Now that we’ve told a bit of the history of remote sensing, you can already get an idea of what Remote Sensing is. But what is your definition?
Although it can be defined as obtaining information without making contact with the object under study, Remote Sensing is usually limited to the earth’s surface and its atmosphere.
Obtaining this information is performed using electromagnetic radiation and being above the study area.
Emitted by any body with a temperature above absolute zero (0 K), electromagnetic radiation can be classified as a function of its wavelength, giving rise to the electromagnetic spectrum (UFRGS).
And what information is this? Why get them?
Imagine if you needed to collect data from a region the size of a continent? How would you go about getting this data in less than 30 minutes? This is precisely the scope of data collection from the meteorological satellite METEOSAT.
Also, imagine if this area contains any areas or countries that are difficult to access? In this sense, remote sensing ends up being a great ally to this type of research.
Among the data that can be obtained by remote sensing, we have some such as:
• Atmosphere Temperature;
• Precipitation;
• Distribution and Types of Clouds;
• Concentration of Gases (eg Water Vapor; CO2; Ozone);
• Topography;
• Soil Temperature;
• Type of Vegetation;
• Use of the soil.
The list of parameters is large and spans disciplines such as agriculture, archaeology, civil engineering, climatology, natural disaster and pollution monitoring, soil characterization, oceanography, glaciology and water resource mapping.
All this information becomes a digital image, facilitating its handling on computers and increasing the role of the “Digital Image Processing” field, which is part of Remote Sensing.
The raw images from the sensors go through several steps before being made available, usually calibrations are carried out in relation to the earth’s surface, removing the effects of propagation from the atmosphere and noise (REES, 2013).
These images are represented by numbers, where higher numbers mean a greater emission of that type of radiation. In this sense, we can divide remote sensing into two types of systems, depending on how electromagnetic radiation is emitted.
We have passive systems, which detect emissions of natural origin and which can originate from the Sun (Ultraviolet, visible light, and near-infrared) or from the object itself (thermal radiation).
And we have the active systems, which emit radiation and analyze what was sent back. In general, any type of electromagnetic radiation can be used, but in practice, it depends on the response of the Earth’s atmosphere to the wavelength range.
Reference: REES. W.G. Physical Principles of Remote Sensing. 3 ed. University of Cambridge, 2013. 492 pg.
