Research On Forward Modeling Of Ice GPR And River Ice Detection By UAV Borne Radar

The rivers and some large-scale water transfer projects in northern China will be frozen in winter.If we want to prevent and control disasters caused by river ice,we must have a deep understanding of the ice layer and the characteristics of each stage of ice growth.As an advanced non-destructive exploration technology,GPR has been successfully applied to ice detection.However,in the field of river ice,there are still problems such as difficulty in interpretation of the images and the large limitation of time and space in the measurement process.Based on this,this thesis establishes an ice layer model based on the FDTD method,performs forward simulation,and establishes an image feature library of common targets under ice.Based on UAV radar technology,we detected the ice layer of the Yellow River Shisifenzi curve,extracted the ice thickness and radar image,verified the accuracy of its ice thickness measurement,and interpreted the measured ice layer radar image.The signal processing method is used to carry out deeper signal processing on the original radar data.The main research results are as follows:(1)Anomalous structures in the ice have strong echoes,usually showing regular or irregular hyperbolic characteristics.The circular abnormal structure presents a regular hyperbola,and the rectangular anomaly structure presents a hyperbola with a relatively flat top,The ice cover with intercalated airs layers echoe shows many hyperbolas with a relatively flat top,and the hyperbolas are arranged without gaps,The ice cover with intercalated waters layers echoe shows multilayer rectangular water zone echo superposition,the fractured zone presents multiple hyperbola irregularly superimposed forms,and the fractures present hyperbola tangent to the interface echo.Strong reflection occurs at the water-bearing abnormal structure,and multiple reflected waves will appear.(2)Different shapes of reflected waves at the ice-water interface have different shapes.Horizontal and inclined interface echo as a straight line,the upper undulating interface echo is three straight lines,the bottom undulating interface echo is in the form of two horizontal lines and a hyperbola embedded in the middle,wave-shaped,large-sawtooth and small-sawtooth interface echoes are irregular fishnet-like waveforms formed by the cross superimposition of hyperbolas,the wave-shaped interface echoes have strong energy,the top of the large sawtooth echoes appear diffracted waves,and the small sawtooth echoes have weak energy,the reverse curved interface echo presents two hyperbolic curves with different positions.(3)The ice thickness is unevenly distributed in the Shisifenzi.The longitudinal ice thickness gradually decreases along the way.In 2019,the ice thickness on the concave bank side was mostly 70-80 cm,and the ice thickness on the convex bank side was mostly50-60 cm.In 2020,the ice thickness on the concave bank side was mostly 60-75 cm,and the ice thickness on the convex bank side was mostly 50-60 cm.Ice thickness of lead section presented a small-large-small trend.The ice thickness measurement error of UAV radar during the stable sealing period was mostly below 5% in 2019 and below 10% in2020.During the opening period of the river,the ice thickness was about 13 cm,the average ice thickness on the concave bank was 14.29 cm,and the average ice thickness on the convex bank was 11.39 cm.(4)The measured radar images can be interpreted with referring to forward simulation image.There are many abnormal structures such as water-bearing zone,fracture zone and broken zone under the ice layer on the concave bank of the bend,and the ice layer of the convex bank is relatively uniform.The radar images of the ice during the river opening period can be basically divided into four types: flat ice layer,complex ice layer,lead and complete ablation,deep signal processing can present a multi-angle radar images.(5)The propagation speed of electromagnetic waves in the ice layer will be affected by the dielectric properties of the ice layer,the structure of the ice layer and the flatness of the ice interface.The propagation velocity in the Yellow River ice layer is between15cm/ns-17cm/ns.The electric constant of the Yellow River ice layer mostly fluctuates around 3.2.