Rafi Uddin Labib
Mahima Haque
S.M Mehady Hasan
S.M. Mohaimenul Islam
Nafisa Ibnat Tasfee
Md. Farhan Masud
Team Name: Aspired dreamers
Challenge Selected: Synthetic Aperture radar (SAR)
What is Synthetic Aperture Radar?
Synthetic Aperture Radar, or SAR. SAR is a type of active data collection where a sensor produces its own energy and then records the amount of that energy reflected back after interacting with the Earth. SAR gives various information about characteristics such as biomass, moisture condition and structural features. They collect data through a mechanism called polarisation.
Why SAR has brought a huge change to mankind?
From a satellite in space operating at a wavelength of about 5 cm (C-band radar), in order to get a spatial resolution of 10m, a radar antenna about 4,250 m long is needed.
An antenna of that size is not practical for a satellite sensor in space. Hence, a synthetic aperture is used. In this concept, a sequence of acquisitions from a shorter antenna are combined to simulate a much larger antenna, thus providing higher resolution data.
The Role of Frequency and Wavelength
The different wavelengths of SAR are often referred to as bands, with letter designations such as X, C, L, and P. The table below notes the band with associated frequency, wavelength, and the application typical for that band.
Polarization and Scattering Mechanisms
Polarization refers to the orientation of the plane in which the transmitted electromagnetic wave oscillates. The horizontal polarization is indicated by the letter H, and the vertical polarization is indicated by V.
The advantage of radar sensors is that signal polarization can be precisely controlled on both transmit and receive. Signals emitted in vertical (V) and received in horizontal (H) polarization would be indicated by a VH. Alternatively, a signal that was emitted in horizontal (H) and received in horizontal (H) would be indicated by HH, and so on. Examining the signal strength from these different polarizations carries information about the structure of the imaged surface, based on the following types of scattering: rough surface, volume, and double bounce.
Rough surface scattering, such as that caused by bare soil or water, is most sensitive to VV scattering. Volume scattering, for example, caused by the leaves and branches in a forest canopy, is most sensitive to cross-polarized data like VH or HV. VH is good for forest detection. The last type of scattering, double bounce, is caused by buildings, tree trunks, or inundated vegetation and is most sensitive to an HH polarized signal
Interferometry (InSAR)
SAR data can also enable an analysis method called interferometry, or InSAR. InSAR uses the phase information recorded by the sensor to measure the distance from the sensor to the target. These measurements are very and can be used to identify areas of deformation from events like volcanic eruptions and earthquakes.
NiSAR (NASA-ISRO SAR)
NiSAR provides a means of clarifying spatially and temporally complex phenomenon. Ranging from ecosystem disturbance to ice sheet collapse and natural hazards including earthquakes, volcanoes, tsunamis and landslides.