Unanswered questions

I want to calculate the radiance (unit: W⋅m^-2⋅m^-1⋅sr^-1) from Superdove reflectance data. How to achieve this goal? Or the reflectance is calculated by radiance? Then how could I get the radiance data? 

I tried to download Planet Scope 8 bands surface reflectance, but when I put the order always returns me a UDM image, I follow the instructions but I am just reciving the same kind of image, an UDM file