Connecting Sensors: SSM/I and QuikSCAT -- the Polar A Train

NSIDC’s 30 th Anniversary, 25 October 2006 Introduction Remote sensing in the microwave portion of the electromagnetic spectrum have found many applications in cryospheric research. Nearly 30 years of continuous and consistent PM observations allow for studies on changes in several cryospheric variables.  1978 – 1987: SMMR  1987 – present: successive SSM/I  2002 – present: AMSR-E Active observations (e.g. scatterometers) also started in the late 1970s, but the record is not continuous or consistent.  6/78 - 9/78: SASS – Ku Band (Seasat)  6/96 – 5/97: NSCAT – Ku Band (ADEOS I)  2/92 – 1/01: EScat – C Band (ERS-1/2)  7/99 – present: SeaWinds on QuikSCAT (Ku Band)  12/02 – present: SeaWinds on ADEOS II (Ku Band)

NSIDC’s 30 th Anniversary, 25 October 2006 Science with Passive Microwave Sea ice mapping

NSIDC’s 30 th Anniversary, 25 October 2006 Science with Passive Microwave Greenland Melt Steffen and Huff Since 1979, the area that experiences melt has increased at a rate of ~18%/decade.

NSIDC’s 30 th Anniversary, 25 October 2006 Science with Passive Microwave Significant trends in late spring and early summer indicating decreasing snow cover Trend (million sq-km/decade) Changes in northern hemisphere snow cover

NSIDC’s 30 th Anniversary, 25 October 2006 Science with Active Microwave Antarctic Iceberg Tracking QuikSCAT tracks Antarctic icebergs (used operationally at NIC)  Icebergs have high backscatter compared to sea ice and open ocean (nearly 55% of all iceberg locations reported by NIC are based on QuikSCAT). Iceberg Tracks from 1978 &

NSIDC’s 30 th Anniversary, 25 October 2006 Science with Active Microwave Time series analysis of the radar backscatter can be used to determine the onset of melt and re-freezing. Note: melt days over open ocean are exaggerated since as the ice edge retreats each pixel previously representing sea-ice now resides over open ocean and accumulates melt days as the summer season progresses.

NSIDC’s 30 th Anniversary, 25 October 2006 Science with Active Microwave Ice extent is easily defined using active microwave data (and doesn’t require a tuning) Ice Extent

NSIDC’s 30 th Anniversary, 25 October 2006 Passive vs. Active Both passive and active remote sensing offer:  Large spatial coverage;  High temporal resolution;  Ability to penetrate clouds;  Derive similar geophysical variables (e.g. snow and ice extent, sea surface wind vectors, melt, etc). Passive microwave pros:  Long consistent time-series of observations. Passive microwave cons:  Variation of surface emissivity and atmospheric water vapor create problems for algorithms. Active microwave pros (Scatterometers):  Less sensitivity to weather effects. Active microwave cons (Scatterometers):  Short time-scale.

NSIDC’s 30 th Anniversary, 25 October 2006 Scatterometer Climate Record Pathfinder (SCP) SCP has been generating high resolution scatterometer imagery to support cryospheric studies from QuikSCAT, NSCAT, ERS and SASS).  Current products include:  Global high resolution data (2.225 and 4.5 km/pixel);  Antarctic ice berg tracking (daily at km/pixel);  Ice motion (daily at 25-km);  Ice extent (daily at km/pixel). NSIDC recently acquired sea ice extents from QuikSCAT spanning  Daily at and 4.5 km/pixel for Arctic and Antarctic

NSIDC’s 30 th Anniversary, 25 October 2006 REaSON CAN Project New research being done:  Incorporation of ADEOS-II Seawinds to ensure continuous Ku-band time-series;  Addition of sea ice motion products and sea ice extent maps derived from combined active/passive microwave data sets;  Addition of seasonal melt-freeze products from combined active/passive microwave data sets;  Seasonal change maps of Greenland and Antarctica from combined active/passive data;  Integrated seasonal change maps of land ice/sea ice/cold regions land cover;  Antarctic iceberg drift database continuation.

NSIDC’s 30 th Anniversary, 25 October 2006 Blending Active and Passive Microwave Generation of enhanced resolution SSM/I and AMSR brightness temperatures to match enhanced resolution scatterometer datasets.  Enhanced resolution images are produced by combining all passes in a single day to improve the spatial resolution of the data at the expense of temporal resolution.  NSIDC currently has enhanced resolution SSM/I data from at pixel size of 8.9 km for GHz and 4.45 km for 85 GHz.

NSIDC’s 30 th Anniversary, 25 October 2006 Examples of SSM/I HIRZ HIRZ 85V January

NSIDC’s 30 th Anniversary, 25 October 2006 Image Artifacts Artifacts arise from Tb changes from pass to pass during the day 7 September 2002

NSIDC’s 30 th Anniversary, 25 October 2006 AMSR Local Time of Day

NSIDC’s 30 th Anniversary, 25 October 2006 Animation of AMSR-E High Resolution Tbs 36.5 V AMSR-E 36.5V from 19 June to 6 October 2002

NSIDC’s 30 th Anniversary, 25 October 2006 Melt Onset/Freeze-up Passive and active microwave radiometers respond to liquid water content of snow  Increase in passive microwave Tbs because of decrease in volume scattering (thus increased emissivity)  Decrease in backscatter because of decrease in volume scattering Before melt After melt 13.9 GHz normalized radar cross section at 40 o incidence angle before (top) and after (bottom) a major melt event. Note the dramatic change in backscatter over the sea ice and along the periphery of the Greenland ice sheet ( Enhanced resolution NSCAT May June 18-23

NSIDC’s 30 th Anniversary, 25 October 2006 Arctic Wide Melt Onset/Freeze B. Holt and K. McDonald are developing melt onset/freeze-up across the polar region (includes sea ice and land) using a synthesis of Ku-band and passive microwave data. Transect that extends from interior Alaska across the Chukchi and Beaufort Seas (inclusive of boreal forest, tundra, the Beaufort coastline, seasonal and multiyear sea ice Melt onset Freeze-up Broken/thin ice floes Brooks Range

NSIDC’s 30 th Anniversary, 25 October 2006 Case Study, Antarctic Peninsula Study by Kunz and Long (2006) developed melt detection from QuikSCAT and compared to SSM/I QuickSCAT method:  PR ratio (  v o –  h o ) together with  h o  Melt classification is determined using ML estimate of ice state Passive microwave method:  HR = T b (19H) – T b (37H) (Anderson, 1987)  T b -  T b (19V) >  T b dry + (1-  )T b wet (Ashcroft and Long, 2006)  XPGR = T b (19H) – T b (37V) (Abdalati and Steffen, 2001) T b (19H) + T b (37V)

NSIDC’s 30 th Anniversary, 25 October 2006 Melt Detection: Antarctica When QuikSCAT backscatter decreases, there is usually a rise in SSM/I brightness temperatures Kunz and Long (2006)

NSIDC’s 30 th Anniversary, 25 October 2006 Melt Detection: Antarctica Melt onset dates from QuikSCAT are usually a few days earlier than those detected by XPGR and T b - . Better consistency is found between QuikSCAT and T b -  than with XPGR. While radiometer data tend to be more sensitive to melt onset, it easily saturates, and is sensitive to weather. Kunz and Long (2006)

NSIDC’s 30 th Anniversary, 25 October 2006 Ice Extent Both active and passive are useful for detecting the ice edge. However, passive microwave is affected by weather effects.  Thus the reason for selecting thresholds for the ice edge Scatterometer ice edge does not require tuning but it doesn’t infer ice concentration.  V/H of SeaWinds does show sensitivity to ice concentration and ice type (at medium-to-high concentrations)

NSIDC’s 30 th Anniversary, 25 October 2006 Ice Extent Differences QuikSCAT Ice ExtentSSM/I Ice Concentration 1 January 2001

NSIDC’s 30 th Anniversary, 25 October 2006 Ice Extent Differences Seasonal difference between QuikSCAT and SSM/I ice extents – match better during austral winter In general, QuikSCAT shows more Antarctic sea ice (~600,000 sq- km) during austral summer and 3,000 sq-km more during austral winter.

NSIDC’s 30 th Anniversary, 25 October 2006 Ice Extent Blending Ideas Fusion of scatterometer and radiometer should enable improved characterization of the ice edge, ice concentration and type. Preliminary results by D. Long suggest scatterometry has improved accuracy during ice- edge advance from thermodynamic growth. Scatterometer data can help define the ice edge when weather effects the passive microwave signal (make the ice edge less patchy). Scatterometer can detect melting well and therefore flag the use of different concentration tables for melting ice.

NSIDC’s 30 th Anniversary, 25 October 2006 Ice Motion Work by Zhao et al. (2002) and Liu et al (1999) found that regions for which sea ice motion derived from passive microwave was erratic or impossible, ice motion could be determined with scatterometer data (and vice versa). Scatterometry doesn’t experience the problems caused by water vapor in SSM/I 85 GHz channel.  Thus, scatterometry data can be used to fill in poorly tracked regions.

NSIDC’s 30 th Anniversary, 25 October 2006 Blended SSM/I and QuikSCAT Ice Motion Merged Arctic sea ice drift map  Provides more complete coverage than from a single data source RMS difference of satellite results from buoy speed is less than 3 cm/s

NSIDC’s 30 th Anniversary, 25 October 2006 Summary Fusion of active and passive microwave observations shows great promise in polar climate and change studies. This is a relatively new research area, with much work still to be done. The availability of enhanced resolution passive and active microwave observations will greatly facilitate research. Future blended products will include sea ice extent, ice type, melt onset/freeze-up and ice motion.  Data will be made available at NSIDC