Frustrated researchers have pointed out that China missed a golden opportunity to exploit the capability of its satellites in the search for Malaysia Airlines flight MH370.
The South China Morning Post quoted Dr Chi Tianhe, a researcher in satellite imaging with the Chinese Academy of Sciences who took part in the search, as saying that when the Boeing 777-200ER was en route from Kuala Lumpur to Beijing last Saturday, no Chinese satellites were observing it.
Chi said while China had enough satellites to monitor a large area around the clock, including the search zone, monitoring every bit of land and sea would require too many people.
"Chinese satellites' real-time surveillance capability will likely be strengthened after this incident," Chi, a professor with the academy's Institute of Remote Sensing and Digital Earth in Beijing, told the South China Morning Post.
China had used its satellites to search for the missing aircraft in the waters between Vietnam and Malaysia several hours after Malaysia Airlines announced that the plane had disappeared.
The failure of the search has raised questions over its strategy and its multinational co-ordination.
Professor Wu Dong, a satellite remote-sensing expert with the Ocean University of China in Qingdao, told South China Morning Post that the lack of satellite evidence of the plane suggested that the designated search zones could be wrong.
Professor Xie Tao, an expert in ocean satellite remote-sensing at Nanjing University of Information Science and Technology, said it was possible that the resolution of the satellites doing the search was not high enough.
"The waves would also distort microwave images and make analysis difficult.
"The longer the search takes, the farther the debris would be carried away by currents from the crash site," Xie said.
Chinese researchers have been using high-resolution satellite imaging equipment to search for the Boeing aircraft. This has included satellites with many different sensors, including high-resolution optical telescopes, infrared cameras, synthetic aperture radar and microwave detectors.
South China Morning Post said the search project has also used military satellites with classified technological details. In addition, China has paid overseas commercial satellite companies to use their advanced satellites and to obtain their data.
The satellite equipment allowed researchers to examine specific areas of the sea for wreckage and debris day and night, under all kinds of weather conditions, Chi said.
Although he would not say the size of objects that could be detected by the satellites, Chi said the resolution was "definitely high enough for the job".
Some US and Canadian satellites can distinguish an object as small as half a metre in size, but the ocean waves could make precise detection difficult.
While civilian satellites might have difficulty finding debris, military spy satellites should be able to do the job because they are designed to search for very small targets, Wu said.
He told the South China Morning Post that judging from the lack of wreckage, it was possible that the plane made a successful water landing, but then sank to the ocean floor in one piece.
"But if the crew achieved such a miracle, why didn't they radio for help?" Wu asked. "From a technical point of view, I cannot find a good explanation for the complete disappearance."
The lack of evidence also frustrates Chi. "If such a large plane had fallen in the ocean, it would leave some signs on the surface," he said. "The plane seems to have disappeared completely. To us it is unreasonable." – March 12, 2014.