**6. Conclusions**

**5. Future and discussions**

38 Multi-purposeful Application of Geospatial Data

resources will become available.

ing years.

data distribution and sharing would become very easy.

ground-based sensors.

A common expectation from the remote sensing community is the ability to acquire data at high resolutions (spatial, spectral, radiometric, and temporal), at low cost, with open resource support and for the creation of new applications by the integration of spatial/aerial and

The development of smaller, cheaper satellite technologies in recent years has led many companies to explore new ways of using low Earth orbit satellites. Many companies have focused on remote imaging, for example, to gather optical or infrared imagery. In the future, a lowcost communications network between low Earth orbit satellites can be established to form a spatial remote sensing network. This network would integrate with a large number of distributed ground sensors to establish ground-space remote sensing. In addition, satellites can easily cover large swaths of territory, thereby supplementing ground-based platforms. Thus,

Openness and sharing resources can promote the utilization of remote sensing and maximize its output. In recent years, open remote sensing resources have made great progress. Beginning on April 1, 2016, all Earth imagery from a widely used Japanese remote sensing instrument operating aboard NASA's Terra spacecraft since late 1999 has been available to users everywhere at no cost [41]. On April 8, 2016, ESA announced that an amazing 40-cm resolution WorldView-2 European cities dataset would be available for download through the Lite Dissemination Server. These data are made available free of charge. This dataset was collected by ESA, in collaboration with European Space Imaging, over the most populated areas in Europe at 40-cm resolution. These data products were acquired between February 2011 and October 2013. The dataset is available to ESA member states (including Canada) and European Union Member states [42]. In open remote sensing resources, NASA (USA) was a pioneer in sharing its imagery data. NASA has been cooperating with the open source community, and many NASA projects are also open source. NASA has also set up a special website to present these projects. In addition, some commercial companies like DigiGlobal (USA) have also partly opened their data to the public. In the future, more and more open

Future applications in remote sensing will combine the available resources from space/ aerial/UAV platforms with ground-based data. The prerequisites of such resource integration are as follows: (i) the spatial resolution of satellite data is high enough to match ground-based data; for example, both spatial data and ground data are in the same order of accuracy. WorldView-3 has achieved a 30-cm spatial resolution, which is comparable with ground-based sub-centimeter data accuracy (e.g., 2 cm in mobile laser point cloud); (ii) cloud-based calculation supports big datasets from crowd-sourced remote sensing resources. The current situation shows promising support for the integration of multiple sources of remote sensing data. We expect to see new applications developing in the comThis paper investigated remote sensing sensor technology both broadly and in depth. First, we reviewed some fundamental knowledge about the electromagnetic spectrum and the interaction of objects and the spectrum. It helps to understand that when a sensor is operated in a certain wavelength how environmental objects will react to it. In addition, we also highlighted the terahertz region of the spectrum. Since little research has been done on this range, in the future, research efforts on new applications of terahertz radiation may be worth exploring. On the interaction of sensors with the environment, typical examples in glass, metal, water, soil, and vegetation were provided. Remote sensors were presented in terms of imaging sensors and non-imaging sensors. Optical imaging sensors and thermal imaging sensors, radar imaging sensors, and laser scanning were highlighted. In addition, commonly used remote sensing satellites, especially those from NASA and ESA, were detailed in terms of launched time, sensors, swath width, spectrum bands, revisit time and spatial resolution.
