2023 Volume 11 Issue 2 Pages 240-258
Historical cities are important types of cultural heritage sites, and their preservation conditions and conservation status require efficient dynamic monitoring. As the national strategy of China has been vigorously developed in recent years, high-resolution remote sensing technology provides new opportunities for dynamic monitoring of historical and cultural heritage. Based on demand analysis of the historical city conservation and support capacities of high-resolution remote sensing technology, this paper developed a general framework of historical cities conservation monitoring supported by high-resolution remote sensing technology, combined with specific case studies. The framework includes three processes: remote sensing image interpolation for historical cities, temporal and spatial change analysis of conservation elements, and quantitative evaluation of the conservation status. The aims of this study are to explore high-resolution remote sensing technology for conservation monitoring of historical cities and promote the conservation and legacy of historical cities.
Historical cities provide a great historical value or revolutionary commemorative significance and retain abundant cultural heritage (State Council of the PRC,2017). These cities comprise an important component of heritage conservation approved by the State Council of the People’s Republic of China (PRC) and an important concept to realize the conservation of urban culture (Zhang, S., 2019; Dong W.L. and Li. W.M., 2018; Lan, W.J, Hu, M., et al., 2019). With the rapid development of the social economy and continuous expansion of urban construction, historical and cultural heritage sites have been damaged to varying degrees. The traditional method of conducting conservation activities through field research increasingly fails to meet the demand. New technical methods must urgently be developed to ensure the conservation, monitoring and evaluation of historical cities (Dang, A.R., Liang, Y.Y., et al., 2021). However, with increasing application maturity of high-resolution remote sensing technology, new opportunities for dynamic and digital conservation and evaluation of historical cities are increasingly generated.
Historical inheritance of human settlementsAcademician Wu Liangyong, the founder of Human Settlements Science, pointed out that historical cities are the spatial carriers of China's precious cultural heritage and that human settlements science should be used to guide the integration of the overall conservation of historical districts and historical buildings with the creation of new urban environments (Wu, L.Y.,2018; Wu, L.Y., 2019). Many scholars have expanded their understanding of historical cities from this perspective. Some scholars have focused on the relationship between historic cities and the human settlement environment. Zhang Jie discussed the connotation, characteristics and laws of ancient Chinese human settlements from the perspectives of ancient astronomy, geography, culture, and institutions and revealed the close association between historical cities and human settlements (Zhang, J., 2016). Wu Tinghai focused on spatial planning and the construction of human settlements and analysed the conflict between the regularity of planning and the creativity of human settlements in the construction of ancient spaces as well as the ideas and methods associated with this conflict (Wu, T.H., 2021). Addressing the history of ancient human settlements in 34 provincial administrative regions, Wang Shusheng explored the basic context and experience of local urban construction in China and revealed the modern value of China's local urban planning (Wang, S.S., 2017). With the advancement of research, an increasing number of scholars have applied the analytical perspective of human settlements to the conservation of historical cities. Sun Shimeng analysed the concepts of human settlements in the ancient Yuncheng area and proposed suggestions for classifying the cultural value of Yanchi and related conservation and development strategies (Sun, S.M., Wu, W.J., et al., 2019). Zhao Yiqing analysed the core mechanism of the current operation of historical ancient cities and used Xi'an as an example to reveal the advantages of viewing the relationship between ancient city conservation and urban development from the perspective of comprehensive human settlements (Yi, Q.Z., Davide, Rui, Z., 2019).
In general, research on historical cities that incorporates human settlements theory is gradually becoming mature. As an important historical heritage, historical cities embody the rich history of ancient human settlements. The multi-level, multi-scale and multi-dimensional value system of historical cities represents the integration of society, politics, economy and humanities in ancient cities. This situation requires us to broaden our perspective in considering historical cities in combination with new technologies. Instead of focusing exclusively on spatial data, we should adopt the perspective of the human settlements system to comprehensively analysed and explore the essence of traditional regional culture. This approach will allow us to creatively develop the conservation of and research on historical cities in the construction of human settlements environment.
Conservation of historical citiesThe conservation of Chinese historical cities has traversed three development stages, including concept establishment, system formation, and continuous improvement. In 1982, the first batch of 24 national historical cities was announced, and a conservation system for this batch of cities was initially established. In 1986, the State Council first clarified the concept of historic conservation districts, further emphasized the importance of historic preservation areas, and defined the levels of historical cities, historic preservation areas, and individual cultural relics in the conservation of cultural heritage. Subsequently, a conservation system for historical cities in China was established. In 2000, the conservation of historical cities was further regulated and informatized. The revised Law of the People's Republic of China on the Conservation of Cultural Relics in 2002 added requirements for the conservation of historic conservation districts and encouraged the application of remote sensing technology in urban construction monitoring. In 2010, the Ministry of Housing and Urban-Rural Development (MOHURD) evaluated and inspected the conservation status and established a dynamic monitoring and inspection system. In 2017, the MOHURD launched an evaluation and inspection campaign of historical cities, towns, and villages. In 2020, the State Cultural Relics Bureau and MOHURD issued the Administrative Measures for the Declaration of National Historical cities, which adjusted the identification standards of historical cities, aiming to integrate a variety of historic resources at the level of historical cities, systematically express the corresponding historical value and preserve excellent traditional culture.
After nearly 40 years of continuous improvement in the conservation system, a multilevel object system including historical environments, historical cities, historic conservation districts, and historical relics has basically been established. The subject of conservation has expanded from the pure cultural relic ontology to multiple aspects, such as spatial patterns, supporting facilities, and cultural continuity, while the goal of conservation has expanded from conservation to multidimensional development of urban characteristics, historical activities, and residential life. However, in the practice of new urbanization, there remain certain issues such as destruction of the overall landscape environment and structure of a given city, a lack of infrastructure and public service facilities in historical blocks, and inadequate conservation of historical relics. The conservation of historical cities still urgently requires comprehensive, systematic and objective exploration and development efforts.
Monitoring of historical citiesHistorical cities are valuable treasures inherited from the development of Chinese culture encompassing a large number of cultural relics and offer a profound historical value (Zhao, Y., 2013; Zheng, Y., 2020; Ruan, Y.S., San, J.H., et al., 1999). Since 1982, the State Council has announced 134 national historical cities. The various types and characteristics of heritage elements in cities highlight an urgent need for systematic conservation and monitoring. Within this context, the demand for the conservation of historical cities combined with innovative technologies and methods is increasing on a daily basis. From 2008 to 2010, the MOHURD proposed the application of remote sensing dynamic monitoring technology to assist planning and promote the construction of a dynamic monitoring mechanism for historical and cultural city conservation and evaluation.
In 2012, the State Cultural Relics Bureau requested the establishment of a dynamic information system and early warning system for world cultural heritage management in China. This institution also issued JG [2017] No. 221 in conjunction with the MOHURD to conduct spot checks regarding the conservation status of historical cities and proposed eight key assessment aspects, including the conservation scope of historical cities, changes in the number of historical buildings, traditional structure of historical areas, traditional features and scales, changes in the number of residents in historical areas, conservation of historical relics, and infrastructure. However, the existing evaluation indicators achieve a limited monitoring coverage of changes in historical urban areas. In evaluation, problems such as high subjectivity and difficulty in promotion are encountered (Xiang, B.J. and Di, W.L., 2020). In addition, many scholars have attempted to apply remote sensing and geographic information system (GIS) technologies in the conservation of historical cities to perform cultural heritage monitoring research (Dang, A.R., 2001; Alwedyan, S., 2023; Tan, J.M., Gu, Y., et al., 2013). Research has mainly focused on the following four aspects: status investigation and characteristic analysis (Xu, J.G., He, Z.Y., et al., 2005; Zheng, Z.P., Wu, F.M., et al., 2019), dynamic monitoring of the conservation status (Ma, F. F., Li, M., 2022; Ren, S.F., Yi, J., et al., 2019), early warning and risk assessment systems (Wu, Z.D., Hu, Y.J., et al., 2016; Yi, J., Ren, S.F., et al., 2019), and decision-making for conservation and development purposes (Li, L., Qi, Q.W., et al., 2014; Zhang, Z., Dang, A.R., et al., 2021).
Generally, high-resolution remote sensing has been widely employed in historical research, but the actual application to historical cities remains insufficient, especially in regard to conservation, monitoring and evaluation research. Recent research has not established a highly objective and systematic technical method, and the monitoring elements and technical processes are relatively vague. It is necessary to conduct in-depth research on the implementation process of the conservation of historical cities with a focus on the contradictions and problems frequently encountered and explore effective technical methods to facilitate the conservation of historical cities.
This study chooses Jingdezhen, Jiangxi Province, as an example. Jingdezhen is one of the first 24 historical cities announced by the State Council and is a world-famous porcelain capital. Jingdezhen is associated with more than 2,000 years of smelting history, more than 1,000 years of official kiln history, and more than 600 years of imperial kiln history. This city has retained a rich and complete porcelain industry system and cultural heritage, which provides an extremely high research value. The identification of historical and cultural city identity of Jingdezhen occurred relatively early, but the systematic and targeted conservation and planning of Jingdezhen commenced relatively late. At present, the conservation framework of Jingdezhen encompasses three spatial levels: city area, central city area, and historical city area. Among these levels, the cultural heritage contained within the historical city area, covering an area of approximately 2.4 square kilometres, constitutes the core and key spatial object, and the historical city area is also the most directly affected by urban construction. Specifically, the historical city area includes 1 historical and cultural city, 6 historical conservation blocks, and a number of cultural relics, which is the core object of this research (Figure 1).
The data considered in this study are retrieved from the Chinese Gaofen (GF) remote sensing series satellites. High-resolution remote sensing is a relatively new concept. In the era when Landsat and Satellite for Observation of Earth (Satellite Pour l’Observation de la Terre or SPOT) remote sensing data originating from the United States and France, respectively, were the main data sources, scholars referred to images with a resolution greater than 10 m as high-resolution remote sensing images (Gong, P., Li, X., et al., 2006), while today's high-resolution remote sensing images often include remote sensing images with a submeter resolution.
At present, the data provided by the third-generation US remote sensing satellites, i.e., WorldView-3 (2014) and WorldView-4 (2016), have reached a spatial resolution of 0.3 m. The submeter resolution remote sensing satellites of China include GF-2 (2014), BJ-2 (2015), JiLin-1 (2015) and SuperView-1 (2016). In particular, the spatial resolution of SuperView-1 data reaches 0.5 m. Although it remains difficult to obtain high-resolution remote sensing data with a cloud-free coverage across China, the commercialization of high-resolution data and observation systems remains an important direction in the future (Xu, G.H., Liu, Q.H., et al., 2016; Dang, A.R., Xu, J., et al., 2016).
The GF series satellite data employed in this study exhibit the following characteristics:
(1) High spatial resolution: High-resolution remote sensing data not only contain spectral information included in medium- and low-resolution data but also contain a large amount of geometric, textural and contextual information on ground objects. Among the various satellites, the spatial resolution of the panchromatic images recorded by the GF-1 and GF-2 satellites can reach 2 and 0.8 m, respectively, and the images more closely reflect the objects perceived by human eyes.
(2) High radiometric resolution: The radiometric resolution of GF-1 and GF-2 remote sensing data can reach 10 bits. The image layers are abundant, the textural, geometric and contextual information of ground features are well refined, and the interpretation effect is excellent (Guan, Y.X. and Cheng, X.Y., 2008).
(3) Multiple spectral resolutions: While exhibiting high spatial and radiometric resolutions, high-resolution remote sensing data contain fewer bands (Du, F.L., Tian, Q.J., et al., 2004). Usually, the data contain one panchromatic band and four bands including blue, green, red, and near-infrared bands. The spectral range of the GF-2 satellite includes panchromatic (0.45–0.90 μm) and multispectral bands (0.45–0.52 μm, 0.52–0.59 μm, 0.63–0.69 μm, and 0.77–0.89 μm).
(4) High temporal resolution: The GF series satellites exhibit the advantage of a perfect combination of high spatial and temporal resolutions. Of these satellites, the revisit cycles of the GF-1 and GF-2 satellites can reach 4 and 5 days, respectively.
(5) Very large amount of data: Due to the high spatial, temporal and radiometric resolutions of the GF series satellites, the amount of remote sensing data has also sharply increased, which has generated great challenges in terms of data storage, processing and analysis (Guan, Y.X., Wang, X.G., et al., 2019).
Research approachMonitoring and analysis of the conservation status of historical cities based on high-resolution remote sensing technology require not only an in-depth understanding of the historical value but also effective strengthening of historical resource management. Moreover, the practice of applying high-resolution remote sensing data is extended to urban space management. Therefore, research should consider not only the technical characteristics of remote sensing data analysis and extraction but also the objective requirements of historical and cultural city conservation.
To achieve the above objectives, this study constructs a technical route, including analysis and extraction of data, monitoring analysis of changes and evaluation analysis of conservation conditions (Figure 2).
(1) Analysis and extraction of data: This task involves the interpretation of basic information on historical cities and constitutes the basis of monitoring and evaluation. The extraction should consider as basic elements all historical heritage levels, which comprise historical cities, historic conservation districts and historical relics.
(2) Monitoring analysis of changes: On the basis of obtaining data results for historical cities, this research selects core elements of dynamic monitoring, constructs a multilayer historical city identification and monitoring element system based on remote sensing images (Table 1) and performs a multiperiod remote sensing image comparison based on the constructed system. The construction of the monitoring element system should combine the objective characteristics of image interpretation, highlights the value of historical cities at all levels and considers the management objects of the conservation laws and regulations associated with historical cities.
(3) Evaluation analysis of the conservation status: Through interpretation of the conservation requirements and values of relevant historical and cultural resources, this research establishes an evaluation framework for historical and cultural city conservation and evaluates the monitored dynamic changes. The assessment framework includes four primary indicators, including overall characteristics, environmental elements, historical areas and historic units, and eleven secondary factors (Table 2), and a quantitative method is further determined for each factor. Finally, the index results are analysed, and a summary conclusion of the conservation status is output.
Based on correction and fusion of multispectral and panchromatic images, cross analysis of the basic element objects of historical cities is conducted with methods such as visual interpretation, supervised classification and machine learning.
The various levels of historical cities include the core conservation scope, construction control zone, environmental coordination area, spatial mechanism and structural elements. The different levels of historic conservation districts include the core conservation scope, construction control zone, structural elements, architectural distribution, material and color. The various levels of historical relics include the core conservation scope, construction control zone, historical relics, other node elements, and color and material elements of building units.
Information extraction of historical cities based on high-resolution remote sensing images allows the clear detection of changes in spatial structure, historical style, architectural mechanism, building spatial distribution, spatial scale and top-view texture and materials. Additionally, dynamic analysis can support quantitative statistical accounting of all kinds of objects. Moreover, through evaluation of the spatial relationships between the extraction object and the conservation control lines of historical cities, historic conservation districts and historical relics extracted from conservation plans, the conservation area of the object can be dynamically and intuitively judged, which is convenient for later monitoring and evaluation.
Dynamic change monitoringMonitoring of historical cities is the core link between the interpretation and extraction of information and evaluation of the conservation status. In this task, multitemporal remote sensing images at intervals of 3-5 years and ground feature elements are compared through spatial registration. The core element system for monitoring includes three levels corresponding to historical cities, namely, the overall, block and element levels. Because monitoring data should encompass historical elements at different levels, the overall level includes spatial patterns, historical features and architectural mechanism. The overall level should focus on the core conservation scope of historical cities and emphasize overall pattern and style monitoring.
The block level includes historical features, spatial patterns and architectural layout. The block level corresponds to the construction control zone and core conservation scope of historic conservation districts and underscores the monitoring of block patterns and the spatial layout of architectural elements in the district.
The element level includes the element status, surrounding environment, and conservation and repair status conditions. The element level focuses on the construction control zone and core conservation scope of historical relics and emphasizes the monitoring of historical relics, surrounding buildings and surrounding environmental features.
In monitoring research within a unique high-integrity environment or considering the notable impact of the surrounding environment and regional factors on historical cities, it is necessary to include the construction control zone, feature coordination area or an even larger area among the target monitoring objects (Table 1).
| Extraction of basic information data | Extraction of monitoring data | ||
|---|---|---|---|
| Historical and cultural city levels | Core conservation scope | Overall level | Spatial pattern |
| Construction control zone | Historical features | ||
| Environmental coordination area | Architectural mechanism | ||
| Structural elements | |||
| Spatial mechanism | |||
| Historic conservation district levels | Core conservation scope | Block level | Spatial pattern |
| Construction control zone | Historical features | ||
| Structural elements | Architectural layout | ||
| Architectural distribution | |||
| Material and color elements | |||
| Historical relic levels | Core conservation scope | Element level | Surrounding space |
| Construction control zone | Surrounding feature | ||
| Historical relics | Spatial and feature changes in relics | ||
| Other historical node elements | |||
| Color and material elements | |||
Evaluation of the conservation status of historical cities based on high-resolution remote sensing entails comprehensive analysis of the dynamic monitoring results obtained from sensing data, thereby fully considering the comprehensive value of the element system for cities. Therefore, to study and construct an evaluation framework for historical cities, we should first consider whether the selected evaluation factors can fully reflect the systematic conservation needs of these cities and whether the obtained factor quantification and interpretation results match the characteristics of remote sensing data.
(1) Analysis of the value of historical cities. The formulation of evaluation factors for historical cities requires systematic coverage, and the objects of concern should include historical, environmental and structural elements. Different levels and categories of protected objects and different degrees of restriction determined through conservation planning yield varying effects on the value of cities, which should be reflected in the factor weight in the evaluation index table. The conservation of historical and cultural heritage should abide by the principles of integrity, authenticity and coordination. Therefore, conservation status evaluation must maintain objectivity, and quantification of the corresponding evaluation factors should objectively reflect the actual conservation status of historical and cultural elements.
(2) Characteristic analysis of dynamic monitoring data. In terms of the classification of changes that can be monitored, the monitoring and evaluation subjects mainly include element, style and pattern changes. Among these aspects, the characteristics of element changes include demolition and reconstruction, demolition and vacancy, demolition and new construction, site construction, current reconstruction and other scenarios. The characteristics of style changes include color, architectural element, spatial scale and natural styles. The characteristics of pattern changes include the architectural spatial pattern, traditional street pattern, urban axis pattern, corridor site pattern, traditional function pattern, and mountain water city overall pattern. The impact of various changes on the value of historical heritage differs. Therefore, evaluation of the conservation status of historical cities should be performed combined with the above changes.
(3) Monitoring and evaluation of historical cities. This study constructs a conservation evaluation indicator system including four first-class indexes, including overall characteristics, environmental elements, historical areas and historic units. Among these indexes, the overall characteristics include traditional pattern and architectural distribution. The environmental elements include both artificial and natural environmental elements. Historical areas include the block quality, block scale, conservation status of the core area and conservation status of the construction control area. Historic units include the cultural conservation level, quantity and conservation status. Each factor adopts the three-segment rating method, and the specific index description and segmentation method are listed in Table 2.
| Index 1 | Weight 1 |
Index 2 |
Weight 2 | Explanation | 80–100 | 60–79 | 0–59 |
|---|---|---|---|---|---|---|---|
| Overall characteristics | 0.25 | Traditional pattern | 0.1 | Retention of roads, open spaces, orientation, axis, skeleton, texture, etc. | Maintained | Certain degree of change |
Great change |
| Architectural distribution | 0.15 | Change degree of the building volume and quantity within the overall scope | <90% | 80%–90% | >80% | ||
| Environmental elements | 0.15 | Natural elements | 0.075 | Retention of surrounding mountains and water systems | Maintained | Certain degree of change |
Great change |
| Artificial elements | 0.075 | Change degree of surrounding roads and major infrastructure elements | Maintained | Certain degree of change |
Great change |
||
| Historical areas | 0.35 | Block quality | 0.05 | Proportion of the area of historical buildings and historical relics to the building area of the core district | >80% | 60%–80% | <60% |
| Block scale | 0.05 | Historical core area size (relative to the national standard of 1 hectare) | >15 | 1–15 | 0–1 | ||
| Conservation status of the core area | 0.15 | Degree of architectural changes within the core conservation area of historic conservation districts | <90% | 80%–90% | >80% | ||
| Conservation status of the construction control area | 0.1 | Degree of architectural changes within the construction control area of historic conservation districts | <90% | 80%–90% | >80% | ||
| Historic units | 0.25 | Level | 0.05 | Conservation level of historical relics | National (above 2) |
Provincial (above 2) |
Municipal (above 2) |
| Quantity | 0.04 | Number of historical relics at each level | Above 15 | 5–15 | Below 15 | ||
| Conservation status | 0.16 | Degree of architectural changes within the construction control area of historical relics |
Good (>95%) |
Average (90%–95%) |
Poor (<90%) |
The selection process of evaluation index factors considers historical relics, historic districts and the overall environment at the urban scale. The quantification and rating of index factors are based on expert judgment and past evaluation research and are combined with the characteristics of data information obtained by GF satellites. It should be noted that the evaluation of the conservation status of historical cities not only focuses on the final score of the indicator system but also focuses on all four factors and each individual factor. The characteristics of the subitem results reflect the development direction and shortcomings of historical cities. Moreover, the identification of weak objects in terms of the conservation status of historical cities can also provide guidance for the further optimization of remote sensing monitoring objectives.
In this research, basic information extraction regarding historical cities in Jingdezhen was conducted, and the scope of the different conservation levels was first determined, including the conservation scope of historical cities in Jingdezhen, the core conservation and construction control zone scopes of 6 historic conservation districts, and the construction scope, core conservation scope and construction control zone of historical relics (Figure 3). In descending order of severity, the conservation requirements of each scope included the core conservation scope of historical relics, core conservation scope of historic conservation districts, construction control zone of historical relics, construction control zone of historic conservation districts and conservation scope of historical cities. Different conservation areas exhibit distinct emphases on the evaluation and monitoring of heritage elements. Among these areas, the core conservation scope of historic conservation districts should maintain the original spatial scale and traditional characteristics, while construction activities should focus on renovation, repair and renewal. In the construction control zone, the integrity of the viewing gallery of the landscape node should be considered, while the relationships between the buildings within the scope and core area should be preserved. Regarding historical relics, no other construction projects should be executed within the core conservation scope. Moreover, construction projects in the construction control zone must not damage historical features of historical relics, and surrounding buildings should be coordinated with historical buildings.
Aiming at the recognition of element features, this paper employs visual interpretation, supervised classification and machine learning to recognize the geographical location, shape, boundary and projected area of ground objects. Ultrahigh buildings are identified by combining building shadow analysis and field evaluation. Through superposition of various elements within the conservation scope, we can quickly distinguish the conservation level of ground features and buildings, which can easily provide a basis for future conservation monitoring and evaluation. Choosing the feature information extracted from Jingdezhen remote sensing data in 2010 as an example, in this study, a building area of 32.64 hectares was identified within the construction control zone, while a building area of 16.3 hectares was identified in the core conservation zone at the historic conservation district level. This study identified building areas of 7.65 and 3.3 hectares in the conservation construction control zone and core conservation area, respectively, at the historical relic level. Moreover, the building area outside the core conservation area of historic conservation districts and within the core conservation area of historical relics covered a construction area of 0.42 hectares.
In general, the accuracy of historical heritage element identification through high-resolution remote sensing data is generally high. In addition, this method can better and more rapidly identify different heritage conservation areas exhibiting certain features and can provide support for dynamic monitoring and evaluation.
Dynamic change monitoringThis research considered the data quality and actual changes, selected years in which historical elements were significantly affected by urban construction and finally acquired remote sensing images pertaining to 2010, 2016, and 2018 as original data for analysis. By inputting the interpretation results obtained during the above three phases into the GIS platform under the unified coordinate system, automatic and accurate comparison of monitoring changes could be realized (Figure 4).
In terms of the types of monitoring targets, the monitoring content covers multiperiod image changes within the area, style, mechanism, function, and structure. In terms of the scope of the monitoring target, the monitoring objects include the scope of historical cities, the construction control zone and core conservation zone of historic conservation districts, and the construction control zone and core conservation areas of historical relics (Table 3).
| 1 | 2 | 3 | 4 | 5 | 6 | Sum | ||
|---|---|---|---|---|---|---|---|---|
| Changes in the construction control zone of historic conservation districts | 2010 decrease | 207.3 | 299.3 | 0 | 0 | 1,276.7 | 0 | 1,783.3 |
| 2016 increase | 1,551.7 | 1,370.8 | 888.8 | 590.7 | 5,457.9 | 0 | 9,859.9 | |
| 2016 decrease | 154.5 | 0 | 0 | 208.3 | 1,688.7 | 1,242.7 | 3,294.2 | |
| 2018 increase | 487.1 | 0 | 0 | 0 | 181.7 | 379.5 | 1,048.3 | |
| Changes in the core conservation zone of historic conservation districts | 2010 decrease | 0 | 0 | 0 | 202.3 | 22.7 | 0 | 225 |
| 2016 increase | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 2016 decrease | 0 | 0 | 0 | 0 | 0 | 1,187.6 | 1,187.6 | |
| 2018 increase | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| Changes in the construction control zone of historical relics | 2010 decrease | 0 | 0 | 0 | 211.4 | 412.6 | 0 | 624 |
| 2016 increase | 0 | 0 | 0 | 430.9 | 0 | 0 | 430.9 | |
| 2016 decrease | 0 | 0 | 0 | 851.8 | 0 | 2,972 | 3,823.8 | |
| 2018 increase | 0 | 0 | 0 | 0 | 313.1 | 380 | 693.1 |
Considering element monitoring at the block level as an example, this paper studied rapid identification of building changes in the different conservation areas based on three-phase image analysis results. The increment and decrement in building elements in the different heritage conservation areas between 2010–2016 and 2016–2018 were monitored and identified. Between these periods, during the period from 2010-2018, the building area within the construction control scope of conservation districts first increased by 10,908.2 square meters and then decreased by 5,077.5 square meters, the building area within the core conservation scope of districts initially exhibited no significant increase but eventually decreased by 1,412.6 square meters, the building area within the construction control scope of historical relics first increased by 4,447.8 square meters and then decreased by 1,124 square meters, and there occurred no notable increase or decrease in the building area within the core conservation scope of historical relics.
In addition to area monitoring of building elements, identification of multiphase image changes in style, mechanism, function and structure was performed in this study. As shown in Figure 5-a, the spatial structure surrounding the core historical resources, especially the demolition and reorganization of buildings on the west side of old street linear historical elements, and the continuity in the old street structure were monitored. As shown in Figure 5-b, this study identified changes in the building mechanism at the plot level, identified non-traditional buildings within the area and finally monitored the demolition of a large number of nonhuman-scale buildings and deviation from the traditional space mechanism. As shown in Figure 5-c, this research identified the current conditions of the disappearance of surrounding traditional buildings and the invasion of large-scale parking lots and service facilities, which provides support for further research on the evaluation of the conservation status of historical cities.
The overall conservation status of Jingdezhen is good, and no significant changes were found in the overall pattern, natural environment or artificial environment of this ancient city (Figure 6). The traditional pattern and architectural distribution in Jingdezhen exhibit a relatively complete continuity. The relationship between the ancient city and the landscape skeleton, functional pattern and spatial distribution system in the surrounding environment has also been greatly protected.
The change types of architectural elements in the ancient city include vacant after demolition, nontraditional building construction, traditional feature building construction, construction of nontraditional buildings after demolition, construction of traditional feature buildings after demolition, and construction of open spaces after demolition (Table 4). To a certain extent, this reflects the characteristics of the balance between development and conservation in the process of rapid urbanization in Jingdezhen. It is rewarding that although this historical city has experienced a large amount of demolition and construction of nontraditional buildings at the initial stage, this situation has been effectively mitigated with the improvement in conservation policies, and the overall pattern of this historical city has been effectively preserved.
| Index 1 | Index 2 | T1-T2 | T2-T3 | T1-T3 |
|---|---|---|---|---|
| Overall characteristics | Traditional pattern | 98 | 98 | 96 |
| Architectural distribution | 92 | 96 | 90 | |
| Environmental elements | Natural elements | 98 | 99 | 98 |
| Artificial elements | 99 | 99 | 99 | |
| Historical areas | Block quality | 98 | 99 | 98 |
| Block scale | 85 | 85 | 85 | |
| Conservation status of the core area | 99 | 98 | 98 | |
| Conservation status of the construction control area | 91 | 97 | 90 | |
| Historic units | Level | 59 | 59 | 59 |
| Quantity | 78 | 78 | 78 | |
| Conservation status | 95 | 87 | 80 | |
| Sum | 92.745 | 92.640 | 89.595 |
Conservation assessment at the level of historic conservation districts and historical relics that contain abundant heritage elements reveals that historical heritage elements within the scope are impacted by urban construction to varying degrees, considerable changes occur in architectural elements, and the impact of the construction control zone is much greater than that of the core conservation zone.
Among these aspects, the cumulative change within the core conservation scope of historic conservation districts reached 0.14 hectares, accounting for 0.8% of the building area within the same scope. Compared to the initial stage of monitoring, the proportion of building area change within the construction control zone of historic conservation districts to the building area within the same scope decreased from 3.5% to 1.3%. Although this change declined to a certain extent, the overall conservation of building elements within the construction control zone is still suitably maintained. It is necessary to strengthen the constraints and supervision of planning policies in regard to urban development in future conservation work.
Although style, mechanism and pattern conservation within the region has basically satisfied the requirements of cultural relic conservation planning, this task has also exerted a certain impact. Choosing the demolition of traditional buildings as an example, large-scale demolition of traditional buildings has occurred within the construction control zone of the Liujianong historic conservation districts, which has affected the architectural mechanism, environmental style and spatial scale in the region to a certain degree. There are large-scale new houses in the Sanlumiao historic conservation districts, thus violating the conservation limit, which exerts a certain impact on the spatial scale and environmental style.
However, there are also actions to improve the regional historical style through building demolition and reconstruction. For example, in the Pengjianong historic conservation districts, many slab-style high-rise buildings exhibiting change patterns were demolished to better maintain the traditional spatial scale. Moreover, low-rise and disorderly buildings were demolished on the west side of the cultural conservation zone and the south side of the block and transformed into open spaces, thereby laying a foundation for further business activation. As another example, in the Sanlumiao historic conservation districts, some disorderly buildings were demolished on the west side of the old historical street and replaced with symbolic landscape nodes of a traditional style and scale, thus establishing an effective continuation of the linear pattern of the old street. Finally, it should be affirmed that all the elements within the scope of historical relics of Jingdezhen have been properly protected. Effective conservation of these key core elements has laid a foundation for further improvement in the conservation evaluation mechanism in the future.
In general, it is highly advantageous to protect and monitor historical cities based on high-resolution remote sensing data. The acquisition of change information on historical heritage elements by analysing remote sensing data has resolved the problems encountered in traditional evaluation research, such as a challenging data acquisition process, long evaluation cycles and difficult monitoring. Dynamic periodic monitoring of historical cities through multitemporal remote sensing data has greatly improved the convenience of conservation evaluation research. In addition, remote sensing data can easily identify changes in historical and cultural city patterns at the urban and even larger scales (macroscopic level) and can provide a better method to recognize the overall systematic value. At the microscopic level, precise understanding of the area, location, form, texture and other contents of the building scale has enhanced the ability to refine the supervision of historical cities, which provides unique advantages.
However, it should be noted that monitoring and evaluation work also suffers certain limitations. For example, the analysis of building details and building facades remains insufficient. Moreover, preservation of the cultural connotation value and maintenance of supporting municipal infrastructure in the conservation of historical cities cannot provide answers only from the perspective of image interpretation and should be supplemented with regular field investigations and analysis. Element change evaluation should also be combined with the actual needs of relevant planning, such as the conservation and development of historical cities, to assess the actual impact and comprehensively determine the quality of cultural heritage conservation. In addition, dynamic change monitoring of the conservation status of historical cities is inseparable from the improvement and guarantee of policy systems and mechanisms.
ConclusionsResearch on the application of high-resolution remote sensing monitoring in the conservation of historical cities involves complex system engineering. This research topic is located at the intersection of human settlements, history, urban planning, architecture, geography, sociology and spatial information science and exhibits obvious interdisciplinary and comprehensiveness features. In this study, a conservation and monitoring method for historical cities based on high-resolution remote sensing data is proposed. By combining the research scope, research content and monitoring objects of the conservation of historical cities and through analysis of basic relevant information, this paper constructs a dynamic monitoring framework and conservation evaluation framework for historical cities. With this method, choosing Jingdezhen as an example, this paper analysed the conservation status and conservation evaluation conditions of this famous city. This method improves the conservation, evaluation and monitoring systems for historical cities and provides a high-quality paradigm for city conservation. Moreover, this research comprehensively considers the characteristics of high-resolution remote sensing satellite data and expands the application scenarios of these data, and beneficial exploration is performed of research on innovative technologies for the conservation of historical cities and dynamic and digital conservation evaluation of historical cities.
Research design, D.A.R., W.G.Q.; methodology, W.G.Q, D.A.R. C.M.N. and L.X.Y.; results analysis, W.G.Q, D.A.R and C.M.N.; statistics, W.G.Q, C.M.N.; writing manuscript, W.G.Q., D.A.R.; revised manuscript, W.G.Q; proof read, D.A.R., W.G.Q. The authors have committed and agreed for the content of manuscript to be published.
The authors declare that this paper is the authors’ own original work, which has not been published elsewhere. There are no conflicts of interest in the team of authors regarding the publication of this paper.
This research was funded by the Major Project of High Resolution Earth Observation System “Demonstration System of Urban Precision Management of High Resolution RS Application（Phase II）” (06-Y30F04-9001-20/22).
