Canadian Forest Service Publications

Pauli Phase Calibration in Compact Polarimetry. 2018. Cloude, S.R., Goodenough, D.G., Chen, H., Rao. Y.S., Hong, W. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Volume: 11, Issue: 12, pp. 4906-4917.

Year: 2018

Issued by: Pacific Forestry Centre

Catalog ID: 39474

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1109/JSTARS.2018.2878454

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In this paper, we consider the problem of true transmitter polarization state estimation for circular compact SAR modes. We employ two methods—the first using point targets such as trihedral reflectors, and the second, a new method, based on the Pauli phase observed over distributed targets like forest canopy. We first show how compact modes allow estimation of the Pauli phase for reflection symmetric scatterers. We show that this phase remains remarkably constant over forest canopies, depending primarily on the dielectric constant of constituent volume particles. We show that small imperfections in the transmit polarization state then lead to large errors in this phase estimate. These errors can then be used as the basis for a calibration strategy that allows estimation of a set of candidate true transmitter states. These can then be compared with the trihedral estimates for validation. We illustrate using L-band compact data from the JAXA ALOS-2 satellite and C-band data from the ISRO RISAT-1 satellite.

Plain Language Summary

The new Canadian Radar Constellation Mission (RCM) has a new radar imaging mode, the circular compact mode that comprises a single transmit polarization (circular) and simultaneous coherent orthogonal linear receive. In reality, system imperfections mean that the true transmitter state will be elliptical i.e. non-circular. Thus, new methods for calibrating and mitigating errors from such imperfect sensors are required. This is a key motivation for us to investigate the true transmitter polarization state for the circular compact mode from the current ALOS-2 satellite and the past RISAT-1 satellite. In this paper, we report on two techniques for estimating the true transmitter state from these compact radar systems. The first is to use point targets, such as trihedral corner reflectors, and the second is a new method based on a parameter, called the “Pauli” phase, observed over distributed targets like forest canopy. We show that small imperfections in the circular transmit polarization state can lead to large errors in the Pauli phase estimate. We also demonstrated two methods for mitigating these errors. The findings in this paper will support future RCM application scenarios for the CFC.