不同叶面积指数遥感产品在浙江省的差异比较研究

本文比较分析了三种基于MODIS数据生成的LAI遥感产品(MOD15 LAI、MCD15 LAI和GLASS LAI)在浙江省的差异;以地面观测的LAI结合TM遥感数据生成的30 m分辨率LAI数据(LAITM)为参考,评价了它们在浙江省天童山常绿阔叶林地区的可靠性。研究发现,三种LAI遥感产品在可靠性、大小、空间格局及变化趋势上均存在显著差异:GLASS LAI表现优于MOD15 LAI和MCD15 LAI,GLASS LAI与LAITM具有较好的相关性(R2=0.61,RMSE=1.20),而MOD15 LAI和MCD15 LAI与LAITM的一致性较差(RMSE分别为1.42和1.63)。2003—2012年期间,基于GLASS LAI得到的浙江省LAI年平均值(2.13 m2/m2)分别高出MOD15 LAI和MCD15 LAI约23%和12%;而GLASS LAI年最大值的10年平均值(3.82 m2/m2)比MOD15 LAI和MCD15 LAI的值都偏低约30%。2003—2012年期间,GLASS LAI年平均值在浙江省显著升高和下降的面积比例分别为16.6%和14.7%;MOD15 LAI和MCD15 LAI分别在全省21.8%和13.7%的地区呈明显下降趋势,明显升高地区分别仅占1.2%和4.0%。三种LAI遥感产品的全省年平均值方面,GLASS LAI具有较大的年际波动,但趋势不明显;MCD15 LAI略有下降;而MOD15 LAI呈现较为明显的下降趋势(0.02 m2/m2,P=0.06)。

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.