Monday, May 6, 2013

Needle work

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.