Ground slope

The Hemisfer software is able to correct for the effect of the slope on the LAI estimation (Schleppi et al., 2007). The slope angle and aspect are either entered directly (in degrees) or changed by clicking on up and down arrows . Before entering the aspect (= azimuth of downhill direction), the position of the north on the picture should be set. Like in geography, the aspect angle is counted from the north (0°) to the east (90°), south (180°), then west (270°). Because the picture is taken upwards, the aspect azimuth is counted here in counter-clockwise direction (the opposite way compared to a map). The position of the soil surface is then displayed as a magenta line on the display. In opposite direction, a magenta dash shows the downhill direction, i.e. the aspect angle.

Notes

1. The method published by Schleppi et al. (2007) results in LAI values expressed by unit of inclined ground. Starting with version 2.1, Hemisfer now gives the slope-corrected LAI per unit of projected (horizontal) surface, which is the general standard. Results from older versions can be converted to this standard by dividing them by the cosine of the slope, cos(ν). Compared to older versions, this increases the effect of slope correction.
2. When a slope is defined, the non-linearity between light transmission and LAI within the rings is automatically corrected, regardless of the corresponding setting in the analysis options.