ALBERT

Description: In February 2019 a Project Authorization Request was approved by the Institute of Electrical and Electronics Engineers (IEEE) Standards Association with the title “Standard for Global Navigation Satellite System Reflectometry (GNSS-R) Data and Metadata Content”. A Working Group has been assembled to draft this standard with the purpose of unifying and documenting GNSS-R measurements, calibration procedures, and product level definitions. The Working Group (http://www.grss-ieee.org/community/technical-committees/standards-or-earth-observations/) includes members, collaborators, and contributors from academia, international space agencies, and private industry. In a recent face-to-face meeting held during the ARSI+KEO 2019 Conference, the need was recognized to develop a standard with a wide range of operations, providing procedure guidelines independently of constraints imposed by current limitations on geophysical parameters retrieval algorithms. As such, this effort aims to establish the fundamentals of a potential virtual network of satellites providing inter-comparable data to the scientific community.

Description: The Institute of Electrical and Electronics Engineers (IEEE) Geoscience and Remote Sensing Society (GRSS) created the GRSS “Standards for Earth Observation Technical Committee” to advance the usability of remote sensing products by experts from academia, industry, and government through the creation and promotion of standards and best practices. In February 2019, a Project Authorization Request was approved by the IEEE Standards Association (IEEE-SA) with the title “Standard for Spaceborne Global Navigation Satellite Systems Reflectometry (GNSS-R) Data and Metadata Content.” At present, 4 GNSS constellations cover the Earth with their navigation signals: The United States of America (USA) Global Positioning System GPS with 31 Medium Earth Orbit (MEO) operational satellites, the Russian GLObal’naya NAvigatsionnaya Sputnikovaya Sistema GLONASS with 24 MEO operational satellites, the European Galileo with 24 MEO operational satellites, and the Chinese BeiDou-3 with 3 Inclined GeoSynchronous Orbit (IGSO), 24 MEO, and 2 Geosynchronous Equatorial Orbit (GEO) operational satellites. Additionally, several regional navigation constellations increase the number of available signals for remote sensing purposes: the Japanese Quasi-Zenith Satellite System QZSS with 1 GSO and 3 Tundra-type orbit operational satellites, and the Indian Regional Navigation Satellite System IRNSS with 3 GEO and 4 IGSO operational satellites. On the other hand, there are different GNSS-R processing techniques, instruments and spaceborne missions, and a wide variety of retrieval algorithms have been used. The heterogeneous nature of these signals of opportunity as well as the numerous working methodologies justify the need of a standard to further advance in the development of GNSS-R towards an operational Earth Observation technique. In particular, the scope of this working group is to develop a standard for data and metadata content arising from past, present, and future spaceborne missions such as the United Kingdom (UK) TechDemoSat-1 TDS-1, and the National Aeronautics and Space Administration (NASA) CYclone Global Navigation Satellite System CYGNSS constellation coordinated by the University of Michigan (UM). In this article we describe the scene study, including fundamental aspects, scientific applications, and historical milestones. The spaceborne standard is under development and it will be published in IEEE-SA.

Description: The time-variable Earth’s gravity field is related to the mass transport and the physical processes within Earth’s system (including the atmosphere, oceans, hydrosphere, and cryosphere), such as melting of ice sheets and glaciers, ocean circulation and sea level variations, hydrological cycle, glacial isostatic adjustment, and earthquake-induced gravity change. The application of precise orbit determination (POD) provides valuable information about the Earth’s mass transport manifested in the temporal variations of the gravity field. This project uses the kinematics orbit-based acceleration approach, which has proven to be effective on the operational temporal gravity field data product generation using the high-low GNSS tracking data collected by the 3-satellite Swarm constellation. This project will utilize geodetic quality, dual-frequency high-low (GNSS-Spire CubeSats) tracking data from Spire Global, Inc.’s ~40 Lemur-2 3U CubeSat constellation. This low Earth orbiting (LEO) constellation is primarily dedicated to operational atmosphere data retrieval using radio occultation, bistatic GNSS-reflectometry forward scattering signals and grazing angle altimetry. The acceleration approach can provide solutions of the Earth’s temporal gravity field in long-wavelength (longer than 1,000 km), but plausibly at higher temporal sampling, weekly or finer with the global coverage of up to 40 simultaneous GNSS-Sensing of Spire CubeSats. This provides an additional observing architecture of gravity field solutions which can be used in conjunction with the more accurate and higher resolution temporal gravity solutions from GRACE-FO to further improve the temporal resolutions of monitoring abrupt-episode natural hazard evolution such as tropical cyclones, wildfires and floods, as well as weekly surface/ground water storage changes.

Description: 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.