Modelling of soil moisture in high spatial resolution for farmed grasslands in China based on airborne thermal data
Final Report Abstract
The aim of this work, which is embedded in the MAGIM project (DFG FOR 536) on farmed grasslands in Inner Mongolia, was to identify spatial patterns of soil moisture in high spatial resolution. Based on TIR (Thermal Infrared) remote sensing with a weight-shift microlite aircraft and atmospheric boundary layer modelling, the data collected during the field campaign of 2009 and sensitivity studies with model HIRVAC were analysed. Though these studies confirmed the theoretical basis of the approach, it was not possible to derive high resolution soil moisture maps, basically for two main reasons: (1) the combined influence of soil moisture and LAI on surface temperature changes would require the decoupling of the signal, and (2) georeferencing of collected TIR data was not possible for a large area, due to high angular deviations (heading, pitch, roll) from the designated flight pattern, which could not be corrected by photogrammetric postprocessing techniques. Thus, the research had to be re-focused within the overall objective (Extrapolating water and carbon fluxes of managed grasslands in time and space based on surface and airborne observations). An innovative approach was developed and applied to analyse the spatial and temporal variability of evapotranspiration (ET) for more than 2.600 km² of managed grasslands in the Xilin river catchment. ET is the dominating process of water balance losses in Inner Mongolia, largely influencing soil moisture and highly variable in both time and space. However, little is known about the variability and distribution of ET in this region. The combination of MODIS data, micrometerological data and the hydrological model BROOK90 allowed for closing the gap between limited local ET measurements on the field scale and a demand for long-term spatial studies in Inner Mongolian grasslands. The study, which was conducted over a period of ten consecutive years (2002-2011), clearly showed the high natural variability of innerannual and interannual ET in this area and the coupling of ET on precipitation during the growing season. The dynamics of spatial ET patterns and variability demonstrate static and intense livestock management to be inappropriate and the exquisite adaptation of traditional nomadism to the inherent local variations. The results of the project could promote the development of a sustainable grazing management in Inner Mongolian grasslands.
Publications
- (2013) Spatial precipitation and evapotranspiration in the typical steppe of Inner Mongolia, China – A model based approach using MODIS data, J Arid Environ 88, 184-193
Schaffrath D, Vetter SH, Bernhofer C
(See online at https://doi.org/10.1016/j.jaridenv.2012.07.021) - (2013) Variability and distribution of spatial evapotranspiration in semi arid Inner Mongolian grasslands from 2002 to 2011, SpringerPlus 2, 547
Schaffrath D, Bernhofer C
(See online at https://doi.org/10.1186/2193-1801-2-547)
