Digital Earth is the inevitable outcome of the space era and evolutionary development of the information society, characterized by global coverage by Earth observing satellites. Thus, the Earth observing satellite is a key technology for building a Digital Earth.
China has placed great importance on the development of Earth observing satellites. The four satellite series in China, which include resource satellites, environment satellites, meteorological satellites and ocean satellites, have been developed within the past few decades. The main characteristics of these satellite series are summarized in .
Table 1. The main characteristics of the four Earth observing satellite series in China.
Resource satellite series
The first resource satellite, the China–Brazil Earth Resources Satellite program (CBERS), was successfully launched in October 1999. Up to now, five satellites have been launched: CBERS-01, 02, 02B and 02C, and the first civilian high-resolution stereo mapping satellite, named ZY-3, was launched in December 2011. The succeeding satellites, CBERS-03 and CBERS-04, will be launched in the coming years.
Environment satellite series
The mission of this satellite series is for both environment and disaster monitoring. The first two satellites of the HJ Satellite Constellation, HJ-1A with a hyperspectral imager and HJ-1B with an infrared camera, were launched in September 2008. The third in the series, the HJ-1C with an S-band SAR, will be launched this year. A follow-up ‘4 + 4’ satellite constellation including four optical and four radar satellites is to be developed.
Meteorological satellite series
A meteorological satellite, the so-called Fengyun (FY), is composed of a sun-synchronous series and geostationary series. So far, a total of six FY polar satellites and five FY geostationary satellites have been launched since 1988. At present, three FY polar satellites and three FY geostationary satellites are operating in orbit. FY-3A and FY-3B constitute a sun-synchronous constellation to provide global observation for the Earth four times each day.
Ocean satellite series
China's first ocean satellite (HY-1) was launched in May 2002, carrying an ocean color scanner and a CCD camera. The HY-2, a dynamic ocean environment satellite, was launched in August2011, with four sensors including a radar altimeter, microwave scatterometer, scanning microwave radiometer, and three-frequency microwave radiometer. An HY-3 satellite is also going to be developed.
In the meantime, China has an ongoing space program – the Shenzhou spacecraft program. Shenzhou spacecraft 1 through 8 have been successfully launched in the past years, some of which carried sensors for Earth observation. Also, China's Tiangong space laboratory has remote sensing abilities. Aside from the national satellite program, there are some small Earth observing satellites owned by companies and universities that have also been launched in recent years, like the Beijing-1 satellite and Tsinghua-1 satellite.
The China Remote Sensing Satellite Ground Station, which was established in 1986, currently has three receiving stations in northern, western, and southern China. The system has the capacity to receive data from 15 international and domestic Earth observation satellites, covering the entire Chinese territory and 70% of Asia. A data-sharing program for medium-resolution Earth observation satellites has been conducted, playing an important role in areas such as land, ocean, and atmospheric resource investigation and environment monitoring.
Seven papers have been collected in this special issue of the International Journal of Digital Earth. Six of them introduce the land, ocean, and meteorological satellites, and the remaining one describes the satellite ground receiving station and data-sharing program. We acknowledge the authors’ contributions to this issue and hope that we have more high-resolution remote sensing satellites for building our next-generation Digital Earth.