Browsing by Subject "lumi"

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  • Metsämäki, Sari (Suomen ympäristökeskus, 2013)
    Monographs of the Boreal Environment Research 43
    This thesis focuses on the determination of fractional snow cover (FSC) from optical data provided by satellite instruments. It describes the method development, starting from a simple regionally applicable linear interpolation method and ending at a globally applicable, semi-empirical modeling approach. The development work was motivated by the need for an easily implementable and feasible snow mapping method that could provide reliable information particularly for forested areas. The contribution of the work to the optical remote sensing of snow is mainly associated with accounting for boreal forest canopy effect to the observed reflectance, thus facilitating accurate fractional snow retrievals also for ground beneath the tree canopies. The first proposed approach was based on a linear interpolation technique, which relies on a priori known reference reflectances at a) full snow cover and b) snow-free conditions for each calculation unit-area. An important novelty in the methodology was the utilization of a forest sparseness index determined from AVHRR reflectance data acquired at full dry snow cover conditions. This index was employed to describe the similarity between different unit-areas. In practice, the index was used to determine the reference reflectances for such unit-areas for which the reflectance level could not be determined otherwise, e.g. due to frequent cloud cover. This approach was found to be feasible for Finnish drainage basins characterized by fragmented landscape with moderate canopies. Using a more physical approach instead of linear interpolation would allow the model parameterization using physical quantities (reflectances), and would therefore leave space for further model developments based on measuring and/or modeling of these quantities. The semi-empirical reflectance model-based method SCAmod originates from radiative transfer theory and describes the scene-level reflectance as a mixture of three major constituents: opaque forest canopy, snow and snow-free ground, which are interconnected through transmissivity and snow fraction. Transmissivity, in turn, can be derived from reflectance observations under conditions that highlight the presence of forest canopy, namely the presence of full snow cover on the ground. Thus, SCAmod requires a priori information on transmissivity, but given that it can be determined with the appropriate accuracy, it enables consideration of the obstructing effects of forests in fractional snow estimation. In continental-scale snow mapping, determination of the transmissivity map becomes a key issue. The preliminary demonstration of transmissivity generation using global land cover data was a part of this study. The first implementations and validations for SCAmod were presented for AVHRR data at Finnish drainage basin scale. In subsequent work, determination of the feasible reflectance constituents was addressed, followed by a sensitivity analysis targeting at selection of optimal spectral bands to be applied with SCAmod. Feasibility of the NDSI-based approach in FSC-retrievals over boreal forests is also discussed. Finally, the implementations and validations for MODIS and AATSR data are presented. The results from relative (using high-resolution Earth Observation data to represent the truth) and absolute validation (using in situ observations) indicate a good performance for both forested and non-forested regions in northern Eurasia. Accounting for the effect of forest canopy in the FSC-retrievals is the key issue in snow remote sensing over boreal regions; this study provides a new contribution to this research field and provides one solution for continental scale snow mapping.
  • Niittynen, Pekka; Heikkinen, Risto K.; Luoto, Miska (2020)
    Proceedings of the National Academy of Sciences of the United States of America 117: 35, 21480-21487
    The Arctic is one of the least human-impacted parts of the world, but, in turn, tundra biome is facing the most rapid climate change on Earth. These perturbations may cause major reshuffling of Arctic species compositions and functional trait profiles and diversity, thereby affecting ecosystem processes of the whole tundra region. Earlier research has detected important drivers of the change in plant functional traits under warming climate, but studies on one key factor, snow cover, are almost totally lacking. Here we integrate plot-scale vegetation data with detailed climate and snow information using machine learning methods to model the responsiveness of tundra communities to different scenarios of warming and snow cover duration. Our results show that decreasing snow cover, together with warming temperatures, can substantially modify biotic communities and their trait compositions, with future plant communities projected to be occupied by taller plants with larger leaves and faster resource acquisition strategies. As another finding, we show that, while the local functional diversity may increase, simultaneous biotic homogenization across tundra communities is likely to occur. The manifestation of climate warming on tundra vegetation is highly dependent on the evolution of snow conditions. Given this, realistic assessments of future ecosystem functioning require acknowledging the role of snow in tundra vegetation models.
  • Soveri, Jouko (National Board of Waters and the Environment, Vesi- ja ympäristöhallitus, 1991)
    Publications of the Water and Environment Research Institute 8, 29-48
  • Borg, L. E. T. (Suomen metsätieteellinen seura, 1936)
  • Päivänen, Juhani (Suomen metsätieteellinen seura, 1973)
  • Korhonen, Johanna (Suomen ympäristökeskus, 2007)
    Suomen ympäristö 44/2007
    Hydrologinen vuosikirja 2001–2005 sisältää yleiskatsaukset vuosien 2001–2005 hydrologisiin oloihin Suomessa sekä taulukoita ja kaavioita hydrologisten muuttujien vuorokausi- tai kuukausikeskiarvoista kyseisinä vuosina. Vertailutietoina on keski- ja ääriarvoja kausille 1961–1990 ja 1991–2005. Jaksoille määritetyt keskiarvot poikkeavat monissa tapauksissa toisistaan, koska 1990-luku ja 2000-luvun alku mm. olivat aiempia vuosikymmeniä lämpimämpiä. Taulukoissa kuvaillaan myös havaintopaikkoja. Ennen kunkin hydrologisen muuttujan havaintotaulukkoa on kuvaus muuttujan havainnointi- tai määritystavasta sekä havaintoverkkojen laajuudesta, eräissä tapauksissa myös havaintopaikkakartta. Yhteenvetoja esitetään seuraavista muuttujista: vedenkorkeus, virtaama, pienten alueiden valuma, aluesadanta (mittarivirheiden suhteen korjaamattomat arvot), lumipeitteen vesiarvon aluearvo, haihdunta Class A -astioista, avoveden pintalämpötila, järvien jäätyminen ja jäänlähtö, jään paksuus, pohjaveden pinnankorkeus sekä lumen ja roudan syvyys.
  • Mustonen, Seppo E. (Suomen metsätieteellinen seura, 1965)
  • Kärnä, Juha-Petri (Finnish Environment Institute, 2012)
    The Finnish Environment 12/2012
    Current remote sensing satellites can provide valuable information relevant to hydrological monitoring. And by using available in situ measurements together with the satellite data the information can be even more valuable. The FloodFore project developed new methods to estimate hydrological parameters from multi source remote sensing and in situ data. These hydrological parameters are important input to the watershed simulation model in order to improve the accuracy of its forecasts. In the project several new methods were either developed or demonstrated: satellite based snow water equivalent (SWE) estimation, weather radar based accumulated precipitation estimation, satellite based soil freezing state determination, and SWE estimation with high spatial resolution using both microwave radiometer and SAR data. Also a visualisation system for multi source information was developed to demonstrate the new products to users. The effect of the snow remote sensing estimates to the hydrological forecasting accuracy was studied for the Kemijoki river basin. The commercialisation possibilities of the results of the project were also studied.
  • Soveri, Jouko (National Board of Waters and the Environment, Vesi- ja ympäristöhallitus, 1991)
    Publications of the Water and Environment Research Institute 8, 3-28
  • Soveri, Jouko (National Board of Waters and the Environment, Vesi- ja ympäristöhallitus, 1991)
    Publications of the Water and Environment Research Institute 8, pp. 49-66
  • Soveri, Jouko (Vesihallitus. National Board of Waters, 1985)
    Vesientutkimuslaitoksen julkaisuja 63
    Sulamisen vaikutus pohjaveden määrään ja laatuun Suomen kvartäärimuodostumissa
  • Metsämäki, Sari; Pulliainen, Jouni; Salminen, Miia; Luojus, Kari; Wiesmann, Andreas; Solberg, Rune; Böttcher, Kristin; Hiltunen, Mwaba; Ripper, Elisabeth (2014)
  • Kuusisto, Esko (Vesihallitus, 1973)
    Vesihallitus. Tiedotus 46
    English summary: On snowmelt and water balance during snowmelt period in Pääjärvi representative basin in 1970-72
  • Kuittinen, Risto (Vesihallitus, 1979)
    Vesihallitus. Tiedotus 185
  • Kubin, Eero (Suomen metsätieteellinen seura, 1990)
  • Rekolainen, Seppo; Verta, Matti; Järvinen, Olli (Vesihallitus. National Board of Waters, 1986)
    Vesientutkimuslaitoksen julkaisuja 65, 3-10
    Sadeveden ja lumen elohopeapitoisuus Suomessa 1983—1984
  • Yli-Vakkuri, Paavo (Suomen metsätieteellinen seura, 1960)
  • Silvennoinen, Unto; Haarlaa, Rihko (Suomen metsätieteellinen seura, 1971)
    Manninen, Terhikki; Roujean, Jean-Louis (Ilmatieteen laitos, 2014)
    Raportteja - Rapporter - Reports 2014:7
  • Kuusisto, Esko (Vesihallitus. National Board of Waters, 1984)
    Vesientutkimuslaitoksen julkaisuja 55
    Lumipeitteen kertyminen ja sulaminen Suomessa