| 1. |
- Eriksson, Leif, 1970, et al.
(författare)
-
ALOS PALSAR Calibration and Validation Results from Sweden
- 2007
-
Ingår i: IEEE Geoscience and Remote Sensing Symposium (IGARSS 2007), Barcelona, Spain, July 23-27, 2007. ; DOI: 10.1109/IGARSS.2007.4423115, s. 1589-1592
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In 2006 calibration activities for ALOS PALSAR wereconducted in Sweden. Four five-metre trihedral corner reflectorsand three smaller dihedral reflectors were deployed and operatedduring eight months. 23 PALSAR scenes were acquired over thecalibration site allowing an evaluation of the quality and temporalstability of the data. Results show that the co-polarized datahave been stable during the whole calibration period with variationsin the trihedral responses lower than 0.7 dB. The measuredresolution in azimuth was 4.4 m and in slant range 4.7 m forsingle polarization images and 9.5 m for polarimetric data. Forthe cross-polarized data large variations in the dihedral responseswere found. It is assumed that this is caused by a larger sensitivityto pointing errors. For the polarimetric data, estimation ofFaraday rotation gave values ranging from 0.1º to 3º.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Fransson, J.E.S., et al.
(författare)
-
Mapping of Wind-Thrown Forests Using VHF/UHF SAR Images
- 2007
-
Ingår i: IEEE 2007 International Geoscience and Remote Sensing Symposium (IGARSS 2007), Barcelona, Spain, July 23-27 2007. ; DOI: 10.1109/IGARSS.2007.4423313, s. 2350-2353
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- SAR images from the Swedish airborne CARABAS-II and LORA systems have been visually analyzed over simulated wind-thrown forest at both single tree and stand level. In ideal conditions, the results show that LORA is more accurate than CARABAS-II at detecting wind-thrown trees, regardless of tree size and direction of the fallen trees relative to flight heading. Furthermore, the visible single trees in the LORA images appeared more distinct than in the CARABAS-II images, which could be explained by the high resolution in the LORA images. Based on visual interpretation, it is likely that the detection of wind-thrown forests could be improved using VHF/UHF SAR images acquired both prior to and after a storm event.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
- Hallberg, Björn, 1973
(författare)
-
Synthetic-Aperture Radar Imaging of Forests in the VHF and UHF Bands: Electromagnetic Models and Data Analysis
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthetic-aperture radar (SAR) is a technique which can image the Earth’s surface, from a spaceborne or airborne platform, irrespective of daylight or cloud cover. During the last decades there has been an increasing interest in using SAR for estimation of forest parameters. It has been shown that the radar image-intensity over forested areas initially increases with increasing biomass up to a certain point referred to as the saturation point. The latter is dependent on forest type but also the frequency of the SAR system and the corresponding biomass level is higher for lower frequencies compared to higher frequencies. Spaceborne systems are the only realistic choice for global forest monitoring but do not currently operate below 1 GHz and saturate at relative low biomasses. Therefore, many studies have addressed the possibility of using frequencies below 1 GHz for future biomass missions.In this thesis, some of the problems and possibilities of using a SAR for forest imaging in the VHF (30-300 MHz) and UHF (300-1000 MHz) bands are studied through the use of electromagnetic models and by observations made by airborne SAR systems which today operate in these frequency bands. A method to co-register and combine multiple VHF SAR images in order to improve spatial and radiometric resolution is proposed and it is found that it is possible to enhance resolution to a degree where measurements on individual trees are possible. By studying these high resolution SAR images it is also found that previously existing models of forest scattering in VHF and UHF bands sometimes must be extended in order to correctly account for the effects of ground topography. A new model based on physical optics and with a generalized ground-parameterization is proposed and validated against observations done with airborne SAR systems. Furthermore, a model for dependency of stem number density on P-band (440 MHz) scattering is proposed and compared with observations. Finally, some problems associated with a P-band SAR satellite for forest monitoring, e.g. degradation of spatial resolution due to ionospheric scintillations and polarization-channel cross-talk due to Faraday rotation, are assessed by model simulations. It is found that these problems are likely to be surmountable, at least for equatorial regions.
|
|
| 13. |
- Hallberg, S., et al.
(författare)
-
Burden of disease and management of osteoarthritis and chronic low back pain: healthcare utilization and sick leave in Sweden, Norway, Finland and Denmark (BISCUITS): study design and patient characteristics of a real world data study
- 2022
-
Ingår i: Scandinavian Journal of Pain. - : Walter de Gruyter GmbH. - 1877-8860 .- 1877-8879. ; 23:1, s. 126-138
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives: Osteoarthritis (OA) and chronic low back pain (CLBP) are common musculoskeletal disorders with substantial patient and societal burden. Nordic administrative registers offer a unique opportunity to study the impact of these conditions in the real-world setting. The Burden of Disease and Management of Osteoarthritis and Chronic Low Back Pain: Health Care Utilization and Sick Leave in Sweden, Norway, Finland and Denmark (BISCUITS) study was designed to study disease prevalence and the societal and economic burden in broad OA and CLBP populations. Methods: Patients in Sweden, Norway, Finland and Denmark with diagnoses of OA or CLBP (low back pain record plus >= 2 pain relief prescriptions to indicate chronicity) were identified in specialty care, in primary care (Sweden and Finland) and in a quality-of-care register (Sweden). Matched controls were identified for the specialty care cohort. Longitudinal data were extracted on prevalence, treatment patterns, patient-reported outcomes, social and economic burden. Results: Almost 1.4 million patients with OA and 0.4 million with CLBP were identified in specialty care, corresponding to a prevalence in the Nordic countries of 6.3 and 1.9%, respectively. The prevalence increased to 11-14% for OA and almost 6% for CLBP when adding patients identified in primary care. OA patients had a higher Elixhauser comorbidity index (0.66 vs. 0.46) and were using opioids (44.7 vs. 10.2%) or long-term nonsteroidal anti-inflammatory drug (NSAIDs) (20.9 vs. 4.5%) more than four times as often as compared to controls. The differences were even larger for CLBP patients compared to their controls (comorbidity index 0.89 vs. 0.39, opioid use 77.7 vs. 9.4%, and long-term NSAID use 37.2 vs. 4.8%). Conclusions: The BISCUITS study offers an unprecedented, longitudinal healthcare data source to quantify the real-world burden of more than 1.8 million patients with OA or CLBP across four countries. In subsequent papers we aim to explore among others additional outcomes and subgroups of patients, primarily those patients who may benefit most from better healthcare management.
|
|
| 14. |
- Sandberg, Gustaf, 1982, et al.
(författare)
-
A Physical-optics Model for Predicting VHF/UHF-band HH-pol Backscatter from Coniferous Forests in Undulating Terrain
- 2007
-
Ingår i: 5th International Symposium on Retrieval of Bio- and Geophysical Parameters from SAR Data, Bari, Italy, September 25-28, 2007, ESA, Istituto di Studi sui Sistemi Intelligenti per l`Automazione.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A physical optics based model for predicting backscatter from coniferous forest in the VHF- and UHF frequency bands is presented. It models the forest as a collection of stems standing on a well characterized undulating ground surface. The model is valid for SAR systems transmitting and receiving horizontal polarization (HH) and is useful for assessing the importance of ground topography in SAR images.SAR data from the airborne systems CARABAS-II (22-82 MHz) and LORA (230-470 MHz) and forest characterization on individual tree level were used to validate the model. It was found that the model was able to predict much of the backscatter variations due to surface topography. At best, coefficients of determination (R2) of 0.44 and 0.65 for the CARABAS and LORA case were found. In comparison it should be noted that R2 drops to about 0.1 if a flat ground is assumed. These results indicate that it is essential to consider ground topography when predicting HH-polarized SAR images in these frequency bands.The model failed to predict the absolute values of the backscatter intensity. Probable explanations are the lack of attenuation effects in the model and/or the value chosen for the dielectric constant of the stems.In the near future efforts will be placed into the task of extending the model to include more polarizations, especially HV. This includes e.g. adding the backscatter from branches and leaves/needles, accounting for attenuation effects and including random small scale variations in the surface description.
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
- Smith Jonforsen, Gary, 1972, et al.
(författare)
-
Effects of Forest Biomass and Stand Consolidation on P-Band Backscatter
- 2007
-
Ingår i: IEEE Geoscience and Remote Sensing Letters. ; 4:4, s. 669-673
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In previous studies, P-band synthetic aperture radar (SAR) has shown potential for biomass retrieval in forests.However, while measurements show a general agreement thatbackscatter increases with increasing biomass, different studies show that the backscatter from stands of similar biomass can significantly vary depending on forest structure, hence making biomass retrieval more challenging. In this letter, we show that, while biomass may be the single most important parameter determiningthe backscatter from a forest, the number densityof trees has also a major impact. This can be explained using simple arguments, leading us to propose the use of the biomassconsolidation index to describe P-band HV-polarized backscatter. This is supported by electromagnetic-modeling studies and by a few measurements from boreal forest made with the AIRSAR system over the BOREAS test site in Canada.
|
|
| 18. |
- Smith Jonforsen, Gary, 1972, et al.
(författare)
-
Forest stem volume estimation using high-resolution lidar and SAR data
- 2002
-
Ingår i: IEEE Geoscience and Remote Sensing Symposium (IGARSS), Toronto, Canada, 24-28 June. - 078037536X ; IV, s. 2084-6
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Presents a comparison of remote sensing of forests using two complementary, high-resolution sensors; namely the TopEye lidar and CARABAS VHF SAR systems. The lidar data are from a small footprint configuration, allowing discrimination between pulses reflected from the tree crowns, and those penetrating through gaps in the canopy. From these data, measurements of tree height and crown size can be made for individual trees, and the tree volume calculated through empirical relationships. The CARABAS VHF SAR provides a more direct measurement of tree volume, since the long wavelengths penetrate the forest canopy and are scattered by the trunk-ground dihedral. Results of stem volume retrieval for individual trees using data from the two systems are presented, and the possibility of using the complementary measurements discussed
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
|
|
