README: fix typo + add Liang et al. (2019) for S1 iono reference

contrib/stack/README.md

@@ -16,7 +16,7 @@ To use a stack processor you need to:
 
 The stack processors do not show up in the install directory of your isce software. They can be found in the isce source directory. Thus, extra path setup is needed.
 
-2.1 Add the following path to your `${PYTHON_PATH}` environment vavriable:
+2.1 Add the following path to your `${PYTHONPATH}` environment vavriable:
 
 ```bash
 export ISCE_STACK={full_path_to_your_contrib/stack}
@@ -53,24 +53,27 @@ Users who use the stack processors may refer to the following literatures:
 
 For TOPS stack processing:
 
-+ H. Fattahi, P. Agram, and M. Simons, “A network-based enhanced spectral diversity approach for TOPS time-series analysis,” IEEE Trans. Geosci. Remote Sens., vol. 55, no. 2, pp. 777–786, Feb. 2017. (https://ieeexplore.ieee.org/abstract/document/7637021/)
++ Fattahi, H., Agram, P., & Simons, M. (2017). A Network-Based Enhanced Spectral Diversity Approach for TOPS Time-Series Analysis. _IEEE Trans. Geosci. Remote Sens., 55_(2), 777-786, doi: [10.1109/TGRS.2016.2614925](https://doi.org/10.1109/TGRS.2016.2614925)
+
+1. Ionospheric correction
+
++ Liang, C., Agram, P., Simons, M., & Fielding, E. J. (2019). Ionospheric Correction of InSAR Time Series Analysis of C-band Sentinel-1 TOPS Data. _IEEE Trans. Geosci. Remote Sens., 59_(9), 6755-6773, doi: [10.1109/TGRS.2019.2908494](https://doi.org/10.1109/TGRS.2019.2908494).
 
 For StripMap stack processor and ionospheric phase estimation:
 
-+ H. Fattahi, M. Simons, and P. Agram, "InSAR Time-Series Estimation of the Ionospheric Phase Delay: An Extension of the Split Range-Spectrum Technique", IEEE Trans. Geosci. Remote Sens., vol. 55, no. 10, 5984-5996, 2017. (https://ieeexplore.ieee.org/abstract/document/7987747/)
++ Fattahi, H., Simons, M., & Agram, P. (2017). InSAR Time-Series Estimation of the Ionospheric Phase Delay: An Extension of the Split Range-Spectrum Technique. _IEEE Trans. Geosci. Remote Sens., 55_(10), 5984-5996, doi: [10.1109/TGRS.2017.2718566](https://doi.org/10.1109/TGRS.2017.2718566)
 
 For ALOS and ALOS-2 stack processing:
 
 1. ScanSAR or multi-mode InSAR processing
 
-+ C. Liang and E. J. Fielding, "Interferometry with ALOS-2 full-aperture ScanSAR data," IEEE Transactions on Geoscience and Remote Sensing, vol. 55, no. 5, pp. 2739-2750, May 2017.
++ Liang, C., & Fielding, E. J. (2017). Interferometry With ALOS-2 Full-Aperture ScanSAR Data. _IEEE Trans. Geosci. Remote Sens., 55_(5), 2739-2750, doi: [10.1109/TGRS.2017.2653190](https://doi.org/10.1109/TGRS.2017.2653190)
 
 2. Ionospheric correction, burst-by-burst ScanSAR processing, and burst-mode spectral diversity (SD) or 
 multi-aperture InSAR (MAI) processing
 
-+ C. Liang and E. J. Fielding, "Measuring azimuth deformation with L-band ALOS-2 ScanSAR interferometry," IEEE Transactions on Geoscience and Remote Sensing, vol. 55, no. 5, pp. 2725-2738, May 2017.
++ Liang, C., & Fielding, E. J. (2017). Measuring Azimuth Deformation With L-Band ALOS-2 ScanSAR Interferometry. _IEEE Trans. Geosci. Remote Sens., 55_(5), 2725-2738, doi: [10.1109/TGRS.2017.2653186](https://doi.org/10.1109/TGRS.2017.2653186)
 
 3. Ionospheric correction
 
-+ C. Liang, Z. Liu, E. J. Fielding, and R. Bürgmann, "InSAR time series analysis of L-band wide-swath SAR data acquired by ALOS-2," IEEE Transactions on Geoscience and Remote Sensing, vol. 56, no. 8, pp. 4492-4506, Aug. 2018.
-
++ Liang, C., Liu, Z., Fielding, E. J., & Bürgmann, R. (2018). InSAR Time Series Analysis of L-Band Wide-Swath SAR Data Acquired by ALOS-2. _IEEE Trans. Geosci. Remote Sens., 56_(8), 4492-4506, doi: [10.1109/TGRS.2018.2821150](https://doi.org/10.1109/TGRS.2018.2821150)