MAPIR Camera Reflectance Calibration Ground Target Package
This package contains 3 ground targets that each have known reflectance curves. The target material has a matte texture with near lambertian reflectance properties, so it does not matter where the sun is in the sky. Before each flight you take a photo using each camera of the entire open package with the targets facing straight up (though no shadows on the entire white target area). You would then use these images in our post processing software to calibrate the index image pixel values. This will further improve the normalization of your surveys over time and allow you to capture images on days that are not perfectly clear.
The material we are using for our reflectance targets is brand new to the market and something we designed custom in order to bring superior results at an affordable cost. Our targets are durable, diffuse, easily reproducible (consistent results from batch to batch) and highly lambertian. They will not fade, peel or change over time, and are highly scratch-resistant. The base substrate is durable processed glass with the coating evaporated in high vacuum. Measurements were made using multiple Shimadzu spectrophotometers incorporating an integrating sphere.
Using our MAPIR plugin for the Fiji (ImageJ) software you can select the photo of this target taken before your survey, the QR code will be auto-detected and the reflectance value of each target will be calculated and applied to each of your images. The resulting individual images will then be calibrated and you can generate your ortho-mosaic in the software of your choosing. Using a rastor/index calculator for the desired index (for example NDVI) will properly compute the calibrated indice values.
Note: We use this same package to create the default values in the Calibration step of our Fiji plugin. While the base calibration works well for perfectly clear sunny days, in order to fully normalize your surveys we recommend using this ground target package each flight.