<p>Whether your data is spaceborn, airborne, or ground measurements, you will need to find out the appropriate equations and coefficients to convert data DN values to radiance. These should be available from your data provider since the equations to use are not all the same. Most use some form of: </p>
<p>Radiance (of some unit, often W/(m^2*sr*um)) = DN * gain + offset </p>
<p>but some require you incorporate the band pass and some are just simple scale factors that you apply to the DN.</p>
<p>Once you have radiance, then you can convert it to reflectance using a standard equation, unless your data provider gives you simple scale factors to apply directly to the DN that convert to reflectance (such is the case with Landsat-8 data). These equations are discussed in the ENVI Help under <a href="http://file:///C:/Program%20Files/Exelis/ENVI53/help/Content/PreprocessImagery/PreprocessImagery.htm" target="_blank" rel="nofollow">Preprocessing</a> > <a href="file:///C:/Program%20Files/Exelis/ENVI53/help/Content/PreprocessImagery/RadiometricCorrectionTools.htm" class="MCBreadcrumbsLink">Radiometric Correction Tools</a> > Radiometric Calibration. Your data provider should be able to provide you some of the parameters for this such as solar irradiance and elevation.</p>
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