Estimation of the variation in target strength of objects in the air

Target strength is one of the key values for sonar systems. The parameter is very useful in activities related to detection and estimation of marine organisms, object identification and sonar calibration. The essential difference between detection and ranging performed in water and air results from characteristics of those media. A common feature for both water and air is the fact that only longitudinal wave propagates in them. Ultrasonic wave propagation velocity in air changes when the medium's physical conditions alter (e.g. temperature, humidity, pressure, presence of other gases or pollution and gas medium heterogeneity). In water environment not all solid state objects can be assumed to be rigid and motionless-this approximation works better in case of air. This aspect is especially vital when analyzing waves penetrating objects reflecting ultrasonic wave. This paper presents calculation and measurement results of target strength of objects, shaped as spheres and cylinders of infinite and finite length, placed in air medium. The difference between the calculated and measured target strength was analyzed and escalation of difference in case of heterogeneous objects was pointed out.