Radiometric Correction of Landsat Data
January 15, 2004
Typically, when one acquires remotely-sensed data for academic or commercial purposes it is unsuitable for immediate use. That is, several types of corrections must be applied. One set of corrections that is crucial to the use of remotely-sensed data, particularly in quantitative geography, is known as radiometric correction. Though there are many classes of radiometric corrections, this paper will focus on the following three: sensor related corrections, earth-sun distance correction and solar zenith angle corrections, and atmospheric corrections. Sensor related effects refer to sensor-specific changes in the data when a remote sensor converts the incoming radiance to digital numbers. Earth-sun distance corrections account for differences in illumination due to the varying distance of the earth from the sun. Similarly, solar zenith angle corrections account for illumination differences due to variations in the apparent position of the sun relative to the earth.
Finally, atmospheric corrections adjust the attenuating and/or scattering effects of the earth's atmosphere on electromagnetic radiation. We will see through example exactly what these corrections do and why they are necessary vis-Ã -vis their application to remotely-sensed data of the city of Ottawa, Canada.
The aim of this study is to achieve an understanding of the principles of the radiometric corrections described above and assess their effect(s) on satellite images as well as data derived from said images, such as vegetation indices and spectral signatures. The data used in this exercise consists of six images of Ottowa, Canada obtained from Landsat TM 5 bands 1-5 and 7.
The purpose of this section of the study is see how at-satellite spectral reflectance varies with changes in the distance between the earth and the sun and the position of the sun relative to the earth.