NASA Builds Sophisticated Earth-observing Microwave Radiometer

A NASA team delivered in May a sophisticated microwave radiometer specifically designed to overcome the pitfalls that have plagued similar Earth-observing instruments in the past.

Literally years in the making, the new radiometer, which is designed to measure the intensity of electromagnetic radiation, specifically microwaves, is equipped with one of the most sophisticated signal-processing systems ever developed for an Earth science satellite mission. Its developers at NASA's Goddard Space Flight Center in Greenbelt, Md., shipped the instrument to NASA's Jet Propulsion Laboratory in Pasadena, Calif., where technicians will integrate it into the agency's Soil Moisture Active Passive spacecraft, along with a synthetic aperture radar system developed by JPL.

With the two instruments, the NASA mission will globally map soil moisture levels -- data that will benefit climate models -- when it begins operations a few months after its launch in late 2014. In particular, the data will give scientists the ability to discern global soil moisture levels, a crucial gauge for drought monitoring and prediction, and fill gaps in scientists' understanding of the water cycle. Also important, it could help crack an unsolved climate mystery: the location of the places in the Earth system that store carbon dioxide.

Building the new radiometer took years to accomplish and involved the development of advanced algorithms and an onboard computing system capable of crunching a deluge of data estimated at 192 million samples per second. Despite the challenges, team members believe they've created a state-of-the-art instrument that is expected to triumph over the data-acquisition troubles encountered by many other Earth-observing instruments.

The signal received by the instrument will have penetrated most non-forest vegetation and other barriers to gather the naturally emitted microwave signal that indicates the presence of moisture. The wetter the soil, the colder it will look in the data.

The instrument's measurements include special features that allow scientists to identify and remove the unwanted "noise" caused by radio-frequency interference from the many Earth-based services that operate near the instrument's microwave-frequency band. The same noise has contaminated some of the measurements gathered by the European Space Agency's Soil Moisture and Ocean Salinity satellite and, to a certain extent, NASA's Aquarius satellite. These spacecraft found that the noise was particularly prevalent over land.

"This is the first system in the world to do all this," said Instrument Scientist Jeff Piepmeier, who came up with the concept at NASA Goddard.