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Landsat-9

Landsat-9 panchromatic and multispectral EO data products are calibrated using the Optical Products Calibration (OPT-Calib) service. The process applied is the same for PAN and MS acquisitions.

Image-001

Figure 1 - True Color composite derived from Landsat-9 OLI L1TP calibrated data acquired on 14/07/2022 over the Gambia river estuary in Gambia. Credits: USGS.

Input

The input is an ingested Landsat-9, find details here.

DN to Reflectance

Reflective band DN’s are converted to TOA reflectance using the rescaling coefficients in the MTL file1:

\[ R(b)′= M_b \times DN + A_b \]

where:

\(R(b)'\) is the Top of Atmosphere planetary reflectance, without correction for solar angle.

Note that \(R(b)'\) does not contain a correction for the sun angle.

  • \(M_b\) is the band-specific multiplicative rescaling factor from the metadata (REFLECTANCE_MULT_BAND_x, where x is the band number)

  • \(A_b\) is the band-specific additive rescaling factor from the metadata (REFLECTANCE_ADD_BAND_x, where x is the band number)

Top of Atmosphere reflectance with a correction for the sun angle is then:

\[ R(b) = R(b)' \times cos(θ_{SZ}) = R(b)' \times sin(θ_{SE}) \]

where:

  • \(R(b)\) is the TOA planetary reflectance

  • \(θ_{SE}\) is the local sun elevation angle. The scene center sun elevation angle in degrees is provided in the metadata (SUN_ELEVATION).

  • \(θ_{SZ}\) is the local solar zenith angle; \(θ_{SZ} = 90° - θ_{SE}\)

Output

The output is a STAC item GeoJSON2 having a similar structure to the Landsat-8 one available here.

  1. USGS, Using the USGS Landsat Level-1 Data Product, available at: https://www.usgs.gov. ↩

  2. Radiant Earth Foundation, STAC item specifications, a single spatiotemporal asset as a GeoJSON feature plus datetime and links, available at:https://github.com. ↩