Change Detection In Time Series Research Articles

BATSCCD: a new change detection method for mapping building age in rapidly changing urban areas using Landsat time series data

ABSTRACT The building age is an important feature in the vulnerability assessment of disasters and building energy consumption modeling. It provides indispensable information for the study of built environment. However, obtaining high-precision maps of building ages is challenging, which impedes the development of relevant research and applications. In this study, a new building age mapping method based on Landsat time series classification and change detection (BATSCCD) was proposed, which integrates Landsat time series data with random forest and LandTrendr algorithm to reflect non-building to building changes, building reconstruction, and corresponding change characteristics. The proposed method achieved overall building age mapping accuracies of 80.45% within a 2-year tolerance and 87.66% within a 3-year tolerance in Guangzhou and accuracies of 78.08% and 87.52%, respectively, in Beijing. The improvement was notable, especially compared with the continuous change detection and classification (CCDC) method, with corresponding accuracy values of 36.22% and 46.31%, respectively, in Guangzhou and 49.7% and 60.19%, respectively, in Beijing. The results suggest that the BATSCCD method can be used to accurately estimate the building age and provide reliable mapping results. Thanks to the accessibility of required data and its high accuracy of building age estimation, the proposed method exhibits great application potential.

Spatial analysis of urban expansion, land-use dynamics and its effects on land surface temperature in Oyo town, Southwestern Nigeria

This paper assessed the expansion of land use and land cover that occurred in Oyo State, Southwestern Nigeria, over a period of thirty-year. This was to assess urban expansion, landuse dynamics and their effects on land surface temperature in the area. The study used four multi-date imageries of the area. Landsat 7 ETM + , 1990, 2000, 2012, and Landsat 8 OLI/TIR, 2021 were collected from the United States Geological Survey (USGS) website were used. The ArcGIS 10.1 environment was utilised to clip the area of interest, and ERDAS Imagine remote sensing software was employed to efficiently improve and categorise the images. The images were then divided into five major: cultivation, built-up area, vegetation, water body, and bare soil using a maximum likelihood supervised classification algorithm. These categories were then utilised to conduct time series analysis or change detection analysis.Results of this study revealed that the built-up area has changed over the preceding three decades because of urban expansion. The built-up area increased from 19.83 km2 to 35.67 km2 in 2012 and 44.84 km2 in 2021, indicating increases of 14.93% to 79.87% and 25.71%, respectively, whereas the vegetative land cover decreased from -0.11% to -3.01 48% and 12.75% during the study period. Findings revealed that anthropogenic factors including urbanisation and agricultural expansion, have significantly altered the surface and atmospheric characteristics of the study area, causing a variety of heat patterns within the area. The built-up area had average temperatures between 35.05 °C and 36.16 °C between 1990 and 2021, which indicated a higher temperature with evidence of an urban heat island.This study concludes that the city’s land surface temperature is rising and that the expanding built-up area’s density and a corresponding decline in vegetation over time significantly impact it. Therefore, the study suggests cultivating and maintaining trees, promoting green environment,, public awareness, campaigns and education on actions that aggravate high temperatures are also required.

Mapping the Age of Subtropical Secondary Forest Using Dense Landsat Time Series Data: An Ensemble Model

Quantifying secondary forest age (SFA) is essential to evaluate the carbon processes of forest ecosystems at regional and global scales. However, the successional stages of secondary forests remain poorly understood due to low-frequency thematic maps. This study aimed to estimate SFA with higher frequency and more accuracy by using dense Landsat archives. The performances of four time-series change detection algorithms—moving average change detection (MACD), Continuous Change Detection and Classification (CCDC), LandTrendr (LT), and Vegetation Change Tracker (VCT)—for detecting forest regrowth were first evaluated. An ensemble model was then developed to determine more accurate timings for forest regrowth based on the evaluation results. Finally, after converting the forest regrowth year to the SFA, the spatiotemporal and topographical distributions of the SFA were analyzed. The proposed ensemble model was validated in Jiangxi province, China, which is located in a subtropical region and has experienced drastic forest disturbances, artificial afforestation, and natural regeneration. The results showed that: (1) the developed ensemble model effectively determined forest regrowth time with significantly decreased omission and commission rates compared to the direct use of the four single algorithms; (2) the optimal ensemble model combining the independent algorithms obtained the final SFA for Jiangxi province with the lowest omission and commission rates in the spatial domain (14.06% and 24.71%) and the highest accuracy in the temporal domain (R2 = 0.87 and root mean square error (RMSE) = 3.17 years); (3) the spatiotemporal and topographic distribution from 1 to 34 years in the 2021 SFA map was analyzed. This study demonstrated the feasibility of using change detection algorithms for estimating SFA at regional to national scales and provides a data foundation for forest ecosystem research.

Cloud-Based Remote Sensing for Wetland Monitoring—A Review

The rapid expansion of remote sensing provides recent and developed advances in monitoring wetlands. Integrating cloud computing with these techniques has been identified as an effective tool, especially for dealing with heterogeneous datasets. In this study, we conducted a systematic literature review (SLR) to determine the current state-of-the-art knowledge for integrating remote sensing and cloud computing in the monitoring of wetlands. The results of this SLR revealed that platform-as-a-service was the only cloud computing service model implemented in practice for wetland monitoring. Remote sensing applications for wetland monitoring included prediction, time series analysis, mapping, classification, and change detection. Only 51% of the reviewed literature, focused on the regional scale, used satellite data. Additionally, the SLR found that current cloud computing and remote sensing technologies are not integrated enough to benefit from their potential in wetland monitoring. Despite these gaps, the analysis revealed that economic benefits could be achieved by implementing cloud computing and remote sensing for wetland monitoring. To address these gaps and pave the way for further research, we propose integrating cloud computing and remote sensing technologies with the Internet of Things (IoT) to monitor wetlands effectively.

CatSight, a direct path to proper multi-variate time series change detection: perceiving a concept drift through common spatial pattern

Detecting changes in data streams, with the data flowing continuously, is an important problem which Industry 4.0 has to deal with. In industrial monitoring, the data distribution may vary after a change in the machine’s operating point; this situation is known as concept drift, and it is key to detecting this change. One drawback of conventional machine learning algorithms is that they are usually static, trained offline, and require monitoring at the input level. A change in the distribution of data, in the relationship between the input and the output data, would result in the deterioration of the predictive performance of the models due to the lack of an ability to generalize the model to new concepts. Drift detecting methods emerge as a solution to identify the concept drift in the data. This paper proposes a new approach for concept drift detection—a novel approach to deal with sudden or abrupt drift, the most common drift found in industrial processes-, called CatSight. Briefly, this method is composed of two steps: (i) Use of Common Spatial Patterns (a statistical approach to deal with data streaming, closely related to Principal Component Analysis) to maximize the difference between two different distributions of a multivariate temporal data, and (ii) Machine Learning conventional algorithms to detect whether a change in the data flow has been occurred or not. The performance of the CatSight method, has been evaluated on a real use case, training six state of the art Machine Learning (ML) classifiers; obtained results indicate how adequate the new approach is.

A temporal-spectral value and shape change detection method integrating thematic index information and spectral band information.

Satellite imagery time series change detection methods are effective in avoiding pseudochange due to vegetation phenology to a certain extent. Traditional time series change detection methods use thematic indexes (e.g., NDVI, RVI) to obtain time series information for corresponding change detection. However, change detection methods using several thematic index time series may not make full use of other spectral band information in remotely sensed images and may still suffer from over- and under-detections. To address this challenge, a temporal-spectral value and shape change detection method integrating thematic index information and spectral band information (TISB) is proposed. Possible clouds and cloud shadowing phenomena are removed according to the changes in the spectral values of the remotely sensed images to avoid the generation of pseudochanges in clouds. The spectral and time series information is used to obtain change information from the value perspective, and then, further possible enhanced change regions from a shape perspective to obtain the final change detection results through the expectation-maximization (EM) method. Experiments with Landsat images have shown that the TISB method improves detection results by approximately 1-4% compared to the comparison method.

A Parametric МА-Algorithm for Gaussian Time Series Change Point Detection from Mathematical Expectation

The problem of online detection of a Gaussian time series change connected with a spontaneous abrupt change in its mathematical expectation is solved. For solving the problem, it is proposed to use a parametric controlling algorithm based on the Moving Average method or the MA- algorithm. It is noted that, despite the fact that this algorithm has been known almost since the first works in the field of statistical control, its properties, capabilities, and efficiency in comparison with other change detection algorithms are still (for a number of reasons) have been studied to a very poor extent. The purpose of this work is to thoroughly study the MA-algorithm’s characteristics with the aim to synthesize an optimal time series change detection procedure. The study was carried out using a simulation modeling method. The article presents the structure and element-wise description of the simulation experiment program, which fully replicates the MA-algorithm operation in the online mode. By using the developed program, it has been found that the conventional way of setting the control procedure deciding threshold h, the value of which should provide the preset value of the average time between false alarms, when an alarm signal about the appearance of a change is generated, although in reality the object remains in the "normal" state, is invalid. For a fixed series of the above-mentioned quantities, the correct values of the threshold h are obtained depending on the width of the moving averaging window N of the controlling MA-algorithm. Similarly, the values of the average delay time of producing an alarm signal when a change with the given fixed level  appears. Based on the data obtained, dependences of the control procedure efficiency indicator E on N for a set of different values of average time between false alarms and  have been found. It has been shown that for each such set there is a value of N at which the control procedure is most effective. This optimal procedure is compared with a similar procedure of the cumulative sum algorithm (a CUSUM algorithm), and it has been shown from the comparison results that the MA-algorithm is in general only slightly inferior to the CUSUM algorithm in efficiency, and in some cases even outperforms it.

Status, Trend, and Prospect of Global Farmland Abandonment Research: A Bibliometric Analysis

Farmland abandonment is one of the most important land use changes in the world today and crucial to the sustainable development of the global environment. The authors carried out extensive research on farmland abandonment from many perspectives, but, due to the variety of the research contents, rich research perspectives, and complex research objects, the current research in this field lacks comprehensiveness, objectivity, and systematization. In this study, the bibliometric R software packages bibliometrix and biblioshiny (K-Synth Srl, Naples, Italy) were used to analyze the development history and current situation of 896 articles on farmland abandonment in the Web of Science core collection database from 1980 to 2021, revealing their research hotspots and predicting the future development trends. Over the past 40 years, the number of published papers on abandoned farmland has continuously increased. Research mainly focused on the ecological environment, with natural succession, biodiversity, and vegetation restoration being high-frequency keywords in this field. Research on the social aspects of farmland abandonment has developed rapidly in the past 6 years. Based on these findings, this paper put forward four future research directions: the data source for the extraction of abandoned farmland should transform to high spatial-temporal resolution and hyperspectral remote sensing images; the method should pay more attention to the time series change detection and the application of the model; future research should focus on the economic costs of the reclamation of abandoned farmland and the ecological consequences of such reclamation; and the global ecological impact of vegetation succession after the abandonment of farmland should be further discussed from a broader perspective.

Time series change detection using reservoir computing networks for remote sensing data

In this study, a multivariate time series forecasting model applicable to high-dimensional short-term forecasting is proposed. The Reservoir Computing Network (RCN) state reduction method is investigated to address the dimensionality arising from high-dimensional data. To enable the states to express very distant dependencies in time so that the RCN satisfies the echo state property, a bidirectional RCN model is investigated to capture the dependencies of the data forward and backward in time. To solve the short-term data prediction, the spatiotemporal transformation theory is combined with the RCN to exploit the conjugate property between delayed and nondelayed embeddings of dynamical systems, and the correlation between variables in high-dimensional systems is used to compensate for the shortcomings of short-term series, design the method of the RCN training, and complete the prediction of future states. In the experiments, four existing models based on two different data sets were used for comparison, and the results showed that our method has better prediction performance.

Risk assessment and validation of farmland abandonment based on time series change detection.

Farmland abandonment, a widespread phenomenon during land-use transition, leads to a cycling or vanishing evolution of farmland resources. As urbanization advances, an increasing number of agricultural laborers migrate from rural to urban areas, causing ongoing farmland abandonment. However, in contrast to the abandoned information extraction and driving mechanisms revelation, the potential risk of farmland abandonment has received insufficient attention. This study took Yangtze River Economic Belt of China as study area, selected multiple aspects to construct a risk assessment system for farmland abandonment, and applied time series change detection to verify the results. The results showed that (1) farmland abandonment risk, with a regional average value of 0.0978, has strong spatial heterogeneity, with high values clustering in Yunnan-Guizhou and Sichuan-Chongqing mountainous areas and low values distributed in the midstream and downstream plains and the Sichuan Basin. (2) The proportion of farmland area gradually decreased as the risk grade increased. Farmland, with low abandonment risk, occupied an area of 204,837 km2, constituting the highest percentage of 35.18% among the overall farmland, and was mainly distributed in the provinces of Jiangsu and Anhui. The area of farmland with high risk was 16,458 km2, only accounting for 2.83%, the majority of which was clustered in Sichuan and Yunnan provinces. (3) The Normalized Difference Vegetation Index (NDVI) time series change detection validated the reliability of the risk assessment system. Samples of farmland having low abandonment risk indeed had the lowest abandonment rate of 10%, and those which indicated high risk had the highest abandonment rate of 32%. We propose differentiated managements for farmland resources with high and low abandonment risk from the perspective of sustainable use. This study provides a more reasonable and scientific system for farmland abandonment risk assessment and helps to fill the research gap.

Near-real-time MODIS-derived vegetation index data products and online services for CONUS based on NASA LANCE

This paper describes a set of Near-Real-Time (NRT) Vegetation Index (VI) data products for the Conterminous United States (CONUS) based on Moderate Resolution Imaging Spectroradiometer (MODIS) data from Land, Atmosphere Near-real-time Capability for EOS (LANCE), an openly accessible NASA NRT Earth observation data repository. The data set offers a variety of commonly used VIs, including Normalized Difference Vegetation Index (NDVI), Vegetation Condition Index (VCI), Mean-referenced Vegetation Condition Index (MVCI), Ratio to Median Vegetation Condition Index (RMVCI), and Ratio to previous-year Vegetation Condition Index (RVCI). LANCE enables the NRT monitoring of U.S. cropland vegetation conditions within 24 hours of observation. With more than 20 years of observations, this continuous data set enables geospatial time series analysis and change detection in many research fields such as agricultural monitoring, natural resource conservation, environmental modeling, and Earth system science. The complete set of VI data products described in the paper is openly distributed via Web Map Service (WMS) and Web Coverage Service (WCS) as well as the VegScape web application (https://nassgeodata.gmu.edu/VegScape/).

Inter-Comparison of Four Models for Detecting Forest Fire Disturbance from MOD13A2 Time Series

Many models for change point detection from time series remote sensing images have been developed to date. For forest ecosystems, fire disturbance detection models have always been an important topic. However, due to a lack of benchmark datasets, it is difficult to determine which model is appropriate. Therefore, we collected and generated a benchmark dataset specifically for forest fire disturbance detection, named CUG-FFireMCD1. The CUG-FFireMCD1 contains a total of 132 pieces of MODIS MOD13A2 time series, and each time series contains at least one fire disturbance. The occurrence time for a forest fire disturbance was determined using the National Cryosphere DesertDataCenter(NCDC) website, and the precise latitude and longitude coordinates were determined using the FireCCI51 dataset. In addition, we selected four commonly used time series change detection models and validate the advantages and limitations of the four models through dataset analysis. Finally, we use the detection results of the models and their applicable scenarios to label the additional change points. The four models we used are breaks for additive season and trend (BFAST), Prophet, continuous change detection and classification (CCDC), and Landsat-based detection of trends in disturbance and recovery (LandTrendR). The experiments show that the BFAST outperformed the other three models in forest fire disturbance detection from MOD13A2 time series, with the successful-detection-proportion rate of 96.2% with the benchmark dataset. The detection effect of the Prophet model is not as good as that of BFAST, but it also performs well, with the successful-detection-proportion rate of 87.9%. The detection results of CCDC and LandTrendR are similar, and the detection success rate is lower than that of BFAST and Prophet, but their detection results can be used as data support for labeling work. However, to apply them perfectly to MOD13A2 time series change detection, it is best to do some model adaptation. In summary, the CUG-FFireMCD1 data were verified using different types of time series change detection models, and the change points we marked are credible. The CUG-FFireMCD1 will surely provide a reliable benchmark for model optimization and the accuracy verification of remote sensing time series change detection.

Recovery of tree community composition across different types of anthropogenic disturbances and characterization of their effect using Landsat time series in Bornean tropical montane forest

Anthropogenic pressure in tropical montane forests is rapidly increasing, becoming a major threat to these complex ecosystems. Studies have shown that the wide variety of human activities in tropical uplands results in different ecological responses of secondary forests, but basic information on the disturbance impacts and underlying recovery processes is lacking. Here, we compared structural characteristics and tree community composition of old growth forest and secondary forests in a montane region of Sabah, Malaysia, which experienced five different anthropogenic disturbances. We also investigated the use of metrics from spectral trajectories of a Landsat time series (LTS) change detection algorithm (LandTrendr) to identify characteristics of disturbance events and their linkage to the recovery of tree community composition, with field validation. Five LTS metrics—time since the greatest disturbance (TSD), magnitude of disturbance (MD), distance to undisturbed forests (d_UND), recovery indicator (RI), and years to recovery (Y2R) were derived and were related to field-based tree community composition. Our analysis revealed a gradient of recovery patterns in community composition and structural attributes among forest disturbance types, suggesting the importance of community composition as an indicator of forest recovery. Among derived LTS metrics, TSD, MD, d_UND, and Y2R 100% were significantly related with the similarity in community composition. Our results suggest that spectral trajectories from LTS can serve as a useful predictor of community composition change in recovering stands. This approach provides an efficient means for developing systematic conservation strategies for high-elevation regions in the tropics, where human-modified landscapes are expanding.

UTRNet: An Unsupervised Time-Distance-Guided Convolutional Recurrent Network for Change Detection in Irregularly Collected Images

Change detection in time series is among the most critical problems in earth monitoring and attracts extensive attention in the remote sensing community. The task is, however, nontrivial because available images are irregularly collected due to interference by clouds and shadows. Traditional recurrent neural networks neglect such information and thus degrade the possibility of distinguishing pseudochanges (caused by intra-annual and inter-annual dynamics) and real changes. To this end, we proposed an unsupervised time-distance-guided convolutional recurrent network (UTRNet) for change detection in irregularly collected images. UTRNet is distinctive because the influence of pseudochanges can be suppressed by adopting a novel time-distance-guided long short-term memory (TLSTM) unit, in which input and forget gates are modified to adapt to irregular time distances. To the best of our knowledge, this is the first time that the influence of pseudochanges can be suppressed using irregular time distances. Moreover, to make UTRNet more applicable, a weighted prechange detection model is proposed to extract the most reliable training samples automatically. In the training process, unlike existing approaches that only care about changed and unchanged sample imbalance, our UTRNet also pays attention to imbalance between hard and easy samples and proposes a new focal weighted cross-entropy loss, which helps to make the training process focus on hard changed samples. The proposed UTRNet is validated on Landsat 8 time series data collected over nine typical scenes in the 2013-2021 period. Qualitative and quantitative comparisons with several state-of-the-art methods suggest the superior performance of UTRNet. Our dataset and codes are available at https://github.com/thebinyang/UTRNet.

IRCNN: An Irregular-Time-Distanced Recurrent Convolutional Neural Network for Change Detection in Satellite Time Series

Deep learning (DL)-based methods incorporating convolutional neural networks (CNNs) and recurrent neural networks (RNNs) have been successfully applied to change detection in satellite time series. However, traditional RNNs assume identical time interval between image sequences, which hardly meets the real case in satellite time series because of clouds and shadows. In this letter, a novel irregular-time-distanced recurrent CNN (IRCNN) is proposed. IRCNN consists of three sub-networks: a multi-branch Siamese CNN, irregular-time-distanced long short-term memory (ILSTM), and fully connected (FC) layers. Superior to the existing methods, IRCNN can account for temporal dependency among time series with irregular time distances. It is end-to-end trainable with samples generated using an automatic annotation generation method, which is proposed based on the prior knowledge from the continuous change detection and classification (CCDC) approach. IRCNN was tested over five study areas using Landsat time series collected between 2013 and 2020. Experiments demonstrate the effectiveness and stability of the proposed network with better performance, compared to the state-of-the-art approaches in terms of both qualitative and quantitative aspects. Our IRCNN Pytorch code and data are available at <uri>https://github.com/thebinyang/IRCNN</uri>.

Large-Area Land-Cover Changes Monitoring With Time-Series Remote Sensing Images Using Transferable Deep Models

Dense time-series remote sensing images have transformed the traditional bitemporal land-cover change detection to continuous monitoring. Previous work mostly employs linear fitting, prediction, or decomposition methods, and the detection accuracy is not high. The latest progress of deep learning (DL) shows its advantages in time-series change monitoring. However, DL models are computationally expensive and require lots of labeled samples, resulting in often employed prediction-threshold-based unsupervised change detection method. However, the determination of a reasonable threshold has always been a big problem. Therefore, we proposed the similarity-measurement-based deep transfer learning for time-series adaptive change detection (SDTL-TSACD) model. First, a standard dynamic time warping (SDTW) distance was proposed and used to cluster large-scale time series into multiple subcategories with high time-series similarity. Second, a time convolutional network (TCN) was used for nonlinear time-series fitting and prediction, and an early stop strategy was used to prevent overfitting. Then, the trained TCN model would be transferred and performed pixel-by-pixel time-series prediction within the same category, and the SDTW was also used to evaluate the prediction accuracy. Finally, the Otsu adaptive threshold was used to detect change points, and the spatial neighbor relationship was used to eliminate the pseudo-change points. Change detection results using 132 benchmark datasets showed that the SDTL-TSACD performed well in both accuracy and efficiency. In addition, the MOD13Q1-EVI images from 2001 to 2020 were used to study the land-cover change of the Loess Plateau, and the SDTL-TSACD also showed a good ability to solve practical problems.

Bi-CCD: Improved Continuous Change Detection by Combining Forward and Reverse Change Detection Procedure

Continuous change detection (CCD) is one of the most famous algorithms in remote sensing time series change detection, making any improvements on it are of great significance for the practice of monitoring land cover dynamics. Inspired by the directionality of CCD, a bidirectional CCD (Bi-CCD) is proposed to improve the accuracy of change detection by selecting the optimal result from the results of CCD running from both the forward and backward directions of time series. Three criteria including root mean square error (RMSE), Akaike information criterion (AIC), and Bayesian information criterion (BIC) were adopted to define the “optimal” in this study, and their effects under three common parameter settings were evaluated in a simulation dataset. The quantitative results show that Bi-CCD based on different result selection criteria can indeed improve the accuracy of change detection in terms of omission error and commission error. In general, Bi-CCD based on RMSE achieved the lowest omission error, while Bi-CCD based on BIC obtained the lowest commission error. Compared with the unidirectional CCD, Bi-CCD reduces the omission error and commission error by at most 11.19% and 15.08%, respectively. In addition, the different effects of different optimal result selection criteria on the accuracy of Bi-CCD enable Bi-CCD more flexible to handle different tasks than the standard CCD.

Hybrid Spatiotemporal Graph Convolutional Network for Detecting Landscape Pattern Evolution From Long-Term Remote Sensing Images

The remote sensing time-series change detection algorithm based on the pixel or single landscape patch ignores the change analysis of spatial structure information. Inspired by graph convolutional network (GCN) modeling, a set of landscapes (nodes) and their relationships (edges) are proposed. In this study, a parallel strategy in spatial GCN and progressive strategy in temporal GCN, called the hybrid GCN model network as a holistic framework, was proposed to accurately capture both spatial and temporal variations in landscape patterns based on yearly Landsat time series. A super-patch (i.e., fixed patch class surrounded by a one-hop neighbor patch) was selected as the input of the GCN network. First, a spatial GCN model with three parallel graph convolutional layers was adopted to classify landscape pattern types. Three dominant categories of landscape patterns over the past three decades have been identified. Second, four landscape metrics in super-patches were proposed for the quantitative characterization of changes in landscape patterns. Finally, a temporal GCN model with two progressive graph convolutional layers was used to detect six types of patch changes, which were applied to continuously detect the landscape pattern evolution processes. Regardless of the spatial GCN and temporal GCN, they provided satisfactory performance using the training and validation sets with overall accuracy > 92% and Kappa coefficient > 0.90, and loss values converging to 0.049 and 0.128, respectively, based on NLLLoss function until 500 epochs. It is believed that the hybrid GCN model has great potential for mining possible implicit spatiotemporal relationships and future evolution of landscape patterns.

A novel change detection method using remotely sensed image time series value and shape based dynamic time warping

Satellite image time series change detection methods provide comprehensive understanding of land cover changes. Traditional bi-temporal change detection methods in satellite image time series require consistent time series lengths and use only time series value or shape to calculate change magnitude maps, which may not fully utilize land cover change information. To address this challenge, we propose a change detection method using remotely sensed image time series value and shape based dynamic time warping (TSVS). Change magnitude maps were obtained from the time series trajectories of NDVI and MNDWI using time series value-based dynamic time warping method and time series shape-based dynamic time warping method. Change detection results were derived by clustering the polar coordinate space of time series value and shape using Gaussian mixture model method. Experiments using Landsat images show that the TSVS method improves about 2.75–5.10% compared to the CVA_GMM method, reducing the generation of false alarms.

Long Time-Series Mapping and Change Detection of Coastal Zone Land Use Based on Google Earth Engine and Multi-Source Data Fusion

Human activities along with climate change have unsustainably changed the land use in coastal zones. This has increased demands and challenges in mapping and change detection of coastal zone land use over long-term periods. Taking the Bohai rim coastal area of China as an example, in this study we proposed a method for the long time-series mapping and change detection of coastal zone land use based on Google Earth Engine (GEE) and multi-source data fusion. To fully consider the characteristics of the coastal zone, we established a land-use function classification system, consisting of cropland, coastal aquaculture ponds (saltern), urban land, rural settlement, other construction lands, forest, grassland, seawater, inland fresh-waters, tidal flats, and unused land. We then applied the random forest algorithm, the optimal classification method using spatial morphology and temporal change logic to map the long-term annual time series and detect changes in the Bohai rim coastal area from 1987 to 2020. Validation shows an overall acceptable average accuracy of 82.30% (76.70–85.60%). Results show that cropland in this region decreased sharply from 1987 (53.97%) to 2020 (37.41%). The lost cropland was mainly transformed into rural settlements, cities, and construction land (port infrastructure). We observed a continuous increase in the reclamation with a stable increase at the beginning followed by a rapid increase from 2003 and a stable intermediate level increase from 2013. We also observed a significant increase in coastal aquaculture ponds (saltern) starting from 1995. Through this case study, we demonstrated the strength of the proposed methods for long time-series mapping and change detection for coastal zones, and these methods support the sustainable monitoring and management of the coastal zone.