This resource (http://earth.esa.int/pub/ESA_DOC/land...) describes how can I convert DN to radiance and reflectance value. How then associate each value of radiance and reflectance with the wavelength, like this graphics (http://www.exelisvis.com/Home/NewsUpd...). Is there a mathematical expression or function is expressed the radiance or reflectance through wavelength. How can I get an array or object pair such as {reflectance;wavelengths} in IDL. I have a multispectral image GeoTiff format (Landsat 4/5, 7 channels). Is there any way to get a pair of values ??reflectance / wavelength using ENVI IDL or maybe other tools. Image resolution of about 8000x7000 pixels. For each point with the DN-value, accordinghttp://earth.esa.int/pub/ESA_DOC/land..., I calculated the reflectance, and then, how to associate each reflectance value to its wavelength? I found just such an example http://www.exelisvis.com/docs/envi_ap..., it is suitable for my data. Thanks.