## 6 Discussion
### How Volcano Monitoring Benefits from PlanetScope Imagery  
In this work, the potentials of PlanetScope data for monitoring volcanic hazards were investigated. Based on the results presented in Section 5, it can be confirmed that PlanetScope is a useful data source in volcano monitoring when using appropriate methods, especially the high geometric resolution (3 m), which brings great advantages over other sensor systems. With this, it is possible to identify small-scale volcanic deposits and activities. [PERSON] et al. [23] encountered a significant underestimation of marginal areas due to partially covered pixels when mapping lahar deposits using Landsat data (30 m). This problem is resolved with the use of higher spatial resolution PlanetScope data. When mapping ash and tephra deposits, satisfactory results can also be obtained even with lower-resolution sensors (e.g., Sentinel-2 MSI (10 m)) [18]. Figure 13 compares the use of the OBIA change detection methodology using Sentinel-2 with the PlanetScope results. For the mapping of the lava area after the Karangetang II eruption phase, only the 10 m bands (B02 (blue), B03 (green), B04 (red), B08 (NIR)) of Sentinel-2 MSI were used to ensure comparability with PlanetScope. The methodology provides satisfactory results even with lower resolution Sentinel-2 (10 m) data. The agreement of the Sentinel-2 lava area with the PlanetScope lava area is 79.65%. At the same time, 13.4% of the Sentinel-2 lava area lies outside the boundaries of the PlanetScope lava area. This suggests that the methodology is robust to the geometric resolution of the input data. However, with lower geometric resolution, the detection of the boundary areas deteriorates, which was also observed in [PERSON] et al. [23]. In addition, the advantages of the object-based approach become blurred [63]. Accordingly, high geometric resolution is an important factor for the application of object-based analysis methods in volcano monitoring [21; 24]. Furthermore, coarser resolution makes texture analysis via GLCM more difficult because there is less contrast in the image [24]. However, when classifying small-scale volcanic hazards, e.g., fine lahar deposits within watercourses, even PlanetScope reaches its limits. Here, even better resolution systems (e.g., WorldView (0.30 m), Pleiades (0.50 m)) are useful. Figure 12: Validation of lava area derived from OBIA methodology based on TanDEM-X drainage model (red) and manually digitized lava area (light blue). The manual digitization took place based on the PlanetScope post-scene (4 May 2019). In the lower area, the edge areas were manually captured in a slightly coarser way. In contrast, the lava delta in the sea was mapped better by manual digitization. In the upper area, the potential misclassifications in the E of the lava flow were omitted. In addition, there is the connection of the small lava flow in the WNW to the North Crater. In the sub-areas of the unvegetated area, manual digitization was difficult to perform because there was little contrast with the background. Accordingly, the optical validation of the lava flow from the OBIA method is given only qualitatively. The spectral resolution of PlanetScope is a limitation for monitoring active volcanoes. Due to the missing SWIR or TIR bands hotspots cannot be detected. Work is currently underway to improve the spectral resolution of PlanetScope. In the future, the Doves will be equipped with an 8-band sensor system, with the addition of a Coastal Blue, Green II, Yellow, and Red Edge band to the existing bands, but unfortunately no SWIR channels [44]. For other sensors with higher spectral resolution (e.g., Moderate Resolution Imaging Spectroradiometer (MODIS), Visible Infrared Imaging Radiometer Suite (VIIRS)), spatial resolution limits the exact localization of thermal anomalies [17]. Thus, via the combination of geometrically high-resolution PlanetScope data and spectrally high-resolution IR data, the full potential of both data sources can be combined.