What is the meaning and definition of remote sensing

What is the meaning and definition of remote sensing? And how image acquisition using remote sensing? Remote sensing is defined as gaining information about anything of object or phenomenon that occurred on Earth. The sense means the information is acquired without having physical contact or touches them although located in long distance. As simple example, our eyes sense a tree through observation without touch it and we get to know its features and how its look like.
In remote sensing, how the sensors collect the data on Earth? The sensors gain the data by spotting the energy that was sent back by the Earth which then being processed, analysed and applied the data in real life. The sensors are mostly on the satellites where vast object or phenomenon can be trace as they are located above the Earth. While the energy that reflected and emitted (thermal infrared) means the electromagnetic waves energy. The sensor needs input of electromagnetic wave to create an image out of it. The wave was then divided into several bands which consist of electromagnetic waves at different wavelength. Each wave has its own strength and uses to ease human being.
The sensors can be divided into passive and active. Passive sensors mean the remote sensors detect the natural reflected energy for example the radiation from the sun or emission from the Earth’s surface. While active sensor means it detects the energy that being emitted by the remote sensors itself which is reflected by the Earth’s surfaces back to the sensors. Figure 1 in appendix shown about active and passive sensors.
For the satellites, there are two types of satellite orbits. The types are geostationary orbits and polar orbit. Figure 2 in appendix shown about the types of satellite orbit. The orbit is referring to the paths that taken by satellites to revolve around the Earth for getting the data. Geostationary orbits are when the satellites revolve the Earth parallel to the equator and follow the Earth’s rotation with the same direction. The result for this orbit is the satellites capture the same spot surface of the Earth as it was stationary to the Earth surface for all the time. Among the features of this orbit is it located at the high latitude approximately 36,000 km away from the Earth. The reason why it located in long distance is because the satellites need complete the orbiting of Earth in 24 hours exactly which same time taken by Earth to successfully revolves around its axis. As this orbit at high latitude, it may cover large area of Earth’ surface. Usually geostationary orbit is used by the meteorological satellites for forecasting the weather.
Another satellite orbit is polar orbit or also called sun synchronous orbit. It name was because of the satellites monitored the section that always radiated by the sun constantly. This orbit was used by many satellites in remote sensing. Polar orbit moves according to the name from polar to polar. So it travels northwards and southwards. Through this type of orbit, the sensor of satellite can discover new area as it revolving around the Earth from polar to polar while the Earth rotates in its axis. Polar orbit differ to geostationary orbit when the polar orbit located less in distance compared to geostationary orbit. Polar orbit located approximately 300km to 1.400 km in latitudes above the Earth.