Canopy leaf area index for apple tree using hemispherical photography in arid region

• LAI estimation by logarithmic ellipse method was close to direct LAI.
• LAI estimation from hemispherical images using logarithmic ellipse method was accurate even without calibrating clumping index.
• Hemispherical photography can provide reliable canopy parameters for evapotranspiration model.

The hemispherical images of apple orchard were collected using fisheye lens in 2010 and then respectively analyzed by the methods of Bonhom, 2000, 2000G, sphere, ellipse, LAI 2000-3 rings, LAI 2000-4 rings and Miller to obtain leaf area index (LAI), plant area index (PAI), gap fraction, leaf inclination angle and clumping index in an arid region of northwest China. Results show that during DOY (day of year) 202–237 (at flourish stage), the estimated LAI by logarithmic ellipse method and PAI by LAI 2000-4 rings method were 1.96 and 1.95 m2 m−2, respectively, which were close to the direct LAI (1.85 m2 m−2). However, the direct LAI was higher than the estimated LAI from ellipse method of Hemiview (1.59 m2 m−2) and lower than the estimated PAI from gap fraction analysis method of Photoshop (2.67 m2 m−2). Thus the methods of logarithmic ellipse and the LAI 2000-4 rings were used to estimate the LAI (PAI) from hemispherical images. And the estimated LAI by the methods of logarithmic ellipse and the LAI 2000-4 rings were used to analyze seasonal variations of canopy parameters. LAI increased rapidly at leaf expanding stage and then maintained at high level from the vigorous to harvest stage. Canopy gap fraction in the south side was similar to that in the north side. The leaf inclination angle tended horizontally to receive more radiation with the development of apple growth. In addition, the estimated LAI from hemispherical images using the methods of logarithmic ellipse and LAI 2000-4 rings was accurate even without calibrating clumping index. Thus the estimated canopy parameters from hemispherical images using the methods of logarithmic ellipse and LAI 2000-4 rings can be used for the modeling of evapotranspiration.