I have been thinking about calculating Actual albedo (Aa) with white sky albedo (Albedo_ws) and black sky albedo (Albedo_bs) retrieved from MODIS43 image for several days. As many of you may know, MODIS43 images have only Albedo_ws and Albedo_bs info, and we need additional value, fraction of diffuse light (Fdl), to calculate Aa. If these values are ready we can calculate Aa this way. Aa = Albedo_ws * Fdl + Albedo_bs * (1-Fdl) Fdl values are provided through the skyl_lut.dat table and the contents are as follows. 2 aerosol types 10 bands (7 MODIS bands + 3 broad bands (VIS, NIR, SW) 90 degrees (0-89 degrees with 1 degree step 50 optical depth ( 0-1 with 0.02 step) The table shown below is a part of skyl_lut.dat. I made this just for testing. ; Skyl_lut.dat00.dat Aerosol_type: Continental MODIS_Band_1: (0.620,0.670) S&O 0.00 0.02 0.04 0.06 0.08 0.10 0 0.029 0.042 0.055 0.067 0.079 0.091 1 0.029 0.042 0.055 0.067 0.079 0.091 2 0.029 0.042 0.055 0.067 0.079 0.091 3 0.029 0.042 0.055 0.067 0.079 0.091 4 0.029 0.042 0.055 0.067 0.079 0.092 MODIS_Band_2: (0.841,0.876) S&O 0.00 0.02 0.04 0.06 0.08 0.10 0 0.016 0.027 0.037 0.047 0.057 0.067 1 0.016 0.027 0.037 0.047 0.057 0.067 2 0.016 0.027 0.037 0.047 0.057 0.067 3 0.016 0.027 0.037 0.047 0.057 0.067 4 0.016 0.027 0.037 0.047 0.057 0.067 Aerosol_type: Maritime MODIS_Band_1: (0.620,0.670) S&O 0.00 0.02 0.04 0.06 0.08 0.10 0 0.029 0.046 0.063 0.080 0.096 0.112 1 0.029 0.046 0.063 0.080 0.096 0.112 2 0.029 0.046 0.063 0.080 0.096 0.112 3 0.029 0.046 0.063 0.080 0.096 0.113 4 0.029 0.047 0.064 0.080 0.097 0.113 MODIS_Band_2: (0.841, 0.876) S&O 0.00 0.02 0.04 0.06 0.08 0.10 0 0.016 0.035 0.054 0.072 0.089 0.106 1 0.016 0.035 0.054 0.072 0.089 0.106 2 0.016 0.035 0.054 0.072 0.089 0.106 3 0.016 0.035 0.054 0.072 0.089 0.106 4 0.016 0.035 0.054 0.072 0.089 0.107 I found a C code tell.skyl.c and I posted it several days ago. (No one replied (T.T)... Maybe the questions was too broad... I think. anyway) After I compiled it, I got tell_sky.exe and tested it with spawn statements like this. ------------------ pro test_spawn dir='C:\Documents and Settings\Yi\harry' cmd='tell_skyl.exe' option=' -od 0.2 -szn 30.0' cd, dir print, cmd+option spawn, cmd+option, result ----------------------- However, my knowledge on C is limited. I believe that trying with IDL is less time-consuming and simpler for me. Now¡¦ I am reading this table with structure in IDL, because this table has different format of data and I have a feeling that structure is the one of the best solutions to read this table. Therefore, I began this way S1 = {Fdl, solza, nb, AOT2, amt} ; where ; Fdl = Fraction of diffuse light ; solza = solar zenith angle: 90 degrees. À§ÀÇ µµÇ¥¿¡¼­´Â 5°³¸¸ (0~4) ; nb = band number: 10 wavelengths À§¿¡¼± 2°³¸¸ (band 1, 2) ; AOT2 = aerosol optical Thichness (depth) at 0.55 À§¿¡¼± 6°³¸¸ (0.00 ~ 0.10) ; amt = aerosol model type: 2 (continental/ maritime) what I want to do now is to read the Fdl values from Skyl_lut00.dat. If input variables are as follows, how can I get the Fdl values from Skyl_lut00? Fdlinput.txt ; solza, nb, AOT2, amt 30 10 0.04 continental 40 9 0.5 continental 55 5 0.4 continental 39 8 0.3 maritime 77 7 0.2 maritime Sorry everyone if I bothered you. Harry