1. NSIDC’s Passive Microwave Sensor Transition for Polar Data
Donna J. Scott
NASA NSIDC DAAC Passive Microwave Team
with Walt Meier
Goddard Space Flight Center

2. Background – PM sensor record
Sensors:
Passive microwave sensors provide continuous and near-complete record from 1978-present
F15 - launched 1999 (>16 years old)
F16 - launched 2003 (>12 years old)
F18 - launched 2009 (>6 years old)
AMSR2 - JAXA sensor launched 2012 (Only AMSR2 is operating within its nominal 5 year mission)
F19 launched 2014 (failed February 2016)
F17 launched 2006 (capability for sea ice ended April 2016)
F20 launch was cancelled (in storage)
Chinese sensors are in orbit, but access to data is not realistic
No other passive microwave sensors are on the horizon until after 2020 → the nearly 40-year record of continuous, consistent monitoring will end if current capabilities do not last significantly longer than planned
Additional Impacts include:
Sea ice concentration/extent
Snow extent
Timing of melt onset over snow & ice
Rainfall, total precipitable water, cloud liquid water
Soil moisture
Ocean wind speed
Timeline of passive microwave sensors
1970
1980
1990
2000
2010
2020
Passive Microwave Era F8
F11
F13
F17
F20
F19
F16
F15
F18
SMMR
AMSR-E
AMSR3,4
AMSR2
NIMBUS-5
NIMBUS-7
DMSP
NASA EOS AQUA
JAXA GCOM-W

3. Background – PM Product Team
USO
OPS
Sci Developer
Scientist
Tech
Writer
LEAD
Non-EOS passive microwave data (SMMR-SSM/I-SSMIS)
In-house data production

4. Timeline of recent satellite transition work
F-17 begins showing bad data
F-18, F-16 parallel processing streams set up
Provisional F-18 data released
Apr 2016
F-19 NRT parallel processing stream set up
Nov 2015
F-16 calibration work complete, data running internally
Jun 2016
NISE F-16 calibrations in work
Aug 2016
Feb 2016
F-19 fails prior to calibration
F-18, F-16 discussed as options
May 2016
F-18 calibration completed, data officially released
F-17 fixes made, data running internally
Jul 2016
NISE F-18 calibrations complete, data running internally
Sept 2016
Wrap up NRT satellite transition
Look to RSS for F-18 data release for time-series data transition

5. Considerations in priority setting
Brightness temperature data vs. sea ice data
Internal NSIDC sea ice data needs
SII
NASA funded ASINA
2.5 million views in 2015
NASA missions needs
Missions use NISE as input. These missions not reporting the impacts in F-17 PM
SII
ASINA
Remaining considerations
Near-real-time and time-series data no longer consistent with platform sensor
F18 not ready for long time series – RSS does not have F18 online yet.
New approach to provenance and stewardship practices related to NSIDC near-real-time data sets

6. Prioritizing transition of DAAC PM data sets

7. F-17: What happened?
4/5/16: Solar panel position change compromised integrity of primary sea ice algorithm channel 16 (37Ghz vertical polarization)
4/13/16: Solar panel repositioned improving channel 16 problems. Sea ice data at NSIDC still showing problems
5/25/16: Reports of optimal sensor function after fix to spike detection algorithm. Long term quality unknown and data still at risk
5/26/16: NSIDC decision to move to F-18
Bad Data Images
April 28, 2016
TBs and Ice Extent
Bad
data

8. Science Scott Stewart – NSIDC PM science contractor
Julienne Stroeve – NSIDC
Walt Meier - GSFC
NSIDC: An overview

9. Sea ice product transition
Sea ice concentration derived from brightness temperature using empirical relationships
Coefficients (tiepoints) assigned for pure surface types (water, two ice types)
Intercalibration approach is to adjust tiepoints to match extent/area between sensors during an overlap period
Weather filters, thresholds of TB ratios, used to reduce false ice retrievals over open water
Effectively help define the ice edge
NSIDC: An overview

10. Calibration Effort for F-18
During the calibration efforts, a provisional F-18 data stream using F-17 tie points was used to enable ASINA to continue reporting sea ice trends
NSIDC investigated the calibration of algorithm tie point values to best match the sea ice extent from F-17 over a 12-month period from 03/01/2015 through 02/29/2016. 
Current F-17 tie points provided the best match in sea ice extent, so no adjustment to the tie points were made for F-18. The average difference between F-17- and F18-derived sea ice extents were approximately 20,000 sq km.

11. F17 to F18 SSMIS sea ice calibration
NSIDC investigators found that brightness temperature values for F18 and F17 were very similar for channels related to sea ice concentration.
Brightness temperatures are highly correlated
(R = 0.996)
Histograms are indistinguishable

12. F17 to F18 SSMIS sea ice calibration
Attempts to adjust the NASA Team tie points led to worse correlation of extent values, so the values used for F17 continue to be used.
This is likely due to the sensitivity of ice edge to small TB changes, including effects of weather filter thresholds
Differences in extent are small
(Average daily difference < 10,000 km2) – is this true; looking at the next plot and from the numbers I have the mean difference is ~20k

13. F16 and F18 extent differences
NSIDC: An overview

14. Science Behind Satellite Transition
Issues matching sea ice area and extent
Simply regressing TBs does produce as close of a match is possible
Daily average of swaths
Difference in observation times and number of observations at a location
Cannot optimize both area and extent – i.e., best area match possible will produce an extent difference that is not minimal
Extent is sensitive to weather filters – can potentially adjust thresholds to better match extent without denigrating area differences too much
Seasonal affects also – summer melt season is problematic

15. Future activities
Goddard will produce a final F18 intercalibration using RSS TBs
There is much potential to improve intercalibration of previous sensor products if/when resources become available
New version of RSS TBs
Longer sensor overlap periods
Use of AMSR-E or AMSR2 as a baseline
Use swath data instead of daily averages?
NSIDC: An overview