Hi,
I have 4 S3 OLCI L2 files which I mosaic together using a GPT script (which applies some masking based on certain flags). There are some pixels which are valid in 2 or more images and I’d like to better understand how SNAP decides which pixel to keep.
What other processing does SNAP apply to the S3 OLCI reflectance bands, as if I load the raw bands in Python using NetCDF the reflectance values are significantly different to those in the mosaicked image.
Thanks
The GPT XML I am using is:
<graph id="Graph">
<version>1.0</version>
<node id="ProductSet-Reader">
<operator>ProductSet-Reader</operator>
<sources/>
<parameters class="com.bc.ceres.binding.dom.XppDomElement">
<fileList>files_to_mosaic/S3B_OL_2_WFR____20230327T075434_20230327T075734_20230328T175956_0179_077_320_3600_MAR_O_NT_003.SEN3/xfdumanifest.xml,files_to_mosaic/S3A_OL_2_WFR____20230327T083047_20230327T083347_20230328T195544_0179_097_078_3420_MAR_O_NT_003.SEN3/xfdumanifest.xml</fileList>
</parameters>
</node>
<node id="Mosaic">
<operator>Mosaic</operator>
<sources>
<sourceProduct refid="ProductSet-Reader"/>
</sources>
<parameters class="com.bc.ceres.binding.dom.XppDomElement">
<variables>
<variable>
<name>Oa01_reflectance</name>
<expression>Oa01_reflectance</expression>
</variable>
<variable>
<name>Oa02_reflectance</name>
<expression>Oa02_reflectance</expression>
</variable>
<variable>
<name>Oa03_reflectance</name>
<expression>Oa03_reflectance</expression>
</variable>
<variable>
<name>Oa04_reflectance</name>
<expression>Oa04_reflectance</expression>
</variable>
<variable>
<name>Oa05_reflectance</name>
<expression>Oa05_reflectance</expression>
</variable>
<variable>
<name>Oa06_reflectance</name>
<expression>Oa06_reflectance</expression>
</variable>
<variable>
<name>Oa07_reflectance</name>
<expression>Oa07_reflectance</expression>
</variable>
<variable>
<name>Oa08_reflectance</name>
<expression>Oa08_reflectance</expression>
</variable>
<variable>
<name>Oa09_reflectance</name>
<expression>Oa09_reflectance</expression>
</variable>
<variable>
<name>Oa10_reflectance</name>
<expression>Oa10_reflectance</expression>
</variable>
<variable>
<name>Oa11_reflectance</name>
<expression>Oa11_reflectance</expression>
</variable>
<variable>
<name>Oa12_reflectance</name>
<expression>Oa12_reflectance</expression>
</variable>
<variable>
<name>CHL_OC4ME</name>
<expression>if WQSF_lsb.OC4ME_FAIL>0 then 0 else CHL_OC4ME</expression>
</variable>
<variable>
<name>medium_glint</name>
<expression>if WQSF_lsb.MEGLINT>0 then 0 else 1</expression>
</variable>
</variables>
<conditions>
<condition>
<name>condition_0</name>
<expression>not WQSF_lsb.INVALID</expression>
<output>false</output>
</condition>
<condition>
<name>condition_1</name>
<expression>not WQSF_lsb.LAND</expression>
<output>false</output>
</condition>
<condition>
<name>condition_2</name>
<expression>not WQSF_lsb.CLOUD</expression>
<output>false</output>
</condition>
<condition>
<name>condition_3</name>
<expression>not WQSF_lsb.TURBID_ATM</expression>
<output>false</output>
</condition>
<condition>
<name>condition_4</name>
<expression>not WQSF_lsb.CLOUD_AMBIGUOUS</expression>
<output>false</output>
</condition>
<condition>
<name>condition_5</name>
<expression>not WQSF_lsb.CLOUD_MARGIN</expression>
<output>false</output>
</condition>
<condition>
<name>condition_6</name>
<expression>not WQSF_lsb.SNOW_ICE</expression>
<output>false</output>
</condition>
<condition>
<name>condition_7</name>
<expression>not WQSF_lsb.COSMETIC</expression>
<output>false</output>
</condition>
<condition>
<name>condition_8</name>
<expression>not WQSF_lsb.SATURATED</expression>
<output>false</output>
</condition>
<condition>
<name>condition_9</name>
<expression>not WQSF_lsb.SUSPECT</expression>
<output>false</output>
</condition>
<condition>
<name>condition_10</name>
<expression>not WQSF_lsb.SNOW_ICE</expression>
<output>false</output>
</condition>
<condition>
<name>condition_11</name>
<expression>not WQSF_lsb.HIGHGLINT</expression>
<output>false</output>
</condition>
<condition>
<name>condition_12</name>
<expression>not WQSF_lsb.AC_FAIL</expression>
<output>false</output>
</condition>
</conditions>
<combine>AND</combine>
<crs>GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.01745329251994328,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4326"]]</crs>
<orthorectify>false</orthorectify>
<elevationModelName>CDEM</elevationModelName>
<resampling>Nearest</resampling>
<westBound>16.0</westBound>
<northBound>-31.0</northBound>
<eastBound>21.0</eastBound>
<southBound>-35.5</southBound>
<pixelSizeX>0.0027</pixelSizeX>
<pixelSizeY>0.0027</pixelSizeY>
</parameters>
</node>
<node id="Write">
<operator>Write</operator>
<sources>
<sourceProduct refid="Mosaic"/>
</sources>
<parameters class="com.bc.ceres.binding.dom.XppDomElement">
<file>temp_mosaicdir/mosaic_am_20230327_oc.nc</file>
<formatName>NETCDF4-BEAM</formatName>
</parameters>
</node>
</graph>
