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.

Friday, June 5, 2009

Field work

We started our field work season on May 14th. Eeva has stayed at Hyytiälä since then, others have visited twice. This week has been our "intensive" measurement campaign, and we've been able to produce at least a few spectra, tree coordinates, hemispherical images and LAI-2000 readings.

Lauri hugging trees and Pola giving out instructions.

Measuring tree variables and coordinates.
Time for (another) coffee break.

Calibrating our camera at Tartu Observatory.

The night shift.

Establishing plots.

& checking

Eeva learning
to use the camera
- four

Wednesday, June 3, 2009

Estonian-Finnish vegetation remote sensing seminar

During the last four years, I've had several chances to visit my friends in Tartu. There have been courses, recreational trips, and like this time, scientific seminars. Tartu is a beautiful city and always worth a vist, even though getting there means way too early wake-ups and traveling well around the clock by foot, train, ferry, taxi, and bus. The world is just too far away from Joensuu.

This year the Estonian-Finnish vegetation remote sensing seminar started with two UAV presentations. It seems that these remotely controlled mini aircrafts will become very useful in small-scale remote sensing. Jouni and Juha from FGI even arranged a show flight with their helicopter just in front of the university main building, which attracted some interested audience also from passers-by. In a nearby park we found more space, so also an aerial group photo of the seminar participants could be taken.

Image by Juha Suomalainen

The seminar continued with radiative transfer session, which have always been a bit too physical to my understanding... But after the lunch there were several less theoretic but just as interesting presentations, including Mait's new method for hemispherical image analysis, Terhikki's winter LAI flights at Sodankylä, and also my own laser scanning stuff in a traditional Joensuu style. The day ended with an evening party with sauna, excellent fruit board, and lots of chocolate.

Next day I, Janne and Eeva visited Tartu observatory to participate in the calibration of our LAI camera. Determination of lens distortion and vignetting functions was done very carefully - actually I was quite stunned by the level of precision (=calculating individual photons) in which physicists can (and bother to) do these things. After that was done we had free time, and ended the night by celebrating Barcelona's UCL victory together with Tartu's seven Barca fans that crowded the streets at midnight. But the morning started with a long return back to normal routines: bus, taxi, ferry...