02 November 2009

SMOS is up!

As I discussed quite a while ago in a post on ESA's Earth Observation Missions, the Soil Moisture and Ocean Salinity (SMOS) mission was successfully launched on Sunday (U.S. time) from a site in northern Russia. With the satellite in a sun-synchronous, nearly circular orbit at about 760 km, mission parameters call for a check-out period of six months followed by an operational period of 2.5-4.5 years. The new science satellite will have a repeat-time of about 23 days but, with its coverage swath, will generate maps of ocean salinity at a resolution of about 200 km (due to spatial averaging) on a monthly basis, providing a great improvement over existing systems that have measured only ocean temperature and surface winds from space (since the 1970s and 1990s, respectively), and ocean surface salinity only from ships and buoys scattered across that 70% of the globe. Observations will be further enhanced with the expected launch of Aquarius, a joint mission by the U.S. and Argentina that is scheduled to begin in late 2010. With ancillary observations of temperature, precipitation and winds from other polar-orbiting and geosynchronous satellites, the ocean current system that depends on both temperature and salinity is coming that much closer to full knowledge for Earth scientists.

Over land, the same instrument that will provide those ocean salinity measurements will give us a first look into large-scale mapping of soil moisture content in the top 1-2 meters of the soil column. According to ESA, we can expect to see global maps of soil moisture at about 50 km resolution and accurate to within 4% volumetric water content every three days, and with ground-truth measurements we should see these new observations bring about significant advances in guidance for practical applications in agriculture and hydrology, as well as a boon to further research in water- and carbon-cycle processes and, by extension, to nutrient-cycle processes related to agriculture and forestry around the world. This might seem like coarse data, but in fact it's an impressive achievement for a first mission due to an ingenious design: instead of a massive and unwieldy (and practically un-launch-able) dish/antenna for receiving the surface microwave signals, the SMOS satellite is a single-instrument platform that carries 69 smaller antennas (antennae?) arrayed in a Y-shape from the center. Using what is basically an interferometric method, the signals received at each smaller dish are correlated and compared with those of every other on the satellite in order to produce a single snapshot-like observation of the surface from which the soil moisture content is then inferred by physical methods. In essence, many small antennas make for one large ''virtual'' antenna that provides better observations than any single, but smaller, antenna and instrument could have produced. Kudos to the Europeans for not compromising on design, and for taking the lead without waiting for the Americans to get their act together...

Alas, we don't quite know the status of NASA's foray into soil moisture measurement from space - the couple American missions that I've heard of have suffered a tumultuous history of delays due to withdrawal of funding (Hydros, in 2005) and then reinstatement of the mission (as SMAP, in 2008) with underfunded progress all the way. NASA's Soil Moisture Active-Passive (SMAP) mission is apparently in the development phase, but was last heard from around April 2008. We can only assume that SMAP remains scheduled for launch in late 2012 or early 2013, which would overlap by a year or two with ESA's SMOS mission and improves on the latter's observations with soil moisture mapping at approximately 10-km resolution. In the meantime, NASA has been focusing on measurements obtained over land using new techniques on existing missions (e.g. AMSR-E on Aqua), and the USDA has a collaborative project with NASA going to further establish and justify the design of SMAP, using SMOS measurements as proxy observations for assimilation into agricultural models and as a hint of what is to come.

With all of the calls now for climate change assessments and predictions, it remains critical to know where we are starting from, or most of the communication remains noise without signal. Missions such as SMOS, and SMAP as it comes about, aim to clarify the signal and provide just such important information to meteorologists, oceanographers, climatologists, water resource and flood hazard managers, and the agricultural community on which we all depend.

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