The blue-green laser has reportedly had some success.The use of sats is increasing.Some years ago,it was revealed that Britain/NATO was detecting sub wakes using sats.Here is some open source info on the same.
1. Asia Times:
US satellites shadow China's submarines
By Peter J Brown
The People's Liberation Army's Navy (PLAN) submarines cannot spot United States satellites high overhead as the submarines leave their bases at Sanya on Hainan Island, Qingdao in Shandong province and Ningbo in Zhejiang province, and head for deeper water.
Plenty of very deep water can be found in the South China Sea, especially in the zone north of the Spratly Islands, east of the Paracels, and south of the Luzon Strait.
"A more challenging area for submarines to operate undetected is the East China Sea, which is quite shallow from the Chinese coastline up to the Okinawa Trough with a depth of only 30 to 60 fathoms [180 to 360 feet] in most places," said associate professor Peter Dutton with the China Maritime Studies Institute at the US Naval War College.
"Much of the water space [in the South China Sea] is more than 2,000 fathoms deep," said Dutton.
Detecting submarines via satellite is a form of Non-Acoustic Anti-Submarine Warfare (NAASW). Lasers, infrared and other detectors and synthetic aperture radar (SAR) in space may be used as part of this NAASW activity. Satellites might see subtle undersea disturbances caused by submarines, watch wave patterns on or beneath the sea surface, or detect subtle variations in ocean temperature.
This is not to be confused with satellite communications, nor is an "EO" or "Earth Observation" satellite to be confused with "EO" as in an "Electro-Optical" means of detecting submarines.
Over the next 18 months, the US National Reconnaissance Office (NRO) - operator of the US spy satellite fleet - is planning multiple satellite launches, and China must assume that one or more of these new US surveillance satellites will help support US Navy efforts to locate and track PLAN submarines.
Satellites form a network along with undersea sensors and detectors fixed on the sea floor or drifting in the open ocean as well as devices mounted on other submarines, ships, unmanned undersea vehicles (UUVs), aircraft, helicopters and unmanned aerial vehicles (UAVs).
Many are skeptical that satellites can perform NAASW missions effectively, reliably and at reasonable cost.
"The natural disturbances of the sea surface due to wind and tides, it seems to me, are very likely to mask any disturbance due to a submarine passage, and so even if this were a viable detection technique, it seems to me so limited in application that it would not be worth the investment," said one former US Navy sonar expert.
In April, a source told RIA Novosti, a Russian newspaper, that Russia had developed a novel satellite module "used for both defense and civilian purposes, in particular, providing meteorological data", and it can "carry out remote sensing of the sea and detect submerged submarines". This will be tested in space perhaps as early as next year. 
"Submarine detection, by any means, is a classified and highly guarded topic. The fact that the Russians are talking about it is the most interesting aspect of this announcement," said Brian Whitehouse, president of Nova Scotia-based OEA Technologies, Inc. He co-authored a paper with Daniel Hutt in 2008 about spaceborne sensors, ocean intelligence, and the maritime battlespace. 
The satellite in question is apparently the first of three small Russian Kanopus (Konopus) remote sensing satellites.
"This satellite is planned for 2011 and it will carry an Earth observing payload that includes a sensor for studying the underwater light environment," said Dr Jonathan McDowell, an astrophysicist at the Massachusetts-based Harvard-Smithsonian Center for Astrophysics who is also the editor of Jonathan's Space Report. "I cannot evaluate the claim that this will let them detect the wakes of submarines. I do not believe that such technology is being used operationally at the moment. I am not aware of relevant flight experiments, but they may have occurred."
Russia has previously demonstrated its satellite sub-hunting skills. Swedish satellite expert Sven Grahn identified the Russian Almaz-1 satellite which was launched in 1991 as a submarine-detection satellite that could see the surface wake or trail of a submerged sub. Besides this satellite, the Russians deployed other large, nuclear-powered and radar-equipped ocean surveillance satellites.
"Russian satellites known as RORSATs used radar to track surface ships, but the US Navy was not concerned that our subs could be detected, much less tracked. The signals, even if they existed, would be so wrapped into random noise that extracting any usable intelligence from them proved impossible," author James Oberg, a top US expert on Soviet and Russian space programs, told Asia Times Online. "The cancellation of that [Soviet] satellite program followed at least three accidental re-entries of debris. The laws of physics compelled them to orbit as low as possible, creating high air drag."
The theoretical boundary below which satellites cannot successfully maintain their orbits is approximately 160 kilometers above the Earth.
The Soviet space station Mir may have served as a platform for related research activities in the same way that the US Skylab once served as a platform for space radar testing in 1970s.
In the late 1990s, sub-hunting satellites made headlines. An American scientist, Peter Lee, was caught and convicted of passing sensitive information to China about the so-called Radar Ocean Imaging (ROI) joint project which involved the United K and the US. A decision by the US Navy based on concerns about further disclosures about the nature and scope of the ROI project echoes to this day.
"Peter Lee's case was they had this guy giving this very sensitive data to the Chinese on underwater detection of submarines. They ran into this case where the navy wouldn't allow a court case against him because of the data. So they had a bargain plea, and he got off, basically. For stealing very high-level stuff, he gets probably, what, a couple of months in a halfway house," former US ambassador to China, James Lilley, told PBS in 2004. 
China obtained relevant information from Russia, too.
"Chinese experts reportedly received technical assistance from Russian satellite experts in years following the Soviet Union's collapse," said associate professor Andrew Erickson at the China Maritime Studies Institute. "Specialists at the State Key Laboratory of Satellite Ocean Environmental Dynamics have researched ship detection using [SAR]."
Maritime surveillance became a top priority at the national level when China's so-called, "863 State High-Technology Development Plan" was activated. And China's fleet of Haiyang ocean surveillance satellites will grow to three when Haiyang-2A is launched later this year
Prior to the ROI program, the US SEASAT ocean satellite project which was launched by the US National Aeronautics and Space Administration (NASA) in 1978 carried a SAR into space for maritime surveillance purposes. After just over 100 days in space, SEASAT suddenly stopped working due to a short circuit in the design of its solar panels.
"Rumors suggested it had been turned off or sabotaged. There was a claim that SEASAT had mapped a field of World War 2-era shipwrecks on the floor of the English Channel," said Oberg.
A US Navy oceanographer from Australia, Paul Scully-Power, who became the first oceanographer in space, flew on the space shuttle Challenger (STS - 41G) in 1984. The US Navy later admitted that the mission had successfully detected the undersea or internal waves generated by a submarine which had been tracked successfully at relatively shallow depths. This was deemed, "incredibly important to us" and was reported by the Washington Post in 1985 - quoting a senior US Navy admiral at the time. 
n mid-May, by the way, the final flight of the space shuttle Atlantis (STS-132) will include a longtime submariner, US Navy captain Stephen Bowen.
According to naval analyst and author Norman Polmar, certain satellites can track submarine wakes, but are unable to do so continuously nor all the time, and not in all underwater environments. A submarine's depth, and speed along with the characteristics of the ocean bottom and water clarity, among other things, come into play here.
"A submarine is a relatively small, finite object - perhaps 300 to
500 feet [91 meters to 152 meters] in length in most cases - but the submarine's wake is persistent and stretches out for miles," said Polmar.
While the PLAN submarine fleet is the largest and most diverse in Asia, and very soon the fastest growing in the world, the PLAN's nuclear submarines are relatively easy to find. It is the diesel/electric submarines - and those equipped with so-called air-independent propulsion systems in particular - that are much harder to detect.
"The US Office of Naval Intelligence's unclassified July 2009 report on the PLAN suggests that some of the PLAN's diesel submarines are already extremely quiet, but its nuclear submarines remain relatively noisy," said Erickson.
US satellites play an increasingly important communications role in ASW, and are critical to the US Navy's Persistent Littoral Undersea Surveillance Network (PLUSNet), ForceNet and Sea Shield programs, to name a few. In addition, the US Defense Advanced Research Projects Agency (DARPA) is funding the Tactical Relay Information Network which uses lasers to instantly beam vital messages to submerged US subs as they are underway and perhaps chasing down other subs.
This writer speculates that as many as a dozen countries have operated sensors aboard satellites involved in some form of NAASW research. Others may disagree with this assessment.
Whitehouse and Hutt, for example, stated that, "many of these sensors are not of immediate practical benefit to military operations".
Keep in mind that commercial satellite ventures, and public - private partnerships such as Germany's RapidEye AG offer all sorts of satellite imagery.
Smaller, less expensive satellites possibly flying in formation over the ocean may offer significant advantages here. They can train their sensors and cameras on a single spot as they pass by in formation. California-based Microcosm Inc, for example, is developing the NanoEye small-satellite system, which comes equipped with basic or advanced electro-optical and infrared sensor payloads.
"Smaller satellites flying in formation may seem attractive for reasons of cost and coverage, but larger satellites offer far more advantages in terms of real capabilities," said Polmar. "Simply because of their small size, the smaller satellites are less capable, offer less electrical power and you cannot put much on them unlike much larger satellites."
The real advantage comes from the entire satellite-enabled infrastructure - or systems of systems - which links the powerful space-based sensors and detectors with those mounted on surrounding ships, subs, UUVs, aircraft, helicopters and UAVs - including the new "Sea Avenger" - so that all this surveillance data merges together to form a "common undersea picture" which can be instantly shared across the entire ASW community.
Aircraft and UAVs lingering overhead can mimic surveillance satellites, and their presence is an important aspect of the US "Maritime Domain Awareness" strategy. Another option involves inserting additional maritime surveillance assets above conventional aircraft and UAVs, and beneath the satellites.
For example, the US Navy is interested in DARPA's "Integrated Sensor Is the Structure" (ISIS) program, which is, in effect, an integrated stratospheric airship/radar - the stratosphere is found at an altitude of roughly 10 to 50 kilometers above Earth - featuring a 600-kilometer-wide sensor radius. In fact, DARPA included a slide during a briefing last year that showed how a single ISIS on station over the Luzon Strait could conduct surveillance operations covering the entire Strait from Taiwan to the northern Philippines, and almost as far west almost as the coast of China.
"No single sensor/platform combination has all the answers. Every sensor has its limitations. As a result, each application usually involves a suite of sensors, platforms and computer-based models," said Whitehouse and Hutt.
Associate professor Kazuto Suzuki of Hokkaido University's Public Policy School described Japan's Maritime Self Defense Force (MSDF) as "one of the best ASW forces without using satellite capability".
"There is no discussion of a satellite infrastructure for ASW. Satellites are only useful for detecting activities [at submarine bases]. MSDF and the 7th Fleet of the US Navy are sharing the work for ASW, and there is a strong confidence between them," said Suzuki.
However, over the years, Japan has launched many advanced remote sensing/earth observation, meteorological, and engineering test satellites - exactly the types of satellites which are ideally suited for conducting satellite-based NAASW research and development.
One relevant joint NASA-Japan Aerospace Exploration Agency project on the International Space Station recently tested a maritime hyperspectral imager. This coincided with work on the same type of imager done as part of the US Navy's Tactical Space Innovative Naval Prototype program involving so-called TacSats and their maritime satellite links to buoys and "unattended" sensors - perhaps UUV-mounted sensors.
China routinely uses ocean-centric satellite imagery provided by the US, Japanese and Europeans. Their own undersea mapping projects such as one done recently as part of a larger and more comprehensive Chinese survey of the South China Sea rely heavily on access to this data. 
The world's vast oceans have not been rendered completely transparent, but for over three decades, satellites have been transforming the way we view them.
As the US Congress scrutinizes the US-Russian START (Strategic Arms Reduction Treaty) successor and possible restrictions on the future use of US submarine launch tubes for anti-missile purposes, new potential threats to submarines need to be examined carefully.
Finally, the sinking in March 2010 of the South Korean destroyer Cheonan - important evidence in the form of "satellite imagery" is surfacing although the investigation is still underway  - serves to remind everyone that work must continue to help thwart future surprise attacks.
1. Russia to build submarine-detecting satellite, RIA NOVOSTI, Apr 15, 2010.
2. Ocean intelligence in the maritime battlespace: the role of spaceborne sensors and hf radar, Canadian Military Journal, July 14, 2008.
3. PBS interviews James Lilley, PBS.org, June 4, 2003.
4. "Shuttle Flight Yields Data on Hiding Subs," The Washington Post, March 22, 1985, p A10. (Not available online.)
5. Using satellite data to map coral reefs in the South China Sea, Spie, February 21, 2007.
6. South Korea Concludes That North Korea Sank Ship, Chosun Says, Bloomberg.com, May 7, 2010.
Peter J Brown, a satellite journalist from the US state of Maine, was part of the team that worked on the 1991 PBS documentary, "Submarine: Steel Boats, Iron Men". )
Since range,time on station,endurance is vital,it is why I keep on wanting upgrades of our Tu-142s which have unmatched range and endurance,far greater than the P-8s even with refuelling.
Here is a lengthy paper by Carlo Kopp of Oz on the same subject.MAD explained diagramatically too.