Frequently Asked Questions

Off-Nadir Delta is a browser-based WebGIS platform for satellite imagery analysis. It allows you to access, visualize, and analyze satellite data from Sentinel-1 (SAR), Sentinel-2 (Optical), NISAR L-Band SAR, VIIRS Nighttime Lights, and NASA FIRMS Active Fire data directly in your web browser, without requiring any GIS software or prior experience.

No, Off-Nadir Delta is designed for beginners who have never used satellite data before. The intuitive interface lets you explore satellite imagery by simply navigating the map, selecting dates, and adding layers. You can learn by exploring — no technical background required.

Create a free account, navigate to the map interface, and use the Satellite Images panel to search for imagery over your area of interest. Select a date range, choose a satellite (Sentinel-1, Sentinel-2, or NISAR), and add the imagery to your map. It takes just a few clicks to see satellite data.

Off-Nadir Delta works on all modern browsers including Google Chrome, Mozilla Firefox, Microsoft Edge, and Safari. For the best experience, we recommend using the latest version of Chrome or Firefox.

Yes, Off-Nadir Delta is responsive and works on tablets and smartphones. However, for the best experience with detailed satellite imagery analysis, we recommend using a desktop or laptop computer with a larger screen.

You can access Sentinel-1 C-Band SAR, Sentinel-2 Optical, NISAR/OPERA L-Band SAR, VIIRS Nighttime Lights (NASA Black Marble), and NASA FIRMS Active Fire hotspots. Sentinel-1 radar works through clouds day or night. Sentinel-2 provides 10m resolution multispectral imagery. NISAR L-Band penetrates deep into vegetation for forest monitoring. VIIRS shows nighttime artificial lighting patterns. FIRMS provides near real-time fire detection at 375m (VIIRS) and 1km (MODIS) resolution.

VIIRS (Visible Infrared Imaging Radiometer Suite) Nighttime Lights, also known as NASA Black Marble, captures artificial light emissions from Earth at night. The VNP46A2 product provides daily cloud-free composite imagery at approximately 500-meter resolution. It is valuable for monitoring urban electrification, assessing disaster impacts on power infrastructure, and analyzing economic activity patterns.

NASA FIRMS (Fire Information for Resource Management System) provides near real-time active fire hotspot data detected by thermal sensors on satellites. VIIRS sensors detect fires at 375m resolution with ~12-hour latency from three satellites (S-NPP, NOAA-20, NOAA-21). MODIS provides 1km resolution detections from Terra and Aqua satellites with records dating back to 2000. Off-Nadir Delta displays this data via NASA GIBS WMS — no API key needed, no token cost.

No. NASA FIRMS active fire data is displayed in Off-Nadir Delta via NASA GIBS (Global Imagery Browse Services) WMS, which is freely accessible without any API key, account registration, or authentication. Fire data also does not consume any of your tokens — it is completely free to view.

Each fire detection from FIRMS is assigned a confidence level. High (red dots) represents the most reliable detections with strong thermal anomaly. Nominal (orange) represents standard-confidence detections. Low (yellow) represents possible fires with lower certainty. For monitoring active wildfires, focus on High and Nominal confidence detections.

Sentinel-1 and Sentinel-2 satellites revisit the same location every 5-6 days on average. VIIRS Nighttime Lights provides daily composite imagery. Actual availability depends on your location and satellite orbit. When you search, you will see all available dates for your area.

Sentinel-2 optical imagery has 10-meter resolution for visible and near-infrared bands. Sentinel-1 SAR imagery has 10-20 meter resolution. NISAR/OPERA L-Band SAR has 30-meter resolution. VIIRS Nighttime Lights has approximately 500-meter resolution. NASA FIRMS Active Fire data has 375m resolution (VIIRS) and 1km (MODIS). These resolutions are suitable for monitoring land use changes, vegetation health, urban development, lighting patterns, and fire activity.

GRD (Ground Range Detected) is the standard Sentinel-1 product with basic processing. RTC (Radiometric Terrain Corrected) products are further processed to correct for terrain-induced distortions using a Digital Elevation Model, providing more accurate backscatter values especially in mountainous areas. Off-Nadir Delta provides access to RTC products via Microsoft Planetary Computer.

SAR is a type of radar imaging that actively sends microwave signals and measures the reflected energy. Unlike optical sensors that rely on sunlight, SAR can capture images day or night and through cloud cover. This makes it invaluable for monitoring areas with frequent cloud coverage or for emergency response situations.

C-Band SAR (Sentinel-1, 5.6cm wavelength) is sensitive to surface features and small vegetation like leaves and branches. L-Band SAR (NISAR, 24cm wavelength) penetrates deeper into forest canopy, reaching tree trunks and the ground. L-Band is ideal for biomass estimation, deforestation detection, and wetland mapping, while C-Band excels at flood detection and surface change monitoring.

VV (Vertical-Vertical) means the radar transmits and receives vertically polarized waves. VH (Vertical-Horizontal) means it transmits vertical and receives horizontal polarization. VV is more sensitive to surface roughness and soil moisture, while VH (cross-polarization) is useful for vegetation analysis and flood mapping since water has very low VH return.

Water surfaces appear very dark in SAR imagery because they reflect radar signals away from the sensor (specular reflection). Compare pre-flood and post-flood SAR images to identify newly flooded areas. VH polarization is particularly effective as flooded vegetation shows dramatically reduced backscatter. SAR can detect floods even through clouds.

Yes, ships appear as bright spots in SAR imagery due to their metal hulls causing strong radar reflection. The surrounding water appears dark, creating high contrast. Ship detection works day or night and through clouds. Off-Nadir Delta is useful for maritime monitoring and vessel tracking applications.

Speckle is a granular noise pattern inherent to SAR imagery caused by coherent interference of radar waves. It appears as a salt-and-pepper texture. Multi-looking (averaging multiple observations) reduces speckle but decreases resolution. The RTC products available in Off-Nadir Delta include multi-looking for reduced noise.

NDVI (Normalized Difference Vegetation Index) measures vegetation health using the formula (NIR - Red) / (NIR + Red). Values range from -1 to +1. Healthy vegetation shows values of 0.3-0.8, water is typically negative, and bare soil is near 0. In Off-Nadir Delta, select the NDVI visualization option when viewing Sentinel-2 imagery to see vegetation health.

Off-Nadir Delta supports multiple spectral indices including NDVI (vegetation health), EVI (Enhanced Vegetation Index for high-biomass areas), NDWI (water content), and custom band combinations. Select different visualization options in the layer settings to apply these indices.

Compare satellite imagery from different dates to detect forest cover changes. Use NDVI to highlight vegetation differences, or compare SAR backscatter changes. L-Band SAR (NISAR) is particularly effective for forest monitoring as it penetrates the canopy. Create time-series comparisons to track gradual deforestation over months or years.

False color composites display non-visible spectral bands (like near-infrared) as visible colors. The common NIR-Red-Green combination shows healthy vegetation as bright red, making it easy to distinguish vegetation types and identify stressed plants. In Off-Nadir Delta, select False Color visualization when viewing Sentinel-2 imagery.

Yes, Off-Nadir Delta is excellent for rapid disaster assessment. You can quickly view before-and-after imagery to assess flood extent, wildfire damage, earthquake impacts, and other natural disasters. NASA FIRMS Active Fire data provides near real-time wildfire hotspot detection. SAR imagery is particularly useful as it can capture images through smoke and clouds. Combine FIRMS fire hotspots with Sentinel-2 NBR for burn severity analysis.

Absolutely. With access to years of satellite archive data, you can compare imagery from different dates to track deforestation, urban expansion, coastline changes, glacier retreat, and seasonal vegetation patterns. The time-series analysis capabilities make it easy to visualize change.

Yes, Sentinel-2 imagery is widely used for agricultural applications. You can monitor crop health using vegetation indices, detect irrigation patterns, identify stressed crops, and track seasonal growing cycles. The regular revisit frequency allows you to follow crop development throughout the season.

Yes, VIIRS Nighttime Lights data correlates with economic activity and electrification. You can monitor urban growth over time, detect power outages after disasters, compare regional development levels, and analyze seasonal economic patterns. The data is updated daily and provides global coverage.

Tokens are consumed when you load satellite imagery tiles on the map. One token equals one tile request. The number of tokens used depends on the zoom level and the area covered. Higher zoom levels and larger areas consume more tokens. Your token balance is displayed in the interface, and you can purchase additional tokens as needed.

Yes, new users receive free tokens to explore the WebGIS and understand its capabilities. The free tier provides enough tokens to evaluate whether Off-Nadir Delta meets your needs before committing to a paid plan. No credit card is required to get started.

When your token balance is depleted, you will not be able to load new satellite imagery tiles. Previously loaded imagery remains visible. You can purchase additional tokens through the Billing page to continue using the service.

Tokens reset monthly based on your subscription plan. Unused tokens from the previous month do not roll over. This ensures fair usage and keeps the service sustainable. Check your Billing page to see your current token balance and reset date.

Off-Nadir Delta uses modern web technologies including OpenLayers for map visualization, STAC (SpatioTemporal Asset Catalog) for satellite data discovery, and Cloud Optimized GeoTIFF (COG) for efficient imagery streaming. Data is sourced from Copernicus (ESA) through AWS Earth Search and Microsoft Planetary Computer.

STAC is an open specification for describing geospatial data assets, enabling standardized search and discovery of satellite imagery. It provides a common language for metadata including spatial extent, temporal coverage, and available assets. Off-Nadir Delta uses STAC APIs from AWS Earth Search and Microsoft Planetary Computer to search and access satellite data.

COG is a GeoTIFF file format optimized for cloud-based access. It uses internal tiling and overviews to allow efficient partial reads over HTTP. This means you can view just the portion of the image you need without downloading the entire file. Off-Nadir Delta streams COG data directly from cloud storage for fast visualization.

Yes, Off-Nadir Delta supports uploading GeoTIFF, Cloud Optimized GeoTIFF (COG), and GeoJSON files. You can overlay your own raster and vector data on satellite imagery for custom analysis. Uploaded data is displayed as layers that can be combined with satellite imagery.

Export and download capabilities are available on select plans. You can export layers as GeoJSON for vector data. For satellite imagery, the WebGIS streams data directly from cloud sources to optimize performance and reduce storage requirements.

Yes, Off-Nadir Delta uses industry-standard security practices including encrypted connections (HTTPS), secure authentication, and data protection measures. Your account information and any custom layers you create are stored securely.