ABSTRACT:There is a growing demand for unmanned aerial systems as autonomous surveillance, exploration and remote sensing solutions. Among the key concerns for robust operation of these systems is the need to reliably navigate the environment without reliance on global navigation satellite system (GNSS). This is of particular concern in Defence circles, but is also a major safety issue for commercial operations. In these circumstances, the aircraft needs to navigate relying only on information from on-board passive sensors such as digital cameras. An autonomous feature-based visual system presented in this work offers a novel integral approach to the modelling and registration of visual features that responds to the specific needs of the navigation system. It detects visual features from Google Earth † to build a feature database. The same algorithm then detects features in an on-board cameras video stream. On one level this serves to localise the vehicle relative to the environment using Simultaneous Localisation and Mapping (SLAM). On a second level it correlates them with the database to localise the vehicle with respect to the inertial frame. The performance of the presented visual navigation system was compared using the satellite imagery from different years. Based on comparison results, an analysis of the effects of seasonal, structural and qualitative changes of the imagery source on the performance of the navigation algorithm is presented.
The present study addresses the seasonal dynamics of productivity and species composition of the meadow and steppe vegetation communities in Khakassia, determined using the ground-based and satellite data of 2017. The MODIS/Terra satellite data were used to analyze the Normalized Difference Vegetation Index (NDVI) and the Land Surface Water Index (LSWI). The NDVI and LSWI were found to be related to the productivity of the meadow and steppe vegetation. The NDVI increased as the portion of the mesophyte grasses in the grass canopy became larger. The LSWI was higher in the steppe communities, which had lower projective coverage, with spots of bare soil, than in the meadow communities, with their abundant vegetation.
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