Pengaruh Koreksi Ionosfer Terhadap Pergeseran Vertikal Pada Citra Satelit ALOS-PALSAR
Studi Kasus: Gempa Bengkulu 12 September 2007
Abstract
Interferometric Synthetic Aperture Radar (InSAR) adalah teknik yang efektif untuk memetakan pergeseran permukaan bumi dengan cakupan area yang luas dan ketelitian tinggi. Namun, ketelitian InSAR dapat dipengaruhi oleh aktivitas perambatan gelombang pada lapisan atmosfer. Medium ionosfer pada lapisan atmosfer mengandung elektron bebas yang menyebabkan gelombang tidak stabil sehingga menghasilkan bias. Oleh karena itu, perlu dilakukan koreksi ionosfer pada pengolahan citra SAR agar tidak mengandung bias. Penelitian ini mengkaji pengaruh koreksi ionosfer terhadap pergeseran vertikal pada citra satelit ALOS-PALSAR. Data yang digunakan meliputi data citra satelit dan GNSS. Data citra diolah dengan mempertimbangkan ada dan tidaknya koreksi ionosfer sehingga hasilnya dapat dianalisis untuk mengetahui pengaruh koreksi ionosfer pada citra SAR. Data GNSS diolah dengan metode statik sehingga menghasilkan koordinat yang dapat digunakan sebagai acuan pada validasi hasil pengolahan citra SAR. Hasil pengolahan citra SAR dan GNSS selanjutnya divisualisasikan dalam bentuk gambar yang menunjukkan pergeseran vertikal untuk memudahkan analisis hasil. Hasil penelitian menunjukkan bahwa arah pergeseran vertikal pada citra satelit yang terkoreksi ionosfer konsisten terhadap arah pergeseran vertikal pada GNSS. Hal tersebut menandakan bahwa koreksi ionosfer berpengaruh terhadap penentuan pergeseran vertikal pada citra satelit. Dalam proses penentuan pergeseran vertikal terdapat kendala yaitu belum adanya referensi titik vertikal sebagai acuan validasi hasil. Selain itu, belum terdapat referensi citra satelit lainnya sebagai pembanding hasil pengolahan citra satelit ALOS-PALSAR.
Interferometric Synthetic Aperture Radar (InSAR) is an effective technique for changing the earth's surface with wide coverage and high accuracy. However, the accuracy of InSAR can be affected by wave propagation activity in the atmosphere. The ionospheric medium in the atmosphere contains free electrons which cause unstable waves to produce bias. Therefore, it is necessary to correct the ionosphere in SAR image processing so that it does not contain bias. This study examines the effect of ionospheric correction on vertical deformation in ALOS-PALSAR satellite imagery. The data used includes satellite image data and GNSS. Image data is processed by considering the presence or absence of ionospheric correction so that the results can be analyzed to determine the effect of the ionosphere on SAR images. GNSS data is processed by a static method to produce coordinates that can be used as a reference for validating the results of SAR image processing. The results of SAR and GNSS image processing are then visualized in the form of a vertical deformation map to facilitate the analysis of the results. The results showed that the direction of the vertical deformation in the ionospheric corrected satellite image was consistent with the direction of the vertical deformation in the GNSS. This indicates that the ionospheric correction affects the vertical deformation in the satellite image. In the process of vertical changes, there are obstacles, namely the vertical point reference has not been used as a validation of the results. In addition, there are no other satellite image references to compare the results of the ALOS-PALSAR satellite image processing.
References
Ali, M., Muhammad Imran Shahzad, M. N., Mahmood, I., & Zia, I. (2021). Estimation of surface deformation due to Pasni earthquake using RADAR interferometry. Geocarto International, 36(14), 1630–1645. https://doi.org/10.1080/10106049.2019.1661031
Biggs, J., & Wright, T. J. (2020). How satellite InSAR has grown from opportunistic science to routine monitoring over the last decade. Nature Communications, 11(1), 10–13. https://doi.org/10.1038/s41467-020-17587-6
Ding, X. L., Li, Z. W., Zhu, J. J., Feng, G. C., & Long, J. P. (2008). Atmospheric effects on InSAR measurements and their mitigation. Sensors, 8(9), 5426–5448. https://doi.org/10.3390/s8095426
Gusman, A. R., Tanioka, Y., Kobayashi, T., Latief, H., & Pandoe, W. (2010). Slip distribution of the 2007 Bengkulu earthquake inferred from tsunami waveforms and InSAR data. Journal of Geophysical Research: Solid Earth, 115(12), 1–14. https://doi.org/10.1029/2010JB007565
Hanssen, R. F. (2018). Radar Interferometry : Data Interpretation and Error Analysis. In Novel Radar Techniques and Applications. https://doi.org/10.1049/SBRA512F_ch6
Islami, N. (2017). Deformasi dan Struktur Batuan. Fisika Bumi, 183–200.
Panuntun, H., Prasidya, A. S., & Mahendra, G. (2022). Present-Day Surface Deformation along the Opak Fault, Yogyakarta, Observed Using Sentinel-1 Interferometric Wide-Swath Data. Technology for Sustainable Development, 112(May 2006), 75–81. https://doi.org/10.4028/p-e3jjj9
Panuntun H (2023) The 2021 Mw 7.2 Haiti earthquake: Blind thrust rupture revealed by space geodetic observations and Bayesian estimation. Journal of Geodynamics 158:101996. doi:https://doi.org/10.1016/j.jog.2023.101996
Panuntun H, Heliani LS, Suryanto W, and Pratama C (2022) Importance of Tropospheric Correction to C-band InSAR Measurements: Application in the 2018 Palu Earthquake. Indonesian Journal of Geography 50 (3):207-213. doi:10.22146/ijg.68984
Parker, A. L. (2017). InSAR Observations of Ground Deformation (Issue D). http://link.springer.com/10.1007/978-3-319-39034-5
Sandwell, D., Mellors, R., Xiaopeng, T., Xiaohua, X., Wei, M., & Wessel, P. (2016). GMTSAR : An InSAR Processing System. 1–107. https://topex.ucsd.edu/gmtsar/tar/GMTSAR_2ND_TEX.pdf
Tanner, D. C., & Brandes, C. (2019). Understanding Faults: Detecting, Dating, and Modeling. In Understanding Faults: Detecting, Dating, and Modeling. https://doi.org/10.1016/B978-0-12-815985-9.00001-1
Zhang, B., Wang, C., Ding, X., Zhu, W., & Wu, S. (2018). Correction of ionospheric artifacts in SAR data: Application to fault slip inversion of 2009 Southern Sumatra earthquake. IEEE Geoscience and Remote Sensing Letters, 15(9), 1327–1331. https://doi.org/10.1109/LGRS.2018.2844686
Zhang B, Wang C, Ding X, Zhu W, and Wu S (2018) Correction of Ionospheric Artifacts in SAR Data: Application to Fault Slip Inversion of 2009 Southern Sumatra Earthquake. IEEE Geoscience and Remote Sensing Letters 15 (9):1327-1331. doi:10.1109/LGRS.2018.2844686
