Surface volcanic rocks identification in active volcano is crucial not only to mitigate volcanic hazards, but also to characterize eruption, urban rehabilitation, and reconstruction especially after eruption. Remote sensing technology provides ground surface data relatively cheap and large coverage area. However, the application of remote sensing technology for identifying volcanic rocks distribution is still limited. The cloud is always the main problem of the optical sensor as well as the vegetation and geometric distortion for microwave sensor. Overcoming the problem, we tried to identify the volcanic rocks distribution using Polarimetric SAR data of The Phased Array type L-band Synthetic Aperture Radar (PALSAR) onboard The Advanced Land Observing Satellite (ALOS). The aim of this study is to evaluate the possibility using polarimetric SAR data for delineating volcanic rocks. The spatial comparison using optical sensor data was used to delineate the Geomorphologic and Structural Features (GSF) in the Polarimetric SAR data. Then, a seed fill method with pixel growth criterion was applied to identify volcanic rocks distribution based on the GSF automatically. The geological map was used to validate this approach. The Advanced Land Imager (ALI) instrument onboard EO-1 satellite and ASTER GDEM 30-m were used as benchmark to predict the effect of vegetation canopy and gradient slope of topography to the SAR backscattering data. Mt. Tangkuban Parahu located in a dense populated area in Bandung City, West Java, Indonesia was selected as study area. The small phreatic historical eruptions at this volcano have been recorded dominantly since the 19th century. The distribution of volcanic rocks at Mt. Tangkuban Parahu followed mainly the GSF of the Polarimetric SAR data. Therefore, delineating the GSF of the Polarimetric SAR data is the key to interpret the volcanic rocks distribution. This approach is supposed to be applicable for other regions which have similar geological setting.
Figure 1. Onset of Mt. Tangkuban Parahu in West Java, Indonesia overlaid on the elevation map.
Figure 2. The illustration of backscatter signal in X-, C-, and L-bands respects to the clouds, vegetation canopy, and ground surface.
Figure 3. The color composite of backscattering intensity image for R=HH, G=HV, and B=VV (A), the local incidence angle in radian unit (B), the ASTER GDEM 30-m (C), and the NDVI originated from EO-1 ALI data (D) show the contribution of the surface condition to the polarimetric SAR data. The Red triangle is the summit of MTP.
Figure 4. The geological map of Mt. Tangkuban Parahu (A), the selected seed locations (B), the color composite of the P image for R=σHH, G=σHV, and B=σVV (C), and the seed fill map overlaid on the P image (D).
Source:
Saepuloh A., Urai M., Bayuaji L., Sumintadireja P., Suparka E., Identifying volcanic rocks using geomorphologic and structural features of polarimetric SAR data, Proceeding of the 5th Indonesia Japan Joint Scientific Symposium (IJJSS-2012), October 2012.