Band Combination: Panchromatic
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 image can be gathered with a higher resolution since the spectral range gives 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 light 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 resulting image looks 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.
The production of the panchromatic images is done by satellites, for example, SPOT6/7 and Landsat’s kind of satellites. This single image’s band “blends” the visible blue, green and red bands information where it is formed using the total energy lighting the visible spectrum instead of it being partitioned into a different spectrum. It concentrates the intensity quantity per pixel which is then visualized in the greyscale image. The Information in each pixel is, therefore, directly related to the intensity of the solar radiation reflected by objects that are in that pixel and the sensor is detected by it. Because of the collected amount of the radiation per pixel, the sensors detect the brightness changes at the smaller spatial levels.
The panchromatic data is usually a representative of a range of wavelengths and bands, for example, the thermal infrared or visible, i.e., it combines different colors hence the name “pan” chromatic. This image is more of a combination of blue, green and red data in a measure of the reflectance. Some, however, can also include radiation at a longer wavelength than the red light, called “the near infrared” radiation.