NASAThe Generic Earth Observation Metadata Standard (GEOMS) is a metadata and data structure framework used for archiving Earth observation data from ground-based instrument networks. It was developed collaboratively by NASA, ESA, and the scientific community to standardize the exchange of validation data for satellite missions, and is required for all data submissions to NASA's Atmospheric composition Validation Data Center (AVDC).
Background
GEOMS traces its origins to the European Commission COSE (Compilation of Atmospheric Observations in Support of Satellite Measurements over Europe) project, initiated in 1998 at the Belgian Institute for Space Aeronomy (BIRA-IASB). The initial goal was to develop uniform metadata guidelines for atmospheric and oceanographic datasets supporting the ESA Envisat satellite validation campaign. The first formal guideline document was published in April 2002, defining metadata requirements for the Envisat Cal/Val Data Centre.
In 2006, the guidelines were extended through an addendum to support NASA's EOS-Aura validation program, carried out in collaboration between ESA, NASA, principal investigators from the Envisat and Aura validation campaigns, and selected investigators from the Network for the Detection of Atmospheric Composition Change (NDACC). The scope was progressively broadened from atmospheric and oceanographic datasets to cover all measurements from Earth observation instruments. The standard was consolidated and formalized as GEOMS version 1.0 in December 2021.
Purpose & Scope
GEOMS outlines metadata and data structure requirements designed to make geophysical datasets portable, accessible, and self-describing. The standard defines both global attributes (describing the dataset as a whole) and variable attributes (describing individual data arrays), organized into three categories:
- Controlled vocabulary attributes -- values drawn from a maintained Table of Attribute Values (TAV)
- Rule-based attributes -- free-form values following specified formatting rules (dates, file names, version strings)
- Free-text attributes -- uncontrolled descriptive fields (caveats, acknowledgements)
The current guidelines cover correlative, experimental, and model data archived for the Aura validation program, Envisat calibration and validation efforts, NDACC data, and ESA's GECA (Generic Environment for Calibration/Validation Analysis) project.
Supported Instruments
GEOMS provides measurement-specific reporting templates for the following instrument types:
| Instrument Type | Abbreviation |
|---|---|
| Ozone Monitoring Instrument | OMI |
| Light Detection And Ranging | LIDAR |
| Microwave Radiometer | MWR |
| Fourier Transform Infrared Spectroscopy | FTIR |
| UV/Vis Differential Optical Absorption Spectroscopy | UVVIS.DOAS |
| Radio Occultation | RO |
| Sondes | -- |
| Buoys | -- |
Each template specifies the required variables, their dimensions, and valid attribute values for that measurement type.
Implementation
GEOMS metadata guidelines are implemented using the Hierarchical Data Format (HDF4 or HDF5) or netCDF file formats. HDF has become the de facto satellite data exchange format for both ESA and NASA Earth observation missions. The netCDF format, maintained by Unidata, is also extensively used in Earth observation. The metadata guidelines are not inherently limited to these formats, though submitting data centers may not support all discussed formats natively.
Governance & Maintenance
The GEOMS group consists of representatives from NASA, ESA, NDACC, and affiliated universities and organizations. The standard is maintained by the AVDC team at NASA Goddard Space Flight Center. Changes are tracked and published as versioned updates to guidelines, attribute value tables, and instrument-specific templates. The IDLcr8 software suite provides tools for generating GEOMS-compliant files, and a quality assurance and harmonization service validates submitted datasets.
Notable Implementations
GEOMS is required by the AVDC for all validation data submissions and is used across multiple satellite validation campaigns and ground-based networks:
- EOS-Aura validation program -- HIRDLS, MLS, OMI, and TES atmospheric instruments
- Envisat Cal/Val -- AATSR, GOMOS, MERIS, MIPAS, and SCIAMACHY sensors
- NDACC -- Network for the Detection of Atmospheric Composition Change
- NASA A-train -- Extended to additional satellite constellation instruments
- GECA project -- ESA's Generic Environment for Calibration/Validation Analysis
Related Standards
GEOMS is complementary to the CF Conventions (Climate and Forecast Conventions), which serve a similar metadata standardization role for NetCDF-formatted climate data. While CF focuses on self-describing NetCDF files for the broader climate science community, GEOMS is specifically tailored to HDF-based and netCDF-based validation datasets in the Earth observation domain.