عنوان مقاله [English]
نویسنده [English]چکیده [English]
A radar altimeter installed on the front of a satellite sends electronic pulses to the Earth, and then receives reflections from the ground surface that pass around the satellite. The propagation speed of these waves in space is equal to the speed of light. The satellite radar measures the elapsed time between sending a pulse and receiving its reflection. This time is equivalent to the time it takes for a pulse to cover the distance between the satellite and the earth twice. Therefore, satellite distance from the ground can be measured with great accuracy through measured time. Free electrons (free ions) in the ionospheric layer and suspended particles of water vapor contained in the troposphere layer of the earth reduce the velocity of propagation of waves when passing through these two layers.
Therefore, this slowdown must always be considered in order to prevent large errors in calculating the satellite's height from the ground. After correcting these errors and considering that the position of the radar altimeter system is independently known, the orbit of radar altimeter is determined. Consequently, satellite elevation measurements can be used to achieve accurate topography of the ground. On the other hand, on the oceans the separation of topographic surface from the equipotential surface of the Earth's gravity (geoid) is created by balancing forces generated by the Earth's rotation and ocean currents. Oceanic flows, which contribute greatly to the exchange of heat between the tropical and Polar Regions are ultimately accessible through
satellite elevation measurements. Therefore, an altimeter is a unique tool for studying the role of the oceans in the Earth's climate system, as well as in understanding global climate change.