We produce two types of results from NIR imagery that you submit to us depending on the capabilities of your camera and how you have calibrated it. Each has their advantages and disadvantages.
Absolutely Calibrated Images = NDVI:
If you have a supported camera that comes with an upward looking sunshine sensor, a calibration panel AND you have calibrated the camera according to the manufacturer’s instructions, (usually this means you have included an image of the calibration panel in the images you have provided us), we will produce an absolutely calibrated image of that field. That means that a color in that image always corresponds to the same reflectance value. This enables you to compare across fields and across time periods. The calibrated image is called an NDVI which stands for ’Normalized Difference Vegetation Index’.
Relative Calibration = CIR
If you are flying with a camera that does not meet the requirements above, we produce an image where the coloring is relative to that field. Specifically, the lowest areas of plant reflectivity in THAT FIELD are set to the lowest end of the color scale (black and red in our case) and the areas with most plat reflectivity are set to the highest end of the color scale (green in our case). To differentiate from the absolutely calibrated NDVI we call this a CIR image (for color infra-red).
One of the advantages of a CIR is that it emphasizes areas on the field that are underperforming and makes them very clear. This disadvantage is that you can’t take a CIR from one field and compare it to a CIR on another field.
Bottom line: the uncalibrated CIR highlights the extremes of a crop's health but the values are relative to that field and time. The NDVI is absolutely calibrated and can be compared across fields and times.
The Case Studies page has some notable examples of applications of CIR and NDVI.