Method for measuring soil compaction degree based on ground penetrating radarTechnical Field
The invention relates to the field of geological exploration, in particular to a method for measuring soil compaction degree based on a ground penetrating radar.
Background
Since the 20 th century, the level of agricultural mechanization has increased, the use of large machines and their associated equipment has increased rapidly, and soil mechanical compaction has increasingly become a major problem in modern agriculture. Soil compaction causes poor soil nutrients in a plough layer and the soil quality is more and more easy to degrade.
Common factors reflecting soil compaction include soil bulk density and soil penetration resistance. But the damage to the soil is serious in the sample collection process, and the time and the labor are wasted; requires skilled manual operation and is greatly influenced by human factors.
Disclosure of Invention
In view of this, the embodiment of the invention provides a method for measuring the soil compaction degree based on a ground penetrating radar, which is mainly used for simply and accurately measuring the soil compaction degree.
In order to achieve the purpose, the invention mainly provides the following technical scheme:
in one aspect, an embodiment of the present invention provides a method for measuring soil compaction degree based on a ground penetrating radar, where the method includes:
measuring the volume weight of the soil by adopting a ground penetrating radar profile method;
processing the obtained measuring signal, and determining a zero point of electromagnetic wave measurement to obtain accurate time domain information;
extracting the propagation speed of the electromagnetic wave, and establishing a regression equation for inverting the volume weight of the soil by combining the speed of the electromagnetic wave with other soil factors;
extracting the amplitude of the electromagnetic wave, and proving the feasibility of measuring the soil compaction degree by using a ground penetrating radar based on the correlation between the amplitude energy value of the electromagnetic wave and the soil penetration resistance;
calculating the attenuation speed of the electromagnetic waves, and proving the feasibility of measuring the soil compaction degree by using a ground penetrating radar based on the correlation between the attenuation coefficient of the electromagnetic waves and the soil penetration resistance;
the average volume weight of the soil body is calculated by using the average speed of the electromagnetic wave propagation, and the characteristics that the soil compaction degree changes gradually along with the depth are reflected by using the amplitude and the attenuation coefficient of the electromagnetic wave.
Preferably, the center frequency of the ground penetrating radar is 500MHz.
Preferably, the time window of the ground penetrating radar during measurement is set to be 20ns-50ns, the sampling time interval is 0.2ns, and the sampling space interval is 0.01m.
Preferably, the processing the acquired measurement signal includes: setting the direct current offset 500, correcting a saturated signal, correcting a zero point, and selecting and using exponential compensation gain, band-pass filtering, vertical filtering, median filtering, spatial low-pass filtering and offset filtering according to actual conditions.
Preferably, the extracted electromagnetic wave propagation speed is specifically: determining the interface and depth of the soil layer, reading the electromagnetic wave in the soil layer, substituting into a formula,wherein v represents the layered electromagnetic wave propagation speed, the unit is m/ns, d represents the soil layered thickness, the unit is m, and t represents the electromagnetic wave double-travel time in the soil layer.
Preferably, the calculating the attenuation speed of the electromagnetic wave is specifically as follows: the following formula can be used for the attenuation coefficient calculation of low-loss soil electromagnetic waves with conductivity below 10mS/m,
wherein α represents an attenuation coefficient, the physical meaning of which is the attenuation of the amplitude in units of distance, in units of Np/m; sigma represents the soil conductivity and has the unit of S/m; epsilon represents the dielectric constant of the soil; c represents the propagation velocity of electromagnetic waves in vacuum of 3X 108 m/s。
Preferably, the other soil factors include: measuring the mass water content of the soil by adopting a drying method, and converting the volume weight of the soil into the volume water content of the soil; collecting a soil volume weight sample by adopting a cutting ring method; measuring soil organic matters by a potassium dichromate volumetric method; determining the total amount of water-soluble salt in the soil by adopting a residue drying method; measuring the soil texture by adopting a laser particle size analyzer; and measuring the change of the soil compactness by adopting a soil compactness meter, and establishing a regression equation by utilizing the soil factor.
Compared with the prior art, the invention has the beneficial effects that:
the invention adopts the ground penetrating radar to measure the volume weight of the soil, and the compaction degree of the soil can be simply, conveniently and accurately measured by processing and analyzing the measurement signal of the radar, extracting the propagation speed of the electromagnetic wave and calculating the attenuation speed of the electromagnetic wave.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description of the embodiments, technical solutions, features and effects according to the present invention will be given with preferred embodiments. The particular features, structures, or characteristics may be combined in any suitable manner in the various embodiments described below.
Examples
A method for measuring soil compaction degree based on ground penetrating radar comprises the following steps:
measuring by adopting a 500MHz center frequency ground penetrating radar profile method, wherein a time window is set to be 20-50ns, a sampling time interval is 0.2ns, and a sampling space interval is 0.01m;
the signal processing comprises the following steps: setting the direct current offset 500, correcting a saturated signal, correcting a zero point, and selecting and using exponential compensation gain, band-pass filtering, vertical filtering, median filtering, spatial low-pass filtering and offset filtering according to actual conditions.
Extracting the electromagnetic wave propagation speed by determining the soil layering interface and depth, and then substituting the two-way travel time of the electromagnetic wave in the soil layer into a formula
Wherein v represents the layered electromagnetic wave propagation speed (m/ns), d represents the soil layered thickness (m), and t represents the electromagnetic wave double-travel time in the soil layer.
Calculating the electromagnetic wave attenuation speed, wherein common soil belongs to non-magnetic materials, and the following formula can be used for calculating the attenuation coefficient of the low-loss soil electromagnetic wave with the conductivity lower than 10mS/m
Wherein α represents the attenuation coefficient, the physical meaning of which is the attenuation of the amplitude over a unit distance, in units of Np/m; sigma represents the soil conductivity and has the unit of S/m; epsilon represents the dielectric constant of the soil; c represents the propagation velocity of the electromagnetic wave in vacuum (3X 108 m/s).
The volume weight of the soil was measured with radar: the experimental site is arranged in a big floating lump village in Yanqing district of Beijing, and aims to invert the volume weight of soil by utilizing the propagation speed of electromagnetic waves; the physical and chemical factors such as the volume weight of the soil are measured by the traditional experimental method: measuring the mass water content of the soil by using a drying method, and converting the mass water content of the soil into the volume water content of the soil through the volume weight of the soil; collecting a soil volume weight sample by using a cutting ring method; measuring soil organic matters by using a potassium dichromate volumetric method (an external heating method); measuring the total amount of water-soluble salt in the soil by using a residue drying method (mass method); measuring the soil texture by using a laser particle size analyzer; and measuring the change of the soil compactness by using a soil compactness tester. The regression equation is established using the above factors.
Soil volume weight is inverted by utilizing ground penetrating radar signals: when the soil volume weight is measured by utilizing a ground penetrating radar electromagnetic wave signal, the following findings are found: under the condition of unsaturated soil moisture, the electromagnetic wave propagation speed and the volume weight of the soil have an obvious positive correlation, and the partial correlation coefficient is 0.917; establishing a regression equation among the electromagnetic wave speed, the soil volume weight, the volume water content, the organic matter content, the soluble salt content and the clay content factor, and mathematically inverting the soil volume weight value; and the soil weight is substituted into a field test for inspection, and compared with the volume weight value obtained by traditional measurement, the accuracy of detecting the soil volume weight by the ground penetrating radar can reach more than 70%. Wherein, a regression equation (B =1.012+ 5.013v-0.004M) is fit by electromagnetic wave velocity and organic matter, wherein B represents soil unit weight g/cm3 V represents layered electromagnetic wave propagation speed M/ns, M represents soil organic matter content g/kg) and the effect of estimating the volume weight of the soil is optimal, and the accuracy is 96.87%.
The relevant change characteristics of the ground penetrating radar signal and the soil penetration resistance are as follows: for the amplitude energy value of the ground penetrating radar echo and soil penetrationCarrying out correlation analysis on the penetration resistance, and finding that when the moisture conditions are consistent or close to each other, the larger the soil penetration resistance is, the smaller the electromagnetic wave amplitude is, and the partial correlation coefficient is-0.657; the attenuation coefficient of the electromagnetic wave reflected by the ground penetrating radar and the soil penetration resistance are subjected to correlation analysis to find that the attenuation coefficient and the soil penetration resistance are in a relatively obvious positive correlation (R)2 >0.7)。
The embodiments of the present invention are not exhaustive, and those skilled in the art can select them from the prior art.
The above disclosure is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and shall be covered by the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the above claims.