Sunday, June 14, 2009


This blog has been too long without a decent Airborne Laser Scanning post. After a few months of laser data processing and one week on an intensive ALS course at Mekrijärvi research station, it is a good time for me to correct this deficiency.

In case that somebody not yet familiar with ALS happens to read this, the idea is that an aircraft equipped with laser scanner and inertia measurement unit flies above a forest area, measuring XYZ coordinates of laser return echoes. This way the 3D-structure of underlying forest can be measured very accurately. Here at University of Joensuu's forest inventory research group, ALS has been the main topic of research since 2004. First Finnish experiment with originally Norwegian area-based laser inventory method started then with the collection of the famous Matalansalo dataset. The idea in this method is that the height distribution of pulses hitting a pre-measured plot can be used to predict predict practically anything, from stem volume and LAI (easy cases) to biodiversity indicators (very difficult). Alternative approach is to detect individual trees in a stand and use allometric models to predict their dimensions, which requires higher pulse density.

Now five years have gone, and forest inventory is going through greatest revolution in its history. Numerous ALS papers have been published during this period, and Joensuu has become one of the leading knowledge centers in this field. Airborne forest inventories have entered commercial stage, first in company and state-owned forests, and next year also first private forest-owners can order a forestry plan that is based on laser inventory. National land survey of Finland has already started gathering data for laser-based elevation model, which will eventually cover entire country. This means that huge amounts of data will be available for practical applications of ALS research.

Personally I've been in great place to see this all happen, but my own start with laser data (which I've had since 2006) has delayed and delayed as other more urgent projects have moved forward. Now I actually feel that I'm a bit late - so many scientific papers concerned with laser measurements of canopy structure have already been published that the remaining job is to figure out how all those studies could be done a little better. Luckily I think I have some new ideas to try... So the last winter months before the yearly travelling season in may-june were quite intensive laser data processing, which will now continue for a few weeks before the start of the holiday season.

Last week's Nova course was certainly one of the highlights of Univ. of Joensuu's ALS history. PhD students and teachers, mostly from the Nordic countries, came together to study basics and more advanced topics of ALS in forestry, and also to have a good time in the peaceful countryside. For me the most interesting part was Ilkka Korpela's photogrammetric/physical approach to ALS, and especially his work with LiDAR-vegetation interactions. I totally agree with his view that also ALS research should next turn to a more physically-based direction, which will however require plenty of work and technological developments. But that's what science is all about - mapping the unknown.

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