Schematic representation of the evolution of satellite sensors and of achievements in forestry and forest study 

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... sensors used for record keeping had a spectacular evolution, especially in the last decade when satellites equipped with sensors that capture images with spatial metric and sub-metric resolutions were launched ( Fig. 1). Satellite remote sensing achievements are closely related to those of satellite sensors that play a key role in taking records. Therefore, satellite remote sensing achievements by launched satellite sensors are beneficial to all sectors of national economy managing natural resources including forestry. They are especially valuable as some remote sensing techniques allow captures in stereoscopic mode. In this respect, analyses can be performed both on single satellite images and stereoscopic images for satellite sensors that have this capability (ASTER, Spot, Ikonos-2). Images taken by optical satellites can be recorded in panchromatic mode (wide range spectral band with high spatial resolution) and in multispectral mode (several bands with narrow width and low spatial resolution). Because of technical reasons it is difficult to make very sensitive sensors with narrow spectral bands, sensors with fine spatial resolution (below 1 meter) operate in the visible range, in enlarged panchromatic mode (about 400 nm). These images allow revealing the limits of forest types, those of tree stands, of clear-cuts, of operating roads, of canopy texture etc. The multispectral mode is more adapted to characterize vegetation and allows canopy density determination, tracking photosynthesis activity, water stress, forest fires etc. The bandwidth of the satellite sensors is generally around 100 nm but some low spatial resolution sensors such as MODIS (500 and 1000 m) show narrow bands (10-30 nm) more adapted to detect biophysical characteristics. Therefore, spectral bands in visible, near infrared and short infrared are used to monitor vegetation. Thermal infrared range is used to study water flows between vegetation and atmosphere, estimation of vegetation canopy evaporation, detection of water stress. For making correct decisions in the forestry sector based on satellite remote sensing data it is necessary to know satellite sensors and their capabilities [13]. The sensors range is wide and, as time goes on, it is diversified. Thus, the satellite sensors that are the most representative and take records used in the forestry sector too, in order to increase spatial resolution are listed as follows. They are: AVHRR (Advanced Very High Resolution Radiometer) ASTER/Advanced Spaceborne Thermal Emission and Reflection Radiometer), MODIS, ALI (Advanced Land Imager), Landsat 5 TM (Thematic Mapper), Landsat 7 ETM + (Enhanced Thematic Mapper Plus), Spot 4 and 5, Ikonos-2, Quickbird-2, Worldview - 2 and GeoEye-2. Each sensor has both advantages and disadvantages in terms of spatial, spectral, radiometric resolution and time, cost and time of capture. Data from sensors are available as raw and processed data, as corrected by atmospheric effects and other effects that cause image distortions. AVHRR-NOAA sensors have been released since June 11, 1978 (NOAA-1) and allow data capture on very large surfaces. Records have one-day time resolution, spectral resolution of 4-5 bands, and spatial resolution of 1.1 km (Local Area Coverage), respectively 4 km (Global Area Coverage). Sensors take images that are used to highlight the limits of land and water, to investigate clouds, snow and ice thickness, recording the beginning of ice or snow melting, nighttime and daytime distribution of clouds, surface temperature distribution of land and water detail. Other applications include evaluation of agricultural land, creating thematic maps of vegetation on large areas [12], mapping fires, and burned areas. Images taken by AVHRR sensors include thermal band of infrared but they lack data on temperature that can be used to estimate evapotranspiration based on energy balance. Due to the records archive that has a long history, the images are very useful to study long-term changes in vegetation. Data are supplied in limited sets and they are provided at a cost of $ 190/georeferenced setting. The disadvantage of using these data in the forestry sector is the poor spatial resolution. MODIS sensors are placed on the Terra satellite, which also carries the sensor ASTER, and on the Aqua satellite. Terra MODIS and ASTER satellites were launched by NASA in 1999. Although Terra ASTER and MODIS sensors are on the same satellite, the temporal resolution of MODIS images is much better than the ASTER images (one day versus 16 days) because the MODIS sensor field of view is larger than the sensor ASTER’s (2300 km 2 versus 60 km 2 ). MODIS images have low spatial resolution (250 m), a spectral resolution in 36 bands and they are free. Because the first seven bands of MODIS sensor were designed to simulate Landsat records, except spatial resolution, users can view MODIS images in the same way as Landsat images. MODIS records are used to classify global vegetation, for biomass estimation, assessment of land degradation, in forest fire monitoring and mapping of areas after fires [8]. MODIS also provides surface temperature and reflectance products enabling ...