Question:
Answer:
During Level1 Radiometric (L1R) product rendering, image pixels are converted to units of absolute radiance using 32bit floating point calculations. Pixel values are then multiplied by 100 and converted to 16bit integers prior to media output, preserving two digits of decimal precision. To convert the L1R image data back to radiance units, divide by 100.
Image artifacts such as banding, striping, and scancorrelated shifting are removed prior to radiometric correction, and these corrections are not reversible.
The L1R product geometry is identical to the input for Level0 reformatted (L0R) data.
During Level1 product rendering, image pixels are converted to units of absolute radiance using 32bit floating point calculations. Pixel values are then scaled to byte values prior to output.
The following general equation is used to convert Digital Numbers (DNs) in a Landsat Level1 product back to radiance (L):
L_{λ} = "gain" * QCAL + "bias"
which is also expressed as:
L_{λ} = ((LMAX_{λ}  LMIN_{λ})/(QCALMAXQCALMIN)) * (QCALQCALMIN) + LMIN_{λ }
Where:  L_{λ}  = Spectral Radiance at the sensor's aperture in watts/(meter squared * ster * µm) 

"gain"  = Rescaled gain (the data product "gain" contained in the Level1 product header or ancillary data record) in watts/(meter squared * ster * µm)  
"bias"  = Rescaled bias (the data product "offset" contained in the Level1 product header or ancillary data record ) in watts/(meter squared * ster * µm)  
QCAL  = the quantized calibrated pixel value in DN  
LMIN_{λ}  = the spectral radiance that is scaled to QCALMIN in watts/(meter squared * ster * µm)  
LMAX_{λ}  = the spectral radiance that is scaled to QCALMAX in watts/(meter squared * ster * µm)  
QCALMIN  = the minimum quantized calibrated pixel value (corresponding to LMIN_{λ}) in DN = 1 for LPGS products = 1 for NLAPS products processed after 4/4/2004 = 0 for NLAPS products processed before 4/5/2004 

QCALMAX  = the maximum quantized calibrated pixel value (corresponding to LMAX_{λ}) in DN = 255 
For information on the processing system (LPGS or NLAPS) used to produce a particular image, refer to the metadata file (_MTL.txt) provided with the data. The LMIN, LMAX, QCALMIN, and QCALMAX values can also be found in the metadata file.
For more information on calculating radiance, visit the following web pages:
Landsat 5 TM: Landsat 5 Thematic Mapper Thermal Band Calibration Update
Landsat 7 ETM+: Landsat 7 Data User Handbook
Landsat 8 OLI/TIRS: Landsat 8 Data Users Handbook