Application of SunScan canopy analysis system in measuring leaf area index of soybean

SunScan canopy analysis system is an instrument for indirectly measuring leaf area index (LAI). The instrument can give LAI values by measuring the ratio of transmitted radiation through canopy to incident radiation, based on the canopy geometry features described by ellipsoidal leaf angle distribution parameter (ELADP). In 2005 and 2006, the LAI values of soybean plants at the Heshan Farm of Nenjiang County, Heilongjiang Province were measured with LI-3100 LAI apparatus and SunScan canopy analysis system, the ELADP value was calibrated for accurate LAI, and the precision of the LAI values measured by SunScan canopy analysis system was validated. The results showed that the ELADP value for soybean canopy was 4.0, and the LAI values measured by SunScan canopy analysis system were consistent with those measured by LI-3100. The regression correlation of the LAI values measured by the two instruments was significant. During the growth season of soybean, the measurement error of SunScan canopy analysis system had a slight change, i.e., the LAI was underestimated by 7.2% from 50 to 85 days after sowing and overestimated by 12.5% from 96 days after sowing, but close to that measured by LI-3100, with an error of 2.0%. In conclasion, SunScan canopy analysis system could be used to measure the LAI accurately if the ELADP was calibrated for different canopies.