Validation of the Effective Resolution of SMAP Enhanced Resolution Backscatter Products

Abstract

NASA's Soil Moisture Active Passive (SMAP) mission originally included both passive and active L-band measurement capability. It was the first satellite instrument to provide global L-band radar observations of normalized radar cross section ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sigma ^{o}$</tex-math></inline-formula> ) at multiple resolutions. The SMAP radar collected high resolution ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 1–3 km) synthetic aperture radar (SAR) measurements over most of the Earth's land mass. It simultaneously collected low resolution 6×30 km “slice” and full-footprint 29×35 km measurements. The SMAP radar operated for 83 days from day of the year 103 to 186 in 2015, before the transmitter failed. The SMAP radar was designed to make vegetation roughness measurements in support of the SMAP primary mission to measure soil moisture, but the radar data is useful for a variety of applications, particularly in the polar regions. Unfortunately, limitations in the data download volume precluded downlink of high resolution data over Antarctica, sea ice in the polar regions, and various islands. Nonetheless, low resolution slice and footprint data were collected and downlinked over these areas. To better exploit this low resolution data, this paper employs image reconstruction techniques to create twice-daily enhanced resolution SMAP radar images from the slice and footprint measurements. To validate the resolution enhancement, the enhanced resolution data are compared to SAR results over Greenland and South America. The new data set is provided to the science community to support cryosphere and climate studies.