In order to test the accuracy of the usually-used fixed calibration factor of the canopy scanner of LAI-2000 for measuring the leaf area index(LAI),a Larix principis-rupprechtii plantation was chosen in the small wate...In order to test the accuracy of the usually-used fixed calibration factor of the canopy scanner of LAI-2000 for measuring the leaf area index(LAI),a Larix principis-rupprechtii plantation was chosen in the small watershed of Xiangshuihe located at the Liupan Mountains of Ningxia Hui Autonomous Region of NW China,the LAI was measured in October 2010,a period from full canopy to the total fall of needles,by using both the LAI- 2000 and litterfall collection method.Then,a comparison was made between the LAI values determined by the litter-fall collection and that calculated based on the figures read from LAI-2000 and the fixed calibration factor(1.49).It showed that the average of LAI measurements of the 2 methods was very close,with a difference of only 5%.However,the calculated LAI from LAI-2000 was obviously higher than the true values determined by litter-fall collection when the canopy was full of needles;and obviously lower than the true value when the canopy was sparse after needle falling.The reason may be that LAI-2000 takes the projection of twigs as needles.So,a dynamic calibration factor is needed,especially in the seasons when the needle amount and the percentage of twigs projection in crown projection change quickly.Therefore,a statistic relation in a quadratic polynomial form between the 2 series of LAI data was well fitted. This relation can be used for a more accurate estimation of LAI based on the data read from the easilyused canopy scanners like LAI-2000.展开更多
文摘In order to test the accuracy of the usually-used fixed calibration factor of the canopy scanner of LAI-2000 for measuring the leaf area index(LAI),a Larix principis-rupprechtii plantation was chosen in the small watershed of Xiangshuihe located at the Liupan Mountains of Ningxia Hui Autonomous Region of NW China,the LAI was measured in October 2010,a period from full canopy to the total fall of needles,by using both the LAI- 2000 and litterfall collection method.Then,a comparison was made between the LAI values determined by the litter-fall collection and that calculated based on the figures read from LAI-2000 and the fixed calibration factor(1.49).It showed that the average of LAI measurements of the 2 methods was very close,with a difference of only 5%.However,the calculated LAI from LAI-2000 was obviously higher than the true values determined by litter-fall collection when the canopy was full of needles;and obviously lower than the true value when the canopy was sparse after needle falling.The reason may be that LAI-2000 takes the projection of twigs as needles.So,a dynamic calibration factor is needed,especially in the seasons when the needle amount and the percentage of twigs projection in crown projection change quickly.Therefore,a statistic relation in a quadratic polynomial form between the 2 series of LAI data was well fitted. This relation can be used for a more accurate estimation of LAI based on the data read from the easilyused canopy scanners like LAI-2000.
