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TERMS: Remote Sensing

Data collection and measurements near the object is not alway possible. For this certain sensors should be applied for this process.

The science and art of obtaining the data of different features or phenomenon in certain area or time, not being able to collect from close contact, and also their analysis is called remote sensing. Our eyes are the best example of such remote sensors. However, field measurements may be required for the correct accuracy. 

How is remote sensing done?

A. Source: illuminates the target; sun is the prime example of the source - the source can be artifical

B. Target: object which is/are illuminated

C. Platform or Sensor: collects the reflectance

D: Receiving (GRS - Ground Receivng Station)

E: Preprocessing: Data freed from errors

F. Distribution: received by users

Atmosphere can interact with the target while with the source or while reaching before the sensor. The part of energy is scattered. Sensors are developed as to choose certain spectral regions where EMR is passed through withou much decrement.

Mainly remote sensing can be clasiified to:

ACTIVE RS:source in the platform; backscattering is collected

PASSIVE RS: any source in the platform is not used

Electromagnetic Radiation: 

Form of energy traveling in the space in the speed of light, visible rays are the parts of it.

The relation between frequnecy and wavelenght is reversely proportional.

Spectral Signautres: 

The variation of different reflectance of different illuminated target. 

Types of Scattering:

Mie: atmospheric molecules similar or larger wavelengths of target, 

Rayleigh: atmospheric molecules too small compared to the wavelength,

Non-selective: size of particles bigger than wavelength of the light,

Scattering leads to haziness of the received signal. 

Resolution: Smallest discrete separable unit that the sytem can detect

Spectral Resolution: Ability to intrepret different ranges Electromagnetic Spectrum

Spatial Resolution: Smallest unit of the distance that can be identified

Temporal Resolution: Times it takes the sensor to arrive at the same point again.

Radiometric Resolution: Information stored in a pixel, ability to differentiate levels of radiance

Orbits Types:

Equatorial: rotates around equator

Prograde: inclined rotation, sliglthly lifted from right side from the equatorial rotation

Polar: roatates around poles

Retrograde: inclined, slightly lifted from the left side from the equatorial rotation

Geostationary: above 36000 km above the equator, orbital inclination is 0,

Sun sycnchronous (Near Polar): satellite crosses the equator at the same time each day,

Swath and Swath Area:

Path of the satellite and the are covered on the earth surface; paths may not be the same next time for satellite


Across Track:  scan direction is cross with the forward motion of the satellite, also called Whisk Broom; Landsat Series of satellites

Along Track: scan direction is along to the satellite's direction,  also called Push Broom


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