Analysis of the spatiotemporal variations of NDVI data from 2011 to 2020 in Ningxia area based on POD

The temporal and spatial variation characteristics of MODIS NDVI data in Ningxia during the past ten years were analyzed by proper orthogonal decomposition(POD) method. The analysis result indicates that the temporal and spatial distribution of NDVI data in Ningxia area has three typical modes, and the accumulation contribution rate of eigenvalues variance of the first three modes is more than 95%. The time coefficients of mode 1 and mode 3 show an upward trend, and that of mode 2 shows a downward trend, with obvious interannual variation. Mode 1 decides that the NDVI trend is consistent, which is characterized by increasing or reducing in the whole region. The eigenvector of mode 2 shows strong oscillating characteristics in some areas of the plain area, which may be strongly related to the rapid urban development in the area. The eigenvector of mode 3 in the southern Liupan Mountain has a small oscillatory performance, which may be related to the local variation of farm land returning to woodland in a decade. The results show that the POD method is also suitable for the analysis of the NDVI flow field.