6Zhao C J,Zhou Q F,Wang J H,et al. Spectral indices redefined in detecting nitrogen availability for wheat canopy[J]. Communications in Soil Science and Plant Analysis, 2004,35 : 853-864.
7Ashcroft P M,Catt J A,Curran P J,et al. The relation between re- fitted radiation and yield on the broad balk winter wheat experi- ment[J]. Int J Remote Sensing, 1990,11 (10) : 1821-1836.
8Huete A, Justice C, Leeuwen V. "MoDIS vegetation index (MoD 13 )" Version 3. Algorithm Theoretical Basis Docu-ment[EB/OL]. [2012- 10-071. http://modis.gsf, atbd.htm.