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Mapping: Essential Geodetic Variables (EGV) to Geodetic Products
This mapping shows which Geodetic Products contribute to the EGVs across all levels, based on the GGOS EGV White Paper V7.0 (January 2026, Gruber, Angermann, Sánchez). V7.0 introduced two structural changes from V6.0: (1) what was "Level 0" is now Basis, covering geodetic infrastructure and standards; (2) a new Level 1 EGV (Geodetic Observations) is formally defined. Total EGV count: 21 (2 Basis + 1 Level 1 + 4 Level 2 + 14 Level 3).
Basis EGVs (Infrastructure and Standards)
| Basis EGV | Domain | Subdomain | Description |
|---|---|---|---|
| Geodetic Infrastructure | Global | Geometric/Physical | Physical station networks, space segments, and observing systems that underpin all EGV production. Not itself an observed variable. |
| Geodetic Standards and Conventions | Global | Geometric/Physical | Numerical standards, background models, and agreed conventions required for consistent EGV determination across all techniques and institutions. |
Level 1 EGVs
| Level 1 EGV | Domain | Subdomain | Contributing Geodetic Products |
|---|---|---|---|
| Geodetic Observations | Global | Geometric/Physical | VLBI Observations, SLR Observations, GNSS Observations (RINEX), DORIS Observations, combined technique solutions (SINEX) |
Level 3 EGVs (High-Level Products)
| Level 3 EGV | Domain | Subdomain | Contributing Geodetic Products |
|---|---|---|---|
| Earth Orientation Parameters (EOP) | Global | Geometric | Celestial Pole Offset (CPO), Universal Time (UT1), Length of Day (LOD), Polar Motion (PM) |
| Global Reference Frames | Global | Geometric/Physical | Celestial Reference Frame (CRF), Terrestrial Reference Frame (TRF), Gravity Reference Frame (GRF), Height Reference Frame (HRF) |
| Global Earth Gravity Field | Global | Physical | Global Gravity Field Models (GGM), Topographic Gravity Field Models (TGFM), Gravity Field Quantities (GFQ) |
| Regional Reference Frames | Land/Ocean | Geometric/Physical | Regional Terrestrial Reference Frame (RTRF), Regional Gravity Reference Frame (RGRF), Regional Height Reference Frame (RHRF), Vertical Datum Parameter (VDP) |
| Regional Gravity Field Model | Land/Ocean | Physical | Regional Geoid Model (RGM), Regional Gravity Field Quantities (RGFQ) |
| Land Geometry | Land | Geometric | Digital Elevation Model (DEM), Digital Terrain Models (DTM), Plate Kinematic Model (PKM), Earth Surface Deformation (ESD) |
| Sea Surface | Ocean | Geometric | Mean Sea Surface (MSS), Sea Level Anomaly (SLA), Sea State (SES), Empirical Ocean Tide Model (EOT) |
| Sea Level | Ocean | Physical | Global Mean Sea Level / Mean Dynamic Topography (MSL/MDT), Mean Geostrophic Currents (MGC), Global Sea Level Change / Dynamic Ocean Topography (SLC/DOT), Relative Mean Sea Level (RMSL), Relative Sea Level Change (RSLC) |
| Sea Ice | Ocean | Geometric | Sea Ice Extension (SIE), Sea Ice Volume (SIV) |
| Ice Sheets | Land | Geometric/Physical | Ice Mass Change (IMC), Ice Sheet Thickness (IST) |
| Glaciers | Land | Geometric/Physical | Glacier Mass Change (GMC), Glacier Ice Thickness (GIT), Glacier Flow Velocities (GFV) |
| Inland Water Level | Land | Geometric/Physical | Mean Regional Water Level (MRWL), Regional Water Level Change (RWLC) |
| Terrestrial Water Storage | Land | Physical | Terrestrial Water Storage Anomaly (TWSA) |
| Atmosphere Parameters | Global | Physical | Integrated Water Vapor (IWV), Global Ionosphere Maps (GIM), Thermosphere Density Model (TDM) |
Level 2 EGVs (Intermediate Products)
| Level 2 EGV | Domain | Subdomain | Contributing Geodetic Products |
|---|---|---|---|
| Satellite Orbits | Global | Geometric | GNSS Satellite Orbits (GSO), GNSS Satellite Clocks (GSC), Earth Observation Satellite Orbits (ESO) |
| Station Positions and Variations | Global | Geometric | Station Position Time Series (SPTS) |
| Sea Water Level Records | Ocean | Geometric | Sea Water Level Records (SWLR) |
| Land and Marine Gravity Data | Land/Ocean | Physical | Land Gravity Measurements (LGM), Marine Gravity Measurements (MGM), Absolute Gravity Measurements (AGM), Time Series Gravity Measurements (TGM) |
Source: Gruber, T.; Angermann, D.; Sánchez, L. (2026), Definition of Essential Geodetic Variables (EGV): Contribution of Geodesy to Earth Observation, White Paper Version 7.0, GGOS, January 2026. Sections 3.1 and 3.2 (Pages 5–17).
Level 2 → Level 3 EGV Dependency Matrix
This section completes the cross-mapping from Level 2 EGVs to the Level 3 EGVs they feed. Relationship strength follows the Table 3 conventions from the GGOS White Paper (Page 18): Primary = the Level 3 EGV cannot be produced without this input; Important = significant contribution, partial substitution possible; Indirect = downstream dependency via another EGV.
| Level 3 EGV | Satellite Orbits | Station Positions & Variations | Sea Water Level Records | Land & Marine Gravity Data |
|---|---|---|---|---|
| Earth Orientation Parameters | Important | Primary | — | — |
| Global Reference Frames (ITRF/CRF/GRF/HRF) | Primary ⚠️ | Primary | — | Important |
| Global Earth Gravity Field | Indirect | Indirect | — | Primary |
| Regional Reference Frames | Important | Primary | — | Important |
| Regional Gravity Field Model | Indirect | Indirect | — | Primary |
| Land Geometry | Important | Primary | — | Indirect |
| Sea Surface | Primary | Important | Primary | — |
| Sea Level | Primary | Important | Primary | Important |
| Sea Ice | Primary | — | — | — |
| Ice Sheets | Primary | Indirect | — | Important |
| Glaciers | Important | Indirect | — | Important |
| Inland Water Level | Important | Indirect | — | — |
| Terrestrial Water Storage | Primary | — | — | Primary |
| Atmosphere Parameters | Primary | Important | — | — |
⚠️ Circular dependency: Global Reference Frames (ITRF) is simultaneously a consumer of Satellite Orbits (GNSS data must be processed using precise orbits before contributing to ITRF combination) and a dependency of Satellite Orbits (SPOCC uses Helmert transformations to align individual AC solutions to the current ITRF). This is the fundamental bootstrapping constraint of geodesy — orbits and the reference frame must be iteratively co-determined. A failure in Satellite Orbits production does not just degrade this one EGV; it progressively degrades the entire ITRF, which then cascades to every EGV with a Primary or Important dependency on Global Reference Frames.
Supply Chain Risk Propagation
If the Satellite Orbits (GNSS) production pipeline fails, the following Level 3 EGVs degrade in order of dependency depth:
| Impact Tier | Affected Level 3 EGVs | Mechanism |
|---|---|---|
| Immediate (hours–days) | Atmosphere (IWV, GIM), Sea Surface, Sea Level, Sea Ice | Real-time and rapid products require current GSO/GSC; altimetry satellite orbit errors propagate directly into geophysical retrievals |
| Short-term (days–weeks) | Global Reference Frames, Earth Orientation Parameters, Ice Sheets, Terrestrial Water Storage, Inland Water Level | Final precise orbits used for ITRF weekly combinations and satellite altimetry/gravimetry reprocessing |
| Medium-term (weeks–months) | Regional Reference Frames, Land Geometry, Glaciers | Depend on ITRF consistency and cumulative satellite-based measurements |
| Long-term (months+) | All Level 3 EGVs | ITRF degradation without fresh GNSS orbit input progressively weakens the reference frame underpinning all geodetic products |
Co-Produced EGVs from the IGS GNSS Pipeline
The GNSS Analysis Center processing that produces Satellite Orbits simultaneously generates additional Level 2 EGV products as byproducts. A disruption to the Tier 2–3 pipeline therefore affects multiple EGVs beyond Satellite Orbits:
| Co-produced EGV | Level | Mechanism | Notes |
|---|---|---|---|
| Station Positions and Variations | Level 2 | AC solutions include station coordinate time series (SPTS) as a natural output of GNSS processing | Same Tier 0–2 infrastructure; produced in the same computational step |
| Atmosphere — Integrated Water Vapor (IWV) | Level 3 input | Tropospheric delay parameters estimated during orbit determination yield IWV directly | Key climate variable; production is inseparable from orbit processing |
| Atmosphere — Global Ionosphere Maps (GIM) | Level 3 input | Ionospheric delay estimation during dual-frequency GNSS processing produces GIM | CODE, JPL, and ESA/ESOC each produce independent GIMs |
| Earth Orientation Parameters (EOP) | Level 3 input | Polar motion and length-of-day estimated as part of GNSS combination at Tier 3 | GNSS-based EOP is an important independent check on VLBI-primary EOP |
Implication for risk assessment: The Tier 3 ACC/SPOCC bottleneck identified as High Risk in the Satellite Orbits workflow is effectively a multi-EGV single point of failure. Its risk classification should be understood in this broader context.
EGV Data Level Progression Through the Supply Chain
The EGV data levels map directly onto the tier structure of the Satellite Orbits workflow. This alignment provides the standard labelling for all EGV workflow documents.
| Workflow Tier | EGV Data Level | Data Type | Latency Class |
|---|---|---|---|
| Tier 0 — Observation | Basis | Physical station infrastructure, calibrated instruments, and first-mile telemetry. Corresponds to Basis EGVs: Geodetic Infrastructure and Geodetic Standards and Conventions. | Real-time |
| Tier 1 — Archiving | Level 1 | RINEX files; geo-located time series with geophysical corrections applied, formatted to agreed IGS standards. Corresponds to Level 1 EGV: Geodetic Observations. | Hours |
| Tier 2 — Analysis Centers | Level 1 → Level 2 (intermediate) | Individual AC precise orbit and clock solutions; processed from Level 1 but not yet combined into the official EGV product | 15 min – 24 h (depending on product latency class) |
| Tier 3 — Combination | Level 2 EGV | SPOCC-combined Satellite Orbits EGV: GNSS Satellite Orbits (GSO), GNSS Satellite Clocks (GSC) | Ultra-Rapid (15 min), Rapid (17 h), Final (12–18 days) |
The Level 2 intermediate label at Tier 2 reflects that individual AC solutions are more than raw data but are not yet the authoritative EGV — they become Level 2 only after the Tier 3 combination. This distinction is significant for FAIR data compliance (Principle 4): both the intermediate solutions and the final combined product should be archived and accessible, as the intermediate solutions are required for independent validation and reprocessing.
Workflow Linkage Annotations
The following annotations should appear in all EGV workflow documents to ensure cross-EGV consistency. These are the standard cross-reference labels to apply at the tier boundary and product nodes.
| Annotation Point | Label | Links To |
|---|---|---|
| Tier 0 → Tier 1 boundary | [EGV Basis → L1] | EGV_Levels_Summary.md Basis and Level 1 definitions |
| Tier 2 → Tier 3 boundary | [EGV L1 → L2 EGV] | EGV_Levels_Summary.md Level 2 definition |
| Final combined product node | [Level 2 EGV: Satellite Orbits — GSO, GSC] | EGV_Product_Mapping.md Level 2 table |
| ITRF dependency at Tier 3 | [Cross-EGV dependency: Global Reference Frames → ITRF] | Level 3 EGV: Global Reference Frames |
| Co-produced outputs at Tier 2–3 | [Co-produces: Station Positions (L2), IWV, GIM, EOP inputs] | Respective Level 2 and Level 3 EGV entries |
| Downstream consumers | [Feeds: EOP, Global Ref Frames, Sea Level, Sea Surface, Ice Sheets, TWS, Atmosphere Parameters] | Level 3 EGV dependency matrix above |
Source Note on Table 3 (GGOS White Paper V7.0)
Table 3 in the GGOS White Paper V7.0 provides the authoritative primary/important/indirect relationship matrix. The dependency matrix above is derived from that table and from the Section 3.1–3.2 product descriptions. Where the White Paper shows primary (Red), important (Blue), and indirect (Orange) relationships, this document uses the equivalent text labels. The TRF note in the original verification entry is captured formally in the circular dependency annotation on the Global Reference Frames row above. The Level 2 → Level 3 dependency matrix is unchanged between V6.0 and V7.0; the structural changes affect only the Basis and Level 1 tiers.