- SO2 mass |
= Sentinel-5P SO2 analysis |
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= gas mass in the atmosphere (PBL layer, DU>0.35, 500x500km area) |
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= images show gas densities in Dobson Unit DU (by default, in PBL layer within a 500×500km box around the volcano, and 100x100km zoom). The detected pixels contaminated with volcanic SO2 are overlaid with a semi-transparent gray mask. |
- hot-spot pixels |
= Sentinel-2 shortwave infrared analysis (bands 8a-11-12) |
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= number of hot pixels x106 in the unzoomed image (Massimetti et al., 2020) |
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= images can be displayed with:
- "visible + infrared" bands (visible bands B4-B3-B2 @10m resolution, with hot pixels enhanced with SWIR bands B12-B11-B8A @20m resolution)
- "infrared" bands (12-11-8A)
- "infrared + detections" (hot pixel cluster highlighted by red bounding box).
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- SAR intensity |
= Sentinel-1 back-scattered radar intensity (VV polarization) |
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= data points are placeholders for image acquisition dates. Crater depth estimation from the intensity images is an experimental stage. |
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= images can be displayed "filtered" (CNN speckle filter, Davis et al. 2020 IGARSS) or "unfiltered", in geocoded coordinates or in radar coordinates. (The image in radar geometry is only available for the 2x2km zoom region.) |
- deformation |
= Sentinel-1 dINSAR analysis between 2 consecutive acquisitions |
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= standard deviation of the unwrapped deformation map (generated by a deformation-detection neural network, Valade et al., 2019) |
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= images can be displayed "wrapped" (interferogram displaying phase value ranging between -π (purple) and π (blue), where 1 full cycle (=fringe) represents 2.8 cm displacement in the radar line-of-sight), or "unwrapped" (deformation map with values in meters). |
- coherence |
= Sentinel-1 phase decorrelation between 2 consecutive acquisitions |
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= number of decorrelated pixels (coherence < 0.5) |
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= images are interferometric coherence maps, derived from the dINSAR analysis. It is a measure of the interferometric quality, as it is related to the level of noise affecting the phase difference between the two SAR images. It ranges between 0 and 1, and reflects the degree of surface change, where values towards 0 (black) indicate a loss of coherence. The main contributions to decorrelation are phase noise due to (i) the temporal change of the scatterers (e.g., vegetation, water, sand-covered areas will appear highly incoherent as the scatterers change continuously), (ii) geometric decorrelation (i.e., images have slightly different look-angles), and (iii) variation in atmospheric water vapor content. Although decorrelation usually renders interferograms useless for measuring ground deformation, it can be used to detect changes in the ground properties (e.g., emplacement of lava flows and eruptive deposits, delineation of eruptive fissures, etc.). |
