Methodology comparison for canopy structure parameters extraction from digital hemispherical photography in boreal forests

Abstract

The retrieval of canopy architectural parameters using off-the-shelf digital cameras with fish-eye lens is investigated. The technique used takes advantage of the sensor's linear response to light of these cameras to improve the estimation of gap fraction using:(1) the digital numbers of mixed sky-canopy pixels to estimate the within-pixel gap fraction; and (2) this process is done considering the variation in view zenith angle to take into account the sky radiance distribution and the canopy multiple scattering effects.The foliage element clumping index is retrieved over a wide range of view zenith angles using:(1) the accumulated gap size distribution theory developed for the TRAC by Chen and Cihlar (1995a); (2) This article is a U.S. government work, and is not subject to copyright in the United States.Using data from Canadian and Russian boreal forests, comparisons of gap fraction, clumping index and plant area index measured with the tracing radiation and architecture of canopies (TRAC) and digital hemispherical photography are presented. Evaluation of the LAI estimated from digital hemispherical photography with allometric LAI of two boreal forest stands suggest that that the clumping index combined method may be more accurate. # 2005 Published by Elsevier B.V.

A simplified methodology for the correction of Leaf Area Index (LAI) measurements obtained by ceptometer with reference to Pinus Portuguese forests

“…Clumping effects accounted for by the LAI-2000 instrument, called the "apparent" clumping index, were dependent on canopy cover, crown shape and canopy height (Ryu et al 2010). The apparent clumping index from LAI-2000 is a clumping correction above the shoot scale, whilst other methods such as TRAC (Chen & Cihlar 1995) and photography can discriminate clumping effects at the shoot scale, therefore exhibiting higher spatial discrimination power (Leblanc et al 2005, Macfarlane et al 2007b, Chianucci & Cutini 2013. Lang & Yuequin (1986) proposed a correction based on log averaging the gap fraction, currently the most widely applied correction for measurements taken by the LAI-2000 ceptometer and photography.…”

“…Lang & Yuequin (1986) proposed a correction based on log averaging the gap fraction, currently the most widely applied correction for measurements taken by the LAI-2000 ceptometer and photography. Leblanc et al (2005) combined this approach with the one from Chen & Cihlar (1995) by tracing radiation and architecture of canopies (TRAC) and photography.…”

Use of a Networked Digital Camera to Estimate Net CO2Uptake of a Desiccation‐Tolerant Moss

“…Hemispherical photography readily lends itself to the use of digital cameras (Leblanc et al 2005), although the technique is primarily concerned with transmitted sun and sky light rather than reflected light from vegetation. Dymond and Trotter (1997) used digital color images of forests and pastures taken from aircraft to determine their reflectance properties, Richardson et al (2001) examined the spectral reflectance of pine needles along an elevational gradient, and Hamerlynck et al (2000) compared surface reflectance to the chlorophyll fluorescence characteristics of the desiccation-tolerant moss Tortula ruralis.…”

Método para estimativa do IAF de árvores isoladas ou de plantações com dossel fechado

“…Dentre os muitos aparelhos comercializados que utilizam modelos que envolvem a fração transmitida de radiação se destacam os sensores quânticos, tais como o "LAI-2000" (LiCor ® ) (Norman & Campbell, 1989;Welles, 1990;Weles & Norman, 1991), o "demon" (Lang et al, 1985), o "ceptômetro" (Welles & Cohen, 1996), os sensores utilizados em fotografias hemisféricas (Rich, 1990;Leblanc et al, 2005;Zhang et al, 2005;Demarez et al, 2008) e os sensores de respostas espectrais (Schlerf et al, 2005;Fuentes et al, 2008;Brantley et al, 2011). As potenciais fontes de erro dos métodos que usam o princípio da transmissão de luz pelo dossel, estão associadas à interceptação da radiação por ramos e troncos, com superestimativa de resultados principalmente em condições de baixo IAF, e à aglomeração de folhas, que fere a pressuposição de distribuição aleatória das folhas no plano de projeção exigida nesse tipo de abordagem (Welles, 1990).…”