Geostationary Littoral Imaging and Monitoring Radiometer (GLIMR) – Pioneering Next-Generation Ocean Color

GLIMR is a NASA Earth Venture Instrument Project managed by the University of New Hampshire (UNH) and led by Principal Investigator Dr. Joseph Salisbury at UNH. The GLIMR investigation uses a hyperspectral radiometer in geostationary orbit built by Raytheon to enable the first large-scale quantification of rapid changes in phytoplankton growth rate, community composition, and fluxes from land to ocean. In announcing the GLIMR project selection, NASA noted: “GLIMR fills significant gaps in the current suite of ocean color sensors. Current NASA ocean color missions do not provide the temporal or spatial resolution necessary to describe processes in the dynamic coastal zone.” GLIMR’s unprecedented spectral (340-1040 nm with 252 channels), temporal (hourly) and spatial (300 m nadir) capabilities significantly advance scientific understanding and management of coastal ecosystems that benefit society. GLIMR data quantifies biological and biogeochemical processes including primary production, tracks carbon inventories in time and space and examines impacts of tides, surface currents, and river discharge on distribution and fluxes of ocean materials. GLIMR provides federal, state, and local agencies with vital information on coastal hazards (oil spills, harmful algal blooms, post-storm assessment, water quality) for improved response, containment and public advisories both at sea and along the coast.

GLIMR’s design is carefully optimized to provide radiometric and spatial and spectral sampling performance required to advance coastal water science using TRL 6+ technology. The earth scanning approach is based on an existing flight proven (TRL 9) two-axis gimbal system that reduces GLIMR development cost. Owned by Raytheon and donated to the program, this gimbal has proven pedigree and validated flightworthiness of components. This two-axis gimbal provides whole earth field of regard, scan regions of interest multiple times per day, and performs special operations collects. It performs data acquisition via rotation about its azimuthal axis (east-west) to provide continuous scan at constant rate over scan region.

The GLIMR “Hyperspectral Imager” combines a dispersive slit spectrometer with a 1.47 deg cross-scan field-of-view with a large Raytheon SB500 focal plane optimized to meet GLIMR signal-to-noise ratio requirements. Configurability of the Hyperspectral Imager focal plane maintains high signal-to-noise ratio and coverage rate under range of solar zenith angles. The focal plane configuration can be commanded for each scan region, allowing for adjustment based on view angle, time of day, and cloud conditions. The Hyperspectral Imager collects multiple frames during the time taken to scan one ground sample distance and co-adds data onboard to improve SNR. A single post-coaddition hyperspectral frame per line scan is downlinked.

A WFOV “Landmark Imager” enables relatively low cost, high performance (< 2 microradian line-of-sight knowledge) image navigation and registration essential for GLIMR mission. The Landmark Imager collects field-offset imagery of nearby land features for hyperspectral image registration. The Landmark Imager focal plane provides sub-array windowing capability, and multiple standard configurations have been defined to provide options for format and number of windows depending on size, location, visibility of landmarks. Window placement and frame rates are commandable, so long as the combination of format, number of windows, and frame rate stay within data rate limitations dictated by bus downlink capability.

The GLIMR program completed its KDP-C milestone in March 2023 and CDR in June 2023. The program is proceeding through build and test activities on the path to instrument delivery in 2025 and anticipated launch in the 2026-27 timeframe. This presentation summarizes key instrument capabilities and program achievements.