Research Of ISAR Imaging And Cross-Range Scaling For Space Non-cooperative Spinning Targets

In recent years,with the continuous advancement of human space exploration,more and more space debris and abandoned man-made spacecraft have gathered in space,resulting in the number of available space orbits decrease at the fast rate,which has caused serious damage to the normally working spacecraft.Therefore,the accurate numbering and identification of space debris and abandoned spacecraft is of great significance for the rational development of space resources.Inverse synthetic aperture radar(ISAR)is an important high-resolution imaging radar.It has the ability to detect and obtain the shape of space non-cooperative targets at all times,all days,and long distances.It has widely practical value in many fields such as military and civilian.However,the detection of non-cooperative targets such as space debris and abandoned spacecraft generally has problems such as long distances,target complex motions,and unknown spinning parameters,which has caused the failure of traditional ISAR imaging methods.Therefore,in order to accurately obtain the position and shape information of the target and accurately number and identify the target,novel ISAR imaging of non-cooperative spinning targets in space need to study.This paper focuses on the above problems.The main research contents and innovations are as follows:(1)For existing imaging methods of the space non-cooperative spinning targets have problems such as low resolution and the failure of the multi-scattering point.This paper proposes a high-resolution ISAR imaging method for space non-cooperative spinning targets based on Synchrosqueezing transform(SST).First,this method analyzes the frequency modulation characteristics of a single range unit echo and uses SST for time-frequency analysis to convert the signal into the time-frequency domain,and then perform curve integration to obtain a high-resolution ISAR image;Compared with the existing method,the proposed method introduces a new efficient time-frequency analysis method with high time-frequency resolution and no cross terms interference,a well-focused ISAR image can be obtain.Experimental results verify the effectiveness of the proposed method.(2)For existing ISAR three-dimensional imaging methods of space non-cooperative spinning targets require multi-dimensional search and interpolation operations,which results in high computation complexity and difficult to realize real-time imaging.This paper proposes an efficient ISAR three-dimensional imaging method for space non-cooperative spinning targets.First,this method analyzes the signal form of the echo data.By mining the intrinsic characteristics of the signal,the echoes of the same scattering point are moved to the same range unit.After the transformation is completed,the signal is a multi-component sinusoidal frequency modulation(SFM)signal at the same range unit,and then use the matched filtering method to obtain two-dimensional ISAR images of different height planes.Finally,three-dimensional images of space non-cooperative spinning targets will be reconstructed.Compared with the existing methods,the proposed method requires only one matching filtering process at different height planes,avoiding interpolation and multi-dimensional search operations,which greatly reduces the computational complexity.Experimental results verify the effectiveness of the proposed method.(3)The ISAR images obtained based on Range-Doppler(RD)algorithms,etc.,cannot accurately reflect the true size of the target,which makes it difficult for subsequent target recognition.This paper proposes an efficient ISAR image cross range scaling method based on two-dimensional wavelet transform(2D-WT)and pseudo-polar fast Fourier transform(PPFFT).First,using the 2D-WT to decompose two adjacent ISAR images to obtain reconstructed low-frequency sub-images,and then,the polar Fourier transform was used to convert the rotational motion of the two ISAR images into a translational motion along the polar axis,and the PPFFT was introduced to reduce the computational complexity further;finally,it defines a new one-dimensional(1D)integral correlation cost function and combined with the dichotomy method to obtain the target's rotation angle velocity(RAV),accomplish the cross range scaling of ISAR images.Compared with the existing methods,the proposed method uses 2D-WT to obtain the sub-images,which reduces the image dimensions.The PPFFT does not require any interpolation operation,it has high accuracy and low calculation load.Therefore,the proposed method is ability to achieve ISAR image cross range scaling quickly,the simulation and real data verify the effectiveness of the proposed method.