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Hakala P.,University of Turku | Muhli P.,National Land Survey of Finland | Charles P.,University of Southampton | Charles P.,University of Cape Town
Monthly Notices of the Royal Astronomical Society | Year: 2014

We report the results of quasi-simultaneous optical and near-IR (NIR) photometry of the lowmass X-ray binary, 4U 1957+115. Our observations cover the B, V, R, I, J, H and K-bands and additional time series NIR photometry. We measure a spectral energy distribution (SED), which can be modelled using a standard multitemperature accretion disc, where the disc temperature and radius follow a power-law relation. Standard accretion disc theory predicts the power-law exponent to be -3/4, and this yields, perhaps surprisingly, acceptable fits to our SED. Given that the source is a persistent X-ray source, it is however likely that the accretion disc temperature distribution is produced by X-ray heating, regardless of its radial dependence. Furthermore, we find no evidence for any emission from the secondary star at any wavelength. However, adding a secondary component to our model allows us to derive a 99 per cent lower limit of 14 or 15 kpc based on Monte Carlo simulations and using either an evolved K2 or G2V secondary star, respectively. In >60 per cent of cases, the distance is >80 kpc. Such large distances favour models with a massive (>15 M) black hole primary. Our quasi-simultaneous J-and V-band time series photometry, together with the SED, reveals that the optical/NIR emission must originate in the same region, i.e. the accretion disc. The likely extreme mass ratio supports suggestions that the accretion disc must be precessing which, depending on the length of the precession period, could play a major part in explaining the variety of optical light-curve shapes obtained over the last two decades. © 2014 The Authors. Source


Honkavaara E.,Finnish Geodetic Institute | Nurminen K.,Finnish Geodetic Institute | Markelin L.,Finnish Geodetic Institute | Suomalainen J.,Finnish Geodetic Institute | Ilves R.,National Land Survey of Finland
Photogrammetric Record | Year: 2011

Novel photogrammetric sensors open up new possibilities for measuring the radiometric and geometric properties of the earth's surface. To ensure optimal use of these complex, rapidly developing, diverse systems, it is becoming crucial to have a means of calibrating and validating complete imaging systems, and even production lines, in operational conditions. This paper presents a calibration and validation methodology based on a permanent test site (Sjökulla) and demonstrates its use in a calibration and validation campaign for a large-format photogrammetric imaging system, the Intergraph DMC. The major objective of the campaign was to perform acceptance testing of the new camera system procured by the National Land Survey of Finland. The evaluation proved the high geometric and radiometric performance of the imaging system and demonstrated the potential of spectrodirectional photogrammetric 3D imaging. The usability aspects of test site calibration and validation from the point of view of a mapping organisation were also considered.© 2011 The Authors. The Photogrammetric Record © 2011 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. Source


Kolis K.,Aalto University | Hiironen J.,Aalto University | Arola E.,National Land Survey of Finland | Vitikainen A.,Aalto University
Silva Fennica | Year: 2014

Buyers of standing timber take not only the market situation but also the harvest costs into consideration when making purchase offers. In Finland, 85% of all timber is sold as standing timber, but there is little information for forest owners and third parties regarding how differences in harvest costs are reflected in the stumpage prices. This article analyses the relationship between salespecific factors and stumpage prices in Finland. Data on 4824 standing timber sales between 2008 and 2012 were gathered from five local Forest Management Associations. Regression analyses were run on the stumpage prices (euros m–3) paid for sawlogs and pulpwood. Seasonal harvest restrictions, the volume of the sale and the timber assortment influenced stumpage prices, as did the presence of forest damages. Prices also differed over time and between locations. Furthermore, the forest haulage distance was statistically significant for pulpwood. The results suggest that the size of the individual sales and the composition of assortments affect the income owners earn from their forest. The results can be used to estimate stumpage prices and the monetary impacts on forest owners of procedures such as forest road network planning and land consolidation, as well as for valuation of forests. © 2014, Finnish Society of Forest Science. All rights reserved. Source


Hakala P.J.,University of Turku | Charles P.A.,South African Astronomical Observatory SAAO | Muhli P.,National Land Survey of Finland
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present results from several years of fast optical photometry of 4U0614+091 (V1055 Orionis), a candidate ultracompact X-ray binary most likely consisting of a neutron star and a degenerate secondary. We find evidence for strong accretion-driven variability at all epochs, which manifests itself as red noise. This flickering produces transient peaks in the observed power spectrum in the 15-65min period range. Only in one of our 12 optical data sets can we see evidence for a period that cannot be reproduced using the red noise model. This period of 51min coincides with the strongest period detected by Shahbaz et al. and can thus be taken as the prime candidate for the orbital period of the system. Furthermore, we find some tentative evidence for the X-ray versus optical flux anticorrelation discovered by Machin et al. using our data together with the all-sky X-ray monitoring data from RXTE/All Sky Monitor. We propose that the complex time series behaviour of 4U0614+09 is a result of drastic changes in the accretion disc geometry/structure on time-scales from hours to days. Finally, we want to draw attention to the interpretation of moderately strong peaks in the power spectra of especially accreting sources. Many of such 'periods' can probably be attributed to the presence of red noise (i.e. correlated events) in the data. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source


Dahlqvist S.,National Land Survey of Finland | Ronnholm P.,Aalto University | Salo P.,Aalto University | Vermeer M.,Aalto University
Remote Sensing | Year: 2011

In this study, we describe a system in which a GPS receiver mounted on the roof of a car is used to provide reference information to evaluate the elevation accuracy and georeferencing of airborne laser scanning (ALS) point clouds. The concept was evaluated in the Klaukkala test area where a number of roads were traversed to collect real-time kinematic data. Two test cases were evaluated, including one case using the real-time kinematic (RTK) method with a dedicated GPS base station at a known benchmark in the area and another case using the GNSSnet virtual reference station service (VRS). The utility of both GPS methods was confirmed. When all test data were included, the mean difference between ALS data and GPS-based observations was -2.4 cm for both RTK and VRS GPS cases. The corresponding dispersions were ±4.5 cm and ±5.9 cm, respectively. In addition, our examination did not reveal the presence of any significant rotation between ALS and GPS data. © 2011 by the authors. Source

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