|Title||Assessment of PALSAR-2 compact non-circularity using Amazonian rainforests|
|Author||Touzi, R; Shimada, M; Motohka, T; Nedelcu, S|
|Source||IEEE Transactions on Geoscience and Remote Sensing (Institute of Electrical and Electronics Engineers) vol. 58, no. 10, 2020 p. 7472-7482, https://doi.org/10.1109/TGRS.2020.2983008|
|Alt Series||Natural Resources Canada, Contribution Series 20200479|
|Media||paper; on-line; digital|
|File format||pdf; html|
|Subjects||geophysics; Science and Technology; remote sensing; satellite imagery; radar methods; models; synthetic aperture radar surveys (SAR); Methodology|
|Illustrations||tables; satellite images; plots; photographs|
|Released||2020 04 14|
|Abstract||Compact-hybrid SAR (CP) is a dual-polarization (dual-pol) SAR mode that transmits a circular polarization (CirP) and measures the received signal at the horizontal and vertical antenna polarization. It
is now admitted that the actual SAR technology does not permit the generation of a perfectly CirP and this may significantly affect CP radiometric and phase information. Since all the existing CP calibration models assume a perfectly transmitted
CirP, there is an immediate need for the development of a new model that permits efficient assessment and calibration of CP non-circularity. In this article, a new general polarimetric hybrid SAR model (PolHyb) is introduced for both dual- (CP) and
quad-polarization hybrid SAR modes. PolHyb explicitly includes the transmitted polarization non-circularity, in addition to conventional radar transmit and receive distortion matrices, channel imbalances and Faraday rotation contamination. The
non-circularity of transmitted polarization is expressed in terms of the axial ratio (AR), which used to be popular in the 1960s for characterization of circularly polarized (transmit and receive) dual- and quad-polarization radar. The new CP model
derived from PolHyb is adapted to PALSAR2-CP and used as the basis of an efficient method for an assessment of CP non-circularity using Amazonian rainforests. PALSAR2-CP data collected at four different beams (H2-6 to H2-9), with incidence angle
varying between 30° and 45°, allows for the first ever demonstration of non-circularity of PALSAR2 CP transmitted polarization. Although it is lower than 0.5 dB for H2-6 and H2-7, the AR of PALSAR2-CP transmitted polarization increases significantly
with incidence angle to reach up to 1 dB at Beam H2-8, and 2.3 dB at the highest incidence angles of Beam H2-9. |
|Summary||(Plain Language Summary, not published)|
The researchers in this article discuss a type of radar system known as Compact-hybrid SAR (CP), which is used for various applications like monitoring
forests and landscapes. CP relies on circular polarization to transmit and receive signals, but in practice, it's tough to create a perfect circular polarization.
The problem is that current calibration models for CP assume perfect circular
polarization, which isn't the case in reality. This discrepancy can affect the accuracy of data collected by CP radar.
To address this issue, the researchers introduced a new model called PolHyb, which accounts for the imperfections in circular
polarization, as well as other distortions and interference that can happen during signal transmission and reception. They applied this model to data collected over the Amazon rainforests using the PALSAR2-CP radar system.
Their findings revealed
that the circular polarization in the PALSAR2-CP radar wasn't perfectly circular, especially at higher incidence angles. This means that when using this radar for tasks like monitoring forests, it's important to consider and correct for these
imperfections in polarization to get more accurate results.
In summary, this research improves our understanding of radar technology and can lead to more precise data for applications like environmental monitoring.