Abstract
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. Satellite-based 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 follow-on 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 (subsurface-probe) 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.
Highlights
Soil moisture is vital for life, environment and energy-chemical cycles, runoff and evapotranspiration, erosion and weathering [1]-[6]
The launch of Seasat and Nimbis-7 in 1978 had the first passive microwave remote sensing instrument the Scanning Multichannel Microwave Radiometer (SMMR) to extract soil moisture information based on the contrast of the dielectric constant of mineral soil and pore water on a global basis [7] [8]
We examine retrievals most recently developed by JAXA (JAXA-algorithm for Advanced Microwave Scanning Radiometer-Earth Observation System (AMSR-E) reprocess and AMSR2) and previously by NASA (NASA-algorithm for Advanced Microwave Scanning Radiometer (AMSR)-E)
Summary
Soil moisture is vital for life, environment and energy-chemical cycles, runoff and evapotranspiration, erosion and weathering [1]-[6]. The launch of Seasat and Nimbis-7 in 1978 had the first passive microwave remote sensing instrument the Scanning Multichannel Microwave Radiometer (SMMR) to extract soil moisture information based on the contrast of the dielectric constant of mineral soil and pore water on a global basis [7] [8]. The design and functionality of AMSR-E deployed on NASA-Aqua satellite for the NASA Earth Observation Mission derives from the earlier designs employed in AMSR versions flown during the JAXA Advanced Earth Observation System missions I and II [13] [15] These and current sensors have legacy with conical-mirror scanning (40 Rotations Per Minute-RPM) design concepts employed in the SMMR and SSM/I (new Figure) [15]-[17]. Improvements in antenna and radio design allow for smaller instantaneous field of view (24-by-42 km 10.65 GHz channel compared to 29-by-51 km 10.65 GHz channel for AMSR-E, Table 1) and post-algorithm product gridding
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