Continuous Transmission Frequency Modulation Detection under Variable Sonar-Target Speed Conditions

Yang Wang,Jun Yang

doi:10.3390/s130303549

Abstract

As a ranging sensor, a continuous transmission frequency modulation (CTFM) sonar with its ability for range finding and range profile formation works effectively under stationary conditions. When a relative velocity exists between the target and the sonar, the echo signal is Doppler-shifted. This situation causes the output of the sensor to deviate from the actual target range, thus limiting its applications to stationary conditions only. This work presents an approach for correcting such a deviation. By analyzing the Doppler effect during the propagation process, the sensor output can be corrected by a Doppler factor. To obtain this factor, a conventional CTFM system is slightly modified by adding a single tone signal with a frequency that locates out-of-sweep range of the transmitted signal. The Doppler factor can be extracted from the echo. Both verification experiments and performance tests are carried out. Results indicate the validity of the proposed approach. Moreover, ranging precision under different processing setups is discussed. For adjacent multiple targets, the discrimination ability is influenced by displacement and velocity. A discrimination boundary is provided through an analysis.

Highlights

Ultrasonic ranging sensors have been widely used in collision avoidance [1], navigation [2,3], mapping [4,5], target classification [6,11], and in travel aid devices for visually impaired individuals [7,8]
With its advantages of high precision, broadband, high signal-to-noise ratio, and high quantity of information, the continuous transmission frequency modulation (CTFM) sonar is capable of detecting multiple targets, classifying primitive indoor targets [11], and even recognizing complex targets such as rough surfaces [12], leafy plants [13], and human faces [14]
Doppler shift information obtained from the echo signal itself is the best match for the propagation procedure

Summary

Introduction

Ultrasonic ranging sensors have been widely used in collision avoidance [1], navigation [2,3], mapping [4,5], target classification [6,11], and in travel aid devices for visually impaired individuals [7,8]. The ultrasonic ranging sensor, which is low cost, accurate in positioning, and easy to operate, is considered as a competitive choice for implementing target detection and recognition. Most of the applications of a CTFM sonar are carried out under stationary conditions. When one or both of the sonar and the target are moving, the echo signal is Doppler-shifted. The output of the system is deviated from the actual target range. This situation limits the application of a CTFM sonar to stationary platforms and motionless-target sensing

Results

Discussion

Conclusion