Digital Correlation Processing Research Articles

Multi-pulse laser ranging method for pre-detection with high frequency resonance

Based on the measurement principle of pulse time-of-flight, non-cooperative target ranging technology using a pulsed laser diode (LD) as a light source has received widespread attention in recent years. Using leading edge timing method to directly detect pulses, its measuring range is about a few tens of meters and only a cm-level single-shot accuracy could be reached due to the limitations of its pulse width and eye-safe laser power of the LD, which cannot meet the needs of most applications. Especially, in order to increase its receiver channel bandwidth from hundreds of MHz to even a few GHz to reduce its work error, its distance measurement accuracy and ranging distance are significantly degraded as its signal-to-noise ratio (SNR) decreases. When a target is out of its measuring range, the back diffused laser pulse signal with an SNR of much less than 1 will be too weak to be extracted even with digital correlation processing technology.In this paper, using a pre-detection with high frequency resonance and multi-pulse correlation processing, a new ranging method to solve long ranging targets with high precision is proposed for the first time. Through the pre-detection circuit with high frequency resonance, a pulsed photocurrent signal is amplified and filtered, and then converted into a bipolar attenuation oscillation signal. Thereafter, its SNR is further improved by a new pulse function constructed through multi-pulse correlation processing. The peak of the new pulse is constant and its zero crossing point is found to be the timing point to calculate the target distance. The method has a better SNR and a high timing accuracy. And the detected ranging distance could be increased over one thousand meters or more. Theoretical calculation results show that the minimum detectable peak current of light pulse is around 17 nA in the method. Comparing with the direct pulse detection method, its SNR can increase 60 times. When a received peak of a photocurrent pulse is within a dynamic range of 1:10000, its work error is less than 0.1 ps. A pulsed laser rangefinder is developed based on the principle. And its average laser emission power is about 1 mW. Its measurement ranging without cooperative target is greater than 2000 m. Its distance measurement accuracy increases up to ± (3 mm+2 ppm) in a range of 1.5-300 m. For a long ranging target, its distance measurement accuracy is ± (10 mm+10 ppm). The rangefinder system is used in a total station product and can be used to measure large-scale engineering structures (such as roads, bridges, dams, tunnels, subways, etc.), building structures and industrial sites.

Determination of the Moduli of Elasticity of Materials by the Method of Digital Image Correlation

On the basis of the results of digital correlation processing of images, we develop a method of noncontact determination of the strain distributions on the surfaces of beam specimens and the moduli of elasticity of the specimens made of duralumin and glass-fiber plastic and loaded by bending moments. We describe the procedure of measurements and the algorithm used for data processing.

Properties of orthogonal signals with direct spectrum spreading based on perfect binary matrices and the algorithm of their correlation processing

A fast algorithm has been developed for digital correlation processing (correlation reception) of orthogonal signals formed on the basis of perfect binary matrices (PBM) using a modified circuit of cyclic shift modulation—Cyclic Code Shift Keying (CCSK). In addition, the ensemble cross-correlation properties of orthogonal signals based on PBM were studied.

Damage and fracture prediction of plastic-bonded explosive by digital image correlation processing

By digital correlation processing of Scanning electronic microscopy (SEM) images, the paper presents the deformation and damage analysis of an energetic material—the plastic-bonded explosive (PBX) on mesoscopic scale. The analysis is made by observing the deformation field resulted from the digital image correlation (DIC) processing of the images corresponding to the loading steps and comparing with the surface profiles of the composite material so as to visualize the matter damage near a preset crack. The results show that the local deformation disturbance can reveal the material damage even happened underneath the specimen surface. The strain distribution in the front of the preset crack, can be used to predict the propagating route of the microcrack initiated from the tip of the pre-crack, which is related to the splitting fracture of the granular-based composite under compressive loading.

Even‐length real‐valued cyclically orthogonal pseudonoise sequences with small absolute value

AbstractThis paper discusses the even‐length real‐valued cyclically orthogonal pseudonoise (PN) sequences with small absolute values as the PN sequence for spread spectrum communication.First, the sequence of maximum absolute value 2 with cubic or inverse phase parameters is considered. By replacing the sequence variable by the power of the primitive root and by regarding the power as the sequence variable, an orthogonal PN sequence is obtained. There exists the same number of such sequences as the number of primitive roots, and the cross‐correlation function is relatively small if the period is large.By convolving a sequence with itself, a set of sequences is obtained which has relatively small absolute value of the sequence and relatively small absolute value of cross correlation. It is proposed also to convolve a sequence with other sets of sequences. The sequence considered in this paper is suited to the digital correlation processing using the fast‐Fourier transform when the period is 4, 16, 256, 65, 536, ….

Experimental verification of real‐valued orthogonal PN sequence applied to pulse compression sonar

AbstractIn the pulse compression sonar, the code with a sharp autocorrelation function is used as in spread spectrum communication, and they share many common technologies. In this paper, the real‐valued orthogonal pseudo‐noise (PN) sequence that can be used in both over a broad frequency range including dc is applied to the pulse compression sonar. By adapting digital correlation processing, a high performance close to the theory has been obtained. The codes are generated from a binary orthogonal PN sequence with a length of 127 and a multivalue orthogonal PN sequence with a length of 256 and are sent into an acoustic transmission path at a frequency of about 40 kHz. The correlation operation of the received code and the transmitted code is carried out on a personal computer. The multiple echo is detected at a low noise while the Gaussian noise and the locked sinusoidal wave can be suppressed with a processing gain close to the one predicted by the theory.