Landsat 8 NIR Relative Scatter Adjustment
An NIR relative scatter adjustment was made to values in the Relative Scatter Lookup Table based on a wildland shrub fuel moisture content (FMC) predictive model developed here from Landsat 8 NDWI ([Band 5 - Band 6] / [Band 5 + Band 6]). NDWI is highly positively correlated to shrub FMC. While developing the model, relative NIR scatter based on the red band was applied. Applying the NIR relative scatter from Relative Scatter Table resulted in the average June 22, 2016, NDWI value being slightly less than the average July 8, 2016, value for the exact same pixels, which should not be the case. The adjustment made, was to apply half of the NIR relative scatter (NIR/2). This adjustment corrected the relationship by deriving an average NDWI value for June 22 that is 0.0054 more than the average for the exact same pixels for the July 8 date. The graphs below represent locations near the center of the model development area and shows that FMC decreases well before to well after the June 22 date and provide substantial evidence that NDWI values for June 22nd should be higher than for July 8. (Graphs are publicly available by the United States Forest Service Wildland Fire Assessment System [USFS-WFAS] at: http://www.wfas.net/index.php/national-fuel-moisture-database-moisture-drought-103.) The date represented on the graph line is directly above the center of the date listed on the axis.
