Maanmittauslaitos: Recent submissions

Now showing items 21-40 of 378
  • Lundvall, Anniina (2019)
    Positio - paikkatiedon erikoislehti
  • Oksanen, Juha; Puranen, Laura (2019)
    Positio - paikkatiedon erikoislehti
  • Karila, Kirsi; Matikainen, Leena; Litkey, Paula; Hyyppä, Juha; Puttonen, Eetu (Taylor & Francis, 2018)
    International Journal of Remote Sensing
    Multispectral airborne laser scanning (MS-ALS) sensors are a new promising source of data for auto-mated mapping methods. Finding an optimal time for data acquisition is important in all mapping applica-tions based on remotely sensed datasets. In this study, three MS-ALS datasets acquired at different times of the growing season were compared for automated land cover mapping and road detection in a suburban area. In addition, changes in the intensity were studied. An object-based random forest classi-fication was carried out using reference points. The overall accuracy of the land cover classification was 93.9% (May dataset), 96.4% (June) and 95.9% (August). The use of the May dataset acquired under leafless conditions resulted in more complete roads than the other datasets acquired when trees were in leaf. It was concluded that all datasets used in the study are applicable for suburban land cover map-ping, however small differences in accuracies between land cover classes exist.
  • Isomäki, Harri (Maanmittauslaitos, 2019)
    Maanmittauslaitoksen julkaisuja
  • Karila, Kirsi; Yu, Xiaowei; Vastaranta, Mikko; Karjalainen, Mika; Puttonen, Eetu; Hyyppä, Juha (Elsevier, 2019)
    ISPRS Journal of Photogrammetry and Remote Sensing
    Satellite images provide spatially explicit information on forest change covering wide areas. In this study, bistatic TanDEM-X (TDX) synthetic aperture radar (SAR) satellite data were used to derive digital surface models (DSMs) of forest areas using SAR interferometry (InSAR). The capability of change features derived from bi-temporal InSAR DSMs to detect forest height (90th percen-tile of canopy height distribution, H90) and density variations was investigated. Moreover, changes in the forest above-ground bio-mass (AGB) were estimated from height changes between two In-SAR DSMs. Bi-temporal airborne laser scanning (ALS) data, aerial orthoimages and an ALS-based AGB change map from a study area in Southern Finland were used as references. The results indicate that the InSAR height change of a forested area correlates more with vegetation density change than with height change. The corre-lation between the InSAR mean height change and the height change feature from ALS was 0.76 at stand level. Correspondingly, the correlation between the InSAR mean height change and the ALS penetration rate change was 0.89. The AGB changes predicted based on InSAR height change agreed well with the reference data; the root-mean-square error (RMSE) was 20.7 Mg/ha (18.5% of the mean biomass in 2012) at stand level and 27.4 Mg/ha (27.0%) for 16 × 16 m grid cells. The results show that TDX DSMs can be used to detect biomass changes of different orders of magnitude, e.g. due to logging and thinning.
  • Mäkinen, Ville; Oksanen, Juha; Sarjakoski, Tapani (Taylor & Francis, 2019)
    International Journal of Geographical Information Science
    Determining stream networks automatically from digital elevation models is an issue that is actively being studied. The quality of elevation models has increased over time, but many hydrologically critical features, such as culverts, are often missing from the elevation data. To analyze the surficial water flow, one must either prepare a special elevation model or post-process an already-existing model. This study builds on the traditional, well-established method of determining the stream network from digital elevation models. We have extended the traditional method by locating culverts automatically, using road network data as an input. We show, by comparison to the reference data, that the culverts being most relevant for the stream network can be found with good accuracy. We demonstrate that by including the automatically located culverts in the automatic stream network determination, the quality of the generated network can be noticeably improved.
  • Rantanen, Jesperi; Ruotsalainen, Laura; Kirkko-Jaakkola, Martti; Mäkelä, Maija (2018)
    IEEE Transactions on Instrumentation and Measurement
  • Rantanen, Jesperi; Mäkelä, Maija; Ruotsalainen, Laura; Kirkko-Jaakkola, Martti (2018)
    2018 International Conference on Indoor Positioning and Indoor Navigation (IPIN)
  • Mäkelä, Maija; Kirkko-Jaakkola, Martti; Rantanen, Jesperi; Ruotsalainen, Laura (2018)
    Proceedings of the International Conference on Information Fusion
    In this paper we discuss the effect of cooperation in foot-mounted pedestrian indoor navigation. We study methods to use Ultra-Wide Band (UWB) range measurements between two pedestrians, as well as sharing location information between them. Our aim is to handle the heading offset between two separate pedestrian inertial navigation solutions and to represent the collaborators in a common coordinate frame. Furthermore, we study the effect of the proposed method also on height estimation. Our approach fuses measurements from several sensors, such as Inertial Measurement Units, UWB radios and a barometer using Bayesian filtering. First results from tests done in a realistic scenario show that the method can work in tactical operations.
  • Mäkelä, Maija; Rantanen, Jesperi; Kirkko-Jaakkola, Martti; Ruotsalainen, Laura (IEEE Sensors Council, 2018)
    IEEE Sensors Journal
    In this paper, we study machine learning methods for recognizing the motion context of a user of an infrastructure-free navigation system. Motion context is information about whether the user is running, crawling, or lying down, for instance. This can be valuable information for the command and control of a tactical or rescue operation, and it can also be used to adapt the positioning algorithm accordingly in order to improve the positioning result. We test our approach in collaboration with the Finnish Defence Forces. With only about 5 min of training data, we are able to detect the users motion context over 93% of the time using a random forest classifier. However, our tests show that the performance of the classifier is highly dependent on the user of the system. For this reason, we experiment with different classification algorithms in order to find a user-independent classifier providing a good compromise between accuracy and computational complexity. With a naïve Bayesian classifier, we achieve 85% detection rate in case when the training data is not produced by the user. In addition, we demonstrate how the motion recognition can be used to adjust the zero velocity update threshold in order to improve the performance of a foot-mounted inertial navigation algorithm.
  • Mäkinen, Kirsi (2018)
    Positio - paikkatiedon erikoislehti
  • Vaniala, Riitta (2018)
    Positio - paikkatiedon erikoislehti
  • Markkanen, Johannes; Agarwal, Jessica; Väisänen, Timo; Penttilä, Antti; Muinonen, Karri (IOP Publishing, 2018)
    The Astrophysical Journal Letters
    We show that the scattering phase functions of the coma and the nucleus of the comet 67P/Churyumov–Gerasimenko measured by the Rosetta/Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) instrument can be reproduced by a particle model involving clustered, densely packed submicrometer-sized grains composed of organic material and larger micrometer-sized silicate grains. The simulated and measured coma phase functions suggest that near the nucleus scattering is dominated by large particles, and the size distribution of dust particles varies with time and/or local coma environment. Further, we show that the measured nucleus phase function is consistent with the coma phase function by modeling a nucleus-sized object consisting of the same particles that explain the coma phase functions.
  • Mattila, Kalevi; Haas, Martin; Haikala, Lauri; Jo, Y.-S.; Lehtinen, Kimmo; Leinert, Christoph; Väisänen, Petri (EDP Sciences, 2018)
    Astronomy & Astrophysics
    Context. Dark nebulae display a surface brightness because dust grains scatter light of the general interstellar radiation field (ISRF). High-galactic-latitudes dark nebulae are seen as bright nebulae when surrounded by transparent areas which have less scattered light from the general galactic dust layer. Aims. Photometry of the bright dark nebulae LDN 1780, LDN 1642, and LBN 406 shall be used to derive scattering properties of dust and to investigate the presence of UV fluorescence emission by molecular hydrogen and the extended red emission (ERE). Methods. We used multi-wavelength optical photometry and imaging at ground-based telescopes and archival imaging and spectroscopic UV data from the spaceborn GALEX and SPEAR/FIMS instruments. In the analysis we used Monte Carlo RT and both observational data and synthetic models for the ISRF in the solar neighbourhood. The line-of-sight extinctions through the clouds have been determined using near infrared excesses of background stars and the 200/250 μm far infrared emission by dust as measured using the ISO and Herschel space observatories. Results. The optical surface brightness of the three target clouds can be explained in terms of scattered light. The dust albedo ranges from ~0.58 at 3500 Å to ~0.72 at 7500 Å. The spectral energy distribution of LDN 1780 is explained in terms of optical depth and background scattered light effects instead of the original published suggestion in terms of ERE. The far-ultraviolet surface brightness of LDN 1780 cannot be explained by scattered light only. In LDN 1780, H2 fluorescent emission in the wavelength range 1400–1700 Å has been detected and analysed. Conclusions. Our albedo values are in good agreement with the predictions of the dust model of Weingartner and Draine and with the THEMIS CMM model for evolved core-mantle grains. The distribution of H2 fluorescent emission in LDN 1780 shows a pronounced dichotomy with a strong preference for its southern side where enhanced illumination is impinging from the Sco OB2 association and the O star ζ Oph. A good correlation is found between the H2 fluorescence and a previously mapped 21-cm excess emission. The H2 fluorescence emission in LDN 1780 has been modelled using a PDR code; the resulting values for H2 column density and the total gas density are consistent with the estimates derived from CO observations and optical extinction along the line of sight.
  • Harju, Jorma; Lehtinen, Kimmo; Romney, Jonathan; Petrov, Leonid; Granvik, Mikael; Muinonen, Karri; Bach, Uwe; Poutanen, Markku (IOP Publishing, 2018)
    The occultation of the radio galaxy 0141+268 by the asteroid (372) Palma on 2017 May 15 was observed using six antennas of the Very Long Baseline Array (VLBA). The shadow of Palma crossed the VLBA station at Brewster, Washington. Owing to the wavelength used, and the size and the distance of the asteroid, a diffraction pattern in the Fraunhofer regime was observed. The measurement retrieves both the amplitude and the phase of the diffracted electromagnetic wave. This is the first astronomical measurement of the phase shift caused by diffraction. The maximum phase shift is sensitive to the effective diameter of the asteroid. The bright spot at the shadow's center, the so called Arago-Poisson spot, is clearly detected in the amplitude time-series, and its strength is a good indicator of the closest angular distance between the center of the asteroid and the radio source. A sample of random shapes constructed using a Markov chain Monte Carlo algorithm suggests that the silhouette of Palma deviates from a perfect circle by 26 +/- 13%. The best-fitting random shapes resemble each other, and we suggest their average approximates the shape of the silhouette at the time of the occultation. The effective diameter obtained for Palma, 192.1 +/- 4.8 km, is in excellent agreement with recent estimates from thermal modeling of mid-infrared photometry. Finally, our computations show that because of the high positional accuracy, a single radio interferometric occultation measurement can reduce the long-term ephemeris uncertainty by an order of magnitude.
  • Kirkko-Jaakkola, Martti; Thombre, Sarang; Honkala, Salomon; Söderholm, Stefan; Kaasalainen, Sanna; Kuusniemi, Heidi; Zelle, Hein; Veerman, Henk; Wallin, Anders (Institute of Electrical and Electronics Engineers, 2017)
    Proceedings of the European Navigation Conference
    This paper proposes a set of Key Performance Indicators (KPIs) for European GNSS (EGNSS)-based timing services that are relevant from the user perspective; these KPIs quantify the accuracy, integrity, and stability of the services. Furthermore, the instrumentation and procedures required for reproducing the threats and evaluating the proposed KPIs are described. The proposed test setup makes use of a precise time/frequency reference distributing a Coordinated Universal Time (UTC) realization and is intended for post-processing. The test results provide an indication of the performance of the envisioned Galileo and EGNOS timing services in terms of the proposed KPIs when the receiver is subject to various abnormal conditions.
  • Kirkko-Jaakkola, Martti; Thombre, Sarang; Honkala, Salomon; Söderholm, Stefan; Kaasalainen, Sanna; Kuusniemi, Heidi; Zelle, Hein; Veerman, Henk; Wallin, Anders; Aarmo, Kjell Arne; Boyero, Juan Pablo (Institute of Navigation, 2017)
    Proceedings of ION GNSS+
    GNSS-based time transfer is utilized in various critical infrastructures as it provides important advantages which are being increasingly exploited. In this paper, we present the various implementation options for robust timing service concepts based on European GNSS (EGNSS), i.e., Galileo and EGNOS, that are expected to further foster the use of EGNSS timing; this concept can make use of the redundancy of measurements and of available GNSS constellations. The stability properties of the local oscillator, which are known to the designer, are also exploited. The algorithms are developed to account for cases where several measurement faults occur simultaneously, which is a possible scenario in land-based reception conditions. Furthermore, we derive time protection level equations to quantify the integrity of the GNSS time solution as a function of the false alarm and missed detection probabilities as well as the maximum number of simultaneous outliers to be accounted for. Some of the considered fault scenarios can only be detected but not rectified by the algorithms: in such case, holdover, i.e. processing based on the local oscillator alone, is triggered. Thus, the performance in these scenarios is dependent on the stability of the local oscillator; in this paper, the analysis is based on a low-cost temperature-compensated crystal oscillator. The effect of the robustness concepts is illustrated with a set of experiments which show that when implemented in a timing GNSS receiver, the algorithms presented can deal with failures that affect individual satellites or even an entire constellation. Local disturbances affecting the receiver can also be effectively detected. Specifying EGNSS timing as proper services along with well-defined procedures for testing receiver compliance paves the road for standardizing and certifying robust EGNSS timing receivers, which would be beneficial for many applications and in particular in safety or liability critical use cases.
  • Markelin, Lauri; Suomalainen, Juha; Hakala, Teemu; Alves de Oliveira, Raquel; Viljanen, Niko; Näsi, Roope; Scott, Barry; Theocharous, Theo; Greenwell, Claire; Fox, Nigel; Honkavaara, Eija (ISPRS Council, 2018)
    The International Archives fo the Photogrammetry, Remote Sensing and Spatial Information Sciences
    We study and analyse performance of a system for direct reflectance measurements from a drone. Key instruments of the system are upwards looking irradiance sensor and downwards looking imaging spectrometer. Requirement for both instruments is that they are radiometrically calibrated, the irradiance sensor has to be horizontally stabilized, and the sensors needs to be accurately synchronized. In our system, irradiance measurements are done with FGI Aerial Image Reference System (FGI AIRS), which uses novel optical levelling methodology and can compensate sensor tilting up to 15°. We performed SI-traceable spectral and radiance calibration of FPI hyperspectral camera at the National Physical Laboratory NPL (Teddington, UK). After the calibration, the radiance accuracy of different channels was between ±4% when evaluated with independent test data. Sensors response to radiance proved to be highly linear and was on average 0.9994 for all channels. The spectral response calibration showed side peaks on several channels that were due to the multiple orders of interference of the FPI and highlighted the importance of accurate calibration. The drone-based direct reflectance measurement system showed promising results with imagery collected over Jokioinen agricultural grass test site, Finland. AIRS-based image- and band wise image adjustment provided homogenous and seamless image mosaics even under varying illumination conditions and under clouds.
  • Ferrara, Nunzia Giorgia; Bhuiyan, Mohammad Zahidul H.; Söderholm, Stefan; Ruotsalainen, Laura; Kuusniemi, Heidi (John Wiley & Sons, 2018)
    GPS Solutions
    Due to the very low power of satellite signals when reaching the earth’s surface, global navigation satellite system receivers are vulnerable to various types of radio frequency interference, and, therefore, countermeasures are necessary. In the case of a narrowband interference (NBI), the adaptive notch filtering technique has been extensively investigated. However, the research on the topic has focused on the adaptation of the notch frequen-cy, but not of the notch width. We present a fully adaptive solution to counter NBI. The technique is capable of de-tecting and characterizing any number of narrow inter-fered bands, and then optimizing the mitigation process based on such characterization, namely the estimates of both interference frequency and width. Its full adaptive-ness makes it suitable to cope with the unpredictable and diverse nature of unintentional interfering events. In addi-tion to a thorough performance evaluation of the pro-posed method, which shows its benefits in terms of sig-nal quality improvement, an analysis of the impact of different NBI profiles on GPS L1 C/A and Galileo E1 is also conducted.
  • Cristodaro, Calogero; Ruotsalainen, Laura; Dovis, Fabio (MDPI, 2018)
    Global navigation satellite systems play a significant role in the development of intelligent transport systems, where the estimation of the vehicle’s position is a key element. How-ever, in strongly constrained environments such as city centers, the definition of quality metrics and the assessment of positioning performances are challenges to be addressed. Due to the variability of different urban scenarios, the model-ing of the dynamics as well as the architecture of the posi-tioning platform, which might embed other sensors and aid-ing means to the GNSS unit, make it hard to define unam-biguous positioning metrics. Performance assessment through analytical models and simulators can be ineffective in terms of cost, complexity, and general validity and scala-bility of the results. This paper shows how a record and replay approach can be an efficient solution to grant fidelity to a realistic scenario. This work discusses advantages and disadvantages with emphasis on the case study of harsh scenarios. Such an approach requires proper data collec-tions that allow the replay phase to test the GNSS-based positioning terminals. This paper presents the results ob-tained on a set of field tests related to different scenarios, selected as representative for the key performance indica-tors assessment.