial horizontal polarization TBH and initial vertical polarization TBV. Subsequently, standard deviation threshold filtering, median absolute deviation filtering, flight state filtering, speed filtering, and attitude filtering were performed to remove observation points in the initial horizontal polarization TBH and initial vertical polarization TBV brightness temperature sampling sequences that involved turning, takeoff and landing, excessive attitude, or abnormal original voltage, ensuring that the brightness temperature data entering the inversion was stable and reliable, thus obtaining the horizontal polarization TBH brightness temperature sampling sequence and the vertical polarization TBV brightness temperature sampling sequence.

[0028] It should be noted that the L-band dual-polarization microwave radiometer PoLRa3.x is mounted on the underside of the multi-rotor UAV via a dedicated bracket, with the antenna facing arms 5 and 6. Due to the 90° installation angle of the sensor relative to the forward direction of the UAV, the heading setting needs to be adjusted synchronously during flight path planning to ensure the radiometer's main line of sight scans forward along the flight path rather than laterally, thus reducing polarization mixing and geometric deviation. The flight mission of the multi-rotor UAV is preferably performed using a fixed flight path, equally spaced parallel survey lines, and a constant flight speed, with a recommended cruising speed of 20–25 km / h. The flight altitude should be controlled below 6 m from the surface of the core wall, preferably approximately 5 m. At this altitude, the minimum pixel minor axis dimension is approximately 3.2 m, and the major axis dimension is approximately 6.0 m. Therefore, the minor axis monitoring resolution is better than 4 m, which meets the needs of rapid inspection of dam surface construction quality. For dam surfaces with elevation variations, a flight altitude relative to the ground can be used to obtain approximately consistent ground footprint dimensions at different measuring points.

[0029] In step S102, geometric projection correction is performed on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projection position of each sampling point on the ground.

[0030] In some embodiments, geometric projection correction is performed on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projected position of each sampling point on the ground, including: Acquire real-time latitude and longitude, as well as attitude angle and flight altitude information of the UAV equipped with an L-band dual-polarized microwave radiometer; Convert real-time latitude and longitude to a plane coordinate system; Based on a planar coordinate system, the brightness temperature sampling points in the brightness temperature sampling sequence are geometrically projected and corrected using attitude angle and flight altitude information to obtain the true projection position of each sampling point on the ground.

[0031] In step S103, the actual projection position of each sampling point on the ground is transformed to the dam body independent coordinate system to obtain the brightness temperature data in the dam body independent coordinate system.

[0032] In some embodiments, the actual projected positions of each sampling point on the ground are transformed to the dam-independent coordinate system to obtain brightness temperature data in the dam-independent coordinate system, including: By using the four corner control points pre-positioned on the dam, an independent coordinate system for the dam body is constructed; Two-dimensional similarity transformation or affine transformation is used to transform the actual projection position of each sampling point on the ground to the dam body independent coordinate system to obtain the brightness temperature data in the dam body independent coordinate system.

[0033] In actual execution, the real-time latitude and longitude of the UAV equipped with an L-band dual-polarized microwave radiometer are obtained. First, the real-time latitude and longitude of the UAV are converted into UTM (Universal Transverse Mercator) intermediate coordinates. Then, the UTM intermediate coordinates are converted into a plane coordinate system. Then, the attitude angle and flight altitude information during the flight are obtained. Based on the plane coordinate system, combined with the attitude angle and flight altitude information and the radiometer viewpoint, the ground lateral projection offset and the pitch correction of the track direction are determined. The above-mentioned ground lateral projection offset and pitch correction of the track direction are rotated to the actual flight direction to perform geometric projection correction on each brightness temperature sampling point in the brightness temperature sampling sequence, so as to obtain the true projection position of each sampling point on the ground.

[0034] The ground lateral projection offset can be expressed as: ,in, For ground height, The radiometer's viewing angle is typically around 40°. The roll angle and pitch correction can be expressed as: The pitch correction, of which, It is the pitch angle.

[0035] Furthermore, in order to meet the requirements of dam project management, the coordinates of the control points are measured using RTK or total station at the four corners or four stable control points pre-deployed on the dam surface. An independent coordinate system for the dam body is constructed, and two-dimensional similarity transformation or affine transformation is used to transform the true projection position of each sampling point on the ground from the global coordinate system to the dam independent coordinate system. This allows the final results to be directly used for compaction zoning, compaction site numbering, construction pile numbering, and closed-loop management of rectification.

[0036] In step S104, the actual volumetric water content data from the surface to the shallow layer of the target dam core wall is obtained and the pre-constructed Topp model is calibrated on-site to establish a quantitative inversion relationship between brightness temperature and volumetric water content.

[0037] In some embodiments, the actual volumetric water content data from the surface to shallow layers of the target dam core wall are obtained to perform on-site calibration and correction of the pre-constructed Topp model, in order to establish a quantitative inversion relationship between brightness temperature and volumetric water content, including: A time-domain reflectometer was used to measure the surface and shallow layers of the core wall of the target dam in real time to obtain the actual volumetric water content data. The Topp model was calibrated on-site using actual volumetric water content data to obtain a corrected Topp model. A quantitative inversion relationship between brightness temperature and volumetric water content was established based on the radiation propagation equation and the modified Topp model.

[0038] In step S105, the brightness temperature data in the independent coordinate system of the dam body is inverted using the quantitative inversion relationship between brightness temperature and volumetric water content to obtain the spatial distribution of volumetric water content from the surface to the shallow layer of the dam core wall.

[0039] In practical implementation, the tau-omega-Ts microwave radiative transfer model is first used to describe the relationship between surface emission, vegetation attenuation, and secondary scattering. In the application scenario of dam core walls, the surface vegetation is extremely weak, so the vegetation optical thickness tau can be set to zero or close to zero, and the single scattering albedo omega is taken as a minimum value. The surface temperature Ts can be measured by infrared thermography, ground temperature sensors, airborne thermal infrared, or on-site temperature measurement. If no relevant equipment is available, it can be preset to an empirical value, thus highlighting the radiative response of the soil itself. The soil dielectric constant is expressed using the Topp model, and the standard form is:

[0040] in, This refers to the volumetric water content.

[0041] To address the difference in dielectric properties between dam core wall materials and natural farmland soil, this invention further introduces a soil property parameter, namely the correction term zs, to form a modified Topp model. The specific expression is as follows:

[0042] Subsequently, a quantitative inversion relationship between brightness temperature and volumetric water content was established based on the radiation propagation equation and the modified Topp model. Based on this relationship, and with the goal of minimizing the residuals between the measured values ​​of TBH and TBV and the calculated values ​​of the model, a one-dimensional bounded optimization method was used to solve for the soil water content. The spatial distribution of volumetric water content (m³ / m³) from the surface to the shallow layer of the dam core wall at each observation point was output.

[0043] Specifically, to adapt the inversion model to specific dam materials, this embodiment of the invention employs a ground-based time domain reflectometer (TDR) with an accuracy better than 0.01 m³ / m³, making it suitable as a field calibration benchmark), the drying method, or other field moisture content benchmark measurement methods to perform real-time measurements on the surface to shallow layers of the target dam core wall, in order to obtain actual volumetric moisture content data. The actual volumetric moisture content data is then used to calibrate the Topp model in the field. During calibration, control points are first set up at the four corners of the core wall surface to be measured, and their coordinates are measured to establish an independent coordinate system and verify the landing position of the UAV. Subsequently, no fewer than five representative points are selected within the surface to represent different compaction degrees, different wet-dry states, and different construction areas. Each representative point was measured five times using a TDR (Transient Resonance Analyzer). Before measurement, surface soil and obvious stones should be removed to ensure full contact between the probe and the soil. The probe direction should be kept as parallel as possible, and the insertion depth should be consistent to avoid gaps, looseness, and obvious cracks. Each reading should be recorded after the instrument has stabilized. If there are obvious outliers among the five measurements, they can be removed according to repeatability criteria, and the average of the remaining measurements can be taken as the representative water content of that point. During calibration, the TDR points and UAV inversion points are matched according to spatial distance. The matching threshold can be controlled within 10 m, preferably 1. On the order of m, the optimal correction term zs or equivalent correction coefficient of the Topp model is obtained by minimizing the root mean square error between the UAV inversion value and the TDR measured value. After this calibration, the differences in core wall material, compaction state and local structure can be absorbed into the model parameters, that is, the optimal correction term zs or equivalent correction coefficient is added to the Topp model to obtain the corrected Topp model, which can significantly improve the engineering applicability of the inversion results. Finally, a quantitative inversion relationship between brightness temperature and volumetric water content is established based on the radiation propagation equation and the corrected Topp model.

[0044] Furthermore, a physical model chain from brightness temperature to dielectric constant to volumetric water content is adopted. The quantitative inversion relationship between brightness temperature and volumetric water content is used to invert the brightness temperature data in the independent coordinate system of the dam body. Specifically, this method takes into account both the dual-polarization brightness temperature information and the geometric characteristics of low-altitude observation, making it suitable for rapid inversion at the core wall construction site.

[0045] After the inversion is completed, the system outputs information such as latitude and longitude, UTM or dam-body independent coordinates, TBV, TBH, inverted water content, attitude angle, velocity, and model parameters for each observation point. It can also generate processed CSV (Comma-Separated Values), raster maps, heat maps, and reports. The final spatial distribution results of volumetric water content from the surface to the shallow layers of the dam core wall include: a spatial distribution map of core wall water content, locations of areas exceeding limits or areas that are too dry or too wet, statistical values ​​of representative sections, a list of anomalies, and rectification suggestions. These results can directly serve construction control aspects such as dam compaction, water replenishment, sun drying, repaving, or local rework. Following the existing workflow, after the flight is completed on-site, a .dat file and flight log can be exported. The processing program automatically completes time registration, attitude correction, brightness temperature inversion, TDR calibration, and result plotting. Under normal laptop computing conditions, the time from drone takeoff to the generation of a monitoring report can be controlled within 3 hours. As an engineering indicator, after completing the positioning of the four corner control points, TDR calibration of the representative points, and outlier removal, the monitoring error of the core wall water content in this embodiment of the invention can be controlled within 0.02 m³ / m³.

[0046] In summary, the method for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles (UAVs) proposed in this embodiment of the invention has the following beneficial effects: (1) This invention is not just about "installing a radiometer on a drone", but rather forms a complete technology chain suitable for the construction quality management of the dam core wall: using low-altitude L-band dual-polarization brightness temperature to perceive the water content of the core wall in a planar manner; using the attitude and altitude information of the drone to perform geometric projection correction on the observation landing point; using the four corner control points to convert the results to the independent coordinate system of the dam body, which is convenient to connect with the construction pile number and the boundary of the dam surface; using TDR to calibrate the modified Topp model on site, so that the results are more suitable for specific dam materials and construction conditions; and compressing the data processing time to a few hours to achieve a closed loop of "monitoring-interpretation-rectification".

[0047] (2) Compared with the method of relying solely on TDR point measurement or manual experience judgment, the present invention has the advantages of large coverage, non-contact, minimal interference with construction, intuitive visualization of results, and fast feedback speed. (3) It can be directly used in scenarios such as dam core wall filling, compaction water content control, layered acceptance and abnormal area verification. It is especially suitable for construction conditions where traditional point measurement is inefficient, has limited coverage, and cannot meet the requirements for rapid rectification. It has high engineering promotion value.

[0048] Next, referring to the accompanying drawings, a monitoring device for the surface water content of the dam core wall based on an unmanned aerial vehicle (UAV) according to an embodiment of the present invention is described.

[0049] Figure 2This is a block diagram of a device for monitoring the surface water content of a dam core wall based on an unmanned aerial vehicle (UAV) according to an embodiment of the present invention.

[0050] like Figure 2 As shown, the monitoring device 20 for the surface water content of the dam core wall based on UAV includes: a scanning module 201, a correction module 202, a conversion module 203, a calibration module 204, and an inversion module 205.

[0051] The scanning module 201 uses a UAV equipped with an L-band dual-polarized microwave radiometer to perform non-contact scanning of the target dam core wall from the surface to the shallow layer, obtaining a brightness temperature sampling sequence. The correction module 202 performs geometric projection correction on each brightness temperature sampling point in the sequence to obtain the true projection position of each sampling point on the ground. The conversion module 203 converts the true projection position of each sampling point on the ground to the dam body's independent coordinate system, obtaining brightness temperature data in the dam body's independent coordinate system. The calibration module 204 uses the actual volumetric water content data of the target dam core wall from the surface to the shallow layer to perform on-site calibration of the pre-constructed Topp model, establishing a quantitative inversion relationship between brightness temperature and volumetric water content. The inversion module 205 uses the quantitative inversion relationship between brightness temperature and volumetric water content to invert the brightness temperature data in the dam body's independent coordinate system, obtaining the spatial distribution of volumetric water content from the surface to the shallow layer of the dam core wall.

[0052] In some embodiments, the scanning module 201 includes: The first acquisition unit is used to acquire the flight logs of the UAV equipped with an L-band dual-polarized microwave radiometer. The interpolation unit is used to interpolate the flight log to each radiometer sampling time according to the time, with the timestamp of the L-band dual-polarized microwave radiometer as the main time stamp, so as to obtain the initialized UAV equipped with the L-band dual-polarized microwave radiometer. The scanning unit is used to perform non-contact scanning of the surface to shallow layers of the core wall of the target dam using an unmanned aerial vehicle equipped with an L-band dual-polarization microwave radiometer after initialization, so as to obtain a brightness temperature sampling sequence, which includes a horizontal polarization brightness temperature sampling sequence and a vertical polarization brightness temperature sampling sequence.

[0053] In some embodiments, the correction module 202 includes: The second acquisition unit is used to acquire the real-time latitude and longitude of the UAV equipped with an L-band dual-polarized microwave radiometer, as well as the attitude angle and flight altitude information during the flight process. The transformation unit is used to convert real-time latitude and longitude into a plane coordinate system; The correction unit is used to perform geometric projection correction on each brightness temperature sampling point in the brightness temperature sampling sequence based on the planar coordinate system and combined with attitude angle and flight altitude information, so as to obtain the true projection position of each sampling point on the ground.

[0054] In some embodiments, the conversion module 203 includes: The first building unit is used to construct an independent coordinate system for the dam body by utilizing the four corner control points pre-laid on the dam. The second transformation unit is used to transform the actual projection position of each sampling point on the ground to the dam body independent coordinate system by using two-dimensional similarity transformation or affine transformation, so as to obtain the brightness temperature data in the dam body independent coordinate system.

[0055] In some embodiments, the calibration module 204 includes: The measurement unit is used to perform real-time measurements on the surface to shallow layers of the core wall of the target dam using a time domain reflectometer to obtain actual volumetric water content data. The calibration unit is used to calibrate the Topp model in the field using actual volumetric water content data to obtain a corrected Topp model. The second building block is used to establish a quantitative inversion relationship between brightness temperature and volumetric water content based on the radiation propagation equation and the modified Topp model.

[0056] It should be noted that the explanation of the above-described embodiment of the method for monitoring the surface water content of the dam core wall based on UAVs also applies to the UAV-based device for monitoring the surface water content of the dam core wall in this embodiment, and will not be repeated here.

[0057] The monitoring device for surface water content of dam core wall based on unmanned aerial vehicle (UAV) according to embodiments of the present invention has the following beneficial effects: (1) This invention is not just about "installing a radiometer on a drone", but rather forms a complete technology chain suitable for the construction quality management of the dam core wall: using low-altitude L-band dual-polarization brightness temperature to perceive the water content of the core wall in a planar manner; using the attitude and altitude information of the drone to perform geometric projection correction on the observation landing point; using the four corner control points to convert the results to the independent coordinate system of the dam body, which is convenient to connect with the construction pile number and the boundary of the dam surface; using TDR to calibrate the modified Topp model on site, so that the results are more suitable for specific dam materials and construction conditions; and compressing the data processing time to a few hours to achieve a closed loop of "monitoring-interpretation-rectification".

[0058] (2) Compared with the method of relying solely on TDR point measurement or manual experience judgment, the present invention has the advantages of large coverage, non-contact, minimal interference with construction, intuitive visualization of results, and fast feedback speed. (3) It can be directly used in scenarios such as dam core wall filling, compaction water content control, layered acceptance and abnormal area verification. It is especially suitable for construction conditions where traditional point measurement is inefficient, has limited coverage, and cannot meet the requirements for rapid rectification. It has high engineering promotion value.

[0059] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0060] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0061] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or N executable instructions for implementing custom logic functions or processes, and the scope of preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

Claims

1. A method for monitoring the surface water content of the core wall of a dam based on unmanned aerial vehicles (UAVs), characterized in that, Includes the following steps: A drone equipped with an L-band dual-polarized microwave radiometer was used to perform non-contact scanning of the core wall of the target dam from the surface to the shallow layer in order to obtain a brightness temperature sampling sequence. Geometric projection correction is performed on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projection position of each sampling point on the ground. The actual projected positions of each sampling point on the ground are transformed into the dam body independent coordinate system to obtain the brightness temperature data in the dam body independent coordinate system. The actual volumetric water content data from the surface to the shallow layer of the core wall of the target dam were obtained and the pre-constructed Topp model was calibrated on-site to establish a quantitative inversion relationship between brightness temperature and volumetric water content. The brightness temperature data in the independent coordinate system of the dam body is inverted using the quantitative inversion relationship between brightness temperature and volumetric water content to obtain the spatial distribution of volumetric water content from the surface to the shallow layer of the dam core wall.

2. The method for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, The method involves using an unmanned aerial vehicle equipped with an L-band dual-polarized microwave radiometer to perform a non-contact scan of the core wall of the target dam from the surface to the shallow layers to obtain a brightness temperature sampling sequence, including: Obtain the flight log of the UAV equipped with an L-band dual-polarized microwave radiometer; Using the timestamp of the L-band dual-polarized microwave radiometer as the primary time stamp, the flight log is interpolated to each radiometer sampling time to obtain the initialized UAV equipped with the L-band dual-polarized microwave radiometer. The UAV equipped with an L-band dual-polarization microwave radiometer, after initialization, performs a non-contact scan of the core wall of the target dam from the surface to the shallow layer to obtain a brightness temperature sampling sequence, wherein the brightness temperature sampling sequence includes a horizontal polarization brightness temperature sampling sequence and a vertical polarization brightness temperature sampling sequence.

3. The method for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, The step of performing geometric projection correction on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projection position of each sampling point on the ground includes: The real-time latitude and longitude, attitude angle and flight altitude information of the UAV equipped with an L-band dual-polarized microwave radiometer are obtained. Convert the real-time latitude and longitude into a plane coordinate system; Based on the planar coordinate system, and in conjunction with the attitude angle and the flight altitude information, geometric projection correction is performed on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projection position of each sampling point on the ground.

4. The method for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, The process of transforming the actual projected positions of each sampling point on the ground to the dam body's independent coordinate system to obtain brightness temperature data in the dam body's independent coordinate system includes: By using the four corner control points pre-positioned on the dam, an independent coordinate system for the dam body is constructed; Two-dimensional similarity transformation or affine transformation is used to transform the actual projection position of each sampling point on the ground to the independent coordinate system of the dam body, so as to obtain the brightness temperature data in the independent coordinate system of the dam body.

5. The method for monitoring the surface water content of the dam core wall based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, The process of obtaining actual volumetric water content data from the surface to shallow layers of the target dam core wall and performing on-site calibration and correction of the pre-constructed Topp model to establish a quantitative inversion relationship between brightness temperature and volumetric water content includes: The surface to shallow layers of the core wall of the target dam were measured in real time using a time domain reflectometer to obtain actual volumetric water content data. The Topp model was calibrated on-site using the actual volumetric water content data to obtain a corrected Topp model. A quantitative inversion relationship between brightness temperature and volumetric water content is established based on the radiation propagation equation and the modified Topp model.

6. A device for monitoring the surface water content of a dam core wall based on unmanned aerial vehicles (UAVs), characterized in that, include: The scanning module is used to perform non-contact scanning of the surface to shallow layers of the core wall of the target dam using a UAV equipped with an L-band dual-polarized microwave radiometer, in order to obtain a brightness temperature sampling sequence. The correction module is used to perform geometric projection correction on each brightness temperature sampling point in the brightness temperature sampling sequence to obtain the true projection position of each sampling point on the ground. The conversion module is used to convert the actual projection position of each sampling point on the ground to the dam body independent coordinate system to obtain the brightness temperature data in the dam body independent coordinate system. The calibration module is used to obtain the actual volumetric water content data from the surface to the shallow layer of the core wall of the target dam and to perform on-site calibration of the pre-constructed Topp model in order to establish a quantitative inversion relationship between brightness temperature and volumetric water content. The inversion module is used to invert the brightness temperature data in the independent coordinate system of the dam body using the quantitative inversion relationship between the brightness temperature and the volumetric water content, so as to obtain the spatial distribution of volumetric water content from the surface to the shallow layer of the dam core wall.

7. The monitoring device for surface water content of dam core wall based on unmanned aerial vehicle (UAV) according to claim 6, characterized in that, The scanning module includes: The first acquisition unit is used to acquire the flight log of the UAV equipped with an L-band dual-polarized microwave radiometer. The interpolation unit is used to interpolate the flight log to each radiometer sampling time according to time, using the timestamp of the L-band dual-polarized microwave radiometer as the main time stamp, so as to obtain the initialized UAV equipped with the L-band dual-polarized microwave radiometer. The scanning unit is used to perform non-contact scanning of the surface to shallow layers of the core wall of the target dam using the UAV equipped with the initialized L-band dual-polarization microwave radiometer, so as to obtain a brightness temperature sampling sequence, wherein the brightness temperature sampling sequence includes a horizontal polarization brightness temperature sampling sequence and a vertical polarization brightness temperature sampling sequence.

8. The monitoring device for surface water content of dam core wall based on unmanned aerial vehicle (UAV) according to claim 6, characterized in that, The correction module includes: The second acquisition unit is used to acquire the real-time latitude and longitude of the UAV equipped with an L-band dual-polarized microwave radiometer, as well as the attitude angle and flight altitude information during the flight process. A conversion unit is used to convert the real-time latitude and longitude into a plane coordinate system; The correction unit is used to perform geometric projection correction on each brightness temperature sampling point in the brightness temperature sampling sequence based on the plane coordinate system and in combination with the attitude angle and the flight altitude information, so as to obtain the true projection position of each sampling point on the ground.

9. The monitoring device for surface water content of dam core wall based on unmanned aerial vehicle (UAV) according to claim 6, characterized in that, The conversion module includes: The first building unit is used to construct an independent coordinate system for the dam body by utilizing the four corner control points pre-laid on the dam. The second conversion unit is used to convert the actual projection position of each sampling point on the ground to the independent coordinate system of the dam body by using two-dimensional similarity transformation or affine transformation, so as to obtain the brightness temperature data in the independent coordinate system of the dam body.

10. The monitoring device for surface water content of dam core wall based on unmanned aerial vehicle (UAV) according to claim 6, characterized in that, The calibration module includes: The measurement unit is used to perform real-time measurements on the surface to shallow layers of the core wall of the target dam using a time-domain reflectometer to obtain actual volumetric water content data. The calibration unit is used to calibrate the Topp model on-site using the actual volumetric water content data to obtain a corrected Topp model. The second building unit is used to establish a quantitative inversion relationship between the brightness temperature and the volumetric water content based on the radiation propagation equation and the modified Topp model.

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