Band Combination: Thermal
This band offers a lower radiometric resolution and extended dynamic range, with a low saturation at high DN (Digital Number) values. It has an indistinct appearance as compared to other bands since the bands ground resolutions cell is 120m with a blocky appearance because the resample of the data is done in the 30-m format of the other bands. This means that the band has a half resolution as compared to other ETM bands.
The thermal band is regulated on-board by a dark-body cavity as an extremely emissive shutter and a hot target at the ambient temperature of the instrument. The data are conveyed as regulated top-of-atmosphere (at-sensor) radiances that are convertible to the equivalent brightness temperatures, per noise equivalent temperature variance.
Usage Of Thermal Band
Thermal band is an excellent tool for measuring the surface temperature. It is used by geologist for geological uses like differentiating clouds from light soils as the clouds are likely to be very cold. The Earth Observatory also uses its measurements to point out fire areas, land temperatures, or the volcanic flows which are mostly issued as grayscale images and occasionally layering the thermal features of interest over a grayscale or true-color image, mainly when there are fire or volcano cases.
The thermal band can also be used to measure plants heat stress and has a potential of being used for a field-based analysis, but it has no steady collection schedule and has a minimal archive. Its vicarious calibration offers an independent way of calculating on-orbit sensor routine by means of instrumented water bodies.
A thermal image recorded on a summer daytime, water bodies entails a lowest radiant temperature and urban areas and roads high radiant temperature. This is an essential component for the computation of the energy on the surface carried out to understand the evapotranspiration. It allows calculation of an entire energy balance of the surface which is used to estimate the consumption of water by the urban landscaping and agricultural irrigation with a more accurate estimate as compared to the shortwave data.