Sentinel-2 includes three bands in the red-edge region (705, 740, and 783 nm). What is the primary purpose of these red-edge bands?
ATo improve the aesthetic quality of true-color images
BTo capture the steep increase in vegetation reflectance between red absorption and NIR reflection, enabling finer discrimination of vegetation health
CTo detect thermal emissions from volcanic regions
DTo penetrate cloud cover more effectively than standard visible bands
The red edge (680-750 nm) is where vegetation reflectance transitions sharply from low (chlorophyll absorption) to high (mesophyll scattering). Three bands sampling this transition enable detection of subtle vegetation condition changes that broad red and NIR bands would miss.
Question 2 True / False
A multispectral image with 4 bands (blue, green, red, NIR) contains only 4 independent pieces of information per pixel.
TTrue
FFalse
Answer: False
While there are 4 measured values per pixel, band ratios, normalized differences, and other indices create derived information. NDVI isolates vegetation signal from soil background. Band ratios suppress illumination variation. The information content exceeds the raw band count because it includes relationships between bands.
Question 3 Short Answer
Why does Landsat include a shortwave infrared (SWIR) band around 1.6 micrometers in addition to visible and NIR bands?
Think about your answer, then reveal below.
Model answer: The 1.6 um SWIR band is sensitive to moisture content because water strongly absorbs at this wavelength. It also reveals clay mineral absorption features useful for geological mapping. For snow/cloud discrimination, snow absorbs at 1.6 um while clouds reflect, allowing automated separation. These capabilities complement visible/NIR bands, which are insensitive to moisture and mineral composition.
Each spectral band targets specific physical properties. SWIR adds moisture and mineral sensitivity that visible/NIR bands lack.