Refereed publications


Peer-reviewed scientific articles such as journal articles, book sections, chapters in research books, or peer-reviewed articles in conference proceedings.

Recent Submissions

  • Maanpää, Jyri; Taher, Josef; Manninen, Petri; Pakola, Leo; Melekhov, Iaroslav; Hyyppä, Juha (IEEE, 2021)
    Proceedings of ICPR 2020: 25th International Conference on Pattern Recognition, Milan, 10 – 15 January 2021
    Autonomous driving is challenging in adverse road and weather conditions in which there might not be lane lines, the road might be covered in snow and the visibility might be poor. We extend the previous work on end-to-end learning for autonomous steering to operate in these adverse real-life conditions with multimodal data. We collected 28 hours of driving data in several road and weather conditions and trained convolutional neural networks to predict the car steering wheel angle from front-facing color camera images and lidar range and reflectance data. We compared the CNN model performances based on the different modalities and our results show that the lidar modality improves the performances of different multimodal sensor-fusion models. We also performed on-road tests with different models and they support this observation.
  • Ouattara, Issouf; Hyyti, Heikki; Visala, Arto (Elsevier, 2020)
    IFAC-PapersOnLine, Proceedings of the 21th IFAC World Congress, Berlin, Germany, 12-17 July 2020
    We propose a novel method to locate spruces in a young stand with a low cost unmanned aerial vehicle. The method has three stages: 1) the forest area is mapped and a digital surface model and terrain models are generated, 2) the locations of trees are found from a canopy height model using local maximum and watershed algorithms, and 3) these locations are used in a convolution neural network architecture to detect young spruces. Our result for detecting young spruce trees among other vegetation using only color images from a single RGB camera were promising. The proposed method is able to achieve a detection accuracy of more than 91%. As low cost unmanned aerial vehicles with color cameras are versatile today, the proposed work is enabling low cost forest inventory for automating forest management.
  • Sandru, Andrei; Hyyti, Heikki; Visala, Arto; Kujala, Pentti (Elsevier, 2020)
    IFAC-PapersOnLine, Proceedings of the 21th IFAC World Congress, Berlin, Germany, 12-17 July 2020
    A sensor instrumentation and an automated process are proposed for sea-ice field analysis using ship mounted machine vision cameras with the help of inertial and satellite positioning sensors. The proposed process enables automated acquisition of sea-ice concentration, floes size and distribution. The process contains pre-processing steps such as sensor calibration, distortion removal, orthorectification of image data, and data extraction steps such as sea-ice floe clustering, detection, and analysis. In addition, we improve the state of the art of floe clustering and detection, by using an enhanced version of the k-means algorithm and the blue colour channel for increased contrast in ice detection. Comparing to manual visual observations, the proposed method gives significantly more detailed and frequent data about the size and distribution of individual floes. Through our initial experiments in pack ice conditions, the proposed system has proved to be able to segment most of the individual floes and estimate their size and area.
  • Koski, Christian; Rönneberg, Mikko; Kettunen, Pyry; Eliasen, Søren; Hansen, Henning Sten; Oksanen, Juha (John Wiley & Sons, 2021)
    Transactions in GIS
    Maritime spatial planning (MSP) needs tools to facilitate discussions and manage spatial data in collaborative workshops that involve actors with various backgrounds and expertise. However, the reported use of spatial tools in real‐world MSP is sparse. A better understanding is needed of how geographic information systems (GIS) can effectively support collaboration in MSP. We studied the utility of GIS tools for collaborative MSP in five steps: first, identifying shortcomings in available GIS for supporting collaborative MSP; second, defining requirements for an effective collaborative GIS (CGIS) for MSP; third, designing and developing a prototype CGIS, Baltic Explorer; fourth, demonstrating the system; and fifth, evaluating the system. In a real‐world MSP workshop, we demonstrated that the functionalities of Baltic Explorer can support and facilitate discussions in collaborative work. We also found that more research is needed about the use of spatial data in collaborative MSP and integration of model‐based geospatial analysis into CGIS.
  • Saari, Timo; Bilker-Koivula, Mirjam; Koivula, Hannu; Nordman, Maaria; Häkli, Pasi; Lahtinen, Sonja (Taylor & Francis, 2021)
    Marine Geodesy
    Traditionally, geoid models have been validated using GNSS-levelling benchmarks on land only. As such benchmarks cannot be established offshore, marine areas of geoid models must be evaluated in a different way. In this research, we present a marine GNSS/gravity campaign where existing geoid models were validated at sea areas by GNSS measurements in combination with sea surface models. Additionally, a new geoid model, calculated using the newly collected marine gravity data, was validated. The campaign was carried out with the marine geology research catamaran Geomari (operated by the Geological Survey of Finland), which sailed back and forth the eastern part of the Finnish territorial waters of the Gulf of Finland during the early summer of 2018. From the GNSS and sea surface data we were able to obtain geoid heights at sea areas with an accuracy of a few centimetres. When the GNSS derived geoid heights are compared with geoid heights from the geoid models differences between the respective models are seen in the most eastern and southern parts of the campaign area. The new gravity data changed the geoid model heights by up to 15 cm in areas of sparse/non-existing gravity data.
  • Adekola, Oluwafemi; Krigsholm, Pauliina; Riekkinen, Kirsikka (Elsevier, 2021)
    Land Use Policy
    Land laws provide a legal basis for addressing a country’s land-related strategies and are the central land policy instruments through which governments realise land policy objectives. Considering their vital role, it is imperative that land laws be evaluated to ensure that policy objectives are followed and that the laws are not ineffective or counterproductive. The extant literature, however, provides only a fragmentary basis for evaluation. The present study addresses this gap and constructs a novel framework to support the holistic evaluation of land law performance in the context of sub-Saharan Africa (SSA). The framework was developed through a review of systematically selected literature on land laws in SSA. Four key evaluation perspectives emerged: land access; land tenure; land use and development; and land administration institutions. The framework was then used to assess the overall performance of Rwanda’s Organic Land Law (OLL) 2005 through a content analysis of secondary data on the land reform outcomes. The OLL application suggests that the framework may provide stakeholders with insights into the overall effects of land law and potential areas of improvement. However, the framework must be further explored in various cases of SSA countries to validate its functionality.
  • Bilker-Koivula, Mirjam; Mäkinen, Jaakko; Ruotsalainen, Hannu; Näränen, Jyri; Saari, Timo (Springer, 2021)
    Journal of Geodesy
    Postglacial rebound in Fennoscandia causes striking trends in gravity measurements of the area. We present time series of absolute gravity data collected between 1976 and 2019 on 12 stations in Finland with different types of instruments. First, we determine the trends at each station and analyse the effect of the instrument types. We estimate, for example, an offset of 6.8 μgal for the JILAg-5 instrument with respect to the FG5-type instruments. Applying the offsets in the trend analysis strengthens the trends being in good agreement with the NKG2016LU_gdot model of gravity change. Trends of seven stations were found robust and were used to analyse the stabilization of the trends in time and to determine the relationship between gravity change rates and land uplift rates as measured with global navigation satellite systems (GNSS) as well as from the NKG2016LU_abs land uplift model. Trends calculated from combined and offset-corrected measurements of JILAg-5- and FG5-type instruments stabilized in 15 to 20 years and at some stations even faster. The trends of FG5-type instrument data alone stabilized generally within 10 years. The ratio between gravity change rates and vertical rates from different data sets yields values between − 0.206 ± 0.017 and − 0.227 ± 0.024 µGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 µGal/yr. These values are larger than previous estimates for Fennoscandia.
  • Junttila, Samuli; Hölttä, Teemu; Puttonen, Eetu; Katoh, Masato; Vastaranta, Mikko; Kaartinen, Harri; Holopainen, Markus; Hyyppä, Hannu (Elsevier, 2021)
    Remote Sensing of Environment
    During the past decades, extreme events have become more prevalent and last longer, and as a result drought-induced plant mortality has increased globally. Timely in-formation on plant water dynamics is essential for under-standing and anticipating drought-induced plant mortality. Leaf water potential (ΨL), which is usually measured de-structively, is the most common metric that has been used for decades for measuring water stress. Remote sensing methods have been developed to obtain information on water dynamics from trees and forested landscapes. However, the spatial and temporal resolutions of the existing methods have limited our understanding of the water dynamics and diurnal variation of ΨL within single trees. Thus, we investi-gated the capability of terrestrial laser scanning (TLS) in-tensity in observing diurnal variation in ΨL during a 50-h monitoring period. We aimed to improve the understanding on how large a part of the diurnal variation in ΨL can be captured using TLS intensity observations. We found that TLS intensity at the 905 nm wavelength measured from a static position was able to explain 77% of the variation in ΨL for three trees of two tree species with a root mean square error of 0.141 MPa. Based on our experiment with three trees, a time series of TLS intensity measurements can be used in detecting changes in ΨL, and thus it is worthwhile to expand the investigations to cover a wider range of tree species and forests and further increase our understanding of plant water dynamics at wider spatial and temporal scales.
  • Campos, Mariana Batista; Litkey, Paula; Wang, Yunsheng; Chen, Yuwei; Hyyti, Heikki; Hyyppä, Juha; Puttonen, Eetu (Frontiers Research Foundation, 2021)
    Frontiers in Plant Science
    The terrestrial laser scanner (TLS) has become standard technology for vegetation dynamics monitoring. TLS time series have significant underlying application in investigating structural development and dynamics on a daily and seasonal scale. However, the high potential of TLS for the monitoring of long-term temporal phenomena in fully grown trees with high spatial and temporal resolution has not yet been fully explored. Automated TLS platforms for long-term data collection and monitoring of forest dynamics are rare; and long-term TLS time series data is not yet readily available to potential end-user, such as forestry researchers and plant biologists. This work presents an automated and permanent TLS measurement station that collects high frequency and high spatial resolution TLS time series, aiming to monitor short- and long-term phenological changes at a boreal forestry field station (0.006◦ angular resolution, one scan per hour). The measurement station is the first of its kind considering the scope, accuracy, and length of the time series it produces. The TLS measurement station provides a unique dataset to monitor the 3D physical structure of a boreal forest, enabling new insights into forest dynamics. For instance, the information collected by the TLS station can be used to accurately detect structural changes in tree crowns surrounding the station. These changes and their timing can be linked with the phenological state of plants, such as the start of leaf-out during spring growing season. As the first results of this novel station, we present time series data products collected with the station and what detailed information it provides about the phenological changes in the test site during the leaf sprout in spring.
  • Herrero-Huerta, Mónica; Bucksch, Alexander; Puttonen, Eetu; Rainey, Katy Martin (American Association for the Advancement of Science (AAAS), 2020)
    Plant Phenomics
    Cost-effective phenotyping methods are urgently needed to advance crop genetics in order to meet the food, fuel, and fiber demands of the coming decades. Concretely, charac-terizing plot level traits in fields is of particular interest. Re-cent developments in high resolution imaging sensors for UAS (unmanned aerial systems) focused on collecting de-tailed phenotypic measurements are a potential solution. We introduce canopy roughness as a new plant plot-level trait. We tested its usability with soybean by optical data collect-ed from UAS to estimate biomass. We validate canopy roughness on a panel of 108 soybean [Glycine max (L.) Merr.] recombinant inbred lines in a multienvironment trial during the R2 growth stage. A senseFly eBee UAS platform obtained aerial images with a senseFly S.O.D.A. compact digital camera. Using a structure from motion (SfM) tech-nique, we reconstructed 3D point clouds of the soybean experiment. A novel pipeline for feature extraction was de-veloped to compute canopy roughness from point clouds. We used regression analysis to correlate canopy roughness with field-measured aboveground biomass (AGB) with a leave-one-out cross-validation. Overall, our models achieved a coefficient of determination (R2) greater than 0.5 in all trials. Moreover, we found that canopy roughness has the ability to discern AGB variations among different geno-types. Our test trials demonstrate the potential of canopy roughness as a reliable trait for high-throughput phenotyping to estimate AGB. As such, canopy roughness provides practical information to breeders in order to select pheno-types on the basis of UAS data.
  • Gruber, Thomas; Ågren, Jonas; Angermann, Detlef; Ellmann, Artu; Engfeldt, Andreas; Gisinger, Christoph; Jaworski, Leszek; Marila, Simo; Nastula, Jolanta; Nilfouroushan, Faramarz; Oikonomidou, Xanthi; Poutanen, Markku; Saari, Timo; Schlaak, Marius; Swiatek, Anna; Varbla, Sander; Zdunek, Ryszard (MDPI, 2020)
    Remote Sensing
    Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national leveling networks and therefore define a height system of a country. One of the main deficiencies to use tide gauge data for geodetic sea level research and height systems unification is that only a few stations are connected to the geometric network of a country by operating permanent GNSS receivers next to the tide gauge. As a new observation technique, absolute positioning by SAR using active transponders on ground can fill this gap by systematically observing time series of geometric heights at tide gauge stations. By additionally knowing the tide gauge geoid heights in a global height reference frame, one can finally obtain absolute sea level heights at each tide gauge. With this information the impact of climate change on the sea level can be quantified in an absolute manner and height systems can be connected across the oceans. First results from applying this technique at selected tide gauges at the Baltic coasts are promising but also exhibit some problems related to the new technique. The paper presents the concept of using the new observation type in an integrated sea level observing system and provides some early results for SAR positioning in the Baltic sea area.
  • Kirkko-Jaakkola, Martti; Marila, Simo; Sarang, Thombre; Honkala, Salomon; Koivula, Hannu; Kuusniemi, Heidi; Söderholm, Stefan (2019)
    Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019) September 16 - 20, 2019, Hyatt Regency Miami, Miami, Florida
    This paper presents a hybrid navigation algorithm based on loose coupling of the on-board speedometer and inertial sensors of a land vehicle with a GNSS receiver. An Extended Kalman Filter estimating ten error states is used as the hybridization framework. The algorithm is developed to serve as a baseline for the evaluation of the navigation infrastructure of the Aurora ecosystem which is an Arctic test bed for autonomous vehicles and intelligent transport systems. In the experimental tests we focus on the performance of the navigation algorithm during GNSS outages. First, the tests indicate that the quality of GNSS updates has an immediate effect on how fast the position errors accumulate when GNSS becomes unavailable. Second, using low-cost sensors together with the current navigation infrastructure available at the Aurora test site, GNSS position fixes need to be obtained at intervals no longer than 4 seconds in order to maintain a 95 % horizontal positioning accuracy better than 0.2 meters. The results serve as a basis for recommendations for further development of the Aurora ecosystem, suggesting that further positioning infrastructure could be deployed for guaranteeing a navigation performance adequate for autonomous vehicles.
  • Perheentupa, Viljami; Mäkinen, Ville; Habicht, Hando-Laur; Oksanen, Juha (Elsevier, 2020)
    Applied Computing and Geosciences
    Post-glacial land uplift and shore displacement are dynamic processes that are challenging to present with cartography and geovisualization. To communicate these phenomena, we have created a dynamic visualization in the form of high-quality animation, utilizing automated processes in the computation and rendering of large raster datasets. We have developed a simplified model to assess the past and future elevation models, and applied it to the High Coast/Kvarken Archipelago UNESCO World Heritage Site, which is considered one of the best places in the world to observe land uplift. Additionally, the ice decline in the area has been evaluated and visualized. Based on the model and the present-day topography/bathymetry data, we provide a 40 fps 4K-resolution animation with an 80-s duration of the post-glacial history at the World Heritage Site and its vicinity, extending from 10,500 years ago to 1000 years in the future. Although they do not aim to contain the precision of thorough paleogeographic reconstructions, we have found that the individual frames of the animation are closely aligned with comparable geological data. We also present the computational process flow and the visualization principles used in the automated rendering, and thus aim to contribute to the cartographic presentation of geodynamic processes.
  • Brauer, Anna; Mäkinen, Ville; Oksanen, Juha (Elsevier, 2021)
    Computers Environment and Urban Systems
    Mobile activity tracking data, i.e. data collected by mobile applications that enable activity tracking based on the use of the Global Navigation Satellite Systems (GNSS), contains information on cycling in urban areas at an un-precedented spatial and temporal extent and resolution. It can be a valuable source of information about the quality of bicycling in the city. Required is a notion of quality that is derivable from plain GNSS trajectories. In this article, we quantify urban cycling quality by esti-mating the fluency of cycling traffic using a large set of GNSS trajectories recorded with a mobile tracking appli-cation. Earlier studies have shown that cyclists prefer to travel continuously and without halting, i.e. fluently. Our method extracts trajectory properties that describe the stopping behaviour and dynamics of cyclists. It aggre-gates these properties to segments of a street network and combines them in a descriptive index. The suitability of the data to describe the cyclists' behaviour with street-level detail is evaluated by comparison with various data from independent sources. Our approach to characterizing cycling traffic fluency offers a novel view on the cyclability of a city that could be valuable for urban planners, application providers, and cyclists alike. We find clear indications for the data's ability to estimate characteristics of city cycling quality correctly, despite behaviour patterns of cyclists not caused by external circumstances and the data's inher-ent bias. The proposed quality measure is adaptable for different applications, e.g. as an infrastructure quality measure or as a routing criterion.
  • Brauer, Anna; Mäkinen, Ville; Oksanen, Juha (2020)
    Proceedings of GISRUK
    Activity tracking data collected by mobile applications opens up a new, data-driven perspective on monitoring cycling in the city. In this work, we demonstrate how a large set of trajectories can be used to measure the cyclability of an urban infrastructure. We achieve this by defining the cycling traffic fuency index that describes the smoothness of cycling traffic on segments of a street network. Bias, uncertainty, and the divergence of infrastructure popularity presents challenges to the method, but within these limits, the index could be applied in city planning or as a routing criterion.
  • Kaasalainen, Sanna (CRC Press, 2020)
    The development of multispectral terrestrial laser scan-ning (TLS) is still at the very beginning, with only four instruments worldwide providing simultaneous three-dimensional (3D) point cloud and spectral measurement. Research on multiwavelength laser returns has been carried out by more groups, but there are still only about ten research instruments published and no commercial availability. This chapter summarizes the experiences from all these studies to provide an overview of the state of the art and future developments needed to bring the multispectral TLS technology into the next level. Alt-hough the current number of applications is sparse, they already show that multispectral lidar technology has po-tential to disrupt many fields of science and industry due to its robustness and the level of detail available.
  • Andrei, Constantin-Octavian; Johansson, Jan; Koivula, Hannu; Poutanen, Markku (IEEE, 2020)
    Proceedings of the International Conference on Localization and GNSS
    On 12 February 2020, the latest four Galileo satellites had completed one full year of space operational service. The satellites were launched on 25 July 2018. The quartet increased the operational capacity of the Galileo constellation to 22 satellites. This study reports on three signal-in-space (SiS) performance indicators - status, availability, and ranging accuracy - from 11 February 2019 to 12 February 2020. In addition, the study looks also at how the on-board satellite clocks have performed. The data analysis shows 100% data validity and signal health status for three our of the four satellites, whereas NAPA (No Accuracy Prediction Available) events accounted for about 2% of the time. In addition, SiS availability was higher than 95% in the first operational year. Furthermore, the 95th percentile of the global average of the instantaneous signal in space error is found to vary between 0.17 to 0.33 m on monthly basis. Lastly, the precise satellite clock biases show high short-term performance with 0.1 ps/s (10-13 s/s) standard deviations during the first operational year. The numerical results indicate a robust performance and high reliability for the youngest Galileo satellites in the constellation. They increase the number of operational satellites in the constellation and thus contribute to the Galileo’s increased popularity in the satellite-based positioning and navigation user community.
  • Ghobadi, Hossein; Spogli, Luca; Alfonsi, Lucilla; Cesaroni, Claudio; Cicone, Antonio; Linty, Nicola; Romano, Vincenzo; Cafaro, Massimo (Springer, 2020)
    GPS Solutions
    We contribute to the debate on the identification of phase scintillation induced by the ionosphere on the global navigation satellite system (GNSS) by introducing a phase detrending method able to provide realistic values of the phase scintillation index at high latitude. It is based on the fast iterative filtering signal decomposition technique, which is a recently developed fast implementation of the well-established adaptive local iterative filtering algorithm. FIF has been conceived to decompose nonstationary signals efficiently and provide a discrete set of oscillating functions, each of them having its frequency. It overcomes most of the problems that arise when using traditional time–frequency analysis techniques and relies on a consolidated mathematical basis since its a priori convergence and stability have been proved. By relying on the capability of FIF to efficiently identify the frequencies embedded in the GNSS raw phase, we define a method based on the FIF-derived spectral features to identify the proper cutoff frequency for phase detrending. To test such a method, we analyze the data acquired from GPS and Galileo signals over Antarctica during the September 2017 storm by the ionospheric scintillation monitor receiver (ISMR) located in Concordia Station (75.10° S, 123.33° E). Different cases of diffraction and refraction effects are provided, showing the capability of the method in deriving a more accurate determination of the σϕ index. We found values of cutoff frequency in the range of 0.73–0.83 Hz, providing further evidence of the inadequacy of the choice of 0.1 Hz, which is often used when dealing with ionospheric scintillation monitoring at high latitudes.
  • Vallet Garcia, José M. (MDPI, 2020)
    Journal of Sensor and Actuator Networks
    Using the classical received signal strength (RSS)-distance log-normal model in wireless sensor network (WSN) applications poses a series of characteristic challenges derived from (a) the model’s structural limitations when it comes to explaining real observations, (b) the inherent hardware (HW) variability typically encountered in the low-cost nodes of WSNs, and (c) the inhomogeneity of the deployment environment. The main goal of this article is to better characterize how these factors impact the model parameters, an issue that has received little attention in the literature. For that matter, I qualitatively elaborate on their effects and interplay, and present the results of two quantitative empirical studies showing how much the parameters can vary depending on (a) the nodes used in the model identification and their position in the environment, and (b) the antenna directionality. I further show that the path loss exponent and the reference power can be highly correlated. In view of all this, I argue that real WSN deployments are better represented by random model parameters jointly accounting for HW and local environmental characteristics, rather than by deterministic independent ones. I further argue that taking this variability into account results in more realistic models and plausible results derived from their usage. The article contains example values of the mean and standard deviation of the model parameters, and of the correlation between the path loss exponent and the reference power. These can be used as a guideline in other studies. Given the sensitivity of localization algorithms to the proper model selection and identification demonstrated in the literature, the structural limitations of the log-normal model, the variability of its parameters and their interrelation are all relevant aspects that practitioners need to be aware of when devising optimal localization algorithms for real WSNs that rely on this popular model.
  • Khoramshahi, Ehsan; Campos, Mariana Batista; Tommaselli, Antonio Maria Garcia; Viljanen, Niko; Mielonen, Teemu; Kaartinen, Harri; Kukko, Antero; Honkavaara, Eija (MDPI, 2019)
    Remote Sensing
    Mobile mapping systems (MMS) are increasingly used for many photogrammetric and computer vision applications, especially encouraged by the fast and accurate geospatial data generation. The accuracy of point position in an MMS is mainly dependent on the quality of calibration, accuracy of sensor synchronization, accuracy of georeferencing and stability of geometric configuration of space intersections. In this study, we focus on multi-camera calibration (interior and relative orientation parameter estimation) and MMS calibration (mounting parameter estimation). The objective of this study was to develop a practical scheme for rigorous and accurate system calibration of a photogrammetric mapping station equipped with a multi-projective camera (MPC) and a global navigation satellite system (GNSS) and inertial measurement unit (IMU) for direct georeferencing. The proposed technique is comprised of two steps. Firstly, interior orientation parameters of each individual camera in an MPC and the relative orientation parameters of each cameras of the MPC with respect to the first camera are estimated. In the second step the offset and misalignment between MPC and GNSS/IMU are estimated. The global accuracy of the proposed method was assessed using independent check points. A correspondence map for a panorama is introduced that provides metric information. Our results highlight that the proposed calibration scheme reaches centimeter-level global accuracy for 3D point positioning. This level of global accuracy demonstrates the feasibility of the proposed technique and has the potential to fit accurate mapping purposes.

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