From energy to data to information
Remote sensing involves several steps starting from a source supplying the energy to generation of a final thematic map for a specific application as shown in the figure above. The various components/steps in remote sensing are described in further detail here:
A - Source: A source supplies electromagnetic energy (referred to as energy here) which is used for generating the remote sensing image. The most common and natural source of energy is the sun (passive remote sensing). Alternatively, a satellite can itself send a pulse of energy that can be used for generating the remote sensing image (active remote sensing).
B - Atmospheric interaction: The energy from the source passes through vacuum and then the Earth’s atmosphere before reaching the target on Earth. The electromagnetic energy in transition is referred to as electromagnetic radiation (referred to as radiation here). During this passage the radiation interacts with the Earth’s atmosphere. Part of the radiation gets absorbed, part of it gets scattered, and a part of it gets transmitted all the way to the target. After hitting the target, this radiation again passes through the Earth’s atmosphere before it reaches the satellite sensor. Therefore, the atmospheric interactions take place twice in this process.
C - Target: The radiation interacts with matter on the Earth and parts are either reflected, refracted, scattered, or absorbed and later emitted from the Earth’s surface. When radiation interacts with matter, it can be detected.
D - Sensor: The sensor is mounted on a satellite and has instruments to detect and record the radiation reflected, scattered or emitted from the target. Some sensors have additional onboard data storage devices and can temporarily store large data volumes.
E - Receiving unit: The data that is detected and recorded by the sensor has to be transmitted or downlinked to a receiving unit or a ground receiving station.
F - Processing unit: The ground receiving stations often have their own data processing facility or they function in close collaboration with other data processing facilities. The processing unit converts the analog signal received from the satellite sensor into a digital signal that can be supplied to data users. NASA owns several receiving and processing units which are also known as the NASA Data Acquisition and Archiving Centers (DAACs).
G - Information system: The remotely sensed data received from the receiving and processing units need to be further processed to extract meaningful information from the data. The processing and conversion of data to information happens through an information system. Modern day computers support powerful information systems. The human brain is still arguably one of the most powerful information systems known.
H – Information: The final step in the remote sensing process is the presentation of user specific information as thematic maps, time series animations, or other value added products.