Bats can ascertain distances, directions, nature and size of the obstacles at night. This is possible by reflection of the emitted :

Bats utilize a biological sonar system known as echolocation to navigate and hunt in darkness [t1][t8]. This process involves the bat emitting high-frequency sound waves, specifically ultrasonic waves, which are defined as frequencies exceeding 20,000 Hz and are inaudible to humans [t2][t9]. These ultrasonic waves have short wavelengths, allowing them to reflect strongly off small objects and obstacles [t2][t5]. When these emitted waves strike an object, they are reflected back as echoes [t1][t3]. By processing the time delay, intensity, and directionality of these returning echoes, bats can accurately ascertain the distance, direction, size, and nature of obstacles or prey [t6][t7]. Therefore, the ability is based on the reflection of ultrasonic waves originally emitted by the bat itself, rather than waves originating from distant objects or supersonic waves (which refers to speeds exceeding the speed of sound).

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC2664374/
2. [2] https://en.wikipedia.org/wiki/Animal_echolocation
3. [3] )00686-X
4. [4] https://www.sciencedirect.com/science/article/abs/pii/0010027789900097