Mes principaux intérêts scientifiques portent sur la compréhension des altérations dans les interactions entre la biosphère et l'atmosphère en réponse aux changements environnementaux mondiaux, utilisant des mesures par exemple : des mesures de covariance des turbulences), la télédétection (satellite et près de la surface) et les techniques de modélisation. Je suis également intéressé par la mesure locale et la cartographie (régionale, mondiale) des paramètres biophysiques pour étudier les changements dans la structure, le fonctionnement et la phénologie des écosystèmes terrestres.

Ma formation initiale est en hydrogéologie (maîtrise de l'Université de Karlsruhe, Allemagne). Après l'obtention de ma maîtrise en 2001, j'ai travaillé pour une entreprise d'arpentage et j'ai étudié pour obtenir une deuxième maîtrise en systèmes et sciences d'information géographique (l'Université de Salzburg, Autriche, en 2003). En 2004, j'ai quitté l'Europe pour le Canada pour commencer un doctorat en géographie physique à l'Université de Toronto. Sous la direction du Dr Jing Chen, j'ai abordé les questions liées à l'influence de la topographie sur les échanges de gaz à effet de serre des tourbières boréales. Après l'obtention de mon doctorat en 2008, j'étais un postdoctorant à l'Université de Californie Berkeley (2008-2010) où j'ai travaillé sur une variété de questions liées à l'hydrologie, la biogéochimie et l'écophysiologie des écosystèmes méditerranéens.

Avant de joindre le Département de géographie de l'Université de Montréal en septembre 2011, j'étais un postdoctorant avec Dr Andrew Richardson à l'Université de Harvard (2010-2011) où j'ai effectué des recherches sur la phénologie des forêts en Nouvelle-Angleterre, en utilisant des mesures de covariance des turbulences et de laps de temps en photographie. À l'Université de Montréal, mes recherches portent sur l'hydrologie, la biogéochimie et l'écophysiologie des tourbières dans des zones où le sol est gelé de façon permanente (pergélisol).

*Membres de mon groupe de recherche.

1. Quinton, W.L., Berg, A.A., Braverman, M. et al. incl. Sonnentag, O. (in review), A synthesis of three decades of eco-hydrological research at Scotty Creek, NWT, Canada.
2. Natalo, S.M., Watts, J.D., Potter, S. et al. incl. Sonnentag, O. (in review), Substantial winter carbon dioxide losses shift the Arctic to a carbon source under current and future climates. 
3. Knox, S.H., Jackson, R.B., Poulter, B. et al. incl. Sonnentag, O. (in review), FLUXNET-methane synthesis activity: objectives, observations, and future directions.
4. Stone, L., Fang, X., Hayes, K. et al. incl. Sonnentag, O. (in review), Modelling the effects of permafrost loss on discharge from a wetland-dominated basin in the discontinuous permafrost zone in northwestern Canada.
5. Eitel, J.U.H., Maguire, A., Boelman, N. et al. incl. Sonnentag, O. (in revision), Remotely sensing tree physiology at the northern treeline: Do late-season changes in the photochemical reflectance index respond to climate or photoperiod? Remote Sensing of Environment.
6. Gielen, B., Op de Beeck, M., Acosta, N. et al. incl. Sonnentag, O. (accepted), Ancillary vegetation measurements at ICOS ecosystem stations. International Agrophysics.
7. Franz, D., Acosta, M., Altimir, N. et al. incl. Sonnentag, O. (accepted), Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe's terrestrial ecosystems. International Agrophysics. 
8. *Roy, A., Toose, P., Mavrovic, A., *Pappas, C. et al. incl. Sonnentag, O. (accepted), Use of L-band ground-based radiometers for freeze/thaw retrieval in a boreal forest site. 38th IEEE International Geosciences and Remote Sensing Symposium (IGARSS).
9. Loranty, M.M., Abbott, B.W., Blok, D. et al. incl. Sonnentag, O. (2018), Changing ecosystem influences on soil thermal regimes in northern high-latitude permafrost regions. Biogeosciences, 15, 5287–5313.
10. Mavrovic, A., *Roy, A., Royer, A., Filali, B., Boone, F., *Pappas, C., Sonnentag, O. (2018), Dielectric characterization of vegetation at L-band using an open-ended coaxial probe. Geoscientific Instrumentation, Methods and Data Systems, 7, 195–208.
11. Peichl, M., Gazovic, M., Vermeij, de Goede, E., Sonnentag, O., Limpens, J., Nilsson, M. (2018), Peatland vegetation composition and phenology drive the seasonal trajectory of maximum gross primary production. Scientific Reports, 8, 8012.
12. Peters, R., Fonti, P., Frank, D., Poyatos, R., *Pappas, C. et al. incl. Sonnentag, O. (2018), Quantification of uncertainties in tree sap flow measured with the thermal dissipation method. New Phytologist, 219, 1283-1299.
13. Pisek, J., Buddenbaum, H., Camacho, F. et al. incl. Sonnentag, O. (2018), Data synergy between leaf area index and clumping index from Earth observation products using photon recollision probability theory. Remote Sensing of Environment, 215, 1-6.
14. *Warren, R.K., *Pappas, C., *Helbig, M., Chasmer, L.E., Berg, A.A., Baltzer, J.L., Quinton, W.L., Sonnentag, O. (2018), Minor contribution of overstory transpiration to landscape evapotranspiration in boreal forest peatlands. Ecohydrology, 11, e1975.
15. *Pappas, C., Matheny, A., Baltzer, J.L., Barr, A., Black, T.A., Bohrer, G.A., Detto, M., Maillet, J., *Roy, A., Sonnentag, O., Stephens, J. (2018), Boreal tree hydrodynamics: asynchronous, diverging, yet complementary. Tree Physiology, 38, 953-964.
16. Fisher, J.B., Hayes D.J., Schwalm, C.R. et al. incl. Sonnentag, O. (2018), Missing pieces to modelling the Arctic-Boreal puzzle. Environmental Research Letters, 13, 020202.
17. Filippa, G., Cremonese, E., Migliavacca, M., Galvagno, M., Sonnentag, O., et al. (2018), NDVI derived from near-infrared-enabled digital cameras: applicability across different plant functional types. Agricultural and Forest Meteorology, 249, 275-285.
18. Rapinski, M., *Payette, F., Sonnentag, O., Herrmann, T.M., Royer, M.-J.S., Currier, A., Siegwart Collier, L., Hermanutz, L., Guanish, G. (2018), Listening to Inuit and Naskapi peoples in the eastern Canadian Subarctic: combining local observations with gridded climate data. Regional Environmental Change, 18, 189-203.
19. *Helbig, M., Quinton, W. L., Sonnentag, O. (2017), Warmer spring conditions increase annual methane emissions from a boreal peat landscape with sporadic permafrost. Environmental Research Letters, 12, 115009.
20. *Roy, A., Toose, P., Derksen, C., Rowlandson, T., Berg, A., Lemmetyinen, J., Royer, A., Tetlock, E., Helgason, W., Sonnentag, O. (2017), Spatial variability of L-band brightness temperature during freeze/thaw events over a prairie environment. Remote Sensing, 9, 894-910.
21. *Helbig, M., Chasmer, L., Desai, A., Kljun, N., Quinton, W.L., Sonnentag, O. (2017), Direct and indirect climate change effects on carbon dioxide fluxes in a thawing boreal forest-wetland landscape. Global Change Biology, 23, 3231-3248.
22. Pelletier, N., Talbot, J., Olefeldt, D., Turetsky, M., Blodau, C., Sonnentag, O., Quinton, W. L. (2017), Influence of Holocene permafrost aggradation and thaw on the paleoecology and carbon storage of a peatland complex in northwestern Canada. The Holocene, 27, 1391-1405.
23. *Helbig, M., Chasmer, L., Kljun, N., Quinton, W.L., Treat, C.C., Sonnentag, O. (2017), The positive net radiative greenhouse gas forcing of increasing methane emissions from a thawing boreal forest-wetland landscape. Global Change Biology, 23, 2413-2427.
24. *Roy, A., Toose, P., Derksen, C., Royer, A.,Makrovic, A., et al. incl. Sonnentag, O. (2016), Analysis of L-band brightness temperature response to freeze/thaw in two prairie environments from surface-based radiometer measurements. 36th IEEE International Geosciences and Remote Sensing Symposium (IGARSS), 1667-1670.
25. *Helbig, M., *Wischnewski, K., Kljun, N., Chasmer, L., Quinton, W. L., Detto, M., Sonnentag, O. (2016), Regional cooling and wetting eect of permafrost thaw-induced boreal forest loss in the sporadic permafrost zone. Global Change Biology, 22, 4048 4066.
26. Moore, C., Brown, T., Keenan, T., Duursma, R., et al. incl. Sonnentag, O. (2016), Australian vegetation phenology: new insights from satellite remote sensing and digital repeat photography. Biogeosciences, 17, 5085-5102.
27. *Roy, A., Royer, A., Derksen, C., Langlois, A., Sonnentag, O. (2016), Monitoring boreal and Arctic freeze/thaw with the first year of SMAP brightness temperatures. 14th Specialist Meeting on MICROwave RADiometry and Remote Sensing of the Environment (MICRORAD), 82-84.
28. *Helbig, M., *Wischnewski, K., *Gosselin, G.H., Biraud, S.C., Bogoev, I., Chan, W.S., Euskirchen, E.S., Glenn, A.J., Marsh, P.M., Quinton, W.L., Sonnentag, O. (2016), Addressing a systematic bias in carbon dioxide flux measurements with the EC150 and the IRGASON open-path gas analyzers, Agricultural and Forest Meteorology, 228, 349-359.
29. Hwang, Y., Ryu, Y., Kimm, H., Jiang, C. Lang, M. Sonnentag, O. (2016), Correction for light scattering combined with sub-pixel classification improves estimation of gap fraction from digital cover photography. Agricultural and Forest Meteorology, 222, 32-44. 
30. *Helbig, M., *Pappas, C., Sonnentag, O. (2016), Permafrost thaw and wildfire: equally important drivers of boreal tree cover changes in the Taiga Plains, Canada. Geophysical Research Letters, 43, GL067193.
31. Brown, T.B., Hultine, K., Steltzer, H. et al. incl. Sonnentag, O. (2016), Using phenocams to monitor our changing Earth: towards a global phenocam network. Frontiers in Ecology and the Environment, 14, 84-93. Featured on the cover of the March 2016 issue.
32. *Garon-Labreque, M.-É., Léveillé-Bourret, É., *Higgins, K., Sonnentag, O. (2015), Additions to the Boreal flora of the Northwest Territories with a preliminary vascular flora of Scotty Creek. Canadian Field-Naturalist, 129, 349-367.
33. Connon, R., Quinton, W., Craig, J., *Hanisch, J., Sonnentag, O. (2015), The hydrology of interconnected bog complexes in discontinuous permafrost regions. Hydrological Processes, 29, 3829-4174. 
34. Matthes, J.H., Knox, S.H., Sturtevant, C., Sonnentag, O., Verfaillie, J., Baldocchi, D.D. (2015), Predicting landscape-scale CO2 flux at a pasture and rice paddy with long-term hyper spectral canopy reflectance measurements. Biogeosciences, 12, 4577-4595.
35. Raabe, K., Pisek, J., Sonnentag, O., Annuk, K. (2015), Variations of leaf inclination angle distribution with height over the growing season and light exposure for eight broadleaf tree species. Agricultural and Forest Meteorology, 214-215, 2-11.
36. Detto, M., Asner, G.P., Mueller-Landau, H.C., Sonnentag, O. (2015), Spatial variability in tropical forest leaf area density from multireturn LiDAR and modeling. Journal of Geophysical Research-Biogeosciences, 120, G002774.
37. Toomey, M., Friedl, M.A., Frolking, S., Hufkens, K., Klosterman, S., Sonnentag, O., et al., (2015), Greenness indices from digital cameras predict the timing and seasonal dynamics of canopy-scale photosynthesis. Ecological Applications, 25, 99-115.  
38. Peichl, M., Sonnentag, O., Nilsson, M.B. (2015), Bringing color into the picture - using digital repeat photography to investigate phenology controls of the carbon dioxide exchange in a boreal mire. Ecosystems, 18, 115-131.
39. Talbot, J., Roulet, N.T., Sonnentag, O., Moore, T.R. (2014), Increases in aboveground biomass and leaf area 85  years after drainage in a bog. Botany, 92, 713-721.  
40. Keenan, T.F., Darby, B., Felts, E., Sonnentag, O., Friedl, M.A,, Hufkens, K., O'Keefe, J., Klosterman, S., Munger, J.W., Toomey, M., Richardson, A.D. (2014), Tracking forest phenology and seasonal physiology using digital repeat photography. Ecological Applications, 24, 1478-1489.
41. Macfarlane, C., Ryu, Y., Odgen, G.N., Sonnentag, O. (2014), Digital camera photography: exposed and in the raw. Agricultural and Forest Meteorology, 197, 244-253.
42. Klosterman, S.T., Hufkens, K., Gray, J., Melaas, E., Sonnentag, O., Lavine, I., Mitchell, L., Norman, R., Friedl, M.A., Richardson, A.D. (2014), Evaluating remote sensing of deciduous forest phenology at multiple spatial scales using PhenoCam imagery. Biogeosciences, 11, 4305-4320.
43. Kross, A., Seaquist, J.W., Roulet, N.T., Fernandes, R., Sonnentag, O. (2013), Estimating carbon dioxide exchange rates of contrasting northern peatlands using MODIS satellite data. Remote Sensing of Environment, 137, 234-243.
44. Royer, M.-J.S., Herrmann, T.M., Sonnentag, O., Delusca, K., Fortier, D. (2013), Linking Cree hunters' and scientific observations of changing inland ice and meteorological conditions in the subarctic Eastern James Bay region, Canada. Climatic Change, 199, 719-732.
45. Peichl, M., Sonnentag, O., Wohlfahrt, G., Baldocchi, D.D., Flanagan, L.B., Kiely, G., Galvagno, M., Gianelle, D., Marcolla, B., Pio, C., Migliavacca, M., Jones, M.B., Saunders, M. (2013), Convergence of potential net ecosystem production across contrasting C3 grasslands. Ecology Letters 16, 502-512.
46. Vargas, R., Sonnentag, O., Abramowitz, G., Carrara, A., Correia, A., Kobayashi, D., Papale, D., Pearson, J., Pereira, S., Piao, S., Rambal, S., Baldocchi, D.D. (2013),  Drought influences the accuracy of simulated ecosystem fluxes: a model-data meta-analysis for Mediterranean oak woodlands. Ecosystems 16, 749-764.
47. Pisek, J., Sonnentag, O., Richardson, A.D., Mottus, M. (2013), Is the spherical leaf inclination angle distribution a valid assumption for temperate and boreal tree species? Agricultural and Forest Meteorology, 169, 186-194. Shared lead authorship between J. Pisek and O. Sonnentag.
48. Richardson, A.D., Keenan, T., Migliavacca, M., Ryu, Y., Sonnentag, O., Toomey, M. (2013), Climate change, phenology, and phenological control of vegetation feedbacks to the climate system. Agricultural and Forest Meteorology, 169, 156-173. Invited review.
49. Ryu, Y., Verfaillie, J., MacFarlane, C., Kobayashi, H., Sonnentag, O., Vargas, R., Ma, S., Baldocchi, D.D. (2012), A new approach for continuous observation of leaf area index at ecosystem scale using upward-pointing digital cameras. Remote Sensing of Environment, 126, 116-125.
50. Sonnentag, O., Hufkens, K., Teshera-Sterne, C., Young, A.M., Friedl, M.A., Braswell, B.H., Miliman, T., O'Keefe, J., Richardson, A.D. (2012), Digital repeat photography for phenological research in forest ecosystems. Agricultural and Forest Meteorology, 152, 159-177.
51. Hufkens, K., Richardson, A.D., Friedl, M.A., Keenan, T.F., Sonnentag, O., Bailey, A., O'Keefe, J. (2012), Ecological impacts of a widespread frost event following early spring leaf-out. Global Change Biology, 18, 2365-2377.
52. Migliavacca, M., Sonnentag, O., Keenan, T.F., Cescatti, A., O'Keefe, O., Richardson, A.D. (2012), On the uncertainty of phenological responses to climate change, and implications for a terrestrial biosphere model. Biogeosciences, 9, 2063-2083.