Don’t cram for the Gaofen satellite any more! Click here to learn what the Gaofen satellite’s high-resolution “eyes” can “see”.

As the understanding and research of the Earth deepens, humans gradually expand their perspectives from the ground and low altitude to space, and the observation of the Earth has increasingly put forward higher requirements for continuity, speed, and accuracy. High-resolution Earth observation satellites can understand the Earth and its surrounding environment more comprehensively, clearly, and deeply, becoming efficient "monitoring eyes" installed by humans in space.

Color fusion image of Daxing Airport from Gaofen-7 satellite

In recent years, the number of high-resolution earth observation satellites has accounted for about 41% of the total number of remote sensing satellites launched, and its effective share has continued to increase. From this point alone, human earth observation has entered the era of high-resolution satellites.

my country launched its first high-resolution earth observation satellite, Gaofen-1, in 2013. On December 6, 2020, the Long March 3B carrier rocket successfully launched Gaofen-14 into orbit. With the development of the Gaofen project, Gaofen data has been widely used in various industries and regions, providing strong spatial information support for the modernization of the national governance system and governance capabilities, and regional economic development.

Gaofen Series: The "Fierce Eyes and Golden Pupils" of Remote Sensing Satellites

The Gaofen series of satellites are all remote sensing satellites. Remote sensing is a technology that obtains images or data of detected targets by photographic or non-photographic means. Remote sensing technology is far away from the target and determines, measures and analyzes the properties of the target without direct contact. Its application field is very wide and has received great attention and rapid development.

Since the Wright brothers took the first aerial photograph on an airplane, the era of aerial remote sensing has arrived, and it was first applied in the military. Since then, aerial remote sensing has been widely used in geology, engineering construction, map making, agricultural land surveys, etc. During World War II, due to the continuous improvement of camouflage technology, military remote sensing developed color, infrared and spectral band photography technologies. In the 1960s, multispectral photography technology developed, and multispectral features can be used to identify terrain and objects, gradually becoming an important direction of aerial remote sensing.

After satellites entered space, remote sensing technology was quickly applied to satellites. In 1972, the first Earth Resources Satellite was launched into space. Since then, the United States, France, Russia, ESA, Japan, India, China and other countries have successively launched numerous earth observation satellites. Satellite data is widely used in scientific experiments, land and resources surveys, crop yield estimation, disaster prevention and mitigation and other fields, playing an important role in the country's social and economic development.

In 1975, China launched its first recoverable remote sensing satellite. Since then, China has launched Fengyun meteorological satellites, environmental satellites, resource satellites, ocean satellites, practical scientific exploration satellites and remote sensing satellites to carry out meteorological observation, environmental and disaster monitoring, land and resources surveys, geological disaster emergency monitoring, marine observation scientific experiments, and surface cover and natural phenomenon observations. It has initially formed a space-based earth observation system for four major civil series: meteorology, ocean, resources, environment and disaster reduction, and has ensured the major strategic needs of modern agriculture, disaster prevention and reduction, resource surveys, environmental protection and national security.

Today, satellite remote sensing has brought mankind into a new era of multi-layer, three-dimensional, multi-angle, all-round and all-weather earth observation. The global earth observation system, which is composed of a combination of high, medium and low orbits, the coordination of large, medium and small satellites, and the complementation of high, medium and low resolutions, can accurately, effectively, quickly and timely provide earth observation data with multiple spatial resolutions, temporal resolutions and spectral resolutions.

The in-orbit service of the Gaofen series of satellites has comprehensively improved my country's ability to independently obtain high-resolution observation data. The Ministry of Land and Resources has an annual demand for "Gaofen" satellite observations of about 1.9×107 square kilometers. In the past, almost all of it relied on foreign satellite data, which was difficult and costly to obtain. However, as Gaofen satellites continue to be launched, "Gaofen data" has gradually replaced nearly 80% of foreign satellite data with the same resolution, strongly supporting national economic construction, social development and national security.

High-scoring brothers, each with their own merits

my country started late in developing high-resolution earth observation satellites, but the high starting point of remote sensing technology has enabled my country to take the initiative in technology. Today, each of the Gaofen brothers has its own strengths.

Among them, the high-resolution and wide-bandwidth "Gaofen-1" has achieved the observation capability combining medium resolution with wide bandwidth; the sub-meter panchromatic "Gaofen-2" marks that my country's civilian remote sensing satellite has officially entered the sub-meter resolution era; the "Gaofen-3" is my country's first 1-meter resolution C-band multi-polarization synthetic aperture radar imaging satellite; the "Gaofen-4" is the world's first geosynchronous orbit high-resolution imaging remote sensing satellite; the "Gaofen-5" has achieved high spectral resolution earth observation capability; the "Gaofen-6" is in the same line as the "Gaofen-1", and is also my country's first multi-spectral remote sensing satellite with a red-edge spectrum.

As the first satellite of the high-resolution Earth observation system, Gaofen-1 has made breakthroughs in key technologies such as high spatial resolution, optical remote sensing combining multi-spectrum and wide coverage. It has a resolution of 2 meters, covers 800 kilometers at a glance, and can see the entire earth in 4 days. The comprehensive indicators of resolution and width have reached the world's leading level.

Since its launch, Gaofen-1 has been operating stably, with clear images in all spectral bands and lifelike and rich colors. It has provided a large amount of remote sensing image data to more than 100 units and institutions, including the land and resources system, geological industry, and scientific research institutes. It has become one of the most widely used satellites by various users and in the remote sensing field, and is praised as a satellite that "sees widely, sees quickly, sees accurately, sees clearly, and has good emergency response effects."

In August 2014, Gaofen-2 was successfully launched into orbit. Gaofen-2 is the civil remote sensing satellite with the highest spatial resolution in my country so far, with a spatial resolution better than 1 meter and a width greater than 45 kilometers. Gaofen-2 has been operating stably for more than 3 years, and the image data it has acquired has been widely used in 18 national ministries and commissions, 28 provincial and municipal industries, as well as in the fields of national defense, military and commercial markets. It distributes more than 200,000 images covering more than 110 million square kilometers per month, and has become the main data source for sub-meter high-resolution images, with a market share of 80%, which has completely changed the situation in which my country's high-resolution earth observation data mainly rely on imports, creating huge economic, military and social benefits.

Huoyan Mountain photographed by the Gaofen-2 satellite

In August 2016, the Gaofen-3 was launched into space. The Gaofen-3 is my country's first 1-meter resolution C-band synthetic aperture radar imaging satellite, with a resolution of 1 meter, breaking the current situation that all civil space-based high-resolution synthetic aperture radar images in my country are imported. The Gaofen-3 adopts a multi-polarization design, has 12 working modes, and carries an active detection payload. It detects by transmitting microwave signals and receiving echo signals reflected from the ground, and is not restricted or affected by light, clouds, and weather. The reliable and stable high-resolution microwave image data it provides widely serves many industries and business departments in my country, such as ocean, disaster reduction, water conservancy, and meteorology.

Gaofen-1 and Gaofen-2 satellites operate in low-Earth orbits with high spatial resolution, but they require a long period of revisiting a fixed area and have low temporal resolution. High-orbit remote sensing satellites can make up for the shortcomings of low-orbit remote sensing satellites, and the combination of the two can bring greater benefits. In response to this demand, Gaofen-4 was launched in December 2015 and operated in geosynchronous orbit, becoming the highest "space eye" for observing the Earth.

The resolution of GF-4 in the visible spectrum is 50 meters, and that in the medium-wave infrared spectrum is 400 meters. It provides fast, reliable and stable optical remote sensing data for my country's disaster reduction, forestry, earthquake, meteorology and other applications, and adds new technical means to disaster risk warning and forecasting, forest fire disaster monitoring, earthquake tectonic information extraction, meteorological weather monitoring and other services, opening up a new field of high-resolution earth observation in my country's geosynchronous orbit.

In 2018, Gaofen-5 and Gaofen-6 were launched into space. Gaofen-5 is the world's first full-spectrum hyperspectral satellite that can realize comprehensive observation of the atmosphere and land. It can realize hyperspectral observation from ultraviolet to long-wave infrared spectrum, with rich detection methods, up to 26 working modes, and the highest calibration accuracy among domestic satellites.

The Gaofen-5 satellite fills the gap that domestic satellites cannot effectively detect regional atmospheric pollutants. By monitoring physical elements such as atmospheric pollutants, greenhouse gases, and aerosols, it dynamically reflects the state of atmospheric pollution in my country. At the same time, the Gaofen-5 satellite can also detect inland water bodies, land surface ecological environment, altered minerals, and rock and mineral categories, providing high-quality and highly reliable hyperspectral data for my country's environmental monitoring, resource exploration, disaster prevention and mitigation and other industries.

Gaofen Satellite Application Map

Gaofen-6 is truly China's agricultural satellite No. 1. Its image data is mainly used in business areas such as agriculture, forestry and disaster reduction, taking into account application needs such as environmental protection, national security and housing construction. The image data will serve as a powerful basis for national macro-decision-making and become a basic and strategic resource.

The Gaofen-7 satellite, which was successfully launched in 2019, is an optical stereo mapping satellite. It will achieve breakthroughs in the fields of high-resolution stereo mapping image data acquisition, high-resolution stereo mapping, high-precision satellite remote sensing for urban and rural construction, and remote sensing statistical surveys.

The Gaofen-8 to 14 satellites are optical remote sensing satellites arranged under the National Key Research and Development Program of the High-Resolution Earth Observation System. They are mainly used in land surveys, urban planning, land rights confirmation, road network design, crop yield estimation, disaster prevention and mitigation, and can provide information support for the construction of the "Belt and Road" initiative.

The satellites of the "Gaofen family" are closely integrated with my country's other remote sensing satellites, and have basically realized the "Skynet" layout of matching high and low orbits, combining optics and SAR, and conducting detailed and general surveys in parallel. They have initially built an autonomous and controllable earth observation "Sky Eye" project with high spatial resolution, high temporal resolution, and high spectral resolution.

With diamonds in hand, I dare to take on porcelain work

The Gaofen series of satellites have advanced capabilities, thanks to the powerful payloads designed and developed for them by Chinese researchers.

The Gaofen-1 is equipped with two panchromatic multispectral high-resolution cameras and four medium-resolution wide-format cameras and a matching high-speed data transmission system. It can achieve a combination of high resolution and wide-format on a single satellite. The 2-meter high-resolution imaging width is greater than 60 kilometers, and the 16-meter resolution imaging width is greater than 800 kilometers. It can adapt to the comprehensive needs of multiple spatial resolutions, multiple spectral resolutions, and multi-source remote sensing data to meet different application requirements. The Gaofen-1 has flexible multi-task working modes, including real-time imaging transmission mode, imaging recording mode, recording and playback mode, playback mode at any time, and imaging capabilities of any camera combination.

Arshan photographed by Gaofen-1 satellite

The Gaofen-2 satellite is equipped with two cameras with the same resolution of 1-meter panchromatic/4-meter multispectral combination. It adopts a long focal length, large F number, and lightweight miniaturized optical system design. The focal length reaches 7.8 meters and the F number is 15, both of which are the largest among my country's in-orbit remote sensing satellites. It uses a TDICCD device that combines panchromatic and multispectral five spectra to achieve ground scene imaging in a push-scan manner. "Gaofen-2" has made breakthroughs in key technologies such as sub-meter-level high-resolution and wide-band imaging, long-focal-length, large-F number, lightweight camera design, high-stability rapid attitude side-swing maneuvering, high-precision image positioning, and long-life and high-reliability design of low-orbit remote sensing satellites, greatly improving the observation efficiency of my country's remote sensing satellites.

"GF-3" is the only civilian microwave remote sensing imaging satellite in the GF family, and is also my country's first C-band, multi-polarization, high-resolution SAR satellite with a resolution of 1 meter. "GF-3" is designed with 12 working modes, including beamforming, azimuth multi-beam, strip, scanning, quad-polarization, and wave, which can obtain C-band multi-polarization SAR images with a resolution of 1 to 500 meters and an observation width of 10 to 650 kilometers, which can greatly expand the satellite's observation and application capabilities. "GF-3" monitors and monitors global ocean and land resources around the clock, and expands the scope of ground observation and improves rapid response capabilities through left and right attitude maneuvers.

The imaging payload of GF-4 is a staring camera, which is equipped with the world's largest integrated visible and infrared optical lens in geosynchronous orbit. It has multi-spectral and infrared imaging capabilities. The visible near-infrared channel includes 5 spectral bands, which can obtain images with a ground pixel resolution better than 50 meters at the sub-satellite point. The infrared channel is medium-wave infrared imaging, which can obtain images with a ground pixel resolution better than 400 meters.

In order to better adapt to the harsh space environment of high orbit and ensure imaging quality, the camera design of "GAOF-4" has created many "firsts": the first use of visible light devices with billions of pixels and medium-wave infrared devices with millions of pixels, the first use of a large-array staring imaging system, the first use of an optical design with a common aperture of medium-wave infrared and visible light, etc.

The Gaofen-5 satellite is equipped with 6 advanced payloads, including: atmospheric environment infrared very high spectral resolution detector, atmospheric trace gas differential absorption spectrometer, full-spectrum spectral imager, atmospheric main greenhouse gas monitor, atmospheric aerosol multi-angle polarization detector, visible short-wave infrared hyperspectral camera, and the observation spectrum covers ultraviolet to long-wave infrared. These 6 major payload "artifacts" give the Gaofen-5 satellite "eagle eyes and golden pupils".

For example, the atmospheric trace gas differential absorption spectrometer has the ability to obtain hyperspectral data from ultraviolet to visible bands, with a spectral resolution of up to 0.5 nanometers, and can be used for quantitative inversion of the distribution and changes of more than 6 atmospheric trace gas components, supporting air quality change monitoring, and the impact of various emission processes on atmospheric composition and global climate change. Visible short-wave infrared hyperspectral cameras and full-spectrum spectral imagers can achieve high-precision and quantitative monitoring of water and land ecological and environmental elements.

"GF-5" is also the optical remote sensing satellite with the most detection methods in China. It has multiple observation methods such as multi-spectral, hyperspectral, polarization, multi-angle, occultation, flare, etc., with as many as 26 working modes, which can realize the fusion application of multiple observation data.

"GF-6" inherits the excellent characteristics of "GF-1" and is also my country's first multi-spectral remote sensing satellite with a red edge spectrum. The wide-format camera design of "GF-6" has made a breakthrough in the ultra-large field of view imaging technology of a single projection center, with rich imaging spectrum and internationally leading imaging width; it further improves the image geometry and radiation accuracy, and supports the improvement of quantitative application capabilities; the satellite adopts a constellation design to improve image storage capacity, image "recording and playback ratio", imaging mission time, attitude maneuverability, etc., to solve the problems of high-time imaging, overseas imaging, weak multi-target imaging capabilities and usability, and greatly improve operational efficiency; at the same time, the satellite has a longer life, higher reliability and localization rate.

Wide-band image of Lop Nur from Gaofen-6 satellite

The Gaofen-7 satellite is equipped with payloads such as a dual-line array stereo camera and a laser altimeter, breaking through the sub-meter stereo mapping camera technology. The Gaofen-7 satellite not only has a sub-meter resolution, but also has the highest positioning accuracy in China, and can easily shoot 3D images in space that are comparable to special effects movies. After it is put into use, it will draw a three-dimensional map of the topography of my country and even the world with an error of less than 1 meter.