5. How to run the CAWA Processing Software¶
5.1. Test of the Installation¶
If all installation steps described in Processing Software Installation were finished successfully, the CAWA TCWV and CTP GPF processors are now ready to run. First, test their availability with:
$SNAP_INSTALL_DIR/bin/gpt -h
The three operators
- CawaTCWV.Meris
- CawaTCWV.Modis
- CawaCTP.Meris
should now appear in the listing of available SNAP operators, together with a short description.
5.2. The Pixel Classification Step¶
The pixel classification with IdePix is applied on the L1b input products. The operators for MERIS and MODIS
- Idepix.Meris
- Idepix.Modis
should also appear in the listing of available SNAP operators, together with a short description.
A more detailed information on the distinct operator can be obtained with
$SNAP_INSTALL_DIR/bin/gpt -h <operator-name>
e.g.
$SNAP_INSTALL_DIR/bin/gpt -h Idepix.Modis
(see Figure 5.1).
Figure 5.1 GPF information for Idepix MODIS operator..
5.2.1. Processing Parameters¶
The gpt command given above shows the possible IdePix processing parameters. To ensure a correct workflow towards the TCWV and CTP processing, the following IdePix processing parameters must be set as they deviate from the default (Table 5.1):
| Operator | Parameter | Value |
|---|---|---|
| Idepix.Meris (for TCWV) | reflBandsToCopy | reflectance_13,reflectance_14,reflectance_15 |
| Idepix.Meris (for CTP) | none | |
| Idepix.Modis (for TCWV) | outputCawaRefSB | true |
Applying these processing parameters, the calls for Idepix.Meris (TCWV, CTP) and Idepix.Modis (TCWV) would look like:
IdePix MERIS TCWV:
gpt Idepix.Meris -SsourceProduct=<path-to-MERIS-L1b-product>
-PreflBandsToCopy=reflectance_13,reflectance_14,reflectance_15
-f NetCDF4-BEAM -t <path-to-idepix-meris-for-tcwv-product>
IdePix MERIS CTP:
gpt Idepix.Meris -SsourceProduct=<path-to-MERIS-L1b-product>
-f NetCDF4-BEAM -t <path-to-idepix-meris-for-ctp-product>
IdePix MODIS TCWV:
gpt Idepix.Modis -SsourceProduct=<path-to-MERIS-L1b-product>
-PreflBandsToCopy=reflectance_13,reflectance_14,reflectance_15
-f NetCDF4-BEAM -t <path-to-idepix-meris-for-tcwv-product>
5.3. TCWV Processing¶
The TCWV processing is applied on the ‘extended’ IdePix products as described in The SNAP CAWA Products. The gpt command in Figure 5.3 and Figure 5.3 shows the possible TCWV processing parameters for MERIS and MODIS, respectively.
Figure 5.2 GPF information for TCWV MERIS operator.
Figure 5.3 GPF information for TCWV MODIS operator.
5.3.1. Processing Parameters¶
The operators for MERIS and MODIS
- CawaTCWV.Meris
- CawaTCWV.Modis
do not require any non-default parameters and are invoked via the SNAP gpt tool like:
<operator-name> -SsourceProduct=<path-to-IdePix-product> -f NetCDF4-CAWA -t
<path-to-target-product>
However, as discussed in The SNAP CAWA Products, it is strongly recommended to use IdePix ‘extended’ products containing ERA-Interim data which provides more realistic prior variables. If these are not available, the processor will use processor parameters for prior 2m temperature, mean sea level pressure and AOT. They can be explicitly provided by the user, so a TCWV processor call may look like:
CawaTCWV.Meris -SsourceProduct=<path-to-IdePix-product> -Ptemperature=285.0
-Ppressure=990.0 -Paot_13=0.25
-f NetCDF4-CAWA -t <path-to-target-product>
However, these values would be constant for all pixels of the given scene, so the resulting TCWV retrieval may be poor.
5.4. CTP Processing¶
The CTP MERIS processing is applied on the ‘extended’ IdePix products as described in The SNAP CAWA Products. The gpt command in Figure 5.4 shows the possible CTP MERIS processing options.
Figure 5.4 GPF information for TCWV MERIS operator.
5.4.1. Processing Parameters¶
The operators for MERIS
- CawaCTP.Meris
does not require any non-default parameters and is invoked via the SNAP gpt tool like:
CawaCTP.Meris -SsourceProduct=<path-to-IdePix-product> -f NetCDF4-CAWA
-t <path-to-target-product>
5.5. Data Analysis Tools¶
5.5.1. SNAP Desktop Application¶
The TCWV and CTP products generated within the CAWA project are provided in CFcompliant NetCDF-4/HDF5 format, which is supported by a variety of tools for further scientific analysis and processing. One of the important tools are the BEAM toolbox and its successor SNAP.
BEAM is the Basic ERS & Envisat (A)ATSR and MERIS Toolbox and is a collection of executable tools and an application programming interface (API) which had been developed to facilitate the use, viewing and processing of data of various sensors. However, it is more recommended to use the latest version of the SNAP toolboxes which do not only provide most of all existing BEAM functionalities and product support, but also various new features as well as support for the new sensors onboard the Sentinel-x satellites. The SNAP desktop application is directly available after having installed SNAP as described in Processing Software Installation.
Figure 5.5 The SNAP desktop application splash screen.