# Development of the User Requirements for the Canadian WildFireSat Satellite Mission
## 3 Definition of the User Requirements
### Measurement Requirements
#### 3.2.2 VIS and NIR Requirements  
Although the VIS and NIR bands support contextual wildfire detection (e.g., [74]), their primary contribution is to cloud masking and false positive identification. These applications are less constraining on band selection and dynamic range than the secondary applications of these bands. Although post-fire mapping products are only of strategic value, the ability to map the burned area of a wildfire adjacent to its active portions is an integral part of FMF-3, which requires measurements in the VIS and NIR bands at a minimum (and ideally would include the short-wave IR, see Discussion). VIS and NIR bands are typically used for measures of vegetation \"greenness\" (e.g., Normalized Difference Vegetation Index; NDVI) to infer vegetation health metrics. Detection of sudden changes in these metrics can be attributed to vegetation disturbance such as wildfires (e.g., [79]). Although numerous systems are capable of mapping global burned area at a relatively fine scale (e.g., [80]), this capability is not typically available as an NRT product in conjunction with active-fire observations as required by FMF-3. Requirements for spectral bands were specified as VIS-red and NIR bands at a minimum. However, the goal band list includes all VIS spectral bands required for forestry observation (Table 5).  
Due to the unique overpass time (and consequently unique solar angles) it was not possible to infer dynamic ranges for these bands based off of other burned area mapping systems (which typically have late morning overpasses). To ensure the bands would cover the full dynamic range, a series of MODTRAN simulations were conducted. In these simulations it was assumed that the VIS and NIR bands are expected to be used for imaging surface reflectances during the late afternoon period over the boreal forest. Solar radiation was modeled using a mid-latitude summer atmosphere, with 407 ppmv CO\({}_{2}\), for a central location in the Canadian landmass (\(\sim\) latitude 58.0\({}^{\circ}\), longitude 101.0\({}^{\circ}\)), at 18:00 local time. Typical boreal forest albedos range from 0.1 to 0.25, while burn scar albedos (\(\sim\)0.05) represent the minimum reflectance of interest, and maximum scene reflectances of \(\sim\)0.9 are expected from clouds. The threshold VIS and NIR dynamic ranges were defined as those required to observe burned areas up to the peak reflectance of boreal forest, while the goal requirements are defined to include cloud measurements within this range (Table 5).  
The objective of burned area mapping with this system is to provide a product suitable for complimenting active-fire detection in FMF-3, not to replace robust techniques used in regional and global carbon accounting (e.g., [81; 82; 83; 84]). With this in mind, fine spatial resolution is not necessary and requirements are relaxed to reduce the volume of data to facilitate NRT calculation. However, as is commonplace in existing systems (e.g., [74; 75]), it was deemed desirable to maintain finer scale  
Figure 3: Simulated Infrared (IR) band saturation temperatures as a function of pixel spatial resolution and sub-pixel wildfire area. This simulation assumes a flame front depth of 50 m with mean temperature of 900 K extending diagonally across the pixel. Sub-pixel wildfire area was computed and the saturation temperatures were defined based on the peak pixel brightness temperatures (BT) at a given spatial resolution (Table 5). The saturation temperatures change with spatial resolution in both the LWIR and MWIR, e.g., at 250 m the MWIR and LWIR saturation temperatures are \(\sim\)690 and \(\sim\)540 K, respectively, while at 500 m the MWIR and LWIR saturation temperatures are \(\sim\)610 and \(\sim\)440 K, respectively. No atmospheric effects on the signal are included in this simulation.  
measurements in the VIS and NIR as compared to the MWIR and LWIR to improve sub-pixel context for cloud masking and resolving cross band misalignments.