EARTH RESOURCES: ZI YUAN

The first Earth observation satellite was America’s Landsat in 1972, followed by similar missions from Europe, Japan, and Russia. An indigenous domestic system was not approved by the Chinese until the mid-1980s and was given the name Zi Yuan (the Chinese word for “resources”). China had to build its Earth resources program from the very beginning. From the early 1970s, China had bought in Landsat data and used it to re-map the country by 1980 on a scale of 1:2,000,000, generating 738 sub-maps, and also bought two Citation light aircraft for instrument tests. China made extensive use of JERS, PROBA, the Space Shuttle, NOAA satellites, and, in particular, Europe’s Earth Resources Satellite (ERS) for rice mapping, land use mapping, following floods, oceanography, seismic activity, the atmosphere, climate, landslides, and forests [7]. With French SPOT data, China established a national medium-resolution (10-30-m) imaging database of 21 ТВ (terrabytes), one updated every five years, to be the basis for land management and ecological assessment. Some features were singled out for more detailed attention, such as forest shelter belts, the Three Gorges dam, the south-to-north water diversion project, and the Tibet plateau, as well as areas of high urban atmospheric pollution. China’s national reports to COSPAR suggest that, until Zi Yuan, they were quite dependent on Western satellite imaging. It would seem that the circulation within China of Fanhui Shi Weixing (FSW) images taken from 1975 (Chapter 4) must have been limited.

The Chinese chose to develop Zi Yuan in collaboration with Brazil as CBERS and this reached orbit first, in October 1999 (see next section), followed by the purely domestic version a year later, on 1st September 2000, put into polar orbit by a Long March 4B. Chief designer of the Zi Yuan was Ye Peijian, born in 1945, educated in Switzerland (1980-85), fluent in French and English, and awarded prizes for the Zi Yuan because it was the first long-life, real-time Earth observation satellite with high data rate transmissions and high-resolution Charge Couple Device (CCD) cameras. Ye later went on to the Chang e lunar program.

Ever watchful Western observers noticed that Zi Yuan’s orbit was a full 40% lower than CBERS 1, at 468-493 km. By 10th September, Zi Yuan had used its engine three times to raise its perigee to 484 km and, between then and the end of October, fired a further three times to maintain an almost circular orbit of 488­496 km – still far lower than CBERS. Zi Yuan continued to trim its orbit every 9-47 days. Whenever the orbit dipped to 94.41 min, a small burst from the engine would send it back to 94.45 min. Its orbit was never quite circular, there being about 10 km between apogee and perigee. This pattern continued into 2002. It was со-planar but in a slightly different inclination from CBERS, both in Sun-synchronous orbits. By October 2001, Zi Yuan had made 21 orbital trims to keep its altitude at a steady 490­495 km, normally within a kilometer each side. It repeated the same orbital path in patterns of 13, 17, 21, 25, and 29 days. It eventually retired in December 2004. So, although Zi Yuan was similar to CBERS, its behavior was different, being in a lower orbit with regular path-keeping maneuvers while CBERS performed no maneuvers after reaching altitude [8]. Zi Yuan came at a time when the pre-digital FSW missions were drawing to a conclusion.

The Republic of China on the island of Taiwan alleged that Zi Yuan was flying the same cameras as CBERS 1 but at a much lower altitude in order to gather images for the military. The Chinese denied this and insisted that Zi Yuan was gathering civilian Earth resources information and played down the slightly different orbit. Evaluation of the nature of the Republic of China’s claims was inconclusive. We know that the ground resolution of CBERS 1 was 20 m so that, for Zi Yuan, at a lower altitude, its resolution was likely to be about 12 m, which was much poorer than could be obtained from the FSW satellites and well below the standards necessary for quality photoreconnaissance. Despite this, rumors of a military association persisted and Zi Yuan was connected by the Washington Times newspaper to a Chinese plan for an electro-optical reconnaissance program called Jian Bing 3, pictures of 5-m resolution (possibly 2-m) being sent back digitally (later, Jian Bing as a designator was confirmed). The Washington Times suggested that, whatever the situation regarding spying on the Republic of China, Zi Yuan was eyeing American forces in Japan and the rest of the Pacific. Zi Yuan imaging does

not appear to have been published until Zi Yuan 3 in 2012, adding to such suspicions.

This Zi Yuan was joined by a companion in a similar orbit on 27th October 2002 and the set became known as Zi Yuan 2A and 2B, respectively. By 12th November 2002, Zi Yuan 2B had maneuvered into an orbit of 475-504 km while Zi Yuan 2A continued in a similar orbit of 488-492 km, retiring in August 2006. Each covered the same ground path every five days so, between them, they could cover any ground location every two and a half days. According to Chinese space officials, the two craft were operating in tandem 120° apart. The third Zi Yuan, 2C, was launched on

Long March 4B from Taiyuan on 6th November 2004, entering orbit 12 min later and swiftly acquired by Xian mission control. Zi Yuan 2C’s orbit was originally around 480 km, similar to the others, but, in June 2008, it was raised to 520-533 km, in September 2008 to 530-590 km, and then in November to 550-610 km. This ended the series for the time being and it is possible that its role was taken over by the Yaogan series (below) [9]. There was a footnote, for there was a final launching in 2011 in the form of Zi Yuan 1-02C, this strange designator being explained away as being a leftover Chinese-built satellite from the original CBERS system constructed with Brazil. It entered a 773-774 km orbit some 13 min after leaving its Taiyuan launch site, then covered in thin snow. It carried two high-resolution cameras and one panchromatic multispectral camera for Earth imaging, being declared operational on 29th February.

The third Zi Yuan series, approved in 2008, was inaugurated as the world’s first launch in 2012. Zi Yuan 3 was a 2,650-kg high-resolution civilian stereo three­dimensional cartographic satellite put into a Sun-synchronous 498-506 km orbit, 97°, on a five-year mission to map the country’s western regions, providing information that would be used for water conservation and energy and transport planning. Xian control center reported its successful separation 12 min after launch and signals were quickly received at the Miyun tracking station of the Centre for Earth Observation and Digital Earth (CEODE) and later that day from stations in Kashi and Sanya. Its use was transferred that summer to the National Administration for Surveying, Mapping and Geo Information and hailed as a significant advance in China’s Earth observational capacity. Transmission rates to the ground marked a radical step forward, 56.6 GB in just 10 min, using a dual – polarized system. Zi Yuan 3’s images were posted just four days later, the first covering an area of 210,000 km2, and were linked to a Chinese Digital Earth project (tianditu. cn). Zi Yuan 3 also carried a small 28-kg satellite for Luxembourg, the LuxSpace Sari microsatellite called Vesselsat to assist Orbcomm’s automated maritime vessel tracking system, made by Deltatec in Liege. Vesselsat 1, a twin, had already been launched by an Indian rocket the previous October.

One of the purposes of Zi Yuan 3 appeared to be to replace foreign commercial sources for imaging China, for the launch announcement referred to the importance of China’s obtaining indigenous access to high-resolution geographical information. Even as Zi Yuan was phased in, China continued to reply on data from other countries, principally Europe, formalized in the Dragon program at a meeting of European and Chinese scientists in Xiamen in April 2004, compli­mented by an agreement signed at European Space Agency (ESA) headquarters in Paris the following year. Dragon gave China access to Envisat optical and radar data with the aim of improving cultivation of rice, forest mapping (a seventh of China), aquifers, floods, air quality, and desertification. Envisat was especially important for rice-monitoring, because China did not then have an operational radar system able to see through clouds and, in addition, Envisat’s SCIAMACHY instrument was able to measure the output of methane, a greenhouse gas, from rice fields. Similarly, Envisat’s radar was able to measure flooding in all weathers and by night. SCIAMACHY could also measure nitrogen dioxide and other pollutants

in the air while the MERIS instrument could measure red tides out from the Yangtze River.

As part of Dragon, Chinese forestry students studied at the ESRIN facility in Frascati, Italy. Sixteen projects were operated jointly by ESA and the National Remote Sensing Centre of China. The Dragon program ran to 2007, the outcomes being discussed at a symposium in Beijing in April 2008. Chinese scientists showed how they had used Envisat data for a broad range of interpretive analyses of the oceans, atmosphere, flooding, water resources, drought, flood plain mapping, forestry, agriculture (e. g. rice), terrain measurement (e. g. landslides), air quality, and even the impact of the Olympic Games on the urban environment. The program was extended as Dragon 2 (2008-12), covering wetlands, sea ice, forest fires, water quality, river deltas, coastal zones, the carbon dioxide budget, ecosystems, and topography. Dragon 2 included advanced training courses in fields such as land, ocean, and atmospheric remote sensing, with defined study areas, 400 scientists, 25 dedicated projects, and a young scientist program. Chinese contributions to the program came from the Haiyang oceanographic satellites, Huanjing land observa­tion satellites, CBERS, and Beijing 1 disaster monitoring satellite [10]. The Dragon 3 program was announced in summer 2012, with 50 projects, 700 scientists, and more advanced training courses. The Dragon program indicated a critical gap in Chinese know-how – one that China worked hard to close with European assistance. The series is reviewed in Table 6.3.