I intend to assess deforestation and forest degradation for a study area?

1. Do i need to perform or convert DN to radiance to reflectance and use its resulting image for Land use/land cover assessment using either supervised/unsupervised classification approach to evaluate Land use change and deforestation.

2. Forest degradation.; i wish to convert DN to Radiance to Reflectance using ENVI, if i use ENVI, can i export the image to ArcMap to perform NDVI using Raster calculator or NDVI function in ArcMap and the pixel value exporting image will not has error

3. Can i also export the image from ENVI and use it in ERDAS IMAGINE fro LULC classification, because i experience that , anytime i open the image exported from ENVI to ArcMap, the report is always that , the data has no compute statics and i should use utilities to compute the statistic