China plans to put it's first high resolution radar satellites in orbit within two years. Oceanic reconnaissance with radar satellites was pioneered by the Soviet Union, which began launching such satellites in the mid-1970s. But their EORSAT program proved too expensive, and no long needed when the Cold War ended, and was gone by the late 1990s, when the last EORSAT bird wore out. 

The United States has some 200 military satellites in orbit. This includes several equipped with radar for ocean surveillance, continuing a program that began in 1978. Most of the American military satellite are used for SIGINT (signals intelligence, picking up wireless messages) and communications. At the end of the Cold War, Russia had about a hundred military satellites in orbit, but that number fell to less than a dozen by the late 1990s. The Russian satellite numbers have since increased to the point where are thought to have a few dozen military satellites in orbit, with more on the way. The Russians are still secretive about their space satellite activities, and often use the same satellites for commercial and military purposes (but under military control). 

Russia also still possess considerable technical knowledge on how to build and operate radar satellites and it is thought that the Chinese have provided the money to keep the Russian radar satellite engineers employed. Thus the Chinese radar satellites will probably be based on proven Russian technology. 

But radar satellites do not automatically give you a picture of what ships are out there. To find and identify warships at sea, you have to focus the radar satellite's attention, otherwise you can cover a wide ocean area and only see dots, which only indicate large ships. You can get much better detail if you are willing to settle for a "soda straw" view. With a 25 meter focus, you can make out the unique outline of an aircraft carrier (which is obviously different from a large container ship or tanker of the same length). If you go to 200 meters resolution you can see a chunk of the Pacific, but the ships only show up as dots.  In effect, unless you know within about 50 kilometers where a ship is, more or less, you aren't going to find specific ships via broad area surveillance. When you do spot dots on the ocean, you can then refocus the satellite radar on the individual dots. Of course, since satellites only have a limited "pass" time, and do not necessarily return to the same area on each pass, you may lose the target before you can properly identify it. Even having a handful of satellites will not necessarily be very helpful. The radar images transmitted back to earth are rough, but in the case of an American aircraft carrier, pretty obvious. Smaller ships are of less distinctive shape, but it is possible to tell a large amphibious ship from a destroyer. 

For the Soviets during the 1970s and 80s, (and the Chinese today) the most important thing their satellite radars were looking for were the American carriers. Next came large merchant ships, that, like the carriers, could be attacked by submarines or anti-ship missiles. For the Chinese, this means having radar satellites (using modern synthetic aperture radars) that can regularly scan the western Pacific, to spot approaching American carriers, and provide targeting information needed by Chinese submarines and missile carrying ships. The Russians never got a chance to use their large, "carrier busting" anti-ship missiles before the Cold War ended. But now these missiles are being sold to China, where they may get a second chance to do what they were built to do.