Amazonia-1

Amazonia-1 multispectral EO data products are calibrated using the Optical Products Calibration (OPT-Calib) service.

Figure 1 - Color Infrared Vegetation false color composite derived from calibrated Amazonia-1 WFI L2 data acquired over the Marrakesh–Safi region in Morocco. Credits: AEB, INPE.

Input

The input is an ingested Amazonia-11 dataset. Find details here.

DN to Reflectance

Amazonia-1 TOA radiance for a band b is derived from DN values using the formula below2:

$L_{(b)} = DN_{(b)} \times abscalibcoeff_{(b)}$

where :

• $$L_{(b)}$$ is the TOA radiance for a Amazonia-1 band b.

• $$DN_{(b)}$$ is the digital number for a band b. The digital number DN=0 represents the “NO_DATA” value.

• $$abscalibcoeff_{(b)}$$ is the scaling factor for the band b. This value is extracted from the ABSOLUTE_CALIBRATION_COEFFICIENT field in the product annotation.

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 conversion from elevation angle to solar zenith angle $$θ$$ (in degrees) is:

$θ = { 90 - elevation_angle }$

The values for the $$ESUN(b)$$ for Amazonia-1 are provided in Table 1:

Common band name (BAND name) λ(nm) Thuillier 2003
blue (BAND13) 450-520 1984.65
green (BAND14) 520-590 1823.40
red (BAND15) 630-690 1536.38
nir (BAND16) 770-890 981.91
Table 1 - ESUN value employed in the conversion of radiance to reflectance for Amazonia-1 products.

Output

The output is a STAC item GeoJSON3 including single band and overview assets in COG format. Below is an example of assets included in the STAC item of a Amazonia-1 WFI L2 compose calibrated dataset.

  "assets": {
"blue": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"data",
"reflectance",
"visual"
],
"href": "https://.../urn_ogc_def_EOP_INPE_AMAZONIA_1_WFI_20210802_029_010_L4_compose-calibrated/blue.tif",
"eo:bands": [
{
"name": "blue",
"common_name": "blue",
"center_wavelength": 0.485,
"solar_illumination": 1984.65
}
],
"raster:bands": [
{
"spatial_resolution": 64
}
},
"green": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"data",
"reflectance",
"visual"
],
"href": "https://.../urn_ogc_def_EOP_INPE_AMAZONIA_1_WFI_20210802_029_010_L4_compose-calibrated/green.tif",
"eo:bands": [
{
"name": "BAND14",
"common_name": "green",
"center_wavelength": 0.555,
"solar_illumination": 1823.40
}
],
"raster:bands": [
{
"spatial_resolution": 64
}
},
"red": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"data",
"reflectance",
"visual"
],
"href": "https://.../urn_ogc_def_EOP_INPE_AMAZONIA_1_WFI_20210802_029_010_L4_compose-calibrated/red.tif",
"eo:bands": [
{
"name": "BAND15",
"common_name": "red",
"center_wavelength": 0.66,
"solar_illumination": 1536.38
}
],
"raster:bands": [
{
"spatial_resolution": 64
}
},
"nir": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"data",
"reflectance",
"visual"
],
"href": "https://.../urn_ogc_def_EOP_INPE_AMAZONIA_1_WFI_20210802_029_010_L4_compose-calibrated/nir.tif",
"eo:bands": [
{
"name": "BAND16",
"common_name": "nir",
"center_wavelength": 0.83,
"solar_illumination": 981.91
}
],
"raster:bands": [
{
"spatial_resolution": 64
}
},
"overview-trc": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"composite",
"reflectance",
"visual"
],
"href": "https://.../urn_ogc_def_EOP_INPE_AMAZONIA_1_WFI_20210802_029_010_L4_compose-calibrated/overview-trc.tif"
},
"overview-civ": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"composite",
"reflectance",
"visual"
],
"href": "https://.../urn_ogc_def_EOP_INPE_AMAZONIA_1_WFI_20210802_029_010_L4_compose-calibrated/overview-civ.tif"
},
"overview-trc-low-res": {
"type": "image/tiff; application=geotiff; profile=cloud-optimized",
"roles": [
"composite",
"overview",
"reflectance"
],
"href": "https://.../urn_ogc_def_EOP_INPE_AMAZONIA_1_WFI_20210802_029_010_L4_compose-calibrated/overview-trc-low-res.tif"
}
}


1. INPE, Amazonia-1, About the satellite, accesible at www.inpe.br/

2. Pinto C., Ponzoni F., Castro R., Leigh L., Mishra N., Aaron D., Helder D. (2016), "First in-Flight Radiometric Calibration of MUX and WFI on-Board CBERS-4", Remote Sens. 2016, 8, 405. DOI:/10.3390/rs8050405

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