The Earth atmosphere is opaque over large regions of infrared light due to absorption by water and carbon dioxide. There are however certain windows with minimal absorption that allow the detection of infrared emission from the Earth surface in space. FUEGO GEO will use observations in two of these windows.
The FUEGO instrument is a telescope operating in the infrared and recording images at 3.8-3.99 µm band (MWIR) for the detection of fires, and in the 8.95-9.2 µm band (LWIR) serving as an emissivity reference for the distinction between fires and reflected sunlight. Additionally, a standard visible camera (RGB) will support the geolocation of fires and the identification of clouds. The important design specifications are shown in the table.
| Parameter | Value |
|---|---|
| Wavelengths | 3.8-3.99 µm (MWIR), 8.95-9.125 µm (LWIR), 400-700 nm (RGB) |
| Mode of Continental Coverage | 6 Steps with 10 second stare at each, 3 steps West to East across the Southern tier, 3 steps East to West across the Northern Tier Image revisit time 60 seconds. |
| Mapped Data | Latency less than 2 minutes (with Human in the Loop Vetting included) |
| Field of view (each step) | 40.96 milliradians (2.35 degrees) |
| Number of pixels | 8192×8192 10 micron pixels for IR wavebands, IFOV = 5.0 microradians |
| Ground sample distance | 183 meters E-W, 222 meters N-S at 40 degrees latitude. Square Root of Area 202 meters. |
| Smallest detectable fire | 200 kilowatts (area approximately 4 square meters at 727⁰ C [1340⁰F]). Spot fires close to main fire may need to be 500 kW to be separated. |
| Spot Fire geo-location | ± 11 meters (98% certainty) |
| Fire Perimeters | ± 30 meters (expected placement accuracy). Maps will depict radiated power, direction and rate of spread (vector). |
| Basemaps types | Topographic, Air Photo, Infrastructure, Fuel type & moisture |
A point design for the FUEGO instrument fulfils most of the requirements. The system is diffraction limited for all relevant IR wavelengths. It covers the desired FOV of 2.35 degrees (40.96 milliradians) by staring with a 8K FPA. A 10 um pixel subtends 2.25 arcsec. A solar VIS blocking filter is upstream of the other optics. This system has a focal length of 917 mm and f/4.1 optics. The FOV is 2.35×2.35 degrees (40.96×40.96 milliradians). The beam splitter and MWIR & LWIR FPAs are located in a cold enclosure that is separated from the system by a window. The steering mirror can shift the scene to avoid bad pixels.