Soil moisture is a vital physical parameter of the active-layer in permafrost environments, and
associated biological and geophysical processes operative at the microscopic to hemispheric
spatial scales and at hourly to multi-decadal time scales. While in-situ measurements can give
the highest quality of information on a site-specific basis, the vast permafrost terrains of North
America and Eurasia require space-based techniques for assessments of cause and effect and
long-term changes and impacts from the changes of permafrost and the active-layer. Satellitebased
6.925 and 10.65 GHz sensor algorithmic retrievals of soil moisture by Advanced Microwave
Scanning Radiometer-Earth Observation System (AMSR-E) onboard NASA-Aqua and followon
AMSR2 onboard JAXA-Global Change Observation Mission—Water-1 are ongoing since July
2002. Accurate land-surface temperature and vegetation parameters are critical to the success
of passive microwave algorithmic retrieval schemes. Strategically located soil moisture measurements
are needed for spatial and temporal co-location evaluation and validation of the
space-based algorithmic estimates. We compare on a daily basis ground-based (subsurfaceprobe)
50- and 70-MHz radio-frequency soil moisture measurements with NASA- and JAXA-algorithmic
retrieval passive microwave retrievals. We find improvements in performance of the
JAXA-algorithm (AMSR-E reprocessed and AMSR2 ongoing) relative to the earlier NASA-algorithm
version. In the boreal forest regions, accurate land-surface temperatures and vegetation
parameters are still needed for algorithmic retrieval success. Over the period of AMSR-E retrievals,
we find evidence of at the high northern latitudes of growing terrestrial radio-frequency
interference in the 10.65 GHz channel soil moisture content. This is an important error source
for satellite-based active and passive microwave remote sensing soil moisture retrievals in Arctic
regions that must be addressed.
