Browsing by Subject "satelliittikuvaus"

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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.
  • Väisänen, Rauno; Heliövaara, Kari (The Society of Forestry in Finland - The Finnish Forest Research Institute, 1994)
    The presence/absence data of twenty-seven forest insect taxa (e.g. Retinia resinella, Formica spp., Pissodes spp., several scolytids) and recorded environmental variation were used to investigate the applicability of modelling insect occurrence based on satellite imagery. The sampling was based on 1800 sample plots (25 m by 25 m) placed along the sides of 30 equilateral triangles (side 1 km) in a fragmented forest area (approximately 100 km2) in Evo, S Finland. The triangles were overlaid on land use maps interpreted from satellite images (Landsat TM 30 m multispectral scanner imagery 1991) and digitized geological maps. Insect occurrence was explained using either environmental variables measured in the field or those interpreted from the land use and geological maps. The fit of logistic regression models varied between species, possibly because some species may be associated with the characteristics of single trees while other species with stand characteristics. The occurrence of certain insect species at least, especially those associated with Scots pine, could be relatively accurately assessed indirectly on the basis of satellite imagery and geological maps. Models based on both remotely sensed and geological data better predicted the distribution of forest insects except in the case of Xylechinus pilosus, Dryocoetes sp. and Trypodendron lineatum, where the differences were relatively small in favour of the models based on field measurements. The number of species was related to habitat compartment size and distance from the habitat edge calculated from the land use maps, but logistic regressions suggested that other environmental variables in general masked the effect of these variables in species occurrence at the present scale.
  • Varjo, Jari (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    A method was developed for relative radiometric calibration of single multitemporal Landsat TM image, several multitemporal images covering each others, and several multitemporal images covering different geographic locations. The radiometricly calibrated difference images were used for detecting rapid changes on forest stands. The nonparametric Kernel method was applied for change detection. The accuracy of the change detection was estimated by inspecting the image analysis results in field. The change classification was applied for controlling the quality of the continuously updated forest stand information. The aim was to ensure that all the manmade changes and any forest damages were correctly updated including the attribute and stand delineation information. The image analysis results were compared with the registered treatments and the stand information base. The stands with discrepancies between these two information sources were recommended to be field inspected.
  • 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.
  • Neumann, Thomas; Koponen, Sampsa; Attila, Jenni; Brockmann, Carsten; Kallio, Kari; Kervinen, Mikko; Mazeran, Constant; Müller, Dagmar; Philipson, Petra; Thulin, Susanne; Väkevä, Sakari; Ylöstalo, Pasi (Copernicus, 2021)
    Geoscientific model development 14: 8, 5049-5062
    Colored dissolved organic matter (CDOM) in marine environments impacts primary production due to its absorption effect on the photosynthetically active radiation. In coastal seas, CDOM originates from terrestrial sources predominantly and causes spatial and temporal changing patterns of light absorption which should be considered in marine biogeochemical models. We propose a model approach in which Earth Observation (EO) products are used to define boundary conditions of CDOM concentrations in an ecosystem model of the Baltic Sea. CDOM concentrations in riverine water derived from EO products serve as forcing for the ecosystem model. For this reason, we introduced an explicit CDOM state variable in the model. We show that the light absorption by CDOM in the model can be improved considerably in comparison to approaches where CDOM is estimated from salinity. The model performance increases especially with respect to spatial CDOM patterns due to the consideration of single river properties. A prerequisite is high-quality CDOM data with sufficiently high spatial resolution which can be provided by the new generation of ESA satellite sensor systems (Sentinel 2 MSI and Sentinel 3 OLCI). Such data are essential, especially when local differences in riverine CDOM concentrations exist.
  • Tomppo, Erkki (The Society of Forestry in Finland - The Finnish Forest Research Institute, 1992)
    The taxation of forests in Finland is based on the average productivity of sites. Two operative forest site class estimation methods were developed using satellite images for an area in S. Finland.
  • Häme, Tuomas (The Society of Forestry in Finland - The Finnish Forest Research Institute, 1991)
    A study was made of the spectral characteristics of sudden changes occurring in a 40x40 km forest in S. Finland in 1984-87 using satellite scanner images (Landsat Thematic Mapper and Spot images and spectroradiometer measurements). Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) were the most common tree species. The changes were (1) clear felling, (2) selective thinning, (3) site preparation on clear felled areas, (4) weeding of deciduous shrubs and/or thinning of conifer seedling regeneration, (5) damage caused by the fungus Gremmeniella abietina and (6) deciduous shrub growth in regeneration areas. A computer model of spectral characteristics was developed and compared with the empirical data. G. abietina damage increased the reflectance in the visible part of the light spectrum and decreased the reflectance in the rear infrared part. Near infrared reflectance was reduced after thinning. A system for automated monitoring of changes is presented.