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Using the USGS Landsat Level-1 Data Product

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Landsat 1-8 Level-1 data products consist of quantized and calibrated scaled Digital Numbers (DN) representing the multispectral image data. Landsat 8 products combine data acquired by both the Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS), and are delivered in 16-bit unsigned integer format. Landsat 1-7 products are generated from single sensor data and are delivered in 8-bit unsigned integer format.

Landsat Level-1 data can be rescaled to the top of atmosphere (TOA) reflectance and/or radiance using radiometric rescaling coefficients provided in the metadata file (MTL.txt) that is delivered with the Level-1 product. The MTL file also contains the thermal constants needed to convert thermal band data to TOA brightness temperature (BT). Formulas for these coversions are provided below.

Specific to Landsat 8, the satellite’s two thermal bands were designed to allow the use of split-window algorithms for applications such as atmospheric correction and retrieval of surface temperature values. Since the satellite’s launch in 2013, however, energy from outside the normal field of view (stray light) has affected the thermal data collected by both thermal bands. The amount of stray light varies throughout each scene, depending upon radiance outside the instrument field of view. The stray light correction applied to Landsat 8 Collection 1 Level-1 data substantially improves image uniformity and absolute calibration in typical scenes. However, additional work is underway to assess whether this correction is adequate for use with the split-window techniques. Until that work is complete, it is not recommended that Band 11 be used for the split-window technique. The Landsat 8 Data User Handbook Appendix A provides more details about Landsat 8 TIRS stray light.

Conversion to TOA Radiance

Landsat Level-1 data can be converted to TOA spectral radiance using the radiance rescaling factors in the MTL file:

Lλ = MLQcal + AL 

where:
Lλ  TOA spectral radiance (Watts/( m2 * srad * μm))
M = Band-specific multiplicative rescaling factor from the metadata (RADIANCE_MULT_BAND_x, where x is the band number)
AL = Band-specific additive rescaling factor from the metadata (RADIANCE_ADD_BAND_x, where x is the band number)
Qcal  =   Quantized and calibrated standard product pixel values (DN)         

 

Conversion to TOA Reflectance

Reflective band DN’s can be converted to TOA reflectance using the rescaling coefficients in the MTL file:  

ρλ' = MρQcal + Aρ 

where:
ρλ'    TOA planetary reflectance, without correction for solar angle.  Note that ρλ' does not contain a correction for the sun angle.
Mρ = Band-specific multiplicative rescaling factor from the metadata (REFLECTANCE_MULT_BAND_x, where x is the band number)
Aρ   = Band-specific additive rescaling factor from the metadata (REFLECTANCE_ADD_BAND_x, where x is the band number)
Qcal  =   Quantized and calibrated standard product pixel values (DN)
     
TOA reflectance with a correction for the sun angle is then:
  Landsat TOA reflectance with correction for sun angle
where:
ρλ =   TOA planetary reflectance
θSE  =   Local sun elevation angle. The scene center sun elevation angle in degrees is provided in the metadata (SUN_ELEVATION).
θSZ  = Local solar zenith angle;  θSZ = 90° - θSE

 

For more accurate reflectance calculations, per-pixel solar angles could be used instead of the scene center solar angle. While per-pixel solar zenith angles are not provided with the Landsat Level-1 products, tools are provided which allow users to create angle bands.

 

Conversion to Top of Atmosphere Brightness Temperature

Thermal band data can be converted from spectral radiance to top of atmosphere brightness temperature using the thermal constants in the MTL file:
Conversion to Top of Atmosphere Brightness Temperature
where: 
T   =   Top of atmosphere brightness temperature (K)where:
Lλ   = TOA spectral radiance (Watts/( m2 * srad * μm))
K1    = Band-specific thermal conversion constant from the metadata (K1_CONSTANT_BAND_x, where x is the thermal band number)
K2   = Band-specific thermal conversion constant from the metadata (K2_CONSTANT_BAND_x, where x is the thermal band number)

 

 

 

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Landsat represents the world's longest continuously acquired collection of space-based moderate-resolution land remote sensing data. Four decades of imagery provides a unique resource for those who work in agriculture, geology, forestry, regional planning, education, mapping, and global change research. Landsat images are also invaluable for emergency response and disaster relief.

 

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