Calibration of a Ground-Based Array Radar for Tomographic Imaging of Natural Media
Abstract
:1. Introduction
- Mutual coupling between antenna elements in the array may produce side-lobes that interfere with the scene reflectivity.
- Magnitude and phase imbalances between antenna elements are usually large enough to completely defocus a rendered scene’s reflectivity.
- The impulse response function of the rendered reflectivity image is space-variant, distorting the scene reflectivity represented by the pixel intensities.
2. Instrument Description
2.1. Observation Geometry
2.2. Radar Instrument
3. Mutual Coupling Suppression
3.1. Signal Model for a Single Channel
3.2. When Mutual Coupling Is a Problem
- The mutual coupling amplitude. A large relative to the scene reflectivity amplitude causes strong interference by mutual coupling. This is the case for BorealScat’s P to L-band observations.
- Signal bandwidth. If B is small, high side-lobes of spread out in range, increasing the interference by mutual coupling. This is the case for BorealScat’s P-band observations.
- Antenna-scene separation. The side-lobe amplitude of decreases with increasing R. A small antenna-scene separation, which is true for most ground-based experiments, increases the interference by mutual coupling.
- Unambiguous range. Due to the circular convolution in (4), the mutual coupling peak is repeated at . The side-lobes from this peak may interfere with scatterers near , such as BorealScat’s trihedral corner reflector.
3.3. Mutual Coupling Side-Lobe Suppression
3.4. Range Profiles
4. Magnitude and Phase Error Calibration
4.1. Properties of the Magnitude and Phase Errors
4.2. Calibration between Polarisation Channels Using a Trihedral Corner Reflector
4.3. Model for Single-Channel Observations of a Reference Target
4.4. Model for Multi-Channel Observations of a Reference Target
4.5. Decomposition of Co-Polarised Channel Errors
4.6. Tomographic Image Formation Validation
4.7. Signal to Clutter and Noise Ratio Requirement
5. Impulse Response Compensation
5.1. Systematic Pixel Gain
5.2. Image Intensity Model
5.3. Impulse Response Estimation
5.4. Impulse Response Compensation
5.5. Validation of Impulse Response Compensation
6. Summary of Calibration Procedure
7. Limitations of the Proposed Calibration
- There exists an unknown magnitude and phase offset between tomographic images of different polarisations. Care should, therefore, be taken when interpreting polarimetric combinations of images such as HH/VV, HH/HV and VV/HV.
- The images are not calibrated in an absolute sense. This means that the intensity and phase distributions in the images are correct, but have an unknown constant offset from the true geophysical value.
8. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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HH | VV | HV | VH | |||||
---|---|---|---|---|---|---|---|---|
Orig. | Cal. | Orig. | Cal. | Orig. | Cal. | Orig. | Cal. | |
Standard deviation [dB] | 3.42 | 1.64 | 4.57 | 1.52 | 3.22 | 1.52 | 3.24 | 1.52 |
Median absolute deviation [dB] | 2.24 | 0.77 | 2.14 | 0.69 | 1.91 | 0.67 | 1.96 | 0.73 |
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Monteith, A.R.; Ulander, L.M.H.; Tebaldini, S. Calibration of a Ground-Based Array Radar for Tomographic Imaging of Natural Media. Remote Sens. 2019, 11, 2924. https://doi.org/10.3390/rs11242924
Monteith AR, Ulander LMH, Tebaldini S. Calibration of a Ground-Based Array Radar for Tomographic Imaging of Natural Media. Remote Sensing. 2019; 11(24):2924. https://doi.org/10.3390/rs11242924
Chicago/Turabian StyleMonteith, Albert R., Lars M. H. Ulander, and Stefano Tebaldini. 2019. "Calibration of a Ground-Based Array Radar for Tomographic Imaging of Natural Media" Remote Sensing 11, no. 24: 2924. https://doi.org/10.3390/rs11242924