Integrated Monitoring of Ice in Selected Swiss Lakes (GCOS Swiss)
Lake ice plays an essential role in the physical, chemical, and biological processes of freshwater systems (e.g., it influences vertical mixing), and it also has many economic implications (e.g., for hydroelectricity, transportation, winter tourism). Lakes featuring a seasonal cycle of ice cover, such as break-up and freeze-up, represent a major component of the terrestrial landscape and variability and trends in their seasonal pattern represent robust and direct indicators of climate change [Latifovic and Pouliot, 2007; Brown and Duguay, 2010]. Despite its robustness as an indicator of climate change and the recognized importance of monitoring lake ice, ground-based observational recordings of lake ice freeze-up, break-up and ice thickness have dramatically declined since the 1980s [Lenormand et al., 2002; Jeffries et al., 2012].
Satellite images provide a powerful alternative means for detecting and measuring the ice cover on lakes. Remote sensing systems with different temporal and spatial resolution have been successfully used to collect recordings of the timing of lake ice phenological events (e.g., freeze-up and break-up) and increase the spatial and temporal coverage of ground-based observations. Therefore, MeteoSwiss in the framework of GCOS(Global Climate Observing System) Switzerland initiated the project “Integrated Monitoring of Ice in Selected Swiss Lakes” that uses and compares satellite images from various sensors and different approaches to perform investigations aimed at integrated monitoring of lake ice in Switzerland and contributing to the collection of lake ice phenology recordings. Furthermore, the use of WEBCAMs for validation and for independent estimation of lake ice will be investigated and in-situ measurements are carried out to characterize the development of the temperature profiles before freezing and under the ice-cover until thawing. Within the framework of this project, the Remote Sensing Research Group of the University of Bern (RSGB) utilizes data acquired in the fine-resolution imagery (I) bands (1–5) of the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor that is mounted onboard the SUOMI-NPP. Compared to AVHRR and MODIS the combination of the high temporal resolution (~2 times per day) with the reasonable spatial resolution (375 m) of the thermal I-channel of the VIIRS sensor (I05) is an advantage for retrieving lake ice phenology dates. As the VIIRS instrument is equipped with one broad-band thermal I-channel, a single-channel LSWT retrieval algorithm is employed to correct for the atmospheric influence. The single channel algorithm applied in this study is a physical mono-window (PMW) model based on the Radiative Transfer for the Television Infrared Observation Satellite Operational Vertical Sounder code (RTTOV) [Duguay-Tetzlaff et al., 2015]. The ice-on/off dates are obtained by applying a threshold method on the LSWT retrievals and NIR reflectance values. A simplified flowchart of the approach is included on the poster below. Further details about the GCOS project and the partners can be found here (Link project page).
Brown, L. C., and C. R. Duguay (2010), The response and role of ice cover in lake-climate interactions, Prog. Phys. Geogr., 34(5), 671–704, doi:10.1177/0309133310375653.
Duguay-Tetzlaff, A., V. A. Bento, F. M. Göttsche, R. Stöckli, J. P. A. Martins, I. Trigo, F. Olesen, J. S. Bojanowski, C. da Camara, and H. Kunz (2015), Meteosat Land Surface Temperature Climate Data Record: Achievable Accuracy and Potential Uncertainties, Remote Sens., 7(10), 13139–13156, doi:10.3390/rs71013139.
Jeffries, M. O., K. Morris, and C. R. Duguay (2012), Floating ice: lake ice and river ice, in Satellite Image Atlas of Glaciers of the World – State of the Earth’s Cryosphere at the Beginning of the 21st Century: Glaciers, Global Snow Cover, Floating Ice, and Permafrost and Periglacial Environments, edited by R. S. Williams and J. G. Ferrigno, pp. A381–A424, U.S. Geological Survey Professional Paper 1386-A.
Latifovic, R., and D. Pouliot (2007), Analysis of climate change impacts on lake ice phenology in Canada using the historical satellite data record, Remote Sens. Environ., 106(4), 492–507, doi:10.1016/j.rse.2006.09.015.
Lenormand, F., C. R. Duguay, and R. Gauthier (2002), Development of a historical ice database for the study of climate change in Canada, Hydrol. Process., 16(18), 3707–3722, doi:10.1002/hyp.1235.