Abstract:Este artigo aborda o estado da arte do sensoriamento remoto por radar e foi elaborado para fazer parte da edição especial de comemoração dos 50 anos desta revista. Neste estudo, é apresentada uma breve introdução sobre os fundamentos do sensoriamento remoto por radar, com destaque para os parâmetros mais importantes de imageamento e da superfície terrestre envolvidos no processo de obtenção de imagens de radar. Ênfase é dada para o comprimento de onda, polarização das ondas eletromagnéticas e geometria de obte… Show more
“…Thus, models were constructed with the combination of Sentinel-1 and Sentinel-2 data through multiple linear regression (R² of 0.52 and RMSEr of 46.98%), and only Sentinel-2 data (R² of 0.63 and RMSEr of 42.03%) were superior to the models constructed using only Sentinel-1 data (R² of 0.18 and RMSEr of 59.48%). These results are similar to those found in the present study (R² of 0.1742), which corroborates the argument that the L-band has a longer wavelength that can penetrate deep into the forest, while the dominant scattering processes in the Xand C-bands (used in this study) occur at the surface of the canopy layer (Sano et al, 2020).…”
Section: Discussionsupporting
confidence: 92%
“…The correlation for the variables arising from the Sentinel-1 image was lower, which can be explained by the characteristics of the sensor, as the backscatter is dependent on surface characteristics, bandwidth (in this case, the C-band: 3.8 cm -7.5 cm), and type of polarization (Mauya et al, 2019). This can influence the degree of signal penetration in the forest, and consequently the degree of response obtained; the longer the wavelength, the greater the penetration capacity of the signals emitted from the vegetation canopy or the ground surface (Sano et al, 2020). Another important factor is the structure of the canopy of the stand.…”
Background:The objective of this study was to estimate the wood volume of a Pinus taeda L. plantation using variables extracted from the Sentinel-1 active sensor and the Sentinel-2 passive sensor. To do so, data from a forest inventory with rectangular plots of 550 m² were used to estimate the stand volume. We derived and adapted average vegetation indices per plot from images obtained by Sentinel-1 and Sentinel-2 sensors. The data were then correlated with the volume per plot based on the forest inventory. The Modified Radar Forest Degradation Index (mRDFI) showed the highest correlation for Sentinel-1 data, while the Difference Vegetation-Index (DVI) performed best for Sentinel-2.
Results:The regression models were built using Stepwise modeling, demonstrating that the models fit with only the Sentinel-2 indices performed better than the others (indices adapted for Sentinel-1 and a combination of Sentinel-1 and Sentinel-2 data), with an R² adjusted between 0.51 to 0.40 and a standard error (Syx%) of 3.66 to 8.97. According to the statistical analyses, we found no significant differences between the volume estimated by the forest inventory (12.56±1.17) and the remote sensing techniques used (Sentinel-2 with 12.56±1.03 and Sentinel-1 with 12.56±0.94). However, further tests should be conducted with other active sensors operating in different spectral bands and polarization modes for other forest species.
Conclusion:We found no significant differences between the volumetric estimates derived from remote sensing data and forest inventory techniques.
“…Thus, models were constructed with the combination of Sentinel-1 and Sentinel-2 data through multiple linear regression (R² of 0.52 and RMSEr of 46.98%), and only Sentinel-2 data (R² of 0.63 and RMSEr of 42.03%) were superior to the models constructed using only Sentinel-1 data (R² of 0.18 and RMSEr of 59.48%). These results are similar to those found in the present study (R² of 0.1742), which corroborates the argument that the L-band has a longer wavelength that can penetrate deep into the forest, while the dominant scattering processes in the Xand C-bands (used in this study) occur at the surface of the canopy layer (Sano et al, 2020).…”
Section: Discussionsupporting
confidence: 92%
“…The correlation for the variables arising from the Sentinel-1 image was lower, which can be explained by the characteristics of the sensor, as the backscatter is dependent on surface characteristics, bandwidth (in this case, the C-band: 3.8 cm -7.5 cm), and type of polarization (Mauya et al, 2019). This can influence the degree of signal penetration in the forest, and consequently the degree of response obtained; the longer the wavelength, the greater the penetration capacity of the signals emitted from the vegetation canopy or the ground surface (Sano et al, 2020). Another important factor is the structure of the canopy of the stand.…”
Background:The objective of this study was to estimate the wood volume of a Pinus taeda L. plantation using variables extracted from the Sentinel-1 active sensor and the Sentinel-2 passive sensor. To do so, data from a forest inventory with rectangular plots of 550 m² were used to estimate the stand volume. We derived and adapted average vegetation indices per plot from images obtained by Sentinel-1 and Sentinel-2 sensors. The data were then correlated with the volume per plot based on the forest inventory. The Modified Radar Forest Degradation Index (mRDFI) showed the highest correlation for Sentinel-1 data, while the Difference Vegetation-Index (DVI) performed best for Sentinel-2.
Results:The regression models were built using Stepwise modeling, demonstrating that the models fit with only the Sentinel-2 indices performed better than the others (indices adapted for Sentinel-1 and a combination of Sentinel-1 and Sentinel-2 data), with an R² adjusted between 0.51 to 0.40 and a standard error (Syx%) of 3.66 to 8.97. According to the statistical analyses, we found no significant differences between the volume estimated by the forest inventory (12.56±1.17) and the remote sensing techniques used (Sentinel-2 with 12.56±1.03 and Sentinel-1 with 12.56±0.94). However, further tests should be conducted with other active sensors operating in different spectral bands and polarization modes for other forest species.
Conclusion:We found no significant differences between the volumetric estimates derived from remote sensing data and forest inventory techniques.
“…This denotes the complexity of soil texture for statistical modelling due to the size magnitude of the soil fractions and the mineral constitution, as well as the reliance of the signal intensity from the SAR beam on how clayey or sandy the soil is. Typically, crosspolarization (VH) measurements are significantly lower than the co-polarization (VV) (Sano et al, 2020;Ulaby et al, 1978;Ulaby et al, 1979), and this was observed over our study area wherein the VV intensity values (in σ 0 units) ranged from 0.01 to 0.31, whereas for VH polarization the coefficient backscatter varied between 0.02 and 0.07. It is worth noting that the Sentinel-1 dataset was acquired during a dry period (03/04/2021).…”
Section: General Aspects Of Soil Particle-size Estimation With Sentin...mentioning
Data derived from Synthetic Aperture Radar (SAR) are widely employed to predict soil properties, particularly soil moisture and soil carbon content. However, few studies address the use of microwave sensors for soil texture retrieval and those that do are typically constrained to bare soil conditions. Here, we test two statistical modelling approaches – linear (with and without interaction terms) and tree‐based models, namely compositional linear regression model (LRM) and Random Forest (RF) – and both non‐geophysical (e.g. surface soil moisture, topographic etc) and geophysical‐based (electromagnetic, magnetic and radiometric) covariates to estimate soil texture (sand %, silt % and clay %), using microwave remote sensing data (ESA Sentinel 1). The statistical models evaluated explicitly consider the compositional nature of soil texture and were evaluated with leave‐one‐out cross validation (LOOCV). Our findings indicate that both modelling approaches yielded better estimates when fitted without the geophysical covariates. Based on the Nash‐Sutcliffe efficiency coefficient (NSE), LRM slightly outperformed RF, with NSE values for sand, silt, and clay of 0.94, 0.62, and 0.46, respectively; for RF, the NSE values were 0.93, 0.59, and 0.44. When interaction terms were included, RF was found to outperform LRM. The inclusion of interactions in the LRM resulted in a decrease in NSE value and an increase in the size of the residuals. Findings also indicate that the use of radar derived variables (e.g. VV, VH, RVI) alone were not able to predict soil particle size without the aid of other covariates. Our findings highlight the importance of explicitly considering the compositional nature of soil texture information in statistical analysis and regression modelling. As part of the continued assessment of microwave remote sensing data (e.g. ESA Sentinel‐1) for predicting topsoil particle‐size, we intend to test surface scattering information derived from the dual‐polarimetric decomposition technique and integrate that predictor into the models in order to deal with the effects of vegetation cover on topsoil backscattering.This article is protected by copyright. All rights reserved.
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