## 5 Results
### TSX Backscatter and NDVI Properties of Radiocarbon-Dated DTLBs (50-10,000 Years since Drainage)
Such parts of DTLBs exhibited high backscatter. Some old DTLBs also contained fully developed large hydrostatic pingos. These pingos exhibited high NDVI compared to the basin floor surrounding it, but their backscatter signal was affected by geometric distortion on the steep pingo slopes. Geometric distortion, an inherent problem in SAR acquisition mainly of rugged terrain, is a spatial distortion due to complex relationship between SAR look direction, incident angle, target object platform altitude and object configuration relative to radar beam. It causes terrain slope of elevated targets, such as large pingos, facing towards the SAR sensor to appear compressed and brighter [55]. Even though some parts of older DTLBs contained features that exhibited higher NDVI and backscatter signals, such features were considerably less in number and, thus, had a small contribution to total mean backscatter and NDVI values of DTLBs, which was therefore relatively lower than younger DTLBs. TSX Backscatter and NDVI Properties of Modern and Radiocarbon-Dated DTLBs (0-10,000 Years since Drainage)  
Analysis of TSX backscatter in the 27 August scene of the entire suite of DTLBs of known age (modern and radiocarbon-dated DTLBs) resulted in a significant logarithmic relation (R\({}^{2}\) = 0.36, p \(<\) 0.05) between basin age and mean basin backscatter (Figure 3). However, a strong relationship could not be established (R\({}^{2}\) \(<\) 0.2, p \(<\) 0.05) between backscatter and basin age for the 09 September TerraSAR-X scene. A significant and even stronger logarithmic relation of R\({}^{2}\) = 0.53 (p \(<\) 0.05) was found between basin age and Landat-5 TM based NDVI (Figure 4). There was a decreasing trend in basin scale backscatter as basin age increased. A similar trend was observed in NDVI, but this relationship did not hold for the ancient basin (older than 5,000 years). NDVI value increased for the only ancient basin in our dataset. The most notable successional transition was found between modern and young DTLBs. Modern DTLBs exhibited a generally higher variability in their spectral and backscatter properties compared to older DTLBs (Figures 5 and 6), indicative of their highly variable surface properties, while young basins were already characterized by tundra vegetation and drier and refrozen soils. Modern basins had a wide range of backscatter values between \(-\)6.8 dB to \(-\)3.2 dB. Several of them had low backscatter values similar to those of young and medium-aged DTLBs, even though they were characterized by different surface properties. We found that the basin productivity decreased significantly within 50-500 years after lake drainage. Modern DTLBs exhibited relatively high NDVI in the range of 0.32 to 0.52, compared to NDVI for radiocarbon-dated DTLBs that ranged from 0.27 to 0.47. We noticed that the rate of basin floor modification was much slower when basins reached medium age, as also reflected from their backscatter and NDVI values that did not vary much after this point. The characteristics of drained basins are illustrated in Figure 7 and summarized in Table 2.  
Figure 4: Plot of mean basin NDVI observed on 13 July 2009 against basin age showing a logarithmic relationship for the period of 0–10,000 years. Basin age class is shown as: I. Modern basins; II. Young basins; III. Medium age basins; IV. Old basins; and V. Ancient basins. Figure 5: Backscatter and NDVI properties of DTLBs at various stages in a subset of the study area on the northern Seward Peninsula as observed in: (**a**) TerraSAR-X image (3 m spatial resolution) on 27 August 2009; and (**b**) Landsat-5 TM based NDVI (30 m spatial resolution) on 13 July 2009. Figure 5: _Cont._  
Figure 6: Distribution of backscatter and NDVI values of DTLBs showing the differences in backscatter and spectral properties of modern and radiocarbon-dated basins. The axes intersect at the median of each parameter.