GEROS-ISS: Ocean Remote Sensing with GNSS Reflectometry from the International Space Station

Abstract

In response to an European Space Agency (ESA) announcement of opportunity for climate change relevant science aboard the ISS, the GEROS-ISS (GEROS hereafter) proposal was submitted in 2011 and accepted by ESA to proceed to Phase A. GEROS-ISS is an innovative experiment primarily focused on exploiting reflected signals of opportunity from Global Navigation Satellite Systems (GNSS) at L-band to measure key parameters of ocean surfaces. GEROS will utilize the U.S. American GPS (Global Positioning System) and pioneer the exploitation of signals from Galileo and possibly other GNSS systems (GLONASS, QZSS, BeiDou), for reflectometry and occultation, thereby improving the accuracy as well as the spatio-temporal resolution of the derived geophysical properties. The primary mission objectives of GEROS are: (1) to measure the altimetric sea surface height of the ocean using reflected GNSS signals to allow methodology demonstration, establishment of error budget and resolutions and comparison/synergy with results of satellite based nadir-pointing altimeters and (2) to retrieve scalar ocean surface mean square slope (MSS), which is related to sea roughness, wind speed and direction, with a GNSS spaceborne receiver to allow methodology testing, establishment of error budget and resolutions. Secondary objectives include the generation of the 2D MSS or directional MSS retrieval and the associated proof-of-concept scientific data product. Secondary mission objectives, which increase the scientific value of the GEROS data, but are not driving the instrument developments, are: (1) to further explore the potential of GNSS radio occultation data (vertical profiles of atmospheric bending angle, refractivity, temperature, pressure, humidity and electron density), particularly in the Tropics, to detect changes in atmospheric temperature and climate relevant parameters (e.g., tropopause height) and to provide additional information for the analysis of the reflectometry data from GEROS and (2) to assess the potential of GNSS scatterometry for land applications and in particular to develop products such as soil moisture, vegetation biomass, and mid-latitudes snow/ice properties to better understand anthropogenic climate change. A Science Advisory Group (SAG) was formed by ESA Mid 2013 and the initial definition of the GEROS mission and system requirements was completed end of 2013. Two industrial phase A studies were started end of 2014, complemented by the scientific study GARCA (GNSS-R – Assessment of Requirements and Consolidation of Retrieval Algorithms) to develop an End2End Simulator for the preparation of the GEROS-Mission and to perform Observing-System Simulation Experiments (OSSE) to assess the oceanographic significance of the expected measurements and to demonstrate the usefulness of the GEROS concept. The presentation will give an overview on the current status of the GEROS experiment, review the science activities within the international GARCA study and related ESA-supported science activities.