Abstract:Studies have shown that Sentinel-2 images have advantages over Landsat images in impervious surface area (ISA) extraction. The performance of index-based methods can be affected by different binary methods and subject to seasonal variation. This study marks the first attempt to assess the performance of different spectral indices for ISA extraction using multi-seasonal Sentinel-2 images. Specifically, five indices (i.e., the Biophysical Composition Index calculated using the Gram-Schmidt orthogonalization meth… Show more
“…As reviewed in Section 2.3, TCT coefficients have not been published for atmospherically corrected S2 imagery, and Landsat's surface reflectance coefficients [96] do not cover all S2 bands. Whereas certain authors have used at-sensor-derived coefficients on surface reflectance S2 imagery [87][88][89][90][91], in a multi-temporal change application, the ever-changing effects of atmosphere result in inconsistent indices of brightness, greenness, and wetness that are directly a result of fluctuating atmospheric conditions. Although the exact effects onto index values such as dDI are not fully understood, Crist et al [42] suggests that changing atmospheric conditions will alter subsequent results derived from TCT indices.…”
Section: Discussionmentioning
confidence: 99%
“…Recently, some authors [85,86] have used coefficients developed for Landsat at-sensor reflectance products on S2 level-2A imagery. Others [87][88][89][90][91] have applied TCT coefficients to S2 level-2A data that were developed for at-sensor S2 (level-1C) imagery [43,92]. The spectral range and similarities of bands from Landsat and S2 bands are well documented [93][94][95], and the coefficients as developed by Crist [96] have been used in various studies using surface reflectance Landsat imagery [51,[97][98][99].…”
Fires are a disturbance that can lead to short term dune destabilisation and have been suggested to be an initiation mechanism of a transgressive dune phase when paired with changing climatic conditions. Fire severity is one potential factor that could explain subsequent coastal dune destabilisations, but contemporary evidence of destabilisation following fire is lacking. In addition, the suitability of conventional satellite Earth Observation methods to detect the impacts of fire and the relative fire severity in coastal dune environments is in question. Widely applied satellite-derived burn indices (Normalised Burn Index and Normalised Difference Vegetation Index) have been suggested to underestimate the effects of fire in heterogenous landscapes or areas with sparse vegetation cover. This work assesses burn severity from high resolution aerial and Sentinel 2 satellite imagery following the 2019/2020 Black Summer fires on Kangaroo Island in South Australia, to assess the efficacy of commonly used satellite indices, and validate a new method for assessing fire severity in coastal dune systems. The results presented here show that the widely applied burn indices derived from NBR differentially assess vegetation loss and fire severity when compared in discrete soil groups across a landscape that experienced a very high severity fire. A new application of the Tasselled Cap Transformation (TCT) and Disturbance Index (DI) is presented. The differenced Disturbance Index (dDI) improves the estimation of burn severity, relative vegetation loss, and minimises the effects of differing soil conditions in the highly heterogenous landscape of Kangaroo Island. Results suggest that this new application of TCT is better suited to diverse environments like Mediterranean and semi-arid coastal regions than existing indices and can be used to better assess the effects of fire and potential remobilisation of coastal dune systems.
“…As reviewed in Section 2.3, TCT coefficients have not been published for atmospherically corrected S2 imagery, and Landsat's surface reflectance coefficients [96] do not cover all S2 bands. Whereas certain authors have used at-sensor-derived coefficients on surface reflectance S2 imagery [87][88][89][90][91], in a multi-temporal change application, the ever-changing effects of atmosphere result in inconsistent indices of brightness, greenness, and wetness that are directly a result of fluctuating atmospheric conditions. Although the exact effects onto index values such as dDI are not fully understood, Crist et al [42] suggests that changing atmospheric conditions will alter subsequent results derived from TCT indices.…”
Section: Discussionmentioning
confidence: 99%
“…Recently, some authors [85,86] have used coefficients developed for Landsat at-sensor reflectance products on S2 level-2A imagery. Others [87][88][89][90][91] have applied TCT coefficients to S2 level-2A data that were developed for at-sensor S2 (level-1C) imagery [43,92]. The spectral range and similarities of bands from Landsat and S2 bands are well documented [93][94][95], and the coefficients as developed by Crist [96] have been used in various studies using surface reflectance Landsat imagery [51,[97][98][99].…”
Fires are a disturbance that can lead to short term dune destabilisation and have been suggested to be an initiation mechanism of a transgressive dune phase when paired with changing climatic conditions. Fire severity is one potential factor that could explain subsequent coastal dune destabilisations, but contemporary evidence of destabilisation following fire is lacking. In addition, the suitability of conventional satellite Earth Observation methods to detect the impacts of fire and the relative fire severity in coastal dune environments is in question. Widely applied satellite-derived burn indices (Normalised Burn Index and Normalised Difference Vegetation Index) have been suggested to underestimate the effects of fire in heterogenous landscapes or areas with sparse vegetation cover. This work assesses burn severity from high resolution aerial and Sentinel 2 satellite imagery following the 2019/2020 Black Summer fires on Kangaroo Island in South Australia, to assess the efficacy of commonly used satellite indices, and validate a new method for assessing fire severity in coastal dune systems. The results presented here show that the widely applied burn indices derived from NBR differentially assess vegetation loss and fire severity when compared in discrete soil groups across a landscape that experienced a very high severity fire. A new application of the Tasselled Cap Transformation (TCT) and Disturbance Index (DI) is presented. The differenced Disturbance Index (dDI) improves the estimation of burn severity, relative vegetation loss, and minimises the effects of differing soil conditions in the highly heterogenous landscape of Kangaroo Island. Results suggest that this new application of TCT is better suited to diverse environments like Mediterranean and semi-arid coastal regions than existing indices and can be used to better assess the effects of fire and potential remobilisation of coastal dune systems.
“…NBAI is calculated by the equation 17 NBAI=ρSWIR2−ρSWIR1ρGreenρSWIR2+ρSWIR1ρGreen=Band12−Band11Band3Band12+Band11Band3.…”
Section: Methodsmentioning
confidence: 99%
“…Many studies have focused on comparing the performance of LULC data derived from Sentinel-2 and Landsat imagery. [12][13][14][15][16][17] In the current and past research, 18,19 we have been using Sentinel-2 imagery, as this data is fully relevant to the research objectives. Generating various-resolution LULC maps require massive amounts of data as huge storage capacities, high processing power, and the flexibility to apply diverse approaches are all required.…”
The main goal of this study is to evaluate different models for further improvement of the accuracy of land use and land cover (LULC) classification on Google Earth Engine using random forest (RF) and support vector machine (SVM) learning algorithms. Ten indices, namely normalized difference vegetation index, normalized difference soil index, index-based built-up index, biophysical composition index, built-up area extraction index (BAEI), urban index, new built-up index, band ratio for built-up area, bare soil index, and normalized built up area index, were used as input parameters for the machine learning algorithms to improve classification accuracy. The combinatorial analysis of the Sentinel-2 bands and the aforementioned indices allowed us to create four combinations based on surface reflectance characteristics. The study includes data from April 2020 to September 2021 and April 2022 to June 2022. The multitemporal Sentinel-2 data with spatial resolutions of 10 m were used to determine the LULC classification. The major land use classes such as water, forest, grassland, urban areas, and other lands were obtained. Generally, the RF algorithm showed higher accuracy than the SVM. The overall accuracy for RF and SVM was 86.56% and 84.48%, respectively, and the mean Kappa was 0.82 and 0.79, respectively. Using the combination 2 with the RF algorithm and combination 4 with the SVM algorithm for LULC classification was more accurate. The additional use of vegetation indices allowed to increase in the accuracy of LULC classification and separate classes with similar reflection spectra.
“…Corresponding author: Z. Shao (email: shaozhenfeng@whu.edu.cn). the urban environment [2], climate [3], [4], and hydrology [5]- [7]. Therefore, the evaluation of ISA distribution should focus on not only its spatial expansion but also its environmental consequences.…”
Mapping impervious surface area (ISA) in an accurate and timely manner is essential for a variety of fields and applications, such as urban heat islands, hydrology, waterlogging, and urban planning and management. However, the large and complex urban landscapes pose great challenges in retrieving ISA information. Spaceborne hyperspectral (HS) remote sensing imagery provides rich spectral information with short revisit cycles, making it an ideal data source for ISA extraction from complex urban scenes. Nevertheless, insufficient single-band energy, the involvement of modulation transfer function (MTF), and the low signal-to-noise ratio (SNR) of spaceborne HS imagery usually result in poor image clarity and noises, leading to inaccurate ISA extraction. To address this challenge, we propose a new deep feature fusion-based classification method to improve 10 m resolution ISA mapping by integrating Zhuhai-1 HS imagery with Sentinel-2 multispectral (MS) imagery. We extract deep features that include spectral and spatial features respectively from MS and HS imagery via a 2D convolutional neural network (CNN), aiming to increase feature diversity and improve the model's recognition capability. The Sentinel-2 imagery is used to enhance the spatial information of the Zhuhai-1 HS image, improving the urban ISA retrieval by reducing the impact of noises. By combining the deep spatial features and deep spectral features, we obtain joint spatial-spectral features, leading to high classification accuracy and robustness. We test the proposed method in two highly urbanized study areas that cover Foshan city and Wuhan city, China. The results reveal that the proposed method obtains an overall accuracy of 96.72% and 96.75% in the two study areas, 18.78% and 8.66% higher than classification results with only HS imagery as input. The final ISA extraction overall accuracy is 95.42% and 95.50% in the two study areas, the highest among the comparison methods.
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