| Summary: | Spire Global is a world-leading commercial provider of GNSS Radio Occultations, producing over 15,000 quality-controlled RO events to meteorological agencies on a daily basis. These RO measurements are collected from a constellation of approximately 40 3U cubesats operating in a variety of low Earth orbits.The cubesats’ GNSS receivers have been reprogrammed to collect surface reflections at grazing angle geometries (elevations ranging from 5 to 30 degrees). At these geometries, it is possible to leverage the coherent phase information of the GNSS signals and extract relative height profiles, particularly over sea ice surfaces. Over 300,000 kms of altimetry tracks are generated on a daily basis in the high-latitude regions. The accuracy of the ellipsoidal heights is below 20 cm, as determined by comparisons against a modeled sea surface height formed by combining an MSS model with ocean tides. Decimeter-level sea ice height signal is routinely detected and corroborated using colocated SAR images; a sea ice freeboard retrieval algorithm is presently developed to estimate freeboard signal on an operational basis, with improvements needed in phase unwrapping and sea ice lead detection. Additionally, we describe an overview of a growing number of studies with promising results for altimetry applications over oceans and inland water bodies.We will present the status of Spire altimetry from its RO constellation, a general roadmap for future research in algorithm development, and challenges faced. Also discussed will be the potential niches and roles that a commercial satellite data provider can play in the provision of scientific climate observations.
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