| 1. |
- Herlitz, Johan, et al.
(author)
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Prognosis among survivors of prehospital cardiac arrest
- 1995
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In: Annals of Emergency Medicine. - : Mosby, Inc.. - 0196-0644 .- 1097-6760. ; 25:1, s. 58-63
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Journal article (peer-reviewed)abstract
- STUDY OBJECTIVE: To describe the prognosis in consecutive patients discharged from hospital after prehospital cardiac arrest. PATIENTS: All patients in the community of Göteborg who were discharged from hospital after out-of-hospital cardiac arrest between 1981 and 1991. RESULTS: Two hundred forty-three patients were discharged from hospital during the observation period, of whom 80% initially experienced ventricular fibrillation. Among patients discharged, 21% died during the first year; after 10 years, 82% had died. Age, sex, previous history of cardiovascular disease, circumstances at the time of cardiac arrest, complications during hospitalization, and discharge medications were assessed as predictors of 1-year mortality. Independent predictors of death during follow-up were history of myocardial infarction (P < .001), no prescription of beta-blockers at discharge (P < .01), age (P < .05), and cerebral performance category (CPC) at discharge (P < .05). CONCLUSION: Among patients who survived out-of-hospital cardiac arrest, one of five died during the first year and one of five survived 10 years after discharge. Prognosis was associated with a history of myocardial infarction, prescription of beta-blockers at discharge, age, and CPC at discharge.
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| 2. |
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| 3. |
- Berg, Lena M, et al.
(author)
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Associations between crowding and ten-day mortality among patients allocated lower triage acuity levels without need of acute hospital care on departure from the emergency department
- 2019
-
In: Annals of Emergency Medicine. - : Elsevier BV. - 0196-0644 .- 1097-6760. ; 74:3, s. 345-356
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Journal article (peer-reviewed)abstract
- STUDY OBJECTIVE: We describe the association between emergency department (ED) crowding and 10-day mortality for patients triaged to lower acuity levels at ED arrival and without need of acute hospital care on ED departure.METHODS: This was a registry study based on ED visits with all patients aged 18 years or older, with triage acuity levels 3 to 5, and without need of acute hospital care on ED departure during 2009 to 2016 (n=705,699). The sample was divided into patients surviving (n=705,076) or dying (n=623) within 10 days. Variables concerning patient characteristics and measures of ED crowding (mean length of stay and ED occupancy ratio) were extracted from the hospital's electronic health records. ED length of stay per ED visit was estimated by the average length of stay for all patients who presented to the ED during the same day and shift and with the same acuity level. The 10-day mortality after ED discharge was used as the outcome measure. Multivariable logistic regression analyses were conducted.RESULTS: The 10-day mortality rate was 0.09% (n=623). The event group had larger proportions of patients aged 80 years or older (51.4% versus 7.7%) and triaged with acuity level 3 (63.3% versus 35.6%), and greater comorbidity (age-combined Charlson comorbidity index median interquartile range 6 versus 0). We observed an increased 10-day mortality for patients with a mean ED length of stay greater than or equal to 8 hours versus less than 2 hours (adjusted odds ratio 5.86; 95% confidence interval [CI] 2.15 to 15.94) and for elevated ED occupancy ratio. Adjusted odds ratios for ED occupancy ratio quartiles 2, 3, and 4 versus quartile 1 were 1.48 (95% CI 1.14 to 1.92), 1.63 (95% CI 1.24 to 2.14), and 1.53 (95% CI 1.15 to 2.03), respectively.CONCLUSION: Patients assigned to lower triage acuity levels when arriving to the ED and without need of acute hospital care on departure from the ED had higher 10-day mortality when the mean ED length of stay exceeded 8 hours and when ED occupancy ratio increased.
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| 4. |
- Ekström, Andreas, et al.
(author)
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Forecasting emergency department visits using internet data
- 2015
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In: Annals of Emergency Medicine. - : Elsevier. - 0196-0644 .- 1097-6760. ; 65:4, s. 436-442.e1
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Journal article (peer-reviewed)abstract
- STUDY OBJECTIVE: Using Internet data to forecast emergency department (ED) visits might enable a model that reflects behavioral trends and thereby be a valid tool for health care providers with which to allocate resources and prevent crowding. The aim of this study is to investigate whether Web site visits to a regional medical Web site, the Stockholm Health Care Guide, a proxy for the general public's concern of their health, could be used to predict the ED attendance for the coming day.METHODS: In a retrospective, observational, cross-sectional study, a model for forecasting the daily number of ED visits was derived and validated. The model was derived through regression analysis, using visits to the Stockholm Health Care Guide Web site between 6 pm and midnight and day of the week as independent variables. Web site visits were measured with Google Analytics. The number of visits to the ED within the region was retrieved from the Stockholm County Council administrative database. All types of ED visits (including adult, pediatric, and gynecologic) were included. The period of August 13, 2011, to August 12, 2012, was used as a training set for the model. The hourly variation of visits was analyzed for both Web site and the ED visits to determine the interval of hours to be used for the prediction. The model was validated with mean absolute percentage error for August 13, 2012, to October 31, 2012.RESULTS: The correlation between the number of Web site visits between 6 pm and midnight and ED visits the coming day was significant (r=0.77; P<.001). The best forecasting results for ED visits were achieved for the entire county, with a mean absolute percentage error of 4.8%. The result for the individual hospitals ranged between mean absolute percentage error 5.2% and 13.1%.CONCLUSION: Web site visits may be used in this fashion to predict attendance to the ED. The model works both for the entire region and for individual hospitals. The possibility of using Internet data to predict ED visits is promising.
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| 5. |
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| 6. |
- Holden, Richard J.
(author)
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Lean Thinking in Emergency Departments : A Critical Review
- 2011
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In: Annals of Emergency Medicine. - : Elsevier BV. - 0196-0644 .- 1097-6760. ; 57:3, s. 265-278
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Research review (peer-reviewed)abstract
- Emergency departments (EDs) face problems with crowding, delays, cost containment, and patient safety. To address these and other problems, EDs increasingly implement an approach called Lean thinking. This study critically reviewed 18 articles describing the implementation of Lean in 15 EDs in the United States, Australia, and Canada. An analytic framework based on human factors engineering and occupational research generated 6 core questions about the effects of Lean on ED work structures and processes, patient care, and employees, as well as the factors on which Lean's success is contingent. The review revealed numerous ED process changes, often involving separate patient streams, accompanied by structural changes such as new technologies, communication systems, staffing changes, and the reorganization of physical space. Patient care usually improved after implementation of Lean, with many EDs reporting decreases in length of stay, waiting times, and proportion of patients leaving the ED without being seen. Few null or negative patient care effects were reported, and studies typically did not report patient quality or safety outcomes beyond patient satisfaction. The effects of Lean on employees were rarely discussed or measured systematically, but there were some indications of positive effects on employees and organizational culture. Success factors included employee involvement, management support, and preparedness for change. Despite some methodological, practical, and theoretic concerns, Lean appears to offer significant improvement opportunities. Many questions remain about Lean's effects on patient health and employees and how Lean can be best implemented in health care.
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| 7. |
- Isbister, Geoffrey K., et al.
(author)
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Activated charcoal decreases the risk of QT prolongation after citalopram overdose
- 2007
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In: Annals of Emergency Medicine. - : Elsevier BV. - 0196-0644 .- 1097-6760. ; 50:5, s. 593-600
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Journal article (peer-reviewed)abstract
- Study objective: We determine whether single-dose activated charcoal (SDAC) administration after citalopram overdose reduces the proportion of patients developing abnormal QT prolongation. Methods: Data were collected retrospectively for citalopram overdose patients presenting to 8 emergency departments. Demographics, dose, coingested drugs, SDAC administration, and serial ECGs were extracted from medical records. The primary outcome was the proportion of patients who had an observed QT,RR combination at any time above an abnormal threshold, established as a predictor of torsade de pointes. We compared the proportion of patients with QT prolongation who received or did not receive SDAC. These data were analyzed within a Bayesian framework, using probabilities of abnormal QT,RR combinations with and without derived from a previous single-center study. WinBUGS was used to generate posterior estimates and credible intervals of the relative risk by combining the prior probabilities and the study data. Results: SDAC was administered on average 2.1 hours (range, 0.5 to 6.25 hours) after ingestion in 48 of 254 admissions, and abnormal QT,RR combinations occurred in 2 cases (4.2%), compared with 23 of 206 (11.2%) cases not receiving SDAC. There did not appear to be any clinically important difference in age, sex, dose, and cardiotoxic coingestants between the 2 groups. No cases of torsade de pointes occurred. The estimated relative risk of having an abnormal QT,RR combination for SDAC compared to no SDAC was 0.28 (0.06 to 0.70) (median with 2.5% and 97.5% credible limits). The probability that the relative risk was less than 1.0 was 0.99, which can be interpreted as very strong evidence in favor of a beneficial effect of SDAC. The absolute risk difference was estimated as 7.5% and the median number needed to treat as 13.3. Conclusion: SDAC may be effective in reducing the risk of a prolonged QT in patients after citalopram overdose. Current trends toward nonuse of activated charcoal should be evaluated to determine whether patients poisoned by specific agents may benefit from activated charcoal administration.
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| 8. |
- Ljung, Lina, et al.
(author)
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A Rule-Out Strategy Based on High-Sensitivity Troponin and HEART Score Reduces Hospital Admissions
- 2019
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In: Annals of Emergency Medicine. - : MOSBY-ELSEVIER. - 0196-0644 .- 1097-6760. ; 73:5, s. 491-499
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Journal article (peer-reviewed)abstract
- Study objective: We evaluate whether a combination of a 1-hour high-sensitivity cardiac troponin algorithm and History, ECG, Age, Risk Factors, and Troponin (HEART) score reduces admission rate (primary outcome) and affects time to discharge, health care-related costs, and 30-day outcome (secondary outcomes) in patients with symptoms suggestive of an acute coronary syndrome.Methods: This prospective observational multicenter study was conducted before (2013 to 2014) and after (2015 to 2016) implementation of a strategy including level of high-sensitivity cardiac troponin T or I at 0 and 1 hour, combined with the HEART score. Patients with a nonelevated baseline high-sensitivity cardiac troponin level, a 1-hour change in high-sensitivity cardiac troponin T level less than 3 ng/L, or high-sensitivity cardiac troponin I level less than 6 ng/L and a HEART score less than or equal to 3 were considered to be ruled out of having acute coronary syndrome. A logistic regression analysis was performed to adjust for differences in baseline characteristics.Results: A total of 1,233 patients were included at 6 centers. There were no differences in regard to median age (64 versus 63 years) and proportion of men (57% versus 54%) between the periods. After introduction of the new strategy, the admission rate decreased from 59% to 33% (risk ratio 0.55 [95% confidence interval {CI} 0.48 to 0.63]; odds ratio 0.33 [95% CI 0.26 to 0.42]; adjusted odds ratio 0.33 [95% CI 0.25 to 0.42]). The median hospital stay was reduced from 23.2 to 4.7 hours (95% CI of difference -20.4 to -11.4); median health care-related costs, from $1,748 to $1,079 (95% CI of difference -$953 to -$391). The number of clinical events was very low.Conclusion: In this before-after study, clinical implementation of a 1-hour high-sensitivity cardiac troponin algorithm combined with the HEART score was associated with a reduction in admission rate and health care burden, with very low rates of adverse clinical events.
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| 9. |
- MOKHTARI, ARASH, et al.
(author)
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Diagnostic Accuracy of High-Sensitivity Cardiac Troponin T at Presentation Combined With History and ECG for Ruling Out Major Adverse Cardiac Events
- 2016
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In: Annals of Emergency Medicine. - : Elsevier BV. - 0196-0644 .- 1097-6760. ; 68:6, s. 649-658
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Journal article (peer-reviewed)abstract
- Study objective: We evaluate the diagnostic accuracy of a high-sensitivity cardiac troponin T (hs-cTnT) level less than 5 ng/L or less than or equal to 14 ng/L at emergency department (ED) presentation, combined with the emergency physician's assessment of history and ECG, for ruling out major adverse cardiac events within 30 days. Methods: This prospective observational study enrolled consecutive ED chest pain patients. Emergency physicians' assessments of patient history and ECG were collected. The primary outcome was 30-day major adverse cardiac events, defined as acute myocardial infarction, unstable angina, cardiogenic shock, ventricular arrhythmia, atrioventricular block, cardiac arrest, or death of cardiac or unknown cause. Results: A total of 1,138 patients were included in the final analysis. The combination of hs-cTnT less than 5 ng/L, a nonischemic ECG result, and a nonhigh risk history was present for 29.2% of all patients and had a sensitivity of 99.2% (95% confidence interval [CI] 95.6% to 100%), negative predictive value (NPV) of 99.7% (95% CI 98.3% to 100%), and a negative likelihood ratio of 0.02 (95% CI 0 to 0.17) for 30-day major adverse cardiac events. The same combination with hs-cTnT less than or equal to 14 ng/L was present in 66.7% of the patients and had a sensitivity of 92% (95% CI 85.8% to 96.1%), NPV of 98.7% (95% CI 97.6% to 99.4%), and negative likelihood ratio of 0.11 (95% CI 0.06 to 0.20). Conclusion: A single hs-cTnT result of less than 5 ng/L at ED presentation when combined with a nonischemic ECG result and a nonhigh risk history identified 29% of chest pain patients at a very low risk of 30-day major adverse cardiac events. A similar strategy with hs-cTnT less than or equal to 14 ng/L was associated with a higher miss rate.
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| 10. |
- Mueller, Christian, et al.
(author)
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Multicenter Evaluation of a 0-Hour/1-Hour Algorithm in the Diagnosis of Myocardial Infarction With High-Sensitivity Cardiac Troponin T
- 2016
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In: Annals of Emergency Medicine. - : Elsevier BV. - 0196-0644 .- 1097-6760. ; 68:1, s. 76-87
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Journal article (peer-reviewed)abstract
- Study objective: We aim to prospectively validate the diagnostic accuracy of the recently developed 0-h/1-h algorithm, using high-sensitivity cardiac troponin T (hs-cTnT) for the early rule-out and rule-in of acute myocardial infarction. Methods: We enrolled patients presenting with suspected acute myocardial infarction and recent (<6 hours) onset of symptoms to the emergency department in a global multicenter diagnostic study. Hs-cTnT (Roche Diagnostics) and sensitive cardiac troponin I (Siemens Healthcare) were measured at presentation and after 1 hour, 2 hours, and 4 to 14 hours in a central laboratory. Patient triage according to the predefined hs-cTnT 0-hour/1-hour algorithm (hs-cTnT beloow 12 ng/L and Delta 1 hour below 3 ng/L to rule out; hs-cTnT at least 52 ng/L r Delta 1 hour at least 5 ng/L to rule in; remaining patients to the "observational zone") was compared against a centrally adjudicated final diagnosis by 2 independent cardiologists (reference standard). The final diagnosis was based on all available information, including coronary angiography and echocardiography results, follow-up data, and serial measurements of sensitive cardiac troponin I, whereas adjudicators remained blinded to hs-cTnT. Results: Among 1,282 patients enrolled, acute myocardial infarction was the final diagnosis for 213 (16.6%) patients. Applying the hs-cTnT 0-hour/1-hour algorithm, 813 (63.4%) patients were classified as rule out, 184 (14.4%) were classified as rule in, and 285 (22.2%) were triaged to the observational zone. This resulted in a negative predictive value and sensitivity for acute myocardial infarction of 99.1% (95% confidence interval [CI] 98.2% to 99.7%) and 96.7% (95% CI 93.4% to 98.7%) in the rule-out zone (7 patients with false-negative results), a positive predictive value and specificity for acute myocardial infarction of 77.2% (95% CI 70.4% to 83.0%) and 96.1% (95% CI 94.7% to 97.2%) in the rule-in zone, and a prevalence of acute myocardial infarction of 22.5% in the observational zone. Conclusion: The hs-cTnT 0-hour/1-hour algorithm performs well for early rule-out and rule-in of acute myocardial infarction.
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| 11. |
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| 12. |
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| 13. |
- Postma, Jeroen, et al.
(author)
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Beyond Volume Indicators and Centralization: Toward a Broad Perspective on Policy for Improving Quality of Emergency Care
- 2017
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In: Annals of Emergency Medicine. - : MOSBY-ELSEVIER. - 0196-0644 .- 1097-6760. ; 69:6, s. 689-697
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Journal article (peer-reviewed)abstract
- Study objective: Policymakers increasingly regard centralization of emergency care as a useful measure to improve quality. However, the clinical studies that are used to justify centralization, arguing that volume indicators are a good proxy for quality of care (practice makes perfect), have significant shortcomings. In light of the introduction of a new centralization policy in the Netherlands, we show that the use of volume indicators in emergency care is problematic and does not do justice to the daily care provided in emergency departments (EDs). Methods: We conducted an ethnographic study in 3 EDs, a primary care facility, and an ambulance call center in the Netherlands, including 109 hours of observation, more than 30 ethnographic interviews with professionals and managers, and 5 semistructured follow-up interviews. Results: We argue that emergency care is a complex, multilayered practice and distinguish 4 different repertoires: acute and complex care, uncertain diagnostics, basic care, and physical, social, and mental care. A repertoire entails a definition of what good care is, what professional skills are needed, and how emergency care should be organized. Conclusion: The first repertoire of acute and complex care might benefit from centralization. The other 3 repertoires, however, equally deserve attention but are made invisible in policies that focus on the first repertoire and extrapolate the idea of centralization to emergency care as a whole. Emergency care research and policies should take all repertoires into account and pay more attention to alternative measures and indicators beyond volume, eg, patient satisfaction, professional expertise, and collaboration between EDs and other facilities.
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| 14. |
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| 15. |
- Ahlberg, Jörgen
(author)
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Optimizing Object, Atmosphere, and Sensor Parameters in Thermal Hyperspectral Imagery
- 2017
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In: IEEE Transactions on Geoscience and Remote Sensing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0196-2892 .- 1558-0644. ; 55:2, s. 658-670
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Journal article (peer-reviewed)abstract
- We address the problem of estimating atmosphere parameters (temperature and water vapor content) from data captured by an airborne thermal hyperspectral imager and propose a method based on linear and nonlinear optimization. The method is used for the estimation of the parameters (temperature and emissivity) of the observed object as well as sensor gain under certain restrictions. The method is analyzed with respect to sensitivity to noise and the number of spectral bands. Simulations with synthetic signatures are performed to validate the analysis, showing that the estimation can be performed with as few as 10-20 spectral bands at moderate noise levels. The proposed method is also extended to exploit additional knowledge, for example, measurements of atmospheric parameters and sensor noise. Additionally, we show how to extend the method in order to improve spectral calibration.
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| 16. |
- Asgarimehr, Milad, et al.
(author)
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Remote Sensing of Precipitation Using Reflected GNSS Signals: Response Analysis of Polarimetric Observations
- 2022
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 60
-
Journal article (peer-reviewed)abstract
- For the first time, rain effects on the polarimetric observations of the global navigation satellite system reflectometry (GNSS-R) are investigated. The physical feasibility of tracking the modifications in the surface roughness by rain splash and the surface salinity by the accumulation of freshwater is theoretically discussed. An empirical analysis is carried out using measurements of a coastal GNSS-R station with two side-looking antennas in right- and left-handed circular polarizations (RHCP and LHCP). Discernible drops in RHCP and LHCP powers are observed during rain over a calm sea. The power drop becomes larger at higher elevation angles. The average LHCP power drops by ≈ 5 dB at an elevation angle of 45°. The amplitude of the correlation sum shows a dampening, responding to rain rate systematically. The LHCP observations show higher sensitivity to rainfall compared to RHCP observations. The retrieved standard deviation of surface heights shows a steady increase with the rain rate. The derived surface salinity shows a decrease at rains higher than 10 mm/h. This study confirms the potential under environmental conditions of the GNSS-R ground-based station, e.g., with salinity mostly lower than 30 psu, over a calm sea, being a starting point for future investigations.
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| 17. |
- Asihene, Elvis, et al.
(author)
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Toward the Detection of Oil Spills in Newly Formed Sea Ice Using C-Band Multipolarization Radar
- 2022
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In: IEEE Transactions on Geoscience and Remote Sensing. - : IEEE Geoscience and Remote Sensing Society. - 0196-2892 .- 1558-0644. ; 60
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Journal article (peer-reviewed)abstract
- Oil spills in the Arctic are becoming more likely as shipping traffic increases in response to climate-related sea ice loss. To improve oil spill detection capability, we used a controlled mesocosm to analyze the multipolarized C-band backscatter response of oil in newly formed sea ice (NI). Artificial sea ice was grown in two cylindrical tubs at the Sea-ice Environmental Research Facility, University of Manitoba. The sea ice physical characteristics, including surface roughness, thickness, temperature, and salinity, were measured before and after oil injection below the ice sheet. Time-series C-band radar backscatter measurements detected the differences in the sea ice evolution and oil migration to the sea ice surface in the oil-contaminated tub, which was compared to uncontaminated ice in a control tub. Immediately prior to the presence of oil on the ice surface, the copolarized backscatter is increased by 13-dB local maximum, while the cross-polarized backscatter is decreased by 9-dB. Ice physical properties suggest that the local backscatter maximum and minimum, which occurred immediately before oil migrated onto the surface, were related to a combination of brine and oil upward migration. The findings of this work provide a baseline data interpretation for oil detection in the Arctic Ocean using current and future C-band multipolarization radar satellites.
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| 18. |
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| 19. |
- Askne, Jan, 1936, et al.
(author)
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Multitemporal Repeat Pass SAR Interferometry of Boreal Forests
- 2005
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 43:6, s. 1219-1228
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Journal article (peer-reviewed)abstract
- Multitemporal interferometric European Remote Sensing 1 and 2 satellite tandem pairs from a forest test site in Finland are examined in order to determine the stem volume retrieval accuracy. A form of multitemporal filtering is introduced to investigate what forest stands show a multitemporal consistency in coherence. It is found that a large stand size is a major factor to obtain accurate retrievals. The effect of heterogeneity of forest stands is also discussed. Based on the stands showing highest multitemporal consistency different models for scattering and coherence are compared. The interferometric water cloud model is chosen for stem volume retrieval. The variation of the model parameters with meteorological parameters is investigated and the results illustrate that the best imaging conditions are obtained for subzero temperatures and windy conditions. It is shown that for the 20 stands showing highest multitemporal consistency the stem volume can be retrieved with a relative error of 21%, deteriorating when the number of testing stands is increased, e.g., for 80 stands the error is 48%. For 37 large forest stands representing 48% of the investigated area the relative stem volume error is 26%. With experience from another site in Sweden we may conclude that the error level for a multitemporal interferometric synthetic aperture radar evaluation of stem volume for large forest stands ( > 2 ha) in a well managed and homogeneous boreal forest may be expected to be in the 15% to 25% range, deteriorating for small and heterogeneous stands and for images acquired under nonwinter conditions. © 2005 IEEE.
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| 20. |
- Bai, Tao, et al.
(author)
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Stealthy Adversarial Examples for Semantic Segmentation in Remote Sensing
- 2024
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In: IEEE Transactions on Geoscience and Remote Sensing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0196-2892 .- 1558-0644. ; 62
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Journal article (peer-reviewed)abstract
- Deep learning methods have been proven effective in remote sensing image analysis and interpretation, where semantic segmentation plays a vital role. These deep segmentation methods are susceptible to adversarial attacks, while most of the existing attack methods tend to manipulate the image globally, leading to noticeable perturbations and chaotic segmentation. In this work, we propose a novel stealthy attack for semantic segmentation (SASS), which can largely increase the effectiveness and stealthiness from the existing attack methods on remote sensing images. SASS manipulates specific victim classes or objects of interest while preserving the original segmentation results for other classes or objects. In practice, as different inference mechanisms, overlapped inference, can be applied in segmentation, the efficacy of SASS may be degraded. To this end, we further introduce the masked SASS (MSASS), which generates augmented adversarial perturbations that only affect victim areas. We evaluate the effectiveness of SASS and MSASS using four state-of-the-art semantic segmentation models on the Vaihingen and Zurich Summer datasets. Extensive experiments demonstrate that our SASS and MSASS methods achieve superior attack performances on victim areas while maintaining high accuracies of other areas (drop less than 2%). The detection success rates of adversarial examples for segmentation, as characterized by Xiao et al., significantly drop from 97.78% for the untargeted projected gradient descent (PGD) attack to 28.71% for our MSASS method on the Zurich Summer dataset. Our work contributes to the field of adversarial attacks in semantic segmentation for remote sensing images by improving stealthiness, flexibility, and robustness. We anticipate that our findings will inspire the development of defense methods to enhance the security and reliability of semantic segmentation models against our stealthy attack.
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| 21. |
- Ban, Yifang, et al.
(author)
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Object-Based Fusion of Multitemporal Multiangle ENVISAT ASAR and HJ-1B Multispectral Data for Urban Land-Cover Mapping
- 2013
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 51:4, s. 1998-2006
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Journal article (peer-reviewed)abstract
- The objectives of this research are to develop robust methods for segmentation of multitemporal synthetic aperture radar (SAR) and optical data and to investigate the fusion of multitemporal ENVISAT advanced synthetic aperture radar (ASAR) and Chinese HJ-1B multispectral data for detailed urban land-cover mapping. Eight-date multiangle ENVISAT ASAR images and one-date HJ-1B charge-coupled device image acquired over Beijing in 2009 are selected for this research. The edge-aware region growing and merging (EARGM) algorithm is developed for segmentation of SAR and optical data. Edge detection using a Sobel filter is applied on SAR and optical data individually, and a majority voting approach is used to integrate all edge images. The edges are then used in a segmentation process to ensure that segments do not grow over edges. The segmentation is influenced by minimum and maximum segment sizes as well as the two homogeneity criteria, namely, a measure of color and a measure of texture. The classification is performed using support vector machines. The results show that our EARGM algorithm produces better segmentation than eCognition, particularly for built-up classes and linear features. The best classification result (80%) is achieved using the fusion of eight-date ENVISAT ASAR and HJ-1B data. This represents 5%, 11%, and 14% improvements over eCognition, HJ-1B, and ASAR classifications, respectively. The second best classification is achieved using fusion of four-date ENVISAT ASAR and HJ-1B data (78%). The result indicates that fewer multitemporal SAR images can achieve similar classification accuracy if multitemporal multiangle dual-look-direction SAR data are carefully selected.
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| 22. |
- Berg, Anders, 1983, et al.
(author)
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Investigation of a Hybrid Algorithm for Sea Ice Drift Measurements Using Synthetic Aperture Radar Images
- 2014
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 52:8, s. 5023 - 5033
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Journal article (peer-reviewed)abstract
- Areal matching by phase correlation and feature tracking are two complementary methods used to measure sea ice drift between synthetic aperture radar images. This paper evaluates a new algorithm that combines the two methods. Areal matching is improved by new methods to handle large motions and rotated ice. It is shown that areal rotation can be resolved using a frequency-domain approach. Image segmentation is a prerequisite for feature tracking and achieved by a new method that performs better than Otsu's method for two-component Gaussian mixture distributions. A circular weighted median filter is found to be suitable for the filtering of the motion field. The algorithm is evaluated through a thorough analysis of the response and sensitivity to various algorithm settings. The accuracy of the algorithm varies by up to 50% for one image pair within the studied range of parameter settings, thus indicating the need for a proper initialization of the algorithm.
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| 23. |
- Berg, Anders, 1983, et al.
(author)
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X-Band Interferometric SAR Observations of Baltic Fast Ice
- 2015
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 53:3, s. 1248-1256
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Journal article (peer-reviewed)abstract
- Detailed mapping of fast-ice deformation can be used to characterize the rheological behavior of fast ice and subsequently improve sea ice modeling. This study uses interferometric synthetic aperture radar to map fast-ice deformation with unprecedented spatial resolution (meter range) and sensitivity (cm-mm range). Two interferometric acquisitions, each with a temporal baseline of 24 h, were performed by the X-band SAR satellite constellation Cosmo-SkyMed over the northeast Bay of Bothnia in the middle of the 2012 ice season. The first interferogram shows deformation of the fast ice due to force from impinging drift ice, and the normal strain within the fast ice is measured. Complementary intensity correlation measurements reveal a slow movement of the drift ice toward the fast ice. The second interferogram exhibits a low fringe rate over the fast ice with fringes being aligned along the coastline. Deformation appears to be stronger around leads, skerries, and grounded ice ridges. It is also observed that the coherence images provide information that is complementary to the information in the backscatter images.
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| 24. |
- Blomberg, Erik, 1987, et al.
(author)
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Evaluating P-Band TomoSAR for Biomass Retrieval in Boreal Forest
- 2021
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 59:5, s. 3793-3804
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Journal article (peer-reviewed)abstract
- P-band synthetic aperture radar (SAR) is sensitive to above-ground biomass (AGB) but retrieval accuracy has been shown to deteriorate in topographic areas. In boreal forest, the signal penetrates through the canopy to interact with the ground producing variations in backscatter depending on ground topography, forest structure, and soil moisture. Tomographic processing of multiple SAR images Tomographic SAR (TomoSAR) provides information about the vertical backscatter distribution. This article evaluates the use of P-band TomoSAR data to improve AGB retrievals from backscattered intensity by suppressing the backscattered signal from the ground. This approach can be used even when the tomographic resolution is insufficient to resolve the vertical backscatter profile. The analysis is based on P-band data from two campaigns: BioSAR-1 (2007) in Remingstorp, southern Sweden, and BioSAR-2 (2008) in Krycklan (KR), northern Sweden. BioSAR airborne data were also processed to correspond as closely as possible to future BIOMASS TomoSAR acquisitions, with BioSAR-2-based results shown. A power law AGB model using volumetric HV polarized backscatter performs best in KR, with training residual root mean-squared error (RMSE) of 30%-36% (27-33 t/ha) for airborne data and 38%-39% for simulated BIOMASS data. Airborne TomoSAR data suggest that both vertical and horizontal tomographic resolution are of importance and that it is possible to greatly reduce AGB retrieval bias when compared with airborne P-band SAR backscatter intensity-based retrievals. A lack of significant ground slopes in Remningstorp reduces the benefit of using TomoSAR data which performs similar to retrievals based solely on P-band SAR backscatter intensity.
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| 25. |
- Carvajal, Gisela, 1983, et al.
(author)
-
Retrieval and Quality Assessment of Wind Velocity Vectors on the Ocean With C-Band SAR
- 2014
-
In: IEEE Transactions on Geoscience and Remote Sensing. - : Institute of Electrical and Electronics Engineers (IEEE). - 0196-2892 .- 1558-0644. ; 52:5, s. 2519-2537
-
Journal article (peer-reviewed)abstract
- Wind vector fields derived from synthetic aperture radar (SAR) sensors show variations at smaller scales than most other globally available surface wind sources. However, few studies have been devoted to the investigation of the accuracy of SAR-derived wind fields at different scales and how they compare with other wind data. In order to investigate these issues, an algorithm for the retrieval of SAR-derived wind vectors has been developed, and a quality assessment between the retrievals and in situ, scatterometer, and numerical weather model (NWM) wind data has been performed. The implemented wind retrieval algorithm detects streak features in the SAR image to estimate wind directions and inverts wind speeds using CMOD-IFR2, CMOD5, or CMOD5.N geophysical model functions. In addition, a regularization method for filtering outliers in the wind direction retrievals is used. Retrievals compared with in situ data indicated better performance at offshore locations for wind speed inversions with CMOD5.N. The bias and standard deviation for offshore regularized wind directions and CMOD5.N speeds are 9 degrees and 25 degrees and -0.1 and 1.4 m/s, respectively. The comparison with the scatterometer and NWM wind data has been performed for retrievals at 5-, 10-, and 20-km resolution. The results indicate a better agreement of the coarser retrievals with the reference data. Nevertheless, mapping of smaller scale features requires wind directions from the SAR image itself.
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| 26. |
- Casella, Daniele, et al.
(author)
-
Transitioning From CRD to CDRD in Bayesian Retrieval of Rainfall From Satellite Passive Microwave Measurements : Part 2. Overcoming Database Profile Selection Ambiguity by Consideration of Meteorological Control on Microphysics
- 2013
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 51:9, s. 4650-4671
-
Journal article (peer-reviewed)abstract
- A new cloud dynamics and radiation database (CDRD) precipitation retrieval algorithm for satellite passive microwave (PMW) radiometer measurements has been developed. It represents a modification to and an improvement upon the conventional cloud radiation database (CRD) algorithms, which have always been prone to ambiguity. This part 2 paper of a series describes the methodology of the algorithm and the modeling verification analysis involved in creating a synthetic CDRD database for the Europe/Mediterranean basin region. This is followed by a proof-of-concept analysis, which demonstrates that the underlying CDRD theory based on use of meteorological parameters for reducing retrieval ambiguity is valid. This paper uses a regional/mesoscale model, applied in cloud resolving model (CRM) mode, to produce a large set of numerical simulations of precipitating storms and extended precipitating systems. The simulations are used for selection of millions of meteorological/microphysical vertical profiles within which surface rainfall is identified. For each of these profiles, top-of-atmosphere brightness temperature (TB) vectors are calculated (the vector dimension associated with the number of relevant cm-mm wavelengths and polarizations), based on an elaborate radiative-transfer equation (RTE) model system (RMS) coupled to the CRM. This entire body of simulation information is organized into the CDRD database, then used as a priori knowledge to guide a physical Bayesian retrieval algorithm in obtaining rainfall and associated precipitation parameters from the PMW satellite observations. We first prove the physical validity of our CRM-RMS simulations, by showing that the simulated TBs are in close agreement with observations. Agreement is demonstrated using dual-channel-frequency TB manifold sections, which quantify the degree of overlap between the simulated and observed TBs extracted from the full manifolds. Nevertheless, the salient result of this paper is a proof that the underlying CDRD theory is valid, found by combining subdivisions of the invoked meteorological parameter ranges of values and showing that such meteorological partitioning associates itself with distinct microphysical profiles. It is then shown that these profiles give rise to similar TB vectors, proving the existence of ambiguity in a CRD-type algorithm. Finally, we show that the CDRD methodology provides significant improvements in reducing retrieval ambiguity and retrieval error, especially for land surface backgrounds where contrasts are typically small between the rainfall TB signatures and surface emission signatures.
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| 27. |
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| 28. |
- Deng, Juan, et al.
(author)
-
Hierarchical Segmentation of Multitemporal RADARSAT-2 SAR Data Using Stationary Wavelet Transform and Algebraic Multigrid Method
- 2014
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 52:7, s. 4353-4363
-
Journal article (peer-reviewed)abstract
- The objective of this paper is to develop a new effective method for hierarchical segmentation of multitemporal ultrafine-beam synthetic aperture radar (SAR) data in urban areas. Multitemporal RADARSAT-2 ultrafine-beam high-resolution horizontal transmit and horizontal receive-Synthetic Aperture Radar (HH-SAR) images acquired in the rural-urban fringe of the Greater Toronto Area during the summer of 2008 are selected for this research. Stationary wavelet transform (SWT) and algebraic multigrid (AMG) method are proposed for segmentation of SAR data. SWT is applied for decomposition of multitemporal SAR images in image preprocessing. The hierarchical and matrix-based AMG method is applied for segmentation. A pyramid of fine-to-coarse grids is constructed by iteration of selecting representative pixels and calculating the interpolation matrix between a fine-level grid and a coarse-level grid. When the pyramid is completed, segments are determined by a top-down scanning based on the interpolation matrices. The AMG techniques provide a complete hierarchical segmentation of SAR data. The experimental results show that our method produces higher accuracy than eCognition.
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| 29. |
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| 30. |
- Elyouncha, Anis, 1978, et al.
(author)
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Empirical Relationship Between the Doppler Centroid Derived From X-Band Spaceborne InSAR Data and Wind Vectors
- 2022
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 60
-
Journal article (peer-reviewed)abstract
- One of the challenges in ocean surface current retrieval from synthetic aperture radar (SAR) data is the estimation and removal of the wave-induced Doppler centroid (DC). This article demonstrates empirically the relationship between the dc derived from spaceborne X-band InSAR data and the ocean surface wind and waves. In this study, we analyzed over 300 TanDEM-X image pairs. It is found that the general characteristics of the estimated dc follow the theoretically expected variation with incidence angle, wind speed, and wind direction. An empirical geophysical model function (GMF) is fit to the estimated dc and compared to existing models and previous experiments. Our GMF is in good agreement (within 0.2 m/s) with other models and data sets. It is found that the wind-induced Doppler velocity contributes to the total Doppler velocity with about 15% of the radial wind speed. This is much larger than the sum of the contributions from the Bragg waves (~0.2 m/s) and the wind-induced drift current (~3% of wind speed). This indicates a significant (dominant) contribution of the long wind waves to the SAR dc. Moreover, analysis of dual-polarized data shows that the backscatter polarization ratio (PR=σ⁰VV/σ⁰HH) and the dc polarization difference (PD=|dcVV|-|dcHH|) are systematically larger than 1 and smaller than 0 Hz, respectively, and both increase in magnitude with incidence angle. The estimated PR and PD are compared to other theoretical and empirical models. The Bragg scattering theory-based (pure Bragg and composite surface) models overestimate both PR and PD, suggesting that other scattering mechanisms, e.g., wave breaking, are involved. In general, it is found that empirical models are more consistent with both backscatter and Doppler data than theory-based models. This motivates a further improvement of SAR dc GMFs.
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| 31. |
- Elyouncha, Anis, 1978, et al.
(author)
-
Measurements of Sea Surface Currents in the Baltic Sea Region Using Spaceborne Along-Track InSAR
- 2019
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 57:11, s. 8584-8599
-
Journal article (peer-reviewed)abstract
- The main challenging problems in ocean current retrieval from along-track interferometric (ATI)-synthetic aperture radar (SAR) are phase calibration and wave bias removal. In this paper, a method based on differential InSAR (DInSAR) technique for correcting the phase offset and its variation is proposed. The wave bias removal is assessed using two different Doppler models and two different wind sources. In addition to the wind provided by an atmospheric model, the wind speed used for wave correction in this work is extracted from the calibrated SAR backscatter. This demonstrates that current retrieval from ATI-SAR can be completed independently of atmospheric models. The retrieved currents, from four TanDEM-X (TDX) acquisitions over the Öresund channel in the Baltic Sea, are compared to a regional ocean circulation model. It is shown that by applying the proposed phase correction and wave bias removal, a good agreement in spatial variation and current direction is achieved. The residual bias, between the ocean model and the current retrievals, varies between 0.013 and 0.3 m/s depending on the Doppler model and wind source used for wave correction. This paper shows that using SAR as a source of wind speed reduces the bias and root-mean-squared-error (RMSE) of the retrieved currents by 20% and 15%, respectively. Finally, the sensitivity of the sea current retrieval to Doppler model and wind errors are discussed.
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| 32. |
- Feng, Peng, 1993, et al.
(author)
-
A Novel Tropospheric Error Formula for Ground-based GNSS Interferometric Reflectometry
- 2023
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 61, s. 1-18
-
Journal article (peer-reviewed)abstract
- We deduce a Novel Interferometric Tropospheric Error (NITE) formula for ground-based GNSS interferometric reflectometry (GNSS-IR). This formula contains two parts: a geometric displacement error that accounts for the reflection point change due to the atmosphere and the earth curvature, and a path delay derived following the definition of the mapping function (with the small curve path effect included). We validate the NITE formula together with two previously used approaches, the bending angle correction and the mapping function path delay (MPF delay) using raytracing and radiosonde data. The raytracing results show that the NITE formula is more accurate than the previous approaches. Numerically, the geometric displacement error is < 5 % of the path delay error for a GNSS antenna located 20 m above sea level. We further evaluate six tropospheric correction strategies for GNSS-IR sea level monitoring through two sets of experiments. With an elevation angle range test, we show that applying no tropospheric correction and applying the bending angle correction plus the MPF delay both introduce large elevation-dependent biases. Analyzing the time series of differences between GNSS-IR and tide gauges sea level, we show that the bending angle correction with the widely used Bennett equation introduces long-term (4 h to several months) trends in the sea-level retrievals. We identify one station where the NITE formula produces better long-term (τ > 4 h) sea-level retrievals. Finally, we show that at low elevation angles, the bending angle correction can be reformulated as an MPF delay.
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| 33. |
- Folkesson, Klas, 1976, et al.
(author)
-
Model-based compensation of topography effects for improved stem volume retrieval from CARABAS-II VHF-band SAR images
- 2009
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 47:4, s. 1045-1055
-
Journal article (peer-reviewed)abstract
- A limiting factor that has been identified for stem-volume retrieval in coniferous forests using VHF synthetic aperture radar is that the backscatter varies depending on ground topography. On sloping ground, the backscatter from a forest is reduced, since the dominant groundtrunk double-bounce scattering mechanism is changed. This leads to underestimation of stem volume, and the variations caused by topography can obscure real variations in stem volume. By using multiple images acquired with different flight headings and combining the image information with ground-topography data in a model-based inversion method, we are able to compensate for the ground-topography influence on the backscatter. The inversion method is based on image segmentation and the optimal estimation method. Using four or more images from the CARABAS-II system and a coarse digital elevation model with 50-m horizontal grid, the stem volume can be retrieved with an average root-mean-square error (rmse) of less than 60 $\hbox{m}^{3}\hbox{ha}^{-1}$ for stem volumes in range of 80700 $\hbox{m}^{3}\hbox{ha}^{-1}$ (in terms of above-ground biomass, this is equivalent to an rmse of less than 40 $\hbox{ton} \cdot\hbox{ha}^{-1}$ over the range of 50400 $\hbox{ton} \cdot\hbox{ha}^{-1}$). The retrieval accuracy is similar to that previously obtained for similar forests standing on flat and horizontal ground.
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| 34. |
- Fransson, J.E.S., et al.
(author)
-
Detection of storm-damaged forested areas using airborne CARABAS-II VHF SAR image data
- 2002
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 40:10, s. 2170-2175
-
Journal article (peer-reviewed)abstract
- Strong winds cause severe damage worldwide to forested land every year. The devastating storms that struck large parts of Europe in late 1999 destroyed the equivalent of several years of normal forest harvesting, amounting to very large economical sums. Therefore, rapid mapping of damaged areas is of major importance for assessment of short-term actions as well as for long-term reforestation purposes. In this paper, the use of airborne CARABAS-II very high frequency (VHF) (20-90 MHz) synthetic aperture radar (SAR) imagery for high spatial resolution mapping of wind-thrown forests has been investigated and evaluated. The investigation was performed at a test site located in southern Sweden and dominated by Norway spruce forests. A regression model estimating radar backscattering amplitude prior to the storm was developed. The estimated amplitudes were compared to measured amplitudes after the storm. The results clearly show that the backscattering amplitude, at a given stem volume, is considerably higher for wind-thrown forests than for unaffected forests. Furthermore, the backscattering from fully harvested storm-damaged areas was, as expected, significantly lower than from unaffected stands. These findings imply that VHF SAR imagery has potential for mapping wind-thrown forests. However, to prevent ambiguities in increased backscattering caused by normal stem volume growth or wind-fellings, multitemporal change detection techniques using VHF SAR images acquired prior to and after wind-fellings would be preferable.
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| 35. |
- Fransson, JES, et al.
(author)
-
Estimation of forest parameters using CARABAS-II VHFSAR data
- 2000
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 38:2, s. 720-727
-
Journal article (peer-reviewed)abstract
- The use of airborne CARABAS-II VHF (20-90 MHz) SAR data for retrieval of forest parameters has been investigated, The investigation was performed at a test site located in the southwest: of Sweden consisting mainly of Norway spruce forests. Regression models predicting forest parameters from radar backscattering amplitude were developed and evaluated. The results showed a linear relationship between backscattering amplitude and forest stem volume, stem diameter, and tree height. The analysis also showed that the radar signal is strongly affected by ground slope conditions. The root mean square errors from the regression analysis, restricted to forest stands on near-horizontal ground, were found to be 66 m(3) ha(-1), 3.2 cm, and 2.3 m for stem volume, stem diameter, and tree height respectively. No saturation of the backscattered signal was observed up to the maximum stem volume of 625 m(3) ha(-1), corresponding to a biomass of 375 tons ha(-1). The results imply that VHF SAR data have significant potential for operational use in forestry.
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| 36. |
- Friman, Ola, et al.
(author)
-
Methods for Large-Scale Monitoring of District Heating Systems Using Airborne Thermography
- 2014
-
In: IEEE Transactions on Geoscience and Remote Sensing. - : IEEE. - 0196-2892 .- 1558-0644. ; 52:8, s. 5175-5182
-
Journal article (peer-reviewed)abstract
- District heating is a common way of providing heat to buildings in urban areas. The heat is carried by hot water or steam and distributed in a network of pipes from a central powerplant. It is of great interest to minimize energy losses due to bad pipe insulation or leakages in such district heating networks. As the pipes generally are placed underground, it may be difficult to establish the presence and location of losses and leakages. Toward this end, this work presents methods for large-scale monitoring and detection of leakages by means of remote sensing using thermal cameras, so-called airborne thermography. The methods rely on the fact that underground losses in district heating systems lead to increased surface temperatures. The main contribution of this work is methods for automatic analysis of aerial thermal images to localize leaking district heating pipes. Results and experiences from large-scale leakage detection in several cities in Sweden and Norway are presented.
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| 37. |
- Gao, Jingyu, et al.
(author)
-
Three-Dimensional Transient Electromagnetic Forward Modeling for Simulating Arbitrary Source Waveform Using Convolution Approach
- 2023
-
In: IEEE Transactions on Geoscience and Remote Sensing. - : Institute of Electrical and Electronics Engineers Inc.. - 0196-2892 .- 1558-0644. ; 61
-
Journal article (peer-reviewed)abstract
- The transient electromagnetic (TEM) method utilizes artificial transmitters and measures electromagnetic (EM) responses to reveal the resistivity information of the subsurface. The current waveform of transmitters has nonnegligible effects on induced fields. Therefore, 3-D TEM forward modeling algorithms need the capability of simulating arbitrary waveforms to obtain accurate responses. In time-stepping-based 3-D TEM forward modeling, the source term (ST) approach is frequently used, which employs the source current density to model the waveform variation during time-stepping. The ST approach, however, requires fine-time discretization to describe complex waveforms, which could significantly raise the computational cost. We present a robust convolution (Conv) approach that computes the convolution between the time derivative of the waveform and the step-off response to incorporate the waveform effects in 3-D TEM modeling. The Conv approach does not discretize the waveform using time steps. Hence, it is advantageous when modeling full-waveform cases. The developed algorithm is based on the finite-element (FE) method using unstructured grids and the implicit backward Euler approach. Both galvanic and inductive transmitters are incorporated. Ground and airborne TEM surveys are tested using an actual airborne TEM waveform, a full waveform of the 2(n) -sequence pseudorandom signal, and various synthetic waveforms. Accuracy is validated against the 1-D and 3-D solutions of published studies. The ST and Conv approaches are compared. Synthetic examples show that the latter approach simplifies the waveform incorporation in TEM modeling and substantially improves time-stepping efficiency without sacrificing accuracy.
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| 38. |
- Granström, Karl, et al.
(author)
-
Gamma Gaussian Inverse Wishart Probability Hypothesis Density for Extended Target Tracking Using X-Band Marine Radar Data
- 2015
-
In: IEEE Transactions on Geoscience and Remote Sensing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0196-2892 .- 1558-0644. ; 53:12, s. 6617-6631
-
Journal article (peer-reviewed)abstract
- X-band marine radar systems represent a flexible and low-cost tool for the tracking of multiple targets in a given region of interest. Although suffering several sources of interference, e.g., the sea clutter, these systems can provide high-resolution measurements, both in space and time. Such features offer the opportunity to get accurate information not only about the target position/motion but also about the targets size. Accordingly, in this paper, we exploit emergent extended target tracking (ETT) methodologies in which the target state, typically position/velocity/acceleration, is augmented with the target length and width. In this paper, we propose an ETT procedure based on the popular probability hypothesis density filter, and in particular, we describe the extended target state through the gamma Gaussian inverse Wishart model. The comparative simplicity of the used models allows us to meet the real-time processing constraint required for the practical surveillance purposes. Real-world data from an experimental and operational campaign, collected during the recovery operations of the Costa Concordia wreckage in October 2013, are used to assess the performance of the proposed target tracking methodology. The full signal processing chain is implemented, and considerations of the experimental results are provided. Important nonideal effects, common to every marine radar, are observed and discussed in relation to the assumptions made for the tracking procedure.
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| 39. |
- Hallberg, B., et al.
(author)
-
A physical-optics model for double-bounce scattering from tree stems standing on an undulating ground surface
- 2008
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 46:9, s. 2607-2621
-
Journal article (peer-reviewed)abstract
- In this paper, a model for prediction of radar backscatter from coniferous forests in the VHF and UHF band is proposed. The model includes the double-bounce scattering originating from vertical stems standing on an undulating ground surface and is based on a physical-optics approach. The model can be used to assess the importance of ground topography in synthetic aperture radar (SAR) imagery of forests, and it is applicable to SAR systems using horizontally transmit and receive polarization (HH). The model was validated against data from the airborne SAR systems CARABAS-II and LORA. Precision measurements of ground topography and forest characterization at a single tree level were used as model input to simulate SAR images. The simulated images were compared to radar data in the frequency bands 22-82 and 225-470 MHz, and it was found that the model could predict much of the variation in backscatter observed in images (R2 = 0.44 and 0.65 at best, for the lower and higher frequency band, respectively), which should be compared to R2 ˜ 0.1 if the same model, but assuming a flat ground, was used. The results thus indicate that ground topography must be considered when predicting the variations in backscatter in the SAR images studied. The model did, however, fail to predict the absolute values of the backscattered intensity. The reason for the discrepancy is believed to be the value chosen for stem dielectric constant and unmodeled effects due to wave attenuation, tilting stems, and small-scale surface roughness. © 2008 IEEE.
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| 40. |
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| 41. |
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| 42. |
- Hirsch, Michael, et al.
(author)
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Reconstruction of Fine-Scale Auroral Dynamics
- 2016
-
In: IEEE Transactions on Geoscience and Remote Sensing. - : Institute of Electrical and Electronics Engineers (IEEE). - 0196-2892 .- 1558-0644. ; 54:5, s. 2780-2791
-
Journal article (peer-reviewed)abstract
- We present a feasibility study for a high-frame-rate Short-baseline auroral tomographic imaging system useful for estimating parametric variations in the precipitating electron number flux spectrum of dynamic auroral events. Of particular interest are auroral substorms, which are characterized by spatial variations of order 100 m and temporal variations of order 10 ms. These scales are thought to be produced by dispersive Alfven waves in the near-Earth magnetosphere. The auroral tomography system characterized in this paper reconstructs the auroral volume emission rate, to estimate the characteristic energy and location in the direction perpendicular to the geomagnetic field of peak electron precipitation flux, using a distributed network of precisely synchronized ground-based cameras. As the observing baseline decreases, the tomographic inverse problem becomes highly ill-conditioned; as the sampling rate increases, the signal-to-noise ratio degrades and synchronization requirements become increasingly critical. Our approach to these challenges uses a physics-based auroral model to regularize the poorly observed vertical dimension. Specifically, the vertical dimension is expanded in a low-dimensional basis, consisting of eigenprofiles computed over the range of expected energies in the precipitating electron flux, while the horizontal dimension retains a standard orthogonal pixel basis. Simulation results show typical characteristic energy estimation error less than 30% for a 3-km baseline achievable within the confines of the Poker Flat Research Range, using GPS-synchronized electron-multiplying charge-coupled device cameras with broadband BG3 optical filters that pass prompt auroral emissions.
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| 43. |
- Hoseini, Mostafa, et al.
(author)
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On the Response of Polarimetric GNSS-Reflectometry to Sea Surface Roughness
- 2021
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 59:9, s. 7945-7956
-
Journal article (peer-reviewed)abstract
- Reflectometry of Global Navigation Satellite Systems (GNSS) signals from the ocean surface has provided a new source of observations to study the ocean-atmosphere interaction. We investigate the sensitivity and performance of GNSS-Reflectometry (GNSS-R) data to retrieve sea surface roughness (SSR) as an indicator of sea state. A data set of one-year observations in 2016 is acquired from a coastal GNSS-R experiment in Onsala, Sweden. The experiment exploits two sea-looking antennas with right- and left-hand circular polarizations (RHCP and LHCP). The interference of the direct and reflected signals captured by the antennas is used by a GNSS-R receiver to generate complex interferometric fringes. We process the interferometric observations to estimate the contributions of direct signals and reflections to the total power. The power estimates are inverted to the SSR using the state-of-the-art model. The roughness measurements from the RHCP and LHCP links are evaluated against match-up wind measurements obtained from the nearest meteorological station. The results report on successful roughness retrieval with overall correlations of 0.76 for both links. However, the roughness effect in LHCP observations is more pronounced. The influence of surrounding complex coastlines and the wind direction dependence are discussed. The analysis reveals that the winds blowing from land have minimal impact on the roughness due to limited fetch. A clear improvement of roughness estimates with an overall correlation of 0.82 is observed for combined polarimetric observations from the RHCP and LHCP links. The combined observations can also improve the sensitivity of GNSS-R measurements to the change of sea state.
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| 44. |
- Israelsson, H, et al.
(author)
-
A coherent scattering model to determine forest backscattering in the VHF-band
- 2000
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 38:1, s. 238-248
-
Journal article (peer-reviewed)abstract
- A coherent scattering model to determine the forest radar backscattering at VHF frequencies (20-90 MHz) has been de developed. The motivation for studying this frequency band is the recent development of the CARABAS Synthetic Aperture Radar (SAR). In order to model the scattering from branches and trunks, homogeneous dielectric cylinders placed above a semi-infinite dielectric ground have been analyzed. An analytical approach, where the theoretically exact currents induced in an infinite cylinder are truncated, has been compared to a numerical solution using the finite difference time domain (FDTD) method, If the first-order coherent ray tracing is included in the analytical approach, the results match well with the numerically exact FDTD solution. The results show that, in order to determine the VHF-backscattering from a forest stand, the coherent ground interaction is an important part and has to be considered. In this paper, modeling results are in good agreement with CARABAS measurements.
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| 45. |
- Jakobsson, Andreas, et al.
(author)
-
Frequency-Selective Detection of Nuclear Quadrupole Resonance Signals
- 2005
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 43:11, s. 2659-2665
-
Journal article (peer-reviewed)abstract
- Nuclear quadrupole resonance (NQR) offers an unequivocal method of detecting and identifying both hidden explosives, such as land mines, and a variety of narcotics. Unfortunately, the practical use of NQR is restricted by a low signal-to-noise ratio (SNR), and means to improve the SNR are vital to enable a rapid, reliable, and convenient system. In this paper, we introduce a frequency-selective approximate maximum-likelihood (FSAML) detector, operating on a subset of the available frequencies, making it robust to the typically present narrow-band interference. The method exploits the inherent temperature dependency of the NQR frequencies as a way to enhance the SNR. Numerical evaluations, using both simulated and real NQR data, indicate a significant gain in probability of accurate detection as compared to a current state-of-the-art approach.
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| 46. |
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| 47. |
- Jarlemark, Per O. J., 1962, et al.
(author)
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Ground-Based GPS for Validation of Climate Models: The Impact of Satellite Antenna Phase Center Variations
- 2010
-
In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 48:10, s. 3847-3854
-
Journal article (peer-reviewed)abstract
- The amount of water vapor in the atmosphere is an important indicator for climate change. Using the Global Positioning System (GPS), it is possible to estimate the integrated water vapor (IWV) above the ground-based GPS receiver. In order to optimally determine the IWV, a correct model of the received signal phase is essential. We have studied the effect of the satellite antenna phase center variations (PCVs) on the IWV estimates by simulating the effect and by studying the estimates of the IWV based on the observed GPS signals. During a period of five years, from 2003 to 2008, a new satellite type was introduced, and it steadily grew in numbers. The antenna PCVs for these satellites deviate from the earlier satellite types and contribute to excess IWV estimates. We find that ignoring satellite antenna phase variations for this time period can lead to an additional IWV trend of about 0.15 kg/m2/year for regular GPS processing.
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| 48. |
- Kakooei, Mohammad, 1988, et al.
(author)
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Increasing the confidence of predictive uncertainty: earth observations and deep learning for poverty estimation
- 2024
-
In: IEEE Transactions on Geoscience and Remote Sensing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0196-2892 .- 1558-0644. ; 62, s. 1-13
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Journal article (peer-reviewed)abstract
- Reducing global poverty, particularly in low- and middle-income countries, is a critical objective of the Sustainable Development Goals (SDGs). To track progress towards these goals, high-frequency, granular geo-temporal data that captures changes at the neighborhood level is essential for researchers and policymakers. Recent advancements in methodology have combined machine learning (ML) and earth observations (EO) for poverty estimation, thereby addressing significant data gaps. However, a notable limitation of these EO-ML methods is their frequent deployment without a robust mechanism to quantify predictive uncertainty. Understanding this uncertainty is crucial for making informed decisions, effectively managing risks, and instilling confidence in users and stakeholders regarding the model’s predictions. Although deep learning (DL) offers methods to quantify predictive uncertainties, their reliability is often constrained, failing to accurately reflect the underlying variations in predictions. Our proposed method aims to enhance confidence in predictive uncertainty without sacrificing accuracy. It begins by integrating an external model to explicitly capture data variability. Subsequently, we employ two orthogonal metrics—accuracy and uncertainty—to evaluate the influence of training data, especially in scenarios involving satellite imagery (e.g., selecting a subset of source domain countries for prediction in the target country). By applying these metrics, we formulate criteria to assess the importance of choosing specific countries from the source domain as training data. Our analysis highlights the effectiveness of this methodology in situations where the target country offers high-dimensional data, like satellite images, but faces a shortage of adequate training samples for deep learning models.
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| 49. |
- Kasai, Y., et al.
(author)
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Stratospheric Ozone Isotope Enrichment Studied by Sub-Millimeter Wave Heterodyne Radiometry: The Observation Capabilities of SMILES
- 2006
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 44:3, s. 676-693
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Journal article (peer-reviewed)abstract
- The isotopic ratio of molecules often provides valuable information about past or presently occurring processes in the atmosphere because chemical and physical processes may give rise to isotope fractionation of molecular species. However, there are so far no published satellite measurements on the spatial and temporal variations of ozone isotopes in the stratosphere. Spectroscopic remote sensing methods can theoretically be used to observe ozone isotope fractionation on a global scale, but sufficient accuracy has not yet been achieved. A new generation of submillimeter-wave receivers employing sensitive superconductor-insulator - superconductor (SIS) detector technology will provide new opportunities for precise remote sensing measurements of ozone isotopes on a global scale. We have estimated the observation capabilities of two different SIS instruments, namely the space-station-borne Japanese Experimental Module/Sub-Millimeter-wave Limb Emission Sounder (JEM/SMILES) instrument, currently planned for launch in 2008, as well as the airborne Submillimeter wave Atmospheric Sounder/Airborne Submillimeter SIS Radiometer (SUMAS/ASUR) sensor. Measurements of the airborne sensor, conducted in 1996, are presented in order to demonstrate the detection of normal-O 3 and asymmetric-18-O 3 in the SMILES frequency bands. In the ideal case, JEM/SMILES has the capability to measure the ozone isotope enrichment (δ M O 3 ) in the middle stratosphere with a precision of ∼12%∼11%‰‰, and ∼9%‰, for asymmetric-18-O 3 , symmetric-17-O 3 , asymmetric-17-O 3 , respectively, for a daily zonal mean product with resolution of 10° in latitude. The systematic error, including contributions of all instrumental and spectroscopic uncertainties, is estimated to be of the order of 100%‰ to 200%‰ and should be reduced by prelaunch laboratory measurements and in-flight calibrations. A remaining bias in the SMILES measurements will have to be quantified by dedicated validation campaigns. JEM/SMILES should then be capable to provide valuable information on the global distribution and seasonal variation of ozone isotope fractionation in the stratosphere. This new technology will allow us to shed new light on this still open issue in atmospheric sciences. © 2006 IEEE.
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| 50. |
- Kononov, Anatoliy, 1951, et al.
(author)
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Statistical Analysis of VHF-Band Tree Backscattering Using Forest Ground Truth Data and PO Scattering Model
- 2011
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 49:8, s. 3035-3046
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Journal article (peer-reviewed)abstract
- This paper analyzes the statistical properties of thevery high frequency (VHF)-band radar backscattering from coniferous trees by incorporating forest ground truth data into a physical-optics (PO) model that assumes horizontally transmit and receive polarizations and dominant double-bounce scattering from vertical stems standing on an undulating ground surface. The analysis shows that a statistically adequate model for the tree backscattering amplitude can be presented as a mixture of generalized gamma or lognormal distribution, and the mixture model can be reduced to a single density model if the trees withtrunk volumes exceeding an appropriate threshold are to be taken into account. The generalized gamma density is shown to provide an appreciably better fit to the exceedance functions associated with the PO model data than that for the lognormal density. The results can be used to design statistically adequate models of forest clutter for VHF synthetic aperture radar systems.
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