Atmosphere effects on sonar sensor model for UAS applications

The use of Unmanned Aerial System (UAS) applications is growing in both civilian and military fields. Fully autonomous UAS applications are useful to a variety of disciplines; for example, they can provide structural damage inspections in critical or dangerous areas (e.g. the L'Aquila earthquake in Italy, or Hurricane Ike in Galveston, Texas, USA). However, in some conditions, such as urban or low altitude operations, the Global Navigation Satellite System (GNSS) receiver antenna is prone to losing the line-of-sight from the satellite, making GNSS unable to deliver high quality positon information. This is quite dangerous for closed-loop control systems during the landing phase. In these cases, an ultrasonic sensor may be very useful for altitude control during the vehicle landing.