Optical remote sensing technology – helping to gradually consolidate and improve my country's remote sensing satellite system

On April 24, 1970, my country successfully launched its first artificial satellite, "Dongfanghong-1," becoming the fifth country in the world to independently develop and launch an artificial satellite. Since then, my country's aerospace industry has undergone decades of development, and satellite remote sensing has become one of the most direct and practical ways to transform aerospace technology into productivity.

On October 26, 2015, my country issued the "National Civil Space Infrastructure Medium and Long-Term Development Plan (2015-2025)," which focuses on developing three series of satellite remote sensing systems: land observation, ocean observation, and atmospheric observation. By constructing a remote sensing satellite system consisting of seven constellations and three types of thematic satellites, a global observation and data acquisition capability with multiple resolution configurations and combinations of observation technologies will be formed.

With the steady advancement of the remote sensing satellite system in the national civil space infrastructure plan, optical remote sensing has become one of the core components of its development, and its application areas and scale are the most extensive. Since the 20th century, my country's optical Earth remote sensing satellites have been mainly divided into recoverable remote sensing satellites, meteorological satellites, Earth resource satellites, marine satellites, and environmental and disaster monitoring satellites. The remote sensors carried by these satellites can be divided into two main categories: spaceborne optical remote sensors and spaceborne microwave remote sensors. The former, also known as space cameras, has played an immeasurable role in satellite Earth exploration.

Land observation satellite

In space infrastructure planning, land observation satellites mainly include high-resolution, resource, environmental, and surveying and mapping satellites.

Gaofen series satellites

Among them, the most famous is the Gaofen series of satellites, officially named the High-Resolution Earth Observation System Major Project. It is one of the 16 major science and technology projects identified in the "National Medium- and Long-Term Science and Technology Development Plan Outline (2006-2020)," and was launched in 2010. The initial goal of this project was to establish a complete set of independently controllable satellites with high temporal resolution, high spatial resolution, and high spectral resolution.

▲Chronology of my country's Gaofen Satellite Series

The Gaofen satellite series comprises numerous satellites. Currently, the civilian satellites in orbit include Gaofen-1, Gaofen-2 to Gaofen-12, which are equipped with sensors including optical and multi-hyperspectral, SAR, and mid-wave infrared sensors. They have achieved high spatial resolution (Gaofen-2 panchromatic 0.8m), high temporal resolution (Gaofen-4 20s), and high spectral resolution (Gaofen-5 330 bands) for Earth observation.

▲The orbit of the Environment-1 satellite

Environmental disaster satellite

my country, with its vast territory, complex terrain, and variable climate, is one of the countries in the world most frequently affected by and suffering severe losses from natural disasters. The environmental disaster mitigation small satellite constellation is a satellite constellation specifically developed by my country to address frequent natural disasters and monitor the environment. It includes three satellites: HJ-1A, HJ-1B, and HJ-1C. Since the launch of HJ-1A in 2008, its high spatiotemporal resolution and wide swath have led to its widespread application in disaster monitoring and ecological environment health assessment. HJ-1A's payload consists of two wide-coverage multispectral visible light cameras and one hyperspectral imager, while HJ-1B's payload consists of two wide-coverage multispectral visible light cameras and one infrared camera. The HJ-1A and HJ-1B satellites, operating in a dual-satellite network, can achieve a rapid revisit capability of two days. HJ-1C's payload is an S-band synthetic aperture radar.

resource satellite

my country's launched Earth resources satellites include the China-Brazil Earth Resources Satellite (CBERS), a joint project between China and Brazil, and my country's independently developed ZY-1 satellite. CBERS comprises the decommissioned CBERS-01, 02, and 02B satellites, and the currently operational CBERS-02C and 04 satellites. ZY-1-04, launched in 2014, carries four cameras: a 5m/10m panchromatic multispectral camera (PAN) and a 40m/80m infrared multispectral scanner (IRS), developed by China; and a 20m multispectral camera (MUX) and a 73m wide field-of-view imager (WFI), developed by Brazil. The ZY-1-02D ​​satellite, launched in September 2019, carries two cameras and can acquire 2.5m/10m optical images and 30m 166-band hyperspectral images.

Mapping satellite

ZY-3 is a civilian high-resolution stereo mapping satellite independently developed by China. Its onboard front, rear, and frontal cameras can acquire stereo image pairs from three different observation angles of the same area, providing rich 3D geometric information. In 2016, ZY-3 02 was successfully launched and began operating in conjunction with ZY-3 01. ZY-3 02 possesses the capability to acquire high-precision 2-meter resolution 3-line array stereo images, providing data support for 1:50,000 and 1:25,000 scale stereo mapping.

Ocean observation satellite

In the space infrastructure planning, the marine observation satellite series consists of two constellations (ocean color satellite constellation and ocean dynamics satellite constellation) and one type of thematic satellites (marine environmental monitoring satellites). my country's marine observation satellites are named the Ocean Series (HY). On May 15, 2002, the first Ocean-1A satellite (HY-1A) was launched. It observes the optical characteristics of seawater, chlorophyll concentration, sea surface temperature, suspended sediment content, soluble organic matter, and marine pollutants, while also observing seawater, shallow sea topography, ocean current characteristics, and atmospheric aerosols above the sea surface. The launch of this satellite filled a gap in my country's marine satellite field and ushered in a new era in the development of the "Ocean-1" series of satellites.

To date, my country has launched a series of ocean color satellites (i.e., the "Haiyang-1" series), a series of ocean dynamic environment satellites (including the "Haiyang-2" series and the Sino-French Ocean Satellite), and ocean surveillance satellites (i.e., the "Haiyang-3" series).

Atmospheric observation satellite

In space infrastructure planning, atmospheric observation satellites consist of two constellations (weather observation satellite constellation and climate observation satellite constellation) and one type of thematic satellites (atmospheric composition detection satellites). my country's atmospheric observation satellites are named Fengyun (FY). Since 1970, Fengyun has developed into two categories and four series of satellites: geostationary meteorological satellites, including Fengyun-2 and Fengyun-4 (eight Fengyun-2 satellites and one Fengyun-4 satellite have been successfully launched); and polar-orbiting meteorological satellites, including Fengyun-1 and Fengyun-3 (four Fengyun-1 and four Fengyun-3 satellites have been successfully launched). Over the past 20 years, Fengyun meteorological satellites have completed the transformation from experimental application-oriented to operational service-oriented, from first-generation to second-generation, from single-detection to comprehensive detection, and from qualitative to quantitative analysis, achieving the development goals of operationalization, serialization, and quantification. Comprehensive progress has been made in Fengyun satellite data preprocessing, product generation, and data application technologies. China's meteorological satellites were among the first to reach internationally recognized standards and are second to none in international meteorological organizations.

Currently, satellite optical remote sensing technology is experiencing an unprecedented period of rapid development. The spatial, spectral, and temporal resolution of optical remote sensing images are constantly achieving new breakthroughs. The number of remote sensing satellites launched in my country is growing explosively, and the ability to acquire satellite remote sensing data is showing a trend of simultaneous improvement in quality.

It is believed that in the near future, satellite optical remote sensing technology will have a wider range of applications, achieve the development goal of faster, more accurate and efficient applications, and move towards a more popular and commercialized development path.