DMSP satellite. Credit: U.S. Air Force/Lockheed Martin artist's concept

WASHINGTON – A sensor aboard one of the U.S. Air Force’s two primary weather satellites has been providing researchers with unreliable sea ice measurements for more than a month, according to the civilian-run National Snow & Ice Data Center.

The Boulder, Colorado-based research center, which is funded by NASA, NOAA and the National Science Foundation, has not updated its index of arctic-wide changes in sea ice since the passive microwave sensor onboard the Air Force’s 10-year-old Defense Meteorological Program-17 (DMSP-17) satellite began returning “spurious” data in early April.

The Air Force told SpaceNews that it is keeping an eye on one of DMSP-17’s sensor, but did not say which one had been flagged for monitoring. The National Snow & Ice Data Center, in announcing April 12 that it was temporarily suspending its daily sea ice updates, identified the sensor as the Special Sensor Microwave Imager and Sounder, or SSMIS.

“One of DMSP F-17’s sensors is currently flagged for monitoring. However, it is within factory tolerance and trending toward optimal temperature range,” said Jennifer Thibault, a spokeswoman for the 50th Space Wing at Schriever Air Force base in Colorado Springs, Colorado.

Thibault said the flagged sensor, one of seven instruments on board DMSP-17,  is not used for cloud characterization or theater weather imagery — the two highest-priority capabilities military commanders count on the aging DMSP system to provide.

DMSP-17, which launched in April 2006, came out of semi-retirement this year to replace the two-year-old DMSP-19, which stopped obeying commands in February.

Thibault said other resources, including the Air Force’s DMSP-18 satellite, are available to generate sea ice, water vapor and wind speed models for the Navy and other users.

Cathy Willis, a spokeswoman for the Naval Meteorology and Oceanography Command at Stennis Space Center in Mississippi, confirmed that the Navy is getting data from DMSP-18.

“DMSP F-18  has not changed status recently and Fleet Numerical Meteorology and Oceanography Center  is receiving data and products from DMSP F-18,” Willis said.

The National Snow & Ice Data Center has also switched over to using DMSP-18 for seaice measurements, but hasn’t used it to produce an updated Sea Ice Index since the data hasn’t been intercalibrated with the DMSP-17 data. In the meantime, the center has been using the uncalibrated data for a daily snapshot of arctic sea ice conditions that carries a disclaimer.

“Initial evaluation of the uncalibrated F-18 data indicates reasonable agreement with F-17, but the data should be considered provisional and quantitative comparisons with other data should not be done at this time,” the center wrote in a May 6 update.

Thibault pointed out that F-17’s sensor, which was built by Northrop Grumman, is operating well beyond its design life of several years and, as such, has experienced some degraded performance due to its time on orbit.  She said Northrop is monitoring the situation to “determine the root cause of the variance.”

Northrop Grumman spokesman Lon Rain referred questions about the sensor to the Air Force.

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.