Notes: How is SAR responded?

 SOIL:

Greater reflectivity due to higher dielectric constant of water; presence of water in soil means the easy detection from the longer wavelength.

VEGETATION:

Vegetation will have volume scattering. Similar the scattering from the soil may result in further scattering; thus wavelength of 2 to 6 cm is better as volume scattering is more and the scattering from the surface is reduced. Longer wavelengths of 10 to 30 cm can be suitable for trees. HH or VV (like polarized are able to penetrate more in vegetation compared to HV or VH (cross-polarized waves). If the crops are aligned in azimuthal direction, more energy is received compared to range direction. 

MOUNTAINS:

The SAR while observes, all the mountains seems to be located at the same distance or the same point from the spacecraft; this is called foreshortening or layover. It happens because all the backscattered signals return to the spacecraft at the same time. 

WATER / ICE:

Smooth water has no results to the antenna. 

For sea ice, the age, roughness, geometry, and other factor may play the role in its detection.


~Regions of calm water and other smooth surfaces appears black as all the incident radar are reflected.

~Surface roughness (rough surface) appears more bright when wet. Surface variations (near the size of the radar's wavelength) can cause strong backscattering.

~Waves in the water surface close to the size of the incident's wavelength can cause backscatter.

~Hills or mountains appear bright on the side that faces the sensor and dim on the other side. Human made structures appear bright acting as corner reflectors. They may appear as a bright cross if the response is strong. 


IN AGRICULTURE:

the use is for 

~soil moisture detection and monitoring: developing soil moisture maps, monitor the effectivity of the irrigation system, flood probability, 

~crop studies and acreage determination: for knowing crop health, plant stress, and timely suggestions in fertilizer application 

~damage mapping from pests or abiotic factors

use of multi-temporal techniques for different dates



Source: esa ASAR Product Handbook

(as part of  learning)




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