Innovative satellite remote sensing method enables more accurate forest ecosystem models | Tartu Observatory

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Contacts of UT units

Faculty of Arts and Humanities
Faculty phone: 
+372 737 5341
Faculty address: 
Jakobi 2, rooms 116–121, 51005 Tartu
  • Dean's Office
    Faculty phone: 
    + 372 737 5341
    Faculty address: 
    Jakobi 2, rooms 116–121, 51005 Tartu
  • Institute of History and Archaeology
    Faculty phone: 
    +372 737 5651
    Faculty address: 
    Jakobi 2, 51005 Tartu
  • Institute of Estonian and General Linguistics
    Faculty phone: 
    +372 737 5221
    Faculty address: 
    Jakobi 2, 51005 Tartu
  • Institute of Philosophy and Semiotics
    Faculty phone: 
    +372 737 5314
    Faculty address: 
    Jakobi 2, rooms 309–352, 51005 Tartu
  • Institute of Cultural Research
    Faculty phone: 
    (+372) 737 5223
    Faculty address: 
    Ülikooli 16, 51003 Tartu
  • School of Theology and Religious Studies
    Faculty phone: 
    +372 737 5301
    Faculty address: 
    Ülikooli 18–310, 50090 Tartu
  • College of Foreign Languages and Cultures
    Faculty address: 
    J. Liivi 4, 50409, Tartu
  • Viljandi Culture Academy
    Faculty phone: 
    +372 435 5232
    Faculty address: 
    Posti 1, 71004 Viljandi
Faculty of Social Sciences
Faculty phone: 
+372 737 5957
Faculty address: 
Lossi 36, 51003 Tartu
  • Dean's Office
    Faculty phone: 
    + 372 737 5900
    Faculty address: 
    Lossi 36, 51003 Tartu
  • Institute of Education
    Faculty phone: 
    +372 737 6440
    Faculty address: 
    Salme 1a–29, 50103 Tartu
  • Johan Skytte Institute of Political Studies
    Faculty phone: 
    +372 737 5582
    Faculty address: 
    Lossi 36–301, 51003 Tartu
  • School of Economics and Business Administration
    Faculty phone: 
    +372 737 6310
    Faculty address: 
    Narva mnt 18, 51009 Tartu
  • Institute of Psychology
    Faculty phone: 
    +372 737 5902
    Faculty address: 
    Näituse 2, 50409 Tartu
  • School of Law
    Faculty phone: 
    +372 737 5390
    Faculty address: 
    Näituse 20–324, 50409 Tartu
  • Institute of Social Studies
    Faculty phone: 
    +372 737 5188
    Faculty address: 
    Lossi 36, 51003 Tartu
  • Narva College
    Faculty phone: 
    +372 740 1900
    Faculty address: 
    Raekoja plats 2, 20307 Narva
  • Pärnu College
    Faculty phone: 
    +372 445 0520
    Faculty address: 
    Ringi 35, 80012 Pärnu
Faculty of Medicine
Faculty phone: 
+372 737 5326
Faculty address: 
Ravila 19, 50411 Tartu
  • Dean's Office
    Faculty phone: 
    +372 737 5326
    Faculty address: 
    Ravila 19, 50411 Tartu
  • Institute of Biomedicine and Translational Medicine
    Faculty phone: 
    +372 737 4210
    Faculty address: 
    Biomeedikum, Ravila 19, 50411 Tartu
  • Institute of Pharmacy
    Faculty phone: 
    +372 737 5286
    Faculty address: 
    Nooruse 1, 50411 Tartu
  • Institute of Dentistry
    Faculty phone: 
    +372 731 9856
    Faculty address: 
    Raekoja plats 6, 51003 Tartu
  • Institute of Clinical Medicine
    Faculty phone: 
    +372 737 5323
    Faculty address: 
    L. Puusepa 8, 50406 Tartu
  • Institute of Family Medicine and Public Health
    Faculty phone: 
    +372 737 4190
    Faculty address: 
    Ravila 19, 50411 Tartu
  • Institute of Sport Sciences and Physiotherapy
    Faculty phone: 
    +372 737 5360
    Faculty address: 
    Jakobi 5–205, 51005 Tartu
Faculty of Science and Technology
Faculty phone: 
+372 737 5820
Faculty address: 
Vanemuise 46–208, 51014 Tartu
  • Dean's Office
    Faculty phone: 
    +372 737 5820
    Faculty address: 
    Vanemuise 46–208, 51003 Tartu
  • Institute of Computer Science
    Faculty phone: 
    +372 737 5445
    Faculty address: 
    Narva mnt 18, 51009 Tartu
  • Estonian Marine Institute
    Faculty phone: 
    +372 671 8902
    Faculty address: 
    Mäealuse 14, 12618 Tallinn
  • Institute of Physics
    Faculty address: 
    W. Ostwaldi 1, 50411 Tartu
  • Institute of Chemistry
    Faculty phone: 
    +372 737 5261
    Faculty address: 
    Ravila 14a, 50411 Tartu
  • Institute of Genomics
    Faculty phone: 
    +372 737 4000
    Faculty address: 
    Riia 23b, 51010 Tartu
  • Institute of Mathematics and Statistics
    Faculty phone: 
    +372 737 5860
    Faculty address: 
    Narva mnt 18, 51009 Tartu
  • Institute of Molecular and Cell Biology
    Faculty phone: 
    +372 737 5027
    Faculty address: 
    Riia 23, 23b–134, 51010 Tartu
  • Tartu Observatory
    Faculty phone: 
    +372 737 4510
    Faculty address: 
    Observatooriumi 1, Tõravere, 61602 Tartumaa
  • Institute of Technology
    Faculty phone: 
    +372 737 4800
    Faculty address: 
    Nooruse 1, 50411 Tartu
  • Institute of Ecology and Earth Sciences
    Faculty phone: 
    +372 737 5835
    Faculty address: 
    Vanemuise 46, 51003 Tartu
Institutions
  • Library
    Faculty phone: 
    +372 737 5702
    Faculty address: 
    W. Struve 1, 50091 Tartu
  • Youth Academy
    Faculty phone: 
    +372 737 5581
    Faculty address: 
    Uppsala 10, 51003 Tartu
  • Museum
    Faculty phone: 
    +372 737 5674
    Faculty address: 
    Lossi 25, 51003 Tartu
  • University of Tartu Natural History Museum and Botanical Garden
    Faculty phone: 
    +372 737 6076
    Faculty address: 
    Vanemuise 46, 51003 Tartu
Support Units
  • Administrative Office
    Faculty phone: 
    +372 737 5606
    Faculty address: 
    Ülikooli 18a, 51005 Tartu
  • Centre for Entrepreneurship and Innovation
    Faculty phone: 
    +372 737 4809
    Faculty address: 
    Narva mnt 18, 51009, Tartu
  • University Office in Tallinn
    Faculty phone: 
    +372 737 6600
    Faculty address: 
    Teatri väljak 3, 10143 Tallinn
  • Estates Office
    Faculty phone: 
    +372 737 5137
    Faculty address: 
    Ülikooli 18a, 51005 Tartu
  • Finance Office
    Faculty phone: 
    +372 737 5125
    Faculty address: 
    Jakobi 4, 51005 Tartu
  • Grant Office
    Faculty phone: 
    +372 737 6215
    Faculty address: 
    Raekoja plats 9, 51004 Tartu
  • Information Technology Office
    Faculty phone: 
    +372 737 6000, IT-help: +372 737 5500
    Faculty address: 
    Ülikooli 18a, 51005 Tartu
  • Human Resources Office
    Faculty phone: 
    +372 737 5145
    Faculty address: 
    Ülikooli 18, rooms 302 and 304, 50090 Tartu
  • Internal Audit Office
    Faculty address: 
    Ülikooli 18-244, 51005 Tartu
  • International Cooperation and Protocol Office
    Faculty phone: 
    +372 737 6123
    Faculty address: 
    Ülikooli 18, rooms 104, 301, 305, 50090 Tartu
  • Marketing and Communication Office
    Faculty phone: 
    +372 737 5687
    Faculty address: 
    Ülikooli 18, rooms 102, 104, 209, 210, 50090 Tartu
  • Office of Academic Affairs
    Faculty phone: 
    +372 737 5620
    Faculty address: 
    Ülikooli 18, 50090 Tartu
  • Procurement Office
    Faculty phone: 
    +372 737 6632
    Faculty address: 
    Ülikooli 18a, 51005 Tartu
  • Rector's Strategy Office
    Faculty phone: 
    +372 737 5600
    Faculty address: 
    Ülikooli 18, 50090 Tartu
  • Student Council
    Faculty address: 
    Ülikooli 18b, 51005 Tartu
  • University of Tartu Press
    Faculty phone: 
    +372 737 5945
    Faculty address: 
    W. Struve 1, 50091 Tartu
Other Units
  • University of Tartu Academic Sports Club
    Faculty phone: 
    +372 737 5371
    Faculty address: 
    Ujula 4, 51008 Tartu
  • Tartu Student Village
    Faculty phone: 
    +372 740 9959
    Faculty address: 
    Narva mnt 25, 51013 Tartu
  • Tartu Students’ Club
    Faculty phone: 
    +372 730 2400
    Faculty address: 
    Kalevi 24, 51010 Tartu
  • Tartu University Hospital
    Faculty address: 
    L. Puusepa 1a, 50406 Tartu
  • University of Tartu Foundation
    Faculty phone: 
    +372 737 5852
    Faculty address: 
    Ülikooli 18, 50090 Tartu
  • View all other units

Innovative satellite remote sensing method enables more accurate forest ecosystem models

Jan Pisek, associate professor with the University of Tartu, Tartu Observatory

To evaluate the development of a forest’s ecosystem, forest floor vegetation needs to be monitored consistently. Currently, this kind of data is missing. In the beginning of the year, Jan Pisek, an associate professor with the University of Tartu, Tartu Observatory, published an article in the scientific journal Biogeosciences with his colleagues. The researchers successfully combined past efforts of measuring forest floor parameters with multi-angle satellite remote sensing.

To validate satellite measurements, Pisek and colleagues used data provided by the new ICOS (Integrated Carbon Observation System) research infrastructure (RI), also proving that the usefulness of ICOS RI goes beyond its designated tasks of measuring carbon exchange and greenhouse gases in the environment. 

Forest floor vegetation often excluded from carbon models

The plants growing on the forest floor are one of the most diverse and least understood components of forests worldwide. These plant communities are especially important because they assist in the cycling of nutrients and can influence what happens to the trees and the canopy above. Measuring the appearance of the forest floor (understory), or its reflectance, over time and different locations is important to accurately estimate the parameters of forest canopy, and therefore for ecosystem modelling. However, this reflectance data from different types of forests is currently missing.

Currently, carbon models often treat the forest floor vegetation as an unknown due to the difficulties in measuring it properly and consistently on a larger scale. Remote sensing could be the technology to provide consistent data in this area. Multi-angle satellite-based remote sensing can capture signals of different forest layers because the observed proportions vary with the viewing angle, making it possible to separate the signals from forest canopy and forest floor. 

Understory is clearly visible through the open overstory and has an impact on the top-of-the canopy signal all year round at the ICOS site Bilos-Sales in France. Picture taken on June 14, 2018. Author: Jan Pisek

New approach and promising results

The aim of the study published by Pisek and colleagues was to combine past efforts of tracking forest floor reflectance and its dynamics with multi-angle satellite remote sensing. The approach, originally developed over the Canadian boreal forests within the research group of prof. Jing Ming Chen at the University of Toronto, was validated against in situ understory reflectance measurements over an extended set of ICOS forest ecosystem sites.

The main findings show that the novel modelling method can deliver good results, especially over different forest types with open canopies. The performance of the method was found limited over forests with closed canopies (high foliage cover), where the signal from understory gets hidden. This actually makes sense – the modelling algorithm relies on the condition that at least a small part of the forest floor is seen from different directions through the overstory canopy. If the tree cover is dense and the forest floor cannot be seen from above, the algorithm cannot provide the correct, independent estimation of the understory signal. “I would be actually really concerned if we were still retrieving ‘correct’ understory signal under these conditions of too dense tree cover. The fact that the algorithm indeed fails when it is supposed to fail, helps me to have more confidence in its performance,” Pisek says.

Using ICOS forest ecosystem sites to validate estimations from remote sensing satellites

To validate satellite measurements, Pisek and colleagues used the data from different sites of the ICOS research infrastructure. The mission of ICOS RI is to enable research to understand the greenhouse gas budgets and perturbations in Europe and adjacent regions. ICOS is based on the collection of high-quality observational data by measurement stations operated long-term (15+ years) as national networks in the RI member states.

Not much light reaches the forest floor and understory signal would be greatly reduced due to dense overstory layer at the Hesse ICOS site in France for the most of the growing season. Picture taken on August 18, 2018. Author: Jan Pisek

Estonia currently has a pending membership status with ICOS. Through collaborations carried within the framework of this project, Pisek and colleagues demonstrated commitment and showcased an innovative way how Estonia-based research can make an impact on the ICOS infrastructure and efficiently use it already now. The researchers showed that ICOS forest ecosystem sites can serve as network for validation of pixel resolution Earth observation products.

“The ICOS RI provided an excellent tool for truly comprehensive and efficient validation exercise thanks to the wide variety of forests types represented in the network,” Jan Pisek says.

For the first time, the study also provides comprehensive spatial representativeness assessment of the included ICOS sites across different spatial scales. “We were happy to see that most of the included ICOS forest ecosystem sites are indeed representative and suitable for validation of Earth observation products across different scales,” adds Pisek. Identifying ways how to properly scale and compare the in situ ground-based measurements with satellite measurements is one of the objectives of the SENSECO project, in which Pisek participates.

When the overstory deciduous trees are still leafless, the understory vegetation, taking advantage of ample light reaching the forest floor, can dominate the top-of-canopy signal in the spring. ICOS site Hainich on April 12, 2018. Author: Jan Pisek

Jan Pisek acknowledges support by the Eesti Teadusagentuur (grant nos. PUT1355 and Mobilitas Pluss MOBERC11).

Also read the news story by ICOS.