Electromagnetic Radiation

Electromagnetic Energy Interactions

When the energy being remotely sensed comes from the Sun, the energy:

Propagates through the vacuum of space
Interacts with the Earth's atmosphere, surface, and atmosphere (reflected, absorbed, transmitted);
Reaches the remote sensor (interacts with various optical systems, filters, emulsions, or detectors);

Electromagnetic Radiation

Transfer of energy from one body to another in the form of electromagnetic waves is referred to as Electromagnetic Radiation.

To understand how electromagnetic radiation is created, how it propagates through space, and how it interacts with other matter, it is useful to describe the processes using two different models popularly known as Electromagnetic Radiation Models:

the wave model;
the particle model

Wave Model of EM Energy

An electromagnetic wave is composed of electric and magnetic vectors that are orthogonal to one another and travel from the source at the speed of light.

Properties of EMR

Frequency: the number of wavelengths that pass a point per unit time. (unit = hertz)

Wavelength: the mean distance between maximums (or minimums) (unit = m)

Common units: micrometers (µm) or nanometers (nm)

One cycle per second is termed one hertz (1 Hz)

Frequency is inversely proportional to wavelength. hence, the longer the wavelength, the lower the frequency, and vice-versa.

Relationship of Wavelength and Frequency

Electromagnetic Wavelengths and their corresponding measurement units

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Basic of Remote Sensing III

Contents Advantages Limitations Applications Advantages of Remote Sensing : Provides a synoptic view over a large region; Offers Geo-referenced information and digital information; Most of the remote sensors operate in every season, every day, every time and even in tough weather; Limitations : Can be expensive; Can be technically difficult; Not direct; Measure surrogate variables e.g. reflectance (%), brightness temperature, backscatter; Applications of Remote Sensing Urban & Regional Planning Scope: Mapping & updation of city/town maps Urban sprawl monitoring Town planning Facility management GIS database development Benefits: Better decision support, planning & management Rapid information updation Infrastructure development monitoring Spatial information analysis Agriculture Scope: Crop acreage estimation Crop modeling for yield & production forecast / estimation Crop & Orchard monitoring Soil sensing Mapping

Basic of Remote Sensing IV

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Resolution

Resolution: sensor characteristic that affect what can be seen in an image Source: NASA Spatial resolution Spectral characteristics Temporal characteristics Sensor sensitivity SPATIAL RESOLUTION Spatial resolution refers to the amount of detail that can be detected by a sensor. It is the smallest unit measured; Images where only large features are visible are said to have coarse or low resolution. In fine or high-resolution images, small objects can be detected. Detailed mapping of land-use practices requires a much greater spatial resolution. Size of an image pixel in ground dimensions. Usually represented by the length of one side of a square (i.e., 30m resolution). The spatial resolution of passive sensors depends primarily on their Instantaneous Field of View (IFOV). The IFOV is the angular cone of visibility of the sensor (A) and determines the area on the Earth’s surface which is “seen” from a given altitude at one particular momen

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