Airborne measurements of surface albedo and leaf area index of
snow-covered boreal forest
Abstract
Helicopter based simultaneous measurements of broadband surface albedo
and the effective leaf area index (LAIeff) were
carried out in subarctic area of Finnish Lapland in spring 2008, 2009
and 2010 under varying illumination and snow cover conditions. Vertical
profile measurements show that the found relationship between albedo and
LAIeff seems to be rather independent of the
flight altitude and therefore the footprint scale. Actually, flights
above 500 m in altitude revealed low variations of the surface albedo
approaching an aerial average at 1 km, meaning that a footprint of 20 km
is representative of the landscape. The albedo was in the area beta
distributed and without LAIeff values below 0.25
the average albedo value of the area would decrease from 0.49 to 0.44
showing the albedo sensitivity to sparse vegetation. The results agreed
with the photon recollision probability based model PARAS and the MODIS
satellite albedo product MCD43A3. However, differences between satellite
based and airborne albedo values were noticed, which could be explained
by a difference in footprint size and/or the strong local heterogeneity
as certain flights were operated on specific targets.