Initial GNSS Phase Altimetry Measurements From the Spire Satellite Constellation

The collection of phase coherent Global Navigation Satellite System (GNSS) reflected signals from radio occultation receivers in low-Earth orbit potentially offers the capability of deriving precise altimetry measurements over open and sea-ice-covered water at unprecedented coverage and low cost. Although past studies have verified the possibility of deriving altimetric measurements from GNSS observations, there is still uncertainty regarding the precision of this technique and its application. This study highlights the extraction of altimetric information from initial grazing angle GNSS reflection events observed by Spire satellites. Results show that the majority of coherent events occur over sea-ice-covered regions. A smaller number of coherent events are observed over the open ocean due to rougher scattering conditions. Altimetric retrieval was performed using dual frequency phase measurements from several events and compared to a model of the sea surface to demonstrate agreement to within 3cm after the removal of the average height difference.