How to measure acceleration and flying altitude on a remote-controlled aircraft, and what is the principle?

Flight speed is measured by pitot tube. The principle is to measure the speed of the aircraft relative to the air by measuring the dynamic pressure between the aircraft and the air, that is, airspeed. There are two methods of height measurement. The total static pressure system in the atmospheric data system is used to measure the height. The principle is no different from ordinary altimeter. Altitude is inversely proportional to air pressure, but this system measures the altitude of the aircraft relative to the international standard sea level. Another system is a radio altimeter, which is used to measure the actual height between the plane and the ground. The principle is that electromagnetic waves are emitted from the plane to the ground, and will be received by the receiver on the plane after being reflected by the ground. Theoretically, the time of transmitting and receiving reflected waves can be measured, and the height can be calculated by adding the propagation speed of electromagnetic waves. However, because the radio altimeter is usually used at low altitude, this time is too short to measure, so it is basically impossible to measure the time directly. Instead, the time is calculated by measuring the frequency difference between the reflected wave and the transmitted wave. Because the plane is moving, there will be Doppler frequency shift between reflected wave and transmitted wave, and the frequency is relatively easy to measure.