Sentinel-2 mineral
exploration, visualised
SpectralExplorer processes Sentinel-2 L2A imagery into spectral index maps for sandstone uranium-vanadium, polymetallic, and critical mineral targeting. Load a SAFE folder, compute 23+ indices in one click, and score drill targets — all in a single desktop app.
Hover over any button or index card for a tooltip description. Keyboard shortcuts active after clicking the image: F fit · R region mode · +/- zoom · arrows pan.
Band Analysis — 12 bands loaded, 24 indices computed across U, V, Fe, Mn, Cu, Ti, Zn, REE and Sc targets
Band Analysis — 10 bands loaded, 23 indices computed across U, V, Fe, Mn, Cu, Ti, Zn, REE and Sc targets
System requirements
SpectralExplorer is a single self-contained Windows executable — no installation, no Python needed. Download, unzip, double-click.
| Item | Requirement |
|---|---|
| Operating system | Windows 10 or 11 (64-bit) |
| RAM | 8 GB minimum · 16 GB recommended for full S2 tiles |
| Display | 1280 × 800 or larger |
| Input data | Sentinel-2 L2A (surface reflectance) |
| File formats | JP2 (classic ESA), GeoTIFF COG (CDSE post-2023), PNG, single-band TIFF |
Indices are calibrated for L2A surface reflectance. Loading L1C top-of-atmosphere data triggers a warning. Download L2A from dataspace.copernicus.eu or use Sen2Cor first.
Your Sentinel-2 data
You need an L2A product from Copernicus. Products after 2023 come as COG GeoTIFF — both formats work automatically.
Free registration. Use the map to select your area of interest.
Choose a scene with < 10% cloud cover. Look for summer acquisitions for minimum vegetation in arid study areas.
Extract it so you have a folder named S2A_MSIL2A_...SAFE with a GRANULE subfolder inside.
Band Analysis
Navigate to ~ Band Analysis in the left sidebar. This is your starting point — load bands here before doing anything else.
Loading a SAFE folder
The fastest method: click 📂 Load SAFE Folder and select your .SAFE directory. The app scans the entire folder tree, finds all band files, and prefers the highest resolution (R10m > R20m > R60m).
Click "Load SAFE Folder" and navigate to your .SAFE directory — the app finds all band files automatically
While loading, the status bar shows which band is currently being read (e.g. "Loading B11...") so the app never appears frozen on large scenes. Each band row turns green with a ✓ TIF or ✓ JP2 badge when done. The status bar then updates to show how many bands loaded and how many indices are computable. Image Viewer automatically shows a Natural Colour composite as soon as B4, B3 and B2 are available — this works whether you load a SAFE folder, a multi-band GeoTIFF, or the three bands individually.
⊞ Load Multi-band GeoTIFF — a single stacked file from ArcGIS/QGIS. A dialog lets you assign each layer to the correct S2 band.
Individual Load buttons — load specific bands one at a time, useful when you only need a subset.
÷10000 and vegetation mask
÷10000 (L2A DN → reflectance) — leave this ticked for standard L2A products where pixel values are in the 0–10 000 range. Untick if data is already in 0–1 reflectance.
Apply NDVI vegetation mask — masks pixels with NDVI > 0.20 before computing, isolating bare rock and soil. Recommended for geological mapping.
Computing indices
Once bands are loaded, click Compute All Indices. Every index whose required bands are available is computed simultaneously — missing-band indices are skipped silently.
Clicking "Compute All Indices" processes all 23 indices simultaneously — results appear as thumbnails
Results tabs
After computing, three tabs appear:
Spectral Indices — colour-coded thumbnail grid. Each card shows mean value, anomalous pixel %, and tier. Click any card to expand to full resolution with a live cursor readout, histogram, and pixel-level value display.
False Colour Composites — eight pre-built RGB composites. The Alteration Composite (R=B11/B12, G=B4/B2, B=B8A/B11) is the primary targeting image for U-V roll-front systems.
Statistics Summary — full ranked table of all indices by anomalous pixel %, group averages by element, and a cross-index Pearson correlation matrix. Click any row to expand that index.
Image Viewer
Navigate to # Image Viewer. Each panel shows one index map with a colour ramp, statistics, live cursor readout, and region prospectivity scoring.
Image Viewer — Fe Oxide Ratio index map with live cursor readout (0.32746), statistics panel, anomaly threshold at 75%, and "From Band Analysis (24)" button in the toolbar
Natural Colour loads automatically
As soon as you load a SAFE folder (or enough individual bands) and bands B4, B3 and B2 are available, Image Viewer pre-loads a Natural Colour composite (R=B4, G=B3, B=B2) so you have geographic context immediately — before running any compute. This happens only when the viewer is empty, so it never overwrites an image you already have open. The 🌍 View Composites button also activates at this point, giving access to all eight false colour composites.
From Band Analysis
After clicking Compute All Indices, the From Band Analysis (23) button activates. Click it to open a thumbnail picker of every computed spectral index — click any to load it instantly into Image Viewer, no file export needed.
View Composites picker
The 🌍 View Composites button opens a picker showing live thumbnails of all eight false colour composites, built directly from your loaded bands. Click any thumbnail to open that composite in the viewer with full pan, zoom, cursor readout and region scoring. Composites that need bands you haven't loaded are greyed out and labelled "missing bands".
Working with composites in the viewer
RGB composites behave like any other image in the viewer — you can zoom, pan, draw regions and read off the prospectivity score. The one difference is the index dropdown: because a composite is already a three-colour image, tagging it to a spectral index won't re-colourise it (the colour ramp only applies to single-band index maps). The statistics panel shows values based on the composite's luminance.
This means you can, for example, open the Alteration Composite, switch to Region mode, and score a candidate roll-front zone directly on the false-colour image — useful when you want to see the geological context and the prospectivity number at the same time.
Tagging and colour ramps
When loading an index manually (via + Load index map), use the dropdown in the panel header to tag it to the correct index. This applies the right element colour ramp and sets the interpretation note and tier.
Region prospectivity scoring
Region scoring works on both single-band index maps and RGB composites, so you can score a target zone directly on the Alteration Composite or any index. Switch to ⬚ Region mode in the panel header (or press R — the header turns amber while active), then drag a rectangle over any area. SpectralExplorer computes a prospectivity score (0–100) from three components:
| Component | Weight | What it measures |
|---|---|---|
| Anomaly density | 50% | % of pixels above/below threshold within the drawn region |
| Intensity | 25% | How far anomalous pixels exceed the threshold on average |
| Regional contrast | 25% | z-score of region mean vs whole-image mean |
Region prospectivity scoring drawn on the Manganese Detection composite — Score 28/100, Tier 3, with the full statistics panel showing the region's distribution and anomaly threshold
Click Save ✚ to save the region permanently on the image. Saved regions persist as colour-coded boxes. Click All ▤ to open the Region Analyzer — a sortable table of all saved regions, editable names, score comparison bar chart, and CSV export.
Index Library
Navigate to = Index Library for full geological descriptions, spectral mechanisms, deposit associations, and correlation values for all 23 indices. Filter by element using the buttons at the top.
False Colour Composites
Eight pre-built RGB composites are available in two places: the False Colour Composites tab of Band Analysis, and the 🌍 View Composites button in Image Viewer. Each is built live from your loaded bands using a 2nd–98th percentile contrast stretch per channel, so colours stay consistent regardless of scene brightness. The viewer version lets you pan, zoom and draw scoring regions on any composite.
| Name | Recipe | Primary use |
|---|---|---|
| Alteration Composite | R=B11/B12, G=B4/B2, B=B8A/B11 | ⭐ Primary U-V targeting. Yellow-orange = ore-roll zone. |
| Natural Colour | R=B4, G=B3, B=B2 | Baseline. Yellow-green = carnotite, black = coal. |
| False Colour IR | R=B8, G=B4, B=B3 | Vegetation stress and geobotanical anomalies. |
| Standard Geology | R=B12, G=B8A, B=B4 | Lithology. Magenta = clay-hydroxyl. |
| SWIR Geology | R=B12, G=B11, B=B8A | Mineralogy. Cyan = carbonates / sulfates. |
| Gossan / Mine Dump | R=B4, G=B11, B=B2 | AML sites. Yellow = Fe-oxide waste. |
| Manganese Detection | R=B11, G=B8A, B=B3 | Mn-oxide rock vs Fe mudstone. |
| Coal / Carbonaceous | R=B8, G=B4, B=B3 | REE host strata. Very dark = coal seam. |
Target Tiers
The ^ Target Tiers page defines four prioritisation levels. The same system applies to Image Viewer anomaly percentages and Region prospectivity scores.
| Tier | Score | Required signature | Action |
|---|---|---|---|
| Tier 1 | 80–100 | Bleaching + V redox both anomalous; clay hydroxyl elevated; Fe oxide ratio shows gradient; ferrous Fe on down-dip side. | Drill-ready. Soil-gas Rn + IP first. |
| Tier 2 | 60–79 | Bleaching OR V redox (not both); clay hydroxyl moderate. | XRF traverse + auger sampling. |
| Tier 3 | 40–59 | Single index anomalous; structural position favourable. | Reconnaissance + rock chips. |
| Context | < 40 | No diagnostic signature; background terrain. | Maintain as background reference. |
Composite Weights
Navigate to % Composite Weights to adjust how much each index contributes to composite scoring. Weights must total 100%. A contribution bar chart updates in real time on the right.
Default weights are calibrated for the Emery and Carbon Counties, Utah U-V sandstone system. For other target types, upweight the relevant commodity indices — for example, increase Cu Carbonate and Azurite for porphyry-adjacent Cu targets.
Field Workflow
The > Field Workflow page provides a seven-step targeting sequence from basin screening to drill verification.
Map anticlinal noses and fault traps. Overlay Ti Silicate to confirm permeable sandstone. Eliminate mudstone areas.
Run V Redox + Fe Oxide Ratio together — the paired anomaly precisely locates the roll-front interface.
Compound Bleaching as primary filter within the redox corridor. Confirm with Clay Hydroxyl.
Overlay Gossan / Fe Enrichment. Co-incident gossan + bleaching + redox = strongest Tier 1 candidate.
Check REE Carbonaceous Shale for organic material in the reduced zone. Absent organics = unfavourable regardless of redox geometry.
Apply NDVI Vegetation Stress as a low-weight tie-breaker. Arid terrain limits this signal.
Tier 1 targets: XRF traverse → radon soil-gas → RC or diamond drilling at 50–100 m spacing along roll-front strike.
Export
| From | Export type | Contents |
|---|---|---|
| Export page | Index library → CSV | All indices with descriptions, correlations, deposit types and field notes. |
| Export page | Weights → CSV | Current weight configuration with normalised scores. |
| Export page | Full report → TXT | Complete plain-text summary of all indices, weights, tiers, workflow. |
| Export page | Save session → JSON | All notes and weights for restoration in a future session. |
| Image Viewer | ⬇ Export GeoTIFF | Float32 (0–1), raw values, or colour-rendered RGB — with original georeference tags. |
| Region Analyzer | Export CSV | All saved regions with scores, stats, pixel coords, tier and index name. |
If the source file contained GeoTIFF georeference tags (tiepoint, pixel scale, transformation matrix) these are preserved in the exported file — your exported index maps will align correctly in ArcGIS or QGIS.
Troubleshooting
"No bands found" when loading a SAFE folder
The error dialog shows exactly what files were found. Common causes:
• The .zip archive was not fully extracted — check the folder contains a GRANULE subfolder.
• You selected a parent folder above .SAFE — select the folder named S2A_MSIL2A_...SAFE directly.
• Unusual band naming — use the individual Load buttons instead.
"Could not load" errors for individual bands
This indicates a codec issue in the bundled exe. Try loading the .tif versions of the same bands (CDSE format) using the individual Load buttons — these use tifffile rather than imagecodecs and are more reliably bundled.
All statistics show 0.000 in Image Viewer
The ÷10000 scaling was applied to a file already in 0–1 reflectance, or the file has very small values. In Band Analysis, untick ÷10000 and reload. The Image Viewer auto-normalises to 0–1 for display — use Export GeoTIFF → Raw values to see original pixel values.
"From Band Analysis" button is greyed out
The button activates only after clicking Compute All Indices in Band Analysis. Load your bands, compute, then navigate to Image Viewer — the button will show the count of available indices.
Natural Colour composite didn't load automatically
The auto-load needs the blue, green and red bands (B2, B3, B4) present. If your SAFE folder is missing any of these, or the viewer already had an image open, the composite won't auto-load. You can always click 🌍 View Composites manually to build it. If the button is greyed out, no bands are loaded yet — load a SAFE folder in Band Analysis first.
Windows SmartScreen blocks the exe
Right-click the exe → Properties → tick Unblock at the bottom → OK. Or click More info → Run anyway in the SmartScreen dialog. The exe is unsigned (code signing certificates are expensive) and safe if downloaded from the original source.