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Pleaides

Pleaides acquisitions are calibrated using the Orfeo Toolbox [RW-01].

DN to Radiance

The Pleaides user guide [RW-02] provides the formula below to convert the DN into radiance:

\[ L_{(b)} = {DN_{(b)} \over rescale gain_{(b)}} + rescale bias_{(b)} \]

For the conversion from \(DN\) (for Digital Numbers) to spectral radiance (or ‘TOA radiance’) \(L \), the following formula is used :

\[ L_\lambda = gain \times DN + offset \]

As such, the calibration uses:

\[ gain_{(b)} = {1 \over rescale gain_{(b)}} \]

and

\[ offset_{(b)} = rescale bias_{(b)} \]

\(L \) in \(W/m^2/steradians/micrometers\) with \(b\) being a band ID.

Radiance to Reflectance

To convert TOA radiance to TOA reflectance, the following formula is used :

\[ R(b) = { {\pi \times L(b) \times d \times d} \over {ESUN(b) \times cos(θ)} } \]

where :

  • \(L(b)\) is the spectral radiance for band b

  • \(pi\) is the famous mathematical constant

  • \(d\) is the earth-sun distance (in astronomical units) and depends on the acquisition’s day and month

  • \(ESUN(b)\) is the mean TOA solar irradiance (or solar illumination) in \(W/m^2/micrometers\)

  • \(θ\) is the solar zenith angle in degrees.

The values for the \(ESUN(b)\) are provided in acquisition metadata.

Input

The input is an ingested Pleaides, see details here.

Output

The output is a STAC item geojson ... including the assets ...

References

[RW01] - OTB Optical calibration

[RW02] - Pleaides User Guide