What is Shortwave Infrared(SWIR) Imagery?
SWIR refers to a non-visible range of light falling between about 1400 and 3000 nanometers in wavelength, outside of the visible range. Due to the unique properties of minerals, man-made material, and other features, SWIR imagery can “see” objects in a way that is invisible to the naked eye and VNIR sensors.
Collecting satellite images in SWIR wavelength has a lot of advantage, such as plant stress condition, soil mineral health, building material condition atmospheric transparency etc. The real data which is used in the analysis of any object can be obtained via SWIR imagery.
NASA has installed SWIR and NIR imagery equipment in the satellites to monitor the plant health of the earth. The Precision Agriculture focuses on the these type of technologies to obtain the images to analyze the crop health. This article by David Herring shows a plethora of options for farmers to build an efficient and economical system. Using the SWIR and NIR images a wide variety of information can be extracted from just images.
Gauging the relative moisture content of leaves helps assess crop health and quality. By selectively imaging at the wavelengths of strongest absorbance for water, items with higher water composition will appear darker than drier tissues.
The bottom portion of the ear on the right is much darker in the area that the visible image shows damage, indicating a pooling of moisture characteristic of bruising. Such bruises can be seen under the skin of fruits that are passing by on an inspection line while they are invisible to the eye. Though perfectly suitable for many processed foods, bruises are not acceptable in fresh produce for retail purchase. The SWIR camera permits sorting high value produce away from the lower grade fruit prior to processing.