Experience gained from response to the many disasters that have been the scourge of China over recent decades has revealed the effectiveness of space technology in providing useful and timely information for emergency management, so that today China widely applies this technology in the management of disasters. Since 6th September 2008 two Chinese satellites have been orbiting the Earth as the first components of a planned larger constellation of Small Satellites for Environment and Disaster Monitoring and Forecasting (SSEDMF).

The National Disaster Reduction Center of China (NDRCC), decision-making support agency for Chinese disaster management, operates this constellation of small satellites, abbreviated as HJ. The two satellites so far launched, HJ-1A and HJ-1B, are both equipped with two CCD cameras that capture the visible and near-infrared parts of the electromagnetic spectrum in four bands: 0.43-0.52μm; 0.52-0.60μm; 0.63-0.69μm and 0.76-0.90μm. Ground sample distance (GSD) is 30m and swath width 360km for a single camera; 700km if two cameras are operating in tandem. HJ-1A is further equipped with a panchromatic camera, swath width 50km and sway of 30 degrees, covering the spectral band 0,45-0,95μm with GSD 100m. An additional payload of HJ-1B consists of an infrared scanner (IRS) covering two channels of the near-infrared (0.75-1.10μm; GSD 150m and 1.55-17.5μm; GSD 150m) and two thermal infrared bands (3.50-3.90μm; GSD 150m and 10.5-12.5μm; GSD 300m).

The satellites work well, and high-quality remote-sensing data is acquired and continuously transmitted to ground stations. With the advantage of wide swath and short revisit period, the constellation has been widely applied in support of government emergency response in China. During the Yellow River ice flood in 2009, ice-jam length and ice-flood area could be assessed from HJ imagery. During the drought that afflicted the south-western part of China in 2010, HJ images enabled monitoring of water reserves and extraction of changes to cropland and ecosystems. The first HJ image became available within five hours of the earthquake that ravaged Kyushu in 2010.

The constellation has also proved beneficial for users abroad. During the tremendous wildfires that afflicted Victoria, Australia, in 2009, the constellation aided assessment of kindling points and burned area from CCD and IRS data. More recently, combining multispectral imagery captured by the CCD cameras with panchromatic imagery allowed determination and prediction of oil spread in the Gulf of Mexico through time-series analysis.

The above examples demonstrate NDRCC capacity to trigger emergency observation plans both for China and abroad. The original images and data products derived to support disaster response can also be useful for other organisations. During the wildfire in Australia, NDRCC supplied continuous data and product services for local government and the University of New South Wales, according to demand.