August 5, 2016 – On January 31, 2015 the Soil Moisture Active and Passive (SMAP) satellite launched atop a United Launch Alliance Delta II rocket with the goal of producing the first high definition global maps of soil moisture. Ultimately, the new data will help improve the understanding of Earth’s water and carbon cycles, as well as the ability to manage water resources worldwide.
While water covers 70 percent of Earth, the majority has a high concentration of salt – leaving just 3 percent as fresh water. Of that 3 percent, the majority is tied up in glaciers and icebergs. Studying the fluctuation of this essential fresh water is vital for survival.
Ohio State University students and faculty involved in the project recently published an update on the mission in the IEEEXplore Transactions on Geoscience and Remote Sensing publication, titled “SMAP L-band Microwave Radiometer: RFI Mitigation Prelaunch Analysis and First Year on-Orbit Observations.”
The principal investigator of the research work, Priscilla Mohammed of the Goddard Earth Sciences Technology and Research, Universities Space Research Association, coordinated with fellow electrical engineers from The Ohio State University, including Mustafa Aksoy, Joel Johnson, Alexandra Bringer of the Ohio State ElectroScience Laboratory, and Jeffrey Piepmeier, Chief Engineer for passive microwave instruments with the Instrument Systems and Technology Division, NASA Goddard Space Flight Center.
Overall, Johnson said, the technology the team included on board the satellite is working well.
“The SMAP radiometer RFI processor seems to be doing a good job of detecting and filtering radio frequency interference from SMAP’s L-band Microwave radiometer measurements,” Johnson said. “The processor appears to be making soil moisture science measurements possible in regions where RFI would have previously prevented success. However, some regions of the globe still remain problematic due to an excess of RFI.”
According to the team’s research, “the results obtained to date indicate that SMAP’s digital back end and associated RFI detection and filtering algorithms are working successfully to improve the quality of SMAP brightness temperature measurements.”
While their technology helps to remove man-made RFI emanating from most of the world, they reported some areas (including most of Japan) remain shrouded in heavy interference.
“On-orbit results indicate that sources which are wideband and occupy much of SMAP’s bandwidth at all times cannot be corrected by any of SMAP’s RFI filtering procedures, resulting in the exclusion of extended spatial regions from soil moisture retrievals,” the research states. “These results highlight the need for continued vigilance in the protection of spectrum for microwave radiometry and the need for active enforcement of these protections.”
NASA reported the project is a complex undertaking. The SMAP spacecraft carries both a synthetic aperture radar and the radiometer. The original plan was to combine the high accuracy of the radiometer and the high spatial resolution of the radar to produce high quality measurements at an intermediate spatial resolution.
“These plans changed when SMAP’s radar unexpectedly stopped transmitting radar pulses after two-and-a-half months of flawless data collection,” NASA reported. “The problem was attributed to a low-voltage power supply in the radar’s high-power amplifier.”
This leaves the team with two-and-a-half months of good radar data they received before the malfunction. Meanwhile, SMAP’s radiometer continues to work fine, and is returning valuable data for scientific research and analysis.
NASA reported the team has entered the next phase of the work: turning raw data collected by instruments on a spacecraft orbiting 426 miles above Earth into more than a dozen data products, and then coordinating the information to users through NASA’s Alaska Satellite Facility (ASF) and National Snow and Ice Data Center (NSIDC) Distributed Active Archive Centers (DAACs).
“For the SMAP team, the release of public soil moisture and freeze/thaw data marks not only the end of more than a half-decade of work, but the start of a challenging period of making sure these data and data products are delivered on time and provide the quality expected by data users around the world,” NASA reported.
SMAP is managed for NASA’s Science Mission Directorate in Washington by JPL, with instrument hardware and science contributions made by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. JPL built the spacecraft and is responsible for project management, system engineering, radar instrumentation, mission operations and the ground data system. Goddard is responsible for the radiometer instrument and science data products. Both centers collaborate on science data processing and delivery to the Alaska Satellite Facility, in Fairbanks, and the National Snow and Ice Data Center in Boulder, Colorado.