## 6 Discussion
### Surface Characteristics of Modern DTLBs (0-50 Years since Drainage)  
Based on our results, a 50-year time period after lake drainage appears too short to observe a predictable succession of vegetation and changes in soil properties using a space-for-time substitution approach with TSX backscatter and Landsat-based NDVI data of DTLBs with varying ages. However, this may not exclude the presence of clear relationships due to successional changes within individual basins that could be observed with a time series of imagery. Local variations of the draining process related to drainage gradient, basin size and watershed size likely played a significant role in determining successional stage and hydrologic regimes of modern basins. For enhanced differentiation, the application of a high resolution Digital Elevation Model (DEM) would be useful to stratify basins based on their hydro-geomorphic regime [11] and allow an enhanced evaluation of the relationship between basin age and backscatter or spectral data on different basin subsets. However, due to a lack of fine resolution DEM for our study region, we could not follow this approach. Similarly, due to variation in surface drainage within a basin floor, the basin floor was characterized by diverse soil moisture and vegetation composition. This resulted in mixed and spatially complex backscatter and spectral pixel-signal that largely prevented a solid discrimination of successional stages of modern DTLBs after lake drainage. [PERSON] and [PERSON] [19] and [PERSON] _et al._[12] have also observed this variability within one basin as an inherent source of error in age classification of basins on the Barrow Peninsula, North Alaska. The high backscatter of sparsely distributed emergent vegetation and floating vegetation mats in our study is likely due to deeper penetration of the shorter wavelength X-band radiation through a vegetation canopy, which then results in the double bounce reflection from the water and vegetation [56]. In our study, incidence angles of all the TSX scenes were very close to each other, ranging from 28.8\({}^{\circ}\) to 35.3\({}^{\circ}\). A smaller incidence angle shortens the path through canopy and reduces the canopy attenuation on the radar signal, allowing it to penetrate deeper [57]. [PERSON] _et al._[58] showed similar results for radar backscattering from flooded willow, grasses and sedges in the Peace-Athabasca Delta, Canada. For very young DTLBs (younger than five years old) with shallow water and an early assemblage of densely populated and productive graminoid vegetation, the low backscatter value can be explained by a decreasing contribution of a signal from the wet soil surface and the increasing biomass [59]. In this case, even at a low incidence angle, the shorter wavelength of X-band cannot penetrate through the denser canopy layer and detect the background. The interaction of canopy and radiation takes place within the volume of the vegetation canopy that is composed of multiple scatterers with different sizes and orientation [56]. This results in volume and multiple scattering with low return signal. Similar radiation-canopy interaction is observed in parts of other modern DTLBs, which have dense graminoid cover. For some dry basin surfaces with moss and lichen cover or exposed ground, likely a result of higher elevated surfaces of the former lake bottom exposed very early in the drainage process, it is possible that X-band could have penetrated the upper thin vegetation layer covering the basin floor [40,60]. Therefore, the moisture of the underlying soil could have contributed more to the total backscatter from dry basin surfaces. [PERSON] _et al._[61] in their analysis of TSX data sensitivity to bare soil moisture and roughness have shown that the sensitivity of the radar signal to soil moisture for TSX is higher at smaller incidence angles similar to the ones we have used in our study. In contrast, it is less sensitive to soil roughness.