Estimation of dry vegetation cover and mass from MODIS data: Verification by roughness length and sand saltation threshold
Estimation of dry vegetation cover and mass from MODIS data: Verification by roughness length and sand saltation threshold
复制标题
根据 MODIS 数据估算干燥植被覆盖度和质量：通过粗糙度长度和沙盐跃移阈值进行验证
DOI：
10.1016/j.jag.2021.102417
复制
发表时间：
2021
影响因子：
7.5
通讯作者：
Liu Jiaqi
中科院分区：
文献类型：
--
作者：
Wu Jing;Kurosaki Yasunori;Gantsetseg Batdelger;Ishizuka Masahide;Sekiyama Tsuyoshi Thomas;Buyantogtokh Batjargal;Liu Jiaqi
监测干旱和半干旱地区的干旱植被对于评估风蚀风险、牲畜饲料和火灾风险等环境调查至关重要。然而，关于估算干植被（非光合作用）盖度和质量的研究很少。在蒙古戈壁沙漠北部的tsott - ovoo （TsO）研究区，利用MODIS数据将观测到的干植被覆盖度（VC d _ obs）和质量（M d _ obs）与归一化植被指数（NDVI）和其他6个潜在的短波红外（SWIR）干植被指数估算值进行了比较。在7个植被指数中，土壤耕作指数（STI）和归一化差异耕作指数（NDTI）都是在SWIR波段6和7上计算的，它们可以很好地估计VC d _ obs和M d _ obs。我们将观测到的粗糙度长度（z0）和阈值摩擦速度（u* t）在由STI确定的干燥植被覆盖的石质和非石质地点进行了比较，验证了它对估计VC d （STI）的适用性。在这两个地点，观测到的z0和u* t随着VC d （STI）的增加而增加。根据它们与STI的关系，我们预测了在没有干植被的情况下z0和u* t的值与已发表的数据一致。在石质和非石质地点，由u* t得到的10 m高度的阈值风速都相当接近于通常用于沙尘模型的值。因此，我们验证了STI是估算戈壁沙漠以及其他干旱和半干旱地区干植被数量的合适指标。虽然z0和u* t与STI的关系有待进一步验证，但STI的使用似乎可以改善未来干旱和半干旱环境下的风蚀风险评估。
Monitoring of dry vegetation in arid and semi-arid regions is crucial in environmental investigations such as assessments of wind erosion risk, livestock forage, and fire risk. However, there has been little research into estimating the coverage and mass of dry (non-photosynthetic) vegetation. In our study area at Tsogt-Ovoo (TsO) in the northern Gobi Desert, Mongolia, we used MODIS data to compare observed dry vegetation cover (VC d _ obs) and mass (M d _ obs) with values estimated from the Normalized Difference Vegetation Index (NDVI) and six other potential Short Wavelength InfraRed (SWIR) dry vegetation indices. Of the seven vegetation indices, the Soil Tillage Index (STI) and Normalized Difference Tillage Index (NDTI), both of which are calculated from SWIR bands 6 and 7, provided good estimates of VC d _ obs and M d _ obs. Our comparisons of observed roughness length (z 0) and threshold friction velocity (u* t) for sand saltation at stony and non-stony sites with dry vegetation cover determined from STI verified its suitability for estimating VC d (STI). At both sites, the observed z 0 and u* t increased with increasing estimated VC d (STI). Based on their relationships with STI, we predicted values of z 0 and u* t in the absence of dry vegetation that were in accordance with published data. The threshold wind speeds at 10 m height derived from u* t at both the stony and non-stony sites were reasonably close to the value that is commonly used in dust models. Thus, we verified that STI is a suitable index for estimating the amount of dry vegetation in the Gobi Desert and, potentially, in other arid and semi-arid regions. Although the relationships of z 0 and u* t with STI require further validation, it appears that the use of STI can improve future wind erosion risk assessments in arid and semi-arid environments.