Temporal Analysis

Compare Satellite Images: Before & After

With Off-Nadir Delta, you can compare satellite images over time to identify environmental changes, urban development, and disaster impacts — all in your browser.

Quick answer — how change detection works

Compare satellite images from different dates to detect changes. Use SAR (Sentinel-1) for floods/all-weather, optical (Sentinel-2) for vegetation/land cover. Archive from 2014. In Off-Nadir Delta, visual before/after comparison runs in the browser; the pixel-difference analysis is on paid plans and metered on your token balance.

Multi-Year Archive

Access imagery from 2014 onwards to analyze long-term changes.

Layer Comparison

Toggle layers on/off and adjust opacity to visually compare before and after.

Difference Analysis

Calculate pixel differences to quantify and visualize changes.

Comparison Methods

Visual Comparison

• Opacity Control: Fade between layers to spot differences
• Layer Toggle: Switch layers on/off for quick comparison
• Layer Reorder: Stack layers to compare overlapping areas

Quantitative Analysis (paid plans)

• Difference Image: Pixel-by-pixel subtraction between dates
• Additive Color Composite: Multi-temporal color mixing for SAR change visualization
• Index Comparison: Compare NDVI or other indices across dates

Best Practices

Same Season

Compare images from similar times of year to avoid seasonal false positives.

Similar Conditions

For optical imagery, match cloud-free conditions when possible.

SAR for Disasters

Use Sentinel-1 when cloud cover obscures optical sensors.

What Changes Can You Detect?

Deforestation

Track forest clearing, logging, and land use change

Urban Expansion

Monitor construction, urban sprawl, and development

Disaster Impact

Before/after analysis of floods, fires, earthquakes

Seasonal Patterns

Agricultural cycles, snow cover, water levels

How It Works

Select Your Area

Navigate to the location you want to analyze.

Choose Two Dates

Select before and after dates for comparison.

Add Both Images

Load satellite imagery for each date into layers.

Compare & Analyze

Use difference analysis, layer opacity, or toggle visibility to identify changes.

Frequently Asked Questions

What types of changes can I detect?▼

You can detect deforestation, urban expansion, flood extent, agricultural changes, construction progress, coastal erosion, and many other environmental and man-made changes.

Should I use SAR or optical for change detection?▼

It depends on your use case. SAR (Sentinel-1) is best for flood detection and works through clouds. Optical (Sentinel-2) is better for vegetation changes and land cover classification.

How far back can I compare?▼

Sentinel-1 data is available from 2014 and Sentinel-2 from 2015, allowing multi-year change analysis.

Can I quantify the changes?▼

Yes — the difference analysis tool calculates pixel-by-pixel changes, helping you understand the magnitude and extent of what changed. It is a paid-plan feature and each run is metered on your token balance; see the pricing page for current details.

What about seasonal variations?▼

For land cover analysis, compare similar seasons (e.g., summer to summer) to avoid false positives from natural seasonal changes.