"A panchromatic band (black and white band) is one band that usually contains a couple of hundred nanometers bandwidth. The bandwidth enables it to hold a high signal-noise, making the panchromatic data available at a high spatial resolution. This images can be gathered with a higher resolution since the spectral range give the smaller detectors allowance to be utilized while sustaining the high signal-noise ratio.
This capability allows the smaller portion to be seen and still acquire strong signals. Therefore the Panchromatic usually resembles a wide band that has a lower spatial resolution (mostly a half less than the multispectral band) that the exploration of the imagery details.
The Panchromatic image is made when the imaging sensor becomes sensitive to a huge amount of lights wavelengths, normally straddling a big spectrum visible part. The sensor is a channel detector that is sensitive to radiation within the range of the broad wavelength. If there is a coincidence of the visible range with the wavelength range, then the image resulting look like a "black-and-white" photo from space. The physical quantity measured is the apparent target brightness, and therefore the “color" of the targets or spectral information is lost. This shows that it allows all colors, which means that the band contains a wide range signal." (EOS Data Analytics Inc., 2019)