High Resolution Satellite Imagery Bands
Multi-spectral imagery bands; Why so many? Years ago, when satellite imagery first came to market, there were only three natural color bands that consisted of red, green and blue. As time and technology advanced, the industry has benefited from more bands being added to each new sensor. With the launch of the newest satellite, WorldView-3, we now have access to a combination of 28 imaging bands. With each new band added to a sensor, imagery has become more useful in making scientific classifications about different aspects of the image that was captured. So, for now, there are as many as 28 bands available, but what are they actually used for?
DigitalGlobe has made many of the advances in band development and deployment. Until the release of WorldView-2 in October of 2009, the main 8 VNIR bands were not collectively available to the commercial sector. The 28 bands currently available from WorldView-3 are grouped together as 8 VNIR, 8 SWIR, and 12 CAVIS. The VNIR or ‘Very Near-InfraRed’ bundle of bands includes blue, coastal blue, green, red, red edge, yellow, near-infrared 1, and near-infrared 2, then there is SWIR or ‘Short Wave Infra-Red’ bands, and CAVIS or ‘Cloud, Aerosol, Vapor, Ice, and Snow.’ By isolating a single band or a group of bands, an analyst is able to view the imagery in a whole new way.
When WorldView-2 was released with 8 bands, visible in the near-infrared spectrum, specific features of a landscape were able to be identified by singling out a certain band or group of bands. The ‘coastal blue,’ for example, is absorbed by water at a lower frequency than any other band, so it can therefore be useful in bathymetric studies, as well as vegetative analysis because it is absorbed more readily by the chlorophyll in plants. When the ‘green’ and ‘yellow’ bands are used together, observers can differentiate between types of plant material. The ability to classify plants or tell which areas of a crop are healthier than others just by looking at a satellite image gives the agricultural industry a major leg up on their competition and the capability to work certain areas of a field without having to send employees out on foot.
With the launch of WorldView-3, CAVIS and SWIR were available together for the first time. The 8 SWIR bands are used to penetrate haze, fog, dust, and smoke in the atmosphere. This grouping of bands can be very useful to emergency response teams immediately after a natural disaster when recovery crews need the clearest image possible. This can be accomplished by using the SWIR bands to view what direction a forest fire is traveling through the smoke or find a group of lost hikers in a very foggy area of land, just to name a few of their many uses. The CAVIS bands are used in a similar manner by mapping clouds, ice and snow, and correcting for aerosols and water vapor that may be in the air.
Satellite imagery’s ability to collect very large areas in a timely manner and the capacity to isolate groupings of imagery bands, permits analysts to quickly and accurately identify important areas of interest. Today, satellites from around the world are orbiting our planet, capturing imagery every second of every day. These multi-spectral high resolution images can now be used for everything from beautiful wall murals to monitoring crops on a global basis and aiding before/during/after a natural disaster. No project is too big or too small and eMap is here to help you get the right imagery product for your project, whatever that may be.