Physical Basis of Remote Sensing: Sources of Energy
Remote Sensing: Sources of Energy
Remote sensing relies on the detection and measurement of electromagnetic radiation emitted or reflected by objects on Earth's surface or in its atmosphere. This radiation, often referred to simply as "energy," is emitted by the sun and subsequently interacts with the Earth's surface and atmosphere. The primary sources of energy involved in remote sensing are:
SOLAR ENERGY: The sun is the primary source of energy for remote sensing. It emits electromagnetic radiation across a wide range of wavelengths, from gamma rays to radio waves. However, only a small portion of this radiation, known as the solar spectrum, is relevant for remote sensing applications. The solar spectrum includes ultraviolet (UV), visible, and near-infrared (NIR) wavelengths, which are essential for many remote sensing techniques.
REFLECTED SOLAR ENERGY: When sunlight strikes an object, some of the energy is absorbed, and the rest is reflected. The composition and properties of the object determine which wavelengths are absorbed and which are reflected. By measuring the reflected solar energy across different wavelengths, remote sensing instruments can gather information about the properties of the object, such as its composition, moisture content, and health.
THERMAL ENERGY: In addition to reflecting solar energy, objects also emit their own radiation, known as thermal or infrared radiation. This radiation is a result of the object's temperature. Everything above absolute zero (-273.15°C or 0 Kelvin) emits thermal radiation. Remote sensing instruments that detect thermal energy, such as thermal infrared sensors, can provide valuable information about the temperature and thermal properties of objects on the Earth's surface.
ARTIFICIAL SOURCES: In some cases, remote sensing relies on energy sources other than the sun. For example, active remote sensing techniques, such as radar and lidar, use their own energy sources to illuminate objects and measure the properties of the reflected or scattered energy. Radar systems emit microwaves, while lidar systems emit laser pulses. By analyzing the properties of the reflected or scattered energy, these techniques can provide detailed information about the shape, surface roughness, and other characteristics of objects on Earth's surface.