Land Surface Temperature (LST) is important data for various fields, especially for monitoring global warming. Landsat-8 satellite imagery provides thermal data with a spatial resolution of 30m (resampled from 100m) as the main data for LST retrieval. This research aims to compare several LST retrieval algorithms such as LST retrieval using band ten, Single Channel Model (SCM), Qin’s Split-Window Algorithm (Q-SWA), Sobrino’s Split-Window Algorithm (S-SWA), and LST from the analysis ready data of Landsat-8 Level two. The study focuses on Dallas, Texas, and surrounding areas in March 2023. We collected air temperature data from 20 U.S. Environmental Protection Agency (EPA) stations for indirect validation. Based on the results, the Q-SWA method outperformed other retrieval algorithms with Mean Absolute Error (MAE) and Root Mean Squared Error (RMSE) were 0.683°C and 0.842°C, respectively. Given that Landsat-8’s thermal band data is resampled from 100m to 30m, this research also explores enhancing the retrieved LST using Deep Neural Network Regression (DNNR). The best retrieved LST from the Q-SWA method served as the target data while several bands and spectral indices from Landsat-8 were used as the input for DNNR model. Due to the large scale of data, we randomly selected ten million pixels and divided into 80% of training and 20% of testing data. The DNNR model achieved MAE of 1.022°C on the testing dataset. The enhanced LST from the DNNR model was also validated with the same air temperature validation data and achieved the MAE score of 1.037°C. Based on the visual comparison result, the DNNR model successfully enhanced the retrieved LST by providing more detailed results at the same 30m resolution and showing promising performance based on error metrics. This finding suggests the potential for using deep learning regression in LST downscaling to achieve better spatial resolution.
Mangroves play important roles in the blue carbon ecosystem. Mangrove map is important data, robust and reproducible methods for mangrove mapping and monitoring are needed. Along with the freely available optical remote sensing satellite data such as Sentinel-2 and the development of deep learning fields, mangrove mapping and monitoring are more reachable. Therefore, the main goal of this study is to evaluate and utilize some state-of-the-art deep learning semantic segmentation architectures (U-Net, LinkNet, PSPNet, and FPN) for mangrove mapping and monitoring. This study will provide evidence of the ability of state-of-the-art deep learning semantic segmentation that can provide a robust and reproducible method for mangrove mapping and monitoring. The study area is the coastal zone of Rookery Bay, Florida, USA. The Sentinel-2 bottom-of-atmosphere corrected reflectance data (2016) with the target data (water body, nonmangrove, and mangrove) used for training and evaluating the capability of U-Net, LinkNet, PSPNet, and FPN for mangrove mapping. While, for the mangrove monitoring evaluation, the best trained deep learning model based on the 2016 dataset was used here to produce a new mangrove map in 2022. The reference data were collected from google earth imagery in 2022 by visual interpretation (250 points for each class) and conducted mangroves monitoring evaluation by calculating class accuracy and overall accuracy for the produced mangrove map in 2022. Based on the experiment results, all of the state-of-the-art deep learning semantic segmentation architectures have promising results and U-Net achieved the highest performance with an average intersection over union (IoU) score of 0.926. Based on the evaluation result, the trained deep learning model based on the 2016 dataset successfully produced a mangrove map using 2022 Sentinel-2 data with an overall accuracy of around 0.98. This finding indicates the ability of U-Net, LinkNet, PSPNet, and FPN for mangrove mapping and monitoring.
Land Surface Temperature (LST) is an important factor in geophysical parameters such as hydrological modeling, soil moisture, monitoring crop, etc. LST data with detailed resolution and the large-scale area is very helpful data in many research fields. Satellite imagery with thermal infrared sensors can be used to produce LST using a retrieval algorithm. Currently, Landsat 8 with TIRS sensor is freely available thermal infrared bands with the highest spatial resolution (resampled from 100m to 30m). Based on that situation, this study aims to build a model from optical bands of Landsat-8 as the input data and LST from Landsat-8 as the target data using Deep Neural Network regression (DNNr) architecture and then applied to Sentinel-2 to get LST at 10m resolution. The main difference of DNNr architecture with DNN for classification is we use linear activation function in the output layer. The study area is located in Yilan County, Taiwan. The input data from Landsat-8 and Sentinel-2 are optical bands (Blue, Green, Red, NIR), NDVI, and emissivity from NDVI. Both the input data have been standardized using the standardscaler function before feeding into the model. The input data were separated as 70% for training, 20% for validation, and the other 10% as testing data. We use air temperature data to calculate indirect validation with LST from Sentinel-2. The result shows, the mean absolute error and mean squared of testing data from DNNr are 0.581oC and 0.766oC. The correlation and maximum difference of air temperature with LST Sentinel-2 from DNNr are 0.92 and 2.94oC. Based on the experiments, our DNNr achieved a more good result than other regression architecture. Our DNNr architecture has been tested in other areas and also shows acceptable result. Based on that results, our LST product at 10m resolution can be used in others research fields.
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