cs.LGMar 8, 2026
SaveWhat on Earth is AlphaEarth? Hierarchical structure and functional interpretability for global land cover
Organizations: Artificial Intelligence for Climate and Sustainability The Institute for Experiential Artificial Intelligence Northeastern University, Portland, ME, USA · Gulf of Maine Research Institute Portland, ME, USA · Sustainability and Data Sciences Laboratory Northeastern University, Boston, MA, USA · School of Engineering and Architecture Universidad Católica de Manizales Manizales, Colombia ·
Abstract
Geospatial foundation models generate high-dimensional embeddings that achieve strong predictive performance, yet their internal organization remains obscure, limiting their scientific use. Recent interpretability studies relate Google AlphaEarth Foundations (GAEF) embeddings to continuous environmental variables, but it is still unclear whether the embedding space exhibits a functional or hierarchical organization, in which some dimensions act as specialized representations while others encode shared or broader geospatial structure. In this work, we propose a functional interpretability framework that reverse-engineers the role of embedding dimensions by characterizing their contribution to land cover structure from observed classification behavior. The approach combines large-scale experimentation with a structural analysis of embedding-class relationships based on feature importance patterns and progressive ablation. Our results show that embedding dimensions exhibit consistent and non-uniform functional behavior, allowing them to be categorized along a hierarchical functional spectrum: specialist dimensions associated with specific land cover classes, low- and mid-generalist dimensions capturing shared characteristics between classes, and highgeneralist dimensions reflecting broader environmental gradients. Critically, we find that accurate land cover classification (98% of baseline performance) can be achieved using as few as 2 to 12 of the 64 available dimensions, depending on the class. This demonstrates substantial redundancy in the embedding space and offers a pathway toward significant reductions in computational cost. Together, these findings reveal that AlphaEarth embeddings are not only physically informative, but also functionally organized into a hierarchical structure, providing practical guidance for dimension selection in operational classification tasks.
Figures & tables
Figure 1: Multi-modal fusion at scale, left) data containing the features, and right) its representation in an embedding.
Figure 2: Flowchart of the methodological framework: from embeddings to functional semantics. The pipeline integrates (1) ESA WorldCover 2020 categorical labels and AEF 64-dimensional embeddings as inputs, (2) a massive experimental framework executing more than 130,000 binary classification experiments using Random Forest, Gradient Boosting, XGBoost, and LightGBM with progressive feature ablation across the top 1 to 30 embedding dimensions, (3) structural mapping via an association matrix and functional taxonomy, and (4) an interactive embedding universe visualization connecting the latent space to semantic space.
| impA01 | impA02 | impA03 | impA04 | impA64 | ||
|---|---|---|---|---|---|---|
| Bare/sparse vegetation | 0.0267 | 0.0223 | 0.0350 | 0.0167 | 0.0409 | |
| Built-up | 0.0044 | 0.1092 | 0.0478 | 0.0057 | 0.0040 | |
| Cropland | 0.0163 | 0.0266 | 0.0564 | 0.0369 | 0.0179 | |
| Grassland | 0.0211 | 0.0315 | 0.0552 | 0.0270 | 0.0161 | |
| Herbaceous wetland | 0.0177 | 0.0449 | 0.0269 | 0.1090 | 0.0199 | |
| Mangroves | 0.0446 | 0.0103 | 0.0112 | 0.0162 | 0.0093 |
Table 1: Excerpt of the association matrix quantifying the normalized frequency with which each embedding dimension ranked among the two most important features by MDI across all experiments targeting each land cover class. Values range from 0 to 1, where higher values indicate stronger discriminative relevance of that dimension for the corresponding class
Figure 3: Embedding Fingerprint plot illustrating the functional dimensional signature of each land cover class at the performance recovery threshold. Analogous to a genomic fingerprint, where the presence and absence of bands at specific loci encodes biological identity, each row represents the characteristic pattern of exclusive (blue) and shared (pink) embedding dimensions that together define the discriminative identity of a land cover class within the AEF embedding space. Exclusive dimensions appear in only one class’s minimum subset, while shared dimensions — encompassing low-, mid-, and high-generalists — contribute to the classification of two or more classes. Gray positions indicate dimensions not required to achieve the threshold for that class. Land cover classes are ordered from top to bottom by increasing spectral complexity, quantified as the mean pixel-wise variance across Sentinel-2 spectral bands computed over 100 randomly selected images per class after standard atmospheric and radiometric corrections. Spectrally homogeneous classes such as Snow/ice and Water — which exhibit low inter-pixel variability due to their uniform reflectance signatures — appear at the bottom, while spectrally heterogeneous classes such as Built-up — whose radiometric response varies substantially across rooftops, roads, and impervious surfaces — appear at the top, reflecting the increasing number of embedding dimensions required to characterize them.
Figure 4: Conceptual structure of the embedding space representation, illustrating the planet-moon organization of the embedding universe. Blue circles represent land cover classes (planets), while green circles represent exclusive embedding dimensions (moons) whose color intensity encodes association strength — dark green indicating strong discriminative relevance, medium green indicating moderate relevance, and light green indicating weak relevance for that class. Gold diamonds represent shared embedding dimensions that connect multiple land cover classes, positioned at the geometric centroid of their associated classes and reflecting ecotonal or spectrally ambiguous regions where land cover boundaries overlap. This conceptual layout serves as the interpretive basis for the embedding universe visualization implemented in the interactive dashboard ( Guthrie and Benavides, 2025b ) and shown in Figure 6 .
Figure 5: Progressive ablation curves and minimum embedding dimensions by land cover class. Panels (a) and (b) show eight classification metrics as a function of MDI-ranked embedding dimensions for Water and Shrubland respectively (red = mean across experiments; blue dashed = 64-dimension baseline; green dotted = tipping point at baseline recovery). Water requires as few as 2 dimensions while Shrubland requires up to 12, reflecting differences in spectral distinctiveness. Panel (c) summarizes the minimum dimensions required to achieve of baseline performance across all 11 ESA WorldCover 2020 land cover classes.
| Exclusive Embedding Dimension | Associated Land Cover Class | Distinctive trait that can justify an exclusive embedding |
|---|---|---|
| A09, A35 | Built-up | Urban surfaces and infrastructure: roofs, roads, concrete. Their radiometric signature is dominated by artificial materials with high SWIR reflectance compared to NIR and strong Sentinel-1 backscatter. No other class combines this angular geometry and artificial-material spectrum, which justifies specific embeddings. |
| A12, A50 | Cropland | Annual crops sown and harvested within a 12-month cycle, with very regular phenology (well-marked greenness peaks), geometric patterns (plots, furrows) and often intensive management. Although they can be confused with grasslands, certain regions of the feature space (e.g. very homogeneous or highly irrigated crops) carry signatures specific to cropland, explaining their exclusive embeddings. |
| A05, A27 | Mangroves | Evergreen woody vegetation tolerant to salinity in the intertidal zone. They show dense canopy like the Tree cover class, but with coastal linear patterns, water mixed between crowns and specific NIR/SWIR signatures due to permanent waterlogging. This combination (dense forest, brackish water and coastal context) is unique to mangroves. |
| A04, A11, A25, A29 | Herbaceous wetland | Areas dominated by herbaceous vegetation that is permanently or regularly flooded (fresh, brackish or saline water). They combine moderate–high NDVI with very high water indices (NDWI, etc.) and floodplain textures; no other type combines herbaceous cover and long-lasting flooding in this way. |
| A18, A21, A26 | Shrubland | Zones dominated by natural shrubs ( 10% cover), typical of semi-arid biomes. Although they mix with grassland and bare/sparse vegetation, subtypes where shrub height, density and spatial pattern (e.g. dense Mediterranean shrublands) generate signatures distinct enough to occupy an exclusive subspace. |
| A16, A23 | Tree cover | Regions dominated by trees ( 10% cover), including plantations, with very high NIR, strong shadows and closed canopy textures. This 3-D structure and phenological persistence (especially in evergreen forests) clearly separate them from shrubland and grassland, allowing embeddings to specialise in representing “dense forests”. |
Table 2: Exclusive embedding dimensions and their associated ESA WorldCover 2020 land cover classes, listing dimensions that appear solely in one class’s minimum subset alongside a biophysical interpretation of the distinctive spectral, structural, or phenological properties that justify their exclusive association.
| Embedding Dimension | Associated ESA Land Covers | Categorization | Identifier | Common trait (ecological–spectral synthesis) |
|---|---|---|---|---|
| A07 | Cropland, Moss/lichen | Low-generalist | Discontinuous vegetation | Areas with low and discontinuous vegetation over mineral soil: croplands in fallow or early phenological stages and lichen mats show a soil and sparse vegetation mixture with high visible albedo and marked seasonal variability. |
| A08 | Built-up, Moss/lichen | Low-generalist | Sparse vegetation over bright surfaces | Bright, sparsely vegetated substrates such as roofs, concrete and rock with lichens share low chlorophyll signal and rough textures that the model groups as mineral surfaces with minimal vegetation. |
| A15 | Moss/lichen, Snow/ice | Low-generalist | High latitude and high albedo | High-latitude or high-altitude cold environments where snow/ice and lichen mats over rock produce bright visible reflectance and spatially homogeneous cryogenic landscapes. |
| A28 | Grassland, Tree cover | Low-generalist | Dense green vegetation | Landscapes dominated by green vegetation with strong NIR response where the main difference is canopy density; the embedding captures forest–grassland mosaics with intermediate canopy fraction. |
| A34 | Shrubland, Tree cover | Low-generalist | Woody perennial | Woody perennial vegetation with relatively high biomass; shrublands and forests differ in height but share canopy textures and similar spectral and SAR responses. |
| A36 | Bare/sparse, Herbaceous wetland | Low-generalist | Soil-moisture gradient | Transition from dry bare soil to wet herbaceous substrates where exposed mud and seasonal wetlands resemble moist bare surfaces, capturing gradients of soil moisture. |
Table 3: Shared embedding dimensions and their functional interpretation, grouped by generalist category (low-, mid-, and high-generalist) according to the number of land cover classes in whose minimum subset they appear. For each dimension, the associated ESA WorldCover 2020 classes and a common ecological–spectral trait are reported, inferred through the two-stage interpretive process described in Section 2.6.
Figure 6: “Embedding Universe” visualization at a 98% baseline performance recovery threshold, generated using the interactive Dashboard ( Guthrie and Benavides, 2025b ) . Green nodes represent specialist dimensions (darker = stronger association); gold nodes represent shared dimensions. See Section 2.5 for a full description of the visual encoding. To interact with this plot, access this link .
Supplementary Figure 1: Embedding frequency distributions by land cover class. For each class, embedding dimensions are ranked by frequency of appearance in the top 2 most important positions across 10,000 experimental runs. Green bars indicate dimensions within the tipping point threshold; blue bars indicate remaining dimensions. Generated using the interactive Dashboard ( Guthrie and Benavides, 2025b ) .
Supplementary Figure 2: Grid-based geographic performance heatmap of classification accuracy across global experiments. Each cell represents the mean classification accuracy aggregated across all experiments conducted within that geographic grid cell. Red cells indicate higher accuracy (>90%), orange cells indicate moderate accuracy (80–90%), and blue cells indicate lower accuracy (<80%). Generated using the interactive Dashboard ( Guthrie and Benavides, 2025b ) .
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