| 1. |
- Huo, Langning, et al.
(författare)
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Comparing spectral differences between healthy and early infested spruce forests caused by bark beetle attacks using satellite images
- 2022
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Ingår i: <em>IGARSS 2022 - 2022 IEEE International Geoscience and Remote Sensing Symposium</em>, Hybrid Symposium, Kuala Lumpur, Malaysia, 17-21 July, 2022. - : IEEE. - 9781665427920 - 9781665427937 ; , s. 7709-7712
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Konferensbidrag (refereegranskat)abstract
- Detecting forest insect damage before the visible discoloration (green attacks) using remote sensing data is challenging, but important for damage control. In recent years, the European spruce bark beetle (Ips typographus, L.) has damaged large amounts of forest in Europe. However, it is still debatable how early the infestations can be detected with remote sensing data. Some studies showed a spectral difference between healthy and green-attacked spruce trees at the plot level, while others showed that spectral differences existed before attacks. Therefore, a hypothesis is proposed that no spectral difference can be identified between green-attacked forests compared to healthy forests if the differences do not exist before the attacks. In this study, we tested this hypothesis using Sentinel-2 and WorldView-3 SWIR images on 24 healthy plots and 24 plots with mild, moderate, and severe attacks. In the results, the severely attacked plots did not show significant spectral differences in the Sentinel-2 images until August, and the sensitivity was found in the blue, red, red-edge, and SWIR band. Only the red band showed a significant difference between the healthy and moderately attacked plots in August, and only the blue, red, and SWIR band showed significant differences in September, October, and November. No significant differences were observed in the WorldView-3 images at the plot or individual tree level. We accepted the hypothesis that green attacks do not show spectral differences with the healthy forests when the differences do not exist before the attacks. We concluded that the SWIR bands were sensitive to attacks in the Sentinel-2 images with 10 m resolution, but not in the WorldView-3 images with 3.7 m resolution. Further studies are needed to explore the methodology of using WorldView-3 SWIR images for the early detection of forest infestation.
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| 2. |
- Huuva, Ivan, et al.
(författare)
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Detectability of Silvicultural Treatments in Time Series of Penetration Depth Corrected Tandem-X Phase Heights
- 2022
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Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS), Volume 2022-July. - : IEEE (Institute of Electrical and Electronics Engineers). - 2153-6996 .- 2153-7003. - 9781665427920 ; , s. 5909-5912
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Konferensbidrag (refereegranskat)abstract
- This study investigated the potential of utilizing time series of TanDEM-X phase heights, corrected for penetration depth, to detect silvicultural treatments in hemi-boreal forest. In total, 34 field plots with 40 m radius were used in conjunction with detailed forest management records to construct a reliable data set of treatments. The study area is situated in Remningstorp, a forest test site in southern Sweden. In the analysis, the temporal mean corrected phase heights were compared before and after a silvicultural treatment in order to quantify the effects of thinnings and clear-cuts on the phase height. As expected clear-cuts were highly distinguishable, but thinnings, while exhibiting a negative change in phase height on average, were not individually distinct from all untreated plots. Moreover, the results regarding the utility of applying penetration depth correction for the task were inconclusive. Overall, the results look very promising for using time series of phase height from TanDEM-X to map thinnings and clear-cuts, especially when several observations are available before and after the silvicultural treatment.
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| 3. |
- Javadi, Saleh, 1986-, et al.
(författare)
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Performance Evaluation of Unsupervised Coregistration Algorithms for Multitemporal SAR Images
- 2022
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Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665427920 ; , s. 64-67
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present three algorithms for the multitemporal synthetic aperture radar (SAR) images coregistration. The proposed algorithms are a 2-D cross correlation, a 1-D parabolic based, and a 2-D projective transformation. The 2-D cross correlation algorithm is used to obtain coarse estimation of the displacement for coregistration. In the second method, two independent 1-D parabolic interpolations are calculated to refine the estimation of the peak location of the cross correlation matrix with subpixel accuracy. Finally, in the third method, a 2-D projective transformation is employed to align the SAR images using point correspondences and the cubic interpolation. The performance evaluation of these algorithms are provided based on the coherence magnitude and the absolute displacement error for a point target using a corner reflector in the scene. The experimental results obtained on real recorded multitemporal satellite SAR data demonstrate the effectiveness and the computational complexity of these algorithms. © 2022 IEEE.
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| 4. |
- Palm, Bruna, et al.
(författare)
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Inflated Rayleigh Distribution for SAR Imagery Modeling
- 2022
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Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS 2022). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665427920 ; , s. 44-47
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Konferensbidrag (refereegranskat)abstract
- Synthetic aperture radars (SAR) data plays an important role in remote sensing applications. It is common knowledge that SAR image amplitude pixels can be approximately modeled by the Rayleigh distribution. However, this model is contin-uous and does not accommodate points with non-zero prob-ability, such as a null pixel amplitude value. Thus, in this paper, we propose an inflated Rayleigh distribution for SAR image modeling that is based on a mixed continuous-discrete distribution and can be used to fit signals with observed values on [0, infty). The maximum likelihood approach is considered to estimate the parameters of the proposed distribution. An empirical experiment with a SAR image is also presented and discussed. © 2022 IEEE.
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| 5. |
- Persson, Henrik J., et al.
(författare)
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Comparison of Boreal Biomass Estimations Using C-and X-Band Polsar
- 2022
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Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS), Volume 2022-July. - : IEEE. - 2153-6996 .- 2153-7003. - 9781665427920 ; , s. 5555-5558
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Konferensbidrag (refereegranskat)abstract
- This study investigated the potential of using polarimetric synthetic aperture radar (PolSAR) data acquired at C-and X-band to estimate forest aboveground biomass (biomass) at a test site in southern Sweden. The SAR data were acquired with RADARSAT-2 and TerraSAR-X in September 2015, and the biomass estimations were cross-validated with 48 field inventoried plots of 40 m radius (0.5 ha), covering dominantly coniferous hemi-boreal forest. The quad-pol SAR data (HH, HV, VH, VV) were decomposed using the Yamaguchi model and the mean modelled scatter components for the plots were extracted and used as predictors in linear regression models to estimate the biomass. The model performances were quantified using the root mean square error (RMSE) and adjusted coefficient of determination, R2adj. The leave-one-out cross-validated RMSEs were 58.1 (37.1%) and 60.6 (38.6%) tons/ha for C-and X-band, respectively, and the R2adj were 0.52 and 0.47, respectively. The regression model for C-band data used the volume and helix scattering components in the Yamaguchi decomposition as predictors, while the corresponding X-band model used the double bounce and surface components. The differences were likely due to the different penetrations at C-and X-band. We noticed a tendency to saturation at about 300 tons/ha in the X-band predictions, while no such tendency was noticed for the C-band model. We conclude that the Yamaguchi polarimetric decomposition technique is a useful approach when estimating biomass in a hemi-boreal forest. The strengths are not comparable to approaches where height information are available (e.g., single-pass interferometry from TanDEM-X), but this polarimetric approach based on single satellite images showed sensitivity to the entire biomass range (0-400 tons/ha) in our dataset. The potential of using quad-pol SAR data is, therefore, important to investigate further.
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| 6. |
- Rodriguez-Fernandez, N., et al.
(författare)
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Paving the Road to Flex and Biomass : The Land Surface Carbon Constellation Study
- 2022
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Ingår i: IGARSS 2022 - 2022 IEEE International Geoscience and Remote Sensing Symposium. - 9781665427920 ; 2022-July, s. 5571-5574
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Konferensbidrag (refereegranskat)abstract
- Remote sensing observations of variables related to vegetation at microwave and optical/infrared wavelengths are presented over three regions in Europe in the Iberian peninsula, northern Finland and central Europe. They include the instrumented sites of Las Majadas, Sodankyla and Reusel. The final goal is to better constrain land carbon cycle models using the complementarities of vegetation optical depth derived at different frequencies from active and passive instruments (related to vegetation water content and biomass) as well as optical data of the fraction of absorbed photosynthetically active radiation or solar induced fluorescence, closely linked to photosynthesis. The first results confirm this complementarity. For instance, time series of different variables exhibit positive correlations in some areas and negative correlations in other areas.
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