| 1. |
- Sandberg, Gustaf, 1982, et al.
(författare)
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L- and P-band backscatter intensity for biomass retrieval in hemiboreal forest
- 2011
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Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 115:11, s. 2874 - 2886
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Tidskriftsartikel (refereegranskat)abstract
- At present, the greatest source of uncertainty in the global carbon cycle is in the terrestrial ecosystems. In orderto reduce these uncertainties it is necessary to provide consistent and accurate global estimates of the worldforest biomass. One of the most promising methods for obtaining such estimates is through polarimetric SARbackscatter measurements at low frequencies. In this paper, the relation between polarimetric SAR backscatterat L- and P-bands and forest biomass is investigated using data acquired within the BioSAR-I campaign insouthern Sweden during 2007. Methods for estimating biomass on stand level using these data are developedand evaluated, and the results for the two frequency bands are compared. For L-band data, the best results wereobtained using HV-polarized backscatter only, giving estimation errors in terms of root mean square errors(RMSE) between 31% and 46% of the mean biomass for stands with biomass ranging from 10 to 290 t/ha, and an(adjusted) coefficient of determination (R2) between 0.4 and 0.6. For P-band data, the results are better thanfor L-band. Models using HV- or HH-polarized P-band backscatter give similar results, as does a modelincluding both HV and HH. The RMSEs were between 18 and 27%, and the R2 values were between 0.7 and 0.8.
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| 2. |
- Ulander, Lars, 1962, et al.
(författare)
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BIOSAR 2010 - A SAR campaign in support to the BIOMASS mission
- 2011
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Ingår i: Proceedings of IGARSS 2011 Symposium, Vancouver, Canada, 24-29 July, 2011. - 9781457710056 ; , s. 1528-1531, s. 1528-1531
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The ESA funded campaign BioSAR 2010 was carried out at the forestry test site Remningstorp in southern Sweden, in support to the BIOMASS satellite mission under study. Fully polarimetric SAR data were successfully acquired at L- and P-band using ONERA's multi-frequency system SETHI. In addition with other data types gathered, e.g. LiDAR and in-situ measurements, the compiled data set will be used for analyses and comparisons with biomass estimation results obtained at the same test site in the campaign BioSAR 2007, in which DLR's E-SAR made the SAR imaging. Detection of forest changes, robustness of biomass retrieval algorithms and long-term P-band coherence will be in focus as well as cross-validations between the two SAR sensors.
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| 3. |
- Askne, Jan, 1936, et al.
(författare)
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Model-Based Biomass Estimation of a Hemi-Boreal Forest from Multitemporal TanDEM-X Acquisitions
- 2013
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 5:11, s. 5574-5597
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Tidskriftsartikel (refereegranskat)abstract
- Above-ground forest biomass is a significant variable in the terrestrial carbon budget, but is still estimated with relatively large uncertainty. Remote sensing methods can improve the characterization of the spatial distribution and estimation accuracy of biomass; in this respect, it is important to examine the potential offered by new sensors. To assess the contribution of the TanDEM-X mission, eighteen interferometric Synthetic Aperture Radar (SAR) image pairs acquired over the hemi-boreal test site of Remningstorp in Sweden were investigated. Three models were used for interpretation of TanDEM-X signatures and above-ground biomass retrieval: Interferometric Water Cloud Model (IWCM), Random Volume over Ground (RVoG) model, and a simple model based on penetration depth (PD). All use an allometric expression to relate above-ground biomass to forest height measured by TanDEM-X. The retrieval was assessed on 201 forest stands with a minimum size of 1 ha, and ranging from 6 to 267 Mg/ha (mean biomass of 105 Mg/ha) equally divided into a model training dataset and a validation test dataset. Biomass retrieved using the IWCM resulted in a Root Mean Square Error (RMSE) between 17% and 33%, depending on acquisition date and image acquisition geometry (angle of incidence, interferometric baseline, and orbit type). The RMSE in the case of the RVoG and the PD models were slightly higher. A multitemporal estimate of the above-ground biomass using all eighteen acquisitions resulted in an RMSE of 16% with R-2 = 0.93. These results prove the capability of TanDEM-X interferometric data to estimate forest aboveground biomass in the boreal zone.
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| 4. |
- Fagerberg, Jonas H., et al.
(författare)
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Computational Prediction of Drug Solubility in Fasted Simulated and Aspirated Human Intestinal Fluid
- 2015
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Ingår i: Pharmaceutical research. - : Springer. - 0724-8741 .- 1573-904X. ; 32:2, s. 578-589
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo develop predictive models of apparent solubility (Sapp) of lipophilic drugs in fasted state simulated intestinal fluid (FaSSIF) and aspirated human intestinal fluid (HIF).MethodsMeasured Sapp values in FaSSIF, HIF and phosphate buffer pH 6.5 (PhBpH6.5) for 86 lipophilic drugs were compiled and divided into training (Tr) and test (Te) sets. Projection to latent structure (PLS) models were developed through variable selection of calculated molecular descriptors. Experimentally determined properties were included to investigate their contribution to the predictions.ResultsModest relationships between Sapp in PhBpH6.5 and FaSSIF (R2 = 0.61) or HIF (R2 = 0.62) were found. As expected, there was a stronger correlation obtained between FaSSIF and HIF (R2 = 0.78). Computational models were developed using calculated descriptors alone (FaSSIF, R2 = 0.69 and RMSEte of 0.77; HIF, R2 = 0.84 and RMSEte of 0.81). Accuracy improved when solubility in PhBpH6.5 was added as a descriptor (FaSSIF, R2 = 0.76 and RMSETe of 0.65; HIF, R2 = 0.86 and RMSETe of 0.69), whereas no improvement was seen when melting point (Tm) or logDpH 6.5 were included in the models.ConclusionComputational models were developed, that reliably predicted Sapp of lipophilic compounds in intestinal fluid, from molecular structures alone. If experimentally determined pH-dependent solubility values were available, this further improved the accuracy of the predictions.
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| 5. |
- Forsberg, Björn, 1971, et al.
(författare)
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Dressed ion theory of size-asymmetric electrolytes: effective ionic charges and the decay length of screened Coulomb potential and pair correlations.
- 2005
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:6
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Tidskriftsartikel (refereegranskat)abstract
- The effects of ionic size asymmetry on long-range electrostatic interactions in electrolyte solutions are investigated within the primitive model. Using the formalism of dressed ion theory we analyze correlation functions from Monte Carlo simulations and the hypernetted chain approximation for size asymmetric 1:1 electrolytes. We obtain decay lengths of the screened Coulomb potential, effective charges of ions, and effective permittivity of the solution. It is found that the variation of these quantities with the degree of size asymmetry depends in a quite intricate manner on the interplay between the electrostatic coupling and excluded volume effects. In most cases the magnitude of the effective charge of the small ion species is larger than that of the large species; the difference increases with increasing size asymmetry. The effective charges of both species are larger (in absolute value) than the bare ionic charge, except for high asymmetry where the effective charge of the large ions can become smaller than the bare charge.
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| 6. |
- Fransson, Johan E.S., et al.
(författare)
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Estimation of Forest Stem Volume using ALOS-2 PALSAR-2 Satellite Images
- 2016
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Ingår i: Proceedings of 36th IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2016; Beijing; China; 10-15 July 2016. - 9781509033324 ; 2016-November, s. Art no 7730388, Pages 5327-5330
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Konferensbidrag (refereegranskat)abstract
- © 2016 IEEE. A first evaluation of ALOS-2 PALSAR-2 data for forest stem volume estimation has been performed at a coniferous dominated test site in southern Sweden. Both the Fine Beam Dual (FBD) polarization and the Quad-polarimetric mode were investigated. Forest plots with stem volume reaching up to a maximum of about 620 m 3 ha -1 (corresponding to 370 tons ha -1 ) were analyzed by relating backscatter intensity to field data using an exponential model derived from the Water Cloud Model. The estimation accuracy of stem volume at plot level (0.5 ha) was calculated in terms of Root Mean Square Error (RMSE). For the best case investigated an RMSE of 39.8% was obtained using one of the FBD HV-polarized images. The corresponding RMSE for the FBD HH-polarized images was 43.9%. In the Quad-polarimetric mode the lowest RMSE at HV- and HH-polarization was found to be 43.1% and 66.1%, respectively.
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| 7. |
- Fransson, Johan E.S., et al.
(författare)
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Estimation of Stem Density in Hemi-Boreal Forests using Airborne Low-Frequency Synthetic Aperture Radar
- 2020
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Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). ; , s. 4152-4155
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Konferensbidrag (refereegranskat)abstract
- In this study, Synthetic Aperture Radar (SAR) backscatter data from the Swedish airborne CARABAS-II and LORA systems were used to estimate stem density. The analysis were performed at the test site Remingstorp, located in the south of Sweden, consisting mainly of coniferous in hemi-boreal forests. In total, ten 80 m × 80 m forested areas, where all trees were measured in situ, with stem densities in the range of 278-552 stems and stem volumes in the range of 70-550 m3 ha-1 were analysed. SAR data from CARABAS-II and LORA were acquired in 2006 with nine unique flight headings. Local maxima of the backscatter were used to estimate stem density. The results were compared with in situ data and the accuracy in terms of root mean square error (RMSE) for CARABAS-II and LORA were found to be 81 stems (20.9%) and 82 stems (20.2%), respectively, in the best cases. The accuracy assessment of the stem density were performed after averaging images from each SAR system. This was done in order to suppress noise to a greater extent compared to using single images. The results show a potential to estimate stem density with low-freqency SAR data for the benefit of forest management.
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| 8. |
- Fransson, Johan E.S., et al.
(författare)
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Estimation of stem volume in hemi-boreal forests using airborne low-frequency Synthetic Aperture Radar and lidar data
- 2013
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Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). - 2153-6996 .- 2153-7003. - 9781479911141 ; , s. 161-164
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Konferensbidrag (refereegranskat)abstract
- Synthetic Aperture Radar (SAR) backscatter data from the Swedish airborne CARABAS-II and LORA systems were used to estimate stem volume at stand level. The study was performed in hemi-boreal forests at the Remningstorp test site, located in southern Sweden. In total, ten 80 m × 80 m stands, where all trees were measured in situ, with stem volumes in the range of 70-530 m 3 ha-1 (on average 347 m3 ha-1) were analyzed. SAR data from CARABAS-II and LORA were acquired from two different years, with nine unique flight headings that were repeated for each system and year. Regression analysis was used to estimate stem volume and the accuracy was assessed in terms of Root Mean Square Error (RMSE). As a first step, stem volume was estimated for each flight heading separately. The accuracy assessment was then performed by weighting the separate estimates for each system and year inversely proportionally to the variance about the regression function. The best results for CARABAS-II and LORA showed a relative RMSE of 7% and 24% of the mean stem volume, respectively. In a previous study, stem volume was estimated using LiDAR data and the same forest stands, resulting in an RMSE of about 12%. In conclusion, the estimation accuracy of stem volume using combined low-frequency CARABAS SAR images was found to be superior to that from using LiDAR data for the stands investigated.
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| 9. |
- Huuva, Ivan, et al.
(författare)
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Measurements of forest biomass change using L- and P-band SAR backscatter
- 2017
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Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). - 9781509049516 ; 2017-July, s. 5818-5821, s. 5818-5821
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Konferensbidrag (refereegranskat)abstract
- Three-year forest above-ground biomass change were measured using L- and P-band Synthetic Aperture Radar (SAR) backscatter. The SAR data were collected in the airborne BioSAR 2007 and BioSAR 2010 campaigns over the hemiboreal Remningstorp test site in southern Sweden. Regression models for biomass were developed using reference biomass maps created using airborne laser scanning data and field measurements. The results from regression analysis show that using HV backscatter (or VH) in a model with above-ground biomass and backscatter change on either natural logarithmic or square root, and decibel scale, respectively, explained most of the variation in the biomass change, both for L- and P-band. In the case of L-band, the two best cases showed R2 values of 66%, when comparing two SAR images acquired 2007 and 2010. For P-band using the same models, the best cases showed R2 values of 62%. In summary, the results look promising using L- and P-band backscattering for mapping biomass change.
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| 10. |
- Huuva, Ivan, et al.
(författare)
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Prediction of Hemi-Boreal Forest Biomass Change Using Alos-2 Palsar-2 L-Band SAR Backscatter
- 2023
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Ingår i: IGARSS 2023 - 2023 IEEE International Geoscience and Remote Sensing Symposium. - : IEEE. - 9798350320107 - 9798350331745 - 9798350320091 ; , s. 3326-3329
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Konferensbidrag (refereegranskat)abstract
- Pairs of fully polarimetric ALOS-2 PALSAR-2 L-band SAR images were used to model biomass on backscatter change over seven growth seasons in a hemi-boreal forest. The biomass change was related to backscatter change via consecutive field surveys of 263 field plots with a 10 m radius. To correct for differences in backscatter not related to biomass abundance, a HV-VV polarization ratio based correction, previously used on airborne L-band data, was applied to the data. The uncertainty of obtained predictions (lowest model mean RMSE 65.1 t/ha, lowest model mean bias 7.1 t/ha) was almost identical whether model fitting and prediction used data from the same scene pair, or different scene pairs. This could possibly attest to the feasibility of the backscatter correction for PALSAR-2 data, but no large backscatter offsets were observed for uncorrected data, and significant variance in predictions, due to the inherent noise in the data and the comparatively small area of evaluation plots, inhibit the analysis.
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