Estimating Mean Daily Surface Temperature over the Tibetan Plateau Based on MODIS LST Products

Land surface temperature(LST) is one of the key factors that indicate the thermal state of the land-atmosphere boundary.It has frequently been applied in many fields such as permafrost mapping and analyzing urban heat island effect.The MODIS LST products merely provide four instantaneous observations every day,whereas,the daily mean LST is often required in practice.In this study,a piecewise function is used to figure out the diurnal circle of ground temperature at the surface.In daytime,the surface temperature takes on the form of a sinusoidal function,while in nighttime it declines almost linearly.Furthermore,two existing methods are reviewed and one new approach(Sin-Linear) is proposed to transfer the instantaneous MODIS LST data to daily mean LST.In order to validate the new approach,four instantaneous temperature data are selected from the hourly observed 0 cm temperature according to the overpass time of the satellites.Then the three methods are applied to estimate the daily mean LST,which are compared with the arithmetic averaged data of the hourly temperature records.It is found that the Sin-Linear method proposed here has the highest precision,with annual mean error within 1 K.On the other hand,the three methods are applied to the MODIS LST data,and the results are compared with the ground daily averaged data(0 cm).The Sin-Linear method indicates the best consistency with the ground observation,with R2 greater than 0.9.