Yes, by measuring the reflected sound waves, you can gather information about the situation you described. This technique is commonly used in applications such as ultrasound imaging, sonar systems, and acoustic sensing.
When you emit sound waves from a transducer and they encounter a surface, part of the energy is reflected back towards the transducer. By analyzing the characteristics of the reflected sound waves, such as their amplitude, phase, and time of flight, you can gain insights into the objects or structures present in the environment.
In the case you described, where the transducer is held 10 cm above the ground or concrete and there is a gap or another wall behind it, the reflected sound waves can provide information about the properties of the ground, the presence of the gap, and the characteristics of the wall.
The frequency range used for such measurements depends on the specific application and the transducer used. Ultrasound imaging, for example, typically operates in the range of a few kilohertz to several tens of megahertz. Lower frequencies can penetrate deeper into materials but may have reduced spatial resolution, while higher frequencies provide better resolution but have more limited penetration.
For concrete or solid surfaces, higher frequencies in the ultrasound range (e.g., 1-10 MHz) are commonly used. These frequencies allow for better resolution and can provide detailed information about surface features, cracks, or structural variations. However, the exact frequency range depends on the specific requirements of the application and the properties of the materials being examined.
It's important to note that the choice of frequency range and the interpretation of the reflected sound waves require careful consideration and analysis to ensure accurate results.