Abstract
Since the late 1970s, satellite passive-microwave brightness temperatures have been a mainstay in remote sensing of the cryosphere. Polar snow and ice-covered ocean and land surfaces are especially sensitive to climate change and are observed to fluctuate on interannual to decadal timescales. In regions of limited sunlight and cloudy conditions, microwave measurements are particularly valuable for monitoring snow- and ice-covered ocean and land surfaces, due to microwave sensitivity to phase changes of water. Historically available at relatively low resolutions (25 km) compared to optical techniques (less than 1 km), passive-microwave sensors have provided short-timescale, large-area spatial coverage, and high temporal repeat observations for monitoring hemispheric-wide changes. However, historically available gridded passive microwave products have fallen short of modern requirements for climate data records, notably by using inconsistently-calibrated input data, including only limited periods of sensor overlaps, employing image-reconstruction methods that tuned for reduced noise rather than enhanced resolution, and using projection and grid definitions that were not easily interpreted by geolocation software. Using a recently completed Fundamental Climate Data Record of the swath format passive-microwave record that incorporated new, cross-sensor calibrations, we have produced an improved, gridded data record. Defined on the EASE-Grid 2.0 map projections and derived with numerically efficient image-reconstruction techniques, the Calibrated, Enhanced-Resolution Brightness Temperature (CETB) Earth System Data Record (ESDR) increases spatial resolution up to 3.125 km for the highest frequency channels, and satisfies modern Climate Data Record (CDR) requirements as defined by the National Research Council. We describe the best practices and development approaches that we used to ensure algorithmic integrity and to define and satisfy metadata, content and structural requirements for this high-quality, reliable, consistently gridded microwave radiometer climate data record.
Highlights
Since 1978, satellite-borne passive-microwave sensors have produced a rich record of Earth’s microwave brightness temperatures
Development of the historical gridded data products was funded by individual programs and for narrowly-defined purposes; much of the original development and product definition was performed in the early 1990s, long before the terms “Climate Data Record”, (CDR [3]) or “Earth System Data Record” (ESDR) were formally defined
In 2004, the National Research Council (NRC) defined a Climate Data Record as “a time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change”, and made the distinction for satellite-based CDRs as “fundamental CDRs (FCDRs), which are calibrated and quality-controlled sensor data that have been improved over time, and thematic CDRs (TCDRs), which are geophysical variables derived from the FCDRs, such as sea surface temperature and cloud fraction” [3]
Summary
Since 1978, satellite-borne passive-microwave sensors have produced a rich record of Earth’s microwave brightness temperatures Gridded versions of these time series have been used to derive and analyze significant climate records, including the dramatically declining Arctic sea ice [1] and variability and change in Arctic melt onset [2].
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