Pléiades multispectral EO data products are calibrated using the Optical Products Calibration (OPT-Calib) service.

Figure 1 - True Color composite derived from calibrated Pléiades PMS ORTHO data acquired on 09/02/2023 over Sekeroba, Kahramanmaras, Turkey. Credits: Airbus DS, CNES.

Input

The input is an ingested Pléiades dataset. Find details here.

The Pléiades user guide1 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.

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.

Output

The output is a STAC item GeoJSON[^6] including single band and overview assets in COG format. Below is given an example of assets included in the STAC item of a Pléiades ORTHO calibrated dataset.

  "assets": {
"blue": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"data",
"reflectance",
"visual"
],
"href": "https://.../DS_PHR1A_202302090834089_FR1_PX_E036N37_1007_01591-calibrated/blue.tif",
"eo:bands": [
{
"name": "blue",
"common_name": "blue",
"solar_illumination": 1915
}
],
"raster:bands": [
{
"spatial_resolution": 0.5,
"statistics": {
"minimum": 0,
"maximum": 10000,
"mean": 1099.1586831026,
"stddev": 890.26671808737,
"valid_percent": 100
},
"file:size": 796455776
},
"green": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"data",
"reflectance",
"visual"
],
"href": "https://.../DS_PHR1A_202302090834089_FR1_PX_E036N37_1007_01591-calibrated/green.tif",
"eo:bands": [
{
"name": "green",
"common_name": "green",
"solar_illumination": 1831
}
],
"raster:bands": [
{
"spatial_resolution": 0.5,
"statistics": {
"minimum": 0,
"maximum": 10000,
"mean": 972.10462845682,
"stddev": 851.7691225341,
"valid_percent": 100
},
"file:size": 775575364
},
"red": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"data",
"reflectance",
"visual"
],
"href": "https://.../DS_PHR1A_202302090834089_FR1_PX_E036N37_1007_01591-calibrated/red.tif",
"eo:bands": [
{
"name": "red",
"common_name": "red",
"solar_illumination": 1594
}
],
"raster:bands": [
{
"spatial_resolution": 0.5,
"statistics": {
"minimum": 0,
"maximum": 10000,
"mean": 845.9111852015,
"stddev": 838.77620859596,
"valid_percent": 100
},
"file:size": 760806521
},
"nir": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"data",
"reflectance",
"visual"
],
"href": "https://.../DS_PHR1A_202302090834089_FR1_PX_E036N37_1007_01591-calibrated/nir.tif",
"eo:bands": [
{
"name": "nir",
"common_name": "nir",
"solar_illumination": 1060
}
],
"raster:bands": [
{
"spatial_resolution": 0.5,
"statistics": {
"minimum": 0,
"maximum": 10000,
"mean": 1716.1581221858,
"stddev": 1363.4867454117,
"valid_percent": 100
},
"file:size": 921686021
},
"overview-trc": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"composite",
"reflectance",
"visual"
],
"href": "https://.../DS_PHR1A_202302090834089_FR1_PX_E036N37_1007_01591-calibrated/overview-trc.tif",
"file:size": 1275368027
},
"overview-civ": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"composite",
"reflectance",
"visual"
],
"href": "https://.../DS_PHR1A_202302090834089_FR1_PX_E036N37_1007_01591-calibrated/overview-civ.tif",
"file:size": 1330749445
},
"overview-trc-low-res": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"composite",
"overview",
"reflectance"
],
"href": "https://.../DS_PHR1A_202302090834089_FR1_PX_E036N37_1007_01591-calibrated/overview-trc-low-res.tif",
"file:size": 1997776
}
}


1. Airbus Defence and Space, Pléiades User Guide, available at https://www.intelligence-airbusds.com