Does SWH-2A Carto processing include radiometric calibration ?
No, the product includes only initial radiometric corrections from instrument distortions (detector egalisation).
Does SWH-2A Carto processing include atmospheric correction ?
SWH-2A-Carto are not corrected for atmospheric conditions.
You can use the SMAC method to correct the data from atmosphere effects. Code and coefficients could be downloaded from CESBIO web site. (http://tully.ups-tlse.fr/olivier/smac-python/tree/master/COEFS)
What is the naming convention for SWH-2A-Carto scenes ?
SWH-2A Carto product identifier is identical to SWH-1A products, except that extension CARTO is added to the archive and product name. It includes:
{archive_product_name}_CARTO.tif
{archive_product_name}_CARTO.xml
Where:
{archive_product_name}_CARTO.tif : projected image level 2A
{archive_product_name}_CARTO.xml : metadata relative to projected image
For SWH-2A Carto generated from supermode data processing chain, the nomenclature is:
{start_of_product_name}_AB_{end_of_product_name}_CARTO.tif
{start_of_product_name}_AB_{end_of_product_name}_CARTO.xml
Where:
{start_of_product_name}_AB_{end_of_product_name}_CARTO.tif : projected Supermode SPOT5 image level 2A
{start_of_product_name}_AB_{end_of_product_name}_CARTO.xml : metadata relative to Supermode SPOT5 projected image
Example: 001-002_S5_039-252-3_2005-11-21-10-57-23_HRG-2_J_DT_TT_CARTO.zip
Means: SPOT5, HRG-2 instrument, Multispectral mode (J), acquired November 11, 2005 at 10 h 57 mn 23 s, located KJ : 039-252 with a shift 3. DT means Direct Transmission, TT is the code station here Toulouse.
How do I rescale SWH-2A-Carto digital numbers to Top Of Atmosphere radiances?
SWH-2A-Carto data is provided in digital count. They can be rescaled to the top of atmosphere (TOA) radiance using radiometric rescaling coefficients provided in the metadata file (xml file) that is delivered with the SWH-2A-Carto product. The formula for this conversion is:
Lλ= DN / G
· L is the radiance of the spectral band expressed in W/m²/sr/µm
· DN is digital count
· G is the gain, referred by <PHYSICAL GAIN> in the xml file
Gains are provided for each spectral band.
How do I rescale SWH-2A-Carto digital numbers to Top Of Atmosphere reflectances?
First, proceed with the conversion in radiances as it is described in the previous item.
Then, the formula for this conversion is:
where
· ρλ is the TOA reflectance.
· Lλ is the TOA radiance
· cos(θs) is the cosine of the solar zenith angle
· Esλ is the extra terrestrial solar irradiance
Esλ is given for a mean earth-sun distance and has to be multiplied by a corrective factor for earth-sun distance defined as:
where
· t is the julian day for the processed image (reference day=01/01 of the current year)
· to = 2
· e = orbit eccentricity (0.01673)
· n = mean rotation angle (0.0172 rad / day)
Recently updated solar irradiances are provided in the table below. They are slightly different from the ones given in the SWH-1A metadata files.
Solar exoatmospheric spectral irradiances (Es) for the SPOT 1-5 data (in W/m2/μm) (Source World Meteorogical Organization spectral solar irradiance).
| Satellite | Instrument | PA | B1 | B2 | B3 | SWIR |
|---|---|---|---|---|---|---|
| SPOT1 | HRV1 | 1681.5 | 1861.7 | 1633.1 | 1089.4 | |
| SPOT1 | HRV2 | 1680.7 | 1853.9 | 1586 | 1043.5 | |
| SPOT2 | HRV1 | 1712.5 | 1873.3 | 1634 | 1082 | |
| SPOT2 | HRV2 | 1675.5 | 1871.1 | 1626.2 | 1088.1 | |
| SPOT4 | HRVIR1 | 1842.9 | 1570.2 | 1052.1 | 235.84 | |
| SPOT4 | HRVIR2 | 1850.9 | 1589 | 1054.8 | 241.93 | |
| SPOT5 | HRG1 | 1764.2 | 1859.8 | 1575.3 | 1043.9 | 238.87 |
| SPOT5 | HRG2 | 1775 | 1859.8 | 1577.6 | 1048.2 | 237.78 |
What are the SWH-2A-Carto data product file sizes?
The file size of SWH-2A-Carto products are listed in the table below.
| Sensor | Size | Compressed Archive Size |
|---|---|---|
| SPOT 1, SPOT 2, SPOT 3 | 100 - 200 Mb | 50 - 100 Mb |
| SPOT 4 | 200 - 250 Mb | 100 - 150 Mb |
| SPOT 5 | 200 - 250 Mb | 100 - 150 Mb |
| SPOT 5 supermode | 1 Gb | 600 Mb |
Is there a cloud mask associated to the product ?
No, at the moment, no cloud mask is available with the product.
What is the geolocation accuracy ?
As no GCPs are used for the product georeferencing, the performance of the geolocation is identical as those of SWH-1A products.
In case of misregistration, we recommend to manually shift the location of the products by applying a translation for additional geometric accuracy.
How to obtain SPOT 5 THR image pairs from the CNES Regards catalog ?
Once you have identified a SPOT 5 image, open its details using the icon 
on the right of the image. On the left, in the "Paramètres" tab, if in the "Couplages" tab you can see "Coupling data THR", it means that a THR pair exists for this image. Click on 
, the two images of the pair appear. For each of them, open the details, and check that they have the same "Shift Value". If it is the case, select the two images and add them to the order basket.
NB: Two THR images of a SPOT 5 pair have the same nomenclature, except a letter ('A' in one, 'B' in the other). Example: 001-002_S5_042-262-2_2004-08-11-10-43-50_HRG-1_A_MX_TT and 001-002_S5_042-262-2_2004-08-11-10-43-50_HRG-1_B_MX_TT.