Hi, I have been computing solar zenith angle values (in the form of 2000x2200 arrays) and wish to save them using the ENVI_OUTPUT_TO_EXTERNAL_FORMAT command. This is the code I have at the current time: sza_16 = uint(sza*100) envi_write_envi_file, sza_16 , ns=ns, nl=nl, nb=1, pixel_size=[psizex,psizey], xstart=xstart, ystart=ystart, map_info = map_info, interleave=0, r_fid = out_fid_sza, data_type=12, out_dt=12, /in_memory out_file =outdir+'test.tif' ENVI_OUTPUT_TO_EXTERNAL_FORMAT, fid=out_fid_sza, out_name=out_file, pos=0, dims=dims, /tiff However, when I examine the 'test.tif' file that is saved I discover that rather than saving the data as a UINT type (data_type=12), it is saving it as byte format (data_type=1). Does anyone have any ideas what could be causing this? The actual sza array itself is definately a UINT (I checked it from the available bands list), so it is just the saving of the file that is causing problems. Cheers, Simon.