Progress of Earth Observation in China*

GUO Huadong LIANG Dong LIU Guang

Progress of Earth Observation in China*

GUO Huadong1,2LIANG Dong1,2LIU Guang1

1 (100094) 2 (100049)

China is expanding and sharing its capacity for Earth observation by developing sensors, platforms, and launch capabilities in tandem with growing lunar and deep space exploration. China is considering the Moon as a viable Earth observation platform to provide high-quality, planetary-scale data. The platform would produce consistent spatiotemporal data because of its long operational life and the geological stability of the Moon. China is also quickly improving its capabilities in processing and transforming Earth observation data into useful and practical information. Programs such as the Big Earth Data Science Engineering Program (CASEarth) provide opportunities to integrate data and develop “Big Earth Data” platforms to add value to data through analysis and integration. Such programs can offer products and services independently and in collaboration with international partners for data-driven decision support and policy development. With the rapid digital transformation of societies, and consequently increasing demand for big data and associated products, Digital Earth and the Digital Belt and Road Program (DBAR) allow Chinese experts to collaborate with international partners to integrate valuable Earth observation data in regional and global sustainable development.

Earth observation, Big Earth Data, Digital Earth, Moon-based Earth observation

1 Introduction

The emergence of the concept of a “Digital China”, and subsequently its adoption as a national strategy, has boosted the development of the digital economy in the country. Enabling technologies such as cloud computing, 5G, and block chain complemented by big data analytics and artificial intelligence are accelerating the pace of our digital transformation[1]. Data, the key component of any digital infrastructure, is increasingly being collected and exploited in new and innovative ways, providing new opportunities to generate insight and information about our behaviors, society, natural and anthropogenic patterns, and our environment. With the systematic collection of Earth observation data over the past several decades and our rapidly improving capabilities to collect this data from various platforms in space, the atmosphere, and on the ground, we have an invaluable resource that has still not been fully utilized[2].

Due to its synoptic coverage, Earth observation provides valuable data to resolve global and regional challenges as growing global economic integration and interdependence are linking and complicating risks. For example, crop failure in one country may have consequences well beyond its borders and, similarly, destruction and disruptions from a disaster event, exacerbated by climate change, may have far reaching consequences both in time and space. China is one of the few nations that has been successful in developing a strong Earth observation system both on the ground and in space. As of 2019, China has successfully launched about 280 satellites, 200 of which host specialized equipment and sensors for meteorological, oceanographic, resource mapping, environmental monitoring, and disaster risk reduction applications. Apart from these, around 80 com-munication, navigation, and positioning satellites have been launched. The concept of Moon-based Earth observation is also progressing steadily[3].

Table1 China’s Earth observation satellites launched in 2018

Table2 China’s Earth observation satelliteslaunched in 2019

The Chinese government has policies to facilitate integrating Earth observation resources for social and economic development, such as infrastructure, logistics, agriculture, and urban and rural plan-ning. Meanwhile, technological concepts such as Digi-tal Earth and Big Earth Data highlight multi-disci-plinary and complex data use scenarios. China’s Earth observation satellites launched in 2018 and 2019 are listed in Table1 and Table 2.

2 Land Observation Satellites

2.1 Resource Satellite: ZY

In 1986, the launch of the first optical remote sensing satellite of the CBERS-1 project marked the beginning of China’s resource satellite program, which has led to the successful deployment of multiple satellite constellations, including CBERS-1, ZY-2, and ZY-3. Within the CBERS-1 constellation, jointly developed by China and Brazil, CBERS-02D was successfully launched in September 2019 to replace the CBE-RS-02C satellite. It is equipped with a 9-band visible near-infrared camera and a 166-band hyperspectral camera that helps to fill the medium-resolution remote sensing data gap and reduce the costs of purchasing foreign data.

The ZY-3 satellites, independently developed by China, are China’s first autonomous, high-resolution, three-dimensional mapping satellites for civilian use. Through stereo observations, they can measure topographic maps at a scale of 1:50000, providing services for land, resources, agriculture, forestry, and other fields. The ZY-3 01 satellite, equipped with a three-line array camera and a multi-spectral camera, can obtain stable high-resolution stereo images and multi-spectral images and auxiliary data covering the whole of China. The ZY-3 02 satellite is a remote sensing commercial satellite, and the main payloads are three-line array cameras, multispectral cameras, and laser rangefinders. The ZY-3 02 satellite has high stereo image resolution and elevation measurement accuracy. Double-satellite networking can shorten the revisit time to 3 days and improve stereo mapping to ensure long-term, stable acquisition of high-resolution stereo mapping data.

The number of China’s resource satellites continues to increase, and the technology is continuously being upgraded. China’s resource satellites play an important role in the monitoring, planning, and management of land resources, agriculture, forestry, water conservancy, environmental protection, and disaster mitigation.

2.2 Environmental Protection and Disaster Monitoring Constellation: HJ

The HJ satellites are a small constellation for environmental and disaster monitoring and forecasting. The system has optical, infrared, hyperspectral, and microwave detection methods. It is mainly used for large-scale, 24 h dynamic monitoring of ecological environments and disasters, and estimating their trends for rapid assessment to coordinate informed and timely emergency response, post-disaster rescue, and reconstruction.

The HJ system, consisting of two optical satellites (HJ-1A and HJ-1B) and a radar satellite (HJ-1C), is used for environmental and disaster monitoring. The HJ-1A/1B satellites, which were launched on 6 September 2008, are both equipped with a CCD camera, and there is a Hyperspectral Imager (HSI) onboard HJ-1A and an infrared camera (IRS) onboard HJ-1B. The CCD cameras on the two platforms are placed symmetrically under the star point, with the field of view equally divided, making parallel observations in four spectral bands at a ground pixel resolution of 30 m. The push-broom hyperspectral imager onboard the HJ-1A satellite provides a ground pixel resolution of 100 m within 110 to 128 spectral bands and also has an onboard calibration function and provides 30° side-look capability. The infrared camera onboard the HJ-1B satellite has four spectral bands with a ground pixel resolution of 150/300 m. The two satellites collectively provide a two-day revisit time, capturing ma-cro-scale, multi-scale characteristics useful for weat-her, environmental, and disaster monitoring. The HJ-1C satellite, launched in November 2012, is China’s first S-band Synthetic Aperture Radar (SAR) satellite. The S-band SAR has two working modes: stripe mode and scan mode. The imaging bandwidths are 40 km and 100 km. The HJ-1C SAR has a single-view mode with a spatial resolution of 5 m and a four-view mode with a spatial resolution of 20 m, and the SAR images provided are mainly on multi-view mode.

2.3 High-resolution Earth Observation System: GF Series

The China High-resolution Earth Observation System (in short referred to as CHEOS) is one of 16 major science and technology projects identified in the Guidelines for The National Mid-term and Long-term Science and Technology Development Plan (2006–2020). Following the successful launches of the GF-1 to GF-4 and GF-8 and GF-9 optical satellites between 2013 and 2015, China successfully launched the GF-5 to GF-7 and GF-10 to GF-12 satellites between 2018 and 2019, putting a total of 12 satellites in orbit for the GF series[4]. The launch dates and payloads from GF-1 to GF-7 are listed in Table3.

The GF-5 satellite is the only land and environmental hyperspectral observation satellite of CHEOS, and the world’s first atmosphere and land hyperspectral observation satellite. TheGF-5 satellite can detect the specific components of substances by high-precision spectral analysis of the whole spectrum from ultraviolet to longwave infrared. The GF-6 satellite is the first low-orbit optical satellite for precision agriculture and the first satellite with a red edge band in China. The GF-6 satellite forms a “2 m/8 m optical imaging satellite system” with the GF-1 satellite, and provides valuable data for agriculture, forestry, and disaster reduction, as well as environmental protection, national security, and residential construction. It is the first submeter-level high-resolution stereo mapping satellite in China. The GF-7 satellite is equipped with a two-line array camera and a laser altimeter. The two-line array camera can continuously obtain overlapping ground images and stereo mapping at 1:10000 scale. The laser altimeter can map areas with complicated terrain conditions and further improve the elevation positioning accuracy with fewer control points. The GF-7 satellite is mainly used in the acquisition of high-resolution three-dimensional mapping imagery for construction and remote sensing statistical surveys.

Table3 China’s high-resolution Earth observation satellites

The GF-10 satellite is a microwave remote sensing satellite of CHEOS. Due to its high, submeter resolution, GF-10 is mainly used for land surveys, urban planning, land approval, road network design, and disaster prevention, as well as information support for the Silk Road Economic Belt and the 21st-century Maritime Silk Road (Belt and Road) initiative and other national strategies. GF-11, like GF-10, has a submeter resolution. However, operating in the optical spectrum, it is mainly used in crop estimation, land surveys, and disaster prevention. The GF-11 satellite also has a massive on-orbit data processing and high-speed data transmission sub-system that enables, for the first time in space, high-speed two-way data transmission between GF-11 and the relay satellite. The GF-12 satellite, the latest to have been launched, is a microwave remote sensing satellite. With a submeter spatial resolution, it is mainly designed for land surveys, urban planning, land approval, and disaster prevention.

2.4 Commercial Satellites

In recent years, China’s national policies have facilitated the development and deployment of commercial remote sensing satellites. These policies stimulated investment from private commercial enterprises, attracted talent, and spurred technological innovation in this sector. With the improving quality and quantity of commercial satellites, there have been several launched in the past two years. A number of these commercial satellites are equipped with high spatial resolution sensors. For example, the Luojia-1 satellite records night-time light imagery at 130 m resolution, which is higher than most of the existing night-time light images to date. Similarly, the Jilin-1 High Resolution-02A and Jilin-1 High Resolution-02B satellites feature an imaging system with a resolution of 0.75 m in panchromatic mode and better than 3 m in multispectral mode. Also, the commercial optical remote sensing satellite Jilin-1 Wideband-01 features a high-resolution (submeter) wide-field-of-view telephoto range imager. The push- br-o-om imager also has a multi-spectral resolution better than 4 m and features high-speed storage and high-speed digital transmission systems. Another satellite, Qiancheng, with Earth observation and nar-row-band communication capabilities, has an imag-ing payload with a resolution of more than two meters. With a mass of 65 kg, Qiancheng is the largest satellite in orbit independently developed by a private satellite start-up company in China. Commercial satellites launched from June 2018 to February 2020 are listed in Table4.

Commercial entities are being allowed to develop and deploy constellations of satellites. In China, Zhu-hai-1 OHS 3A/3B/3C/3D was launched in September 2019. This constellation of four satellites with a ground resolution of 10 m, spectral resolution of 2.5 nm, and a swath width of 150 km can cover the entire globe in 5 days and provide multiple revisits a day to monitor a specific site. Another constellation, the Ningxia-1 01/02/03/04/05 satellites, was successfully launched on 13 November 2019. They are a commercially operated global EM spectrum signal monitoring satellite system (SIGINT).

A couple of experimental commercial satellites have also been launched. Jingshi-1 or BNU1, a small 16 kg experimental satellite by Beijing Normal Uni-versity (BNU), conducts all-weather polar climate and environmental observations. Weilai-1 (Future1) is a small satellite for space-based science experiments and remote sensing by CCTV (China Central Television). Also, Bufeng 1A/1B, which marks China’s first maritime launch mission, measures the velocity of the wind by measuring the signals of navigation satellites reflected on the ocean’s surface (GNSS-R). With the continuous development of the domestic remote sensing market, commercial satellite remote sensing will continue to grow.

Table4 Commercial satellites launched from June 2018 to February 2020

3 Scientific Satellites

3.1 Satellite Platforms

China has successfully developed and launched se-v-eral specialized scientific satellites since 2018. The first was the Sino-French ocean satellite, adopting the CAST2000 satellite platform, which was successfully launched on 29 October 2018, with a design life of 3 years. It is the first satellite jointly developed by China and France, and simultaneously observes sea wind and waves, utilizing information from a mic-rowave radiometer (SCAT) and radar spectrometer (SWIM). SCAT uses a wide fan beam direction map of the scanning antenna at a speed of 35 revolutions every 10 min to measure the wind, improving the number of observations per direction and thereby improving the sea surface wind speed and wind direction inversion accuracy. Both SCAT and SWIM are unique achievements, as the SCAT scanning sys-tem is the first of its kind, and SWIM is the world’s first satellite-borne sea wave spectrometer. SWIM can obtain wave direction spectrum data and obtain marine dynamics information such as wavelength and propagation direction through further data processing.

China also launched Taiji-1 on 31 August 2019. It is China’s first experimental space gravitational wave detection satellite. At present, Taiji-1 has suc-cessfully completed the first phase of on-orbit testing tasks. It has laid a solid foundation for China’s space gravity wave detection. On 12 September 2019, China also launched Jingshi-1, which is the first satellite of China’s Weijing constellation, and also China’s first satellite dedicated to polar climate and environmental monitoring. Aboard the CAST5 micro-nano satellite platform, Jingshi-1 has a revisit period of 5 days, and an observation range between 60° to 80° north-south latitude. It is equipped with three kinds of payloads, including a wide-angle camera with a resolution of 73.69 m and a swath of 744 km and a medium-resolution camera with a nadir resolution of 8 m and a swath of 25 km. It has a high dynamic push scan for glaciers and terrestrial water bodies and is also equipped with an AIS receiver, which can receive AIS signals from ships in global waters. Jingshi-1 is a significant achievement as it makes up for the lack of polar observation data in China.

The China Seismo-Electromagnetic Satellite Zhangheng-1 (ZH-1), launched on 2 February 2018, is the first space-based platform for China’s stereoscopic seismic observation system, with a dynamic, wide viewing angle and all-weather space-to-Earth observation. The satellite can provide data on the global electromagnetic field, ionospheric plasma, and high-energy particles using several instruments: a search coil magnetometer, high-precision magnetome-ter, electric field detector, GNSS occult receiver, plasma analyzer, high-energy particle detector, Lang-muir probe, and three-frequency beacon transmitter. The satellite is used to study the interaction and effects of the Earth system, especially the ionosphere, with Earth’s other spheres. Real-time monitoring of ionospheric dynamics and seismic precursor tracking in China and its surrounding areas can make up for the lack of ground observation. It is expected that by 2022, China will have three electromagnetic monitoring satellites in orbit including Zhangheng-1 and 2, Macao’s first scientific satellite. The three satellites in orbit will effectively support the scientific exploration of seismic monitoring and prediction, as well as the early warning of space weather, for years to come.

China’s Global Carbon Dioxide Monitoring Science Experiment Satellite, known as TANSAT or CarbonSat, is the first experimental satellite for observing global atmospheric carbon dioxide and the third satellite with the capability to detect greenhouse gases with high precision. Launched on 22 December 2016, the satellite can provide basic data for research in the fields of greenhouse gas emissions and carbon verification, provide data support for macro-decision-making such as energy conservation and emission reduction, and increase China’s voice in international carbon emissions. The satellite is equi-pped with two scientific payloads in an integrated design, the Atmospheric Carbon-dioxide Grating Spectroradiometer (ACGS) and the Cloud Aerosol Polarization Imager (CAPI). Using TANSAT’s data, scientists have successfully developed two products: a global chlorophyll fluorescence product in 2017, found to be highly consistent in terms of value, distribution, and change when compared with Japan’s Orbital Carbon Observation 2 (OCO-2) satellite pro-ducts and relevant data from NASA; and the first map of the global distribution of atmospheric carbon dioxide at the beginning of 2018. These demonstrate China’s achievements in developing a world-class global carbon monitoring system.

The Big Earth Data Science Engineering Program (CASEarth), is preparing the first Earth science satellite in China and the first human trace satellite in the world. The CASEarth satellite will provide necessary information about national urban growth, monitor the quality of coastal and offshore environments, and give insights into the status, patterns, and regional gaps in socioeconomic development in China at a very fine scale. The acquired Earth observation data will be released to the world through CASEarth, which will contribute to the Sustainable Development Goals (SDGs) and the Community of a Shared Future for Mankind. The CASEarth satellite, still in the prototype phase, will be carrying multiple sensors onboard including a Thermal Infrared Imager, the world’s first high-reso-lution noctilucent Urban Low-light Imager, and an Offshore Multispectral Imager. Tests were successfully conducted in early 2020, and on-orbit deployment is targeted for 2021.

3.2 Moon-based Earth Observation

Aside from traditional satellites, Chinese scientists have proposed a radically different approach: establish a long-term Earth observation system on the Moon to collect high-quality, planetary-scale Earth observation data that is spatiotemporally consistent because of the Moon’s stability and the platform’s long operational life. Sensors installed on the Moon will be able to simultaneously observe Earth’s whole Moon-facing surface, thus providing the opportunity to integrate data from these sensors. Moon-based Earth observation can provide key insights to solve a series of key scientific problems related to multi- sphere interaction on Earth, enhancing our understanding of the dynamic Earth system[5]. The possibility of establishing an Earth observation system on the lunar surface has become quite possible with China’s growth in lunar and deep space exploration and continued improvements in sensor and spacecraft design, especially after gaining experience and confidence from the successful Chang’E-1~4 missions. Several studies have been completed and are also underway in Chinese institutions to establish the principles and feasibility of Moon-based Earth observation systems.

A Moon-based Earth observation system presents new challenges to sensor design and function due to its distance from Earth. Research has been conducted on the operation and imaging mechanisms of Moon-based sensors, such as multispectral imagers, cavity radiometers, and SAR, using rigorous geometric models to simulate the conditions on the Moon. In addition, the effects of the traveling time of light, light aberration, and bending due to gravity have been assessed. Possible errors due to signal propagation have been evaluated by a geometric error estimation method, which is an automatic geometric correction approach for cross-platform imagery. A geometric expression method for sub-lu-nar points in polar coordinate systems is currently being tested to ensure the integrity and authenticity of imagery[6-8].

Similarly, studies on sensors and observation strategies have proposed phase scanning control for lunar SAR, which can aid in centering radar beams to improve the pointing accuracy in the direction of the zero Doppler surface on Earth. Studying beam pointing errors revealed that look-angle pointing errors and azimuth pointing errors in lunar Doppler radar would lead to the emergence of residual error. For estimating the global energy balance, the radiative transfer model and the surface bi-directional reflection distribution function are used to calculate the correlation between the shortwave reflected radiation from the top of Earth’s atmosphere and the surface. These models are also applied to simulations of observation geometry that calculate the emission energy distribution characteristics of the space between the Moon and Earth[9,10].

To make better use of the lunar surface as a natural platform, research on the lunar environment and observation site are being conducted, which is critical to ensuring maximum benefit from a relatively permanent Earth observation station. These studies have considered topographic features such as relief, roughness, slope, and slope direction at three lunar sites. The Chang’E-2 Digital Elevation Model (DEM), SLDEM2015, and LOLA DEM products were used to calculate and develop a database of long-term evolution of the illumination characteristics of the lunar surface. A preliminary site selection framework for a Moon-based Earth observation system has been established based on a number of characteristics such as Sun-Earth-Moon motion, the lunar surface environment, long-term illumination, visibility, the ionosphere, and the structural morphology of the lunar surface[11].

This is an area of active and promising research. The successful launch of the Changzheng-5 vehicle furthered China’s lunar and deep space exploration capabilities. With close collaboration with other countries, and continued improvements in technology, the vision for a Moon-based Earth observation system will begin to take shape in the next decade or two, providing valuable global-scale data for understanding our planet and supporting sustainable human development.

4 Key Contributions in Global Applications

China’s ongoing digital transformation, resulting from fast-paced scientific research, technological development, and innovation in utilizing digital space technologies, is fueling rapid development of digital infrastructure, value-added services, and data-driven decision making, not only in China but also in other countries. China is supporting, participating in, contributing to, and leading international research programs and collaborations in management of the environment, resources, disaster risk reduction, marine ecosystems, coastal areas, and cities.

4.1 Towards a Digital Earth

China’s Digital Earth scientific research and technological applications have achieved fruitful results in establishing technical platforms that provide strong support to China’s response to global climate change, disaster mitigation, urban management, heritage protection, sustainable development, and other fields[12]. With data-driven technology as the engine, Digital Earth will enable deep integration of spatial data in the digital economy and enhance China’s core competitiveness in the field[13]. The ef-f-orts towards a Digital Earth system would benefit from our experiences in developing the Digital China infrastructure and would help to improve our understanding of natural processes and consequently help decision making.

Due to this potential, the Digital Earth community in China is actively engaging both national and international experts by holding conferences and publishing journals and books, such as the recent “Manual of Digital Earth”[14].

4.2 Facilitating Sustainable Development along the Belt and Road Region

Many countries along the Belt and Road are facing developmental challenges such as water shortages, frequent occurrences of disasters, and huge ecosystem changes. In the Belt and Road region, the speed of data processing and analysis is much lower than the speed of data acquisition, leaving massive amounts of scientific data and information unprocessed and underutilized. The Digital Belt and Road Program (DBAR), an international collaborative research program, is committed to developing a platform for sharing advanced Earth observation technologies among the Belt and Road regions. DBAR has five priority areas[15]: (i) enhance infrastructure with an open platform for shared data, code, and algorithms to analyze vast amounts of data; (ii) promote data sharing and interoperability for open exchange of data between users in the region towards the collective benefit; (iii) extend applications to more people, and diversify users and disciplines that can utilize Earth observation and Big Earth Data towards development across the region; (iv) identify research opportunities and discover knowledge within huge multidisciplinary datasets; and (v) strengthen international collaboration to set up bilateral or multilateral arrangements and stronger links with international scientific programs and organizations.

To work on these five priority areas, DBAR has established nine working groups focused on Big Earth Data, agriculture and food security, coastal zones, environmental change, natural and cultural heritage, disaster risk reduction, water, high-moun-tain and cold regions, and urban environments. DBAR has also launched eight International Centers of Excellence (ICoEs), located in Thailand, Pakistan, Finland, Italy, Russia, Morocco, Zambia, and the United States.

Since starting in 2018, DBAR members have developed the DBAR Big Earth Data System, a spatial information repository and decision-making tool for the Belt and Road region. It aims to develop a cloud-based scalable platform for handling Big Earth Data, giving access to vast amounts of satellite imagery and socioeconomic data. Currently, the sys-tem provides real-time hardware and software monitoring, online data sharing for more than 100000 images, and online viewing and analysis for public users. For the next three years, the system will serve the countries along the Belt and Road, providing Big Earth Data sharing and cloud-based online analysis features at the regional, sub-regional, and national levels.

4.3 Data-driven Services Towards Solutions for Global Challenges

At present, the United Nations as well as governments and international organizations are conducting research on constructing SDG indexes that can be monitored and evaluated. This needs to be done in three broad aspects: (i) fill in missing data and deve-lop technologies to generate data for SDG evaluation; (ii) develop Big Earth Data methods and models to evaluate SDGs; and (iii) provide decision support to SDGs by monitoring and identifying progress.

CASEarth and DBAR selected 20 indicators of 6 SDGs for analysis and carried out 27 case studies to demonstrate the benefits of using Earth observation within the Big Earth Data framework. These cases were presented in the report titledBig Earth Data in Support of the Sustainable Development Goals (2019)”, which was selected as one of four official documents that the Chinese government submitted during the 74th UN General Assembly and one of two documents officially submitted to the UN Sustainable Development Summit[16].

4.4 Disaster Risk Reduction

Deepening disaster system theory and the rapid development of Earth observation technology has benefited China’s research in disaster risk reduction. After more than 40 years of development, China has established satellite programs such as the FY meteo-rological satellites, the ZY Earth resources series, and the HJ-1A/B/C small satellite constellation. The GF satellites launched in the past seven years have considerably improved China’s disaster monitoring and management capabilities in monitoring risk, loss, and post-disaster reconstruction[17].

Monitoring seismic activity has been an important focus in Chinese disaster research since the 1970s. An important recent achievement in this field is the launch of China’s first seismic-electromagnetic satellite, Zhangheng-1, under the National Geophysical Field Exploration Satellite Program. Since entering its present orbit on 2 February 2018[18], it has significantly facilitated the development of China’s first global geomagnetic map by filling in data gaps in the global geophysical field. With a growing collection of post-disaster Earth observation images, Chinese scientists have proposed a multi-source heterogeneous Earth observation image change detection method using multi-temporal remote sensing imagery before and after an earthquake[19]. The met-hod overcomes requirements for data types and te-mporal consistency, assimilates multi-sensor data, and allows collaborative information processing. Am-ong the Earth observation data, SAR has become an inv-aluable data source for earthquake damage assessment.

For example, following the Jiuzhaigou earthquake, high-resolution optical and SAR imagery were used to investigate the consequences from different perspectives including road damage analysis, extraction of secondary disasters (., landslides), and calculation of the co-seismic displacement field[20, 21]. Additionally, to evaluate the earthquake recovery progress in Wenchuan, the Chinese Academy of Sci-ences integrated multi-temporal, massive satellite and aerial observation data over the past 10 years, and found valuable information about disaster chain effects and potential future disasters, long-term recovery processes of the natural ecology, and the progress of post-disaster reconstruction in cities and towns[22].

Forest fires are another important application for Earth observation data. On 2 June 2018, after the onset of forest fires in the Greater Khingan Mountains in Inner Mongolia, the Chinese government swiftly moved to acquire satellite data to monitor the situation. Using FY meteorological satellites, GF-4 satellites, and multiple polar-orbit optical and SAR satellites, forest fires and burned areas were actively monitored to coordinate relief and emergency response activities[23]. Similarly, ZY-3, GF-1, and Lan-dsat-TM data combined with LiDAR point clouds and CCD images also enable dynamic monitoring of forest fires. Important components of improving the quality of forests are the study of forest fire intensity and the restoration of vegetation. Multi-modal Earth observation can help improve the efficiency of regional-scale forest structure monitoring by providing horizontal and vertical forest structure information, Fractional Vegetation Cover (FVC), Above-Ground Biomass (AGB), and canopy height. The parameters allow for quantitative analysis of the effects of fire on forests[23].

4.5 Environmental Change Monitoring

Since May 2018, China has launched over 20 Earth observation satellites including but not limited to: GF-5, the world’s first full-spectrum hyperspectral satellite, which can capture comprehensive observations of both the atmosphere and land surface; HY-1C, which can obtain 24 h water color, sea surface temperature, coastal zone and inland water information with 50 m resolution globally; and BNU-1, which is the first Chinese polar observation minisatellite. These missions have improved our observation capabilities in the Arctic and Antarctic. Civil and commercial satellites such as Jilin-1, OVS-1 03, Yunhai-1, Ningxia-1, and ZY-1 02D also consider environmental observations as an important part of their operations.

Chinese scientists have released numerous environmental observation products, which include the first global CO2map measured by China’s carbon satellite[24]; global chlorophyll fluorescence products, which can support the distribution analysis of CO2concentration[25]; the first global fire mask and forest cover product with 30 m resolution[26]; comprehensive surface reflectance products over China; and the first global map of fine-mode Aerosol Optical Depth (AODf) at a spatial scale of 3.3 km, which achieves the highest spatial resolution among similar products[27]. Moreover, primary products such as global sea surface wind field, wave spectrum, and other dynamic marine environmental parameters have been obtained with CFOSAT[28].

Earth observation technologies have also faci-litated monitoring programs on key ecological and environmental problems. China’s annual dynamic monitoring of soil erosion conducted by the Ministry of Water Resources also incorporates Earth observation data in their analysis. The national key research and development program “Marine Environmental Security” and “Cooperation Platform for Arctic Environmental Satellite Remote Sensing and Numerical Prediction” have been launched to promote three-dimensional ocean observation in polar regions. Earth observing technology is also an important component of special actions of the Ministry of Ecology and Environment, such as the “Green Shield”, “Clairvoyance Plan”, “Waste Removal Action”, and blue-green algae bloom prevention in key lakes and reservoirs.

Earth observation data has enabled important breakthroughs in environmental change studies. Multi-source satellite data being used to monitor the environment and resources in the Belt and Road region revealed that solar energy is affected by latitude and the spatial distribution of the water budget is uneven[29]. The global internal thermal structure of oceans in different seasons has been inverted based on data on ocean surface height, temperature, salinity, and wind field. This has shown that the spatial heterogeneity of marine internal temperature ano-malies in shallow water varies with different seasons, while that in deep water (>300 m) is basically invar-iant. Earth observation has also been used to study the effects of climate change on the Arctic ecosystem[30]. The relationships between surface temperature and radiation change under clouds detected by thermal infrared remote sensing have shown that the radiation change has a linear relationship with the magnitude of surface temperature[31].

China is also cooperating with other countries to improve their Earth observation capability; for example, under the framework of South-South Cooperation on Climate Action, the Ministry of Ecology and Environment gifted the Ethiopian Ministry of Science and Technology a wide-range, multi-spectral Earth observation mini-satellite, which has enhanced Ethiopia’s capacity to cope with climate change and promoted Chinese aerospace technology in the global market.

5 Perspective on Trends in Earth Observation

The global acquisition, analysis, distribution, and use of Earth observation data is increasingly becoming viable, in particular due to cloud computing infrastructure, data analysis capabilities, improved connectivity, e-commerce, and other associated technologies. This creates the potential for commercial exploitation of data in online services and data analytics. This has resulted in attracting investments in, and acquisitions of, companies specializing in a wide variety of Earth observation-re-lated services.

In the last two decades, investment in the Earth observation sector in China and the rest of the world has largely gone towards technological development – improving Earth observation systems, sensors, platforms, and the viability of data. This includes algorithms and methodologies to process raw data to quantify different parameters. The increasing demand for big data as societies digitally transform has also increased the demand for Earth observation data, creating an industry that provides global data services to big businesses and government organizations.

Agriculture, disaster risk reduction, urban planning, and other large-scale planning, monitoring, and data processing sectors are already utilizing Earth observation data. The integration and utilization of Earth observation data will continue to be improved and simplified through advancements such as 5G network integrations, economically viable cloud computing infrastructure and services, increasing online data analysis services, and growing competitive products. Innovative commercial applications and services for Earth observation data and products will increasingly be the focus in the coming years. Commercial enterprises can adopt the use cases of Earth observation from large-scale operations and transform them for adoption by more local-scale operations. For example, large agricultural setups are already using Earth observation products, but in the future, new online services powered by cloud technology and 5G would be able to simplify interfaces and information that would facilitate their adoption by local farmers.

China is successfully developing its capacity in all aspects of the Earth observation industry. Grow-ing numbers of satellites, high-tech sensors, research into ambitious Moon-based Earth observation sys-tems, and increasing support to commercial satellite programs will drive China’s data acquisition capabilities and establish a viable data acquisition, pro-cessing, and analysis industry. Based on these gains in infrastructure, programs such as CASEarth will facilitate research and development of platforms for data integration and Big Earth Data analysis to create value-added products and facilitate data-dri-ven policy development and decision support systems. Digital Earth and DBAR will provide collaborative platforms to China towards regional and global sus-tainable development, collaborative research, and hu-man resources[32,33].

Acknowledgements The authors are grateful for helpful comments from many researchers and coll-eagues. Thanks go to CHEN Fang, YAN Dongmei, LI Xiaoming, LI Xinwu, CHEN Liangfu, SUN Zhongchang, LIU Zhen, and Zeeshan SHIRAZI for feedback, as well as the editor and anonymous referees. All views and errors are the responsibility of the authors.

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P35

GUO Huadong, LIANG Dong, LIU Guang. Progress of Earth Observation in China., 2020, 40(5): 908-919. DOI:10.11728/cjss2020.05.908

* Supported by the Chinese Academy of Sciences Strategic Priority Research Program of the Big Earth Data Science Engineering Program (XDA19090000, XDA19030000)

March 16, 2020

E-mail: liangdong@radi.ac.cn