Investigating the relationship between ground-measured LAI and vegetation indices in an alpine meadow, north-west China

A field campaign was carried out in the alpine meadow of Heihe River Basin, north-west China on 11-15 July 2002. Several bio-geophysical parameters such as leaf area index (LAI) were measured according to VALERI sampling procedures within 38 elementary sampling units (ESUs) in the 3 kin x 3 km 'VALERI' site. A quarter scene of Landsat 7 ETM+ with acquisition times close to the field campaign time was atmospherically and geographically corrected. Three kinds of spectral vegetation index maps including NDVI SR and MSAVI in the sampling area were derived from the corrected ETM + image. The two sets of LAI data measured with LAI-2000 and TRAC instrument at the same site were inter-compared. This is particularly meaningful for assessing the accuracy of LAI measurements. The relationships between the measured LAI and the three kinds of vegetation indices were also investigated. These comparisons found good relationships between the measured LAI and the different vegetation indices in most cases. Among them, NDVI seems the most promising estimator for extraction of LAI for the alpine meadow. In addition, the LAI-2000 seems to perform better for LAI measurement in the alpine meadow than the TRAC instrument.