Discrepancies of satellite-derived leaf area index products in Zhejiang Province

This study was devoted to identify discrepancies of three MODIS- based leaf area index (LAI) products (i.e., GLASS LAI, MOD15 LAI, and MCD15 LAI) in Zhejiang Province. The reliability of three LAI products for evergreen broadleaf forests in the Tiantongshan regions was assessed using 30 m resolution LAI map (LAITM), which is produced by combining field LAI measurements and TM remote sensing data. Results showed that the three LAI products differed in reliability, magnitude, spatial patterns, and trends. The GLASS LAI product outperforms the MOD15 and MCD15 LAI products for evergreen broadleaf forests over Tiantongshan. GLASS LAI had a better correlation with LAITM (R2=0.61, RMSE=1.20) than that of MOD15 LAI (RMSE=1.42) and MCD15 LAI (RMSE=1.63). The mean annual LAI of Zhejiang Province based on GLASS LAI (2.13 m2/m2) was about 23% and 12% higher than that of MOD15 LAI and MCD15 LAI, respectively. However, provincial means of annual maximum GLASS LAI averaged 3.82 m2/m2 over the study period, lower than corresponding values of MOD15 LAI and MCD15 LAI by approximate 30%. From 2003 to 2012, GLASS LAI significantly increased and decreased in 16.6% and 14.7% areas of Zhejiang Province, respectively. MOD15 LAI and MCD15 LAI obviously decreased over 21.8% and 13.7% areas of Zhejiang Province, respectively, while noticeably increased in only 1.2% and 4.0% areas of this province, respectively. The provincial average of annual mean GLASS LAI exhibited large interannual variability and unobvious temporal trends. The provincial average of annual mean MCD15 LAI decreased slightly while the corresponding value of MOD15 LAI (0.02 m2/m2, p=0.06) showed a noticeable downward trend.