Landsat TM的辐射定标

1.Conversion of DN values to Absolute Radiance

The per-band sensitivity of the instrument is set by adjusting the gain to conditions expected for that time of year. Bands 1, 2 and 3 are set to high or low gain as a group. Gain settings for bands 5 and 7 are set similarly. Band 6 acquired in both high and low gain mode, while bands 4 and 8 are set individually according to land surface brightness conditions. Band gains are set on a month by month basis. The DN values of each Landsat image band were scaled from the absolute radiance measure to byte values prior to media output using the gain and bias (offset) values given for each band. The DN values can be converted back to the radiance units using the following equation:

Radiance = gain*DN + offset

Which can also be expressed as

Radiance = ((LMAX-LMIN)/(QCALMAX-QCALMIN))*(QCAL-QCALMIN) + LMIN

or L=(Lmax-Lmin)/(QCALmax-QCALmin)*(DN-QCALmin)+Lmin

Where:

QCALMIN=0

QCALMAX=255

QCAL=Digital Number

2.radiance---->reflectance at top of atmosphere（大气上层的反射率）

reflectance=L*3.14*d^2/[ESUN*cos(sza)]

note:
Lmin = minimum radiance
Lmax = maximum radiance
QCALmax = maximum DN value possible (=255)
QCALmin = minimum DN value possible ( = 0 or 1)
d:Earth-Sun Distance (AU)
sza:Solar Zenith Angle (deg)
ESUN = Band dependent Exoatmospheric Irradiance