| 1. |
- Santoro, Maurizio, et al.
(author)
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Forest growing stock volume of the northern hemisphere : Spatially explicit estimates for 2010 derived from Envisat ASAR
- 2015
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In: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 168, s. 316-334
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Journal article (peer-reviewed)abstract
- This paper presents and assesses spatially explicit estimates of forest growing stock volume (GSV) of the northern hemisphere (north of 10 degrees N) from hyper-temporal observations of Envisat Advanced Synthetic Aperture Radar (ASAR) backscattered intensity using the BIOMASAR algorithm. Approximately 70,000 ASAR images at a pixel size of 0.01 degrees were used to estimate GSV representative for the year 2010. The spatial distribution of the GSV across four ecological zones (polar, boreal, temperate, subtropical) was well captured by the ASAR-based estimates. The uncertainty of the retrieved GSV was smallest in boreal and temperate forest (<30% for approximately 80% of the forest area) and largest in subtropical forest. ASAR-derived GSV averages at the level of administrative units were mostly in agreement with inventory-derived estimates. Underestimation occurred in regions of very high GSV (>300 m(3)/ha) and fragmented forest landscapes. For the major forested countries within the study region, the relative RMSE between ASAR-derived GSV averages at provincial level and corresponding values from National Forest Inventory was between 12% and 45% (average: 29%).
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| 2. |
- Bertilsson, Johan, et al.
(author)
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Stress Levels Escalate When Repeatedly Performing Tasks Involving Threats
- 2019
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In: Frontiers in Psychology. - : Frontiers Media SA. - 1664-1078. ; 10, s. 1562-1562
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Journal article (peer-reviewed)abstract
- Police work may include performing repeated tasks under the influence of psychological stress, which can affect perceptual, cognitive and motor performance. However, it is largely unknown how repeatedly performing stressful tasks physically affect police officers in terms of heart rate and pupil diameter properties. Psychological stress is commonly assessed by monitoring the changes in these biomarkers. Heart rate and pupil diameter was measured in 12 male police officers when performing a sequence of four stressful tasks, each lasting between 20 and 130 s. The participants were first placed in a dimly illuminated anteroom before allowed to enter a brightly lit room where a scenario was played out. After each task was performed, the participants returned to the anteroom for about 30 s before performing the next sequential task. Performing a repeated sequence of stressful tasks caused a significant increase in heart rate (p = 0.005). The heart rate started to increase already before entering the scenario room and was significantly larger just after starting the task than just before starting the task (p < 0.001). This pattern was more marked during the first tasks (p < 0.001). Issuance of a verbal "abort" command which terminated the tasks led to a significant increase of heart rate (p = 0.002), especially when performing the first tasks (p = 0.002). The pupil diameter changed significantly during the repeated tasks during all phases but in a complex pattern where the pupil diameter reached a minimum during task 2 followed by an increase during tasks 3 and 4 (p ≤ 0.020). During the initial tasks, the pupil size (p = 0.014) increased significantly. The results suggest that being repeatedly exposed to stressful tasks can produce in itself an escalation of psychological stress, this even prior to being exposed to the task. However, the characteristics of both the heart rate and pupil diameter were complex, thus, the findings highlight the importance of studying the effects and dynamics of different stress-generating factors. Monitoring heart rate was found useful to screen for stress responses, and thus, to be a vehicle for indication if and when rotation of deployed personnel is necessary to avoid sustained high stress exposures.
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| 3. |
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| 4. |
- Fransson, Åsa, 1971, et al.
(author)
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Characterization of fractured crystalline rock: two Swedish in situ field experiments
- 2014
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In: 1st International Discrete Fracture Network Engineering Conference, 20-22 oct 2014, Vancouver, Canada.
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Conference paper (peer-reviewed)abstract
- Construction of a nuclear waste repository requires information and an understanding of the fractured rock. The Swedish concept for nuclear waste deposition that is currently being developed by the Swedish Nuclear Fuel and Waste Management Co (SKB) includes a natural barrier in the form of crystalline rock, and engineered barriers in the form of bentonite and a copper canister. This paper aims to present two in situ field experiments: the first is the Large fractures experiment and the second is BRIE, the Bentonite Rock Interaction Experiment. Important issues include possible deformation (shearing) of fractures and deformation zones influencing the localization of canisters, and fluid flow, resulting in hydration of the bentonite. The aim of Large fractures is to further develop strategies and integrated investigation and modelling methodology for the identification and characterization of geological structures to ensure that (size) determination of large fractures or minor deformation zones to a greater extent can be based on real properties and to a lesser degree on a criterion related to the existence of a full perimeter fracture – tunnel intersection. BRIE is a field experiment which addresses the hydraulic interaction between the system components of compacted bentonite and the near-field host rock composed of hard and fractured bedrock. The above experiments are presented in terms of investigations performed to obtain discrete fracture descriptions. Grouting of fractures intersecting the investigation borehole of the Large fractures experiment was designed based on field data and a decrease in flow from above 200 liters/min to below 1 liter/min was achieved. The magnitude of the transmissivity of the fracture/deformation zone that was grouted indicates a large fracture size. This is also indicated by the ongoing integrated interpretation (geology, hydrogeology and geophysics). Results from BRIE show that hydration is uneven and is controlled by the main conductive fracture, highlighting the need for a relevant fracture description.
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| 5. |
- Fransson, Åsa, 1971, et al.
(author)
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Swedish grouting design: hydraulic testing and grout selection
- 2016
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In: Ground Improvement. - : Thomas Telford Ltd.. - 1365-781X. ; 169:4, s. 275-285
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Journal article (peer-reviewed)abstract
- © 2016, Thomas Telford Services Ltd. All rights reserved. To ensure successful sealing of rock and soil, an adequate description of the system to be grouted is required as a basis for the grouting design and the selection of the grouting material. In rock, the individual fractures and the hydraulic apertures of these fractures form the basis of the Swedish grouting design concept. The hydraulic aperture is a key parameter when describing grouting behaviour and it is used to determine the extent to which the grout can enter fractures - that is, the penetrability. The hydraulic aperture also determines the penetration length, and therefore the grout parameters (e.g. yield stress and viscosity) as well as the grouting pressure and time needed to be adopted to the hydraulic aperture. Once these parameters are chosen, a suitable grouting technique can be adopted. Simple, practical rock and grout tests are important inputs to ensure correct design and performance. The aim of this paper is to present a testing procedure and provide examples from laboratory and field experience to demonstrate that the approach also works in practice.
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| 6. |
- Kaluza, Johan, 1986-
(author)
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Sjukskrivnas arbetsbörda : Arbetande medborgare möter en kundorienterad byråkrati
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Denna avhandling är baserad på en empirisk studie av Försäkringskassan. Teoretiskt tar avhandlingen sitt avstamp i litteraturen om arbetande konsumenter och kundorienterade byråkratier. Följande paradox utgör avhandlingens utgångspunkt: för att kvalificera för sjukförsäkring måste medborgarens förmåga att utföra sitt arbete vara begränsad samtidigt som handläggningen av sjukförsäkringen förutsätter att medborgaren utför arbete för att få tillgång till den. För att förklara hur paradoxen hanteras så är syftet med avhandlingen att kartlägga och förklara de praktiker som arbetande medborgares samt kundorienterade byråkrater, med stöd av andra aktörer, utför för att realisera sjukförsäkringen. Kartläggningen resulterar i konstaterandet att arbetet består av åtta praktiker uppdelade i två teman; stödpraktiker och kontrollpraktiker. Utifrån praktikteori diskuteras sedan hur dessa praktiker samspelar med varandra samt vad som inträffar då samspelet misslyckas. Avhandlingen identifierar även tre strategier som aktörerna använder när samspelet mellan praktiker misslyckas, nämligen korrigering, påtryckning och övertagande.Avhandlingen bidrar med ny kunskap genom att utveckla begreppet arbetande medborgare och genom att kartlägga arbetet som utförs för att realisera offentliga tjänster. Arbetet stimuleras delvis av medborgarnas oro av att göra fel inom försäkringen. Handläggare använder medborgarnas arbete för att underlätta sin arbetssituation genom vad som i avhandlingen benämns byråkratiskt samskapande. Utvecklingen av detta begrepp utgör avhandlingens andra centrala forskningsbidrag. Genom begreppet vidareutvecklas teorin om kundorienterade byråkratier. Begreppet skapar också en grund för en kritisk diskussion av begreppet samskapande inom tjänsteforskningen som förutsätter att medborgare fritt kan påverka utfallet av handläggningen. Avhandlingen visar dock att samskapande för medborgarna i princip uteslutande består av rutinmässig insamling och kontroll av uppgifter.
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| 7. |
- Neumann, M., et al.
(author)
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Assessing Performance of L- and P-Band Polarimetric Interferometric SAR Data in Estimating Boreal Forest Above-Ground Biomass
- 2012
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 50:3, s. 714-726
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Journal article (peer-reviewed)abstract
- Biomass estimation performance using polarimetric interferometric synthetic aperture radar (PolInSAR) data is evaluated at L- and P-band frequencies over boreal forest. PolInSAR data are decomposed into ground and volume contributions, retrieving vertical forest structure and polarimetric layer characteristics. The sensitivity of biomass to the obtained parameters is analyzed, and a set of these parameters is used for biomass estimation, evaluating one parametric and two non-parametric methodologies: multiple linear regression, support vector machine, and random forest. The methodology is applied to airborne SAR data over the Krycklan Catchment, a boreal forest test site in northern Sweden. The average forest biomass is 94 tons/ha and goes up to 183 tons/ha at forest stand level (317 tons/ha at plot level). The results indicate that the intensity at HH-VV is more sensitive to biomass than any other polarization at L-band. At P-band, polarimetric scattering mechanism type indicators are the most correlated with biomass. The combination of polarimetric indicators and estimated structure information, which consists of forest height and ground-volume ratio, improved the root mean square error (rmse) of biomass estimation by 17%-25% at L-band and 5%-27% at P-band, depending on the used parameter set. Together with additional ground and volume polarimetric characteristics, the rmse was improved up to 27% at L-band and 43% at P-band. The cross-validated biomass rmse was reduced to 20 tons/ha in the best case. Non-parametric estimation methods did not improve the cross-validated rmse of biomass estimation, but could provide a more realistic distribution of biomass values.
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| 8. |
- Neumann, M., et al.
(author)
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Parametric and non-parametric forest biomass estimation from PolInSAR data
- 2011
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In: IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2011. Vancouver, 24-29 July 2011. - 9781457710056 ; , s. 420-423, s. 420-423
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Conference paper (peer-reviewed)abstract
- Biomass estimation performance from model-based polarimetric SAR interferometry (PolInSAR) using generic parametric and non-parametric regression methods is evaluated at L- and P-band frequencies over boreal forest. PolInSAR data is decomposed into ground and volume contributions, estimating vertical forest structure, and using a set of obtained parameters for biomass regression. The considered estimation methods include multiple linear regression, support vector machine and random forest. The biomass estimation performance is evaluated on DLR's airborne SAR data at L- and P-bands over Krycklan Catchment, a boreal forest test site in Northern Sweden. The combination of polarimetric indicators and estimated structure information has improved the root mean square error (RMSE) of biomass estimation up to 28% at L-band and up to 46% at P-band. The cross-validated biomass RMSE was reduced to 20 tons/ha.
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| 9. |
- Nyström, Mattias, et al.
(author)
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Detection of windthrown trees using airborne laser scanning
- 2014
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In: International Journal of Applied Earth Observation and Geoinformation. - : Elsevier BV. - 0303-2434 .- 1569-8432. ; 30, s. 21-29
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Journal article (peer-reviewed)abstract
- In this study, a method has been developed for the detection of windthrown trees under a forest canopy, using the difference between two elevation models created from the same high density (65 points/m(2)) airborne laser scanning data. The difference image showing objects near the ground was created by subtracting a standard digital elevation model (DEM) from a more detailed DEM created using an active surface algorithm. Template matching was used to automatically detect windthrown trees in the difference image. The 54 ha study area is located in hemi-boreal forest in southern Sweden (Lat. 58 degrees 29' N, Long. 13 degrees 38' E) and is dominated by Norway spruce (Picea abies) with 3.5% deciduous species (mostly birch) and 1.7% Scots pine (Pinus sylvestris). The result was evaluated using 651 field measured windthrown trees. At individual tree level, the detection rate was 38% with a commission error of 36%. Much higher detection rates were obtained for taller trees; 89% of the trees taller than 27 m were detected. For pine the individual tree detection rate was 82%, most likely due to the more easily visible stem and lack of branches. When aggregating the results to 40 m square grid cells, at least one tree was detected in 77% of the grid cells which according to the field measurements contained one or more windthrown trees. (C) 2014 Elsevier B.V. All rights reserved.
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| 10. |
- Sandberg, Gustaf, 1982, et al.
(author)
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L- and P-band backscatter intensity for biomass retrieval in hemiboreal forest
- 2011
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In: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 115:11, s. 2874 - 2886
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Journal article (peer-reviewed)abstract
- At present, the greatest source of uncertainty in the global carbon cycle is in the terrestrial ecosystems. In orderto reduce these uncertainties it is necessary to provide consistent and accurate global estimates of the worldforest biomass. One of the most promising methods for obtaining such estimates is through polarimetric SARbackscatter measurements at low frequencies. In this paper, the relation between polarimetric SAR backscatterat L- and P-bands and forest biomass is investigated using data acquired within the BioSAR-I campaign insouthern Sweden during 2007. Methods for estimating biomass on stand level using these data are developedand evaluated, and the results for the two frequency bands are compared. For L-band data, the best results wereobtained using HV-polarized backscatter only, giving estimation errors in terms of root mean square errors(RMSE) between 31% and 46% of the mean biomass for stands with biomass ranging from 10 to 290 t/ha, and an(adjusted) coefficient of determination (R2) between 0.4 and 0.6. For P-band data, the results are better thanfor L-band. Models using HV- or HH-polarized P-band backscatter give similar results, as does a modelincluding both HV and HH. The RMSEs were between 18 and 27%, and the R2 values were between 0.7 and 0.8.
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