1. Introduction
Remote sensing analysis technology is rapidly developing, and this has resulted in an expanding range of applications. At the same time, the types of remote sensing images are also expanding. By analyzing remote sensing images, humans are able to gain a more comprehensive understanding of the Earth’s environment, both in time and space [
1,
2]. It is important to note that, when applied to complex or large remote sensing image processing applications, a single type of remote sensing image may not be sufficient in providing adequate source information and image features [
3,
4,
5]. Consequently, multiple experts must collaborate across disciplines in order to obtain a better processing and analysis of remote sensing images’ results, or even to collaborate with experts outside the field of remote sensing image processing in order to solve complex geographic problems, as well as to improve the extraction or segmentation accuracy of remote sensing images. For example, in the processing and analysis of many types of remote sensing images, such as multispectral, hyperspectral, SAR, etc., it is often necessary to use algorithms, such as clustering, segmentation, and imaging in the field of computer vision, to improve the accuracy and spectral responsivity of the remote sensing images to achieve a more accurate and comprehensive data analysis and application [
6,
7,
8,
9,
10,
11,
12]. However, multidisciplinary online collaboration analysis usually poses two challenges for processors and analysts. Firstly, due to limited energy, expertise, and resources, it is difficult for an expert to complete the whole problem and to analyze it independently [
13]. Therefore, multifaceted collaboration is essential in solving complex problems [
14]. The second problem is the data problem. Currently, the majority of data that is used in geographic analysis are remote sensing data. However, remote sensing image data have the following characteristics: large data volumes, spatial and spectral correlations that are more complicated than natural images, and unstable data quality [
15,
16]. These characteristics may result in certain problems, such as difficulties in the processing of remote sensing data, limitations in data processing via computer hardware and software, and difficulties in the exchange of information. With the development of online remote sensing processing and analysis technology, the method of solving data problems is no longer limited to replacing more advanced computer equipment but is based on the method of online network analysis, utilizing servers, cloud platforms, and other methods to solve data-related problems [
17]. Therefore, the combination of collaborative technology with online remote sensing analysis technology is crucial for resolving complex interdisciplinary remote sensing image processing problems.
In the research field of collaborative analysis, scholars have explored interdisciplinary approaches that are aimed at collaboratively solving complex remote sensing processing and analysis problems in the fields of humans and nature, earth sciences, and decision analysis; in addition, they have also developed collaborative prototyping systems to validate these approaches [
18,
19]. Alternatively, certain scholars have focused on customizing collaborative analysis processes and visualizing collaborative analysis to enhance collaboration among participants in complex problems [
20,
21,
22]. Although all of the above studies have adopted workflow technology as their main engine of collaborative analysis and have achieved certain results, there are still two problems: (1) the majority of collaborative analysis workflows employ non-standardized methods, which have poor shareability and reusability issues, and (2) the studies that use standardized workflows only examine collaborative modeling or visualization, and no studies specifically address collaborative online remote sensing processing images and analysis. To solve the above problems, the BPMN2.0 standard provides a standardized workflow framework with graphical symbols, rules, and sub-processes. This effectively addresses the problem of poor data sharing and reuse during cross-disciplinary analysis [
23,
24], while reducing the errors encountered when constructing collaborative processes [
25]. However, to achieve collaborative and effective online remote sensing image processing and analysis, more effective collaboration models are needed, in addition to standardized workflow engines, in order to enable multifaceted collaboration for image processing and analysis in complex problems.
The term “online remote sensing analysis” refers to a method of processing and analyzing remotely sensed images when using a web-based platform, and this is achieved by manipulating the input data and producing the desired output results [
26,
27]. However, due to the complexity of spectral and spatial remote sensing data information as opposed to general natural images, certain problems, such as poor sharing and difficult interaction, often occur when interacting with remote sensing information on the Web [
28,
29,
30,
31,
32]. There is a need for an online remote sensing data interaction standardization method in order to solve this problem. Currently, most solutions use the Open Geospatial Consortium (OGC) service standard to standardize the processing and analysis of remotely sensed data. This standard aims to standardize the processing and analysis of remote sensing images when using syntactically interoperable services. Thus far, scholars have conducted a substantial amount of research and application practice on the OGC standard. Several scholars have recognized the importance of the OGC standard in the field of geographic information [
33,
34,
35], and certain scholars have designed prototype systems based on the OGC standard [
36,
37,
38,
39]. However, scholars with limited development abilities must learn how to develop before they can process and analyze remote sensing images, which makes collaborative remote sensing analysis more difficult. To solve this problem, integrating OGC standards into existing geospatial applications on the market can effectively reduce the difficulty of code development for collaborative online remote sensing image processing and analysis systems, while improving the ability of information sharing and generalization [
40,
41]. Currently, there are mature open-source geospatial applications in the field of geographic information, such as GeoServer, which uses the OGC standard to edit and create maps [
42]. Even though certain scholars have proposed the use of geospatial applications for online remote sensing data processing and analysis, they have not combined the use of online remote sensing data processing and analysis with collaborative analysis. Therefore, a standardized model for online remote sensing image analysis and processing that incorporates geospatial components is needed at this stage to achieve a collaborative processing and analysis of online remote sensing images.
In order to help participants establish a complete and clear online remote sensing collaborative processing and analysis procedure, this paper has been based on proposing a conceptual model framework, as well as both a standardized online remote sensing image collaborative processing analysis process construction model and a standardized online remote sensing image processing analysis model. Using the process construction model, a collaborative standardized online remote sensing processing and analysis procedure can be defined to help participants solve the challenges of collaborative multifaceted remote sensing image processing and analysis. The online remote sensing processing analysis model is intended to provide a methodology for collaborative analysis of standardized online remote sensing image processing and analysis that helps participants to define the interaction of remotely sensed information between collaborative processes and between analysis activities.
In this paper,
Section 1 analyzes current research progress in collaborative online remote sensing image processing and analysis, and outlines existing problems. In
Section 2, we describe the composition of the conceptual model framework for collaborative online remote sensing image processing and analysis. Following this,
Section 3 introduces the implementation framework of the collaborative remote sensing image processing analysis process construction model, based on BPMN2.0, and the collaborative online remote sensing image processing analysis model, based on the OGC standard (hereinafter collectively referred to as the process construction model and the online remote sensing image processing analysis model, respectively). A case study of the post-disaster assessment of a forest fire caused by drought and strong winds is analyzed in
Section 4 in order to demonstrate the effectiveness of a synergistic online remote sensing image processing analysis framework and model that is based on the OGC and BPMN2.0 dual standards. In
Section 5, the paper comes to a conclusion.
2. A Conceptual Modeling Framework for Collaborative Online Remote Sensing Image Processing and Analysis
A well-structured collaborative online remote sensing analysis and image processing procedure, with clear types of collaborative activities, is essential for analysts and processors when carrying out collaborative online geographic problem analysis. For this reason, when constructing a collaborative online remote sensing analysis process, it is imperative to take into account the structure of the collaborative process, as well as the activities undertaken by remote sensing analysts and remote sensing image processors during the analysis stage. For the structure of the collaborative process, certain studies have shown that hierarchical and progressive structures are suitable [
22]. Furthermore, it has been shown that collaborative geographic analysis activities can be classified into four categories based on their purpose: awareness-related activities, data-related activities, model-related activities, and application-related activities [
43,
44]. This paper presented a conceptual framework for collaborative online remote sensing analysis that addresses the above two aspects, thereby aiming to assist participants in building a hierarchical collaborative process that integrates these four types of collaboration. This is illustrated in
Figure 1.
As a result of the proposed conceptual model, collaborative online remote sensing analysis involves four phases, including the phase of context definition for collaborative analysis, the phase of resource collection, the phase of construction of the standardized analysis processing flow, and the phase of collaborative implementation. Four types of collaborative analysis activities are carried out by participants during these four phases. As an example, during the context definition phase, participants engage in activities related to awareness, such as discussing the process of geographical problems and the resources and tools required to address them; during the resource collection and standardized analytical treatment process construction phases, participants engage in activities related to the data and models; during the process implementation phase, participants conduct remote sensing analyses and image processing activities in accordance with the constructed analysis process. These phases are important components of the collaborative analysis process and linking these phases with each other is necessary to solve various problems and complete the collaborative process construction for various problems.
Figure 1 illustrates the relationships between the stages using arrows. The results obtained in the context definition stage may, for example, guide participants’ behavior in the resource collection stage and also serve as a basis for the standardized analysis and processing process construction stage; the collaborative online remote sensing analysis process is built around the definition of the context and the collection of resources; the collaborative implementation phase involves participants cooperating with each other to resolve practical problems based on standardized processes.
This conceptual model framework describes a collaborative online problem solving process, in which participants collaborate with each other at different stages, share information and knowledge, and engage in a variety of collaborative activities. In the four phases of collaborative online remote sensing image processing and analysis, the following main activities were accomplished by the participants.
2.1. The Context Definition Phase
The context definition phase is the first step in the collaborative online geographic problem solving process. This phase involves participants exchanging ideas and discussing the problem from a macro perspective in order to determine the analysis process and the resources that are required. It is possible to divide the participants into two categories when determining the collaborative online processing and analysis process. The first category of participants discussed the problem from a macro perspective, thereby identifying the main processes of collaborative online analysis. For example, the main process of collaborative disaster analysis begins with the extraction of the disaster area, after which the results obtained from the extraction of the disaster area can be used to further assess the disaster event, i.e., the analysis of the disaster event is divided into a number of sub-problems. A second category of participants discussed the specific implementation of remote sensing analysis sub-problems within the main process. This included, for example, during the disaster region extraction sub-problem, data, remote sensing image preprocessing models, and semantic segmentation models being used.
2.2. The Resource Collection Phase
In the resource collection phase, the participants focus on activity preparations, such as data collection and sharing for collaborative online analytics, model construction and sharing for analytical processing, and sub-process model construction and sharing. The data collected and shared during the data collection and sharing activities include both online and offline data. Offline data can be directly used for activities or can be shared using the OGC standards. Then, the data are called, processed, and analyzed by other participants in the collaborative process. Online data can be accessed through the OGC services, and the way in which these remote sensing data are shared and accessed using the OGC standards contributes to an improvement in data utilization [
45,
46]. A key objective of the online remote sensing analysis model’s construction and sharing activity is to enable the online analysis and sharing of models, as well as to provide a method for sharing and executing remote sensing analysis and processing models. As an example, the OGC service is used to encapsulate the disaster area semantic segmentation model, the disaster loss assessment model, and the remote sensing image preprocessing model into a WPS service process. This is then utilized to set the corresponding model’s input and output parameters, as well as to realize the online analysis of the disaster model. In the collection and sharing of the sub-process models’ activity, participants store, share, and transfer sub-processes that are created in other domains with the extensible markup language (XML). It is important to note that the “sub-process model” refers to processes that are constructed, while other issues related to remote sensing analysis are being addressed.
2.3. The Construction Phase
In the construction phase of the standardized analysis and processing process, participants must construct the image processing and analysis processes by adopting the relevant standards of workflow in a problem- and resource-oriented manner. In other words, the aim is to develop a standardized collaborative online analysis and processing process based on the processing and analysis processes determined in the first phase, with the resources collected in the second phase. This standardized remote sensing analysis process helps to improve the resource reuse rate of collaborative online analysis, as well as greatly helps to improve the collaborative nature of the participants in the collaborative analysis process. In addition, participants are able to gain a better understanding of the problem solving process in another domain, thereby reducing the possibility of the errors attributable to individual understandings during a collaborative process. It is evident in the results of the first stage of process customization that the main process consists of a number of sub-problems. Each of these sub-problems are composed of multiple solution steps, i.e., multiple analytical sub-processes. In order to improve the manageability of collaborative online analysis processes, it is necessary to separate remote sensing analysis workspaces, sub-processes, and realization activities. Consequently, standard processes should be constructed in accordance with hierarchical structures.
2.4. The Collaborative Implementation Phase
In the collaborative implementation phase, participants complete the corresponding analysis and processing sub-processes in accordance with the constructed analysis and processing process, as well as cooperate with one another to complete the implementation of the entire analysis and processing process. In other words, each step of the sub-problem is performed by a different participant, and the participant only needs to complete the corresponding analysis and processing steps according to the sub-processes, and this is achieved without having to understand or master remote sensing analysis methods or the processes of other procedures.
4. The Case for a Collaborative Online Forest Fire Post-Disaster Assessment
4.1. Background
Extreme droughts and strong winds tend to trigger forest fires. Forest fires not only disrupt the local ecological balance, but they can also exhibit several impacts on human survival. The assessments of forest fires following a disaster can assist in observing the changes in forests before and after a catastrophe, as well as provide effective assistance in the recovery and management of soils following a disaster. Several participants decided to analyze the post-disaster assessment of fires using optical remote sensing and radar remote sensing data.
4.2. Participants, the Study Area, and the Experimental Data
As part of this experiment, participants from different research fields, and with different domains of expertise, collaborated on the post-disaster assessment of the “3.30 forest fire in Xichang”. For example, several experts in optical and radar remote sensing image processing and analysis, a BPMN2.0 process builder, and a project stakeholder were involved in this collaborative disaster analysis project. Participants from different domains collaborated and shared resources during the analysis process to define their needs, goals, and expected results for the forest fire post-disaster assessment.
The research object of this study was a forest fire that occurred in Sichuan Province between 30 March 2020 and 3 April 2020, known as the “Xichang 3.30 Forest Fire”. The forest fire area is located at 102°15′12′′ E, 27°50′30′′ N, and it is surrounded by residential areas, roads, lakes, and other such features.
Figure 4 shows the fire area and nearby features.
This experiment was conducted using the raster data downloaded from the Copernicus Open Access Center (
https://scihub.copernicus.eu/), accessed on 24 June 2023, which includes four types of image data, the adjacent Sentinel I radar image data before and after the fire, and the Sentinel II optical image data. As opposed to the raster data, the vector data corresponded to the approximate extent of the fire as determined via visual interpretation. This experiment provided one vegetation index calculation, two fire index calculations, and two microwave parameter calculation models, as well as one fire trace discrimination model and one fire class segmentation model to be used by the online fire post-disaster assessment model. In addition, this paper utilized the image-cropping WPS process already available in the GeoServer WPS extension.
Table 1 and
Table 2 provide details on the raster data and model information used in this experiment.
4.3. Forest Fire Post-Disaster Assessment Case Implementation
Participants are required to go through four stages to complete a collaborative online assessment of fire after fire events, as outlined in the conceptual modeling framework. Participants perform different activities during each phase.
During the context definition phase of the problem, the participants analyzed and discussed the forest fire post-disaster assessment problem, identified the resources required for the problem, and defined the corresponding analysis process. As an example, the participants defined the fire analysis process as a three-step process. As a first step, the participants discussed the needs, objectives, and expected outcomes proposed by stakeholders, as well as identified two sub-problem workspaces for the extraction of fire trace areas and the classification of fires. After identifying the sub-problems, participants should then discuss, in depth, the steps for analyzing the sub-problems. As a result, the participants developed several sub-processes for the two sub-problems in the second step of the collaborative online fire post-disaster assessment. As a final step in the analysis process, the participants identified the basic data and analytical models that were used in this post-fire assessment.
Figure 5 illustrates both the sub-problems and the sub-processes developed in this experiment.
Based on the results of the first phase’s discussion, the participants are required to collect, construct, and share analytical resources in the preparation phase of the post-fire assessment. As an example, the participants first collected optical and microwave data for each phase of the fire, and then subsequently shared them within GeoServer, a geospatial application. Secondly, they collected models for calculating the characteristic parameters of fire analysis, extracting fire track areas, and classifying the fire levels. These were then converted into a WPS process, such that they could be integrated into geospatial applications for the purposes of allowing online analytical models to be called. Lastly, although this experiment did not result in the discovery of relevant sub-process models, the sub-processes constructed in this experiment may still be applied in other situations.
Figure 6 illustrates the structure of the WPS process for this experiment, and
Figure 7 illustrates the built WPS process call reference.
During the construction phase of the fire post-disaster assessment process, the participants constructed an online fire post-disaster assessment analysis process based on the online collaborative remote sensing analysis process construction model, which was based on the BPMN2.0 standard. The participants constructed two sub-problem workspaces for the extraction of fire trace areas and the classification of fires, as well as a number of sub-processes. For example, the fire trail region extraction workspace included an image cropping sub-process, five feature parameter calculation sub-processes, a decision tree extraction sub-process, and three gateways. There is a sub-process in the fire intensity rating sub-problem workspace that performs a fire rating, which is the process of obtaining a dNBR index that is obtained from the extraction of the fire trace regions. In this experiment, the thresholds for fire classification were derived from the forest fire intensity classification criteria developed by Key et al. in the USGS Firewall project [
47]. This classification standard includes five classification levels: the unburned area, the lightly burned area, the medium-low burned area, the medium-high burned area, and the highly burned area. Finally, each sub-process established the three realization activities of data acquisition, online remote sensing analysis model implementation, and the sharing of results.
Figure 7 illustrates the BPMN2.0 process for the collaborative online analysis of forest fire post-disasters. The workspace, sub-process structure, and realization activities (in the case of the realization activities of the dNBR sub-process) of the BPMN2.0 process extensible document for a standardized online fire post-disaster assessment are outlined in
Figure 8. The extensible document consists of events (e.g., startEvent and endEvent), activities (e.g., subProcess and userTask), gateways (e.g., parallelGateway and exclusiveGateway), and process links (subProcess). The events in this experiment were divided into startEvent nodes and endEvent nodes, which control the start and end of the process, respectively; the activities were divided into subProcess nodes and userTask nodes, with subProcess nodes being used to describe the workspace and analyze the sub-processes, and userTask nodes being used to describe the realization of the activities. There are two types of gateways: parallel gateways and exclusive gateways. Parallel gateways include branch gateways and merge gateways, which control the simultaneous beginning and end of the parallel sub-processes for the computation of five parameters, whereas exclusive gateways determine the end of the sub-processes for cropping raster images.
It is worth noting that the activity nodes in this experiment were divided into subProcess nodes and userTask nodes. SubProcess nodes are used to describe the workspace and analyze the sub-processes. UserTask nodes are used to describe the realization activities. In the process implementation stage, the participants in different fields complete the corresponding sub-processes by providing process parameters, including data input and output parameters, as well as WPS process call parameters. For example, the optical remote sensing processing expert obtained the corresponding vegetation index and fire index by processing the optical image; the microwave remote sensing processing expert obtained the SAR-related parameters by processing the microwave image; the analytical model expert extracted the fire track area and classified the fire level according to the provided optical and radar parameters. The analysis results obtained in this experiment are shown in
Figure 9.
To quantitatively judge whether the accuracy of the overfire area extraction of this experiment was qualified or not, this experiment involved the use of ENVI 5.3 software to extract the overfire area according to the same steps, as well as compared the accuracy with that extracted via the collaborative online remote sensing analysis. The comparison results of the overfire area and extraction accuracy are shown in
Table 3. The accuracy calculation formula is shown in Equation (1):
where
is the extraction precision,
is the area of the overfire area (3047.7805 hectares) provided by the official website (
http://www.sc.gov.cn/), accessed on 24 June 2023, and
is the area of the extracted overfire area.
4.4. Discussion of Experimental Results
A comprehensive online collaborative forest fire post-disaster assessment process was demonstrated in this paper to validate the effectiveness of this collaborative online remote sensing image processing framework for solving geographical problems. In the collaborative assessment process, participants identified the assessment process, as well as the resources needed by discussing the post-fire assessment process; the collection and sharing of the four image datasets and the WPS model formalization of the seven models were accomplished, thereby reducing the difficulty of reusing the online remote sensing image processing and analysis models. The construction of a collaborative online fire post-disaster assessment process based on the BPMN2.0 and OGC standards was completed using the process construction model and the online remote sensing analysis model. Through the implementation of this process, the extraction of fire trace areas and the classification of fire intensity levels were accomplished, and the analytical results of the intermediate processing steps were shared, thereby assisting in the post-disaster assessment process and in the analysis of fire traceability. In addition, this paper proposed a collaborative online fire analysis process that uses the BPMN2.0 and OGC standards to solve the problems related to poor sharing and reusing in the collaborative online remote sensing process, as well as processing difficulties, high hardware requirements, and the difficult information interactions due to the characteristics of remote sensing data. In the standardized collaborative online fire analysis process construction, the participants constructed two sub-problem workspaces, several analysis sub-processes, sub-process realization activities based on the process construction model, and standardized information interactions based on the online fire analysis model. This standardized collaboration framework not only realized a multifaceted collaboration among participants, but also significantly reduced the amount of time occupied by individual participants in the analysis process. In addition, it also enhanced the manageability and reusability of the collaborative online fire analysis process.
Compared to a non-collaborative and offline analysis, collaborative online processing and analysis offers significant advantages. In collaborative online fire analysis, stakeholders and researchers from various disciplines can cooperate to construct and implement the analysis process to ensure that the analysis’ purpose is achieved, and that technical feasibility is ensured, thus achieving an interdisciplinary fire analysis. Online fire analysis can reduce the requirements for computer hardware and can solve the problem of difficult remote sensing data processing when compared with offline fire analysis.
5. Conclusions
In order to solve complex geographic problems for experts, it is difficult for one expert to complete the analysis and processing tasks alone with their, in comparison, limited energy, expertise, and resources; as such, the development of collaborative online processing and analysis by multidisciplinary experts is essential. A collaborative online analysis and processing process can help experts from different disciplines collaborate with each other to resolve complex geographical problems, but an effective model remains to be developed in order to assist participants in developing a collaborative online remote sensing image processing and analysis process that is effective. Therefore, this study constructed a conceptual framework of collaborative online remote sensing image processing. This framework was divided into four phases, in which a range of activities, from the definition of the collaborative process context to the gathering of resources to the design of standardized collaborative online processing and analysis procedures, and finally to the completion of the implementation process, was encompassed.
By standardizing the collaborative online analysis and processing process, it is possible to address the problems of poor sharing and reuse in collaborative analysis, as well as in the difficulty in processing data, the high demands of analysis hardware, and the difficulty in interacting with information due to the characteristics of remote sensing data. Therefore, in this study, on the basis of constructing a complete conceptual model framework for the collaborative online remote sensing image processing and analysis process, we developed a collaborative remote sensing image processing and analysis procedure based on the BPMN2.0 standard, as well as an online remote sensing analysis model based on the OGC standards. Participants can construct a standardized collaborative online remote sensing processing and analysis procedure using the process construction model. By standardizing the process, errors and repetitive construction work can be reduced, and the process of collaborative remote sensing analysis can become more controlled and standardized. As such, the problem of the inadequate sharing of remote sensing analysis resources will be solved; thus, participants will have a better understanding of each other’s work and will be able to collaborate more effectively. Additionally, the online remote sensing processing and analysis model provides a standardized method for the interactions between sub-processes and other sub-processes, as well as between activities and other activities, which reduces unnecessary communication between participants and enhances the collaboration capability of collaborative online remote sensing analysis. Last but not least, the online remote sensing analysis model can effectively combine online remote sensing processing and analysis with collaborative processes in order to achieve collaborative online remote sensing image processing and analysis.
This study provided a conceptual framework for collaborative online remote sensing processing and analysis, as well as a standardized methodology for collaborative online remote sensing analysis. However, certain issues still require further investigation. In the case of the remote sensing processing and analysis model, WPS processualization, sub-process model integration, and professional personnel are still required to operate this model, and there is a lack of automated and effective methods available. A methodology that enables an automatic WPS processing of the remote sensing processing analysis model and the integration of sub-process models into the analysis process is necessary in order to solve the above problems and to improve participants’ resource management efficiency. The purpose of this method is to allow participants to complete a WPS processing operation by providing the relevant models without requiring manual intervention, thereby indirectly enhancing the efficiency of collaborative online processing and analysis.