Simple calculation of extinction coefficient of forest stands

✍ Scribed by Anders Lindroth; Kurth Perttu

• Book ID: 102981333
• Publisher: Elsevier Science
• Year: 1981
• Weight: 801 KB
• Volume: 25
• Category: Article
• ISSN: 0002-1571
• DOI: 10.1016/0002-1571(81)90065-0

✦ Synopsis

A method to determine the extinction coefficient without extensive radiation measurements is proposed. The crown density, which is a necessary parameter for estimation of sun path length within the canopy, is determined by the use of an instrument similar to the Cajanus cylinder. Sky obscuration factors (SOF) at different solar elevations are estimated from fish-eye photographs. The photographs are also used to determine the relative amount of completely transparent and completely opaque parts of the canopy. Combination of the results from these investigations makes it possible to calculate the extinction coefficient. The calculations are tested against measurements of short-wave radiation above 'and below a Scots pine canopy. For a sparse stand such as this, the calculations are quite sensitive to the determination of SOF. At ground level 35% of the radiation comes through the obstructed part of the canopy when the solar elevation is 45 ° .