Radiometric Calibration
The radiometric calibration of the MMRS image consist in the conversion of the digital values or digital counts (DN) to radiance values Lk, applying for each band the following equation:
where:
k: band (k: 1, 2, 3, 4, 5)
DNmax: maximum digital value (254)
Lkmax: radiance corresponding to DNk
= DNmax, for k: 1,2,3,4,5
Lkmin: radiance corresponding to DNk
= 0, for k: 1,2,3,4,5
Values for maximum and minimum radiance, Lmax and Lmin, have been adjusted since launch by mean of cross-calibration techniques with quasi-simultaneous information obtained from Landsat 7 satellite. These values are detailed in the following table:
|
Radiance[mW/sr
cm2] |
Band 1 |
Band 2 |
Band 3 |
Band 4 |
Band 5 | |
|
Since 1/3/2001 |
Lmax |
0.3144923 |
0.5804151 |
1.3410108 |
0.748974 |
0.29013505 |
|
Lmin |
-0.0021441 |
-0.0054613 |
-0.013114 |
-0.0056346 |
-0.0054989 | |
|
Since 1/6/2002 |
Lmax |
0.29706451 |
0.55411993 |
1.24914382 |
0.75416343 |
0.29824818 |
|
Lmin |
-0.00771011 |
-0.00297874 |
-0.00760405 |
-0.00707665 |
-0.01044926 | |
Reflectance calculation
at sensor level
Reflectance measured by the sensor at the top of the atmosphere (rksen), for each band, is given by the following equation:
where:
Lk [mW/sr cm2]: radiance measured by the sensor, for band (k: 1, 2, 3, 4, 5)
q 0: zenith solar angle
: Effective exoatmospheric solar
irradiance, corrected by astronomical day and calculated from:
where:
dj: day of the year or Julian Day.
Values of the effective exoatmospheric solar irradiance are showed in the following table:
|
Exoatmospheric
solar irradiance [mW/cm2] | ||||
|
Band 1 |
Band 2 |
Band 3 |
Band 4 |
Band 5 |
|
3.73548285 |
3.59676353 |
9.11480917 |
3.79003169 |
2.67703979 |
