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Acta Prataculturae Sinica ›› 2023, Vol. 32 ›› Issue (8): 28-39.DOI: 10.11686/cyxb2022385

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Integrating MODIS and Landsat data to reconstruct the Landsat NDVI of a typical region in the Qinghai Lake Basin and changes in the intra-annual NDVI maximum

Fang LI1(), Guang-jun WANG1(), Hai-bo DU2, Meng LI1, Si-hai LIANG3, Hong-ming PENG4,5   

  1. 1.School of Land Science and Technology,China University of Geosciences (Beijing),Beijing 100083,China
    2.Inner Mongolia Survey Team of Coalfield Geology Bureau,Hohhot 010010,China
    3.School of Water Resources and Environment,China University of Geosciences (Beijing),Beijing 100083,China
    4.Qinghai Bureau of Environmental Geology Exploration,Xining 810007,China
    5.Key Laboratory of Environmental Geology of Qinghai Province,Xining 810007,China
  • Received:2022-09-27 Revised:2022-12-09 Online:2023-08-20 Published:2023-06-16
  • Contact: Guang-jun WANG

Abstract:

The normalized difference vegetation index (NDVI) can provide accurate information about vegetation cover and growing status, and the changes in NDVI over a period of time are important indicators of vegetation growth on a global, national, or regional scale. However, there are two main problems to address: First, the spatial resolution of existing NDVI long-time-series products is coarse, so these data can only be used on a large scale, and not on a fine scale. Second, NDVI data obtained from medium-resolution images at different times, such as Landsat images, are greatly influenced by seasonal and inter-annual changes in vegetation as well as the quality of the ecological environment. To solve these two problems, we used the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM), which integrates MOD09Q1 and Landsat data, to predict and interpolate the Landsat NDVI for the annual growing season. Then, the Logistic model was used to reconstruct NDVI curves covering vegetation growth seasons from 2001 to 2020. The date corresponding to the annual maximum of Landsat NDVI was obtained from the MODIS daily NDVI data. After reconstructing the curve, we introduced the date parameter to solve the optimal intra-annual NDVI maximum pixel by pixel. Finally, we used the annual maximum of Landsat NDVI to analyze the vegetation growth status and evaluate the change in vegetation in a typical local area near the Buha River in the Qinghai Lake basin. The results show that: 1) The annual maximum of Landsat NDVI was fitted after combining the MODIS and Landsat data. Most (98.5%) of the pixels in the results were within the triple root mean square error (RMSE), indicative of high precision of the model. 2) When assessing vegetation growth status, the annual maximum value of Landsat NDVI was able to capture detailed changes in vegetation and reduced the errors caused by time differences in the Landsat data. 3) The spatial distribution of the maximum NDVI of vegetation in the study area was high in the north and south and low in the middle. The inter-annual variation first decreased and then increased, and vegetation growth showed an increasing trend. The annual maximum NDVI in the Kobresia and forb meadow in the Qinghai Lake Basin showed a decreasing trend and fluctuated sharply. Further studies should be conducted to investigate these changes in more detail.

Key words: Qinghai Lake basin, Landsat NDVI intra-annual maximum value, spatio-temporal fusion algorithm, Logistic model, spatio-temporal variation