Principal Investigator (PI): John Kimball, University of Montana, Missoula

This project extends and enhances an existing Earth System Data Record (ESDR) quantifying daily landscape freeze/thaw (FT) state dynamics over all global land areas where seasonal frozen temperatures are a significant constraint to terrestrial water, energy, and carbon cycle processes. The freeze/thaw ESDR (FT-ESDR) captures dynamic spatial and temporal trends in frozen temperature constraints to surface water mobility and ecosystem processes in response to recent climate change. FT-ESDR continuity and enhancements will provide a continuous global data record spanning more than 40 years and representing one of the longest satellite environmental data records in existence, while providing finer resolution and increased science utility over the current baseline.

These activities are the logical extension of another MEaSUREs activity, "An Earth System Data Record for Land Surface Freeze-Thaw State: Quantifying Terrestrial Water Mobility Constraints to Global Ecosystem Processes", Kimball, PI, and build on a successful FT-ESDR developed from similar overlapping satellite microwave brightness temperature (Tb) records from Scanning Multi-channel Microwave Radiometer (SMMR), Special Sensor Microwave Imager (SSM/I), Special Sensor Microwave Imager/Sounder (SSMIS), Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E), and Advanced Microwave Scanning Radiometer-2 (AMSR2) sensors. The FT-ESDR provides consistent and precise (>80% mean spatial classification accuracy) daily (AM and PM) classification of the predominant frozen and non-frozen status of the landscape for both global and northern polar grid domains, with respective 25-km and 6-km gridding, and detailed metadata describing product quality.

The FT-ESDR has benefitted from four major reprocessing epochs incorporating product and algorithm refinements and lessons learned from early adopter and science application users. Product successes include more than 120 peer-reviewed scientific publications involving the data, incorporation of a FT-ESDR derived climate indicator for the National Climate Assessment, and informing development of an operational FT product for the NASA Soil Moisture Active Passive (SMAP) mission. We will extend the data record using continuing Tb observations from SSMI and AMSR2, while documenting product accuracy in relation to global weather station observations, other satellite records, and land surface models.

We will evaluate potential FT-ESDR enhancements, including production of both northern and southern polar grid FT records derived from AMSR-E and AMSR2 that provide up to eight-fold spatial enhancement over the global baseline. We will incorporate recent algorithm advances using machine learning, physics based interpolation, and data fusion techniques for deriving continuous probabilistic daily FT retrievals with enhanced resolution and performance. We will test a similar approach combining AMSR2 and SMAP Tb records for probabilistic classification of daily surface soil FT dynamics over the northern polar (≥45N) domain; we will exploit and document the value of SMAP L-band Tb observations for distinguishing soil FT relative to higher frequency Tb retrievals from AMSR2.

These activities will benefit the SMAP mission by supporting ongoing refinements to the L3FT operational product and by documenting the value of L-band Tb retrievals for soil FT and will provide a benchmark for assessing the performance and significance of the SMAP FT record for meeting mission objectives.

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