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Muinonen K.,University of Helsinki | Muinonen K.,Finnish Geospatial Research Institute FGI | Lumme K.,University of Helsinki
Astronomy and Astrophysics | Year: 2015

Context. The scattering of light by an asteroid's surface depends on the properties of its particles, volume density, and roughness. It is described by the reflection coefficient which, upon integration over the illuminated and observed part of the surface, yields the disk-integrated photometric brightness of the asteroid. The Lommel-Seeliger reflection coefficient is applicable to dark, low-albedo C-class asteroids, with prospects for moderate-albedo S-class and M-class asteroids. Aims. We calculate the disk-integrated brightness for an ellipsoidal asteroid with a Lommel-Seeliger reflection coefficient (LS ellipsoid). Furthermore, we calculate the photocenter for the LS ellipsoid, that is, the distance of the center of light from the barycenter. Methods. Because of their analytical nature, the closed-form expressions can be readily utilized in numerical simulations. Results. We show lightcurves and photocenter variations for realistic examples of ellipsoidal shapes for a number of pole orientations. The results highlight the reciprocity principle of the radiative-transfer theory and suggest a nontrivial dependence of the photocenter on the pole orientation and viewing geometry. Conclusions. Finally, we outline a number of applications and future prospects. © ESO, 2015.

Moreno-Ibanez M.,Institute of Space science CSIC IEEC | Gritsevich M.,Finnish Geospatial Research Institute FGI | Gritsevich M.,Moscow State University of Geodesy and Cartography | Trigo-Rodriguez J.M.,Institute of Space science CSIC IEEC
Icarus | Year: 2015

Despite ablation and drag processes associated with atmospheric entry of meteoroids were a subject of intensive study over the last century, little attention was devoted to interpret the observed fireball terminal height. This is a key parameter because it not only depends on the initial mass, but also on the bulk physical properties of the meteoroids and hence on their ability to ablate in the atmosphere. In this work we have developed a new approach that is tested using the fireball terminal heights observed by the Meteorite Observation and Recovery Project operated in Canada between 1970 and 1985 (hereafter referred as MORP). We then compare them to the calculation made. Our results clearly show that the new methodology is able to forecast the degree of deepening of meteoroids in the Earth's atmosphere. Then, this approach has important applications in predicting the impact hazard from cm- to meter-sized bodies that are represented, in part, in the MORP bolide list. © 2015 Elsevier Inc..

Muinonen K.,University of Helsinki | Muinonen K.,Finnish Geospatial Research Institute FGI | Wilkman O.,University of Helsinki | Cellino A.,National institute for astrophysics | And 2 more authors.
Planetary and Space Science | Year: 2015

We derive initial rotation, shape, and scattering properties for asteroids from sparse and dense photometry based on the so-called Lommel-Seeliger ellipsoid (LS ellipsoid). Due to the analytical disk-integrated brightness, the LS ellipsoid allows for fast rotation-period, pole-orientation, and shape analyses, as well as efficient Markov-chain Monte Carlo solutions (MCMC). We apply the methods to simulated sparse Gaia photometry, as well as to ground-based photometry composed of dense lightcurves. For a specific Gaia simulation, we make use of a numerical reflection coefficient developed for particulate surfaces, and utilize the LS ellipsoid in the inversion of the simulated data. We conclude that, in a majority of cases, initial LS ellipsoid retrieval of the parameters is satisfactory. Finally, we formulate a single-scattering phase function that, for a spherical asteroid, results in the H,G1,G2 photometric phase function. © 2015.

Hakala T.,Finnish Geospatial Research Institute FGI | Nevalainen O.,Finnish Geospatial Research Institute FGI | Kaasalainen S.,Finnish Geospatial Research Institute FGI | Makipaa R.,Finnish Forest Research Institute
Biogeosciences | Year: 2015

We present an empirical application of multispectral laser scanning for monitoring the seasonal and spatial changes in pine chlorophyll (a + b) content and upscaling the accurate leaf-level chlorophyll measurements into branch and tree level. The results show the capability of the new instrument for monitoring the changes in the shape and physiology of tree canopy: the spectral indices retrieved from the multispectral point cloud agree with laboratory measurements of the chlorophyll a and b content. The approach opens new prospects for replacing destructive and labour-intensive manual sampling with remote observations of tree physiology. © Author(s) 2015.

Matikainen L.,Finnish Geospatial Research Institute FGI | Hyyppa J.,Finnish Geospatial Research Institute FGI | Litkey P.,Finnish Geospatial Research Institute FGI
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives | Year: 2016

During the last 20 years, airborne laser scanning (ALS), often combined with multispectral information from aerial images, has shown its high feasibility for automated mapping processes. Recently, the first multispectral airborne laser scanners have been launched, and multispectral information is for the first time directly available for 3D ALS point clouds. This article discusses the potential of this new single-sensor technology in map updating, especially in automated object detection and change detection. For our study, Optech Titan multispectral ALS data over a suburban area in Finland were acquired. Results from a random forests analysis suggest that the multispectral intensity information is useful for land cover classification, also when considering ground surface objects and classes, such as roads. An out-of-bag estimate for classification error was about 3% for separating classes asphalt, gravel, rocky areas and low vegetation from each other. For buildings and trees, it was under 1%. According to feature importance analyses, multispectral features based on several channels were more useful that those based on one channel. Automatic change detection utilizing the new multispectral ALS data, an old digital surface model (DSM) and old building vectors was also demonstrated. Overall, our first analyses suggest that the new data are very promising for further increasing the automation level in mapping. The multispectral ALS technology is independent of external illumination conditions, and intensity images produced from the data do not include shadows. These are significant advantages when the development of automated classification and change detection procedures is considered.

de Oliveira R.A.,São Paulo State University | Tommaselli A.M.G.,São Paulo State University | Honkavaara E.,Finnish Geospatial Research Institute FGI
Photogrammetric Record | Year: 2016

Recently, miniaturised hyperspectral sensors operable from small unmanned airborne vehicle platforms have entered the market. The emerging hyperspectral imaging technologies, based on frame cameras and tuneable filters, are attractive alternatives to hyperspectral pushbroom sensors. This paper addresses the geometric calibration process of a hyperspectral frame camera based on a Fabry–Pérot interferometer. However, the addition of more optical elements in front of the image sensor can affect the parameters related to the internal geometry of the camera, and a deficiency in knowledge regarding these parameters can have a critical effect on the accuracy of 3D measurements in photogrammetric applications. The experiments focused on assessing the self-calibrating bundle adjustment to verify the behaviour of the interior parameters, considering different spectral bands. The results indicated that the applied self-calibration method can accurately characterise the interior parameters of this camera and that one set of parameters is required for each internal sensor. © 2016 The Authors. The Photogrammetric Record © 2016 The Remote Sensing and Photogrammetry Society and John Wiley & Sons Ltd

Kaijaluoto R.,Finnish Geospatial Research Institute FGI | Kukko A.,Finnish Geospatial Research Institute FGI | Hyyppa J.,Finnish Geospatial Research Institute FGI
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives | Year: 2015

Accurate 3D data is of high importance for indoor modeling for various applications in construction, engineering and cultural heritage documentation. For the lack of GNSS signals hampers use of kinematic platforms indoors, TLS is currently the most accurate and precise method for collecting such a data. Due to its static single view point data collection, excessive time and data redundancy are needed for integrity and coverage of data. However, localization methods with affordable scanners are used for solving mobile platform pose problem. The aim of this study was to investigate what level of trajectory accuracies can be achieved with high quality sensors and freely available state of the art planar SLAM algorithms, and how well this trajectory translates to a point cloud collected with a secondary scanner. In this study high precision laser scanners were used with a novel way to combine the strengths of two SLAM algorithms into functional method for precise localization. We collected five datasets using Slammer platform with two laser scanners, and processed them with altogether 20 different parameter sets. The results were validated against TLS reference. The results show increasing scan frequency improves the trajectory, reaching 20 mm RMSE levels for the best performing parameter sets. Further analysis of the 3D point cloud showed good agreement with TLS reference with 17 mm positional RMSE. With precision scanners the obtained point cloud allows for high level of detail data for indoor modeling with accuracies close to TLS at best with vastly improved data collection efficiency. © 2015, Copernicus. All rights reserved.

Hietanen E.,Finnish Geospatial Research Institute FGI | Lehto L.,Finnish Geospatial Research Institute FGI | Latvala P.,Finnish Geospatial Research Institute FGI
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives | Year: 2016

In this study, a prototype service to provide data from Web Feature Service (WFS) as linked data is implemented. At first, persistent and unique Uniform Resource Identifiers (URI) are created to all spatial objects in the dataset. The objects are available from those URIs in Resource Description Framework (RDF) data format. Next, a Web Ontology Language (OWL) ontology is created to describe the dataset information content using the Open Geospatial Consortium's (OGC) GeoSPARQL vocabulary. The existing data model is modified in order to take into account the linked data principles. The implemented service produces an HTTP response dynamically. The data for the response is first fetched from existing WFS. Then the Geographic Markup Language (GML) format output of the WFS is transformed on-the-fly to the RDF format. Content Negotiation is used to serve the data in different RDF serialization formats. This solution facilitates the use of a dataset in different applications without replicating the whole dataset. In addition, individual spatial objects in the dataset can be referred with URIs. Furthermore, the needed information content of the objects can be easily extracted from the RDF serializations available from those URIs. A solution for linking data objects to the dataset URI is also introduced by using the Vocabulary of Interlinked Datasets (VoID). The dataset is divided to the subsets and each subset is given its persistent and unique URI. This enables the whole dataset to be explored with a web browser and all individual objects to be indexed by search engines.

Lehtinen K.,Finnish Geospatial Research Institute FGI | Bach U.,Max Planck Institute for Radio Astronomy | Muinonen K.,Finnish Geospatial Research Institute FGI | Muinonen K.,University of Helsinki | And 2 more authors.
Astrophysical Journal Letters | Year: 2016

Stellar occultations by asteroids observed at visual wavelengths have been an important tool for studying the size and shape of asteroids and for revising the orbital parameters of asteroids. At radio frequencies, a shadow of an asteroid on the Earth is dominated by diffraction effects. Here, we show, for the first time, that a single observation of an occultation of a compact radio source at a frequency of 5 GHz can be used to derive the effective size of the occulting object and to derive the distance between the observer and the center of the occultation path on the Earth. The derived diameter of the occulting object, asteroid (115) Thyra, is 75 ± 6 km. The observed occultation profile shows features that cannot be explained by diffraction of a single asteroid. © 2016. The American Astronomical Society. All rights reserved.

Gritsevich M.,Finnish Geospatial Research Institute FGI | Gritsevich M.,Moscow State University of Geodesy and Cartography
Planetary and Space Science | Year: 2016

This paper examines the effects of the atmospheric density, more specifically, the effects that the changes of isobaric altitude have on the accuracy of a fireball's analysis. During winter, especially over high latitude regions like Finland, the true isobaric level may be more than three kilometers below the heights predicted by the US Standard Atmosphere 1976 model. It can differ even more when compared with the heights predicted by the simplified exponential scaled height model. Thus, the true mass of a fireball may differ significantly from those obtained by using either the isobaric altitudes derived from the Standard Atmosphere or the exponential atmospheric model, i.e. without taking into account the corrections for true atmospheric conditions. Likewise, the solutions for the ablation coefficient derived by the generalized models will be less accurate than those that do consider the true atmospheric conditions. This becomes especially crucial for potential meteorite droppers, i.e. low velocity fireballs, with small ablation rates and consequently, high terminal-to-initial mass ratio. We propose an atmospheric height correction method that utilizes real atmospheric data to analysis of the fireball. We demonstrate the proposed method by analyzing the data of three fireballs that were recently recorded by the Finnish Fireball Network and finally, we compare our results against those derived by using the US Standard Atmosphere 1976 model and the exponential atmosphere model. © 2015 Elsevier Ltd. All rights reserved.

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