How to Monitor a Wildfire on Santa Rosa Island Using Satellite Imagery

Introduction

On May 15, 2026, a wildland fire ignited on Santa Rosa Island—the second-largest island in California’s Channel Islands National Park. By May 19, the fire had scorched approximately 16,600 acres, primarily through grassland, coastal sage scrub, and island chaparral. Satellite imagery, such as that captured by Landsat 9’s OLI (Operational Land Imager), offers a powerful tool to monitor remote wildfires in real time. This step-by-step guide teaches you how to use both natural-color and false-color satellite images to track active fires, assess burn extent, and interpret smoke patterns—using the Santa Rosa Island fire as a case study.

What You Need

• Access to Landsat 9 imagery – available free from the USGS EarthExplorer or NASA’s Earth Observatory archives (search for May 16, 2026, scene over Santa Rosa Island).
• Image processing software – such as QGIS, ArcGIS, or even web-based tools like NASA Worldview that can display false-color composites.
• Basic knowledge of spectral bands – understand that false color typically uses shortwave infrared (SWIR), near-infrared (NIR), and red bands to highlight fire and burn scars.
• Reference data – park boundary maps and pre-fire vegetation information to contextualize the burn.
• Time series capability – ability to compare images from different dates (e.g., May 16 and May 19) to see fire growth.

Step-by-Step Instructions

Step 1: Acquire Satellite Images of the Fire

Obtain Landsat 9 imagery for the Santa Rosa Island area from before, during, and after the fire. For this guide, focus on the May 16, 2026 image, which captured the fire when the burned area was 5,690 acres. Use the USGS EarthExplorer platform with coordinates approximately 34°N, 120°W, and filter for Landsat 9 Collection 2 Level-2 products. Download both the natural-color (bands 4,3,2) and false-color (bands 7,6,5 or similar SWIR-NIR combinations) datasets.

Step 2: Load the Imagery into Your Software

Import the downloaded GeoTIFF files into your chosen GIS or image display tool. For natural color, combine bands 4 (red), 3 (green), and 2 (blue) as RGB. For false color, combine bands 7 (SWIR2), 6 (SWIR1), and 5 (NIR) as RGB. This latter combination is excellent for detecting active fires and burn scars because SWIR bands sense thermal energy and pass through smoke.

Step 3: Interpret the Natural-Color Image

Open the natural-color composite first. The image will appear mostly brown, reflecting the dry summer vegetation of Santa Rosa Island. Look for a darker brown patch on the southeastern quadrant—this indicates the burned area. Gray-white smoke drifting southeastward over the dark blue Pacific Ocean highlights the active fire’s location and wind direction. Note that thick smoke can obscure the ground; in the May 16 image, smoke partly hides the burn scar edges.

Step 4: Interpret the False-Color Image

Switch to the false-color composite. Now the burned area appears as a distinct dark brown or black region, sharply contrasting with the lighter brown unburned vegetation. The active fire front is visible as a thin, bright orange line traversing the burned area. This orange line represents the flaming combustion zone, where SWIR reflectance is extremely high due to thermal emissions. The false-color view cuts through most smoke, giving you a clear picture of the fire perimeter.

Step 5: Delineate the Burn Scar

Using the false-color image, digitize the perimeter of the dark brown area using polygon tools in your software. On May 16, this area measured about 5,690 acres. Confirm this by calculating the polygon’s area (e.g., using the field calculator in QGIS). Compare with official figures from the National Park Service, which confirmed the fire by aerial reconnaissance on May 15. The burn scar includes grassland, coastal sage scrub, and island chaparral—all visible as different textures within the dark patch.

Step 6: Monitor Fire Progression Over Time

Acquire a second image from a later date, such as May 19, 2026, when the fire had grown to approximately 16,600 acres. Repeat steps 2–5 for this new image. Overlay the May 16 and May 19 burn scar polygons to visualize expansion. The southeastern quadrant of the island is almost entirely charred by May 19, and the perimeter remained uncontained. Use difference maps to quantify the acreage change (about 10,910 acres in three days) and identify areas of rapid spread.

Step 7: Correlate with On-the-Ground Reports

Satellite imagery is most powerful when combined with ground truth. The National Park Service closed Santa Rosa Island to the public during the fire. Use reports from park rangers and fire crews to verify your satellite-based observations. For example, the location of the active fire front (orange line in false color) should match incident command updates. This cross-validation improves accuracy for future fire monitoring.

Tips for Success

• Use multiple false-color band combinations – Experiment with different SWIR-NIR-red composites (e.g., 7,5,4) to enhance burn scar contrast. The 7,6,5 combination used here is standard but may vary by sensor.
• Consider resolution – Landsat 9’s 30-meter resolution is adequate for island-scale fires but might miss small spot fires; supplement with Sentinel-2 (10m) if available.
• Factor in atmospheric effects – Smoke and haze can reduce visible-light clarity; false color mitigates this, but still check for cloud shadows that may mimic burned areas.
• Time of day matters – Landsat 9 overpasses at ~10:30 AM local time; afternoon fires may appear more active in later satellite passes (e.g., from MODIS or VIIRS on polar orbiting satellites).
• Archive pre-fire imagery – Having a baseline image from the same season without fire helps distinguish burn scars from bare soil or natural dark features.
• Share your analysis – Publish your findings or share maps with agencies like the NPS to support fire management decisions. The Earth Observatory often features such citizen contributions.

By following these steps, you can effectively monitor wildfires like the one that charred Santa Rosa Island in May 2026. Satellite imagery not only aids real-time situational awareness but also provides a permanent record for ecological recovery studies. Happy analyzing!