We have
been lacking a spectral database on boreal tree species for a long time. Most
data available have been measured for North American species or for ‘mats of
needles’ i.e. not for single needles. Another problem has been that the
previous spectral databases lack a detailed description of the structural and
biochemical properties of the tree leaves and needles needed in many
ecophysiological applications.
Collecting samples in the forest with 16-meter long scissors.
Finally, to fill the large gap in our knowledge, Petr et al. toiled in Hyytiälä last
summer for several weeks measuring the optical
properties of the most common (and nearly only..) tree species in Finland:
Scots pine, Norway spruce and Silver birch. Measuring the reflectance and transmittance of
single needles is really tough due to their small size and twisted shape. There
are no commercial gear available and in-house solutions have to be developed
for holding the small samples. The task was further complicated by our
ambitious plans: we wanted (whenever possible) to measure separate the adaxial
and abaxial sides of the foliage elements and both for shaded and sunlit crown
positions.
Yes, it
does take a lot of patience and a peaceful lab environment to prepare the
samples for the spectroradiometer (and other) measurements. Another challenge
was acting very quickly: the needles are, after all, alive and their spectra
may begin to change if they have been detached from the branch for a long time.
Quick fingers (accustomed to needle work or playing a musical instrument) were
definitely an asset in operating the tweezers. Bare fingers were not, of
course, allowed to touch the samples and contaminate them.
Detaching young and very soft spruce needles for spectral measurements.
The hard
work paid off, and we are now proud to present a carefully measured data set on
the reflectance and transmittance spectra of needles and leaves of boreal tree
species. And just a couple of weeks ago, the paper presenting the data was
published! The data are now freely available and can be downloaded from the
SPECCHIO database.
For more
info, see Petr’s paper:
Lukeš, P., Stenberg, P., Rautiainen, M., Mõttus, M. &
Vanhatalo, K.M. 2013. Optical
properties of leaves and needles for boreal tree species in Europe. Remote
Sensing Letters, 4(7): 667-676.
