25,879 research outputs found
Geometric calibration of Colour and Stereo Surface Imaging System of ESA's Trace Gas Orbiter
There are many geometric calibration methods for "standard" cameras. These
methods, however, cannot be used for the calibration of telescopes with large
focal lengths and complex off-axis optics. Moreover, specialized calibration
methods for the telescopes are scarce in literature. We describe the
calibration method that we developed for the Colour and Stereo Surface Imaging
System (CaSSIS) telescope, on board of the ExoMars Trace Gas Orbiter (TGO).
Although our method is described in the context of CaSSIS, with camera-specific
experiments, it is general and can be applied to other telescopes. We further
encourage re-use of the proposed method by making our calibration code and data
available on-line.Comment: Submitted to Advances in Space Researc
Low cost multimedia sensor networks for obtaining lighting maps
In many applications, video streams, images, audio streams and scalar data are
commonly used. In these fields, one of the most important magnitudes to be collected and
controlled is the light intensity in different spots. So, it is extremely important to be able to
deploy a network of light sensors which are usually integrated in a more general Wireless
Multimedia Sensor Network (WMSN). Light control systems have increasing applications in
many places like streets, roads, buildings, theaters, etc. In these situations having a dense grid
of sensing spots significantly enhances measuring precision and control performance. When a
great number of measuring spots are required, the cost of the sensor becomes a very important
concern. In this paper the use of very low cost light sensors is proposed and it is shown how to
overcome its limited performance by directionally correcting its results. A correction factor is
derived for several lighting conditions. The proposed method is firstly applied to measure light
in a single spot. Additionally a prototype of a sensor network is employed to draw the lighting
map of a surface. Finally the sensor grid is employed to estimate the position and power of a
set of light sources in a certain region of interest (street, building,…). These three applications
have shown that using low cost sensors instead of luxmeters is a feasible approach to estimate
illuminance levels in a room and to derive light sources maps. The obtained error measuring
spots illuminance or estimating lamp emittances are quite acceptable in many practical
applications.Telefonica Chair "Intelligence in Networks" of the University of Seville (Spain
A Comparative Analysis of Phytovolume Estimation Methods Based on UAV-Photogrammetry and Multispectral Imagery in a Mediterranean Forest
Management and control operations are crucial for preventing forest fires, especially in Mediterranean forest areas with dry climatic periods. One of them is prescribed fires, in which the biomass fuel present in the controlled plot area must be accurately estimated. The most used methods for estimating biomass are time-consuming and demand too much manpower. Unmanned aerial vehicles (UAVs) carrying multispectral sensors can be used to carry out accurate indirect measurements of terrain and vegetation morphology and their radiometric characteristics. Based on the UAV-photogrammetric project products, four estimators of phytovolume were compared in a Mediterranean forest area, all obtained using the difference between a digital surface model (DSM) and a digital terrain model (DTM). The DSM was derived from a UAV-photogrammetric project based on the structure from a motion algorithm. Four different methods for obtaining a DTM were used based on an unclassified dense point cloud produced through a UAV-photogrammetric project (FFU), an unsupervised classified dense point cloud (FFC), a multispectral vegetation index (FMI), and a cloth simulation filter (FCS). Qualitative and quantitative comparisons determined the ability of the phytovolume estimators for vegetation detection and occupied volume. The results show that there are no significant differences in surface vegetation detection between all the pairwise possible comparisons of the four estimators at a 95% confidence level, but FMI presented the best kappa value (0.678) in an error matrix analysis with reference data obtained from photointerpretation and supervised classification. Concerning the accuracy of phytovolume estimation, only FFU and FFC presented differences higher than two standard deviations in a pairwise comparison, and FMI presented the best RMSE (12.3 m) when the estimators were compared to 768 observed data points grouped in four 500 m2 sample plots. The FMI was the best phytovolume estimator of the four compared for low vegetation height in a Mediterranean forest. The use of FMI based on UAV data provides accurate phytovolume estimations that can be applied on several environment management activities, including wildfire prevention. Multitemporal phytovolume estimations based on FMI could help to model the forest resources evolution in a very realistic way
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