Remote sensing technology for disaster mitigation and regional infrastructure planning in urban area: a review

A Very high intensity of regional development is ubiquitous in urban areas. Therefore, urban development requires a proper spatial development strategy in many facets, especially social aspect and disaster potential. The essence of social aspect lies in the prevailing norms and local wisdom that have long existed and become the basis of community life. Inducing various effects on infrastructure development, disaster potential has to be considered as well. Disaster mitigation measures can start with the use of continually developing remote sensing technology, which provides a basis for preparing sustainable development planning. The realization of these measures in urban areas demands specific adjustment to the environmental conditions. This study aimed to examine the capacity of remote sensing data to support disaster mitigation and infrastructure planning based on energy conservation in urban areas. The results indicate that remote sensing technology can be an option for sustainable development planning in urban areas.


Introduction
Urban area is characterized by the intensive construction of infrastructures. As a developing area, it becomes an indicator of regional growth rate. One of its characteristics is observable in the activities of the community. Most of which, people in urban area rely on the industrial sector [1,2,3] and trade [4]. Industrial growth in urban areas has to be followed by proper urban area management. The expected output from this management is sustainable development. Also, elements like local cultural wisdom [5] that have long existed in urban areas have to be appropriately maintained as they are the characteristics and the identity of a region. Sustainable development in urban areas has to pay attention to various elements, such as environment and society [6]. Sustainable development demands by Yan et al., in [7] not only sustainable natural resources and environment but also sustainable human welfare and happiness.
Infrastructure is inseparable from sustainable development. Basic network facilities, is a part of infrastructure development that cannot be separated, in order to fulfill the harmony of human life [8]. For successful implementation, infrastructure development planning has to take social and environmental aspects into account so that potential adversity on human life and the environment can be avoided. A shortcoming in this planning may lead to both natural and social disasters [9]. Disasters occurring in urban areas include fires [10,11], floods [12,13], earthquakes [14,15,16], social conflicts [17,18,19], and technological failures [20].
Infrastructure development planning can be implemented in either a short or a long term period. It can also cover a narrow or a wide region. The primary supporting factor in development planning is data availability, including quantitative, qualitative, and geospatial data. Geospatial data is crucial point in providing basic information for infrastructure development planning [21,22] in urban areas [23]. It contains geographic information of objects, either natural or artificial, in a region. The method used to obtain this data is, for instance, remote sensing. It produces geospatial data in the forms of aerial photos and satellite images. An aerial photograph can be acquired using Unmanned Aerial Vehicle (UAV), while a satellite image is obtained from the geospatial data providers. The UAV has higher spatial resolution than satellite images. UAV technology is equipped with camera and apply the 2D triangulation principle. If a triangle altitude d and angles α and β are known, the distance e [24] can be calculated. The basic principle of triangulation in a 2D plane shown in Figure 1. Figure 1. The basic principle of triangulation in a 2D plane [24] Urban development planning also needs to consider the efforts put into preserving energy resources effectively and efficiently, called energy conservation. Accentuating these measures, an area with sustainable development planning can be created. This research applied remote sensing technology to disaster mitigation and regional infrastructure planning with an emphasis on energy conservation, particularly the electricity in urban areas.

Research Method
The data source in this study included aerial photos and satellite images. The aerial photograph was obtained primarily by taking pictures of the field using Unmanned Aerial Vehicle (UAV). In general, there are two types of UAV, namely wing and rotor. In this research, we used rotor (multi-rotor) UAV with 4 (four) propelers which we know as quadcopter. UAV utilization with a simple mechanical design, now can be used as a commercial and scientific purposes [25]. Multi-rotors usually composed of more than two rotor propellers have various advantages, such as simple structure, high mobility, easy maintenance, vertical take-off and landing, and good safety [26]. Multy-body model of the quadcopter tiltrotor shown in Figure 2.
. Current technology of remote sensing can provide high-resolution satellite imagery [27][28][29][30][31][32][33][34]. Furthermore, the resultant images cover broader areas and some of which are also complemented with spectral and radiometric data. The research data source is presented in Table 1.

Study Area
This research was conducted in urban areas close to the administrative borders of Yogyakarta City and two regencies in the Special Region of Yogyakarta. They included Depok District (in Sleman Regency), Sewon District (in Bantul Regency), and Sayidan (in Yogyakarta City). The first two districts are directly adjacent to Yogyakarta City. In the recent years, they have experienced very rapid development. Sampling location of this research can be observed in Figure 3. Sayidan is a densely populated residential area in Gondomanan District, Yogyakarta City. The settlements are separated by Code River. Based on landscape analysis, they are located in mid-channel bars, river valleys, and natural levees [35]. Depok, Sewon, and Sayidan are urban areas with different characteristics of infrastructure development.

Results and Analysis
In this research, geospatial data was used to show the condition, particularly the infrastructure development, of the study area. It included aerial photos and satellite images with different spatial resolutions. This difference determines the amount of information obtained from the data. The level of spatial data resolution will affect accuracy of the analysis results. The higher the level of spatial data resolution will be directly proportional to the level of accuracy. Figure 4 presents the satellite images of several study sites. The Landsat image was formatted with a scale of 1:500,000, while the satellite images and aerial photos were produced with similar scale (i.e., 1:5,000) in accordance to the need of the research. These geospatial data have different spatial resolutions. Landsat-8 image (A) has a low resolution. It is suitable for a preliminary study in regional planning because it is equipped with several bands that represent specific wavelengths. In this research, the preliminary assessment included land use estimation and natural resource inventory (e.g., water bodies, soil and rocks). Landsat-8 imagery is periodically available and relatively complete. However, the data obtained from it cannot be used in large scale mapping. ArcGIS Online Imagery (B), Bing Maps Imagery (C), and Google Maps (D) have a similar spatial resolution. These data can be used for land use inventory as a further study. Their relatively high spatial resolution helps to identify objects such as buildings and public facilities. Among the geospatial data used in this research, UAV-derived photographs in Figure 5 (E) have the highest resolution. They perform the condition of the latest land cover and land use in detail. The accuracy level of the inventory of buildings and public facilities is relatively high. Therefore, an error in object classification can be avoided. Figure 5. UAV data and DEM part of Sayidan [35] In connection with disaster mitigation measures in urban areas, geospatial data in the form of satellite imagery and aerial photograph provide many benefits. Satellite imagery can be used in disaster analysis or monitoring [36,37] in extensive areas. For example, Landsat-8 satellite imagery is equipped with multiple bands, and when complemented with COSMO-SkyMed radar imagery, it can identify inundation [36]. Aerial photographs can be used in disaster monitoring or mapping analysis, for instance, in the events of fires [38], floods [39], earthquakes [40,41] and infectious diseases [42]. Figure 5 shows aerial photos with different spatial resolutions. The aerial photography produced a 2.1cm spatial resolution, which is categorically very high. It enables land use identification on a more detailed scale. Regarding disaster mitigation, an aerial photograph can be used to identify damages in the affected areas.
Regarding energy conservation measures, geospatial data can be applied using several approaches. Satellite images equipped with a radiometric sensor can be utilized for small scale. For instance, the satellite images from the National Ocean and Atmospheric Administration (NOAA) are suitable for analyzing the impact of light pollution [43] caused by electricity consumption. Meanwhile, high resolution satellite images on spatial data can be applied to create large-scale maps. The primary concept in utilizing satellite image is visual-spatial analysis. The term 'visual' means performing inventory and identification directly on an aerial photograph or a high-resolution satellite image. For example, there are several variables considered in electricity consumption, namely building, road, and the geographical factor of a location. Buildings with specific form are assumed to use a particular amount of electricity. Meanwhile, roads describe the access in the study area. Different types of roads are considered to represent different electrification channels. As for the geographical factors, they can give an overview of the priority areas for development.

Conclusion
Nowadays, geospatial data generated from remote sensing technology has a high resolution. Therefore, it can be applied to disaster mitigation and urban infrastructure planning. Urban development also has to pay attention to energy consumption, especially electricity. Excessive use of electricity has a negative impact, such as light pollution. Remote sensing technology grows rapidly, as evidenced by the scope of the resultant data that can be used widely in different fields. It produces geospatial data, which are especially suitable for disaster mitigation and infrastructure development based on energy conservation, all of which are the contributing factors of sustainable development planning.