## 4 Discussion
Due to the small spatial scale of the hummocks and hollows, 1 m does not retain their integrity [31], resulting in a mixing of both the elevation and water table at the transition between hummocks and hollows. If these analyses were to be conducted at a finer spatial resolution (e.g., 5 cm), achievable from low-altitude UAV platforms, the correlation between microtopography and water table depth would likely be stronger. Further work investigating this relationship at fine spatial scales is important because UAV-based microtopography modeling is less expensive and more accessible than UAV based SWIR HSI. Peatland hydrology is one of the most important factors influencing ecology and functioning, with WT depth an important predictor of vegetation structure and composition [28]. In areas with a deeper WT, vascular vegetation in hummocks is taller, with the establishment of trees in areas with the lowest WT [59]. Therefore, long-term changes in the WT depth could alter the spatial distribution and structure of the vascular plants. The position of the WT in the peat profile indicates the depth of the soil air in the pore space, while the vertical range between the surface and the maximum water table depth encompasses the thickness of the acrotelm in which most of the biogeochemical processes take place [28]. Because the roots of many vascular plants require a minimum proportion of soil pore air, temporal monitoring of the WT depth (in a spatial context) could facilitate forecasting succession (i.e., changes in species composition or community structure). The vertical profile of _Sphagnum_ is a dense canopy with spaces and dead hyaline cells of the leaves and branches providing the mechanism for the retention of capillary water above the water table [28]. Lowering of the WT decreases the soil water pressure [60], increasing the possibility of desiccation of the mosses thus resulting in a loss of productivity and carbon sequestration [61]. Substantial lowering of the WT through draining accelerates the decomposition process in the peat and releases of CO\({}_{2}\) to the atmosphere [62]. In order to estimate WT with NDWI\({}_{1240}\) from airborne HSI, the illumination and acquisition geometries should be carefully considered. As shown in Figure 4, during the summer, with the vascular plants in full foliage, the illumination geometry affects the utility of the image for WT position estimation. The residuals (Figure A1) indicate that the flight lines in the summer (leaf on) with the RAA diagonal to the field of view (128.7-151.8\({}^{\circ}\)) were greater than \(\pm\)10 cm. A non-parametric quantile density plot (Figure A2) further illustrates the dissimilarity between the NDWI\({}_{1240}\):WT relationship in these HSI and the rest of the sampling dates. As a result, these four images were not used in the estimation of the WT depth. In contrast, the spring (leaf off) his, with an RAA of 145.9\({}^{\circ}\) (black triangle in Figure 3A), was not an outlier in the NDWI\({}_{1240}\):WT relationship due to lack of leaves on the vascular plants (Figures 3D and 4). While additional data collection (e.g., HSI collected over a broader range of solar zenith angle (SZA) and SAA throughout the growing season) and analysis are planned to fully understand the reason for this, we believe it is potentially related to the anisotropy of the bog. When reflectance properties of a surface are not perfectly diffuse, they have some degree of anisotropy. This directional characteristic of the surface reflectance when accounted for from all angles is referred to as the bidirectional reflectance distribution function (BRDF) [63]. Vegetation, in general, has long been accepted as having anisotropic reflectance properties [64], however, the majority of studies have focused on modeling and quantifying other ecosystems with minimal studies examining peatlands [65].