Landsat Missions
Question:
How is radiance calculated?
Answer:
Please note: Level 0R and Level 1R processing is no longer available for standard products through the USGS EROS. Level 1G products will only become available if a standard Level 1T terrain corrected product cannot be processed. The information below explains where values are derived during processing. For information on current product availability, please visit http://landsat.usgs.gov/products_data_at_no_charge.php
During Level 1 Radiometric (L1R) product rendering, image pixels are converted to units of absolute radiance using 32-bit floating point calculations. Pixel values are then multiplied by 100 and converted to 16-bit 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 scan-correlated shifting are removed prior to radiometric correction, and these corrections are not reversible.
The L1R product geometry is identical to the input for Level 0 reformatted (L0R) data.
During Level 1 Geometric (L1G-Systematic) product rendering, image pixels are converted to units of absolute radiance using 32-bit 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 L1T, L1Gt or L1G product back to radiance (L):
Lλ = "gain" * QCAL + "bias"
which is also expressed as:
Lλ = ((LMAXλ - LMINλ)/(QCALMAX-QCALMIN)) * (QCAL-QCALMIN) + LMINλ
| where: | Lλ | = Spectral Radiance at the sensor's aperture in watts/(meter squared * ster * µm) |
|---|---|---|
| "gain" | = Rescaled gain (the data product "gain" contained in the Level 1 product header or ancillary data record) in watts/(meter squared * ster * µm) |
|
| "bias" | = Rescaled bias (the data product "offset" contained in the Level 1 product header or ancillary data record ) in watts/(meter squared * ster * µm) |
|
| QCAL | = the quantized calibrated pixel value in DN | |
| LMINλ | = the spectral radiance that is scaled to QCALMIN in watts/(meter squared * ster * µm) |
|
| LMAXλ | = the spectral radiance that is scaled to QCALMAX in watts/(meter squared * ster * µm) |
|
| QCALMIN | = the minimum quantized calibrated pixel value (corresponding to LMINλ) 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 LMAXλ) 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 how to calculate radiance for Landsat 5 TM data, refer to:
http://landsat.usgs.gov/documents/2007_Barsi_L5TMB6_IEEE.pdf
For more information on how to calculate radiance for Landsat 7 ETM+ data, refer to Section 11.3.1 of the Landsat 7 Science Data User Handbook.
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://landsat.usgs.gov
Page Contact Information: Ask Landsat
Page Last Modified: 04/13/11 02:42 pm
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