Topographic Wetness Index (3" resolution) derived from 1" SRTM DEM-H

TWI is calculated as log_e(specific catchment area / slope) and estimates the relative wetness within a catchment. The TWI product was derived from the partial contributing area product (CA_MFD_PARTIAL), which was computed from the Hydrologically enforced Digital Elevation Model (DEM-H; ANZCW0703014615), and from the percent slope product, which was computed from the Smoothed Digital Elevation Model (DEM-S; ANZCW0703014016). Both DEM-S and DEM-H are based on the 1 second resolution SRTM data acquired by NASA in February 2000. Note that the partial contributing area product does not always represent contributing areas larger than about 25 km2 because it was processed on overlapping tiles, not complete catchments. This only impacts on TWI values in river channels and does not affect values on the land around the river channels. Since the index is not intended for use in river channels this limitation has no impact on the utility of TWI for spatial modelling. The 3 second resolution TWI product was generated from the 1 second TWI product and masked by the 3” water and ocean mask datasets.

地形湿度指数（TWI）通过计算自然对数（log_e）下的单位汇水面积与坡度的比值，用于估算流域内的相对湿润程度。该TWI数据集由部分贡献面积数据集（CA_MFD_PARTIAL）与坡度百分比数据集计算生成：其中部分贡献面积数据集由水文约束数字高程模型（Hydrologically Enforced Digital Elevation Model，DEM-H；编号ANZCW0703014615）计算得到，坡度百分比数据集则由平滑数字高程模型（Smoothed Digital Elevation Model，DEM-S；编号ANZCW0703014016）生成。DEM-S与DEM-H均基于美国国家航空航天局（National Aeronautics and Space Administration，NASA）2000年2月获取的1秒分辨率航天飞机雷达地形测绘任务（Shuttle Radar Topography Mission，SRTM）数据。
需注意，由于部分贡献面积数据集是在重叠瓦片而非完整流域上进行处理的，因此其无法始终表征面积大于约25平方千米的汇水区域。该缺陷仅会影响河道内的TWI数值，不会对河道周边陆地区域的数值造成影响。由于该指数本就并非为河道区域设计，因此该局限性不会对TWI用于空间建模的实用性产生任何影响。
3秒分辨率的TWI数据集由1秒分辨率的TWI数据集生成，并通过3弧秒分辨率的水体与海洋掩膜数据集完成掩膜处理。