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A key success criterion for any long-term ESDR (Earth System Data Record) is how well it retains internal consistency upon input from multiple data sources. Our approach to achieving internal consistency of a soil moisture ESDR is based on mature data records derived from established cross-calibration procedures leveraged from the GPM mission.
The X-band soil moisture estimates in our soil moisture ESDR will be derived from the GPM Level 1C Common Calibrated Brightness Temperatures (GPMXCAL, Biswas et al., 2014). This product suite contains cross-calibrated brightness temperatures from all radiometers considered in the GPM constellation using the GMI as the calibration reference. The double-difference cross-calibration procedures deployed in the GPMXCAL development have been extensively published, evaluated and refined throughout the development and operation of GPM (Berg et al., 2016). The result is a stable and consistent dataset among radiometers (GMI, AMSR2, WindSat, AMSR-E, and TMI) whose X-band cross-calibrated brightness temperatures cover a period of more than two decades (1997–present), providing the basis for producing a long-term consistent multi-satellite soil moisture ESDR.
We then apply the same set of inversion algorithms, physical models, and ancillary data to the cross-calibrated brightness temperatures above. This gives us another means to reinforce ESDR consistency because for a given frequency, cross-calibrated brightness temperatures, regardless of their underlying sources, are all now subject to the same analytical inversion procedures to produce soil moisture estimates.
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