A new method to assess land surface fractional open water (fw) inundation dynamics was developed using high frequency (89 GHz) brightness temperatures (Tb) from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E), with other ancillary inputs from AMSR-E and MODIS (Moderate Resolution Imaging Spectroradiometer). The resulting 89 GHz fw (fwWBand) retrievals provide 10-day temporal fidelity and enhanced (5 km) resolution relative to other passive microwave sensor based land observations. A look-up table was first established to provide reference microwave emissivities for water and land endmembers under a range of atmosphere and land surface conditions. The fwWBand retrievals were then obtained on a per pixel basis using difference ratio and double difference methods for respective barren and vegetated soil conditions. The resulting fwWBand summer (JJA) seasonal composites correspond favorably (R ≥ 0.86, p < 0.001) with alternative, finer resolution (≤ 300 m) static open water maps derived from satellite radar and optical-infrared sensors over a pan-Arctic (≥ 45°N) domain. The fwWBand retrievals also capture significant seasonal drought and flooding events inferred from river discharge records within the major Arctic basins. The fwWBand retrievals are found to be reliable for discriminating open water in moderately dense vegetation areas, but with greater uncertainty over barren land. The ability of the fw retrievals to detect surface water under vegetation also decreases exponentially with increasing canopy optical thickness. The new fwWBand dataset provides an improved resolution satellite environmental data record documenting open water patterns and inundation dynamics in boreal-Arctic ecosystems experiencing rapid climate change.
- Fractional land surface open water