## 3 Results  
### Water Table (WT) Position  
We found a strong and significant (\(P<0.0001\)) linear relationship between NDWI\({}_{1240}\) (5 years of SASI imagery) (Table 1) and the WT position (Figure 3). The negative slope of the relationship is indicative of both liquid water content in the plant tissues and phenology. As described by [14], NDWI\({}_{1240}\) is sensitive to both vegetation foliar water content and the shape of the reflectance spectra, with more negative values seen for pixels that are not representative of live green vegetation, such as early spring in the bog prior to vascular plant green up (Figure 3B). As shown by [51], the surface of the bog experiences considerable changes to the spectral response of hummocks and hollows as the vascular plants green up. It is also during the spring following snow melt that the water table is closest to the surface, whereas the end of the summer experiences the lowest water table.  
The regression model shown in Figure 3A does not include four summer (leaf on) outliers (red triangles) from imagery acquired 10 July 2014, 17 June 2015, 23 June 2016, and 24 June 2016 (Table 1, Figure A1). With the acquisition time greatest from solar noon, the resultant illumination and viewing geometries revealed that these flights lines were collected with a solar azimuth angle relative to aircraft heading (RAA) that places the illumination diagonal to the SASI's field of view (Figure 4). Examination of the 14 remaining HSI, collected before and after solar noon separately, revealed no difference in slope (F = 0.002, \(P=0.97\)) nor intercept (F = 1.231, \(P=0.29\)).  
Figure 3: (**A**) Ordinary least squares (OLS) regression between narrowband index (NDWI\({}_{1240}\)) from the SASI and water table position (WT). Confidence intervals (95%) are shown as the dashed lines; (**B**) field photograph of the bog taken 27 April 2016, prior to the green up of the vascular plants (spring); (**C**) field photograph of the bog taken 23 June 2016, illustrating the vascular plants in full foliage (summer); (**D**) field photograph of the bog taken 27 September 2017, illustrating senescence of the vascular plants (fall). The black triangle in A is the image acquired 27 April 2016 (Table 1) under similar RAA as the summer outliers.  
Figure 5 illustrates the NDWI\({}_{1240}\):WT function from Figure 3A applied to a SASI flight line subset from 20 July 2011. The values--expressed as the difference with respect to the water table position recorded at the tower potentiometer--are a general representation of the surface microtopography. Figure 6 illustrates an example of a 400 m\({}^{2}\) plot from [12]. Following degradation of the spatial resolution of the original digital surface model (DSM) to 1 m, there was a correlation of \(r\) = 0.54 between the water table depth surface and the DSM.  
Figure 4: Illumination and viewing geometry of the SASI HSI lines from 2011–2016 used for the water table position model. The lengths of the arrows represent the solar zenith angle (in degrees) and the direction is the solar azimuth relative to the heading of the flight line (RAA from Table 1). The RAA values reported in degrees in Table 1 are shown in Cartesian coordinates. Black = spring (leaf off), green = summer (leaf on), and orange = fall (senescence). Red represents the summer (leaf on) outliers not included in the WT model (Figure 3A). The RAA places the illumination direction diagonal to the SASI’s field of view for the four summer outliers (red) and one spring (black) image (leaf off).  
Figure 5: Example of a spatial map of water table position (cm from the surface) from the 20 July 2011 SASI image expressed as the difference from the value recorded at the eddy covariance tower hummock potentiometer (\(-\)40.6 cm). Background image source: DMTI 2005 Satellite Streetview.